KEYPROV Working Group A. Doherty
Internet-Draft RSA, The Security Division of EMC
Intended status: Standards Track M. Pei
Expires: May 1, 2008 Verisign, Inc.
S. Machani
Diversinet Corp.
M. Nystrom
RSA, The Security Division of EMC
October 29, 2007
Dynamic Symmetric Key Provisioning Protocol (DSKPP)
draft-ietf-keyprov-dskpp-01.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on May 1, 2008.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
DSKPP is a client-server protocol for initialization (and
configuration) of symmetric keys to locally and remotely accessible
cryptographic modules. The protocol can be run with or without
Doherty, et al. Expires May 1, 2008 [Page 1]
Internet-Draft DSKPP October 2007
private-key capabilities in the cryptographic modules, and with or
without an established public-key infrastructure.
Three variations of the protocol support multiple usage scenarios.
The four-pass (i.e., two round-trip) variant enables key generation
in near real-time. With the four-pass variant, keys are mutually
generated by the provisioning server and cryptographic module;
provisioned keys are not transferred over-the-wire or over-the-air.
Two- and one-pass variants enable secure and efficient download and
installation of symmetric keys to a cryptographic module in
environments where near real-time communication may not be possible.
This document builds on information contained in [RFC4758], adding
specific enhancements in response to implementation experience and
liaison requests. It is intended, therefore, that this document or a
successor version thereto will become the basis for subsequent
progression of a symmetric key provisioning protocol specification on
the standards track.
Doherty, et al. Expires May 1, 2008 [Page 2]
Internet-Draft DSKPP October 2007
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.2. Background . . . . . . . . . . . . . . . . . . . . . . . 7
2. Requirements Notation and Terminology . . . . . . . . . . . . 8
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1. Single Key Request . . . . . . . . . . . . . . . . . . . 11
3.2. Multiple Key Requests . . . . . . . . . . . . . . . . . . 11
3.3. Session Time-Out Policy . . . . . . . . . . . . . . . . . 11
3.4. Outsourced Provisioning . . . . . . . . . . . . . . . . . 12
3.5. Key Renewal . . . . . . . . . . . . . . . . . . . . . . . 12
3.6. Pre-Loaded Key Replacement . . . . . . . . . . . . . . . 12
3.7. Pre-Shared Transport Key . . . . . . . . . . . . . . . . 12
3.8. SMS-Based Key Transport . . . . . . . . . . . . . . . . . 13
3.9. Non-Protected Transport Layer . . . . . . . . . . . . . . 13
3.10. Non-Authenticated Transport Layer . . . . . . . . . . . . 13
4. DSKPP Overview . . . . . . . . . . . . . . . . . . . . . . . 13
4.1. Entities . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2. Overview of Protocol Usage . . . . . . . . . . . . . . . 15
4.3. Four-Pass Protocol Usage . . . . . . . . . . . . . . . . 18
4.3.1. Message Flow . . . . . . . . . . . . . . . . . . . . 19
4.3.2. Generation of Symmetric Keys for Cryptographic
Modules . . . . . . . . . . . . . . . . . . . . . . . 20
4.3.3. Client Authentication . . . . . . . . . . . . . . . . 23
4.3.4. Key Confirmation . . . . . . . . . . . . . . . . . . 23
4.3.5. Server Authentication . . . . . . . . . . . . . . . . 23
4.4. Two-Pass Protocol Usage . . . . . . . . . . . . . . . . . 24
4.4.1. Message Flow . . . . . . . . . . . . . . . . . . . . 26
4.4.2. Key Confirmation . . . . . . . . . . . . . . . . . . 27
4.4.3. Server Authentication . . . . . . . . . . . . . . . . 27
4.5. One-Pass Protocol Usage . . . . . . . . . . . . . . . . . 28
4.5.1. Message Flow . . . . . . . . . . . . . . . . . . . . 29
4.5.2. Key Confirmation . . . . . . . . . . . . . . . . . . 30
4.5.3. Server Authentication . . . . . . . . . . . . . . . . 30
5. Methods Common to More Than One Protocol Variant . . . . . . 31
5.1. The DSKPP One-Way Pseudorandom Function, DSKPP-PRF . . . 31
5.1.1. Introduction . . . . . . . . . . . . . . . . . . . . 31
5.1.2. Declaration . . . . . . . . . . . . . . . . . . . . . 32
5.2. Encryption of Pseudorandom Nonces Sent from the DSKPP
Client (Applicable to Four-Pass and Two-Pass DSKPP) . . . 32
5.3. Client Authentication Mechanisms (Applicable to Four-
and Two-Pass DSKPP) . . . . . . . . . . . . . . . . . . . 32
5.3.1. Device Certificate . . . . . . . . . . . . . . . . . 33
5.3.2. Device Identifier . . . . . . . . . . . . . . . . . . 33
5.3.3. Authentication Code . . . . . . . . . . . . . . . . . 33
5.4. Client Authentication Examples . . . . . . . . . . . . . 36
5.4.1. Example Using a MAC from an Authentication Code . . . 36
Doherty, et al. Expires May 1, 2008 [Page 3]
Internet-Draft DSKPP October 2007
5.4.2. Example Using a Device Certificate . . . . . . . . . 36
6. Four-Pass Protocol . . . . . . . . . . . . . . . . . . . . . 36
6.1. XML Basics . . . . . . . . . . . . . . . . . . . . . . . 36
6.2. Round-Trip #1: <KeyProvClientHello> and
<KeyProvServerHello> . . . . . . . . . . . . . . . . . . 37
6.2.1. Examples . . . . . . . . . . . . . . . . . . . . . . 37
6.2.2. Components of the <KeyProvClientHello> Request . . . 41
6.2.3. Components of the <KeyProvServerHello> Response . . . 45
6.3. Round-Trip #2: <KeyProvClientNonce> and
<KeyProvServerFinished> . . . . . . . . . . . . . . . . . 46
6.3.1. Examples . . . . . . . . . . . . . . . . . . . . . . 46
6.3.2. Components of a <KeyProvClientNonce> Request . . . . 47
6.3.3. Components of a <KeyProvServerFinished> Response . . 48
6.4. DSKPP Server Results: The StatusCode Type . . . . . . . 49
7. Two-Pass Protocol . . . . . . . . . . . . . . . . . . . . . . 50
7.1. XML Basics . . . . . . . . . . . . . . . . . . . . . . . 50
7.2. Round-Trip #1: <KeyProvClientHello> and
<KeyProvServerFinished> . . . . . . . . . . . . . . . . . 51
7.2.1. Examples . . . . . . . . . . . . . . . . . . . . . . 51
7.2.2. Components of the <KeyProvClientHello> Request . . . 59
7.2.3. Components of a <KeyProvServerFinished> Response . . 60
7.3. DSKPP Server Results: The StatusCode Type . . . . . . . 62
8. One-Pass Protocol . . . . . . . . . . . . . . . . . . . . . . 63
8.1. XML Basics . . . . . . . . . . . . . . . . . . . . . . . 63
8.2. Server to Client Only: <KeyProvServerFinished> . . . . . 64
8.2.1. Example . . . . . . . . . . . . . . . . . . . . . . . 64
8.2.2. Components of a <KeyProvServerFinished> Response . . 65
9. Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
9.1. XML Basics . . . . . . . . . . . . . . . . . . . . . . . 66
9.2. Example . . . . . . . . . . . . . . . . . . . . . . . . . 67
9.3. Components of the <KeyProvTrigger> Message . . . . . . . 67
10. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 68
10.1. The ClientInfoType Type . . . . . . . . . . . . . . . . . 68
10.2. The ServerInfoType Type . . . . . . . . . . . . . . . . . 68
10.3. The KeyInitializationDataType Type . . . . . . . . . . . 68
11. Key Initialization Profiles of Two- and One-Pass DSKPP . . . 69
11.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 69
11.2. Key Transport Profile . . . . . . . . . . . . . . . . . . 69
11.2.1. Introduction . . . . . . . . . . . . . . . . . . . . 69
11.2.2. Identification . . . . . . . . . . . . . . . . . . . 69
11.2.3. Payloads . . . . . . . . . . . . . . . . . . . . . . 69
11.3. Key Wrap Profile . . . . . . . . . . . . . . . . . . . . 70
11.3.1. Introduction . . . . . . . . . . . . . . . . . . . . 70
11.3.2. Identification . . . . . . . . . . . . . . . . . . . 71
11.3.3. Payloads . . . . . . . . . . . . . . . . . . . . . . 71
11.4. Passphrase-Based Key Wrap Profile . . . . . . . . . . . . 72
11.4.1. Introduction . . . . . . . . . . . . . . . . . . . . 72
11.4.2. Identification . . . . . . . . . . . . . . . . . . . 72
Doherty, et al. Expires May 1, 2008 [Page 4]
Internet-Draft DSKPP October 2007
11.4.3. Payloads . . . . . . . . . . . . . . . . . . . . . . 72
12. Protocol Bindings . . . . . . . . . . . . . . . . . . . . . . 73
12.1. General Requirements . . . . . . . . . . . . . . . . . . 74
12.2. HTTP/1.1 Binding for DSKPP . . . . . . . . . . . . . . . 74
12.2.1. Introduction . . . . . . . . . . . . . . . . . . . . 74
12.2.2. Identification of DSKPP Messages . . . . . . . . . . 74
12.2.3. HTTP Headers . . . . . . . . . . . . . . . . . . . . 74
12.2.4. HTTP Operations . . . . . . . . . . . . . . . . . . . 74
12.2.5. HTTP Status Codes . . . . . . . . . . . . . . . . . . 75
12.2.6. HTTP Authentication . . . . . . . . . . . . . . . . . 75
12.2.7. Initialization of DSKPP . . . . . . . . . . . . . . . 75
12.2.8. Example Messages . . . . . . . . . . . . . . . . . . 75
13. DSKPP Schema . . . . . . . . . . . . . . . . . . . . . . . . 76
14. Security Considerations . . . . . . . . . . . . . . . . . . . 85
14.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 85
14.2. Active Attacks . . . . . . . . . . . . . . . . . . . . . 85
14.2.1. Introduction . . . . . . . . . . . . . . . . . . . . 85
14.2.2. Message Modifications . . . . . . . . . . . . . . . . 85
14.2.3. Message Deletion . . . . . . . . . . . . . . . . . . 87
14.2.4. Message Insertion . . . . . . . . . . . . . . . . . . 87
14.2.5. Message Replay . . . . . . . . . . . . . . . . . . . 87
14.2.6. Message Reordering . . . . . . . . . . . . . . . . . 88
14.2.7. Man-in-the-Middle . . . . . . . . . . . . . . . . . . 88
14.3. Passive Attacks . . . . . . . . . . . . . . . . . . . . . 88
14.4. Cryptographic Attacks . . . . . . . . . . . . . . . . . . 88
14.5. Attacks on the Interaction between DSKPP and User
Authentication . . . . . . . . . . . . . . . . . . . . . 89
14.6. Additional Considerations Specific to 2- and 1-pass
DSKPP . . . . . . . . . . . . . . . . . . . . . . . . . . 89
14.6.1. Client Contributions to K_TOKEN Entropy . . . . . . . 89
14.6.2. Key Confirmation . . . . . . . . . . . . . . . . . . 90
14.6.3. Server Authentication . . . . . . . . . . . . . . . . 90
14.6.4. Client Authentication . . . . . . . . . . . . . . . . 90
14.6.5. Key Protection in the Passphrase Profile . . . . . . 91
15. Internationalization Considerations . . . . . . . . . . . . . 91
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 92
17. Intellectual Property Considerations . . . . . . . . . . . . 92
18. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 92
19. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 92
20. References . . . . . . . . . . . . . . . . . . . . . . . . . 93
20.1. Normative references . . . . . . . . . . . . . . . . . . 93
20.2. Informative references . . . . . . . . . . . . . . . . . 94
Appendix A. Integration with PKCS #11 . . . . . . . . . . . . . 95
A.1. The 4-pass Variant . . . . . . . . . . . . . . . . . . . 96
A.2. The 2-pass Variant . . . . . . . . . . . . . . . . . . . 96
A.3. The 1-pass Variant . . . . . . . . . . . . . . . . . . . 98
Appendix B. Example of DSKPP-PRF Realizations . . . . . . . . . 100
B.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 101
Doherty, et al. Expires May 1, 2008 [Page 5]
Internet-Draft DSKPP October 2007
B.2. DSKPP-PRF-AES . . . . . . . . . . . . . . . . . . . . . . 101
B.2.1. Identification . . . . . . . . . . . . . . . . . . . 101
B.2.2. Definition . . . . . . . . . . . . . . . . . . . . . 101
B.2.3. Example . . . . . . . . . . . . . . . . . . . . . . . 102
B.3. DSKPP-PRF-SHA256 . . . . . . . . . . . . . . . . . . . . 102
B.3.1. Identification . . . . . . . . . . . . . . . . . . . 102
B.3.2. Definition . . . . . . . . . . . . . . . . . . . . . 103
B.3.3. Example . . . . . . . . . . . . . . . . . . . . . . . 104
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 104
Intellectual Property and Copyright Statements . . . . . . . . . 106
Doherty, et al. Expires May 1, 2008 [Page 6]
Internet-Draft DSKPP October 2007
1. Introduction
1.1. Scope
This document describes a client-server protocol for initialization
(and configuration) of symmetric keys to locally and remotely
accessible cryptographic modules. The protocol can be run with or
without private-key capabilities in the cryptographic modules, and
with or without an established public-key infrastructure. The
objectives of this protocol are to:
o Provide a secure method of initializing cryptographic modules
with symmetric keys without exposing generated, secret material
to any other entities than the server and the cryptographic
module itself.
o Provide a secure method of generating and transporting
symmetric keys to a cryptographic module in environments where
near real-time communication is not possible.
o Provide a secure method of transporting pre-generated (i.e.,
legacy) keys to a cryptographic module.
o Provide a solution that is easy to administer and scales well.
The mechanism is intended for general use within computer and
communications systems employing symmetric key cryptographic modules
that are locally (i.e., over-the-wire) or remotely (i.e., over-the-
air) accessible.
1.2. Background
A locally accessible symmetric key cryptographic module may be hosted
by, for example, a hardware device connected to a personal computer
through an electronic interface, such as USB, or a software
application resident on a personal computer. A remotely accessible
symmetric key cryptographic module may be hosted by, for example, any
device that can support over-the-air communication, such as a hand-
held hardware device (e.g., a mobile phone). The cryptographic
module itself offers symmetric key cryptographic functionality that
may be used to authenticate a user towards some service, perform data
encryption, etc. Increasingly, these modules enable their
programmatic initialization as well as programmatic retrieval of
their output values. This document intends to meet the need for an
open and inter-operable mechanism to programmatically initialize and
configure symmetric keys to locally and remotely accessible
cryptographic modules.
The target mechanism makes use of a symmetric key provisioning
server. In an ideal deployment scenario, near real-time
communication is possible between the provisioning server and the
Doherty, et al. Expires May 1, 2008 [Page 7]
Internet-Draft DSKPP October 2007
cryptographic module. In such an environment, it is possible for the
cryptographic module and provisioning server to mutually generate a
symmetric key, and to ensure that keys are not transported between
them.
There are, however, several deployment scenarios that make mutual key
generation less suitable. Specifically, scenarios where near real-
time communication between the symmetric key provisioning server and
the cryptographic module is not possible, and scenarios with
significant design constraints. Examples include work-flow
constraints (e.g., policies that require incremental administrative
approval), network design constraints that create network latency,
and budget constraints that sustain reliance upon legacy systems that
already have supplies of pre-generated keys. In these situations,
the cryptographic module is required to download and install a
symmetric key from the provisioning server in a secure and efficient
manner.
This document tries to meet the needs of these scenarios by
describing three variations to DSKPP for the provisioning of
symmetric keys in two round trips or less. The four-pass (i.e., two
round-trip) variant enables key generation in near real-time. With
this variant, keys are mutually generated by the provisioning server
and cryptographic module; provisioned keys are not transferred over-
the-wire or over-the-air. In contrast, two- and one-pass variants
enable secure and efficient download and installation of symmetric
keys to a cryptographic module in environments where near real-time
communication is not possible.
2. Requirements Notation and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The following notations are used in this document:
|| String concatenation
[x] Optional element x
A ^ B Exclusive-OR operation on strings A and B (where A
and B are of equal length)
Doherty, et al. Expires May 1, 2008 [Page 8]
Internet-Draft DSKPP October 2007
ENC_X(Y) Encryption of message Y with symmetric key X, using a
defined block cipher
ENC_PX(Y) Encryption using message Y with a public key X
KDF_X(Y) Key derivation function that generates an arbitrary
number of octets of output using secret X and seed Y
DSKPP-PRF_X(Y,Z) Pseudo random function that generates a fixed
number Z of octets using secret X and seed Y (used in
DSKPP methods for MAC computations and key
derivation)
MAC_X(Y) Keyed message authentication code computed over Y
with symmetric key X
SIGN_x(Y) Function that provides authentication and integrity
protection of message content Y using private key x
B64(X) Base 64 encoding of string X
H(X) Hash function applied to X
Alg_List List of encryption and MAC algorithms supported by
the client
Alg_Sel Algorithms list selected by the server for the DSKPP
protocol run
DSKPP client Manages communication between the symmetric key
cryptographic module and the DSKPP server
DSKPP server The symmetric key provisioning server that
participates in the DSKPP protocol run
Issuer The organization that issues or authorizes issuance
of the symmetric key to the end user of the symmetric
key cryptographic module (e.g., a bank who issues
one-time password authentication tokens to their
retail banking users)
ID_C Identifier for DSKPP client
ID_S Identifier for DSKPP server
Doherty, et al. Expires May 1, 2008 [Page 9]
Internet-Draft DSKPP October 2007
AUTHCODE Client Authentication Code comprised of a string of
numeric characters known to the device and the server
and containing an identifier and a password (the
AUTHCODE may be used to derive the AUTHDATA during
the DSKPP protocol exchange)
AUTHDATA Client Authentication Data that may be derived from
the AUTHCODE or using the client private key,
k_CLIENT
K Key used to encrypt R_C (either K_SERVER or K_SHARED)
K_AUTHCODE Secret key that is derived from AUTHCODE and used for
client authentication purposes
k_CLIENT Private key of the DSKPP client
K_CLIENT Public key of the DSKPP client
K_DERIVED Secret key derived from a passphrase that is known to
both the DSKPP client or user and the DSKPP server
K_MAC Secret key used for key confirmation and server
authentication purposes, and generated in DSKPP
K_MAC' A second secret key used for server authentication
purposes in 2- and 1-pass DSKPP
K_SERVER Public key of the DSKPP server
K_SHARED Secret key shared between the DSKPP client and the
DSKPP server
K_TOKEN Secret key used for cryptographic module
computations, and generated in DSKPP
K_CONFDATA Key configuration data carried within the key
container
R Pseudorandom value chosen by the DSKPP client and
used for MAC computations, which is mandatory for
2-pass DSKPP and optional for 4-pass
R_C Pseudorandom value chosen by the DSKPP client and
used as input to the generation of K_TOKEN
Doherty, et al. Expires May 1, 2008 [Page 10]
Internet-Draft DSKPP October 2007
R_S Pseudorandom value chosen by the DSKPP server and
used as input to the generation of K_TOKEN
URL_S Server address as a URL
I Unsigned integer representing a counter value that is
monotonically increasing and guaranteed not to be
used again by the server towards the cryptographic
module
I' Similar to I except I' is always higher than I
The following typographical convention is used in the body of the
text: <XMLElement>.
3. Use Cases
This section describes typical use cases.
3.1. Single Key Request
A cryptographic module hosted by a device, such as a mobile phone,
makes a request for a symmetric key from a provisioning server.
Depending upon how the system is deployed, the provisioning server
may generate a new key on-the-fly or use a pre-generated key, e.g.,
one provided by a legacy back-end issuance server. The provisioning
server assigns a unique key ID to the symmetric key and provisions it
to the cryptographic module.
3.2. Multiple Key Requests
A cryptographic module makes multiple requests for symmetric keys
from the same provisioning server. The symmetric keys may or may not
be of the same type, i.e., the keys may be used with different
symmetric key cryptographic algorithms, including one-time password
authentication algorithms, and AES encryption algorithm.
3.3. Session Time-Out Policy
Once a cryptographic module initiates a symmetric key request, the
provisioning server may require that any subsequent actions to
complete the provisioning cycle occur within a certain time window.
For example, an issuer may provide a time-limited authentication code
to a user during registration, which the user will input into the
cryptographic module to authenticate themselves with the provisioning
server. If the user inputs a valid authentication code within the
Doherty, et al. Expires May 1, 2008 [Page 11]
Internet-Draft DSKPP October 2007
fixed time period established by the issuer, the server will allow a
key to be provisioned to the cryptographic module hosted by the
user's device.
3.4. Outsourced Provisioning
A symmetric key issuer outsources its key provisioning to a third
party key provisioning server provider. The issuer is responsible
for authenticating and granting rights to users to acquire keys while
acting as a proxy to the cryptographic module to acquire symmetric
keys from the provisioning server; the cryptographic module
communicates with the issuer proxy server, which forwards
provisioning requests to the provisioning server.
3.5. Key Renewal
A cryptographic module requests renewal of a symmetric key using the
same key ID already associated with the key. Such a need may occur
in the case when a user wants to upgrade her device that houses the
cryptographic module or when a key has expired. When a user uses the
same cryptographic module to, for example, perform strong
authentication at multiple Web login sites, keeping the same key ID
removes the need for the user to register a new key ID at each site.
3.6. Pre-Loaded Key Replacement
This use case represents a special case of symmetric key renewal in
which a local administrator can authenticate the user procedurally
before initiating the provisioning process. It also allows for an
issuer to pre-load a key onto a cryptographic module with a
restriction that the key is replaced with a new key prior to use of
the cryptographic module. Another variation of this use case is the
issuer who recycles devices. In this case, an issuer would provision
a new symmetric key to a cryptographic module hosted on a device that
was previously owned by another user.
Note that this use case is essentially the same as the last use case
wherein the same key ID is used for renewal.
3.7. Pre-Shared Transport Key
A cryptographic module is loaded onto a smart card after the card is
issued to a user. The symmetric key for the cryptographic module
will then be provisioned using a secure channel mechanism present in
many smart card platforms. This allows a direct secure channel to be
established between the smart card chip and the provisioning server.
For example, the card commands (i.e., Application Protocol Data
Units, or APDUs) are encrypted with a pre-shared transport key and
Doherty, et al. Expires May 1, 2008 [Page 12]
Internet-Draft DSKPP October 2007
sent directly to the smart card chip, allowing secure post-issuance
in-the-field provisioning. This secure flow can pass Transport Layer
Security (TLS) and other transport security boundaries.
Note that two pre-conditions for this use case are for the protocol
to be tunneled and the provisioning server to know the correct pre-
established transport key.
3.8. SMS-Based Key Transport
A mobile device supports Short Message Service (SMS) but is not able
to support a data service allowing for HTTP or HTTPS transports. In
addition, an application may use a cryptographic module to enforce an
acceptable level of protection for download of the symmetric key via
SMS. In such a case, the cryptographic module hosted by the mobile
device may initiate a symmetric key request from a desktop computer
and ask the server to send the key to the mobile device through SMS.
User authentication is carried out via the online communication
established between the desktop computer and the provisioning server.
3.9. Non-Protected Transport Layer
Some devices are not able to support a secure transport channel such
as SSL or TLS to provide data confidentiality. A cryptographic
module hosted by such a device requests a symmetric key from the
provisioning server. It is up to DSKPP to ensure data
confidentiality over non-secure networks.
3.10. Non-Authenticated Transport Layer
Some devices are not able to use a transport protocol that provides
server authentication such as SSL or TLS. A cryptographic module
hosted by such a device wants to be sure that it sends a request for
a symmetric key to a legitimate provisioning server. It is up to
DSKPP to provide proper client and server authentication.
4. DSKPP Overview
4.1. Entities
In principle, the protocol involves a DSKPP client and a DSKPP
server. The DSKPP client manages communication between the
cryptographic module and the provisioning server. The DSKPP server
herein represents the provisioning server.
A high-level object model that describes the client-side entities and
how they relate to each other is shown in Figure 1.
Doherty, et al. Expires May 1, 2008 [Page 13]
Internet-Draft DSKPP October 2007
----------- -------------
| User | | Device |
|---------|* owns *|-----------|
| UserID |--------->| DeviceID |
| ... | | ... |
----------- -------------
| 1
|
| contains
|
| *
V
-----------------------
|Cryptographic Module |
|---------------------|
|CryptoModuleID
|Encryption Algorithms|
|MAC Algorithms |
|... |
-----------------------
| 1
|
| contains
|
| *
V
-----------------------
|Key Container |
|---------------------|
|KeyID |
|Key Type |
|... |
-----------------------
Figure 1: Object Model
Conceptually, each entity represents the following:
User: The person or client to whom devices are
issued
UserID: A unique identifier for the user or client
Device: A physical piece of hardware or software
framework that hosts symmetric key
cryptographic modules
Doherty, et al. Expires May 1, 2008 [Page 14]
Internet-Draft DSKPP October 2007
DeviceID: A unique identifier for the device
Cryptographic Module: A component of an application, which enables
symmetric key cryptographic functionality
CryptoModuleID: A unique identifier for an instance of the
cryptographic module
Encryption Algorithms: Encryption algorithms supported by the
cryptographic module
MAC Algorithms: MAC algorithms supported by the cryptographic
module
Key Container: An object that encapsulates a symmetric key
and its configuration data
KeyID: A unique identifier for the symmetric key
Key Type: The type of symmetric key cryptographic
methods for which the key will be used (e.g.,
OATH HOTP or RSA SecurID authentication, AES
encryption, etc.)
It is assumed that a device will host an application layered above
the cryptographic module, and this application will manage
communication between the DSKPP client and cryptographic module. The
manner in which the communicating application will transfer DSKPP
protocol elements to and from the cryptographic module is transparent
to the DSKPP server. One method for this transfer is described in
[CT-KIP-P11].
4.2. Overview of Protocol Usage
DSKPP enables symmetric key provisioning between a DSKPP server and
DSKPP client. The DSKPP protocol supports the following types of
requests and responses:
<KeyProvClientHello>
With this request, a DSKPP client initiates contact with the
DSKPP server, indicating what protocol versions and variants,
key types, encryption and MAC algorithms that it supports. In
addition, the request may include client authentication data
that the DSKPP server uses to verify proof-of-possession of
the device.
<KeyProvServerHello>
Doherty, et al. Expires May 1, 2008 [Page 15]
Internet-Draft DSKPP October 2007
Upon reception of a <KeyProvClientHello> request, the DSKPP
server uses the <KeyProvServerHello> response to specify which
protocol version and variant, key type, encryption algorithm,
and MAC algorithm that will be used by the DSKPP server and
DSKPP client during the protocol run. The decision of which
variant, key type, and cryptographic algorithms to pick is
policy- and implementation-dependent and therefore outside the
scope of this document.
The <KeyProvServerHello> response includes the DSKPP server's
random nonce, R_S. The response also consists of information
about either a shared secret key, or its own public key, that
the DSKPP client uses when sending its protected random nonce,
R_C, in the <KeyProvClientNonce> request (see below).
Optionally, the DSKPP server may provide a MAC that the DSKPP
client may use for server authentication.
<KeyProvClientNonce>
With this request, a DSKPP client and DSKPP server securely
exchange protected data, e.g., the protected random nonce R_C.
In addition, the request may include client authentication
data that the DSKPP server uses to verify proof-of-possession
of the device.
<KeyProvServerFinished>
The <KeyProvServerFinished> response is a confirmation message
that includes a key container that holds configuration data,
and may also contain protected key material (this depends on
the protocol variant, as discussed below).
Optionally, the DSKPP server may provide a MAC that the DSKPP
client may use for server authentication.
To initiate a DSKPP session:
1. A user may use a browser to connect to a web server that is
running on some host. The user may then identify (and optionally
authenticate) herself (through some means that essentially are
out of scope for this document) and request a symmetric key.
2. A client application may request a symmetric key by invoking the
DSKPP client.
3. A DSKPP server may send a trigger message to a client
application, which would then invoke the DSKPP client.
To contact the DSKPP server:
Doherty, et al. Expires May 1, 2008 [Page 16]
Internet-Draft DSKPP October 2007
1. A user may indicate how the DSKPP client is to contact a certain
DSKPP server during a browsing session.
2. A DSKPP client may be pre-configured to contact a certain DSKPP
server.
3. A user may be informed out-of-band about the location of the
DSKPP server.
Once the location of the DSKPP server is known, the DSKPP client and
the DSKPP server engage in a 4-pass, 2-pass, or 1-pass protocol.
Depending upon the policy and implementation, a DSKPP server selects
which variant of the protocol to use: 4-pass, 2-pass, or 1-pass.
With the four-pass variant, keys are mutually generated by the DSKPP
server and DSKPP client; provisioned keys are not transferred over-
the-wire or over-the-air. Two- and one-pass variants enable secure
and efficient download and installation of symmetric keys to a DSKPP
client in environments where near real-time communication may not be
possible.Figure 2 shows which messages get exchanged during each type
of protocol run (4-pass, 2-pass, or 1-pass).
+---------------+ +---------------+
| | | |
| DSKPP client | | DSKPP server |
| | | |
+---------------+ +---------------+
| |
| [ <---- DSKPP trigger ----- ] |
| |
| ------- Client Hello -------> |
| (Applicable to 4- and 2-pass) |
| |
| <------ Server Hello -------- |
| (Applicable to 4-pass only) |
| |
| ------- Client Nonce -------> |
| (Applicable to 4-pass only) |
| |
| <----- Server Finished ------ |
| (Applicable to 4-, 2-, and 1-pass) |
| |
Figure 2: The DSKPP protocol (with OPTIONAL preceding trigger)
The table below identifies which protocol variants may be applied to
the use cases from Section 3:
Doherty, et al. Expires May 1, 2008 [Page 17]
Internet-Draft DSKPP October 2007
----------------------------------------------------------
Protocol Applicable Applicable
Variant Use Cases Deployment Scenarios
----------------------------------------------------------
4-pass All but 3.6 and Near real-time
3.8 if mutual key communication is
generation is desired; possible
none if transport of
a pre-generated key
2-pass All Either near real-time
or non real-time
communication may be
possible
1-pass All but 3.8 Either near real-time
or non real-time
communication may be
possible
Figure 3: Mapping of protocol variants to use cases
4.3. Four-Pass Protocol Usage
The 4-pass protocol flow is suitable for environments wherein there
is near real-time communication possible between the DSKPP client and
DSKPP server. It is not suitable for environments wherein
administrative approval is a required step in the flow, nor for
provisioning of pre-generated keys.
The full four-pass protocol exchange is as follows:
[<Trigger>]:
[ID_Device], [ID_K], [URL_S], [R_S]
<KeyProvClientHello>:
[ID_Device], [ID_K], [R_S], Alg_List
<KeyProvServerHello>:
R_S, Alg_Sel, [K_SERVER], [DSKPP-PRF_K_MAC'("MAC 1 Computation" ||
[R] || R_S, len(R_S))
<KeyProvClientNonce>:
Doherty, et al. Expires May 1, 2008 [Page 18]
Internet-Draft DSKPP October 2007
AUTHDATA, ENC_PK_SERVER(R_C) OR AUTHDATA, ENC_K_SHARED(R_C)
<KeyProvServerFinished>:
K_CONFDATA, DSKPP-PRF_K_MAC("MAC 2 Computation"||R_C, len(R_C))
The following subsections describe the exchange in more detail.
4.3.1. Message Flow
The 4-pass protocol flow consists of two round trips between the
DSKPP client and DSKPP server (see Figure 2), where each round-trip
involves two "passes", i.e., one request message and one response
message:
Round-trip #1: Pass 1 = <KeyProvClientHello>, Pass 2 =
<KeyProvServerHello>
Round-trip #2: Pass 3 = <KeyProvClientNonce>, Pass 4 =
<KeyProvServerFinished>
4.3.1.1. Round-trip #1: <KeyProvClientHello> and <KeyProvServerHello>
The DSKPP client sends a <KeyProvClientHello> message to the DSKPP
server. The message provides information to the DSKPP server about
the DSKPP versions, protocol variants, key types, encryption and MAC
algorithms supported by the cryptographic module for the purposes of
this protocol.
The DSKPP server responds to the DSKPP client with a
<KeyProvServerHello> message, whose content includes a random nonce,
R_S, along with information about the type of key to generate, and
the encryption algorithm chosen to protect sensitive data sent in the
protocol. The length of the nonce R_S may depend on the selected key
type. The <KeyProvServerHello> message also provides information
about either a shared secret key to use for encrypting the
cryptographic module's random nonce (see description of
<KeyProvClientNonce> below), or its own public key. Optionally,
<KeyProvServerHello> may include a MAC that the DSKPP client may use
for server authentication during key replacement.
4.3.1.2. Round-trip #2: <KeyProvClientNonce> and
<KeyProvServerFinished>
Based on information contained in the <KeyProvServerHello> message,
the cryptographic module generates a random nonce, R_C. The length of
the nonce R_C may depend on the selected key type. The cryptographic
module encrypts R_C using the selected encryption algorithm and with
Doherty, et al. Expires May 1, 2008 [Page 19]
Internet-Draft DSKPP October 2007
a key, K, that is either the DSKPP server's public key, K_SERVER, or
a shared secret key, K_SHARED, as indicated by the DSKPP server. If
K is equivalent to K_SERVER, then the cryptographic module SHOULD
verify the server's certificate before using it to encrypt R_C in
accordance with [RFC3280]. The DSKPP client then sends the encrypted
random nonce to the DSKPP server in a <KeyProvClientNonce> message,
and may include client authentication data, such as a certificate or
MAC derived from an authentication code and R_C. Finally, the
cryptographic module calculates a symmetric key, K_TOKEN, of the
selected type from the combination of the two random nonces R_S and
R_C, the encryption key K, and possibly some other data, using the
DSKPP-PRF function defined in Section 5.1.
The DSKPP server decrypts R_C, calculates K_TOKEN from the
combination of the two random nonces R_S and R_C, the encryption key
K, and possibly some other data, using the DSKPP-PRF function defined
in Section 5.1. The server then associates K_TOKEN with the
cryptographic module in a server-side data store. The intent is that
the data store later on will be used by some service that needs to
verify or decrypt data produced by the cryptographic module and the
key.
Once the association has been made, the DSKPP server sends a
confirmation message to the DSKPP client called
<KeyProvServerFinished>. Optionally, <KeyProvServerFinished> may
include a MAC that the DSKPP client may use for server
authentication. The confirmation message includes a key container
that holds an identifier for the generated key (but not the key
itself) and additional configuration information, e.g., the identity
of the DSKPP server. The default symmetric key container format that
is used in the <KeyProvServerFinished> message is based on the
Portable Symmetric Key Container (PSKC) defined in [PSKC].
Alternative formats MAY include PKCS#12 [PKCS-12] or PKCS#5 XML
[PKCS-5-XML] format.
Upon receipt of the DSKPP server's confirmation message, the
cryptographic module associates the provided key container with the
generated key K_TOKEN, and stores any provided configuration data.
4.3.2. Generation of Symmetric Keys for Cryptographic Modules
With 4-pass DSKPP, the symmetric key that is the target of
provisioning, is generated on-the-fly without being transferred
between the DSKPP client and DSKPP server. A sample data flow
depicting how this works followed by computational information are
provided in the subsections below.
Doherty, et al. Expires May 1, 2008 [Page 20]
Internet-Draft DSKPP October 2007
4.3.2.1. Data Flow
A sample data flow showing key generation during the 4-pass protocol
is shown in Figure 4.
+----------------------+ +-------+ +----------------------+
| +------------+ | | | | |
| | Server key | | | | | |
| +<-| Public |------>------------->-------------+---------+ |
| | | Private | | | | | | | |
| | +------------+ | | | | | | |
| | | | | | | | | |
| V V | | | | V V |
| | +---------+ | | | | +---------+ | |
| | | Decrypt |<-------<-------------<-----------| Encrypt | | |
| | +---------+ | | | | +---------+ | |
| | | +--------+ | | | | ^ | |
| | | | Server | | | | | | | |
| | | | Random |--->------------->------+ +----------+ | |
| | | +--------+ | | | | | | Client | | |
| | | | | | | | | | Random | | |
| | | | | | | | | +----------+ | |
| | | | | | | | | | | |
| | V V | | | | V V | |
| | +------------+ | | | | +------------+ | |
| +-->| DSKPP PRF | | | | | | DSKPP PRF |<----+ |
| +------------+ | | | | +------------+ |
| | | | | | | |
| V | | | | V |
| +-------+ | | | | +-------+ |
| | Key | | | | | | Key | |
| +-------+ | | | | +-------+ |
| +-------+ | | | | +-------+ |
| |Key Id |-------->------------->------|Key Id | |
| +-------+ | | | | +-------+ |
+----------------------+ +-------+ +----------------------+
DSKPP Server DSKPP Client DSKPP Client
(PC Host) (cryptographic module)
Figure 4: Principal data flow for DSKPP key generation -
using public server key
Note: Conceptually, although R_C is one pseudorandom string, it may
be viewed as consisting of two components, R_C1 and R_C2, where R_C1
is generated during the protocol run, and R_C2 can be pre-generated
and loaded on the cryptographic module before the device is issued to
the user. In that case, the latter string, R_C2, SHOULD be unique
for each cryptographic module.
Doherty, et al. Expires May 1, 2008 [Page 21]
Internet-Draft DSKPP October 2007
The inclusion of the two random nonces R_S and R_C in the key
generation provides assurance to both sides (the cryptographic module
and the DSKPP server) that they have contributed to the key's
randomness and that the key is unique. The inclusion of the
encryption key K ensures that no man-in-the-middle may be present, or
else the cryptographic module will end up with a key different from
the one stored by the legitimate DSKPP server.
Note: A man-in-the-middle (in the form of corrupt client software or
a mistakenly contacted server) may present his own public key to the
cryptographic module. This will enable the attacker to learn the
client's version of K_TOKEN. However, the attacker is not able to
persuade the legitimate server to derive the same value for K_TOKEN,
since K_TOKEN is a function of the public key involved, and the
attacker's public key must be different than the correct server's (or
else the attacker would not be able to decrypt the information
received from the client). Therefore, once the attacker is no longer
"in the middle," the client and server will detect that they are "out
of sync" when they try to use their keys. In the case of encrypting
R_C with K_SERVER, it is therefore important to verify that K_SERVER
really is the legitimate server's key. One way to do this is to
independently validate a newly generated K_TOKEN against some
validation service at the server (e.g. by using a connection
independent from the one used for the key generation).
4.3.2.2. Computing the Symmetric Key
In DSKPP, keys are generated using the DSKPP-PRF function defined in
Section 5.1, a secret random value R_C chosen by the DSKPP client, a
random value R_S chosen by the DSKPP server, and the key k used to
encrypt R_C. The input parameter s of DSKPP-PRF is set to the
concatenation of the (ASCII) string "Key generation", k, and R_S, and
the input parameter dsLen is set to the desired length of the key,
K_TOKEN (the length of K_TOKEN is given by the key's type):
dsLen = (desired length of K_TOKEN)
K_TOKEN = DSKPP-PRF (R_C, "Key generation" || k || R_S, dsLen)
When computing K_TOKEN above, the output of DSKPP-PRF MAY be subject
to an algorithm-dependent transform before being adopted as a key of
the selected type. One example of this is the need for parity in DES
keys.
Doherty, et al. Expires May 1, 2008 [Page 22]
Internet-Draft DSKPP October 2007
4.3.3. Client Authentication
To ensure that a generated key K_TOKEN ends up associated with the
correct cryptographic module and user, the DSKPP client using any of
the methods described in Section 5.3. Whatever the method, the DSKPP
server MUST ensure that a generated key is associated with the
correct cryptographic module, and if applicable, the correct user.
4.3.4. Key Confirmation
In four-pass DSKPP, the client includes a nonce R_C in the
<KeyProvClientHello> message. The MAC value in the
<KeyProvServerFinished> message MUST be computed on the (ASCII)
string "MAC 2 computation", the client nonce R_C using a MAC key
K_MAC. This key MUST be generated together with K_TOKEN using R_C
and R_S.
The MAC value in <KeyProvServerFinished> MAY be computed by using the
DSKPP-PRF function of Section 5.1, in which case the input parameter
s MUST consist of the concatenation of the (ASCII) string "MAC 2
computation", R_C, the parameter dsLen MUST be set to the length of
R_C:
dsLen = len(R_C)
MAC = DSKPP-PRF (K_MAC, "MAC 2 computation" || R_C, dsLen)
4.3.5. Server Authentication
A DSKPP server MUST authenticate itself to avoid a false "Commit" of
a symmetric key that which could cause the cryptographic module to
end up in an initialized state for which the server does not know the
stored key. To do this, the DSKPP server authenticates itself by
including a MAC value in the <KeyProvServerHello> message when
replacing a existing key. The MAC value is generated using the
existing the MAC key K_MAC' (the MAC key that existed before this
protocol run). The MAC algorithm MUST be the same as the algorithm
used for key confirmation purposes. In addition, a DSKPP server can
leverage transport layer authentication if it is available.
When the MAC value is used for server authentication, the value MAY
be computed by using the DSKPP-PRF function of Section 5.1, in which
case the input parameter s MUST be set to the concatenation of the
(ASCII) string "MAC 1 computation", R (if sent by the client), and
R_S, and k MUST be set to the existing MAC key K_MAC' . The input
parameter dsLen MUST be set to the length of R_S:
dsLen = len(R_S)
Doherty, et al. Expires May 1, 2008 [Page 23]
Internet-Draft DSKPP October 2007
MAC = DSKPP-PRF (K_MAC', "MAC 1 computation" || [R ||] R_S, dsLen)
4.4. Two-Pass Protocol Usage
The 2-pass protocol flow is suitable for environments wherein near
real-time communication between the DSKPP client and server may not
be possible. It is also suitable for environments wherein
administrative approval is a required step in the flow, and for
provisioning of pre-generated keys. In the 2-pass protocol flow, the
client's initial <KeyProvClientHello> message is directly followed by
a <KeyProvServerFinished> message. There is no exchange of the
<KeyProvServerHello> message or the <KeyProvClientNonce> message.
However, as the two-pass variant of DSKPP consists of one round trip
to the server, the client is still able to include its random nonce,
R_C, algorithm preferences and supported key types in the
<KeyProvClientHello> message. Note that by including R_C in
<KeyProvClientHello>, the DSKPP client is able to ensure the server
is alive before "committing" the key. Also note that the DSKPP
"trigger" message MAY be used to trigger the client's sending of the
<KeyProvClientHello> message.
Essentially, two-pass DSKPP is a transport of key material from the
DSKPP server to the DSKPP client. Two-pass DSKPP supports multiple
key initialization methods that ensure K_TOKEN is not exposed to any
other entity than the DSKPP server and the cryptographic module
itself. Currently, three such key initialization methods are defined
(refer to Section 11), each supporting a different usage of 2-pass
DSKPP:
Key Transport This profile is intended for PKI-capable
devices. Key transport is carried out
using a public key, K_CLIENT, whose
private key part resides in the
cryptographic module as the transport
key.
Key Wrap This profile is ideal for pre-keyed
devices, e.g., SIM cards. Key wrap is
carried out using a symmetric key-
wrapping key, K_SHARED, which is known in
advance by both the cryptographic module
and the DSKPP server.
Passphrase-Based Key Wrap This profile is a variation of the Key
Wrap Profile. It is applicable to
constrained devices with keypads, e.g.,
mobile phones. Key wrap is carried out
using a passphrase-derived key-wrapping
key, K_DERIVED, which is known in advance
by both the cryptographic module and
Doherty, et al. Expires May 1, 2008 [Page 24]
Internet-Draft DSKPP October 2007
DSKPP server.
The full 2-pass protocol exchange when the key is transported using
the client public key is as follows:
[<Trigger>]:
[ID_Device], [ID_K], [URL_S],[R_S]
<KeyProvClientHello>:
[ID_Device], ID_K, R_S, R_C, AUTHDATA, Alg_List
<KeyProvServerFinished>:
ENC_K_CLIENT ( K_TOKEN || K_MAC)), K_CONFDATA, ID_S, DSKPP-
PRF_K_MAC("MAC 1 Computation" || ID_S || R_C, len(R_C) ), [ DSKPP-
PRF_K_MAC'("MAC 1 Computation" || ID_S || R_C), 16]
The full 2-pass protocol exchange when the key is wrapped using a
shared key is as follows:
[<Trigger>]:
[ID_Device], [ID_K], [URL_S],[R_S]
<KeyProvClientHello>:
[ID_Device], ID_K, R_S, R_C, AUTHDATA, Alg_List
<KeyProvServerFinished>:
ENC_K_SHARED(K_TOKEN || K_MAC), K_CONFDATA, ID_S, DSKPP-
PRF_K_MAC("MAC 1 Computation" || ID_S || R_C), [ DSKPP-
PRF_K_MAC'("MAC 1 Computation "|| ID_S||R_C)]
The full 2-pass protocol when the key is wrapped using a passphrase
based derived key is as follows:
[<Trigger>]:
[ID_Device], [ID_K], [URL_S],[R_S]
<KeyProvClientHello>:
Doherty, et al. Expires May 1, 2008 [Page 25]
Internet-Draft DSKPP October 2007
[ID_Device], ID_K, R_S, R_C, AUTHDATA, Alg_List
<KeyProvServerFinished>:
ENC_K_DERIVED(K_TOKEN || K_MAC), K_CONFDATA, ID_S, DSKPP-
PRF_K_MAC("MAC 1 Computation" || ID_S || R_C), [ DSKPP-
PRF_K_MAC'("MAC 1 Computation" || ID_S || R_C)]
The following subsections describe these exchanges in more detail.
4.4.1. Message Flow
The 2-pass protocol flow consists of one round trip between the DSKPP
client and DSKPP server, which consists of two "passes", i.e., one
request message and one response message:
Round-trip #1: Pass 1=<KeyProvClientHello>, Pass
2=<KeyProvServerFinished>
a. The DSKPP client sends a <KeyProvClientHello> message to the
DSKPP server. The message provides the client nonce, R_C, and
information about the DSKPP versions, protocol variants, key
types, encryption and MAC algorithms supported by the
cryptographic module for the purposes of this protocol. The
message may also include client authentication data, such as
device certificate or MAC derived from authentication code and
R_C. Authentication code is sent in clear only when underlying
transport layer can ensure data confidentiality. Unlike 4-pass
DSKPP, 2-pass DSKPP client uses the <KeyProvClientHello> message
to declare which key initialization method it supports, providing
required payload information, e.g., K_CLIENT for the Key
Transport Profile.
b. The DSKPP server generates a key K from which two keys, K_TOKEN
and K_MAC are derived. (Alternatively, the key K may have been
pre-generated as described in Section 3.1. K is either
transported or wrapped in accordance with the key initialization
method specified by the DSKPP client in the <KeyProvClientHello>
message. The server then associates K_TOKEN with the
cryptographic module in a server-side data store. The intent is
that the data store later on will be used by some service that
needs to verify or decrypt data produced by the cryptographic
module and the key.
c. Once the association has been made, the DSKPP server sends a
confirmation message to the DSKPP client called
<KeyProvServerFinished>. The confirmation message includes a key
container that holds an identifier for the key, the key K from
which K_TOKEN and K_MAC are derived, and additional configuration
information (note that the latter MUST include the identity of
Doherty, et al. Expires May 1, 2008 [Page 26]
Internet-Draft DSKPP October 2007
the DSKPP server for authentication purposes). In addition,
<KeyProvServerFinished> MUST include two MACs whose values are
calculated with contribution from the client nonce, R_C, provided
in the <KeyProvClientHello> message. The data will allow the
cryptographic module to perform key confirmation and server
authentication before "committing" the key. Note that the second
MAC value that is intended for key confirmation MAY only be used
for replacing and existing key.
d. Upon receipt of the DSKPP server's confirmation message, the
cryptographic module extracts the key data from the provided key
container, uses the provided MAC values to perform key
confirmation and server authentication, and stores the key
material locally.
4.4.2. Key Confirmation
In two-pass DSKPP, the client is REQUIRED to include a nonce R in the
<KeyProvClientHello> message. Further, the server is REQUIRED to
include an identifier, ID_S, for itself (via the key container) in
the <KeyProvServerFinished> message. The MAC value in the
<KeyProvServerFinished> message MUST be computed on the (ASCII)
string "MAC 1 computation", the server identifier ID_S, and R using a
MAC key K_MAC. This key MUST be provided together with K_TOKEN to
the cryptographic module.
If DSKPP-PRF is used as the MAC algorithm, then the input parameter s
MUST consist of the concatenation of the (ASCII) string "MAC 1
computation" and R, and the parameter dsLen MUST be set to the length
of R:
dsLen = len(R)
MAC = DSKPP-PRF (K_MAC, "MAC 1 computation" || ID_S || R, dsLen)
4.4.3. Server Authentication
A server MUST authenticate itself when attempting to replace an
existing K_TOKEN. In 2-pass DSKPP, servers authenticate themselves
by including a second MAC value in the AuthenticationDataType element
of <KeyProvServerFinished>. The MAC value in the
AuthenticationDataType element MUST be computed on the (ASCII) string
"MAC 1 computation", the server identifier ID_S, and R, using the
existing MAC key K_MAC' (the MAC key that existed before this
protocol run). The MAC algorithm MUST be the same as the algorithm
used for key confirmation purposes.
If DSKPP-PRF is used as the MAC algorithm, then the input parameter s
MUST consist of the concatenation of the (ASCII) string "MAC 1
Doherty, et al. Expires May 1, 2008 [Page 27]
Internet-Draft DSKPP October 2007
computation" ID_S, and R. The parameter dsLen MUST be set to at least
16 (i.e. the length of the MAC MUST be at least 16 octets):
dsLen >= 16
MAC = DSKPP-PRF (K_MAC', "MAC 1 computation" || ID_S || R, dsLen)
4.5. One-Pass Protocol Usage
The one-pass protocol flow is suitable for environments wherein near
real-time communication between the DSKPP client and server may not
be possible. It is also suitable for environments wherein
administrative approval is a required step in the flow, and for
provisioning of pre-generated keys. In one-pass DSKPP, the server
simply sends a <KeyProvServerFinished> message to the DSKPP client.
In this case, there is no exchange of the <KeyProvClientHello>,
<KeyProvServerHello>, and <KeyProvClientNonce> DSKPP messages, and
hence there is no way for the client to express supported algorithms
or key types. Before attempting one-pass DSKPP, the server MUST
therefore have prior knowledge not only that the client is able and
willing to accept this variant of DSKPP, but also of algorithms and
key types supported by the client.
Essentially, one-pass DSKPP is a transport of key material from the
DSKPP server to the DSKPP client. As with two-pass DSKPP, the one-
pass variant relies on key initialization methods that ensure K_TOKEN
is not exposed to any other entity than the DSKPP server and the
cryptographic module itself. The same key initialization profiles
are defined as described in Section 4.4 and Section 11.
Outside the specific cases where one-pass DSKPP is desired, clients
SHOULD be constructed and configured to only accept DSKPP server
messages in response to client-initiated transactions.
The 1-pass protocol when the key is transported using the client
public Key is as follows:
<KeyProvServerFinished>:
ENC_K_CLIENT ( K_TOKEN || K_MAC)), K_CONFDATA, DSKPP-PRF_K_MAC
("MAC 1 Computation" || ID_S || I), [ DSKPP-PRF_K_MAC'("MAC 2
Computation"||ID_S||I')]
The 1-pass protocol when the key is wrapped using a shared key is as
follows:
<KeyProvServerFinished>:
Doherty, et al. Expires May 1, 2008 [Page 28]
Internet-Draft DSKPP October 2007
ENC_K_SHARED (K_TOKEN || K_MAC), K_CONFDATA, DSKPP-PRF_K_MAC("MAC
1 Computation" || ID_S || I), [ PRF_K_MAC'("MAC 2 Computation" ||
ID_S || I')]
The 1-pass protocol when the key is wrapped using a passphrase
derived key is as follows:
<KeyProvServerFinished>:
ENC_K_DERIVED(K_TOKEN || K_MAC), K_CONFDATA, DSKPP-PRF_K_MAC("MAC
1 Computation" || ID_S || I), [DSKPP-PRF_K_MAC'("MAC 2
Computation" || ID_S || I')]
The subsections below describe the 1-pass protocol in more detail.
4.5.1. Message Flow
The 1-pass protocol flow consists of one "pass", i.e., a single
message sent from the DSKPP server to the DSKPP client:
Pass 1: <KeyProvServerFinished>
a. The DSKPP server generates a key K from which two keys, K_TOKEN
and K_MAC are derived. K is either transported or wrapped in
accordance with the key initialization method known in advance by
the DSKPP server. The server then associates K_TOKEN with the
cryptographic module in a server-side data store. The intent is
that the data store later on will be used by some service that
needs to verify or decrypt data produced by the cryptographic
module and the key.
b. Once the association has been made, the DSKPP server sends a
confirmation message to the DSKPP client called
<KeyProvServerFinished>. The confirmation message includes a key
container that holds an identifier for the key, the key K from
which K_TOKEN and K_MAC are derived, and additional configuration
information (note that the latter MUST include the identity of
the DSKPP server for authentication purposes). In addition,
<KeyProvServerFinished> MUST include two MACs, which will allow
the cryptographic module to perform key confirmation and server
authentication before "commuting" the key. Note that unlike two-
pass DSKPP, in the one-pass variant, the server does not have the
client nonce, R_C, and therefore the MACs values are calculated
with contribution from an unsigned integer, I, generated by the
server during the protocol run.
Doherty, et al. Expires May 1, 2008 [Page 29]
Internet-Draft DSKPP October 2007
c. Upon receipt of the DSKPP server's confirmation message, the
cryptographic module extracts the key data from the provided key
container, uses the two MAC values to perform key confirmation
and server authentication, and stores the key material locally.
4.5.2. Key Confirmation
In one-pass DSKPP, the server MUST include an identifier, ID_S, for
itself (via the key container) in the <KeyProvServerFinished>
message. The MAC value in the <KeyProvServerFinished> message MUST
be computed on the (ASCII) string "MAC 1 computation", the server
identifier ID_S, and an unsigned integer value I, using a MAC key
K_MAC. The value I MUST be monotonically increasing and guaranteed
not to be used again by this server towards this cryptographic
module. It could for example be the number of seconds since some
point in time with sufficient granularity, a counter value, or a
combination of the two where the counter value is reset for each new
time value. In contrast to the MAC calculation in four-pass DSKPP,
the MAC key K_MAC MUST be provided together with K_TOKEN to the
cryptographic module.
Note: The integer I does not necessarily need to be maintained by the
DSKPP server on a per cryptographic module basis (it is enough if the
server can guarantee that the same value is never being sent twice to
the same cryptographic module).
If DSKPP-PRF is used as the MAC algorithm, then the input parameter s
MUST consist of the concatenation of the (ASCII) string "MAC 1
computation", ID_S, and I. The parameter dsLen MUST be set to at
least 16 (i.e. the length of the MAC MUST be at least 16 octets):
dsLen >= 16
MAC = DSKPP-PRF (K_MAC, "MAC 1 computation" || ID_S || I, dsLen)
The server MUST provide I to the client in the Nonce attribute of the
<Mac> element of the <KeyProvServerFinished> message using the
AuthenticationCodeMacType defined in Section 6.2.2.4.
4.5.3. Server Authentication
As discussed in , servers need to authenticate themselves when
attempting to replace an existing K_TOKEN. In 1-pass DSKPP, servers
authenticate themselves by including a second MAC value in the
AuthenticationDataType element of <KeyProvServerFinished>. The MAC
value in the AuthenticationDataType element MUST be computed on the
(ASCII) string "MAC 1 computation", the server identifier ID_S, and a
new value I', I' > I, using the existing MAC key K_MAC' (the MAC key
Doherty, et al. Expires May 1, 2008 [Page 30]
Internet-Draft DSKPP October 2007
that existed before this protocol run). The MAC algorithm MUST be
the same as the algorithm used for key confirmation purposes.
If DSKPP-PRF is used as the MAC algorithm, then the input parameter s
MUST consist of the concatenation of the (ASCII) string "MAC 1
computation" ID_S, and I'. The parameter dsLen MUST be set to at
least 16 (i.e. the length of the MAC MUST be at least 16 octets):
dsLen >= 16
MAC = DSKPP-PRF (K_MAC', "MAC 1 computation" || ID_S || I', dsLen)
The server MUST provide I' to the client in the Nonce attribute of
the <Mac> element of the AuthenticationDataType extension. If the
protocol run is successful, the client stores I' as the new value of
I for this server.
5. Methods Common to More Than One Protocol Variant
The mechanisms contained in this section are used in more than one
variant of DSKPP.
5.1. The DSKPP One-Way Pseudorandom Function, DSKPP-PRF
5.1.1. Introduction
All of the protocol variants depend on DSKPP-PRF. The general
requirements on DSKPP-PRF are the same as on keyed hash functions: It
MUST take an arbitrary length input, and be one-way and collision-
free (for a definition of these terms, see, e.g., [FAQ]). Further,
the DSKPP-PRF function MUST be capable of generating a variable-
length output, and its output MUST be unpredictable even if other
outputs for the same key are known.
It is assumed that any realization of DSKPP-PRF takes three input
parameters: A secret key k, some combination of variable data, and
the desired length of the output. The combination of variable data
can, without loss of generalization, be considered as a salt value
(see PKCS#5 Version 2.0 [PKCS-5], Section 4), and this
characterization of DSKPP-PRF SHOULD fit all actual PRF algorithms
implemented by cryptographic modules. From the point of view of this
specification, DSKPP-PRF is a "black-box" function that, given the
inputs, generates a pseudorandom value.
Separate specifications MAY define the implementation of DSKPP-PRF
for various types of cryptographic modules. Appendix B contains two
example realizations of DSKPP-PRF.
Doherty, et al. Expires May 1, 2008 [Page 31]
Internet-Draft DSKPP October 2007
5.1.2. Declaration
DSKPP-PRF (k, s, dsLen)
Input:
k secret key in octet string format
s octet string of varying length consisting of variable data
distinguishing the particular string being derived
dsLen desired length of the output
Output:
DS pseudorandom string, dsLen-octets long
For the purposes of this document, the secret key k MUST be at least
16 octets long.
5.2. Encryption of Pseudorandom Nonces Sent from the DSKPP Client
(Applicable to Four-Pass and Two-Pass DSKPP)
During 4- and 2-pass message exchanges, DSKPP client random nonce(s)
are either encrypted with the public key provided by the DSKPP server
or by a shared secret key. For example, in the case of a public RSA
key, an RSA encryption scheme from PKCS #1 [PKCS-1] MAY be used.
In the case of a shared secret key, to avoid dependence on other
algorithms, the DSKPP client MAY use the DSKPP-PRF function described
herein with the shared secret key K_SHARED as input parameter k (in
this case, K_SHARED SHOULD be used solely for this purpose), the
concatenation of the (ASCII) string "Encryption" and the server's
nonce R_S as input parameter s, and dsLen set to the length of R_C:
dsLen = len(R_C)
DS = DSKPP-PRF(K_SHARED, "Encryption" || R_S, dsLen)
This will produce a pseudorandom string DS of length equal to R_C.
Encryption of R_C MAY then be achieved by XOR-ing DS with R_C:
Enc-R_C = DS ^ R_C
The DSKPP server will then perform the reverse operation to extract
R_C from Enc-R_C.
5.3. Client Authentication Mechanisms (Applicable to Four- and Two-Pass
DSKPP)
To ensure that a generated K_TOKEN ends up associated with the
Doherty, et al. Expires May 1, 2008 [Page 32]
Internet-Draft DSKPP October 2007
correct cryptographic module and user, the DSKPP server MAY couple an
initial user authentication to the DSKPP execution in several ways,
as discussed in the following sub-sections. Whatever the method, the
DSKPP server MUST ensure that a generated key is associated with the
correct cryptographic module, and if applicable, the correct user.
For a further discussion of this, and threats related to man-in-the-
middle attacks in this context, see Section 14.
5.3.1. Device Certificate
Instead of requiring an Authentication Code for in-band
authentication, a device private key and certificate could be used,
which was supplied with the cryptographic module by its issuer for
client authentication at the transport layer e.g TLS/HTTPS. When the
Device certificate is available and client authentication is not
provided in the transport layer, the DSKPP client may include a
device's certificate signed data for the authentication data.
5.3.2. Device Identifier
The DSKPP server could be pre-configured with a unique device
identifier corresponding to a particular cryptographic module. The
DSKPP server MAY then include this identifier in the DSKPP
initialization trigger, and the DSKPP client would include it in its
message(s) to the DSKPP server for authentication. Note that it is
also legitimate for a DSKPP client to initiate the DSKPP protocol run
without having received an initialization message from a server, but
in this case any provided device identifier MUST NOT be accepted by
the DSKPP server unless the server has access to a unique key for the
identified device and that key will be used in the protocol.
5.3.3. Authentication Code
As shown in Figure 5, a key issuer may provide a one-time value,
called an Authentication Code, to the user or device out-of-band and
require this value to be used by the DSKPP client when contacting the
DSKPP server. The DSKPP client MAY include the authentication data
in its <KeyProvClientHello> (and <KeyProvClientNonce> for four-pass)
message, and the DSKPP server MUST verify the data before continuing
with the protocol run.
Note: An alternate method for getting the Authentication Code to the
client, is for the DSKPP server to place the value in the
<TriggerNonce> element of the DSKPP initialization trigger (if
triggers are used; see Section 12.2.7) . When this method is used, a
transport providing privacy and integrity MUST be used to deliver the
DSKPP initialization trigger from the DSKPP server to the DSKPP
client, e.g. HTTPS.
Doherty, et al. Expires May 1, 2008 [Page 33]
Internet-Draft DSKPP October 2007
+------------+ Get Authentication Code +------------+
| User |<------------------------->| Issuer |
+------------+ +------------+
| |
| |
| |
V V
+--------------+ +--------------+
| DSKPP | Authentication Data | DSKPP |
| Client |----------------------->| Server |
+--------------+ +--------------+
Figure 5: User Authentication with One-Time Code
The Authentication Code, AUTHCODE, may be considered as a special
form of a shared secret between a User and a DSKPP server. The
Issuer may generate the Authentication Code as follows:
AUTHCODE = passwordLen || identifier || password || checksum
where
passwordLen : 1 digit indicating the 'password' length. The maximum
length of the password is 10. A passwordLen value '0'
indicates a password of 10 digits.
identifier : A globally unique identifier of the user's order for
token provisioning. The length of the identifier may be
fixed e.g. 10 digits or variable e.g. 1 to 20 digits. The
identifier may be generated as a sequence number.
password : 6 to 10 digits. The password should be generated by the
system as a random number to make the AUTHCODE more
difficult to guess.
checksum : 1 digit calculated from the remaining digits in the code.
The Authentication Data, AUTHDATA, may be derived from the AUTHCODE
and other information as follows:
MAC = DSKPP-PRF-AES(K_AUTHCODE, AUTHCODE->Identifier || URL_S ||
[R_S], 16)
where
Doherty, et al. Expires May 1, 2008 [Page 34]
Internet-Draft DSKPP October 2007
Refer to Section 5.1 for a description of DSKPP-PRF in general and
Appendix B for a description of DSKPP-PRF-AES.
In four-pass DSKPP, the cryptographic module uses the client nonce
R_C, the server nonce R_S, and the server URL URL_S to calculate
the MAC. In two-pass DSKPP, the cryptographic module does not
have access to the server nonce R_S therefore only the client
nonce R_C is used in combination with the server URL URL_S to
produce the MAC.
The K_AUTHCODE MAY be derived from AUTHCODE>password as follows:
K_AUTHCODE = truncate( Hash( Hash(...n times...(
AUTHCODE->password ||R_C||[K]) ) ) )
where
K is optional and MAY be one of the following:
K_CLIENT: The device public key when a device
certificate is available and used for key transport
in 2-pass
K_SHARED: The shared key between the Client and the
Server when it is used for key wrap in two-pass or
for R_C protection in four-pass
K_DERIVED: when a passphrase derived key is used for
key wrap in two-pass.
'truncate()' returns the first 16 bytes from the result of the
last hash iteration, and n is the number of hash iterations. n
may be any number between 10 and 1000.
Notes:
1 Authentication data MAY be omitted if client certificate
authentication has been provided by the transport channel such as
TLS.
2 When an issuer delegates symmetric key provisioning to a third
party provisioning service provider, both client authentication
and issuer authentication are required by the provisioning server.
Client authentication to the issuer MAY be in-band or out-of-band
as described above. The issuer acts as a proxy for the
provisioning server. The issuer authenticates to the provisioning
service provider either using a certificate or a pre-established
secret key.
Doherty, et al. Expires May 1, 2008 [Page 35]
Internet-Draft DSKPP October 2007
5.4. Client Authentication Examples
5.4.1. Example Using a MAC from an Authentication Code
<AuthenticationData>
<ClientID>31300257</ClientID>
<AuthenticationCodeMac>
<IterationCount>512</IterationCount>
<Mac>4bRJf9xXd3KchKoTenHJiw==</Mac>
</AuthenticationCodeMac>
</AuthenticationData>
5.4.2. Example Using a Device Certificate
<AuthenticationData>
<DigitalSignature>
<ds:SignedInfo>
<ds:CanonicalizationMethod
Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315" />
<ds:SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"/>
<ds:Reference URI="#Nonce">
<ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
<ds:DigestValue></ds:DigestValue>
</ds:Reference>
</ds:SignedInfo>
<ds:SignatureValue></ds:SignatureValue>
<ds:KeyInfo>
<ds:X509Data>
<ds:X509Certificate>miib</ds:X509Certificate>
</ds:X509Data>
</ds:KeyInfo>
<ds:Object Id="Nonce">xwQzwEl0CjPAiQeDxwRJdQ==</ds:Object>
</DigitalSignature>
6. Four-Pass Protocol
In this section, example messages are used to describe parameters,
encoding and semantics in a 4-pass DSKPP exchanges. The examples are
written using XML. While they are syntactically correct, MAC and
cipher values are fictitious.
6.1. XML Basics
The DSKPP XML schema can be found in Section 13. Some DSKPP elements
rely on the parties being able to compare received values with stored
values. Unless otherwise noted, all elements in this document that
have the XML Schema "xs:string" type, or a type derived from it, MUST
Doherty, et al. Expires May 1, 2008 [Page 36]
Internet-Draft DSKPP October 2007
be compared using an exact binary comparison. In particular, DSKPP
implementations MUST NOT depend on case-insensitive string
comparisons, normalization or trimming of white space, or conversion
of locale-specific formats such as numbers.
Implementations that compare values that are represented using
different character encodings MUST use a comparison method that
returns the same result as converting both values to the Unicode
character encoding, Normalization Form C [UNICODE], and then
performing an exact binary comparison.
No collation or sorting order for attributes or element values is
defined. Therefore, DSKPP implementations MUST NOT depend on
specific sorting orders for values.
6.2. Round-Trip #1: <KeyProvClientHello> and <KeyProvServerHello>
6.2.1. Examples
Doherty, et al. Expires May 1, 2008 [Page 37]
Internet-Draft DSKPP October 2007
6.2.1.1. Example Without a Preceding Trigger
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvClientHello Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:1.0:container"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:1.0:protocol
keyprov-dskpp-1.0.xsd">
<DeviceIdentifierData>
<DeviceId>
<pskc:Manufacturer>ManufacturerABC</pskc:Manufacturer>
<pskc:SerialNo>XL0000000001234</pskc:SerialNo>
<pskc:Model>U2</pskc:Model>
</DeviceId>
</DeviceIdentifierData>
<SupportedKeyTypes>
<Algorithm>urn:ietf:params:xml:schema:keyprov:otpalg#HOTP</Algorithm>
<Algorithm>
http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES
</Algorithm>
</SupportedKeyTypes>
<SupportedEncryptionAlgorithms>
<Algorithm>http://www.w3.org/2001/05/xmlenc#rsa_1_5</Algorithm>
<Algorithm>
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes
</Algorithm>
</SupportedEncryptionAlgorithms>
<SupportedMacAlgorithms>
<Algorithm>
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes
</Algorithm>
</SupportedMacAlgorithms>
<SupportedProtocolVariants><FourPass/></SupportedProtocolVariants>
<SupportedKeyContainers>
<KeyContainerFormat>
urn:ietf:params:xml:schema:keyprov:container#KeyContainer
</KeyContainerFormat>
</SupportedKeyContainers>
</dskpp:KeyProvClientHello>
Doherty, et al. Expires May 1, 2008 [Page 38]
Internet-Draft DSKPP October 2007
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvServerHello Version="1.0" SessionID="4114" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:1.0:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:1.0:protocol
keyprov-dskpp-1.0.xsd">
<KeyType>
urn:ietf:params:xml:schema:keyprov:otpalg#SecurID-AES
</KeyType>
<EncryptionAlgorithm>
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes
</EncryptionAlgorithm>
<MacAlgorithm>
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes
</MacAlgorithm>
<EncryptionKey>
<ds:KeyName>KEY-1</ds:KeyName>
</EncryptionKey>
<KeyContainerFormat>
urn:ietf:params:xml:schema:keyprov:container#KeyContainer
</KeyContainerFormat>
<Payload>
<Nonce>qw2ewasde312asder394jw==</Nonce>
</Payload>
</dskpp:KeyProvServerHello>
6.2.1.2. Example Assuming a Preceding Trigger
Doherty, et al. Expires May 1, 2008 [Page 39]
Internet-Draft DSKPP October 2007
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvClientHello Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:1.0:container"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:1.0:protocol
keyprov-dskpp-1.0.xsd">
<DeviceIdentifierData>
<DeviceId>
<pskc:Manufacturer>ManufacturerABC</pskc:Manufacturer>
<pskc:SerialNo>XL0000000001234</pskc:SerialNo>
<pskc:Model>U2</pskc:Model>
</DeviceId>
</DeviceIdentifierData>
<KeyID>SE9UUDAwMDAwMDAx</KeyID>
<TriggerNonce>112dsdfwf312asder394jw==</TriggerNonce>
<SupportedKeyTypes>
<Algorithm>urn:ietf:params:xml:schema:keyprov:otpalg#HOTP</Algorithm>
<Algorithm>
http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES
</Algorithm>
</SupportedKeyTypes>
<SupportedEncryptionAlgorithms>
<Algorithm>http://www.w3.org/2001/05/xmlenc#rsa_1_5</Algorithm>
<Algorithm>
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes
</Algorithm>
</SupportedEncryptionAlgorithms>
<SupportedMacAlgorithms>
<Algorithm>
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes
</Algorithm>
</SupportedMacAlgorithms>
<SupportedProtocolVariants><FourPass/></SupportedProtocolVariants>
<SupportedKeyContainers>
<KeyContainerFormat>
urn:ietf:params:xml:schema:keyprov:container#KeyContainer
</KeyContainerFormat>
</SupportedKeyContainers>
</dskpp:KeyProvClientHello>
Doherty, et al. Expires May 1, 2008 [Page 40]
Internet-Draft DSKPP October 2007
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvServerHello Version="1.0" SessionID="4114" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:1.0:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:1.0:protocol
keyprov-dskpp-1.0.xsd">
<KeyType>
http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES
</KeyType>
<EncryptionAlgorithm>
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes
</EncryptionAlgorithm>
<MacAlgorithm>
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes
</MacAlgorithm>
<EncryptionKey>
<ds:KeyName>KEY-1</ds:KeyName>
</EncryptionKey>
<KeyContainerFormat>
urn:ietf:params:xml:schema:keyprov:container#KeyContainer
</KeyContainerFormat>
<Payload>
<Nonce>qw2ewasde312asder394jw==</Nonce>
</Payload>
<Mac MacAlgorithm=
"urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes">
cXcycmFuZG9tMzEyYXNkZXIzOTRqdw==
</Mac>
</dskpp:KeyProvServerHello>
6.2.2. Components of the <KeyProvClientHello> Request
The components of this message have the following meaning:
o Version: (attribute inherited from the AbstractRequestType type)
The highest version of this protocol the client supports. Only
version one ("1.0") is currently specified.
o <DeviceIdentifierData>: An identifier for the cryptographic module
as defined in Section 5.3 above. The identifier MUST only be
present if such shared secrets exist or if the identifier was
provided by the server in a <KeyProvTrigger> element (see
Section 12.2.7 below). In the latter case, it MUST have the same
value as the identifier provided in that element.
o <KeyID>: An identifier for the key that will be overwritten if the
protocol run is successful. The identifier MUST only be present
if the key exists or if the identifier was provided by the server
in a <KeyProvTrigger> element, in which case, it MUST have the
Doherty, et al. Expires May 1, 2008 [Page 41]
Internet-Draft DSKPP October 2007
same value as the identifier provided in that element (see a
(Section 9) and Section 12.2.7 below).
o <KeyProvClientNonce>: This is the nonce R, which, when present,
MUST be used by the server when calculating MAC values (see
below). It is RECOMMENDED that clients include this element
whenever the <KeyID> element is present.
o <TriggerNonce>: This OPTIONAL element MUST be present if and only
if the DSKPP run was initialized with a <KeyProvTrigger> message
(see Section 12.2.7 below), and MUST, in that case, have the same
value as the <TriggerNonce> child of that message. A server using
nonces in this way MUST verify that the nonce is valid and that
any device or key identifier values provided in the
<KeyProvTrigger> message match the corresponding identifier values
in the <KeyProvClientHello> message.
o <SupportedKeyTypes>: A sequence of URIs indicating the key types
for which the cryptographic module is willing to generate keys
through DSKPP.
o <SupportedEncryptionAlgorithms>: A sequence of URIs indicating the
encryption algorithms supported by the cryptographic module for
the purposes of DSKPP. The DSKPP client MAY indicate the same
algorithm both as a supported key type and as an encryption
algorithm.
o <SupportedMacAlgorithms>: A sequence of URIs indicating the MAC
algorithms supported by the cryptographic module for the purposes
of DSKPP. The DSKPP client MAY indicate the same algorithm both
as an encryption algorithm and as a MAC algorithm (e.g.,
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes defined
in Appendix B).
o <SupportedProtocolVariants>: This OPTIONAL element is used by the
DSKPP client to indicate support for four-pass or two-pass DSKPP.
If two-pass support is specified, then <KeyProvClientNonce> MUST
be set to nonce R in the <KeyProvClientHello> message unless
<TriggerNonce> is already present.
o <SupportedKeyContainers>: This OPTIONAL element is a sequence of
URIs indicating the key container formats supported by the DSKPP
client. If this element is not provided, then the DSKPP server
MUST proceed with
"urn:ietf:params:xml:schema:keyprov:container#KeyContainer" (see
[PSKC]).
o <AuthenticationData>: This OPTIONAL element contains data that the
DSKPP client uses to authenticate the user or device to the DSKPP
server. The element is set as specified in Section 5.3.
o <Extensions>: A sequence of extensions. One extension is defined
for this message in this version of DSKPP: the ClientInfoType (see
Section 10).
Doherty, et al. Expires May 1, 2008 [Page 42]
Internet-Draft DSKPP October 2007
6.2.2.1. The DSKPP Client: The DeviceIdentifierDataType Type
The DeviceIdentifierDataType type is used to uniquely identify the
device that houses the cryptographic module, e.g., a mobile phone.
The device identifier allows the DSKPP server to find, e.g., a pre-
shared transport key for 2-pass DSKPP and/or the correct shared
secret for MAC'ing purposes. The default DeviceIdentifierDataType is
defined in [PSKC].
6.2.2.2. Selecting a Protocol Variant: The ProtocolVariantsType Type
The ProtocolVariantsType type is OPTIONAL for a DSKPP client, who MAY
use it to indicate the number of passes of the DSKPP protocol that it
supports. The ProtocolVariantsType MAY be used to indicate support
for 4-pass or 2-pass DSKPP. Because 1-pass DSKPP does not include a
client request to the server, the ProtocolVariantsType type MAY NOT
be used to indicate support for 1-pass DSKPP. If the
ProtocolVariantsType is not used, then the DSKPP server will proceed
with ordinary 4-pass DSKPP. However, it does not support 4-pass
DSKPP, then the server MUST find a suitable two-pass variant or else
the protocol run will fail.
The TwoPassSupportType type signals client support for the 2-pass
version of DSKPP, informs the server of supported two-pass variants,
and provides OPTIONAL payload data to the DSKPP server. The payload
is sent in an opportunistic fashion, and MAY be discarded by the
DSKPP server if the server does not support the two-pass variant the
payload is associated with. The elements of this type have the
following meaning:
o <SupportedKeyInitializationMethod>: A two-pass key initialization
method supported by the DSKPP client. Multiple supported methods
MAY be present, in which case they MUST be listed in order of
precedence.
o <Payload>: An OPTIONAL payload associated with each supported key
initialization method.
A DSKPP client that indicates support for two-pass DSKPP MUST also
include the nonce R in its <KeyProvClientHello> message (this will
enable the client to verify that the DSKPP server it is communicating
with is alive).
6.2.2.3. Selecting a Key Container Format: The KeyContainersFormatType
Type
The OPTIONAL KeyContainersFormatType type is a list of type-value
pairs that a DSKPP client or server MAY use to define key container
formats it supports. Key container formats are identified through
URIs, e.g., the PSKC KeyContainer URI
"urn:ietf:params:xml:schema:keyprov:container#KeyContainer" (see
Doherty, et al. Expires May 1, 2008 [Page 43]
Internet-Draft DSKPP October 2007
[PSKC]).
6.2.2.4. Selecting a Client and Server Authentication Mechanism: The
AuthenticationDataType Type
The OPTIONAL AuthenticationDataType type is used by DSKPP clients and
server to carry authentication values in DSKPP messages. The element
MAY contain a device certificate or MAC derived from an
authentication code as follows:
a. A DSKPP client MAY include a one-time use AuthenticationCode that
was given by the issuer to the user for acquiring a symmetric
key. An AuthenticationCode MAY or MAY NOT contain alphanumeric
characters in addition to numeric digits depending on the device
type and policy of the issuer. For example, if the device is a
mobile phone, a code that the user enters on the keypad would
typically be restricted to numeric digits for ease of use. An
authentication code MAY be sent to the DSKPP server as MAC data
calculated according to section Section 5.3.3.
b. A DSKPP client MAY contain Authentication Data consisting of
signed data of client Nonce with a client certificate's private
key. A service provider may have a policy to issue symmetric
keys for a device only if it has a trusted device certificate.
An authentication code isn't required in this case.
c. A DSKPP server MAY use the AuthenticationDataType element
AuthenticationCodeMac to carry a MAC for authenticating itself to
the client. For example, when a successful 1- or 2-pass DSKPP
protocol run will result in an existing key being replaced, then
the DSKPP server MUST include a MAC proving to the DSKPP client
that the server knows the value of the key it is about to
replace.
The element of the AuthenticationDataType type have the following
meaning:
o <ClientID>: A requester's identifier. The value MAY be a user ID,
a device ID, or a keyID associated with the requester's
authentication value. When the authentication data is based on a
certificate, <ClientID> can be omitted, as the certificate itself
is typically sufficient to identify the requester. Also, if a
<KeyProvTrigger> message was provided by the server to initiate
the DSKPP protocol run, <ClientID> can be omitted, as the
DeviceID, KeyID, and/or nonce provided in the
<InitializationTriggerType> element ought to be sufficient to
identify the requester.
o <AuthenticationCodeMac>: An authentication MAC and OPTIONAL
additional information (e.g., MAC algorithm). The value could be
a one-time use value sent as a MAC value to the DSKPP server; or,
it could be a MAC value sent to the DSKPP client. Refer to
section Section 5.3.3 for calculation of MAC with an
Doherty, et al. Expires May 1, 2008 [Page 44]
Internet-Draft DSKPP October 2007
authentication code.
o <DigitalSignature>: Client nonce R_C signed using the device
certificate and sent in KeyProvClientHello for two-pass protocol
or in KeyProvClientNonce for four-pass protocol.
6.2.3. Components of the <KeyProvServerHello> Response
This message is the first message sent from the DSKPP server to the
DSKPP client (assuming a trigger message has not been sent to
initiate the protocol, in which case, this message is the second
message sent from the DSKPP server to the DSKPP client). It is sent
upon reception of a <KeyProvClientHello> message. The components of
this message have the following meaning:
o Version: (attribute inherited from the AbstractResponseType type)
The version selected by the DSKPP server. MAY be lower than the
version indicated by the DSKPP client, in which case, local policy
at the client MUST determine whether or not to continue the
session.
o SessionID: (attribute inherited from the AbstractResponseType
type) An identifier for this session.
o Status: (attribute inherited from the AbstractResponseType type)
Return code for the <KeyProvClientHello>. If Status is not
"Continue", only the Status and Version attributes will be
present; otherwise, all the other element MUST be present as well.
o <KeyType>: The type of the key to be generated.
o <EncryptionAlgorithm>: The encryption algorithm to use when
protecting R_C.
o <MacAlgorithm>: The MAC algorithm to be used by the DSKPP server.
o <EncryptionKey>: Information about the key to use when encrypting
R_C. It will either be the server's public key (the <ds:KeyValue>
alternative of ds:KeyInfoType) or an identifier for a shared
secret key (the <ds:KeyName> alternative of ds:KeyInfoType).
o <KeyContainerFormat>: The key container format type to be used by
the DSKPP server. The default setting relies on the
KeyContainerType element defined in
"urn:ietf:params:xml:schema:keyprov:container" [PSKC].
o <Payload>: The actual payload. For this version of the protocol,
only one payload is defined: the pseudorandom string R_S.
o <Extensions>: A list of server extensions. Two extensions are
defined for this message in this version of DSKPP: the
ClientInfoType and the ServerInfoType (see Section 10).
o <Mac>: The MAC MUST be present if the DSKPP run will result in the
replacement of an existing symmetric key with a new one (i.e., if
the <KeyID> element was present in the <ClientHello message). In
this case, the DSKPP server MUST prove to the cryptographic module
that it is authorized to replace it.
Doherty, et al. Expires May 1, 2008 [Page 45]
Internet-Draft DSKPP October 2007
The DSKPP client MUST verify the MAC if the successful execution
of the protocol will result in the replacement of an existing
symmetric key with a newly generated one. The DSKPP client MUST
terminate the DSKPP session if the MAC does not verify, and MUST
delete any nonces, keys, and/or secrets associated with the failed
run of the DSKPP protocol.
The MacType's MacAlgorithm attribute MUST, when present, identify
the negotiated MAC algorithm.
6.3. Round-Trip #2: <KeyProvClientNonce> and <KeyProvServerFinished>
6.3.1. Examples
6.3.1.1. Example Using Default Encryption
This message contains the nonce chosen by the cryptographic module,
R_C, encrypted by the specified encryption key and encryption
algorithm.
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvClientNonce Version="1.0" SessionID="4114"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:1.0:protocol
keyprov-dskpp-1.0.xsd">
<EncryptedNonce>VXENc+Um/9/NvmYKiHDLaErK0gk=</EncryptedNonce>
<AuthenticationData>
<ClientID>31300257</ClientID>
<AuthenticationCodeMac>
<IterationCount>512</IterationCount>
<Mac>4bRJf9xXd3KchKoTenHJiw==</Mac>
</AuthenticationCodeMac>
</AuthenticationData>
</dskpp:KeyProvClientNonce>
Doherty, et al. Expires May 1, 2008 [Page 46]
Internet-Draft DSKPP October 2007
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvServerFinished Version="1.0" SessionID="4114" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:1.0:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:1.0:protocol
keyprov-dskpp-1.0.xsd">
<KeyContainer>
<KeyContainer Version="1.0">
<pskc:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#hmac-sha1"/>
<pskc:Device>
<pskc:Key
KeyAlgorithm=
"http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES"
KeyId="XL0000000001234">
<pskc:Issuer>CredentialIssuer</pskc:Issuer>
<pskc:Usage otp="true">
<pskc:ResponseFormat format="DECIMAL" length="6"/>
</pskc:Usage>
<pskc:FriendlyName>MyFirstToken</pskc:FriendlyName>
<pskc:Data Name="TIME">
<pskc:Value>AAAAADuaygA=</pskc:Value>
</pskc:Data>
<pskc:Expiry>10/30/2012</pskc:Expiry>
</pskc:Key>
</pskc:Device>
</KeyContainer>
</KeyContainer>
<Mac
MacAlgorithm="urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes">
miidfasde312asder394jw==
</Mac>
</dskpp:KeyProvServerFinished>
6.3.2. Components of a <KeyProvClientNonce> Request
The components of this message have the following meaning:
o Version: (inherited from the AbstractRequestType type) MUST be the
same version as in the <KeyProvServerHello> message.
o <SessionID>: MUST have the same value as the SessionID attribute
in the received <KeyProvServerHello> message.
o <EncryptedNonce>: The nonce generated and encrypted by the
cryptographic module. The encryption MUST be made using the
selected encryption algorithm and identified key, and as specified
in Section 5.1.
Doherty, et al. Expires May 1, 2008 [Page 47]
Internet-Draft DSKPP October 2007
o <AuthenticationData>: The authentication data value MUST be set as
specified in Section 5.3 and Section 6.2.2.4.
o <Extensions>: A list of extensions. Two extensions are defined
for this message in this version of DSKPP: the ClientInfoType and
the ServerInfoType (see Section 10)
6.3.3. Components of a <KeyProvServerFinished> Response
This message is the last message of the DSKPP protocol run. In a
4-pass exchange, the DSKPP server sends this message in response to a
<KeyProvClientNonce> message, whereas in a 2-pass exchange, the DSKPP
server sends this message in response to a <KeyProvClientHello>
message. In a 1-pass exchange, the DSKPP server sends only this
message to the client. The components of this message have the
following meaning:
o Version: (inherited from the AbstractResponseType type) The DSKPP
version used in this session.
o SessionID: (inherited from the AbstractResponseType type) The
previously established identifier for this session.
o Status: (inherited from the AbstractResponseType type) Return code
for the <KeyProvServerFinished> message. If Status is not
"Success", only the Status, SessionID, and Version attributes will
be present (the presence of the SessionID attribute is dependent
on the type of reported error); otherwise, all the other elements
MUST be present as well. In this latter case, the
<KeyProvServerFinished> message can be seen as a "Commit" message,
instructing the cryptographic module to store the generated key
and associate the given key identifier with this key.
o <KeyContainer>: The key container containing symmetric key values
(in the case of a 2- or 1-pass exchange) and configuration data.
The default container format is based on the KeyContainerType type
from PSKC, as defined in [PSKC].
o <Extensions>: A list of extensions chosen by the DSKPP server.
For this message, this version of DSKPP defines one extension, the
ClientInfoType (see Section 10).
o <Mac>: To avoid a false "Commit" message causing the cryptographic
module to end up in an initialized state for which the server does
not know the stored key, <KeyProvServerFinished> messages MUST
always be authenticated with a MAC. The MAC MUST be made using
the already established MAC algorithm.
When receiving a <KeyProvServerFinished> message with
Status="Success" for which the MAC verifies, the DSKPP client MUST
associate the generated key K_TOKEN with the provided key
identifier and store this data permanently. After this operation,
it MUST NOT be possible to overwrite the key unless knowledge of
an authorizing key is proven through a MAC on a later
<KeyProvServerHello> (and <KeyProvServerFinished>) message.
Doherty, et al. Expires May 1, 2008 [Page 48]
Internet-Draft DSKPP October 2007
The DSKPP client MUST verify the MAC. The DSKPP client MUST
terminate the DSKPP session if the MAC does not verify, and MUST,
in this case, also delete any nonces, keys, and/or secrets
associated with the failed run of the DSKPP protocol.
The MacType's MacAlgorithm attribute MUST, when present, identify
the negotiated MAC algorithm.
6.4. DSKPP Server Results: The StatusCode Type
The StatusCode type enumerates all possible return codes. Upon
transmission or receipt of a message for which the Status attribute's
value is not "Success" or "Continue", the default behavior, unless
explicitly stated otherwise below, is that both the DSKPP server and
the DSKPP client MUST immediately terminate the DSKPP session. DSKPP
servers and DSKPP clients MUST delete any secret values generated as
a result of failed runs of the DSKPP protocol. Session identifiers
MAY be retained from successful or failed protocol runs for replay
detection purposes, but such retained identifiers MUST NOT be reused
for subsequent runs of the protocol.
When possible, the DSKPP client SHOULD present an appropriate error
message to the user.
These status codes are valid in all 4-Pass DSKPP Response messages
unless explicitly stated otherwise:
o "Continue" indicates that the DSKPP server is ready for a
subsequent request from the DSKPP client. It cannot be sent in
the server's final message.
o "Success" indicates successful completion of the DSKPP session.
It can only be sent in the server's final message.
o "Abort" indicates that the DSKPP server rejected the DSKPP
client's request for unspecified reasons.
o "AccessDenied" indicates that the DSKPP client is not authorized
to contact this DSKPP server.
o "MalformedRequest" indicates that the DSKPP server failed to parse
the DSKPP client's request.
o "UnknownRequest" indicates that the DSKPP client made a request
that is unknown to the DSKPP server.
o "UnknownCriticalExtension" indicates that a critical DSKPP
extension (see below) used by the DSKPP client was not supported
or recognized by the DSKPP server.
o "UnsupportedVersion" indicates that the DSKPP client used a DSKPP
protocol version not supported by the DSKPP server. This error is
only valid in the DSKPP server's first response message.
o "NoSupportedKeyTypes" indicates that the DSKPP client only
suggested key types that are not supported by the DSKPP server.
This error is only valid in the DSKPP server's first response
message.
Doherty, et al. Expires May 1, 2008 [Page 49]
Internet-Draft DSKPP October 2007
o "NoSupportedEncryptionAlgorithms" indicates that the DSKPP client
only suggested encryption algorithms that are not supported by the
DSKPP server. This error is only valid in the DSKPP server's
first response message.
o "NoSupportedMacAlgorithms" indicates that the DSKPP client only
suggested MAC algorithms that are not supported by the DSKPP
server. This error is only valid in the DSKPP server's first
response message.
o "NoProtocolVariants" indicates that the DSKPP client only
suggested a protocol variant (either 2-pass or 4-pass) that is not
supported by the DSKPP server. This error is only valid in the
DSKPP server's first response messagei
o "NoSupportedKeyContainers" indicates that the DSKPP client only
suggested key container formats that are not supported by the
DSKPP server. This error is only valid in the DSKPP server's
first response message.
o "AuthenticationDataMissing" indicates that the DSKPP client didn't
provide authentication data that the DSKPP server required.
o "AuthenticationDataInvalid" indicates that the DSKPP client
supplied user or device authentication data that the DSKPP server
failed to validate.
o "InitializationFailed" indicates that the DSKPP server could not
generate a valid key given the provided data. When this status
code is received, the DSKPP client SHOULD try to restart DSKPP, as
it is possible that a new run will succeed.
o "ProvisioningPeriodExpired" indicates that the provisioning period
set by the DSKPP server has expired. When the status code is
received, the DSKPP client SHOULD report the key initialization
failure reason to the user and the user MUST register with the
DSKPP server to initialize a new key.
7. Two-Pass Protocol
In this section, example messages are used to describe parameters,
encoding and semantics in a 2-pass DSKPP exchanges. The examples are
written using XML. While they are syntactically correct, MAC and
cipher values are fictitious.
7.1. XML Basics
The DSKPP XML schema can be found in Section 13. Some DSKPP elements
rely on the parties being able to compare received values with stored
values. Unless otherwise noted, all elements in this document that
have the XML Schema "xs:string" type, or a type derived from it, MUST
be compared using an exact binary comparison. In particular, DSKPP
implementations MUST NOT depend on case-insensitive string
comparisons, normalization or trimming of white space, or conversion
Doherty, et al. Expires May 1, 2008 [Page 50]
Internet-Draft DSKPP October 2007
of locale-specific formats such as numbers.
Implementations that compare values that are represented using
different character encodings MUST use a comparison method that
returns the same result as converting both values to the Unicode
character encoding, Normalization Form C [UNICODE], and then
performing an exact binary comparison.
No collation or sorting order for attributes or element values is
defined. Therefore, DSKPP implementations MUST NOT depend on
specific sorting orders for values.
7.2. Round-Trip #1: <KeyProvClientHello> and <KeyProvServerFinished>
7.2.1. Examples
7.2.1.1. Example Using the Key Transport Profile
The client indicates support all the Key Transport, Key Wrap, and
Passphrase-Based Key Wrap profiles (see Section 11):
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvClientHello Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:1.0:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:1.0:protocol
keyprov-dskpp-1.0.xsd">
<DeviceIdentifierData>
<DeviceId>
<pskc:Manufacturer>ManufacturerABC</pskc:Manufacturer>
<pskc:SerialNo>XL0000000001234</pskc:SerialNo>
<pskc:Model>U2</pskc:Model>
</DeviceId>
</DeviceIdentifierData>
<ClientNonce>xwQzwEl0CjPAiQeDxwRJdQ==</ClientNonce>
<SupportedKeyTypes>
<Algorithm>urn:ietf:params:xml:schema:keyprov:otpalg#HOTP</Algorithm>
<Algorithm>
http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES
</Algorithm>
</SupportedKeyTypes>
<SupportedEncryptionAlgorithms>
<Algorithm>http://www.w3.org/2001/05/xmlenc#rsa_1_5</Algorithm>
<Algorithm>http://www.w3.org/2001/04/xmlenc#kw-aes128</Algorithm>
<Algorithm>urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes</Algorithm>
</SupportedEncryptionAlgorithms>
Doherty, et al. Expires May 1, 2008 [Page 51]
Internet-Draft DSKPP October 2007
<SupportedMacAlgorithms>
<Algorithm>urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes</Algorithm>
</SupportedMacAlgorithms>
<SupportedProtocolVariants>
<TwoPass>
<SupportedKeyInitializationMethod>
urn:ietf:params:xml:schema:keyprov:protocol#wrap
</SupportedKeyInitializationMethod>
<Payload xsi:type="ds:KeyInfoType">
<ds:KeyName>Key_001</ds:KeyName>
</Payload>
<SupportedKeyInitializationMethod>
urn:ietf:params:xml:schema:keyprov:protocol#transport
</SupportedKeyInitializationMethod>
<SupportedKeyInitializationMethod>
urn:ietf:params:xml:schema:keyprov:protocol#passphrase-wrap
</SupportedKeyInitializationMethod>
<Payload xsi:type="ds:KeyInfoType">
<ds:X509Data>
<ds:X509Certificate>miib</ds:X509Certificate>
</ds:X509Data>
</Payload>
</TwoPass>
</SupportedProtocolVariants>
<SupportedKeyContainers>
<KeyContainerFormat>
urn:ietf:params:xml:schema:keyprov:container#KeyContainer
</KeyContainerFormat>
</SupportedKeyContainers>
<AuthenticationData>
<DigitalSignature>
<ds:SignedInfo>
<ds:CanonicalizationMethod
Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315" />
<ds:SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"/>
<ds:Reference URI="#Nonce">
<ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
<ds:DigestValue></ds:DigestValue>
</ds:Reference>
</ds:SignedInfo>
<ds:SignatureValue></ds:SignatureValue>
<ds:KeyInfo>
<ds:X509Data>
<ds:X509Certificate>miib</ds:X509Certificate>
</ds:X509Data>
</ds:KeyInfo>
<ds:Object Id="Nonce">xwQzwEl0CjPAiQeDxwRJdQ==</ds:Object>
</DigitalSignature>
Doherty, et al. Expires May 1, 2008 [Page 52]
Internet-Draft DSKPP October 2007
</AuthenticationData>
</dskpp:KeyProvClientHello>
In this example, the server responds to the previous request using
the key transport profile.
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvServerFinished Version="1.0" SessionID="4114" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:1.0:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:1.0:protocol
keyprov-dskpp-1.0.xsd">
<KeyContainer>
<KeyContainer Version="1.0">
<pskc:EncryptionMethod
Algorithm="http://www.w3.org/2001/05/xmlenc#rsa_1_5">
<pskc:KeyInfo>
<ds:X509Data>
<ds:X509Certificate>miib</ds:X509Certificate>
</ds:X509Data>
</pskc:KeyInfo>
</pskc:EncryptionMethod>
<pskc:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#hmac-sha1"/>
<Device xmlns="urn:ietf:params:xml:ns:keyprov:1.0:container">
<Key KeyAlgorithm="urn:ietf:params:xml:schema:keyprov:otpalg#HOTP"
KeyId="SDU312345678">
<Issuer>CredentialIssuer</Issuer>
<Usage otp="true">
<ResponseFormat format="DECIMAL" length="6"/>
</Usage>
<FriendlyName>MyFirstToken</FriendlyName>
<Data Name="SECRET">
<Value>
7JHUyp3azOkqJENSsh6b2vxXzwGBYypzJxEr+ikQAa229KV/BgZhGA==
</Value>
<ValueDigest>
i8j+kpbfKQsSlwmJYS99lQ==
</ValueDigest>
</Data>
<Data Name="COUNTER">
<Value>AAAAAAAAAAA=</Value>
</Data>
<Expiry>10/30/2012</Expiry>
</Key>
</Device>
Doherty, et al. Expires May 1, 2008 [Page 53]
Internet-Draft DSKPP October 2007
</KeyContainer>
</KeyContainer>
<Mac
MacAlgorithm="urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes">
miidfasde312asder394jw==
</Mac>
<AuthenticationData>
<AuthenticationCodeMac>
<Mac>4bRJf9xXd3KchKoTenHJiw==</Mac>
</AuthenticationCodeMac>
</AuthenticationData>
</dskpp:KeyProvServerFinished>
7.2.1.2. Example Using the Key Wrap Profile
The client sends a request that specifies a shared key to protect the
K_TOKEN, and the server responds using the Key Wrap Profile.
Authentication data in this example is basing on an authentication
code rather than a device certificate.
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvClientHello Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:1.0:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:pkcs-5="http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:1.0:protocol
keyprov-dskpp-1.0.xsd">
<DeviceIdentifierData>
<DeviceId>
<pskc:Manufacturer>ManufacturerABC</pskc:Manufacturer>
<pskc:SerialNo>XL0000000001234</pskc:SerialNo>
<pskc:Model>U2</pskc:Model>
</DeviceId>
</DeviceIdentifierData>
<ClientNonce>xwQzwEl0CjPAiQeDxwRJdQ==</ClientNonce>
<SupportedKeyTypes>
<Algorithm>urn:ietf:params:xml:schema:keyprov:otpalg#HOTP</Algorithm>
<Algorithm>
http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES
</Algorithm>
</SupportedKeyTypes>
<SupportedEncryptionAlgorithms>
<Algorithm>http://www.w3.org/2001/05/xmlenc#rsa_1_5</Algorithm>
<Algorithm>http://www.w3.org/2001/04/xmlenc#kw-aes128</Algorithm>
<Algorithm>
http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbes2
Doherty, et al. Expires May 1, 2008 [Page 54]
Internet-Draft DSKPP October 2007
</Algorithm>
<Algorithm>
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes
</Algorithm>
</SupportedEncryptionAlgorithms>
<SupportedMacAlgorithms>
<Algorithm>
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes
</Algorithm>
</SupportedMacAlgorithms>
<SupportedProtocolVariants>
<TwoPass>
<SupportedKeyInitializationMethod>
urn:ietf:params:xml:schema:keyprov:protocol#wrap
</SupportedKeyInitializationMethod>
<Payload xsi:type="ds:KeyInfoType">
<ds:KeyName>Key_001</ds:KeyName>
</Payload>
</TwoPass>
</SupportedProtocolVariants>
<SupportedKeyContainers>
<KeyContainerFormat>
urn:ietf:params:xml:schema:keyprov:container#KeyContainer
</KeyContainerFormat>
</SupportedKeyContainers>
<AuthenticationData>
<ClientID>31300257</ClientID>
<AuthenticationCodeMac>
<IterationCount>512</IterationCount>
<Mac>4bRJf9xXd3KchKoTenHJiw==</Mac>
</AuthenticationCodeMac>
</AuthenticationData>
</dskpp:KeyProvClientHello>
In this example, the server responds to the previous request using
the key wrap profile.
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvServerFinished Version="1.0" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:1.0:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:1.0:protocol
keyprov-dskpp-1.0.xsd">
<KeyContainer>
<ServerID>https://www.somedskppservice.com/</ServerID>
Doherty, et al. Expires May 1, 2008 [Page 55]
Internet-Draft DSKPP October 2007
<KeyContainer Version="1.0">
<EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#kw-aes128"
xmlns="urn:ietf:params:xml:ns:keyprov:1.0:container">
<KeyInfo>
<ds:KeyName>Key-001</ds:KeyName>
</KeyInfo>
</EncryptionMethod>
<pskc:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#hmac-sha1"/>
<Device xmlns="urn:ietf:params:xml:ns:keyprov:1.0:container">
<Key KeyAlgorithm="urn:ietf:params:xml:schema:keyprov:otpalg#HOTP"
KeyId="SDU312345678">
<Issuer>CredentialIssuer</Issuer>
<Usage otp="true">
<ResponseFormat format="DECIMAL" length="6"/>
</Usage>
<FriendlyName>MyFirstToken</FriendlyName>
<Data Name="SECRET">
<Value>
JSPUyp3azOkqJENSsh6b2hdXz1WBYypzJxEr+ikQAa22M6V/BgZhRg==
</Value>
<ValueDigest>
i8j+kpbfKQsSlwmJYS99lQ==
</ValueDigest>
</Data>
<Data Name="COUNTER">
<Value>AAAAAAAAAAA=</Value>
</Data>
<Expiry>10/30/2012</Expiry>
</Key>
</Device>
</KeyContainer>
</KeyContainer>
<Mac MacAlgorithm="urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes">
miidfasde312asder394jw==
</Mac>
<AuthenticationData>
<AuthenticationCodeMac>
<Mac>4bRJf9xXd3KchKoTenHJiw==</Mac>
</AuthenticationCodeMac>
</AuthenticationData>
</dskpp:KeyProvServerFinished>
7.2.1.3. Example Using the Passphrase-Based Key Wrap Profile
The client sends a request similar to that in Section 7.2.1.1 with
authentication data basing on an authentication code, and the server
responds using the Passphrase-Based Key Wrap Profile. The
authentication data is set in clear text when it is sent over a
Doherty, et al. Expires May 1, 2008 [Page 56]
Internet-Draft DSKPP October 2007
secure transport channel such as TLS.
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvClientHello Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:1.0:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:pkcs-5="http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:1.0:protocol
keyprov-dskpp-1.0.xsd">
<DeviceIdentifierData>
<DeviceId>
<pskc:Manufacturer>ManufacturerABC</pskc:Manufacturer>
<pskc:SerialNo>XL0000000001234</pskc:SerialNo>
<pskc:Model>U2</pskc:Model>
</DeviceId>
</DeviceIdentifierData>
<ClientNonce>xwQzwEl0CjPAiQeDxwRJdQ==</ClientNonce>
<SupportedKeyTypes>
<Algorithm>urn:ietf:params:xml:schema:keyprov:otpalg#HOTP</Algorithm>
<Algorithm>
http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES
</Algorithm>
</SupportedKeyTypes>
<SupportedEncryptionAlgorithms>
<Algorithm>http://www.w3.org/2001/05/xmlenc#rsa_1_5</Algorithm>
<Algorithm>http://www.w3.org/2001/04/xmlenc#kw-aes128</Algorithm>
<Algorithm>
http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbes2
</Algorithm>
<Algorithm>
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes
</Algorithm>
</SupportedEncryptionAlgorithms>
<SupportedMacAlgorithms>
<Algorithm>
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes
</Algorithm>
</SupportedMacAlgorithms>
<SupportedProtocolVariants>
<TwoPass>
<SupportedKeyInitializationMethod>
urn:ietf:params:xml:schema:keyprov:protocol#wrap
</SupportedKeyInitializationMethod>
<Payload xsi:type="ds:KeyInfoType">
<ds:KeyName>Key_001</ds:KeyName>
</Payload>
Doherty, et al. Expires May 1, 2008 [Page 57]
Internet-Draft DSKPP October 2007
<SupportedKeyInitializationMethod>
urn:ietf:params:xml:schema:keyprov:protocol#passphrase-wrap
</SupportedKeyInitializationMethod>
</TwoPass>
</SupportedProtocolVariants>
<SupportedKeyContainers>
<KeyContainerFormat>
urn:ietf:params:xml:schema:keyprov:container#KeyContainer
</KeyContainerFormat>
</SupportedKeyContainers>
<AuthenticationData>
<ClientID>31300257</ClientID>
<AuthenticationCodeMac>
<IterationCount>512</IterationCount>
<Mac>4bRJf9xXd3KchKoTenHJiw==</Mac>
</AuthenticationCodeMac>
</AuthenticationData>
</dskpp:KeyProvClientHello>
In this example, the server responds to the previous request using
the Passphrase-Based Key Wrap Profile.
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvServerFinished Version="1.0" SessionID="4114" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:1.0:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:1.0:protocol
keyprov-dskpp-1.0.xsd">
<KeyContainer>
<KeyContainer Version="1.0">
<EncryptionMethod
Algorithm="http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbes2"
xmlns="urn:ietf:params:xml:ns:keyprov:1.0:container">
<PBEEncryptionParam
EncryptionAlgorithm="http://www.w3.org/2001/04/xmlenc#kw-aes128-cbc">
<PBESalt>y6TzckeLRQw=</PBESalt>
<PBEIterationCount>1024</PBEIterationCount>
</PBEEncryptionParam>
<IV>c2FtcGxlaXY=</IV>
</EncryptionMethod>
<pskc:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#hmac-sha1"/>
<Device xmlns="urn:ietf:params:xml:ns:keyprov:1.0:container">
<Key KeyAlgorithm="urn:ietf:params:xml:schema:keyprov:otpalg#HOTP"
KeyId="SDU312345678">
<Issuer>CredentialIssuer</Issuer>
Doherty, et al. Expires May 1, 2008 [Page 58]
Internet-Draft DSKPP October 2007
<Usage otp="true">
<ResponseFormat format="DECIMAL" length="6"/>
</Usage>
<FriendlyName>MyFirstToken</FriendlyName>
<Data Name="SECRET">
<Value>
JSPUyp3azOkqJENSsh6b2hdXz1WBYypzJxEr+ikQAa22M6V/BgZhRg==
</Value>
<ValueDigest>
i8j+kpbfKQsSlwmJYS99lQ==
</ValueDigest>
</Data>
<Data Name="COUNTER">
<Value>AAAAAAAAAAA=</Value>
</Data>
<Expiry>10/30/2012</Expiry>
</Key>
</Device>
</KeyContainer>
</KeyContainer>
<Mac MacAlgorithm="urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes">
miidfasde312asder394jw==
</Mac>
<AuthenticationData>
<AuthenticationCodeMac>
<Mac>4bRJf9xXd3KchKoTenHJiw==</Mac>
</AuthenticationCodeMac>
</AuthenticationData>
</dskpp:KeyProvServerFinished>
7.2.2. Components of the <KeyProvClientHello> Request
The components of this message have the following meaning:
o Version: (attribute inherited from the AbstractRequestType type)
The highest version of this protocol the client supports. Only
version one ("1.0") is currently specified.
o <DeviceIdentifierData>: An identifier for the cryptographic module
as defined in Section 5.3 above. The identifier MUST only be
present if such shared secrets exist or if the identifier was
provided by the server in a <KeyProvTrigger> element (see
Section 12.2.7 below). In the latter case, it MUST have the same
value as the identifier provided in that element.
o <KeyID>: An identifier for the key that will be overwritten if the
protocol run is successful. The identifier MUST only be present
if the key exists or the identifier was provided by the server in
a <KeyProvTrigger> element (see Section 12.2.7 below). In the
latter case, it MUST have the same value as the identifier
provided in that element.
Doherty, et al. Expires May 1, 2008 [Page 59]
Internet-Draft DSKPP October 2007
o <KeyProvClientNonce>: This is the nonce R, which, when present,
MUST be used by the server when calculating MAC values (see
below). It is RECOMMENDED that clients include this element
whenever the <KeyID> element is present.
o <TriggerNonce>: This OPTIONAL element MUST be present if and only
if the DSKPP run was initialized with a <KeyProvTrigger> message
(see Section 12.2.7 below), and MUST, in that case, have the same
value as the <TriggerNonce> child of that message. A server using
nonces in this way MUST verify that the nonce is valid and that
any device or key identifier values provided in the
<KeyProvTrigger> message match the corresponding identifier values
in the <KeyProvClientHello> message.
o <SupportedKeyTypes>: A sequence of URIs indicating the key types
for which the cryptographic module is willing to generate keys
through DSKPP.
o <SupportedEncryptionAlgorithms>: A sequence of URIs indicating the
encryption algorithms supported by the cryptographic module for
the purposes of DSKPP. The DSKPP client MAY indicate the same
algorithm both as a supported key type and as an encryption
algorithm.
o <SupportedMacAlgorithms>: A sequence of URIs indicating the MAC
algorithms supported by the cryptographic module for the purposes
of DSKPP. The DSKPP client MAY indicate the same algorithm both
as an encryption algorithm and as a MAC algorithm (e.g.,
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes defined
in Appendix B).
o <SupportedProtocolVariants>: This OPTIONAL element is used by the
DSKPP client to indicate support for four-pass or two-pass DSKPP.
If two-pass support is specified, then <KeyProvClientNonce> MUST
be set to nonce R in the <KeyProvClientHello> message unless
<TriggerNonce> is already present.
o <SupportedKeyContainers>: This OPTIONAL element is a sequence of
URIs indicating the key container formats supported by the DSKPP
client. If this element is not provided, then the DSKPP server
MUST proceed with
"urn:ietf:params:xml:schema:keyprov:container#KeyContainer" (see
[PSKC].
o <AuthenticationData>: This OPTIONAL element contains data that the
DSKPP client uses to authenticate the user or device to the DSKPP
server. The element is set as specified in Section 5.3.
o <Extensions>: A sequence of extensions. One extension is defined
for this message in this version of DSKPP: the ClientInfoType (see
Section 10).
7.2.3. Components of a <KeyProvServerFinished> Response
This message is the last message of the DSKPP protocol run. In a
4-pass exchange, the DSKPP server sends this message in response to a
Doherty, et al. Expires May 1, 2008 [Page 60]
Internet-Draft DSKPP October 2007
<KeyProvClientNonce> message, whereas in a 2-pass exchange, the DSKPP
server sends this message in response to a <KeyProvClientHello>
message. In a 1-pass exchange, the DSKPP server sends only this
message to the client. The components of this message have the
following meaning:
o Version: (inherited from the AbstractResponseType type) The DSKPP
version used in this session.
o SessionID: (inherited from the AbstractResponseType type) The
previously established identifier for this session.
o Status: (inherited from the AbstractResponseType type) Return code
for the <KeyProvServerFinished> message. If Status is not
"Success", only the Status, SessionID, and Version attributes will
be present (the presence of the SessionID attribute is dependent
on the type of reported error); otherwise, all the other elements
MUST be present as well. In this latter case, the
<KeyProvServerFinished> message can be seen as a "Commit" message,
instructing the cryptographic module to store the generated key
and associate the given key identifier with this key.
o <KeyContainer>: The key container containing symmetric key values
(in the case of a 2- or 1-pass exchange) and configuration data.
The default container format is based on the KeyContainerType type
from PSKC, as defined in [PSKC].
o <Extensions>: A list of extensions chosen by the DSKPP server.
For this message, this version of DSKPP defines one extension, the
ClientInfoType (see Section 10).
o <Mac>: To avoid a false "Commit" message causing the cryptographic
module to end up in an initialized state for which the server does
not know the stored key, <KeyProvServerFinished> messages MUST
always be authenticated with a MAC. The MAC MUST be made using
the already established MAC algorithm.
o <AuthenticationData>: This OPTIONAL element contains data that
allows the DSKPP client to authenticate the DSKPP server. The MAC
value is calculated with K_MAC' as specified in Section 4.4.3.
When receiving a <KeyProvServerFinished> message with
Status="Success" for which the MAC verifies, the DSKPP client MUST
associate the generated key K_TOKEN with the provided key
identifier and store this data permanently. After this operation,
it MUST not be possible to overwrite the key unless knowledge of
an authorizing key is proven through a MAC on a later
<KeyProvServerHello> (and <KeyProvServerFinished>) message.
The DSKPP client MUST verify the MAC. The DSKPP client MUST
terminate the DSKPP session if the MAC does not verify, and MUST,
in this case, also delete any nonces, keys, and/or secrets
associated with the failed run of the DSKPP protocol.
The MacType's MacAlgorithm attribute MUST, when present, identify
the negotiated MAC algorithm.
Doherty, et al. Expires May 1, 2008 [Page 61]
Internet-Draft DSKPP October 2007
7.3. DSKPP Server Results: The StatusCode Type
The StatusCode type enumerates all possible return codes. Upon
transmission or receipt of a message for which the Status attribute's
value is not "Success" or "Continue", the default behavior, unless
explicitly stated otherwise below, is that both the DSKPP server and
the DSKPP client MUST immediately terminate the DSKPP session. DSKPP
servers and DSKPP clients MUST delete any secret values generated as
a result of failed runs of the DSKPP protocol. Session identifiers
MAY be retained from successful or failed protocol runs for replay
detection purposes, but such retained identifiers MUST not be reused
for subsequent runs of the protocol.
When possible, the DSKPP client SHOULD present an appropriate error
message to the user.
These status codes are valid in all DSKPP Response messages unless
explicitly stated otherwise:
o "Continue" indicates that the DSKPP server is ready for a
subsequent request from the DSKPP client. It cannot be sent in
the server's final message.
o "Success" indicates successful completion of the DSKPP session.
It can only be sent in the server's final message.
o "Abort" indicates that the DSKPP server rejected the DSKPP
client's request for unspecified reasons.
o "AccessDenied" indicates that the DSKPP client is not authorized
to contact this DSKPP server.
o "MalformedRequest" indicates that the DSKPP server failed to parse
the DSKPP client's request.
o "UnknownRequest" indicates that the DSKPP client made a request
that is unknown to the DSKPP server.
o "UnknownCriticalExtension" indicates that a critical DSKPP
extension (see below) used by the DSKPP client was not supported
or recognized by the DSKPP server.
o "UnsupportedVersion" indicates that the DSKPP client used a DSKPP
protocol version not supported by the DSKPP server. This error is
only valid in the DSKPP server's first response message.
o "NoSupportedKeyTypes" indicates that the DSKPP client only
suggested key types that are not supported by the DSKPP server.
This error is only valid in the DSKPP server's first response
message.
o "NoSupportedEncryptionAlgorithms" indicates that the DSKPP client
only suggested encryption algorithms that are not supported by the
DSKPP server. This error is only valid in the DSKPP server's
first response message. Note that the error will only occur if
the DSKPP server does not support any of the DSKPP client's
suggested encryption algorithms.
Doherty, et al. Expires May 1, 2008 [Page 62]
Internet-Draft DSKPP October 2007
o "NoSupportedMacAlgorithms" indicates that the DSKPP client only
suggested MAC algorithms that are not supported by the DSKPP
server. This error is only valid in the DSKPP server's first
response message. Note that the error will only occur if the
DSKPP server does not support any of the DSKPP client's suggested
MAC algorithms.
o "NoProtocolVariants" indicates that the DSKPP client only
suggested a protocol variant (either 2-pass or 4-pass) that is not
supported by the DSKPP server. This error is only valid in the
DSKPP server's first response message. Note that the error will
only occur if the DSKPP server does not support any of the DSKPP
client's suggested protocol variants.
o "NoSupportedKeyContainers" indicates that the DSKPP client only
suggested key container formats that are not supported by the
DSKPP server. This error is only valid in the DSKPP server's
first response message. Note that the error will only occur if
the DSKPP server does not support any of the DSKPP client's
suggested key container formats.
o "AuthenticationDataMissing" indicates that the DSKPP client didn't
provide authentication data that the DSKPP server required.
o "AuthenticationDataInvalid" indicates that the DSKPP client
supplied user or device authentication data that the DSKPP server
failed to validate.
o "InitializationFailed" indicates that the DSKPP server could not
generate a valid key given the provided data. When this status
code is received, the DSKPP client SHOULD try to restart DSKPP, as
it is possible that a new run will succeed.
o "ProvisioningPeriodExpired" indicates that the provisioning period
set by the DSKPP server has expired. When the status code is
received, the DSKPP client SHOULD report the key initialization
failure reason to the user and the user MUST register with the
DSKPP server to initialize a new key.
8. One-Pass Protocol
In this section, example messages are used to describe parameters,
encoding and semantics in a 1-pass DSKPP protocol. The examples are
written using XML. While they are syntactically correct, MAC and
cipher values are fictitious.
8.1. XML Basics
The DSKPP XML schema can be found in Section 13. Some DSKPP elements
rely on the parties being able to compare received values with stored
values. Unless otherwise noted, all elements in this document that
have the XML Schema "xs:string" type, or a type derived from it, MUST
be compared using an exact binary comparison. In particular, DSKPP
Doherty, et al. Expires May 1, 2008 [Page 63]
Internet-Draft DSKPP October 2007
implementations MUST NOT depend on case-insensitive string
comparisons, normalization or trimming of white space, or conversion
of locale-specific formats such as numbers.
Implementations that compare values that are represented using
different character encodings MUST use a comparison method that
returns the same result as converting both values to the Unicode
character encoding, Normalization Form C [UNICODE], and then
performing an exact binary comparison.
No collation or sorting order for attributes or element values is
defined. Therefore, DSKPP implementations MUST NOT depend on
specific sorting orders for values.
8.2. Server to Client Only: <KeyProvServerFinished>
8.2.1. Example
The Server sends a provisioned key to a client with prior knowledge
about the client's capabilities:
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvServerFinished Version="1.0" SessionID="4114" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:1.0:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:1.0:protocol
keyprov-dskpp-1.0.xsd">
<KeyContainer>
<KeyContainer Version="1.0">
<pskc:EncryptionMethod
Algorithm="http://www.w3.org/2001/05/xmlenc#rsa_1_5">
<pskc:KeyInfo>
<ds:X509Data>
<ds:X509Certificate>miib</ds:X509Certificate>
</ds:X509Data>
</pskc:KeyInfo>
</pskc:EncryptionMethod>
<pskc:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#hmac-sha1"/>
<Device xmlns="urn:ietf:params:xml:ns:keyprov:1.0:container">
<Key KeyAlgorithm="urn:ietf:params:xml:schema:keyprov:otpalg#HOTP"
KeyId="SDU312345678">
<Issuer>CredentialIssuer</Issuer>
<Usage otp="true">
<ResponseFormat format="DECIMAL" length="6"/>
</Usage>
Doherty, et al. Expires May 1, 2008 [Page 64]
Internet-Draft DSKPP October 2007
<FriendlyName>MyFirstToken</FriendlyName>
<Data Name="SECRET">
<Value>
7JHUyp3azOkqJENSsh6b2vxXzwGBYypzJxEr+ikQAa229KV/BgZhGA==
</Value>
<ValueDigest>
i8j+kpbfKQsSlwmJYS99lQ==
</ValueDigest>
</Data>
<Data Name="COUNTER">
<Value>AAAAAAAAAAA=</Value>
</Data>
<Expiry>10/30/2009</Expiry>
</Key>
</Device>
</KeyContainer>
</KeyContainer>
<Mac MacAlgorithm="urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes">
miidfasde312asder394jw==
</Mac>
<AuthenticationData>
<AuthenticationCodeMac>
<Mac>4bRJf9xXd3KchKoTenHJiw==</Mac>
</AuthenticationCodeMac>
</AuthenticationData>
</dskpp:KeyProvServerFinished>
8.2.2. Components of a <KeyProvServerFinished> Response
This message is the last message of the DSKPP protocol run. In a
4-pass exchange, the DSKPP server sends this message in response to a
<KeyProvClientNonce> message, whereas in a 2-pass exchange, the DSKPP
server sends this message in response to a <KeyProvClientHello>
message. In a 1-pass exchange, the DSKPP server sends only this
message to the client. The components of this message have the
following meaning:
o Version: (inherited from the AbstractResponseType type) The DSKPP
version used in this session.
o SessionID: (inherited from the AbstractResponseType type) The
previously established identifier for this session.
o Status: (inherited from the AbstractResponseType type) Return code
for the <KeyProvServerFinished> message. If Status is not
"Success", only the Status, SessionID, and Version attributes will
be present (the presence of the SessionID attribute is dependent
on the type of reported error); otherwise, all the other elements
MUST be present as well. In this latter case, the
<KeyProvServerFinished> message can be seen as a "Commit" message,
Doherty, et al. Expires May 1, 2008 [Page 65]
Internet-Draft DSKPP October 2007
instructing the cryptographic module to store the generated key
and associate the given key identifier with this key.
o <KeyContainer>: The key container containing symmetric key values
(in the case of a 2- or 1-pass exchange) and configuration data.
The default container format is based on the KeyContainerType type
from PSKC, as defined in [PSKC].
o <Extensions>: A list of extensions chosen by the DSKPP server.
For this message, this version of DSKPP defines one extension, the
ClientInfoType (see Section 10).
o <Mac>: To avoid a false "Commit" message causing the cryptographic
module to end up in an initialized state for which the server does
not know the stored key, <KeyProvServerFinished> messages MUST
always be authenticated with a MAC. The MAC MUST be made using
the already established MAC algorithm.
o <AuthenticationData>: This OPTIONAL element contains data that
allows the DSKPP client to authenticate the DSKPP server. The MAC
value is calculated with K_MAC' as specified in Section 4.5.3.
When receiving a <KeyProvServerFinished> message with
Status="Success" for which the MAC verifies, the DSKPP client MUST
associate the generated key K_TOKEN with the provided key
identifier and store this data permanently. After this operation,
it MUST not be possible to overwrite the key unless knowledge of
an authorizing key is proven through a MAC on a later
<KeyProvServerHello> (and <KeyProvServerFinished>) message.
The DSKPP client MUST verify the MAC. The DSKPP client MUST
terminate the DSKPP session if the MAC does not verify, and MUST,
in this case, also delete any nonces, keys, and/or secrets
associated with the failed run of the DSKPP protocol.
The MacType's MacAlgorithm attribute MUST, when present, identify
the negotiated MAC algorithm.
9. Trigger
In this section, an example is used to describe parameters, encoding
and semantics in a DSKPP Trigger message. The example is written
using XML.
9.1. XML Basics
The DSKPP XML schema can be found in Section 13. Some DSKPP elements
rely on the parties being able to compare received values with stored
values. Unless otherwise noted, all elements in this document that
have the XML Schema "xs:string" type, or a type derived from it, MUST
be compared using an exact binary comparison. In particular, DSKPP
implementations MUST NOT depend on case-insensitive string
comparisons, normalization or trimming of white space, or conversion
of locale-specific formats such as numbers.
Doherty, et al. Expires May 1, 2008 [Page 66]
Internet-Draft DSKPP October 2007
Implementations that compare values that are represented using
different character encodings MUST use a comparison method that
returns the same result as converting both values to the Unicode
character encoding, Normalization Form C [UNICODE], and then
performing an exact binary comparison.
No collation or sorting order for attributes or element values is
defined. Therefore, DSKPP implementations MUST NOT depend on
specific sorting orders for values.
9.2. Example
<dskpp:KeyProvTrigger Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:1.0:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:1.0:protocol
keyprov-dskpp-1.0.xsd">
<InitializationTrigger>
<DeviceIdentifierData>
<DeviceId>
<pskc:Manufacturer>ManufacturerABC</pskc:Manufacturer>
<pskc:SerialNo>XL0000000001234</pskc:SerialNo>
<pskc:Model>U2</pskc:Model>
</DeviceId>
</DeviceIdentifierData>
<KeyID>SE9UUDAwMDAwMDAx</KeyID>
<TokenPlatformInfo KeyLocation="Hardware" AlgorithmLocation="Software"/>
<TriggerNonce>112dsdfwf312asder394jw==</TriggerNonce>
<DSKPPServerUrl>https://www.somekeyprovservice.com/</DSKPPServerUrl>
</InitializationTrigger>
</dskpp:KeyProvTrigger>
9.3. Components of the <KeyProvTrigger> Message
The DSKPP server MAY initialize the DSKPP protocol by sending a
<KeyProvTrigger> message. This message MAY, e.g., be sent in
response to a user requesting key initialization in a browsing
session.
The <KeyProvTrigger> element is intended for the DSKPP client and MAY
inform the DSKPP client about the identifier for the device that
houses the cryptographic module to be initialized, and optionally of
the identifier for the key on that module. The latter would apply to
key renewal. The trigger always contains a nonce to allow the DSKPP
server to couple the trigger with a later DSKPP <KeyProvClientHello>
request. Finally, the trigger MAY contain a URL to use when
Doherty, et al. Expires May 1, 2008 [Page 67]
Internet-Draft DSKPP October 2007
contacting the DSKPP server. The <xs:any> elements are for future
extensibility. Any provided <DeviceIdentifierData> or <KeyID> values
MUST be used by the DSKPP client in the subsequent
<KeyProvClientHello> request. The OPTIONAL <TokenPlatformInfo>
element informs the DSKPP client about the characteristics of the
intended cryptographic module platform, and applies in the public-key
variant of DSKPP in situations when the client potentially needs to
decide which one of several modules to initialize.
10. Extensibility
10.1. The ClientInfoType Type
present in a <KeyProvClientHello> or a <KeyProvClientNonce> message,
the OPTIONAL ClientInfoType extension contains DSKPP client-specific
information. DSKPP servers MUST support this extension. DSKPP
servers MUST NOT attempt to interpret the data it carries and, if
received, MUST include it unmodified in the current protocol run's
next server response. Servers need not retain the ClientInfoType's
data after that response has been generated.
10.2. The ServerInfoType Type
When present, the OPTIONAL ServerInfoType extension contains DSKPP
server-specific information. This extension is only valid in
<KeyProvServerHello> messages for which Status = "Continue". DSKPP
clients MUST support this extension. DSKPP clients MUST NOT attempt
to interpret the data it carries and, if received, MUST include it
unmodified in the current protocol run's next client request (i.e.,
the <KeyProvClientNonce> message). DSKPP clients need not retain the
ServerInfoType's data after that request has been generated. This
extension MAY be used, e.g., for state management in the DSKPP
server.
10.3. The KeyInitializationDataType Type
This extension is used for 2- and 1-pass DSKPP exchange; it carries
an identifier for the selected key initialization method as well as
key initialization method-dependent payload data.
Servers MAY include this extension in a <KeyProvServerFinished>
message that is being sent in response to a received
<KeyProvClientHello> message if and only if that <KeyProvClientHello>
message selected TwoPassSupport as the ProtocolVariantType and the
client indicated support for the selected key initialization method.
Servers MUST include this extension in a <KeyProvServerFinished>
message that is sent as part of a 1-pass DSKPP.
Doherty, et al. Expires May 1, 2008 [Page 68]
Internet-Draft DSKPP October 2007
The elements of this type have the following meaning:
o <KeyInitializationMethod>: A two-pass key initialization method
supported by the DSKPP client.
o <Payload>: A payload associated with the key initialization
method. Since the syntax is a shorthand for <xs:element
name="Payload" type="xs:anyType"/>, any well-formed payloads can
be carried in this element.
11. Key Initialization Profiles of Two- and One-Pass DSKPP
11.1. Introduction
This appendix introduces three profiles of DSKPP for key
initialization. They MAY all be used for two- as well as one-pass
initialization of cryptographic modules. Further profiles MAY be
defined by external entities or through the IETF process.
11.2. Key Transport Profile
11.2.1. Introduction
This profile initializes the cryptographic module with a symmetric
key, K_TOKEN, through key transport and key derivation. The key
transport is carried out using a public key, K_CLIENT, whose private
key part resides in the cryptographic module as the transport key. A
key K from which two keys, K_TOKEN and K_MAC are derived MUST be
transported.
11.2.2. Identification
This profile MUST be identified with the following URN:
urn:ietf:params:xml:schema:keyprov:protocol#transport
11.2.3. Payloads
In the two-pass version of DSKPP, the client MUST send a payload
associated with this key initialization method. The payload MUST be
of type ds:KeyInfoType ([XMLDSIG]), and only those choices of the ds:
KeyInfoType that identify a public key are allowed. The ds:
X509Certificate option of the ds:X509Data alternative is RECOMMENDED
when the public key corresponding to the private key on the
cryptographic module has been certified.
The server payload associated with this key initialization method
MUST be of type xenc:EncryptedKeyType ([XMLENC]), and only those
Doherty, et al. Expires May 1, 2008 [Page 69]
Internet-Draft DSKPP October 2007
encryption methods utilizing a public key that are supported by the
DSKPP client (as indicated in the <SupportedEncryptionAlgorithms>
element of the <KeyProvClientHello> message in the case of 2-pass
DSKPP, or as otherwise known in the case of 1-pass DSKPP) are allowed
as values for the <xenc:EncryptionMethod> element. Further, in the
case of 2-pass DSKPP, the <ds:KeyInfo> element MUST contain the same
value (i.e. identify the same public key) as the <Payload> of the
corresponding supported key initialization method in the
<KeyProvClientHello> message that triggered the response. The
<CarriedKeyName> element MAY be present, but MUST, when present,
contain the same value as the <KeyID> element of the
<KeyProvServerFinished> message. The Type attribute of the xenc:
EncryptedKeyType MUST be present and MUST identify the type of the
wrapped key. The type MUST be one of the types supported by the
DSKPP client (as reported in the <SupportedKeyTypes> of the preceding
<KeyProvClientHello> message in the case of 2-pass DSKPP, or as
otherwise known in the case of 1-pass DSKPP). The transported key
MUST consist of two parts of equal length. The first half
constitutes K_MAC and the second half constitutes K_TOKEN. The
length of K_TOKEN (and hence also the length of K_MAC) is determined
by the type of K_TOKEN.
DSKPP servers and cryptographic modules supporting this profile MUST
support the http://www.w3.org/2001/04/xmlenc#rsa-1_5 key-wrapping
mechanism defined in [XMLENC].
When this profile is used, the MacAlgorithm attribute of the <Mac>
element of the <KeyProvServerFinished> message MUST be present and
MUST identify the selected MAC algorithm. The selected MAC algorithm
MUST be one of the MAC algorithms supported by the DSKPP client (as
indicated in the <SupportedMacAlgorithms> element of the
<KeyProvClientHello> message in the case of 2-pass DSKPP, or as
otherwise known in the case of 1-pass DSKPP). The MAC MUST be
calculated as described in Section 4.4 for Two-Pass DSKPP and
Section 4.5 for One-Pass DSKPP.
In addition, DSKPP servers MUST include the AuthenticationDataType
element in their <KeyProvServerFinished> messages whenever a
successful protocol run will result in an existing K_TOKEN being
replaced.
11.3. Key Wrap Profile
11.3.1. Introduction
This profile initializes the cryptographic module with a symmetric
key, K_TOKEN, through key wrap and key derivation. The key wrap MUST
be carried out using a (symmetric) key-wrapping key, K_SHARED, known
Doherty, et al. Expires May 1, 2008 [Page 70]
Internet-Draft DSKPP October 2007
in advance by both the cryptographic module and the DSKPP server. A
key K from which two keys, K_TOKEN and K_MAC are derived MUST be
wrapped.
11.3.2. Identification
This profile MUST be identified with the following URI:
urn:ietf:params:xml:schema:keyprov:protocol#wrap
11.3.3. Payloads
In the 2-pass version of DSKPP, the client MUST send a payload
associated with this key initialization method. The payload MUST be
of type ds:KeyInfoType ([XMLDSIG]), and only those choices of the ds:
KeyInfoType that identify a symmetric key are allowed. The ds:
KeyName alternative is RECOMMENDED.
The server payload associated with this key initialization method
MUST be of type xenc:EncryptedKeyType ([XMLENC]), and only those
encryption methods utilizing a symmetric key that are supported by
the DSKPP client (as indicated in the <SupportedEncryptionAlgorithms>
element of the <KeyProvClientHello> message in the case of 2-pass
DSKPP, or as otherwise known in the case of 1-pass DSKPP) are allowed
as values for the <xenc:EncryptionMethod> element. Further, in the
case of 2-pass DSKPP, the <ds:KeyInfo> element MUST contain the same
value (i.e. identify the same symmetric key) as the <Payload> of the
corresponding supported key initialization method in the
<KeyProvClientHello> message that triggered the response. The
<CarriedKeyName> element MAY be present, and MUST, when present,
contain the same value as the <KeyID> element of the
<KeyProvServerFinished> message. The Type attribute of the xenc:
EncryptedKeyType MUST be present and MUST identify the type of the
wrapped key. The type MUST be one of the types supported by the
DSKPP client (as reported in the <SupportedKeyTypes> of the preceding
<KeyProvClientHello> message in the case of 2-pass DSKPP, or as
otherwise known in the case of 1-pass DSKPP). The wrapped key MUST
consist of two parts of equal length. The first half constitutes
K_MAC and the second half constitutes K_TOKEN. The length of K_TOKEN
(and hence also the length of K_MAC) is determined by the type of
K_TOKEN.
DSKPP servers and cryptographic modules supporting this profile MUST
support the http://www.w3.org/2001/04/xmlenc#kw-aes128 key-wrapping
mechanism defined in [XMLENC].
When this profile is used, the MacAlgorithm attribute of the <Mac>
element of the <KeyProvServerFinished> message MUST be present and
Doherty, et al. Expires May 1, 2008 [Page 71]
Internet-Draft DSKPP October 2007
MUST identify the selected MAC algorithm. The selected MAC algorithm
MUST be one of the MAC algorithms supported by the DSKPP client (as
indicated in the <SupportedMacAlgorithms> element of the
<KeyProvClientHello> message in the case of 2-pass DSKPP, or as
otherwise known in the case of 1-pass DSKPP). The MAC MUST be
calculated as described in Section 4.4.
In addition, DSKPP servers MUST include the AuthenticationDataType
element in their <KeyProvServerFinished> messages whenever a
successful protocol run will result in an existing K_TOKEN being
replaced.
11.4. Passphrase-Based Key Wrap Profile
11.4.1. Introduction
This profile is a variation of the key wrap profile. It initializes
the cryptographic module with a symmetric key, K_TOKEN, through key
wrap and key derivation, using a passphrase-derived key-wrapping key,
K_DERIVED. The passphrase is known in advance by both the device
user and the DSKPP server. To preserve the property of not exposing
K_TOKEN to any other entity than the DSKPP server and the
cryptographic module itself, the method SHOULD be employed only when
the device contains facilities (e.g. a keypad) for direct entry of
the passphrase. A key K from which two keys, K_TOKEN and K_MAC are
derived MUST be wrapped.
11.4.2. Identification
This profile MUST be identified with the following URI:
urn:ietf:params:xml:schema:keyprov:protocol#passphrase-wrap
11.4.3. Payloads
In the 2-pass version of DSKPP, the client MUST send a payload
associated with this key initialization method. The payload MUST be
of type ds:KeyInfoType ([XMLDSIG]). The ds:KeyName option MUST be
used and the key name MUST identify the passphrase that will be used
by the server to generate the key-wrapping key. As an example, the
identifier could be a user identifier or a registration identifier
issued by the server to the user during a session preceding the DSKPP
protocol run.
The server payload associated with this key initialization method
MUST be of type xenc:EncryptedKeyType ([XMLENC]), and only those
encryption methods utilizing a passphrase to derive the key-wrapping
key that are supported by the DSKPP client (as indicated in the
Doherty, et al. Expires May 1, 2008 [Page 72]
Internet-Draft DSKPP October 2007
<SupportedEncryptionAlgorithms> element of the <KeyProvClientHello>
message in the case of 2-pass DSKPP, or as otherwise known in the
case of 1-pass DSKPP) are allowed as values for the <xenc:
EncryptionMethod> element. Further, in the case of 2-pass DSKPP, the
<ds:KeyInfo> element MUST contain the same value (i.e. identify the
same passphrase) as the <Payload> of the corresponding supported key
initialization method in the <KeyProvClientHello> message that
triggered the response. The <CarriedKeyName> element MAY be present,
and MUST, when present, contain the same value as the <KeyID> element
of the <KeyProvServerFinished> message. The Type attribute of the
xenc:EncryptedKeyType MUST be present and MUST identify the type of
the wrapped key. The type MUST be one of the types supported by the
DSKPP client (as reported in the <SupportedKeyTypes> of the preceding
<KeyProvClientHello> message in the case of 2-pass DSKPP, or as
otherwise known in the case of 1-pass DSKPP). The wrapped key MUST
consist of two parts of equal length. The first half constitutes
K_MAC and the second half constitutes K_TOKEN. The length of K_TOKEN
(and hence also the length of K_MAC) is determined by the type of
K_TOKEN.
DSKPP servers and cryptographic modules supporting this profile MUST
support the PBES2 password based encryption scheme defined in
[PKCS-5] (and identified as
http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbes2 in
[PKCS-5-XML]), the PBKDF2 passphrase-based key derivation function
also defined in [PKCS-5] (and identified as
http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbkdf2 in
[PKCS-5-XML]), and the http://www.w3.org/2001/04/xmlenc#kw-aes128
key-wrapping mechanism defined in [XMLENC].
When this profile is used, the MacAlgorithm attribute of the <Mac>
element of the <KeyProvServerFinished> message MUST be present and
MUST identify the selected MAC algorithm. The selected MAC algorithm
MUST be one of the MAC algorithms supported by the DSKPP client (as
indicated in the <SupportedMacAlgorithms> element of the
<KeyProvClientHello> message in the case of 2-pass DSKPP, or as
otherwise known in the case of 1-pass DSKPP). The MAC MUST be
calculated as described in Section 4.4.
In addition, DSKPP servers MUST include the AuthenticationDataType
element in their <KeyProvServerFinished> messages whenever a
successful protocol run will result in an existing K_TOKEN being
replaced.
12. Protocol Bindings
Doherty, et al. Expires May 1, 2008 [Page 73]
Internet-Draft DSKPP October 2007
12.1. General Requirements
DSKPP assumes a reliable transport.
12.2. HTTP/1.1 Binding for DSKPP
12.2.1. Introduction
This section presents a binding of the previous messages to HTTP/1.1
[RFC2616]. Note that the HTTP client normally will be different from
the DSKPP client, i.e., the HTTP client will only exist to "proxy"
DSKPP messages from the DSKPP client to the DSKPP server. Likewise,
on the HTTP server side, the DSKPP server MAY receive DSKPP PDUs from
a "front-end" HTTP server.
12.2.2. Identification of DSKPP Messages
The MIME-type for all DSKPP messages MUST be
application/vnd.ietf.keyprov.dskpp+xml
12.2.3. HTTP Headers
HTTP proxies MUST NOT cache responses carrying DSKPP messages. For
this reason, the following holds:
o When using HTTP/1.1, requesters SHOULD:
* Include a Cache-Control header field set to "no-cache, no-
store".
* Include a Pragma header field set to "no-cache".
o When using HTTP/1.1, responders SHOULD:
* Include a Cache-Control header field set to "no-cache, no-must-
revalidate, private".
* Include a Pragma header field set to "no-cache".
* NOT include a Validator, such as a Last-Modified or ETag
header.
There are no other restrictions on HTTP headers, besides the
requirement to set the Content-Type header value according to
Section 12.2.2.
12.2.4. HTTP Operations
Persistent connections as defined in HTTP/1.1 are assumed but not
required. DSKPP requests are mapped to HTTP POST operations. DSKPP
responses are mapped to HTTP responses.
Doherty, et al. Expires May 1, 2008 [Page 74]
Internet-Draft DSKPP October 2007
12.2.5. HTTP Status Codes
A DSKPP HTTP responder that refuses to perform a message exchange
with a DSKPP HTTP requester SHOULD return a 403 (Forbidden) response.
In this case, the content of the HTTP body is not significant. In
the case of an HTTP error while processing a DSKPP request, the HTTP
server MUST return a 500 (Internal Server Error) response. This type
of error SHOULD be returned for HTTP-related errors detected before
control is passed to the DSKPP processor, or when the DSKPP processor
reports an internal error (for example, the DSKPP XML namespace is
incorrect, or the DSKPP schema cannot be located). If the type of a
DSKPP request cannot be determined, the DSKPP responder MUST return a
400 (Bad request) response.
In these cases (i.e., when the HTTP response code is 4xx or 5xx), the
content of the HTTP body is not significant.
Redirection status codes (3xx) apply as usual.
Whenever the HTTP POST is successfully invoked, the DSKPP HTTP
responder MUST use the 200 status code and provide a suitable DSKPP
message (possibly with DSKPP error information included) in the HTTP
body.
12.2.6. HTTP Authentication
No support for HTTP/1.1 authentication is assumed.
12.2.7. Initialization of DSKPP
The DSKPP server MAY initialize the DSKPP protocol by sending an HTTP
response with Content-Type set according to Section 12.2.2 and
response code set to 200 (OK). This message MAY, e.g., be sent in
response to a user requesting key initialization in a browsing
session. The initialization message MAY carry data in its body. If
this is the case, the data MUST be a valid instance of a
<KeyProvTrigger> element.
12.2.8. Example Messages
a. Initialization from DSKPP server:
HTTP/1.1 200 OK
Cache-Control: no-store
Content-Type: application/vnd.ietf.keyprov.dskpp+xml
Content-Length: <some value>
DSKPP initialization data in XML form...
Doherty, et al. Expires May 1, 2008 [Page 75]
Internet-Draft DSKPP October 2007
b. Initial request from DSKPP client:
POST http://example.com/cgi-bin/DSKPP-server HTTP/1.1
Cache-Control: no-store
Pragma: no-cache
Host: example.com
Content-Type: application/vnd.ietf.keyprov.dskpp+xml
Content-Length: <some value>
DSKPP data in XML form (supported version, supported
algorithms...)
c. Initial response from DSKPP server:
HTTP/1.1 200 OK
Cache-Control: no-store
Content-Type: application/vnd.ietf.keyprov.dskpp+xml
Content-Length: <some value>
DSKPP data in XML form (server random nonce, server public key,
...)
13. DSKPP Schema
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:1.0:container"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
targetNamespace="urn:ietf:params:xml:ns:keyprov:1.0:protocol"
elementFormDefault="unqualified" attributeFormDefault="unqualified"
version="1.0">
<xs:import namespace="http://www.w3.org/2000/09/xmldsig#"
schemaLocation="http://www.w3.org/TR/2002/REC-xmldsig-core-20020212/xmldsig-core-schema.xsd"/>
<xs:import namespace="urn:ietf:params:xml:ns:keyprov:1.0:container"
schemaLocation="keyprov-pskc-1.0.xsd"/>
<!-- Basic types -->
<xs:complexType name="AbstractRequestType" abstract="true">
<xs:attribute name="Version" type="dskpp:VersionType" use="required"/>
</xs:complexType>
<xs:complexType name="AbstractResponseType" abstract="true">
Doherty, et al. Expires May 1, 2008 [Page 76]
Internet-Draft DSKPP October 2007
<xs:attribute name="Version" type="dskpp:VersionType" use="required"/>
<xs:attribute name="SessionID" type="dskpp:IdentifierType"/>
<xs:attribute name="Status" type="dskpp:StatusCode" use="required"/>
</xs:complexType>
<xs:simpleType name="VersionType">
<xs:restriction base="xs:string">
<xs:pattern value="\d{1,2}\.\d{1,3}"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="IdentifierType">
<xs:restriction base="xs:string">
<xs:maxLength value="128"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="StatusCode">
<xs:restriction base="xs:string">
<xs:enumeration value="Continue"/>
<xs:enumeration value="Success"/>
<xs:enumeration value="Abort"/>
<xs:enumeration value="AccessDenied"/>
<xs:enumeration value="MalformedRequest"/>
<xs:enumeration value="UnknownRequest"/>
<xs:enumeration value="UnknownCriticalExtension"/>
<xs:enumeration value="UnsupportedVersion"/>
<xs:enumeration value="NoSupportedKeyTypes"/>
<xs:enumeration value="NoSupportedEncryptionAlgorithms"/>
<xs:enumeration value="NoSupportedMacAlgorithms"/>
<xs:enumeration value="NoProtocolVariants"/>
<xs:enumeration value="NoSupportedKeyContainers"/>
<xs:enumeration value="AuthenticationDataMissing"/>
<xs:enumeration value="AuthenticationDataInvalid"/>
<xs:enumeration value="InitializationFailed"/>
</xs:restriction>
</xs:simpleType>
<xs:complexType name="DeviceIdentifierDataType">
<xs:choice>
<xs:element name="DeviceId" type="pskc:DeviceIdType"/>
<xs:any namespace="##other" processContents="strict"/>
</xs:choice>
</xs:complexType>
<xs:simpleType name="PlatformType">
<xs:restriction base="xs:string">
<xs:enumeration value="Hardware"/>
Doherty, et al. Expires May 1, 2008 [Page 77]
Internet-Draft DSKPP October 2007
<xs:enumeration value="Software"/>
<xs:enumeration value="Unspecified"/>
</xs:restriction>
</xs:simpleType>
<xs:complexType name="TokenPlatformInfoType">
<xs:attribute name="KeyLocation" type="dskpp:PlatformType"/>
<xs:attribute name="AlgorithmLocation" type="dskpp:PlatformType"/>
</xs:complexType>
<xs:simpleType name="NonceType">
<xs:restriction base="xs:base64Binary">
<xs:minLength value="16"/>
</xs:restriction>
</xs:simpleType>
<xs:complexType name="AlgorithmsType">
<xs:sequence maxOccurs="unbounded">
<xs:element name="Algorithm" type="dskpp:AlgorithmType"/>
</xs:sequence>
</xs:complexType>
<xs:simpleType name="AlgorithmType">
<xs:restriction base="xs:anyURI"/>
</xs:simpleType>
<xs:complexType name="ProtocolVariantsType">
<xs:sequence>
<xs:element name="FourPass" minOccurs="0"/>
<xs:element name="TwoPass" type="dskpp:TwoPassSupportType"
minOccurs="0"/>
<xs:element name="OnePass" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="TwoPassSupportType">
<xs:sequence maxOccurs="unbounded">
<xs:element name="SupportedKeyInitializationMethod"
type="xs:anyURI"/>
<xs:element name="Payload" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="KeyContainersFormatType">
<xs:sequence maxOccurs="unbounded">
<xs:element name="KeyContainerFormat"
type="dskpp:KeyContainerFormatType"/>
</xs:sequence>
Doherty, et al. Expires May 1, 2008 [Page 78]
Internet-Draft DSKPP October 2007
</xs:complexType>
<xs:simpleType name="KeyContainerFormatType">
<xs:restriction base="xs:anyURI"/>
</xs:simpleType>
<xs:complexType name="AuthenticationDataType">
<xs:annotation>
<xs:documentation xml:lang="en">
Authentication data can consist of either authentication code
for authenticating a user of the protocol, or an X.509 Certificate for
authenticating a device. When a device certificate is used over a
transport layer that is not secure, the Signature is calculated over
a nonce value specified in ds:Signature/Object. When used in
conjunction with the KeyProvServerFinished PDU, it contains a MAC
authenticating the DSKPP server to the client.
</xs:documentation>
</xs:annotation>
<xs:sequence>
<xs:element name="ClientID" type="dskpp:IdentifierType"
minOccurs="0"/>
<xs:choice minOccurs="0">
<xs:element name="AuthenticationCodeMac"
type="dskpp:AuthenticationCodeMacType"/>
<xs:element name="DigitalSignature"
type="ds:SignatureType"/>
</xs:choice>
</xs:sequence>
</xs:complexType>
<xs:complexType name="AuthenticationCodeMacType">
<xs:annotation>
<xs:documentation xml:lang="en">
An authentication MAC calculated from an authentication code and
optionally server information as well as nonce value if they are
available.
</xs:documentation>
</xs:annotation>
<xs:sequence>
<xs:element name="Nonce" type="dskpp:NonceType" minOccurs="0"/>
<xs:element name="IterationCount" type="xs:int" minOccurs="0"/>
<xs:element name="Mac" type="dskpp:MacType"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="MacType">
<xs:simpleContent>
<xs:extension base="xs:base64Binary">
Doherty, et al. Expires May 1, 2008 [Page 79]
Internet-Draft DSKPP October 2007
<xs:attribute name="MacAlgorithm" type="xs:anyURI"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<xs:complexType name="KeyContainerType">
<xs:sequence>
<xs:element name="ServerID" type="xs:anyURI" minOccurs="0"/>
<xs:choice>
<xs:element name="KeyContainer" type="pskc:KeyContainerType"/>
<xs:any namespace="##other" processContents="strict"/>
</xs:choice>
</xs:sequence>
</xs:complexType>
<xs:complexType name="InitializationTriggerType">
<xs:sequence>
<xs:element name="DeviceIdentifierData"
type="dskpp:DeviceIdentifierDataType" minOccurs="0"/>
<xs:element name="KeyID" type="xs:base64Binary" minOccurs="0"/>
<xs:element name="TokenPlatformInfo"
type="dskpp:TokenPlatformInfoType" minOccurs="0"/>
<xs:element name="TriggerNonce" type="dskpp:NonceType"/>
<xs:element name="DSKPPServerUrl" type="xs:anyURI" minOccurs="0"/>
<xs:any namespace="##other" processContents="strict"
minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<!-- Extension types -->
<xs:complexType name="ExtensionsType">
<xs:sequence maxOccurs="unbounded">
<xs:element name="Extension" type="dskpp:AbstractExtensionType"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="AbstractExtensionType" abstract="true">
<xs:attribute name="Critical" type="xs:boolean"/>
</xs:complexType>
<xs:complexType name="ClientInfoType">
<xs:complexContent>
<xs:extension base="dskpp:AbstractExtensionType">
<xs:sequence>
<xs:element name="Data"
type="xs:base64Binary"/>
</xs:sequence>
</xs:extension>
Doherty, et al. Expires May 1, 2008 [Page 80]
Internet-Draft DSKPP October 2007
</xs:complexContent>
</xs:complexType>
<xs:complexType name="ServerInfoType">
<xs:complexContent>
<xs:extension base="dskpp:AbstractExtensionType">
<xs:sequence>
<xs:element name="Data"
type="xs:base64Binary"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="PayloadType">
<xs:choice>
<xs:element name="Nonce" type="dskpp:NonceType"/>
<xs:any namespace="##other" processContents="strict"/>
</xs:choice>
</xs:complexType>
<xs:complexType name="KeyInitializationDataType">
<xs:annotation>
<xs:documentation xml:lang="en">
This extension is only valid in KeyProvServerFinished PDUs. It
contains key initialization data and its presence results in a
two-pass (or one-pass, if no KeyProvClientHello was sent) DSKPP
exchange.
</xs:documentation>
</xs:annotation>
<xs:complexContent>
<xs:extension base="dskpp:AbstractExtensionType">
<xs:sequence>
<xs:element name="KeyInitializationMethod" type="xs:anyURI"/>
<xs:element name="Payload" type="dskpp:PayloadType"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- DSKPP PDUs -->
<xs:element name="KeyProvTrigger" type="dskpp:KeyProvTriggerType"/>
<xs:complexType name="KeyProvTriggerType">
<xs:annotation>
<xs:documentation xml:lang="en">
Message used to trigger the device to initiate a
Doherty, et al. Expires May 1, 2008 [Page 81]
Internet-Draft DSKPP October 2007
DSKPP protocol run.
</xs:documentation>
</xs:annotation>
<xs:sequence>
<xs:choice>
<xs:element name="InitializationTrigger"
type="dskpp:InitializationTriggerType"/>
<xs:any namespace="##other" processContents="strict"/>
</xs:choice>
</xs:sequence>
<xs:attribute name="Version" type="dskpp:VersionType"/>
</xs:complexType>
<!-- KeyProvClientHello PDU -->
<xs:element name="KeyProvClientHello" type="dskpp:KeyProvClientHelloPDU"/>
<xs:complexType name="KeyProvClientHelloPDU">
<xs:annotation>
<xs:documentation xml:lang="en">
Message sent from DSKPP client to DSKPP server to initiate a
DSKPP session.
</xs:documentation>
</xs:annotation>
<xs:complexContent>
<xs:extension base="dskpp:AbstractRequestType">
<xs:sequence>
<xs:element name="DeviceIdentifierData"
type="dskpp:DeviceIdentifierDataType" minOccurs="0"/>
<xs:element name="KeyID" type="xs:base64Binary"
minOccurs="0"/>
<xs:element name="ClientNonce" type="dskpp:NonceType"
minOccurs="0"/>
<xs:element name="TriggerNonce" type="dskpp:NonceType"
minOccurs="0"/>
<xs:element name="SupportedKeyTypes"
type="dskpp:AlgorithmsType"/>
<xs:element name="SupportedEncryptionAlgorithms"
type="dskpp:AlgorithmsType"/>
<xs:element name="SupportedMacAlgorithms"
type="dskpp:AlgorithmsType"/>
<xs:element name="SupportedProtocolVariants"
type="dskpp:ProtocolVariantsType" minOccurs="0"/>
<xs:element name="SupportedKeyContainers"
type="dskpp:KeyContainersFormatType" minOccurs="0"/>
<xs:element name="AuthenticationData"
type="dskpp:AuthenticationDataType" minOccurs="0"/>
<xs:element name="Extensions" type="dskpp:ExtensionsType"
minOccurs="0"/>
Doherty, et al. Expires May 1, 2008 [Page 82]
Internet-Draft DSKPP October 2007
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- KeyProvServerHello PDU -->
<xs:element name="KeyProvServerHello" type="dskpp:KeyProvServerHelloPDU"/>
<xs:complexType name="KeyProvServerHelloPDU">
<xs:annotation>
<xs:documentation xml:lang="en">
Message sent from DSKPP server to DSKPP client
in response to a received KeyProvClientHello PDU.
</xs:documentation>
</xs:annotation>
<xs:complexContent>
<xs:extension base="dskpp:AbstractResponseType">
<xs:sequence minOccurs="0">
<xs:element name="KeyType"
type="dskpp:AlgorithmType"/>
<xs:element name="EncryptionAlgorithm"
type="dskpp:AlgorithmType"/>
<xs:element name="MacAlgorithm"
type="dskpp:AlgorithmType"/>
<xs:element name="EncryptionKey"
type="ds:KeyInfoType"/>
<xs:element name="KeyContainerFormat"
type="dskpp:KeyContainerFormatType"/>
<xs:element name="Payload"
type="dskpp:PayloadType"/>
<xs:element name="Extensions"
type="dskpp:ExtensionsType" minOccurs="0"/>
<xs:element name="Mac" type="dskpp:MacType"
minOccurs="0"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- KeyProvClientNonce PDU -->
<xs:element name="KeyProvClientNonce" type="dskpp:KeyProvClientNoncePDU"/>
<xs:complexType name="KeyProvClientNoncePDU">
<xs:annotation>
<xs:documentation xml:lang="en">
Second message sent from DSKPP client to
DSKPP server in a DSKPP session.
</xs:documentation>
Doherty, et al. Expires May 1, 2008 [Page 83]
Internet-Draft DSKPP October 2007
</xs:annotation>
<xs:complexContent>
<xs:extension base="dskpp:AbstractRequestType">
<xs:sequence>
<xs:element name="EncryptedNonce"
type="xs:base64Binary"/>
<xs:element name="AuthenticationData"
type="dskpp:AuthenticationDataType" minOccurs="0"/>
<xs:element name="Extensions"
type="dskpp:ExtensionsType" minOccurs="0"/>
</xs:sequence>
<xs:attribute name="SessionID" type="dskpp:IdentifierType"
use="required"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- KeyProvServerFinished PDU -->
<xs:element name="KeyProvServerFinished" type="dskpp:KeyProvServerFinishedPDU"/>
<xs:complexType name="KeyProvServerFinishedPDU">
<xs:annotation>
<xs:documentation xml:lang="en">
Final message sent from DSKPP server to DSKPP client in a DSKPP
session. A MAC value serves for key confirmation, and optional
AuthenticationData servers for server authentication.
</xs:documentation>
</xs:annotation>
<xs:complexContent>
<xs:extension base="dskpp:AbstractResponseType">
<xs:sequence minOccurs="0">
<xs:element name="KeyContainer"
type="dskpp:KeyContainerType"/>
<xs:element name="Extensions"
type="dskpp:ExtensionsType" minOccurs="0"/>
<xs:element name="Mac"
type="dskpp:MacType"/>
<xs:element name="AuthenticationData"
type="dskpp:AuthenticationDataType" minOccurs="0"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:schema>
Doherty, et al. Expires May 1, 2008 [Page 84]
Internet-Draft DSKPP October 2007
14. Security Considerations
14.1. General
DSKPP is designed to protect generated key material from exposure.
No other entities than the DSKPP server and the cryptographic module
will have access to a generated K_TOKEN if the cryptographic
algorithms used are of sufficient strength and, on the DSKPP client
side, generation and encryption of R_C and generation of K_TOKEN take
place as specified in the cryptographic module. This applies even if
malicious software is present in the DSKPP client. However, as
discussed in the following, DSKPP does not protect against certain
other threats resulting from man-in-the-middle attacks and other
forms of attacks. DSKPP SHOULD, therefore, be run over a transport
providing privacy and integrity, such as HTTP over Transport Layer
Security (TLS) with a suitable ciphersuite, when such threats are a
concern. Note that TLS ciphersuites with anonymous key exchanges are
not suitable in those situations.
14.2. Active Attacks
14.2.1. Introduction
An active attacker MAY attempt to modify, delete, insert, replay, or
reorder messages for a variety of purposes including service denial
and compromise of generated key material. Section 14.2.2 through
Section 14.2.7.
14.2.2. Message Modifications
Modifications to a <DSKPPTrigger> message will either cause denial-
of-service (modifications of any of the identifiers or the nonce) or
will cause the DSKPP client to contact the wrong DSKPP server. The
latter is in effect a man-in-the-middle attack and is discussed
further in Section 14.2.7.
An attacker may modify a <KeyProvClientHello> message. This means
that the attacker could indicate a different key or device than the
one intended by the DSKPP client, and could also suggest other
cryptographic algorithms than the ones preferred by the DSKPP client,
e.g., cryptographically weaker ones. The attacker could also suggest
earlier versions of the DSKPP protocol, in case these versions have
been shown to have vulnerabilities. These modifications could lead
to an attacker succeeding in initializing or modifying another
cryptographic module than the one intended (i.e., the server
assigning the generated key to the wrong module), or gaining access
to a generated key through the use of weak cryptographic algorithms
or protocol versions. DSKPP implementations MAY protect against the
Doherty, et al. Expires May 1, 2008 [Page 85]
Internet-Draft DSKPP October 2007
latter by having strict policies about what versions and algorithms
they support and accept. The former threat (assignment of a
generated key to the wrong module) is not possible when the shared-
key variant of DSKPP is employed (assuming existing shared keys are
unique per cryptographic module), but is possible in the public-key
variant. Therefore, DSKPP servers MUST NOT accept unilaterally
provided device identifiers in the public-key variant. This is also
indicated in the protocol description. In the shared-key variant,
however, an attacker may be able to provide the wrong identifier
(possibly also leading to the incorrect user being associated with
the generated key) if the attacker has real-time access to the
cryptographic module with the identified key. In other words, the
generated key is associated with the correct cryptographic module but
the module is associated with the incorrect user. See further
Section 14.5 for a discussion of this threat and possible
countermeasures.
An attacker may also modify a <KeyProvServerHello> message. This
means that the attacker could indicate different key types,
algorithms, or protocol versions than the legitimate server would,
e.g., cryptographically weaker ones. The attacker may also provide a
different nonce than the one sent by the legitimate server. Clients
MAY protect against the former through strict adherence to policies
regarding permissible algorithms and protocol versions. The latter
(wrong nonce) will not constitute a security problem, as a generated
key will not match the key generated on the legitimate server. Also,
whenever the DSKPP run would result in the replacement of an existing
key, the <Mac> element protects against modifications of R_S.
Modifications of <KeyProvClientNonce> messages are also possible. If
an attacker modifies the SessionID attribute, then, in effect, a
switch to another session will occur at the server, assuming the new
SessionID is valid at that time on the server. It still will not
allow the attacker to learn a generated K_TOKEN since R_C has been
wrapped for the legitimate server. Modifications of the
<EncryptedNonce> element, e.g., replacing it with a value for which
the attacker knows an underlying R'C, will not result in the client
changing its pre-DSKPP state, since the server will be unable to
provide a valid MAC in its final message to the client. The server
MAY, however, end up storing K'TOKEN rather than K_TOKEN. If the
cryptographic module has been associated with a particular user, then
this could constitute a security problem. For a further discussion
about this threat, and a possible countermeasure, see Section 14.5
below. Note that use of Secure Socket Layer (SSL) or TLS does not
protect against this attack if the attacker has access to the DSKPP
client (e.g., through malicious software, "trojans").
Finally, attackers may also modify the <KeyProvServerFinished>
Doherty, et al. Expires May 1, 2008 [Page 86]
Internet-Draft DSKPP October 2007
message. Replacing the <Mac> element will only result in denial-of-
service. Replacement of any other element may cause the DSKPP client
to associate, e.g., the wrong service with the generated key. DSKPP
SHOULD be run over a transport providing privacy and integrity when
this is a concern.
14.2.3. Message Deletion
Message deletion will not cause any other harm than denial-of-
service, since a cryptographic module MUST NOT change its state
(i.e., "commit" to a generated key) until it receives the final
message from the DSKPP server and successfully has processed that
message, including validation of its MAC. A deleted
<KeyProvServerFinished> message will not cause the server to end up
in an inconsistent state vis-a-vis the cryptographic module if the
server implements the suggestions in Section 14.5.
14.2.4. Message Insertion
An active attacker may initiate a DSKPP run at any time, and suggest
any device identifier. DSKPP server implementations MAY receive some
protection against inadvertently initializing a key or inadvertently
replacing an existing key or assigning a key to a cryptographic
module by initializing the DSKPP run by use of the <KeyProvTrigger>.
The <TriggerNonce> element allows the server to associate a DSKPP
protocol run with, e.g., an earlier user-authenticated session. The
security of this method, therefore, depends on the ability to protect
the <TriggerNonce> element in the DSKPP initialization message. If
an eavesdropper is able to capture this message, he may race the
legitimate user for a key initialization. DSKPP over a transport
providing privacy and integrity, coupled with the recommendations in
Section 14.5, is RECOMMENDED when this is a concern.
Insertion of other messages into an existing protocol run is seen as
equivalent to modification of legitimately sent messages.
14.2.5. Message Replay
During 4-pass DSKPP, attempts to replay a previously recorded DSKPP
message will be detected, as the use of nonces ensures that both
parties are live. For example, a DSKPP client knows that a server it
is communicating with is "live" since the server MUST create a MAC on
information sent by the client.
The same is true for 2-pass DSKPP thanks to the requirement that the
client sends R in the <KeyProvClientHello> message and that the
server includes R in the MAC computation.
Doherty, et al. Expires May 1, 2008 [Page 87]
Internet-Draft DSKPP October 2007
In 1-pass DSKPP clients that record the latest I used by a particular
server (as identified by ID_S) will be able to detect replays.
14.2.6. Message Reordering
An attacker may attempt to re-order 4-pass DSKPP messages but this
will be detected, as each message is of a unique type. Note: Message
re-ordering attacks cannot occur in 2- and 1-pass DSKPP since each
party sends at most one message each.
14.2.7. Man-in-the-Middle
In addition to other active attacks, an attacker posing as a man in
the middle may be able to provide his own public key to the DSKPP
client. This threat and countermeasures to it are discussed in
Section 4.3. An attacker posing as a man-in-the-middle may also be
acting as a proxy and, hence, may not interfere with DSKPP runs but
still learn valuable information; see Section 14.3.
14.3. Passive Attacks
Passive attackers may eavesdrop on DSKPP runs to learn information
that later on may be used to impersonate users, mount active attacks,
etc.
If DSKPP is not run over a transport providing privacy, a passive
attacker may learn:
o What cryptographic modules a particular user is in possession of;
o The identifiers of keys on those cryptographic modules and other
attributes pertaining to those keys, e.g., the lifetime of the
keys; and
o DSKPP versions and cryptographic algorithms supported by a
particular DSKPP client or server.
Whenever the above is a concern, DSKPP SHOULD be run over a transport
providing privacy. If man-in-the-middle attacks for the purposes
described above are a concern, the transport SHOULD also offer
server-side authentication.
14.4. Cryptographic Attacks
An attacker with unlimited access to an initialized cryptographic
module may use the module as an "oracle" to pre-compute values that
later on may be used to impersonate the DSKPP server. Section 5.2
and Section 4 contain discussions of this threat and steps
RECOMMENDED to protect against it.
Doherty, et al. Expires May 1, 2008 [Page 88]
Internet-Draft DSKPP October 2007
14.5. Attacks on the Interaction between DSKPP and User Authentication
If keys generated in DSKPP will be associated with a particular user
at the DSKPP server (or a server trusted by, and communicating with
the DSKPP server), then in order to protect against threats where an
attacker replaces a client-provided encrypted R_C with his own R'C
(regardless of whether the public-key variant or the shared-secret
variant of DSKPP is employed to encrypt the client nonce), the server
SHOULD not commit to associate a generated K_TOKEN with the given
cryptographic module until the user simultaneously has proven both
possession of the device that hosts the cryptographic module
containing K_TOKEN and some out-of-band provided authenticating
information (e.g., a temporary password). For example, if the
cryptographic module is a one-time password token, the user could be
required to authenticate with both a one-time password generated by
the cryptographic module and an out-of-band provided temporary PIN in
order to have the server "commit" to the generated OTP value for the
given user. Preferably, the user SHOULD perform this operation from
another host than the one used to initialize keys on the
cryptographic module, in order to minimize the risk of malicious
software on the client interfering with the process.
Note: This scenario, wherein the attacker replaces a client-provided
R_C with his own R'C, does not apply to 2- and 1-pass DSKPP as the
client does not provide any entropy to K_TOKEN. The attack as such
(and its countermeasures) still applies to 2- and 1-pass DSKPP,
however, as it essentially is a man-in-the-middle attack.
Another threat arises when an attacker is able to trick a user to
authenticate to the attacker rather than to the legitimate service
before the DSKPP protocol run. If successful, the attacker will then
be able to impersonate the user towards the legitimate service, and
subsequently receive a valid DSKPP trigger. If the public-key
variant of DSKPP is used, this may result in the attacker being able
to (after a successful DSKPP protocol run) impersonate the user.
Ordinary precautions MUST, therefore, be in place to ensure that
users authenticate only to legitimate services.
14.6. Additional Considerations Specific to 2- and 1-pass DSKPP
14.6.1. Client Contributions to K_TOKEN Entropy
In 4-pass DSKPP, both the client and the server provide randomizing
material to K_TOKEN , in a manner that allows both parties to verify
that they did contribute to the resulting key. In the 1- and 2-pass
DSKPP versions defined herein, only the server contributes to the
entropy of K_TOKEN. This means that a broken or compromised
(pseudo-)random number generator in the server may cause more damage
Doherty, et al. Expires May 1, 2008 [Page 89]
Internet-Draft DSKPP October 2007
than it would in the 4-pass variant. Server implementations SHOULD
therefore take extreme care to ensure that this situation does not
occur.
14.6.2. Key Confirmation
4-pass DSKPP servers provide key confirmation through the MAC on R_C
in the <KeyProvServerFinished> message. In the 1- and 2-pass DSKPP
variants described herein, key confirmation is provided by the MAC
including I (in the 1-pass case) or R (2-pass case), using K_MAC.
14.6.3. Server Authentication
DSKPP servers MUST authenticate themselves whenever a successful
DSKPP 1- or 2-pass protocol run would result in an existing K_TOKEN
being replaced by a K_TOKEN', or else a denial-of-service attack
where an unauthorized DSKPP server replaces a K_TOKEN with another
key would be possible. In 1- and 2-pass DSKPP, servers authenticate
by including the AuthenticationDataType extension containing a MAC as
described in Section 4.4 for Two-Pass DSKPP and Section 4.5 for One-
Pass DSKPP.
14.6.4. Client Authentication
A DSKPP server MUST authenticate a client to ensure that K_TOKEN is
delivered to the intended device. The following measures SHOULD be
considered:
o When a device certificate is used for client authentication, the
DSKPP server SHOULD follow standard certificate verification
processes to ensure that it is a trusted device.
o When an Authentication Code is used for client authentication, a
password dictionary attack on the authentication data is possible.
o The length of the Authentication Code when used over a non-secure
channel SHOULD be longer than what is used over a secure channel.
When a device, e.g., some mobile phones with small screens, cannot
handle a long Authentication Code in a user-friendly manner, DSKPP
SHOULD rely on a secure channel for communication.
o In the case that a non-secure channel has to be used, the
Authentication Code SHOULD be sent to the server MAC's as
specified in Section 5.3. The Authentication Code and nonce value
MUST be strong enough to prevent offline brute-force recovery of
the Authentication Code from the HMAC data. Given that the nonce
value is sent in plaintext format over a non-secure transport, the
cryptographic strength of the AuthenticationData depends more on
the quality of the AuthenticationCode.
o When the AuthenticationCode is sent from the DSKPP server to the
device in a DSKPP initialization trigger message, an eavesdropper
may be able to capture this message and race the legitimate user
Doherty, et al. Expires May 1, 2008 [Page 90]
Internet-Draft DSKPP October 2007
for a key initialization. To prevent this, the transport layer
used to send the DSKPP trigger MUST provide privacy and integrity
e.g. secure browser session.
14.6.5. Key Protection in the Passphrase Profile
The passphrase-based key wrap profile uses the PBKDF2 function from
[PKCS-5] to generate an encryption key from a passphrase and salt
string. The derived key, K_DERIVED is used by the server to encrypt
K_TOKEN and by the cryptographic module to decrypt the newly
delivered K_TOKEN. It is important to note that passphrase-based
encryption is generally limited in the security that it provides
despite the use of salt and iteration count in PBKDF2 to increase the
complexity of attack. Implementations SHOULD therefore take
additional measures to strengthen the security of the passphrase-
based key wrap profile. The following measures SHOULD be considered
where applicable:
o The passphrase SHOULD be selected well, and usage guidelines such
as the ones in [NIST-PWD] SHOULD be taken into account.
o A different passphrase SHOULD be used for every key initialization
wherever possible (the use of a global passphrase for a batch of
cryptographic modules SHOULD be avoided, for example). One way to
achieve this is to use randomly-generated passphrases.
o The passphrase SHOULD be protected well if stored on the server
and/or on the cryptographic module and SHOULD be delivered to the
device's user using secure methods.
o User pre-authentication SHOULD be implemented to ensure that
K_TOKEN is not delivered to a rogue recipient.
o The iteration count in PBKDF2 SHOULD be high to impose more work
for an attacker using brute-force methods (see [PKCS-5] for
recommendations). However, it MUST be noted that the higher the
count, the more work is required on the legitimate cryptographic
module to decrypt the newly delivered K_TOKEN. Servers MAY use
relatively low iteration counts to accommodate devices with
limited processing power such as some PDA and cell phones when
other security measures are implemented and the security of the
passphrase-based key wrap method is not weakened.
o Transport level security (e.g. TLS) SHOULD be used where possible
to protect a 2-pass or 1-pass protocol run. Transport level
security provides a second layer of protection for the newly
generated K_TOKEN.
15. Internationalization Considerations
The DSKPP protocol is mostly meant for machine-to-machine
communications; as such, most of its elements are tokens not meant
Doherty, et al. Expires May 1, 2008 [Page 91]
Internet-Draft DSKPP October 2007
for direct human consumption. If these tokens are presented to the
end user, some localization may need to occur. DSKPP exchanges
information using XML. All XML processors are required to understand
UTF-8 and UTF-16 encoding, and therefore all DSKPP clients and
servers MUST understand UTF-8 and UTF-16 encoded XML. Additionally,
DSKPP servers and clients MUST NOT encode XML with encodings other
than UTF-8 or UTF-16.
16. IANA Considerations
This document calls for registration of new URNs within the IETF sub-
namespace per RFC3553 [RFC3553]. The following URNs are RECOMMENDED:
o DSKPP XML schema: "urn:ietf:params:xml:schema:keyprov:protocol"
o DSKPP XML namespace: "urn:ietf:params:xml:ns:keyprov:protocol"
17. Intellectual Property Considerations
RSA and RSA Security are registered trademarks or trademarks of RSA
Security Inc. in the United States and/or other countries. The names
of other products and services mentioned may be the trademarks of
their respective owners.
18. Contributors
This work is based on information contained in [RFC4758], authored by
Magnus Nystrom, with enhancements (esp. Client Authentication, and
support for multiple key container formats) from an individual
Internet-Draft co-authored by Mingliang Pei and Salah Machani.
We would like to thank Shuh Chang for contributing the DSKPP object
model, and Philip Hoyer for his work in aligning DSKPP and PSKC
schemas.
We would also like to thank Hannes Tschofenig for his draft reviews,
feedback, and text contributions.
19. Acknowledgements
We would like to thank the following for detailed review of previous
DSKPP document versions:
o Dr. Ulrike Meyer (Review June 2007)
Doherty, et al. Expires May 1, 2008 [Page 92]
Internet-Draft DSKPP October 2007
o Niklas Neumann (Review June 2007)
o Shuh Chang (Review June 2007)
o Hannes Tschofenig (Review June 2007 and again in August 2007)
o Sean Turner (Review August 2007)
o John Linn (Review August 2007)
o Philip Hoyer (Review September 2007)
We would also like to thank the following for their input to selected
design aspects of the DSKPP protocol:
o Anders Rundgren (Key Container Format and Client Authentication
Data)
o Hannes Tschofenig (HTTP Binding)
o Phillip Hallam-Baker (Registry for Algorithms)
Finally, we would like to thank Robert Griffin for opening
communication channels for us with the IEEE P1619.3 Key Management
Group, and facilitating our groups in staying informed of potential
areas (esp. key provisioning and global key identifiers of
collaboration) of collaboration.
20. References
20.1. Normative references
[UNICODE] Davis, M. and M. Duerst, "Unicode Normalization Forms",
March 2001,
<http://www.unicode.org/unicode/reports/tr15/
tr15-21.html>.
[XMLDSIG] W3C, "XML Signature Syntax and Processing",
W3C Recommendation, February 2002,
<http://www.w3.org/TR/2002/REC-xmldsig-core-20020212/>.
[XMLENC] W3C, "XML Encryption Syntax and Processing",
W3C Recommendation, December 2002,
<http://www.w3.org/TR/2002/REC-xmldsig-core-20020212/>.
Doherty, et al. Expires May 1, 2008 [Page 93]
Internet-Draft DSKPP October 2007
20.2. Informative references
[CT-KIP-P11]
RSA Laboratories, "PKCS #11 Mechanisms for the
Cryptographic Token Key Initialization Protocol", PKCS #11
Version 2.20 Amd.2, December 2005,
<http://www.rsasecurity.com/rsalabs/pkcs/>.
[FAQ] RSA Laboratories, "Frequently Asked Questions About
Today's Cryptography", Version 4.1, 2000.
[FIPS180-SHA]
National Institute of Standards and Technology, "Secure
Hash Standard", FIPS 180-2, February 2004, <http://
csrc.nist.gov/publications/fips/fips180-2/
fips180-2withchangenotice.pdf>.
[FIPS197-AES]
National Institute of Standards and Technology,
"Specification for the Advanced Encryption Standard
(AES)", FIPS 197, November 2001, <http://csrc.nist.gov/
publications/fips/fips197/fips-197.pdf>.
[FSE2003] Iwata, T. and K. Kurosawa, "OMAC: One-Key CBC MAC. In Fast
Software Encryption", FSE 2003, Springer-Verlag , 2003,
<http://crypt.cis.ibaraki.ac.jp/omac/docs/omac.pdf>.
[NIST-PWD]
National Institute of Standards and Technology, "Password
Usage", FIPS 112, May 1985,
<http://www.itl.nist.gov/fipspubs/fip112.htm>.
[OATH] "Initiative for Open AuTHentication", 2005,
<http://www.openauthentication.org>.
[PKCS-1] RSA Laboratories, "RSA Cryptography Standard", PKCS #1
Version 2.1, June 2002,
<http://www.rsasecurity.com/rsalabs/pkcs/>.
[PKCS-11] RSA Laboratories, "Cryptographic Token Interface
Standard", PKCS #11 Version 2.20, June 2004,
<http://www.rsasecurity.com/rsalabs/pkcs/>.
[PKCS-12] "Personal Information Exchange Syntax Standard", PKCS #12
Version 1.0, 2005,
<ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-12/
pkcs-12v1.pdf>.
Doherty, et al. Expires May 1, 2008 [Page 94]
Internet-Draft DSKPP October 2007
[PKCS-5] RSA Laboratories, "Password-Based Cryptography Standard",
PKCS #5 Version 2.0, March 1999,
<http://www.rsasecurity.com/rsalabs/pkcs/>.
[PKCS-5-XML]
RSA Laboratories, "XML Schema for PKCS #5 Version 2.0",
PKCS #5 Version 2.0 Amd.1 (FINAL DRAFT), October 2006,
<http://www.rsasecurity.com/rsalabs/pkcs/>.
[PSKC] "Portable Symmetric Key Container", 2005, <http://
www.ietf.org/internet-drafts/
draft-hoyer-keyprov-portable-symmetric-key-container-
00.txt>.
[RFC2104] Krawzcyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
February 1997.
[RFC2119] "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997,
<http://www.ietf.org/rfc/rfc2119.txt>.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999,
<http://www.ietf.org/rfc/rfc2616.txt>.
[RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.
[RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
IETF URN Sub-namespace for Registered Protocol
Parameters", RFC 3553, BCP 73, June 2003.
[RFC4758] RSA, The Security Division of EMC, "Cryptographic Token
Key Initialization Protocol (CT-KIP)", November 2006,
<http://www.ietf.org/rfc/rfc4758.txt>.
Appendix A. Integration with PKCS #11
A DSKPP client that needs to communicate with a connected
cryptographic module to perform a DSKPP exchange MAY use PKCS #11
[PKCS-11]as a programming interface.
Doherty, et al. Expires May 1, 2008 [Page 95]
Internet-Draft DSKPP October 2007
A.1. The 4-pass Variant
When performing 4-pass DSKPP with a cryptographic module using the
PKCS #11 programming interface, the procedure described in
[CT-KIP-P11], Appendix B, is RECOMMENDED.
A.2. The 2-pass Variant
A suggested procedure to perform 2-pass DSKPP with a cryptographic
module through the PKCS #11 interface using the mechanisms defined in
[CT-KIP-P11] is as follows:
a. On the client side,
1. The client selects a suitable slot and token (e.g. through
use of the <DeviceIdentifier> or the <PlatformInfo> element
of the DSKPP trigger message).
2. A nonce R is generated, e.g. by calling C_SeedRandom and
C_GenerateRandom.
3. The client sends its first message to the server, including
the nonce R.
b. On the server side,
1. A generic key K = K_TOKEN | K _MAC (where '|' denotes
concatenation) is generated, e.g. by calling C_GenerateKey
(using key type CKK_GENERIC_SECRET). The template for K MUST
allow it to be exported (but only in wrapped form, i.e.
CKA_SENSITIVE MUST be set to CK_TRUE and CKA_EXTRACTABLE MUST
also be set to CK_TRUE), and also to be used for further key
derivation. From K, a token key K_TOKEN of suitable type is
derived by calling C_DeriveKey using the PKCS #11 mechanism
CKM_EXTRACT_KEY_FROM_KEY and setting the CK_EXTRACT_PARAMS to
the first bit of the generic secret key (i.e. set to 0).
Likewise, a MAC key K_MAC is derived from K by calling
C_DeriveKey using the CKM_EXTRACT_KEY_FROM_KEY mechanism,
this time setting CK_EXTRACT_PARAMS to the length of K (in
bits) divided by two.
2. The server wraps K with either the token's public key
K_CLIENT, the shared secret key K_SHARED, or the derived
shared secret key K_DERIVED by using C_WrapKey. If use of
the DSKPP key wrap algorithm has been negotiated then the
CKM_KIP_WRAP mechanism MUST be used to wrap K. When calling
C_WrapKey, the hKey handle in the CK_KIP_PARAMS structure
MUST be set to NULL_PTR. The pSeed parameter in the
CK_KIP_PARAMS structure MUST point to the nonce R provided by
the DSKPP client, and the ulSeedLen parameter MUST indicate
the length of R. The hWrappingKey parameter in the call to
C_WrapKey MUST be set to refer to the wrapping key.
Doherty, et al. Expires May 1, 2008 [Page 96]
Internet-Draft DSKPP October 2007
3. Next, the server needs to calculate a MAC using K_MAC. If
use of the DSKPP MAC algorithm has been negotiated, then the
MAC is calculated by calling C_SignInit with the CKM_KIP_MAC
mechanism followed by a call to C_Sign. In the call to
C_SignInit, K_MAC MUST be the signature key, the hKey
parameter in the CK_KIP_PARAMS structure MUST be set to
NULL_PTR, the pSeed parameter of the CT_KIP_PARAMS structure
MUST be set to NULL_PTR, and the ulSeedLen parameter MUST be
set to zero. In the call to C_Sign, the pData parameter MUST
be set to the concatenation of the string ID_S and the nonce
R, and the ulDataLen parameter MUST be set to the length of
the concatenated string. The desired length of the MAC MUST
be specified through the pulSignatureLen parameter and MUST
be set to the length of R.
4. If the server also needs to authenticate its message (due to
an existing K_TOKEN being replaced), the server MUST
calculate a second MAC. Again, if use of the DSKPP MAC
algorithm has been negotiated, then the MAC is calculated by
calling C_SignInit with the CKM_KIP_MAC mechanism followed by
a call to C_Sign. In this call to C_SignInit, the K_MAC
existing before this DSKPP protocol run MUST be the signature
key, the hKey parameter in the CK_KIP_PARAMS structure MUST
be set to NULL, the pSeed parameter of the CT_KIP_PARAMS
structure MUST be set to NULL_PTR, and the ulSeeidLen
parameter MUST be set to zero. In the call to C_Sign, the
pData parameter MUST be set to the concatenation of the
string ID_S and the nonce R, and the ulDataLen parameter MUST
be set to the length of concatenated string. The desired
length of the MAC MUST be specified through the
pulSignatureLen parameter and MUST be set to the length of R.
5. The server sends its message to the client, including the
wrapped key K, the MAC and possibly also the authenticating
MAC.
c. On the client side,
1. The client calls C_UnwrapKey to receive a handle to K. After
this, the client calls C_DeriveKey twice: Once to derive
K_TOKEN and once to derive K_MAC. The client MUST use the
same mechanism (CKM_EXTRACT_KEY_FROM_KEY) and the same
mechanism parameters as used by the server above. When
calling C_UnwrapKey and C_DeriveKey, the pTemplate parameter
MUST be used to set additional key attributes in accordance
with local policy and as negotiated and expressed in the
protocol. In particular, the value of the <KeyID> element in
the server's response message MAY be used as CKA_ID for
K_TOKEN. The key K MUST be destroyed after deriving K_TOKEN
and K_MAC.
Doherty, et al. Expires May 1, 2008 [Page 97]
Internet-Draft DSKPP October 2007
2. The MAC is verified in a reciprocal fashion as it was
generated by the server. If use of the CKM_KIP_MAC mechanism
has been negotiated, then in the call to C_VerifyInit, the
hKey parameter in the CK_KIP_PARAMS structure MUST be set to
NULL_PTR, the pSeed parameter MUST be set to NULL_PTR, and
ulSeedLen MUST be set to 0. The hKey parameter of
C_VerifyInit MUST refer to K_MAC. In the call to C_Verify,
pData MUST be set to the concatenation of the string ID_S and
the nonce R, and the ulDataLen parameter MUST be set to the
length of the concatenated string, pSignature to the MAC
value received from the server, and ulSignatureLen to the
length of the MAC. If the MAC does not verify the protocol
session ends with a failure. The token MUST be constructed
to not "commit" to the new K_TOKEN or the new K_MAC unless
the MAC verifies.
3. If an authenticating MAC was received (REQUIRED if the new
K_TOKEN will replace an existing key on the token), then it
is verified in a similar vein but using the K_MAC associated
with this server and existing before the protocol run.
Again, if the MAC does not verify the protocol session ends
with a failure, and the token MUST be constructed no to
"commit" to the new K_TOKEN or the new K_MAC unless the MAC
verifies.
A.3. The 1-pass Variant
A suggested procedure to perform 1-pass DSKPP with a cryptographic
module through the PKCS #11 interface using the mechanisms defined in
[CT-KIP-P11] is as follows:
a. On the server side,
1. A generic key K = K_TOKEN | K _MAC (where '|' denotes
concatenation) is generated, e.g. by calling C_GenerateKey
(using key type CKK_GENERIC_SECRET). The template for K MUST
allow it to be exported (but only in wrapped form, i.e.
CKA_SENSITIVE MUST be set to CK_TRUE and CKA_EXTRACTABLE MUST
also be set to CK_TRUE), and also to be used for further key
derivation. From K, a token key K_TOKEN of suitable type is
derived by calling C_DeriveKey using the PKCS #11 mechanism
CKM_EXTRACT_KEY_FROM_KEY and setting the CK_EXTRACT_PARAMS to
the first bit of the generic secret key (i.e. set to 0).
Likewise, a MAC key K_MAC is derived from K by calling
C_DeriveKey using the CKM_EXTRACT_KEY_FROM_KEY mechanism,
this time setting CK_EXTRACT_PARAMS to the length of K (in
bits) divided by two.
Doherty, et al. Expires May 1, 2008 [Page 98]
Internet-Draft DSKPP October 2007
2. The server wraps K with either the token's public key,
K_CLIENT, the shared secret key, K_SHARED, or the derived
shared secret key, K_DERIVED by using C_WrapKey. If use of
the DSKPP key wrap algorithm has been negotiated, then the
CKM_KIP_WRAP mechanism MUST be used to wrap K. When calling
C_WrapKey, the hKey handle in the CK_KIP_PARAMS structure
MUST be set to NULL_PTR. The pSeed parameter in the
CK_KIP_PARAMS structure MUST point to the octet-string
representation of an integer I whose value MUST be
incremented before each protocol run, and the ulSeedLen
parameter MUST indicate the length of the octet-string
representation of I. The hWrappingKey parameter in the call
to C_WrapKey MUST be set to refer to the wrapping key.
Note: The integer-to-octet string conversion MUST be made
using the I2OSP primitive from [PKCS-1]. There MUST be no
leading zeros.
3. For the server's message to the client, if use of the DSKPP
MAC algorithm has been negotiated, then the MAC is calculated
by calling C_SignInit with the CKM_KIP_MAC mechanism followed
by a call to C_Sign. In the call to C_SignInit, K_MAC MUST
be the signature key, the hKey parameter in the CK_KIP_PARAMS
structure MUST be set to NULL_PTR, the pSeed parameter of the
CT_KIP_PARAMS structure MUST be set to NULL_PTR, and the
ulSeedLen parameter MUST be set to zero. In the call to
C_Sign, the pData parameter MUST be set to the concatenation
of the string ID_S and the octet-string representation of the
integer I, and the ulDataLen parameter MUST be set to the
length of concatenated string. The desired length of the MAC
MUST be specified through the pulSignatureLen parameter as
usual, and MUST be equal to, or greater than, sixteen (16).
4. If the server also needs to authenticate its message (due to
an existing K_TOKEN being replaced), the server calculates a
second MAC. If the DSKPP MAC mechanism is used, the server
does this by calling C_SignInit with the CKM_KIP_MAC
mechanism followed by a call to C_Sign. In the call to
C_SignInit, the K_MAC existing on the token before this
protocol run MUST be the signature key, the hKey parameter in
the CK_KIP_PARAMS structure MUST be set to NULL_PTR, the
pSeed parameter of the CT_KIP_PARAMS structure MUST be set to
NULL_PTR, and the ulSeedLen parameter MUST be set to zero.
In the call to C_Sign, the pData parameter MUST be set to the
concatenation of the string ID_S and the octet-string
representation of the integer I+1 (i.e. I MUST be
incremented before each use), and the ulDataLen parameter
MUST be set to the length of the concatenated string. The
desired length of the MAC MUST be specified through the
pulSignatureLen parameter as usual, and MUST be equal to, or
Doherty, et al. Expires May 1, 2008 [Page 99]
Internet-Draft DSKPP October 2007
greater than, sixteen (16).
5. The server sends its message to the client, including the MAC
and possibly also the authenticating MAC.
b. On the client side,
1. The client calls C_UnwrapKey to receive a handle to K. After
this, the client calls C_DeriveKey twice: Once to derive
K_TOKEN and once to derive K_MAC. The client MUST use the
same mechanism (CKM_EXTRACT_KEY_FROM_KEY) and the same
mechanism parameters as used by the server above. When
calling C_UnwrapKey and C_DeriveKey, the pTemplate parameter
MUST be used to set additional key attributes in accordance
with local policy and as negotiated and expressed in the
protocol. In particular, the value of the <KeyID> element in
the server's response message MAY be used as CKA_ID for
K_TOKEN. The key K MUST be destroyed after deriving K_TOKEN
and K_MAC.
2. The MAC is verified in a reciprocal fashion as it was
generated by the server. If use of the CKM_KIP_MAC mechanism
has been negotiated, then in the call to C_VerifyInit, the
hKey parameter in the CK_KIP_PARAMS structure MUST be set to
NULL_PTR, the pSeed parameter MUST be set to NULL_PTR, and
ulSeedLen MUST be set to 0. The hKey parameter of
C_VerifyInit MUST refer to K_MAC. In the call to C_Verify,
pData MUST be set to the concatenation of the string ID_S and
the octet-string representation of the provided value for I,
and the ulDataLen parameter MUST be set to the length of the
concatenated string, pSignature to the MAC value received
from the server, and ulSignatureLen to the length of the MAC.
If the MAC does not verify or if the provided value of I is
not larger than any stored value I' for the identified server
ID_S the protocol session ends with a failure. The token
MUST be constructed to not "commit" to the new K_TOKEN or the
new K_MAC unless the MAC verifies. If the verification
succeeds, the token MUST store the provided value of I as a
new I' for ID_S.
3. If an authenticating MAC was received (REQUIRED if K_TOKEN
will replace an existing key on the token), it is verified in
a similar vein but using the K_MAC existing before the
protocol run. Again, if the MAC does not verify the protocol
session ends with a failure, and the token MUST be
constructed no to "commit" to the new K_TOKEN or the new
K_MAC unless the MAC verifies.
Appendix B. Example of DSKPP-PRF Realizations
Doherty, et al. Expires May 1, 2008 [Page 100]
Internet-Draft DSKPP October 2007
B.1. Introduction
This example appendix defines DSKPP-PRF in terms of AES [FIPS197-AES]
and HMAC [RFC2104].
B.2. DSKPP-PRF-AES
B.2.1. Identification
For cryptographic modules supporting this realization of DSKPP-PRF,
the following URI MAY be used to identify this algorithm in DSKPP:
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes
When this URI is used to identify the encryption algorithm to use,
the method for encryption of R_C values described in Section 5.2 MUST
be used.
B.2.2. Definition
DSKPP-PRF-AES (k, s, dsLen)
Input:
k Encryption key to use
s Octet string consisting of randomizing material. The
length of the string s is sLen.
dsLen Desired length of the output
Output:
DS A pseudorandom string, dsLen-octets long
Steps:
1. Let bLen be the output block size of AES in octets:
bLen = (AES output block length in octets)
(normally, bLen = 16)
2. If dsLen > (2**32 - 1) * bLen, output "derived data too long" and
stop
3. Let n be the number of bLen-octet blocks in the output data,
rounding up, and let j be the number of octets in the last block:
n = ROUND( dsLen / bLen)
j = dsLen - (n - 1) * bLen
Doherty, et al. Expires May 1, 2008 [Page 101]
Internet-Draft DSKPP October 2007
4. For each block of the pseudorandom string DS, apply the function
F defined below to the key k, the string s and the block index to
compute the block:
B1 = F (k, s, 1) ,
B2 = F (k, s, 2) ,
...
Bn = F (k, s, n)
The function F is defined in terms of the OMAC1 construction from
[FSE2003], using AES as the block cipher:
F (k, s, i) = OMAC1-AES (k, INT (i) || s)
where INT (i) is a four-octet encoding of the integer i, most
significant octet first, and the output length of OMAC1 is set to
bLen.
Concatenate the blocks and extract the first dsLen octets to product
the desired data string DS:
DS = B1 || B2 || ... || Bn<0..j-1>
Output the derived data DS.
B.2.3. Example
If we assume that dsLen = 16, then:
n = 16 / 16 = 1
j = 16 - (1 - 1) * 16 = 16
DS = B1 = F (k, s, 1) = OMAC1-AES (k, INT (1) || s)
B.3. DSKPP-PRF-SHA256
B.3.1. Identification
For cryptographic modules supporting this realization of DSKPP-PRF,
the following URI MAY be used to identify this algorithm in DSKPP:
urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-sha256
When this URI is used to identify the encryption algorithm to use,
the method for encryption of R_C values described in Section 5.2 MUST
be used.
Doherty, et al. Expires May 1, 2008 [Page 102]
Internet-Draft DSKPP October 2007
B.3.2. Definition
DSKPP-PRF-SHA256 (k, s, dsLen)
Input:
k Encryption key to use
s Octet string consisting of randomizing material. The
length of the string s is sLen.
dsLen Desired length of the output
Output:
DS A pseudorandom string, dsLen-octets long
Steps:
1. Let bLen be the output size of SHA-256 in octets of [FIPS180-SHA]
(no truncation is done on the HMAC output):
bLen = 32
(normally, bLen = 16)
2. If dsLen > (2**32 - 1) * bLen, output "derived data too long" and
stop
3. Let n be the number of bLen-octet blocks in the output data,
rounding up, and let j be the number of octets in the last block:
n = ROUND( dsLen / bLen)
j = dsLen - (n - 1) * bLen
4. For each block of the pseudorandom string DS, apply the function
F defined below to the key k, the string s and the block index to
compute the block:
B1 = F (k, s, 1) ,
B2 = F (k, s, 2) ,
...
Bn = F (k, s, n)
The function F is defined in terms of the HMAC construction from
[RFC2104], using SHA-256 as the digest algorithm:
F (k, s, i) = HMAC-SHA256 (k, INT (i) || s)
where INT (i) is a four-octet encoding of the integer i, most
significant octet first, and the output length of HMAC is set to
bLen.
Concatenate the blocks and extract the first dsLen octets to product
the desired data string DS:
Doherty, et al. Expires May 1, 2008 [Page 103]
Internet-Draft DSKPP October 2007
DS = B1 || B2 || ... || Bn<0..j-1>
Output the derived data DS.
B.3.3. Example
If we assume that sLen = 256 (two 128-octet long values) and dsLen =
16, then:
n = ROUND ( 16 / 32 ) = 1
j = 16 - (1 - 1) * 32 = 16
B1 = F (k, s, 1) = HMAC-SHA256 (k, INT (1) || s)
DS = B1<0 ... 15>
That is, the result will be the first 16 octets of the HMAC output.
Authors' Addresses
Andrea Doherty
RSA, The Security Division of EMC
174 Middlesex Tpk.
Bedford, MA 01730
USA
Email: adoherty@rsa.com
Mingliang Pei
Verisign, Inc.
487 E. Middlefield Road
Mountain View, CA 94043
USA
Email: mpei@verisign.com
Salah Machani
Diversinet Corp.
2225 Sheppard Avenue East, Suite 1801
Toronto, Ontario M2J 5C2
Canada
Email: smachani@diversinet.com
Doherty, et al. Expires May 1, 2008 [Page 104]
Internet-Draft DSKPP October 2007
Magnus Nystrom
RSA, The Security Division of EMC
Arenavagen 29
Stockholm, Stockholm Ln 121 29
SE
Email: mnystrom@rsa.com
Doherty, et al. Expires May 1, 2008 [Page 105]
Internet-Draft DSKPP October 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Doherty, et al. Expires May 1, 2008 [Page 106]
