KEYPROV Working Group A. Doherty
Internet-Draft RSA, The Security Division of EMC
Intended status: Standards Track M. Pei
Expires: January 9, 2008 VeriSign, Inc.
M. Nystroem
RSA, The Security Division of EMC
S. Machani
Diversinet Corp.
July 8, 2007
Dynamic Symmetric Key Provisioning Protocol (DSKPP)
draft-doherty-keyprov-dskpp-01.txt
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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
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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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 7
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.2. Background . . . . . . . . . . . . . . . . . . . . . . . 7
2. Notation and Terminology . . . . . . . . . . . . . . . . . . 8
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. A cryptographic module obtains a symmetric key . . . . . 9
3.2. A cryptographic module acquires multiple symmetric
keys of different types . . . . . . . . . . . . . . . . . 9
3.3. A provisioning server imposes a validity period policy
for provisioning sessions . . . . . . . . . . . . . . . . 10
3.4. A symmetric key issuer uses a third party provisioning
service provider . . . . . . . . . . . . . . . . . . . . 10
3.5. A cryptographic module renews its symmetric key with
the same key ID . . . . . . . . . . . . . . . . . . . . . 10
3.6. An administrator initiates a symmetric key replacement
before it can be used . . . . . . . . . . . . . . . . . . 10
3.7. A cryptographic module hosted by a smart card uses a
pre-shared transport key to communicate with the
provisioning server . . . . . . . . . . . . . . . . . . . 11
3.8. A cryptographic module hosted by a mobile device
downloads a symmetric key through SMS . . . . . . . . . . 11
3.9. A cryptographic module acquires a symmetric key over a
transport protocol that does not ensure data
confidentiality . . . . . . . . . . . . . . . . . . . . . 12
3.10. A cryptographic module acquires a symmetric key over a
transport protocol that does not provide authentication . 12
4. DSKPP . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Entities . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2. Principles of Operation . . . . . . . . . . . . . . . . . 14
4.2.1. Four-pass DSKPP . . . . . . . . . . . . . . . . . . . 15
4.2.2. Two-pass DSKPP . . . . . . . . . . . . . . . . . . . 19
4.2.3. One-pass DSKPP . . . . . . . . . . . . . . . . . . . 21
4.3. Authentication . . . . . . . . . . . . . . . . . . . . . 22
4.3.1. Client Authentication (Applicable to Four- and
Two-Pass DSKPP) . . . . . . . . . . . . . . . . . . . 22
4.3.2. Server Authentication . . . . . . . . . . . . . . . . 25
4.4. Symmetric Key Container Format . . . . . . . . . . . . . 25
4.5. The DSKPP One-Way Pseudorandom Function, DSKPP-PRF . . . 25
4.5.1. Introduction . . . . . . . . . . . . . . . . . . . . 25
4.5.2. Declaration . . . . . . . . . . . . . . . . . . . . . 26
4.6. Generation of Symmetric Keys for Cryptographic Modules . 26
4.7. Encryption of Pseudorandom Nonces Sent from the DSKPP
Client . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.8. MAC calculations . . . . . . . . . . . . . . . . . . . . 27
4.8.1. Four-pass DSKPP . . . . . . . . . . . . . . . . . . . 27
4.8.2. Two-pass DSKPP . . . . . . . . . . . . . . . . . . . 28
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4.8.3. One-pass DSKPP . . . . . . . . . . . . . . . . . . . 29
4.9. DSKPP Schema Basics . . . . . . . . . . . . . . . . . . . 30
4.9.1. The AbstractRequestType Type . . . . . . . . . . . . 31
4.9.2. The AbstractResponseType Type . . . . . . . . . . . . 31
4.9.3. The VersionType Type . . . . . . . . . . . . . . . . 32
4.9.4. The IdentifierType Type . . . . . . . . . . . . . . . 32
4.9.5. The StatusCode Type . . . . . . . . . . . . . . . . . 32
4.9.6. The DeviceIdentifierDataType Type . . . . . . . . . . 34
4.9.7. The TokenPlatformInfoType and PlatformType Types . . 35
4.9.8. The NonceType Type . . . . . . . . . . . . . . . . . 35
4.9.9. The AlgorithmsType Type . . . . . . . . . . . . . . . 36
4.9.10. The ProtocolVariantsType and the
TwoPassSupportType Types . . . . . . . . . . . . . . 36
4.9.11. The KeyContainersFormatTypeType . . . . . . . . . . . 37
4.9.12. The AuthenticationDataType Type . . . . . . . . . . . 38
4.9.13. The PayloadType Type . . . . . . . . . . . . . . . . 40
4.9.14. The MacType Type . . . . . . . . . . . . . . . . . . 40
4.9.15. The KeyContainerType Type . . . . . . . . . . . . . . 40
4.9.16. The ExtensionsType and the AbstractExtensionType
Types . . . . . . . . . . . . . . . . . . . . . . . . 41
4.10. DSKPP Messages . . . . . . . . . . . . . . . . . . . . . 41
4.10.1. Introduction . . . . . . . . . . . . . . . . . . . . 41
4.10.2. DSKPP Initialization (OPTIONAL) . . . . . . . . . . . 41
4.10.3. The DSKPP Client's Initial PDU (2- and 4-Pass) . . . 43
4.10.4. The DSKPP Server's Initial PDU (4-Pass Only) . . . . 46
4.10.5. The DSKPP Client's Second PDU (4-Pass Only) . . . . . 47
4.10.6. The DSKPP Server's Final PDU (1-, 2-, and 4-Pass) . . 48
4.11. Protocol Extensions . . . . . . . . . . . . . . . . . . . 50
4.11.1. The ClientInfoType Type . . . . . . . . . . . . . . . 50
4.11.2. The ServerInfoType Type . . . . . . . . . . . . . . . 50
4.11.3. The KeyInitializationDataType Type . . . . . . . . . 51
5. Protocol Bindings . . . . . . . . . . . . . . . . . . . . . . 52
5.1. General Requirements . . . . . . . . . . . . . . . . . . 52
5.2. HTTP/1.1 Binding for DSKPP . . . . . . . . . . . . . . . 52
5.2.1. Introduction . . . . . . . . . . . . . . . . . . . . 52
5.2.2. Identification of DSKPP Messages . . . . . . . . . . 53
5.2.3. HTTP Headers . . . . . . . . . . . . . . . . . . . . 53
5.2.4. HTTP Operations . . . . . . . . . . . . . . . . . . . 53
5.2.5. HTTP Status Codes . . . . . . . . . . . . . . . . . . 53
5.2.6. HTTP Authentication . . . . . . . . . . . . . . . . . 54
5.2.7. Initialization of DSKPP . . . . . . . . . . . . . . . 54
5.2.8. Example Messages . . . . . . . . . . . . . . . . . . 54
6. DSKPP Schema . . . . . . . . . . . . . . . . . . . . . . . . 55
7. Security Considerations . . . . . . . . . . . . . . . . . . . 63
7.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 63
7.2. Active Attacks . . . . . . . . . . . . . . . . . . . . . 63
7.2.1. Introduction . . . . . . . . . . . . . . . . . . . . 63
7.2.2. Message Modifications . . . . . . . . . . . . . . . . 64
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7.2.3. Message Deletion . . . . . . . . . . . . . . . . . . 65
7.2.4. Message Insertion . . . . . . . . . . . . . . . . . . 65
7.2.5. Message Replay . . . . . . . . . . . . . . . . . . . 66
7.2.6. Message Reordering . . . . . . . . . . . . . . . . . 66
7.2.7. Man-in-the-Middle . . . . . . . . . . . . . . . . . . 66
7.3. Passive Attacks . . . . . . . . . . . . . . . . . . . . . 66
7.4. Cryptographic Attacks . . . . . . . . . . . . . . . . . . 67
7.5. Attacks on the Interaction between DSKPP and User
Authentication . . . . . . . . . . . . . . . . . . . . . 67
7.6. Additional Considerations Specific to 2- and 1-pass
DSKPP . . . . . . . . . . . . . . . . . . . . . . . . . . 68
7.6.1. Client Contributions to K_TOKEN Entropy . . . . . . . 68
7.6.2. Key Confirmation . . . . . . . . . . . . . . . . . . 68
7.6.3. Server Authentication . . . . . . . . . . . . . . . . 68
7.6.4. Client Authentication . . . . . . . . . . . . . . . . 68
7.6.5. Key Protection in the Passphrase Profile . . . . . . 69
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 70
9. Intellectual Property Considerations . . . . . . . . . . . . 70
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 70
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 70
11.1. Normative references . . . . . . . . . . . . . . . . . . 70
11.2. Informative references . . . . . . . . . . . . . . . . . 71
Appendix A. Key Initialization Profiles of DSKPP . . . . . . . . 72
A.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 73
A.2. Key Transport Profile . . . . . . . . . . . . . . . . . . 73
A.2.1. Introduction . . . . . . . . . . . . . . . . . . . . 73
A.2.2. Identification . . . . . . . . . . . . . . . . . . . 73
A.2.3. Payloads . . . . . . . . . . . . . . . . . . . . . . 73
A.3. Key wrap profile . . . . . . . . . . . . . . . . . . . . 74
A.3.1. Introduction . . . . . . . . . . . . . . . . . . . . 74
A.3.2. Identification . . . . . . . . . . . . . . . . . . . 74
A.3.3. Payloads . . . . . . . . . . . . . . . . . . . . . . 74
A.4. Passphrase-based key wrap profile . . . . . . . . . . . . 76
A.4.1. Introduction . . . . . . . . . . . . . . . . . . . . 76
A.4.2. Identification . . . . . . . . . . . . . . . . . . . 76
A.4.3. Payloads . . . . . . . . . . . . . . . . . . . . . . 76
Appendix B. Example Messages . . . . . . . . . . . . . . . . . . 77
B.1. Example Messages in a Four-pass Exchange . . . . . . . . 77
B.1.1. Example of a DSKPP Initialization (Trigger) Message . 78
B.1.2. Example of a <ClientHello> Message . . . . . . . . . 79
B.1.3. Example of a <ServerHello> Message . . . . . . . . . 80
B.1.4. Example of a <ClientNonce> Message . . . . . . . . . 80
B.1.5. Example of a <ServerFinished> Message . . . . . . . . 80
B.2. Example Messages in a Two- or One-pass Exchange . . . . . 81
B.2.1. Example of a <ClientHello> Message Indicating
Support for Two-pass DSKPP . . . . . . . . . . . . . 81
B.2.2. Example of a <ServerFinished> Message Using the
Key Transport Profile . . . . . . . . . . . . . . . . 83
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B.2.3. Example of a <ServerFinished> Message Using the
Key Wrap Profile . . . . . . . . . . . . . . . . . . 85
B.2.4. Example of a <ServerFinished> Message using the
Passphrase-based Key Wrap Profile . . . . . . . . . . 86
Appendix C. Requirements . . . . . . . . . . . . . . . . . . . . 88
Appendix D. Integration with PKCS #11 . . . . . . . . . . . . . 90
D.1. The 4-pass Variant . . . . . . . . . . . . . . . . . . . 91
D.2. The 2-pass Variant . . . . . . . . . . . . . . . . . . . 91
D.3. The 1-pass Variant . . . . . . . . . . . . . . . . . . . 93
Appendix E. Example of DSKPP-PRF Realizations . . . . . . . . . 95
E.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 96
E.2. DSKPP-PRF-AES . . . . . . . . . . . . . . . . . . . . . . 96
E.2.1. Identification . . . . . . . . . . . . . . . . . . . 96
E.2.2. Definition . . . . . . . . . . . . . . . . . . . . . 96
E.2.3. Example . . . . . . . . . . . . . . . . . . . . . . . 97
E.3. DSKPP-PRF-SHA256 . . . . . . . . . . . . . . . . . . . . 97
E.3.1. Identification . . . . . . . . . . . . . . . . . . . 97
E.3.2. Definition . . . . . . . . . . . . . . . . . . . . . 98
E.3.3. Example . . . . . . . . . . . . . . . . . . . . . . . 99
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 99
Intellectual Property and Copyright Statements . . . . . . . . . 100
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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 cryptographic modules that
are locally (i.e., over-the-wire) or remotely (i.e., over-the-air)
accessible.
1.2. Background
A symmetric cryptographic module may be hosted by a hand-held
hardware device (e.g., a mobile phone), a hardware device connected
to a personal computer through an electronic interface, such as USB,
or a software application resident on a personal computer. The
cryptographic module offers symmetric 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 addressed herein is a symmetric key provisioning
server. In an ideal deployment scenario, near real-time
communication is possible between the provisioning server and the
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
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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. 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)
DSKPP client Manages communication between the symmetric
cryptographic module and the DSKPP server
DSKPP server The symmetric key provisioning server that
participates in the DSKPP protocol run
ID_C Identifier for DSKPP client
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ID_S Identifier for DSKPP server
K Key used to encrypt R_C (either K_SERVER or K_SHARED)
K_AUTH Secret key used for server authentication purposes in
4-pass DSKPP
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
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
R_S Pseudorandom value chosen by the DSKPP server and
used as input to the generation of K_TOKEN
The following typographical convention is used in the body of the
text: <XMLElement>.
3. Use Cases
This section describes typical use cases.
3.1. A cryptographic module obtains a symmetric key
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. A cryptographic module acquires multiple symmetric keys of
different types
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
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symmetric cryptographic algorithms, including the HMAC-Based One-Time
Password (HOTP), RSA SecurID, challenge-response, etc.
3.3. A provisioning server imposes a validity period policy for
provisioning sessions
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. As long as the user inputs a valid authentication code
within the fixed time period established by the issuer, the server
will provision a key to the cryptographic module hosted by the user's
device.
3.4. A symmetric key issuer uses a third party provisioning service
provider
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. A cryptographic module renews its symmetric key with the same key
ID
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. An administrator initiates a symmetric key replacement before it
can be used
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.
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Bulk initialization under controlled conditions, e.g., during
manufacture, is likely to meet the security needs of most
applications. However, reliance on a pre-disclosed secret is
unacceptable in some circumstances. One such circumstance is when
cryptographic modules are issued for classified government use or
high security applications. In such cases, the issuer requires the
ability to remove all secret information already installed on the
cryptographic module and replace it with symmetric keys established
under conditions controlled by the issuer.
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. A cryptographic module hosted by a smart card uses a pre-shared
transport key to communicate with the provisioning server
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
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. A cryptographic module hosted by a mobile device downloads a
symmetric key through SMS
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, the cryptographic module can ensure that SMS will provide
an acceptable level of protection for download of the symmetric key.
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.
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3.9. A cryptographic module acquires a symmetric key over a transport
protocol that does not ensure data confidentiality
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. A cryptographic module acquires a symmetric key over a transport
protocol that does not provide authentication
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
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. 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 that hosts
symmetric cryptographic modules
DeviceID A unique identifier for the device
Cryptographic Module A low-level component of an application,
which enables symmetric cryptographic
functionality
CryptoModuleID A unique identifier for an instance of the
cryptographic module
Encryption Algorithms Encryption algorithms supported by the
cryptographic module
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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 cryptographic methods
for which the key will be used (e.g., OATH
HOTP or RSA SecurID authentication, AES
encryption, etc.)
----------- -------------
| 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
It is assumed that a device will host an application layered above
the cryptographic module, and this application will manage
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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. Principles of Operation
To initiate a DSKPP session, a user may use a browser to connect to a
web server. The user may then identify and optionally authenticate
herself and possibly indicate how the DSKPP client has to contact the
DSKPP server. There are also other alternatives for DSKPP session
initiation, such as the DSKPP client being pre-configured to contact
a certain DSKPP server, or the user being informed out-of-band about
the address 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.
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.
DSKPP protocol variants may be applied to the use cases described in
Section 3, as shown below:
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==========================================================
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
is required
-----------------------------------------------------------
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 2: Mapping of use cases to protocol variants
4.2.1. Four-pass DSKPP
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 4-pass protocol flow, shown
in Figure 3 and expanded in Figure 4, consists of two round trips
between the DSKPP client and server.
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+---------------+ +---------------+
| | | |
| DSKPP client | | DSKPP server |
| | | |
+---------------+ +---------------+
| |
| [ <---- DSKPP trigger ----- ] |
| |
| ------- Client Hello -------> |
| |
| <------ Server Hello -------- |
| |
| ------- Client Nonce -------> |
| |
| <----- Server Finished ------ |
| |
Figure 3: The 4-pass DSKPP protocol (with OPTIONAL preceeding
trigger)
a. The DSKPP client sends a <ClientHello> 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 message may also
include client authentication data, such as a certificate or
authentication code.
b. The DSKPP server responds to the DSKPP client with a
<ServerHello> 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 <ServerHello> message also
provides information about either a shared secret key to use
for encrypting the cryptographic module's random nonce (see
description of <ClientNonce> below), or its own public key.
Optionally, <ServerHello> may include a MAC that the DSKPP
client may use for server authentication.
c. Based on information contained in the <ServerHello> 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 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. The DSKPP
client then sends the encrypted random nonce to the DSKPP
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server in a <ClientNonce> message, and may include client
authentication data, such as a certificate or authentication
code. 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 4.5.
d. 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 4.5. 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.
e. Once the association has been made, the DSKPP server sends a
confirmation message to the DSKPP client called
<ServerFinished>. 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. Optionally,
<ServerFinished> may include a MAC that the DSKPP client may
use for server authentication.
f. 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.
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.
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
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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 synch" 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).
+----------------------+ +-------+ +----------------------+
| +------------+ | | | | |
| | 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
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4.2.2. Two-pass DSKPP
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,
shown in Figure 5, the client's initial <ClientHello> message is
directly followed by a <ServerFinished> message. There is no
exchange of the <ServerHello> message or the <ClientNonce> 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
<ClientHello> message. Note than by including R_C in <ClientHello>,
the DSKPP client is able to ensure the server is alive before
"commiting" the key. Also note that the DSKPP "trigger" message MAY
be used to trigger the client's sending of the <ClientHello> 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 Appendix A), 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
DSKPP server.
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+---------------+ +---------------+
| | | |
| DSKPP client | | DSKPP server |
| | | |
+---------------+ +---------------+
| |
| [ <---- DSKPP trigger ----- ] |
| |
| ------- Client Hello -------> |
| |
| <----- Server Finished ------ |
| |
Figure 5: The 2-pass DSKPP protocol (with OPTIONAL preceding trigger)
a. The DSKPP client sends a <ClientHello> 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 a
certificate or authentication code. Unlike 4-pass DSKPP,
2-pass DSKPP client uses the <ClientHello> 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. K is either transported or wrapped in
accordance with the key initialization method specified by the
DSKPP client in the <ClientHello> 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
<ServerFinished>. 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, <ServerFinished> MUST include two MACs whose
values are calculated with contribution from the client nonce,
R_C, provided in the <ClientHello> message. The MAC values
will allow the cryptographic module to perform key confirmation
and server authentication before "commiting" the key.
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d. 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.
4.2.3. One-pass DSKPP
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, shown in
Figure 6, the server simply sends a <ServerFinished> message to the
DSKPP client. In this case, there is no exchange of the
<ClientHello>, <ServerHello>, and <ClientNonce> 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 4.2.2 and Appendix A.
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.
+---------------+ +---------------+
| | | |
| DSKPP client | | DSKPP server |
| | | |
+---------------+ +---------------+
| |
| <----- Server Finished ------ |
| |
Figure 6: The 1-pass DSKPP protocol
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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
<ServerFinished>. 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, <ServerFinished> MUST include two MACs, which will
allow the cryptographic module to perform key confirmation and
server authentication before "commiting" 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.
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.
4.3. Authentication
4.3.1. Client Authentication (Applicable to Four- and Two-Pass DSKPP)
To ensure that a generated K_TOKEN ends up associated with the
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 7.
4.3.1.1. Device Certificate
Instead of requiring an Authentication Code for in-band
authentication, a device certificate could be used, which was
supplied with the cryptographic module by its issuer.
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4.3.1.2. Device Identifier
The provisioning server could be pre-configured with a device
identifier. 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.
4.3.1.3. One-time Use Authentication Code
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 <ClientHello> (and
<ClientNonce> 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 5.2.7) .
+------------+ Get Authentication Code +------------+
| User |<------------------------->| Issuer |
+------------+ +------------+
| |
| |
| |
V V
+--------------+ +--------------+
| Provisioning | Authentication Data | Provisioning |
| Client |----------------------->| Server |
+--------------+ +--------------+
Figure 7: User Authentication with One-Time Code
Considering an Authentication Code as a special form of shared secret
between a user and a provisioning server, Authentication Data can
have one of the following forms:
o AuthenticationData = Hash (Authentication Code)
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When an Authentication Code is used to initiate the protocol run,
the Authentication Code MUST be sent to the DSKPP server in a
secure manner. If the underlying transport channel is secure, the
authentication data MAY contain the plaintext format or the hashed
format of the Authentication Code using a hash function.
o AuthenticationData = HMAC(Authentication Code, K_AUTH)
If the underlying transport is not secure, the client MUST use a
key K_AUTH and the Authentication Code to derive authentication
data. For example, if the Authentication Code has a fixed format,
e.g.,
AuthenticationCode = passwordLength || ID || password || checksum
then AuthenticationData MAY be calculated as follows:
AuthenticationData = AuthenticationCode->ID || B64(Digest)
where for four-pass DSKPP, the cryptographic module uses the
server nonce R_S in combination with the server URL to calculate
the Digest:
Digest = DSKPP-PRF-AES(K_AUTH, AuthCode->ID || serverURL || R_S,
16)
Refer to Section 4.5 for a description of DSKPP-PRF in general and
Appendix E for a description of DSKPP-PRF-AES.
For two-pass DSKPP, the cryptographic module does not have access
to the server nonce R_S in combination and so:
Digest = DSKPP-PRF-AES(K_AUTH, AuthenticationCode->ID ||
serverURL, 16)
In either case, K_AUTH MAY be derived AES key from
AuthenticationCode->password as in:
K_AUTH = truncate( Hash( Hash(...n times...( AuthCode->password )
) ) )
where truncate() returns the first 16 bytes from the result of the
last hash iteration, and n is the number of hash iterations (set
to fixed values, e.g., between 10 and 100).
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o AuthenticationData = <Signed data with a client certificate>
When a certificate is used for authentication, the authentication
data MAY be client-signed. Authentication data MAY be omitted if
client certificate authentication has been provided by the
transport channel such as TLS.
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.
4.3.2. 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 in each of its responses to the client. In 2-pass
and 1-pass DSKPP, servers authenticate themselves by including a
second MAC value in the response message. In addition, a DSKPP
server can leverage transport layer authentication if it is
available.
4.4. Symmetric Key Container Format
The default symmetric key container format that is used in the
<ServerFinished> 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.
4.5. The DSKPP One-Way Pseudorandom Function, DSKPP-PRF
4.5.1. Introduction
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
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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 E contains two
example realizations of DSKPP-PRF.
4.5.2. 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 16 octets
long.
4.6. Generation of Symmetric Keys for Cryptographic Modules
In DSKPP, keys are generated using the DSKPP-PRF function, 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.
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4.7. Encryption of Pseudorandom Nonces Sent from the DSKPP Client
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.
Note: It may appear that an attacker, who learns a previous value of
R_C, may be able to replay the corresponding R_S and, hence, learn a
new R_C as well. However, this attack is mitigated by the
requirement for a server to show knowledge of K_AUTH (see below) in
order to successfully complete a key re-generation.
4.8. MAC calculations
4.8.1. Four-pass DSKPP
4.8.1.1. Server Authentication: <ServerHello>
The MAC value MUST be computed on the (ASCII) string "MAC 1
computation", the client's nonce R (if sent), and the server's nonce
R_S using an authentication key K_AUTH that SHOULD be a special
authentication key used only for this purpose but MAY be the current
K_TOKEN.
The MAC value MAY be computed by using the DSKPP-PRF function of
Section 4.5, 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 K_AUTH. The input
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parameter dsLen MUST be set to the length of R_S:
dsLen = len(R_S)
MAC = DSKPP-PRF (K_AUTH, "MAC 1 computation" || [R ||] R_S, dsLen)
4.8.1.2. Server Authentication: <ServerFinished>
The MAC value MUST be computed on the (ASCII) string "MAC 2
computation" and R_C using an authentication key K_AUTH. Again, this
SHOULD be a special authentication key used only for this purpose,
but MAY also be an existing K_TOKEN. (In this case, implementations
MUST protect against attacks where K_TOKEN is used to pre-compute MAC
values.) If no authentication key is present in the cryptographic
module, and no K_TOKEN existed before the DSKPP run, K_AUTH MUST be
the newly generated K_TOKEN.
If DSKPP-PRF is used as the MAC algorithm, then 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_AUTH, "MAC 2 computation" || R_C, dsLen)
4.8.2. Two-pass DSKPP
4.8.2.1. Key Confirmation
In two-pass DSKPP, the client is REQUIRED to include a nonce R in the
<ClientHello> message. Further, the server is REQUIRED to include an
identifier, ID_S, for itself (via the key container) in the
<ServerFinished> message. The MAC value in the <ServerFinished>
message MUST be computed on the (ASCII) string "MAC 1 computation",
the server identifier ID_S, and R using a MAC key K_MAC. Again, in
contrast with the MAC calculation in the four-pass DSKPP, this key
MUST be provided together with K_TOKEN to the cryptographic module,
and hence there is no need for a K_AUTH 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" and R, and the parameter dsLen MUST be set to the length
of R:
dsLen = len(R)
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MAC = DSKPP-PRF (K_MAC, "MAC 1 computation" || ID_S || R, dsLen)
4.8.2.2. Server Authentication
As discussed in Section 4.3.2, servers need to authenticate
themselves 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. 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
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)
4.8.3. One-pass DSKPP
4.8.3.1. Key Confirmation
In one-pass DSKPP, the server MUST include an identifier, ID_S, for
itself (via the key container) in the <ServerFinished> message. The
MAC value in the <ServerFinished> 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, and hence
there is no need for a K_AUTH for key confirmation purposes.
Note: The integer I does not necessarily need to be maintained per
cryptographic module by the DSKPP server (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
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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 <ServerFinished> message using the
AuthenticationCodeMacType defined in Section 4.9.12.
4.8.3.2. Server Authentication
As discussed in Section 4.3.2, 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. 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 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.
4.9. DSKPP Schema Basics
This section describes the schema used by DSKPP. The DSKPP XML
schema itself can be found in Section 6. Specific protocol message
elements are defined in Section 4.10. Examples can be found in
Appendix B.
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
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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.
4.9.1. The AbstractRequestType Type
All DSKPP requests are defined as extensions to the abstract
AbstractRequestType type. The elements of the AbstractRequestType,
therefore, apply to all DSKPP requests. All DSKPP requests MUST
contain a Version attribute. For this version of this specification,
Version MUST be set to "1.0".
<xs:complexType name="AbstractRequestType" abstract="true">
<xs:attribute name="Version" type="VersionType" use="required"/>
</xs:complexType>
4.9.2. The AbstractResponseType Type
All DSKPP responses are defined as extensions to the abstract
AbstractResponseType type. The elements of the AbstractResponseType,
therefore, apply to all DSKPP responses. All DSKPP responses contain
a Version attribute indicating the version that was used. A Status
attribute, which indicates whether the preceding request was
successful or not MUST also be present. Finally, all responses MAY
contain a SessionID attribute identifying the particular DSKPP
session. The SessionID attribute needs only be present if more than
one roundtrip is REQUIRED for a successful protocol run (this is the
case with the protocol version described herein).
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<xs:complexType name="AbstractResponseType" abstract="true">
<xs:attribute name="Version" type="VersionType" use="required"/>
<xs:attribute name="SessionID" type="IdentifierType"/>
<xs:attribute name="Status" type="StatusCode" use="required"/>
</xs:complexType>
4.9.3. The VersionType Type
The VersionType type is used within DSKPP messages to identify the
highest version of this protocol supported by the DSKPP client and
server.
<xs:simpleType name="VersionType">
<xs:restriction base="xs:string">
<xs:pattern value="\d{1,2}\.\d{1,3}"/>
</xs:restriction>
</xs:simpleType>
4.9.4. The IdentifierType Type
The IdentifierType type is used to identify various DSKPP elements,
such as sessions, users, and services. Identifiers MUST NOT be
longer than 128 octets.
<xs:simpleType name="IdentifierType">
<xs:restriction base="xs:string">
<xs:maxLength value="128"/>
</xs:restriction>
</xs:simpleType>
4.9.5. The StatusCode Type
The StatusCode type enumerates all possible return codes:
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<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="AuthenticationDataInvalid"/>
<xs:enumeration value="InitializationFailed"/>
</xs:restriction>
</xs:simpleType>
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.
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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.
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 "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.
4.9.6. The DeviceIdentifierDataType Type
The DeviceIdentifierDataType type is used to uniquely identify the
device that houses the cryptographic module, e.g., a mobile phone.
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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].
<xs:complexType name="DeviceIdentifierDataType">
<xs:choice>
<xs:element name="DeviceID" type="pskc:DeviceIdType"/>
<xs:any namespace="##other" processContents="strict"/>
</xs:choice>
</xs:complexType>
4.9.7. The TokenPlatformInfoType and PlatformType Types
The TokenPlatformInfoType type is used to carry characteristics of
the intended cryptographic module platform, and applies in the
public-key variant of DSKPP in situations when the client potentially
needs to select a cryptographic module to initialize.
<xs:simpleType name="PlatformType">
<xs:restriction base="xs:string">
<xs:enumeration value="Hardware"/>
<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>
4.9.8. The NonceType Type
The NonceType type is used to carry pseudorandom values in DSKPP
messages. A nonce, as the name implies, MUST be used only once. For
each DSKPP message that requires a nonce element to be sent, a fresh
nonce MUST be generated each time. Nonce values MUST be at least 16
octets long.
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<xs:simpleType name="NonceType">
<xs:restriction base="xs:base64Binary">
<xs:minLength value="16"/>
</xs:restriction>
</xs:simpleType>
4.9.9. The AlgorithmsType Type
The AlgorithmsType type is a list of type-value pairs that define
algorithms supported by a DSKPP client or server. Algorithms are
identified through URIs.
<xs:complexType name="AlgorithmsType">
<xs:sequence maxOccurs="unbounded">
<xs:element name="Algorithm" type="AlgorithmType"/>
</xs:sequence>
</xs:complexType>
<xs:simpleType name="AlgorithmType">
<xs:restriction base="xs:anyURI"/>
</xs:simpleType>
4.9.10. The ProtocolVariantsType and the TwoPassSupportType Types
The ProtocolVariantsType type is OPTIONALLY used by the DSKPP client
to indicate the number of passes of the DSKPP protocol that it
supports (see Section 4.2). 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.
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<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>
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 <ClientHello> message (this will enable
the client to verify that the DSKPP server it is communicating with
is alive).
4.9.11. The KeyContainersFormatTypeType
The KeyContainersFormatType type is a list of type-value pairs that
are OPTIONALLY used to define key container formats supported by a
DSKPP client or server. Key container formats are identified through
URIs, e.g., the PSKC URI
"http://www.openauthentication.org/OATH/2006/10/PSKC#KeyContainer"
(see [PSKC].
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<xs:complexType name="KeyContainersFormatType">
<xs:sequence maxOccurs="unbounded">
<xs:element name="KeyContainerFormat"
type="dskpp:KeyContainerFormatType"/>
</xs:sequence>
</xs:complexType>
<xs:simpleType name="KeyContainerFormatType">
<xs:restriction base="xs:anyURI"/>
</xs:simpleType>
4.9.12. The AuthenticationDataType Type
The AuthenticationDataType type is OPTIONALLY used to carry client or
server authentication values in DSKPP messages (see Section 4.3).
The element MAY be used 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
activation code can be sent to the DSKPP server in plaintext
form, hashed data form, or keyed hash data form depending on the
underlying transport protocol.
b. A DSKPP client MAY include an AuthenticationCertificate that
contains a certificate issued with the device by the issuer.
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.
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<xs:complextype name="AuthenticationDataType">
<xs:sequence>
<xs:element name="ClientID" type="dskpp:IdentifierType"
minOccurs="0"/>
<xs:choice minOccurs="0">
<xs:element name="AuthenticationCode"
type="dskpp:AuthenticationCodeType"/>
<xs:element name="AuthenticationCodeDigest"
type="dskpp:AuthenticationCodeDigestType"/>
<xs:element name="AuthenticationCodeMac"
type="dskpp:AuthenticationCodeMacType"/>
<xs:element name="AuthenticationCertificate"
type="ds:KeyInfoType"/>
</xs:choice>
</xs:sequence>
</xs:complexType>
<xs:simpleType name="AuthenticationCodeType">
<xs:restriction base="xs:string">
<xs:maxLength value="20"/>
</xs:restriction>
</xs:simpleType>
<xs:complexType name="AuthenticationCodeDigestType">
<xs:simpleContent>
<xs:extension base="xs:base64Binary">
<xs:attribute name="HashAlgorithm" type="xs:anyURI"
use="required"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<xs:complexType name="AuthenticationCodeMacType">
<xs:sequence>
<xs:element name="Data" type="xs:base64Binary">
<xs:element name="Nonce" type="dskpp:NonceType"/>
</xs:sequence>
<attribute name="HMACAlgorithm" type="xs:anyURI"
use="required"/>
<attribute name="NonceId" type="dskpp:IdentifierType"/>
</xs:complexType>
The element of the AuthenticationDataType type have the following
meaning:
o <ClientID>: A requestor's identifier. The value MAY be a user ID,
a device ID, or a keyID associated with the requestor's
authentication value. When the authentication data is based on a
certificate, <ClientID> can be omitted, as the certificate itself
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is typically sufficient to identify the requestor. Also, if a
<DSKPPTrigger> 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 requestor.
o <AuthenticationCode>: A one-time use value sent in the clear to
the DSKPP server.
o <AuthenticationCodeDigest>: A one-time use value sent in digest
form to the DSKPP server.
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, where the MAC is
calculated as described in Section 4.8.
o <AuthenticationCertificate>: A device certificate sent to the
DSKPP server.
4.9.13. The PayloadType Type
The PayloadType type is used to carry data in a DSKPP client or
server message. For this version of the protocol, only one payload
is defined, the pseudorandom string R_S, for one message, the DSKPP
<ServerHello>.
<xs:complexType name="PayloadType">
<xs:choice>
<xs:element name="Nonce" type="dskpp:NonceType"/>
<xs:any namespace="##other" processContents="strict"/>
</xs:choice>
</xs:complexType>
4.9.14. The MacType Type
The MacType type is used by the DSKPP server to carry a MAC value
that the DSKPP server uses to authenticate itself to the client.
<xs:complexType name="MacType">
<xs:simpleContent>
<xs:extension base="xs:base64Binary">
<xs:attribute name="MacAlgorithm" type="xs:anyURI"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
4.9.15. The KeyContainerType Type
The KeyContainerType type is used by the DSKPP server in its final
message to carry symmetric key(s) (in the 2- and 1-pass exchanges)
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and configuration data. The default element defined for the
KeyContainerType is contained in the namespace defined in the PSKC
namespace as KeyContainerType (see [PSKC].
<xs:complexType name="KeyContainerType">
<xs:choice>
<xs:element name="KeyContainer"
type="pskc:KeyContainerType"/>
<xs:element name="##other" processContents="strict"/>
</xs:choice>
</xs:complexType>
4.9.16. The ExtensionsType and the AbstractExtensionType Types
The ExtensionsType type is a list of type-value pairs that define
OPTIONAL DSKPP features supported by a DSKPP client or server.
Extensions MAY be sent with any DSKPP message. Please see the
description of individual DSKPP messages in Section 4.11 of this
document for applicable extensions. All DSKPP extensions are defined
as extensions to the AbstractExtensionType type. The elements of the
AbstractExtensionType, therefore, apply to all DSKPP extensions.
Unless an extension is marked as Critical, a receiving party need not
be able to interpret it. A receiving party is always free to
disregard any (non-critical) extensions.
<xs:complexType name="ExtensionsType">
<xs:sequence maxOccurs="unbounded">
<xs:element name="Extension" type="AbstractExtensionType"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="AbstractExtensionType" abstract="true">
<xs:attribute name="Critical" type="xs:boolean"/>
</xs:complexType>
4.10. DSKPP Messages
4.10.1. Introduction
In this section, DSKPP messages, including their parameters, encoding
and semantics are defined.
4.10.2. DSKPP Initialization (OPTIONAL)
The DSKPP server MAY initialize the DSKPP protocol by sending a
<DSKPPTrigger> message. This message MAY, e.g., be sent in response
to a user requesting key initialization in a browsing session.
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<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="DSKPP_URL" type="xs:anyURI" minOccurs="0"/>
<xs:any namespace="##other" processContents="strict"
minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<xs:element name="DSKPPTrigger" type="DSKPPTriggerType"/>
<xs:complexType name="DSKPPTriggerType">
<xs:annotation>
<xs:documentation xml:lang="en">
Message used to trigger the device to initiate a
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>
The <DSKPPTrigger> 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 <ClientHello>
request. Finally, the trigger MAY contain a URL to use when
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 <ClientHello>
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.
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The Version attribute MUST be set to "1.0" for this version of DSKPP.
4.10.3. The DSKPP Client's Initial PDU (2- and 4-Pass)
This message is the initial message sent from the DSKPP client to the
DSKPP server.
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<xs:element name="ClientHello" type="ClientHelloPDU"/>
<xs:complexType name="ClientHelloPDU">
<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="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"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
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 4.3.1 above. The identifier MUST only be
present if such shared secrets exist or if the identifier was
provided by the server in a <DSKPPTrigger> element (see
Section 5.2.7 below). In the latter case, it MUST have the same
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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 was provided by the server in a
<DSKPPTrigger> element (see Section 5.2.7 below). In the latter
case, it MUST have the same value as the identifier provided in
that element.
o <ClientNonce>: 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 <DSKPPTrigger> message
(see Section 5.2.7 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 <DSKPPTrigger>
message match the corresponding identifier values in the
<ClientHello> 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 E).
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 <ClientNonce> MUST be set
to nonce R in the <ClientHello> 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
"http://www.openauthentication.org/OATH/2006/10/PSKC#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 4.3.1.
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o <Extensions>: A sequence of extensions. One extension is defined
for this message in this version of DSKPP: the ClientInfoType (see
Section 4.11).
4.10.4. The DSKPP Server's Initial PDU (4-Pass Only)
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 <ClientHello> message.
<xs:element name="ServerHello" type="ServerHelloPDU"/>
<xs:complexType name="ServerHelloPDU">
<xs:annotation>
<xs:documentation xml:lang="en">
Message sent from DSKPP server to DSKPP client
in response to a received ClientHello PDU.
</xs:documentation>
</xs:annotation>
<xs:complexContent>
<xs:extension base="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>
The components of this message have the following meaning:
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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 <ClientHello>. 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 4.11).
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. The MAC value MUST be
computed as defined in Section 4.8.1.1.
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.
4.10.5. The DSKPP Client's Second PDU (4-Pass Only)
This message contains the nonce chosen by the cryptographic module,
R_C, encrypted by the specified encryption key and encryption
algorithm.
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<xs:element name="ClientNonce" type="ClientNoncePDU"/>
<xs:complexType name="ClientNoncePDU">
<xs:annotation>
<xs:documentation xml:lang="en">
Second message sent from DSKPP client to
DSKPP server in a DSKPP session.
</xs:documentation>
</xs:annotation>
<xs:complexContent>
<xs:extension base="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>
The components of this message have the following meaning:
o Version: (inherited from the AbstractRequestType type) MUST be the
same version as in the <ServerHello> message.
o <SessionID>: MUST have the same value as the SessionID attribute
in the received <ServerHello> 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 4.5.
o <AuthenticationData>: The authentication data value, which MAY
OPTIONALLY be the same as provided in the <ClientHello>, MUST be
set as specified in Section 4.3.1.
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 4.11).
4.10.6. The DSKPP Server's Final PDU (1-, 2-, and 4-Pass)
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
<ClientNonce> message, whereas in a 2-pass exchange, the DSKPP server
sends this message in response to a <ClientHello> message. In a
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1-pass exchange, the DSKPP server sends only this message to the
client.
<xs:element name="ServerFinished" type="ServerFinishedPDU"/>
<xs:complexType name="ServerFinishedPDU">
<xs:annotation>
<xs:documentation xml:lang="en">
Final message sent from DSKPP server to
DSKPP client in a DSKPP session.
</xs:documentation>
</xs:annotation>
<xs:complexContent>
<xs:extension base="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:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
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 <ServerFinished> 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 <ServerFinished>
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 4.11).
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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, <ServerFinished> messages MUST always be
authenticated with a MAC. The MAC MUST be made using the already
established MAC algorithm. The MAC value MUST be computed as
specified in Section 4.8.1.2.
When receiving a <ServerFinished> 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 <ServerHello> (and
<ServerFinished>) 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.
4.11. Protocol Extensions
4.11.1. The ClientInfoType Type
When present in a <ClientHello> or a <ClientNonce> 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.
<xs:complexType name="ClientInfoType">
<xs:complexContent>
<xs:extension base="AbstractExtensionType">
<xs:sequence>
<xs:element name="Data"
type="xs:base64Binary"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
4.11.2. The ServerInfoType Type
When present, the OPTIONAL ServerInfoType extension contains DSKPP
server-specific information. This extension is only valid in
<ServerHello> messages for which Status = "Continue". DSKPP clients
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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 <ClientNonce> 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.
<xs:complexType name="ServerInfoType">
<xs:complexContent>
<xs:extension base="AbstractExtensionType">
<xs:sequence>
<xs:element name="Data"
type="xs:base64Binary"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
4.11.3. 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 <ServerFinished> message that
is being sent in response to a received <ClientHello> message if and
only if that <ClientHello> message selected TwoPassSupport as the
ProtocolVariantType and the client indicated support for the selected
key initialization method. Servers MUST include this extension in a
<ServerFinished> message that is sent as part of a 1-pass DSKPP.
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<xs:complexType name="KeyInitializationDataType">
<xs:annotation>
<xs:documentation xml:lang="en">
This extension is only valid in ServerFinished PDUs. It
contains key initialization data and its presence results in a
two-pass (or one-pass, if no ClientHello 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"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
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.
5. Protocol Bindings
5.1. General Requirements
DSKPP assumes a reliable transport.
5.2. HTTP/1.1 Binding for DSKPP
5.2.1. 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.
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5.2.2. Identification of DSKPP Messages
The MIME-type for all DSKPP messages MUST be
application/vnd.ietf.keyprov.dskpp+xml
5.2.3. 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 5.2.2.
5.2.4. 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.
5.2.5. 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.
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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.
5.2.6. HTTP Authentication
No support for HTTP/1.1 authentication is assumed.
5.2.7. Initialization of DSKPP
The DSKPP server MAY initialize the DSKPP protocol by sending an HTTP
response with Content-Type set according to Section 5.2.2 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
<DSKPPTrigger> element.
5.2.8. 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...
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>
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DSKPP data in XML form (server random nonce, server public key,
...)
6. DSKPP Schema
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
targetNamespace="urn:ietf:params:xml:ns:keyprov:protocol"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:protocol"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
<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"/>
<!-- Basic types -->
<xs:complexType name="AbstractRequestType" abstract="true">
<xs:attribute name="Version" type="VersionType" use="required"/>
</xs:complexType>
<xs:complexType name="AbstractResponseType" abstract="true">
<xs:attribute name="Version" type="VersionType" use="required"/>
<xs:attribute name="SessionID" type="IdentifierType"/>
<xs:attribute name="Status" type="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"/>
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<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="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"/>
<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="AlgorithmType"/>
</xs:sequence>
</xs:complexType>
<xs:simpleType name="AlgorithmType">
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<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>
</xs:complexType>
<xs:simpleType name="KeyContainerFormatType">
<xs:restriction base="xs:anyURI"/>
</xs:simpleType>
<xs:complextype name="AuthenticationDataType">
<xs:sequence>
<xs:element name="ClientID" type="dskpp:IdentifierType"
minOccurs="0"/>
<xs:choice minOccurs="0">
<xs:element name="AuthenticationCode"
type="dskpp:AuthenticationCodeType"/>
<xs:element name="AuthenticationCodeDigest"
type="dskpp:AuthenticationCodeDigestType"/>
<xs:element name="AuthenticationCodeMac"
type="dskpp:AuthenticationCodeMacType"/>
<xs:element name="AuthenticationCertificate"
type="ds:KeyInfoType"/>
</xs:choice>
</xs:sequence>
</xs:complexType>
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<xs:simpleType name="AuthenticationCodeType">
<xs:restriction base="xs:string">
<xs:maxLength value="20"/>
</xs:restriction>
</xs:simpleType>
<xs:complexType name="AuthenticationCodeDigestType">
<xs:simpleContent>
<xs:extension base="xs:base64Binary">
<xs:attribute name="HashAlgorithm" type="xs:anyURI"
use="required"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<xs:complexType name="AuthenticationCodeMacType">
<xs:sequence>
<xs:element name="Data" type="xs:base64Binary">
<xs:element name="Nonce" type="dskpp:NonceType"/>
</xs:sequence>
<attribute name="HMACAlgorithm" type="xs:anyURI"
use="required"/>
<attribute name="NonceId" type="dskpp:IdentifierType"/>
</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="MacType">
<xs:simpleContent>
<xs:extension base="xs:base64Binary">
<xs:attribute name="MacAlgorithm" type="xs:anyURI"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<xs:complexType name="KeyContainerType">
<xs:choice>
<xs:element name="KeyContainer"
type="pskc:KeyContainerType"/>
<xs:element name="##other" processContents="strict"/>
</xs:choice>
</xs:complexType>
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<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="DSKPP_URL" 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="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="AbstractExtensionType">
<xs:sequence>
<xs:element name="Data"
type="xs:base64Binary"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="ServerInfoType">
<xs:complexContent>
<xs:extension base="AbstractExtensionType">
<xs:sequence>
<xs:element name="Data"
type="xs:base64Binary"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="KeyInitializationDataType">
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<xs:annotation>
<xs:documentation xml:lang="en">
This extension is only valid in ServerFinished PDUs. It
contains key initialization data and its presence results in a
two-pass (or one-pass, if no ClientHello 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"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- DSKPP PDUs -->
<!-- DSKPP trigger -->
<xs:element name="DSKPPTrigger" type="DSKPPTriggerType"/>
<xs:complexType name="DSKPPTriggerType">
<xs:annotation>
<xs:documentation xml:lang="en">
Message used to trigger the device to initiate a
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>
<!-- ClientHello PDU -->
<xs:element name="ClientHello" type="ClientHelloPDU"/>
<xs:complexType name="ClientHelloPDU">
<xs:annotation>
<xs:documentation xml:lang="en">
Message sent from DSKPP client to DSKPP server to initiate a
DSKPP session.
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</xs:documentation>
</xs:annotation>
<xs:complexContent>
<xs:extension base="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"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- ServerHello PDU -->
<xs:element name="ServerHello" type="ServerHelloPDU"/>
<xs:complexType name="ServerHelloPDU">
<xs:annotation>
<xs:documentation xml:lang="en">
Message sent from DSKPP server to DSKPP client
in response to a received ClientHello PDU.
</xs:documentation>
</xs:annotation>
<xs:complexContent>
<xs:extension base="AbstractResponseType">
<xs:sequence minOccurs="0">
<xs:element name="KeyType"
type="dskpp:AlgorithmType"/>
<xs:element name="EncryptionAlgorithm"
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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>
<!-- ClientNonce PDU -->
<xs:element name="ClientNonce" type="ClientNoncePDU"/>
<xs:complexType name="ClientNoncePDU">
<xs:annotation>
<xs:documentation xml:lang="en">
Second message sent from DSKPP client to
DSKPP server in a DSKPP session.
</xs:documentation>
</xs:annotation>
<xs:complexContent>
<xs:extension base="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>
<!-- ServerFinished PDU -->
<xs:element name="ServerFinished" type="ServerFinishedPDU"/>
<xs:complexType name="ServerFinishedPDU">
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<xs:annotation>
<xs:documentation xml:lang="en">
Final message sent from DSKPP server to
DSKPP client in a DSKPP session.
</xs:documentation>
</xs:annotation>
<xs:complexContent>
<xs:extension base="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:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:schema>
7. Security Considerations
7.1. 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 and 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.
7.2. Active Attacks
7.2.1. Introduction
An active attacker MAY attempt to modify, delete, insert, replay, or
reorder messages for a variety of purposes including service denial
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and compromise of generated key material. Section 7.2.2 through
Section 7.2.7.
7.2.2. Message Modifications
Modifications to a <DSKPPPTrigger> message will either cause denial-
of-service (modifications of any of the identifiers or the nonce) or
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 7.2.7.
An attacker may modify a <ClientHello> 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
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 7.5 for a discussion of this threat and possible
countermeasures.
An attacker may also modify a <ServerHello> 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 could also provide a
different nonce than the one sent by the legitimate server. Clients
will 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
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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 <ClientNonce> 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 7.5
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 <ServerFinished> 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.
7.2.3. 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 <ServerFinished>
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 7.5.
7.2.4. 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 <DSKPPTrigger>.
The <TriggerNonce> element allows the server to associate a DSKPP
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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 7.5, 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.
7.2.5. 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 <ClientHello> message and that the server
includes R in the MAC computation.
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.
7.2.6. 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.
7.2.7. 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 4.2. 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 7.3.
7.3. 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.
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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 crypotgraphic 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 concer, 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.
7.4. 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 4.7
and Section 4.10 contain discussions of this threat and steps
RECOMMENDED to protect against it.
7.5. 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.
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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.
7.6. Additional Considerations Specific to 2- and 1-pass DSKPP
7.6.1. 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
than it would in the 4-pass variant. Server implementations SHOULD
therefore take extreme care to ensure that this situation does not
occur.
7.6.2. Key Confirmation
4-pass DSKPP servers provide key confirmation through the MAC on R_C
in the <ServerFinished> 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.
7.6.3. 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 4.8 above.
7.6.4. 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:
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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.
When a secure channel, e.g., SSL or TLS, is established between a
DSKPP client and server, an attacker could successfully brute-
force guess an Authentication Code, allowing him to illegitimately
receive K_TOKEN.
o The length the 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 with a
DSKPP server's nonce value. The Authentication Code and nonce
value MUST be strong enough to prevent offline brute-force
recovery of the Authentication Code from the HMAC data. Because
the nonce value is almost public across a non-secure channel, the
key strength is dependent on the Authentication Code.
7.6.5. 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.
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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.
8. 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"
9. 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.
10. Acknowledgements
The authors would like to thank all the members of OATH [OATH] and
participants of OTPS workshops for their review and comments related
to this document.
11. References
11.1. Normative references
[UNICODE] Davis, M. and M. Duerst, "Unicode Normalization Forms",
March 2001,
<http://www.unicode.org/unicode/reports/tr15/
tr15-21.html>.
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[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/>.
11.2. 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
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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>.
[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>.
[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. Key Initialization Profiles of DSKPP
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A.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.
A.2. Key Transport Profile
A.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.
A.2.2. Identification
This profile MUST be identified with the following URN:
urn:ietf:params:xml:schema:keyprov:protocol#transport
A.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
encryption methods utilizing a public key that are supported by the
DSKPP client (as indicated in the <SupportedEncryptionAlgorithms>
element of the <ClientHello> 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
<ClientHello> 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 <ServerFinished>
message. The Type attribute of the xenc:EncryptedKeyType MUST be
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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 <ClientHello> 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 <ServerFinished> 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
<ClientHello> 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 4.8
In addition, DSKPP servers MUST include the AuthenticationDataType
element (see further Section 4.8) in their <ServerFinished> messages
whenever a successful protocol run will result in an existing K_TOKEN
being replaced.
A.3. Key wrap profile
A.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
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.
A.3.2. Identification
This profile MUST be identified with the following URI:
urn:ietf:params:xml:schema:keyprov:protocol#wrap
A.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
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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 <ClientHello> 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
<ClientHello> 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 <ServerFinished>
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 <ClientHello> 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.
DSKP 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 <ServerFinished> 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
<ClientHello> 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 4.8
In addition, DSKPP servers MUST include the AuthenticationDataType
element (see further Section 4.8) in their <ServerFinished> messages
whenever a successful protocol run will result in an existing K_TOKEN
being replaced.
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A.4. Passphrase-based key wrap profile
A.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.
A.4.2. Identification
This profile MUST be identified with the following URI:
urn:ietf:params:xml:schema:keyprov:protocol#passphrase-wrap
A.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
<SupportedEncryptionAlgorithms> element of the <ClientHello> 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 <ClientHello> 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
<ServerFinished> 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
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DSKPP client (as reported in the <SupportedKeyTypes> of the preceding
<ClientHello> 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 <ServerFinished> 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
<ClientHello> 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 4.8
In addition, DSKPP servers MUST include the AuthenticationDataType
element (see further Section 4.8) in their <ServerFinished> messages
whenever a successful protocol run will result in an existing K_TOKEN
being replaced.
Appendix B. Example Messages
All examples are syntactically correct. MAC and cipher values are
fictitious however.
B.1. Example Messages in a Four-pass Exchange
The examples below illustrate a complete four-pass DSKPP exchange.
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B.1.1. Example of a DSKPP Initialization (Trigger) Message
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:DSKPPTrigger Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:schema:keyprov:protocol">
<InitializationTrigger>
<DeviceIdentifierData>
<pskc:DeviceID>
<Manufacturer>ManufacturerABC</Manufacturer>
<SerialNo>XL0000000001234</SerialNo>
<Model>U2</Model>
</DeviceID>
</DeviceIdentifierData>
<TriggerNonce>112dsdfwf312asder394jw==</TriggerNonce>
</InitializationTrigger>
</dskpp:DSKPPTrigger>
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B.1.2. Example of a <ClientHello> Message
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:ClientHello Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
<DeviceIdentifierData>
<pskc:DeviceID>
<Manufacturer>ManufacturerABC</Manufacturer>
<SerialNo>XL0000000001234</SerialNo>
<Model>U2</Model>
</DeviceID>
</DeviceIdentifierData>
<TriggerNonce>112dsdfwf312asder394jw==</TriggerNonce>
<SupportedKeyTypes>
<Algorithm>http://www.rsa.com/rsalabs/otps/schemas/2005/09/
otps-wst#SecurID-AES</Algorithm>
<Algorithm>http://www.openauthentication.org/OATH/2006/10/PSKC#
HOTP</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>
</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
</KeyContainerFormat>
</SupportedKeyContainers>
<AuthenticationData>
<AuthenticationCode>1erd354657689102abcd</AuthenticationCode>
</AuthenticationData>
</dskpp:ClientHello>
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B.1.3. Example of a <ServerHello> Message
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:ServerHello Version="1.0" SessionID="4114" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
<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
</KeyContainerFormat>
<Payload>
<Nonce>qw2ewasde312asder394jw==</Nonce>
</Payload>
</dskpp:ServerHello>
B.1.4. Example of a <ClientNonce> Message
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:ClientNonce Version="1.0" SessionID="4114"
xmlns:dskpp="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#">
<EncryptedNonce>VXENc+Um/9/NvmYKiHDLaErK0gk=</EncryptedNonce>
<AuthenticationData>
<AuthenticationCode>1erd354657689102abcd</AuthenticationCode>
</AuthenticationData>
</dskpp:ClientNonce>
B.1.5. Example of a <ServerFinished> Message
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<?xml version="1.0" encoding="UTF-8"?>
<dskpp:ServerFinished Version="1.0" SessionID="4114" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:schema:keyprov:protocol">
<pskc:KeyContainer version="1.0">
<Device>
<Secret SecretAlgorithm="other" SecretAlgorithm-ext="SecurID"
SecretId="XL0000000001234">
<Issuer>CredentialIssuer</Issuer>
<Usage otp="true">
<ResponseFormat format="DECIMAL" length="6"/>
</Usage>
<FriendlyName>MyFirstToken</FriendlyName>
<Data Name="TIME">
<Value>Time</Value>
</Data>
<Expiry>10/30/2009</Expiry>
</Secret>
</Device>
</pskc:KeyContainer>
<Mac>miidfasde312asder394jw==</Mac>
</dskpp:ServerFinished>
B.2. Example Messages in a Two- or One-pass Exchange
The examples illustrate a complete two-pass DSKPP exchange. The
server messages MAY also constitute the only messages in a one-pass
DSKPP exchange.
B.2.1. Example of a <ClientHello> Message Indicating Support for Two-
pass DSKPP
The client indicates support both for the two-pass key transport
variant as well as the two-pass key wrap variant.
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:ClientHello Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:pkcs-5=
"http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#">
<DeviceIdentifierData>
<pskc:DeviceID>
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<Manufacturer>ManufacturerABC</Manufacturer>
<SerialNo>XL0000000001234</SerialNo>
<Model>U2</Model>
</DeviceID>
</DeviceIdentifierData>
<ClientNonce>1523sdfxe798jowie913ol==</ClientNonce>
<SupportedKeyTypes>
<Algorithm>
http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#
SecurID-AES
</Algorithm>
<Algorithm>
http://www.openauthentication.org/OATH/2006/10/PSKC#HOTP
</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>
</SupportedMACAlgorithms>
<Algorithm>urn:ietf:params:xml:schema:keyprov:protocol#
dskpp-prf-aes</Algorithm>
</SupportedMACAlgorithms>
<SupportedProtocolVariants>
<Variant>
<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>
<Payload xsi:type="ds:KeyInfoType">
<ds:X509Data>
<ds:X509Certificate>miib</ds:X509Certificate>
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</ds:X509Data>
</Payload>
</TwoPass>
</Variant>
</SupportedProtocolVariants
<SupportedKeyContainers>
<KeyContainerFormat>
urn:ietf:params:xml:schema:keyprov:container
</KeyContainerFormat>
</SupportedKeyContainers>
<AuthenticationData>
<AuthenticationCode>1erd354657689102abcd</AuthenticationCode>
</AuthenticationData>
</dskpp:ClientHello>
B.2.2. Example of a <ServerFinished> Message Using the Key Transport
Profile
In this example, the server responds to the previous request using
the key transport profile.
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<?xml version="1.0" encoding="UTF-8"?>
<dskpp:ServerFinished Version="1.0" SessionID="4114" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
<pskc:KeyContainer version="1.0">
<EncryptionMethod
algorithm="http://www.w3.org/2001/05/xmlenc#rsa_1_5">
<EncKeyLabel>43212093<
<ds:KeyInfo>
<ds:X509Data>
<ds:X509Certificate>miib</ds:X509Certificate>
</ds:X509Data>
</ds:KeyInfo>
</EncryptionMethod>
<Device>
<Secret SecretAlgorithm="HOTP" SecretId="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>
9AEDpd4td44mRSASab625oPqlvHHIplzADer+pPOlL118JW/AhIoHB==
</ValueDigest>
</Data>
<Data Name="COUNTER">
<Value>1</Value>
</Data>
<Expiry>10/30/2009</Expiry>
</Secret>
</Device>
</pskc:KeyContainer>
<Mac MacAlgorithm=
"urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes">
miidfasde312asder394jw==
</Mac>
</dskpp:ServerFinished>
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B.2.3. Example of a <ServerFinished> Message Using the Key Wrap Profile
In this example, the server responds to the previous request using
the key wrap profile.
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<?xml version="1.0" encoding="UTF-8"?>
<dskpp:ServerFinished Version="1.0" SessionID="4114" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#">
<pskc:KeyContainer version="1.0">
<EncryptionMethod
algorithm="http://www.w3.org/2001/05/xmlenc#kw-aes128">
<EncKeyLabel>43212093</EncKeyLabel>
<ds:KeyInfo>
<ds:KeyName>Key-001</ds:KeyName>
</ds:KeyInfo>
</EncryptionMethod>
<Device>
<Secret SecretAlgorithm="HOTP" SecretId="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>
9AEDpd4td44mRSASab625oPqlvHHIplzADer+pPOlL118JW/AhIoHB==
</ValueDigest>
</Data>
<Data Name="COUNTER">
<Value>1</Value>
</Data>
<Expiry>10/30/2009</Expiry>
</Secret>
</Device>
</pskc:KeyContainer>
<Mac MacAlgorithm=
"urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes">
miidfasde312asder394jw==
</Mac>
</dskpp:ServerFinished>
B.2.4. Example of a <ServerFinished> Message using the Passphrase-based
Key Wrap Profile
In this example, the server responds to the previous request using
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the passphrase-based key wrap profile.
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:ServerFinished Version="1.0" SessionID="4114" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:schema:keyprov:protocol"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xenc=http://www.w3.org/2001/04/xmlenc#
xmlns:pkcs-5=
"http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#">
<pskc:KeyContainer version="1.0">
<EncryptionMethod algorithm=
"http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbes2">
<pkcs-5:PBES2-params>
<KeyDerivationFunc Algorithm=
"http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#
pbkdf2">
<pkcs-5:PBKDF2-params>
<Salt>
<Specified>32113435</Specified>
</Salt>
<IterationCount>1024</IterationCount>
<KeyLength>128</KeyLength>
<PRF/>
</pkcs-5:PBKDF2-params>
</KeyDerivationFunc>
<EncryptionScheme Algorithm=
"http://www.w3.org/2001/04/xmlenc#kw-aes128-cbc">
</EncryptionScheme
</pkcs-5:PBES2-params>
<EncKeyLabel>43212093</EncKeyLabel>
<ds:KeyInfo>
<ds:KeyName>Passphrase1</ds:KeyName>
</ds:KeyInfo>
</EncryptionMethod>
<Device>
<Secret SecretAlgorithm="HOTP" SecretId="SDU312345678">
<Issuer>CredentialIssuer</Issuer>
<Usage otp="true">
<ResponseFormat format="DECIMAL" length="6"/>
</Usage>
<FriendlyName>MyFirstToken</FriendlyName>
<Data Name="SECRET">
<Value>
7JHUyp3azOkqJENSsh6b2vxXzwGBYypzJxEr+ikQAa229KV/BgZhGA==
</Value>
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<ValueDigest>
9AEDpd4td44mRSASab625oPqlvHHIplzADer+pPOlL118JW/AhIoHB==
</ValueDigest>
</Data>
<Data Name="COUNTER">
<Value>1</Value>
</Data>
<Expiry>10/30/2009</Expiry>
</Secret>
</Device>
</pskc:KeyContainer>
<Mac MacAlgorithm=
"urn:ietf:params:xml:schema:keyprov:protocol#dskpp-prf-aes">
miidfasde312asder394jw==
</Mac>
</dskpp:ServerFinished>
Appendix C. Requirements
This section specifies mandatory and desirable protocol requirements.
Req-1:
The protocol MUST support provisioning of keys for use with
multiple types of symmetric cryptographic algorithms.
Req-2:
The protocol MUST support pre-generated symmetric keys (by
separate key issuance service) or locally generated keys in real-
time (by provisioning server).
Req-3:
The protocol MUST support mutually generated symmetric keys by
both client and server (i.e., joint key control).
Req-4:
The protocol MUST allow cryptographic modules to acquire multiple
symmetric keys; each key MAY be acquired in a separate
provisioning session.
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Req-5:
The protocol MUST support renewal of a symmetric key with the
original key ID.
Req-6:
The protocol MUST allow clients to specify their cryptographic
capabilities to the server and the server to indicate the
cryptography and algorithm types that it will be using.
Req-7:
The protocol MUST support mutual authentication and
confidentiality of sensitive data during provisioning.
Req-8:
The protocol MAY use a public-key infrastructure and the use of
client certificates for device authentication or symmetric key
data protection. The protocol MUST allow for other mechanisms,
such as symmetric key-based techniques, to be used.
Req-9:
The protocol SHOULD NOT only rely on transport layer security. It
SHOULD be compatible with transport layer security when available.
Req-10:
The protocol SHOULD allow the server to use pre-loaded symmetric
transport keys if available on the device that hosts the
cryptographic module (i.e., smart card update keys, such as used
by Global Platform for establishing a secure channel).
Req-11:
The protocol MUST protect against replay attacks.
Req-12:
The protocol MUST protect against MITM attacks.
Req-13:
The protocol MAY support a cryptographic module request to acquire
multiple symmetric keys in the same session.
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Req-14:
The protocol MAY allow the provisioning server to verify that the
key has been correctly provisioned to the cryptographic module
(i.e., key confirmation).
Req-15:
The protocol MAY allow a cryptographic module to notify the
provisioning server upon symmetric key deletion.
Req-16:
The protocol MAY limit a protocol run to complete within a certain
time window.
Req-17:
The protocol MAY support download of a key to a cryptographic
module via SMS depending upon whether the application can provide
an acceptable level of protection for transport of the symmetric
key.
The following is a list of features that are not required by the
protocol:
Non-Req-1:
Support for cryptographic module generated symmetric key upload to
a provisioning server.
Non-Req-2:
Support for other key lifecycle management functions, such as key
suspension, lock, and activation. These functions are supported
in a symmetric key-based application, such as an authentication
system.
Non-Req-3:
Support for asymmetric key pair provisioning.
Appendix D. Integration with PKCS #11
A DSKPP client that needs to communicate with a conncected
cryptographic module to perform a DSKPP exchange MAY use PKCS #11
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[PKCS-11]as a programming interface.
D.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.
D.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.
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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.
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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.
D.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.
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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
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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 E. Example of DSKPP-PRF Realizations
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E.1. Introduction
This example appendix defines DSKPP-PRF in terms of AES [FIPS197-AES]
and HMAC [RFC2104].
E.2. DSKPP-PRF-AES
E.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 4.7 MUST
be used.
E.2.2. Definition
DSKPP-PRF-AES (k, s, dsLen)
Input:
k Encryption keyto 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
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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.
E.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)
E.3. DSKPP-PRF-SHA256
E.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 4.7 MUST
be used.
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E.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:
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DS = B1 || B2 || ... || Bn<0..j-1>
Output the derived data DS.
E.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
Email: adoherty@rsa.com
Mingliang Pei
VeriSign, Inc.
Email: mpei@verisign.com
Magnus Nystroem
RSA, The Security Division of EMC
Email: magnus@rsa.com
Salah Machani
Diversinet Corp.
Email: smachani@diversinet.com
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Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
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Doherty, et al. Expires January 9, 2008 [Page 100]