KEYPROV Working Group A. Doherty
Internet-Draft RSA, The Security Division of EMC
Intended status: Standards Track M. Pei
Expires: July 28, 2008 Verisign, Inc.
S. Machani
Diversinet Corp.
M. Nystrom
RSA, The Security Division of EMC
January 25, 2008
Dynamic Symmetric Key Provisioning Protocol (DSKPP)
draft-ietf-keyprov-dskpp-02.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.
Two 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.
The two-pass variant enables 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 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 . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1. Usage Scenarios . . . . . . . . . . . . . . . . . . . . . 7
1.1.1. Single Key Request . . . . . . . . . . . . . . . . . . 7
1.1.2. Multiple Key Requests . . . . . . . . . . . . . . . . 7
1.1.3. Session Time-Out Policy . . . . . . . . . . . . . . . 7
1.1.4. Outsourced Provisioning . . . . . . . . . . . . . . . 8
1.1.5. Key Renewal . . . . . . . . . . . . . . . . . . . . . 8
1.1.6. Pre-Loaded Key Replacement . . . . . . . . . . . . . . 8
1.1.7. Pre-Shared Transport Key . . . . . . . . . . . . . . . 8
1.1.8. End-to-End Protection of Key Material . . . . . . . . 9
1.2. Protocol Entities . . . . . . . . . . . . . . . . . . . . 9
1.3. Initiating DSKPP . . . . . . . . . . . . . . . . . . . . . 10
1.4. Determining Which Protocol Variant to Use . . . . . . . . 11
1.4.1. Criteria for Using the Four-Pass Protocol . . . . . . 11
1.4.2. Criteria for Using the Two-Pass Protocol . . . . . . . 12
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.1. Key Words . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 12
2.3. Notation . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.4. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 15
3. DSKPP Protocol Details . . . . . . . . . . . . . . . . . . . . 15
3.1. Four-Pass Protocol Usage . . . . . . . . . . . . . . . . . 17
3.1.1. Message Flow . . . . . . . . . . . . . . . . . . . . . 17
3.1.2. Generation of Symmetric Keys for Cryptographic
Modules . . . . . . . . . . . . . . . . . . . . . . . 20
3.1.3. MAC Calculations . . . . . . . . . . . . . . . . . . . 22
3.2. Two-Pass Protocol Usage . . . . . . . . . . . . . . . . . 23
3.2.1. Message Flow . . . . . . . . . . . . . . . . . . . . . 24
3.2.2. Key Protection Profiles . . . . . . . . . . . . . . . 26
3.2.3. MAC Calculations . . . . . . . . . . . . . . . . . . . 30
3.3. User Authentication . . . . . . . . . . . . . . . . . . . 31
3.3.1. Device Identifier . . . . . . . . . . . . . . . . . . 32
3.3.2. Authentication Data . . . . . . . . . . . . . . . . . 32
3.4. The DSKPP One-Way Pseudorandom Function, DSKPP-PRF . . . . 34
3.4.1. Introduction . . . . . . . . . . . . . . . . . . . . . 34
3.4.2. Declaration . . . . . . . . . . . . . . . . . . . . . 35
3.5. Encryption of Pseudorandom Nonces Sent from the DSKPP
Client . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4. DSKPP Message Formats . . . . . . . . . . . . . . . . . . . . 36
4.1. General XML Schema Requirements . . . . . . . . . . . . . 36
4.2. Components of the <KeyProvTrigger> Message . . . . . . . . 36
4.3. Components of the <KeyProvClientHello> Request . . . . . . 37
4.3.1. The DeviceIdentifierDataType Type . . . . . . . . . . 40
4.3.2. The ProtocolVariantsType Type . . . . . . . . . . . . 40
4.3.3. The KeyContainersFormatType Type . . . . . . . . . . . 41
4.3.4. The AuthenticationDataType Type . . . . . . . . . . . 42
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4.4. Components of the <KeyProvServerHello> Response (Used
Only in Four-Pass DSKPP) . . . . . . . . . . . . . . . . . 44
4.5. Components of a <KeyProvClientNonce> Request (Used
Only in Four-Pass DSKPP) . . . . . . . . . . . . . . . . . 45
4.6. Components of a <KeyProvServerFinished> Response . . . . . 46
4.7. The StatusCode Type . . . . . . . . . . . . . . . . . . . 48
5. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 50
5.1. The ClientInfoType Type . . . . . . . . . . . . . . . . . 50
5.2. The ServerInfoType Type . . . . . . . . . . . . . . . . . 50
6. Protocol Bindings . . . . . . . . . . . . . . . . . . . . . . 50
6.1. General Requirements . . . . . . . . . . . . . . . . . . . 50
6.2. HTTP/1.1 Binding for DSKPP . . . . . . . . . . . . . . . . 50
6.2.1. Introduction . . . . . . . . . . . . . . . . . . . . . 50
6.2.2. Identification of DSKPP Messages . . . . . . . . . . . 50
6.2.3. HTTP Headers . . . . . . . . . . . . . . . . . . . . . 51
6.2.4. HTTP Operations . . . . . . . . . . . . . . . . . . . 51
6.2.5. HTTP Status Codes . . . . . . . . . . . . . . . . . . 51
6.2.6. HTTP Authentication . . . . . . . . . . . . . . . . . 52
6.2.7. Initialization of DSKPP . . . . . . . . . . . . . . . 52
6.2.8. Example Messages . . . . . . . . . . . . . . . . . . . 52
7. DSKPP Schema . . . . . . . . . . . . . . . . . . . . . . . . . 53
8. Conformance Requirements . . . . . . . . . . . . . . . . . . . 61
9. Security Considerations . . . . . . . . . . . . . . . . . . . 62
9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 62
9.2. Active Attacks . . . . . . . . . . . . . . . . . . . . . . 62
9.2.1. Introduction . . . . . . . . . . . . . . . . . . . . . 62
9.2.2. Message Modifications . . . . . . . . . . . . . . . . 62
9.2.3. Message Deletion . . . . . . . . . . . . . . . . . . . 64
9.2.4. Message Insertion . . . . . . . . . . . . . . . . . . 64
9.2.5. Message Replay . . . . . . . . . . . . . . . . . . . . 65
9.2.6. Message Reordering . . . . . . . . . . . . . . . . . . 65
9.2.7. Man-in-the-Middle . . . . . . . . . . . . . . . . . . 65
9.3. Passive Attacks . . . . . . . . . . . . . . . . . . . . . 65
9.4. Cryptographic Attacks . . . . . . . . . . . . . . . . . . 66
9.5. Attacks on the Interaction between DSKPP and User
Authentication . . . . . . . . . . . . . . . . . . . . . . 66
9.6. Additional Considerations . . . . . . . . . . . . . . . . 67
9.6.1. Client Contributions to K_TOKEN Entropy . . . . . . . 67
9.6.2. Key Confirmation . . . . . . . . . . . . . . . . . . . 67
9.6.3. Server Authentication . . . . . . . . . . . . . . . . 67
9.6.4. User Authentication . . . . . . . . . . . . . . . . . 67
9.6.5. Key Protection in the Two-Pass Passphrase Profile . . 68
10. Internationalization Considerations . . . . . . . . . . . . . 69
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 69
12. Intellectual Property Considerations . . . . . . . . . . . . . 69
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 69
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 69
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 70
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15.1. Normative references . . . . . . . . . . . . . . . . . . . 70
15.2. Informative references . . . . . . . . . . . . . . . . . . 71
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 72
A.1. Trigger Message . . . . . . . . . . . . . . . . . . . . . 73
A.2. Four-Pass Protocol . . . . . . . . . . . . . . . . . . . . 73
A.2.1. <KeyProvClientHello> Without a Preceding Trigger . . . 73
A.2.2. <KeyProvClientHello> Assuming a Preceding Trigger . . 74
A.2.3. <KeyProvServerHello> Without a Preceding Trigger . . . 75
A.2.4. <KeyProvServerHello> Assuming a Preceding Trigger . . 76
A.2.5. <KeyProvClientNonce> Using Default Encryption . . . . 77
A.2.6. <KeyProvServerFinished> Using Default Encryption . . . 78
A.3. Two-Pass Protocol . . . . . . . . . . . . . . . . . . . . 79
A.3.1. Example Using the Key Transport Profile . . . . . . . 79
A.3.2. Example Using the Key Wrap Profile . . . . . . . . . . 82
A.3.3. Example Using the Passphrase-Based Key Wrap Profile . 85
Appendix B. Integration with PKCS #11 . . . . . . . . . . . . . . 88
B.1. The 4-pass Variant . . . . . . . . . . . . . . . . . . . . 88
B.2. The 2-pass Variant . . . . . . . . . . . . . . . . . . . . 88
Appendix C. Example of DSKPP-PRF Realizations . . . . . . . . . . 91
C.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 91
C.2. DSKPP-PRF-AES . . . . . . . . . . . . . . . . . . . . . . 91
C.2.1. Identification . . . . . . . . . . . . . . . . . . . . 91
C.2.2. Definition . . . . . . . . . . . . . . . . . . . . . . 91
C.2.3. Example . . . . . . . . . . . . . . . . . . . . . . . 92
C.3. DSKPP-PRF-SHA256 . . . . . . . . . . . . . . . . . . . . . 93
C.3.1. Identification . . . . . . . . . . . . . . . . . . . . 93
C.3.2. Definition . . . . . . . . . . . . . . . . . . . . . . 93
C.3.3. Example . . . . . . . . . . . . . . . . . . . . . . . 94
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 94
Intellectual Property and Copyright Statements . . . . . . . . . . 96
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1. Introduction
A symmetric key cryptographic module provides data authentication and
encryption services to software (or firmware) applications hosted on
hardware devices, such as personal computers, handheld mobile phones,
one-time password tokens, USB flash drives, tape drives, etc. Until
recently, provisioning symmetric keys to these modules has been labor
intensive, involving manual operations that are device-specific, and
inherently error-prone.
Fortunately, an increasing number of hardware devices enable
programmatic initialization of their applications. For example, a
U3-ready thumb drive lets users load and configure applications
locally through a USB port on their PC. Other hardware devices, such
as Personal Digital Assistant (PDA) phones, allow users to load and
configure applications over-the-air. Likewise, programmable
cryptographic modules enable issuers to provision symmetric keys via
the Internet, whether over-the-wire or over-the-air.
This document describes the Dynamic Symmetric Key Provisioning
Protocol (DSKPP), which leverages these recent technological
developments. DSKPP provides an open and interoperable mechanism for
initializing and configuring symmetric keys to cryptographic modules
that are accessible over the Internet. The description is based on
the information contained in RFC4758, and contains specific
enhancements, such as User Authentication and support for the [PSKC]
format for transmission of key material.
DSKPP is a client-server protocol with two variations. One variation
establishes a symmetric key by mutually authenticated key agreement.
The other variation relies on key distribution. In the former case,
key agreement enables two parties (a cryptographic module and key
provisioning server) to establish a symmetric cryptographic key using
an exchange of four messages, such that the key is not transported
over the Internet. In the latter case, key distribution enables a
key provisioning server to transport a symmetric key to a
cryptographic module over the Internet using an exchange of two
messages. In either case, DSKPP is flexible enough to be run with or
without private-key capability in the cryptographic module, and with
or without an established public-key infrastructure.
All DSKPP communications consist of pairs of messages: a request and
a response. Each pair is called an "exchange", and each message sent
in an exchange is called a "pass". Thus, an implementation of DSKPP
that relies on mutually authenticated key agreement is called the
"four-pass protocol"; an implementation of DSKPP that relies on key
distribution is called the "two-pass protocol".
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DSKPP message flow always consists of a request followed by a
response. It is the responsibility of the client to ensure
reliability. If the response is not received with a timeout
interval, the client needs to retransmit the request (or abandon the
connection). Number of retries and lengths of timeouts are not
covered in this document because they do not affect interoperability.
1.1. Usage Scenarios
DSKPP is expected to be used to provision symmetric keys to
cryptographic modules in a number of different scenarios, each with
its own special requirements.
1.1.1. Single Key Request
The usual scenario is that a cryptographic module makes a request for
a symmetric key from a provisioning server that is located on the
local network or somewhere on the Internet. Depending upon the
deployment scenario, 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.
1.1.2. Multiple Key Requests
A cryptographic module makes multiple requests for symmetric keys
from the same provisioning server. The symmetric keys need not be of
the same type, i.e., the keys may be used with different symmetric
key cryptographic algorithms, including one-time password
authentication algorithms, and AES encryption algorithm.
1.1.3. Session Time-Out Policy
Once a cryptographic module initiates a symmetric key request, the
provisioning server may require that any subsequent actions to
complete the provisioning cycle occur within a certain time window.
For example, an issuer may provide a time-limited authentication code
to a user during registration, which the user will input into the
cryptographic module to authenticate themselves with the provisioning
server. If the user inputs a valid authentication code within the
fixed time period established by the issuer, the server will allow a
key to be provisioned to the cryptographic module hosted by the
user's device.
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1.1.4. Outsourced Provisioning
A symmetric key issuer outsources its key provisioning to a third-
party key provisioning server provider. The issuer is responsible
for authenticating and granting rights to users to acquire keys while
acting as a proxy to the cryptographic module to acquire symmetric
keys from the provisioning server; the cryptographic module
communicates with the issuer proxy server, which forwards
provisioning requests to the provisioning server.
1.1.5. Key Renewal
A cryptographic module requests renewal of a symmetric key using the
same key ID already associated with the key. Such a need may occur
in the case when a user wants to upgrade her device that houses the
cryptographic module or when a key has expired. When a user uses the
same cryptographic module to, for example, perform strong
authentication at multiple Web login sites, keeping the same key ID
removes the need for the user to register a new key ID at each site.
1.1.6. Pre-Loaded Key Replacement
This scenario represents a special case of symmetric key renewal in
which a local administrator can authenticate the user procedurally
before initiating the provisioning process. It also allows for an
issuer to pre-load a key onto a cryptographic module with a
restriction that the key is replaced with a new key prior to use of
the cryptographic module. Another variation of this scenario 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 usage scenario is essentially the same as the last
scenario wherein the same key ID is used for renewal.
1.1.7. Pre-Shared Transport Key
A cryptographic module is loaded onto a smart card after the card is
issued to a user. The symmetric key for the cryptographic module
will then be provisioned using a secure channel mechanism present in
many smart card platforms. This allows a direct secure channel to be
established between the smart card chip and the provisioning server.
For example, the card commands (i.e., Application Protocol Data
Units, or APDUs) are encrypted with a pre-shared transport key and
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.
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Note that two pre-conditions for this usage scenario are for the
protocol to be tunneled and the provisioning server to know the
correct pre-established transport key.
1.1.8. End-to-End Protection of Key Material
In this scenario, transport layer security does not provide end-to-
end protection of key material transported from the provisioning
server to the cryptographic module. For example, TLS may terminate
at an application hosted on a PC rather than at the cryptographic
module (i.e., the endpoint) located on a data storage device.
Mutually authenticated key agreement provides end-to-end protection,
which TLS cannot provide.
1.2. Protocol 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. In this document,
the DSKPP server 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 is represented by the definitions found in Section 2.2.
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----------- -------------
| User | | Device |
|---------|* owns *|-----------|
| UserID |--------->| DeviceID |
| ... | | ... |
----------- -------------
| 1
|
| contains
|
| *
V
--------------------------
|Cryptographic Module |
|------------------------|
|Crypto Module ID |
|Security Attribute List |
|... |
--------------------------
| 1
|
| contains
|
| *
V
-----------------------
|Key Container |
|---------------------|
|Key ID |
|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
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].
1.3. Initiating DSKPP
To initiate DSKPP:
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1. A server may first send a DSKPP trigger message to a client
application (e.g., in response to a user browsing to a Web site
that requires a symmetric key for authentication), although this
step is optional.
2. A client application calls on the DSKPP client to send a
symmetric key request to a DSKPP server, thus beginning a DSKPP
protocol run.
One of the following actions may be used to contact a DSKPP server:
1. A user may indicate how the DSKPP client is to contact a certain
DSKPP server during a browsing session.
2. A DSKPP client may be pre-configured to contact a certain DSKPP
server.
3. A user may be informed out-of-band about the location of the
DSKPP server.
Once the location of the DSKPP server is known, the DSKPP client and
the DSKPP server engage in a 4-pass or 2-pass protocol.
1.4. Determining Which Protocol Variant to Use
The four-pass and two-pass protocols are appropriate in different
deployment scenarios, as described in the sub-sections below.
1.4.1. Criteria for Using the Four-Pass Protocol
The four-pass protocol is needed under one or more of the following
conditions:
o The cryptographic module is not pre-populated with a transport
key, nor hosted on a pre-keyed device (e.g., a SIM card), nor has
a keypad that can be used for entering a passphrase (such as
present on a mobile phone).
o The hardware device will be used within multiple security domains,
which means that each domain will need to provision its own
symmetric key. However, the cryptographic module does not have a
transport key, or other type of key that can be used with multiple
provisioning servers.
o A cryptographic module does not have private-key capabilities.
o When the system provides a single point for exposing key material.
This risk can be mitigated by ensuring that both parties
contribute entropy to the key, such as with key agreement.
o A consumer of the protocol requires algorithm agility, esp. the
ability to negotiate which encryption mechanisms and key types are
used during a protocol run.
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1.4.2. Criteria for Using the Two-Pass Protocol
The two-pass protocol is needed under one or more of the following
conditions:
o A device is not able to support near real-time communications.
o Pre-existing (i.e., legacy) keys must be provisioned to the
cryptographic module.
o The cryptographic module has a transport key and is capable of
performing private-key operations.
o The cryptographic module has a pre-shared key (e.g., a mobile
phone with a SIM card).\
o The cryptographic module has a keypad in which a user may enter a
passphrase, useful for deriving a key-wrapping key for
distribution of key material.
o A consumer of the protocol requires algorithm agility, esp. the
ability to negotiate which encryption mechanisms and key types are
used during a protocol run.
o Workflow dictates that an approval process is required as part of
the protocol run (e.g., for user authorization).
o Near real-time communication between the client and server is not
possible.
2. Terminology
2.1. Key Words
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].
2.2. Definitions
Authentication Code (AC): Client Authentication Code comprised of a
string of numeric characters known to the device and the server
and containing an identifier and a password
Authentication Data (AD): Client Authentication Data that may be
derived from the Authentication Code (AC)
Cryptographic Module: A component of an application, which enables
symmetric key cryptographic functionality
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CryptoModule ID: A unique identifier for an instance of the
cryptographic module
Device: A physical piece of hardware or software framework that
hosts symmetric key cryptographic modules
Device ID (DeviceID): A unique identifier for the device
DSKPP Client: Manages communication between the symmetric key
cryptographic module and the DSKPP server
DSKPP Server: The symmetric key provisioning server that
participates in the DSKPP protocol run
DSKPP Server ID (ServerID): The unique identifier of a DSKPP server
Key Container (KC): An object that encapsulates a symmetric key and
its configuration data
Key Container Header (KCH): Information about the Key Container,
useful for two-pass DSKPP, e.g., the ServerID and KPM
Key ID (KeyID): A unique identifier for the symmetric key
Key Protection Method (KPM): The key protection profile used during
two-pass DSKPP
Key Protection Method List (KPML): The list of key protection
methods supported by a cryptographic module
Key Type: The type of symmetric key cryptographic methods for which
the key will be used (e.g., OATH HOTP or RSA SecurID
authentication, AES encryption, etc.)
Security Attribute List (SAL): A payload that contains the DSKPP
version, DSKPP variation (four- or two-pass), key container
formats, key types, and cryptographic algorithms that the
cryptographic module is capable of supporting
Security Context (SC): A payload that contains the DSKPP version,
DSKPP variation (four- or two-pass), key container format, key
type, and cryptographic algorithms relevant to the current
protocol run
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User: The person or client to whom devices are issued
User ID: A unique identifier for the user or client
2.3. Notation
|| String concatenation
[x] Optional element x
A ^ B Exclusive-OR operation on strings A and B (where A
and B are of equal length)
<XMLElement> A typographical convention used in the body of the
text
DSKPP-PRF(k,x,l) A keyed psuedo-random function (see Section 3.4)
E(k,m) Encryption of m with the key k
K Key used to encrypt R_C (either K_SERVER, K_SHARED
or K_DERIVED), or in MAC or DSKPP_PRF computations
K_AC Secret key that is derived from the Authentication
Code and used for user authentication purposes
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-pass DSKPP
K_SERVER Public key of the DSKPP server
K_SHARED Secret key shared between the DSKPP client and the
DSKPP server
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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
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
R_TRIGGER Pseudorandom value chosen by the DSKPP server and
used as input in a trigger message.
URL_S Server address as a URL
2.4. Abbreviations
AC Authentication Code
AD Authentication Data
DSKPP Dynamic Symmetric Key Provisioning Protocol
HTTP Hypertext Transfer Protocol
KC Key Container
KCH Key Container Header
KPM Key Protection Method
KPML Key Protection Method List
MAC Message Authentication Code
PC Personal Computer
PDU Protocol Data Unit
PKCS Public-Key Cryptography Standards
PRF Pseudo-Random Function
PSKC Portable Symmetric Key Container
SAL Security Attribute List (see Section 2.2)
SC Security Context (see Section 2.2)
TLS Transport Layer Security
URL Uniform Resource Locator
USB Universal Serial Bus
XML eXtensible Markup Language
3. DSKPP Protocol Details
DSKPP enables symmetric key provisioning between a DSKPP server and
DSKPP client. The DSKPP protocol supports the request and response
messages shown in Figure 2. These messages are described below.
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+---------------+ +---------------+
| | | |
| DSKPP Client | | DSKPP Server |
| | | |
+---------------+ +---------------+
| |
| [ <--------- <KeyProvTrigger> --------- ] |
| |
| ------- <KeyProvClientHello> -------> |
| (Applicable to 4- and 2-pass) |
| |
| <------ <KeyProvServerHello> -------- |
| (Applicable to 4-pass only) |
| |
| ------- <KeyProvClientNonce> -------> |
| (Applicable to 4-pass only) |
| |
| <---- <KeyProvServerFinished> ------- |
| (Applicable to 4- and 2-pass) |
| |
Figure 2: The DSKPP protocol (with OPTIONAL preceding trigger)
[<KeyProvTrigger>]: A DSKPP server may initiate the DSKPP protocol
by sending a <KeyProvTrigger> message. For example, this message
may be sent in response to a user requesting a symmetric key in a
browsing session. The trigger message always contains a nonce to
allow the server to couple the trigger with a later
<KeyProvClientHello> request.
<KeyProvClientHello>: With this request, a DSKPP client initiates
contact with the DSKPP server, indicating which protocol versions
and variations (four-pass or two-pass), key types, encryption and
MAC algorithms that it supports. In addition, the request may
include client authentication data that the DSKPP server uses to
verify proof-of-possession of the device.
<KeyProvServerHello>: Upon receiving a <KeyProvClientHello> request,
the DSKPP server uses the <KeyProvServerHello> response to
specify which protocol version and variation, key type,
encryption algorithm, and MAC algorithm that will be used by the
DSKPP server and DSKPP client during the protocol run. The
decision of which variation, key type, and cryptographic
algorithms to pick is policy- and implementation-dependent and
therefore outside the scope of this document.
The <KeyProvServerHello> response includes the DSKPP server's
random nonce, R_S. The response also consists of information
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about either a shared secret key, or its own public key, that the
DSKPP client uses when sending its protected random nonce, R_C,
in the <KeyProvClientNonce> request (see below).
Optionally, the DSKPP server may provide a MAC that the DSKPP
client may use for server authentication.
<KeyProvClientNonce>: With this request, a DSKPP client and DSKPP
server securely exchange protected data, e.g., the protected
random nonce R_C. In addition, the request may include client
authentication data that the DSKPP server uses to verify proof-
of-possession of the device.
<KeyProvServerFinished>: The <KeyProvServerFinished> response is a
confirmation message that includes a key container that holds
configuration data, and may also contain protected key material
(this depends on the protocol variation, as discussed below).
Optionally, the DSKPP server may provide a MAC that the DSKPP
client may use for server authentication.
3.1. Four-Pass Protocol Usage
This section describes the message flow and methods that comprise the
four-pass protocol variant.
3.1.1. Message Flow
The four-pass protocol flow consists of two message exchanges:
1: Pass 1 = <KeyProvClientHello>, Pass 2 = <KeyProvServerHello>
2: Pass 3 = <KeyProvClientNonce>, Pass 4 = <KeyProvServerFinished>
The first pair of messages negotiate cryptographic algorithms and
exchange nonces. The second pair of messages establishes a symmetric
key using mutually authenticated key agreement.
The DSKPP server MUST ensure that a generated key is associated with
the correct cryptographic module, and if applicable, the correct
user. To do this, the DSKPP server MAY couple an initial user
authentication to the DSKPP execution using one of the mechanisms
described in Section 3.3.
The purpose and content of each message are described below,
including the optional <KeyProvTrigger>.
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DSKPP Client DSKPP Server
------------ ------------
[<---] R_TRIGGER, [DeviceID],
[KeyID], [URL_S]
The DSKPP server optionally sends a <KeyProvTrigger> message to the
DSKPP client. The trigger message MUST contain a nonce, R_TRIGGER,
to allow the server to couple the trigger with a later
<KeyProvClientHello> request. <KeyProvTrigger> MAY include DeviceID
to allow the client to select the device with which it will
communicate. The DeviceID MAY also be used later to authenticate the
client (see Section 3.3.1). In the case of key renewal,
<KeyProvTrigger> MAY include the identifier for the key, KeyID, that
is being replaced. Finally, the trigger MAY contain a URL for the
DSKP client to use when contacting the DSKPP server.
DSKPP Client DSKPP Server
------------ ------------
SAL, [R_TRIGGER],
[DeviceID], [KeyID] --->
The DSKPP client sends a <KeyProvClientHello> message to the DSKPP
server. This message MUST contain a Security Attribute List (SAL),
identifying which DSKPP versions, protocol variations (in this case
"four-pass"), key container formats, key types, encryption and MAC
algorithms that the client supports. In addition, if a trigger
message preceded <KeyProvClientHello>, then it passes the parameters
received in <KeyProvTrigger> back to the DSKPP Server. In
particular, it MUST include R_TRIGGER so that the DSKPP server can
associate the client with the trigger message, and SHOULD include
DeviceID and KeyID.
DSKPP Client DSKPP Server
------------ ------------
<--- SC, R_S, [K], [MAC]
The DSKPP server responds to the DSKPP client with a
<KeyProvServerHello> message, whose content MUST include a Security
Context (SC). The client will use the SC to select the DSKPP version
and variation (e.g., four-pass), type of key to generate, and
cryptographic algorithms that it will use for the remainder of the
protocol run. <KeyProvServerHello> MUST also include the server's
random nonce, R_S, whose length may depend on the selected key type.
In addition, the <KeyProvServerHello> message MAY provide K, which
represents its own public key (K_SERVER) or information about a
shared secret key (K_SHARED) to use for encrypting the cryptographic
module's random nonce (see description of <KeyProvClientNonce>
below). Optionally, <KeyProvServerHello> MAY include a MAC that the
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DSKPP client can use for server authentication in the case of key
renewal (Section 3.1.3.1 describes how to calculate the MAC).
DSKPP Client DSKPP Server
------------ ------------
E(K,R_C), [AD] --->
Based on the Security Context (SC) provided in the
<KeyProvServerHello> message, the cryptographic module generates a
random nonce, R_C. The length of the nonce R_C will 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.
Note: If K is equivalent to K_SERVER, then the cryptographic module
SHOULD verify the server's certificate before using it to encrypt R_C
in accordance with [RFC3280].
Note: If successful execution of the protocol will result in the
replacement of an existing key with a newly generated one, the DSKPP
client MUST verify the MAC provided in the <KeyProvServer> message.
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.
The DSKPP client MUST send the encrypted random nonce to the DSKPP
server in a <KeyProvClientNonce> message, and MAY include client
Authentication Data (AD), such as a MAC derived from an
authentication code and R_C (refer to Section 3.3.2). Finally, the
cryptographic module calculates and stores a symmetric key, K_TOKEN,
of the key type specified in the SC received in <KeyProvServerHello>
(refer to Section 3.1.2.2.<KeyProvServerFinished> for a description
of how K_TOKEN is generated).
DSKPP Client DSKPP Server
------------ ------------
<--- KC, MAC
If Authentication Data (AD) was received in the <KeyProvClientNonce>
message, then the DSKPP server MUST authenticate the user in
accordance with Section 3.3.2. If authentication fails, then DSKPP
server MUST abort. Otherwise, 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 3.4. 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
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by some service that needs to verify or decrypt data produced by the
cryptographic module and the key.
Once the association has been made, the DSKPP server sends a
confirmation message to the DSKPP client called
<KeyProvServerFinished>. The confirmation message MUST include a Key
Container (KC) that holds an identifier for the generated key (but
not the key itself) and additional configuration information, e.g.,
the identity of the DSKPP server. The default symmetric key
container format 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. In addition to a Key
Container, <KeyProvServerFinished> MUST also include a MAC that the
DSKPP client will use to authenticate the message before commiting
K_TOKEN.
After receiving a <KeyProvServerFinished> message with Status =
"Success", 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 protocol. If
<KeyProvServerFinished> has Status = "Success" and the MAC was
verified, then the DSKPP client MUST associate the provided key
container with the generated key K_TOKEN, and store this data
permanently. After this operation, it MUST NOT be possible to
overwrite the key unless knowledge of an authorizing key is proven
through a MAC on a later <KeyProvServerHello> (and
<KeyProvServerFinished>) message.
3.1.2. Generation of Symmetric Keys for Cryptographic Modules
With 4-pass DSKPP, the symmetric key that is the target of
provisioning, is generated on-the-fly without being transferred
between the DSKPP client and DSKPP server. A sample data flow
depicting how this works followed by computational information are
provided in the subsections below.
3.1.2.1. Data Flow
A sample data flow showing key generation during the 4-pass protocol
is shown in Figure 8.
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+----------------------+ +-------+ +----------------------+
| +------------+ | | | | |
| | 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 8: Principal data flow for DSKPP key generation -
using public server key
Note: Conceptually, although R_C is one pseudorandom string, it may
be viewed as consisting of two components, R_C1 and R_C2, where R_C1
is generated during the protocol run, and R_C2 can be pre-generated
and loaded on the cryptographic module before the device is issued to
the user. In that case, the latter string, R_C2, SHOULD be unique
for each cryptographic module.
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
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encryption key K ensures that no man-in-the-middle may be present, or
else the cryptographic module will end up with a key different from
the one stored by the legitimate DSKPP server.
Note: A man-in-the-middle (in the form of corrupt client software or
a mistakenly contacted server) may present his own public key to the
cryptographic module. This will enable the attacker to learn the
client's version of K_TOKEN. However, the attacker is not able to
persuade the legitimate server to derive the same value for K_TOKEN,
since K_TOKEN is a function of the public key involved, and the
attacker's public key must be different than the correct server's (or
else the attacker would not be able to decrypt the information
received from the client). Therefore, once the attacker is no longer
"in the middle," the client and server will detect that they are "out
of sync" when they try to use their keys. In the case of encrypting
R_C with K_SERVER, it is therefore important to verify that K_SERVER
really is the legitimate server's key. One way to do this is to
independently validate a newly generated K_TOKEN against some
validation service at the server (e.g. by using a connection
independent from the one used for the key generation).
3.1.2.2. Computing the Symmetric Key
In DSKPP, keys are generated using the DSKPP-PRF function defined in
Section 3.4, 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.
3.1.3. MAC Calculations
3.1.3.1. Server Authorization in the Case of Key Renewal
A MAC MUST be present in the <KeyProvServerHello> message if the
DSKPP run will result in the replacement of an existing key with a
new one as proof that the DSKPP server is authorized to perform the
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action. When the MAC value is used for server authentication, the
value MAY be computed by using the DSKPP-PRF function of Section 3.4,
in which case the input parameter s MUST be set to the concatenation
of the (ASCII) string "MAC 1 computation", R (if sent by the client),
and R_S, and K MUST be set to the existing MAC key K_MAC' . The
input parameter dsLen MUST be set to the length of R_S:
dsLen = len(R_S)
MAC = DSKPP-PRF (K_MAC', "MAC 1 computation" || [R ||] R_S, dsLen)
3.1.3.2. Key Confirmation
To avoid a false "Commit" message causing the cryptographic module to
end up in an initialized state in which the server does not recognize
the stored key, <ServerFinished> messages MUST be authenticated with
a MAC. The MAC MUST be calculated using the already established MAC
algorithm and MUST be computed on the (ASCII) string "MAC 2
computation" and R_C using the existing the MAC key K_MAC' (i.e., the
MAC key that existed before this protocol run). If DSKPP-PRFof
Section 3.4 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, and dsLen as follows:
dsLen = len(R_C)
MAC = DSKPP-PRF (K_MAC, "MAC 2 computation" || R_C, dsLen)
3.2. Two-Pass Protocol Usage
Two-pass DSKPP is essentially a transport of key material from the
DSKPP server to the DSKPP client. Two-pass DSKPP supports multiple
key protection 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 protection methods are defined
(refer to Section 3.2.2), 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.
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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.
This section describes the message flow and methods that comprise the
two-pass protocol variant.
3.2.1. Message Flow
The two-pass protocol flow consists of one exchange:
1: Pass 1 = <KeyProvClientHello>, Pass 2 = <KeyProvServerFinished>
The client's initial <KeyProvClientHello> message is directly
followed by a <KeyProvServerFinished> message (unlike the four-pass
variant, there is no exchange of the <KeyProvServerHello> and
<KeyProvClientNonce> messages). However, as the two-pass variation
of DSKPP consists of one round trip to the server, the client is
still able to include its random nonce, R_C, algorithm preferences
and supported key types in the <KeyProvClientHello> message. Note
that by including R_C in <KeyProvClientHello>, the DSKPP client is
able to ensure the server is alive before "committing" the key.
To ensure that a generated key 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 using one of the
mechanisms described in Section 3.3. Whatever the mechanism, the
DSKPP server MUST ensure that a generated key is associated with the
correct cryptographic module, and if applicable, the correct user.
The purpose and content of each message are described below,
including the optional <KeyProvTrigger>.
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DSKPP Client DSKPP Server
------------ ------------
[<---] R_TRIGGER, [DeviceID],
[KeyID], [URL_S]
The DSKPP server optionally sends a <KeyProvTrigger> message to the
DSKPP client. The trigger message MUST contain a nonce, R_TRIGGER,
to allow the server to couple the trigger with a later
<KeyProvClientHello> request. <KeyProvTrigger> MAY include DeviceID
to allow the client to select the device with which it will
communicate. In the case of key renewal, <KeyProvTrigger> SHOULD
include the identifier for the key, KeyID, that is being replaced.
Finally, the trigger MAY contain a URL for the DSKP client to use
when contacting the DSKPP server.
DSKPP Client DSKPP Server
------------ ------------
R_C, SAL, KPML, [AD],
[R_TRIGGER],
[DeviceID], [KeyID] --->
The DSKPP client sends a <KeyProvClientHello> message to the DSKPP
server. <KeyProvClientHello> MUST include client nonce, R_C, and a
Security Attribute List (SAL), identifying which DSKPP versions,
protocol variations (in this case "two-pass"), key container formats,
key types, encryption and MAC algorithms that the client supports.
Unlike 4-pass DSKPP, the 2-pass DSKPP client uses the
<KeyProvClientHello> message to declare the list of Key Protection
Methods (KPML) it supports, providing required payload information in
accordance with Section 3.2.2. Optionally, the message MAY include
client Authentication Data (AD), such as a MAC derived from an
authentication code and R_C (refer to Section 3.3.2). In addition,
if a trigger message preceded <KeyProvClientHello>, then it passes
the parameters received in <KeyProvTrigger> back to the DSKPP Server.
In particular, it MUST include R_TRIGGER so that the DSKPP server can
associate the client with the trigger message, and SHOULD include
DeviceID and KeyID.
DSKPP Client DSKPP Server
------------ ------------
<--- KCH, KC, E(K,K_PROV),
MAC, AD
If Authentication Data (AD) was received, then the DSKPP server MUST
authenticate the user in accordance with Section 3.3.2. If
authentication fails, then DSKPP server MUST abort. Otherwise, the
DSKPP server generates a key K_PROV from which two keys, K_TOKEN and
K_MAC, are derived. (Alternatively, the key K_PROV may have been
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pre-generated as described in Section 1.1.1. The DSKPP server
selects a Key Protection Method (KPM) and applies it to K_PROV in
accordance with Section 3.2.2. The server then associates K_TOKEN
with the cryptographic module in a server-side data store. The
intent is that the data store later will be used by some service that
needs to verify or decrypt data produced by the cryptographic module
and the key.
Once the association has been made, the DSKPP server sends a
confirmation message to the DSKPP client called
<KeyProvServerFinished>. For two-pass DSKPP, the confirmation
message MUST include a Key Container Header (KCH) that contains the
DSKPP Server's ID and KPM. The ServerID is used for authentication
purposes, and the KPM informs the DSKPP client of the security
context in which it will operate. In addition to the KCH, the
confirmation message MUST include the Key Container (KC) that holds
the KeyID, K_PROV from which K_TOKEN and K_MAC are derived, and
additional configuration information. The default symmetric key
container format 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]. Finally, <ServerFinished> MUST
include two MACs (MAC and AD) 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 (see Section 3.2.3 for more information).
After receiving a <KeyProvServerFinished> message with Status =
"Success", the DSKPP client MUST verify both MAC values (MAC and AD).
The DSKPP client MUST terminate the DSKPP session if either MAC does
not verify, and MUST, in this case, also delete any nonces, keys,
and/or secrets associated with the failed run of the protocol. If
<KeyProvServerFinished> has Status = "Success" and the MACs were
verified, then the DSKPP client MUST extract the key data from the
provided key container, and store data locally. 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
<KeyProvServerFinished> message.
3.2.2. Key Protection Profiles
This section introduces three profiles of two-pass DSKPP for key
protection. Further profiles MAY be defined by external entities or
through the IETF process.
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3.2.2.1. Key Transport Profile
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_PROV from which two keys, K_TOKEN and K_MAC are derived MUST be
transported.
This profile MUST be identified with the following URN:
urn:ietf:params:xml:schema:keyprov:protocol#transport
In the two-pass version of DSKPP, the client MUST send a payload
associated with this key protection 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 protection 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
<KeyProvClientHello> message in the case of 2-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 protection method in the
<KeyProvClientHello> message that triggered the response. The
<CarriedKeyName> element MAY be present, but MUST, when present,
contain the same value as the <KeyID> element of the
<KeyProvServerFinished> message. The Type attribute of the xenc:
EncryptedKeyType MUST be present and MUST identify the type of the
wrapped key. The type MUST be one of the types supported by the
DSKPP client (as reported in the <SupportedKeyTypes> of the preceding
<KeyProvClientHello> message in the case of 2-pass DSKPP). The
transported key MUST consist of two parts of equal length. The first
half constitutes K_MAC and the second half constitutes K_TOKEN. The
length of K_TOKEN (and hence also the length of K_MAC) is determined
by the type of K_TOKEN.
DSKPP servers and cryptographic modules supporting this profile MUST
support the http://www.w3.org/2001/04/xmlenc#rsa-1_5 key-wrapping
mechanism defined in [XMLENC].
When this profile is used, the MacAlgorithm attribute of the <Mac>
element of the <KeyProvServerFinished> message MUST be present and
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MUST identify the selected MAC algorithm. The selected MAC algorithm
MUST be one of the MAC algorithms supported by the DSKPP client (as
indicated in the <SupportedMacAlgorithms> element of the
<KeyProvClientHello> message in the case of 2-pass DSKPP). The MAC
MUST be calculated as described in Section 3.2 for Two-Pass DSKPP.
In addition, DSKPP servers MUST include the AuthenticationDataType
element in their <KeyProvServerFinished> messages whenever a
successful protocol run will result in an existing K_TOKEN being
replaced.
3.2.2.2. Key Wrap Profile
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_PROV from which two keys, K_TOKEN and K_MAC are derived MUST be
wrapped.
This profile MUST be identified with the following URI:
urn:ietf:params:xml:schema:keyprov:protocol#wrap
In the 2-pass version of DSKPP, the client MUST send a payload
associated with this key protection method. The payload MUST be of
type ds:KeyInfoType ([XMLDSIG]), and only those choices of the ds:
KeyInfoType that identify a symmetric key are allowed. The ds:
KeyName alternative is RECOMMENDED.
The server payload associated with this key protection method MUST be
of type xenc:EncryptedKeyType ([XMLENC]), and only those encryption
methods utilizing a symmetric key that are supported by the DSKPP
client (as indicated in the <SupportedEncryptionAlgorithms> element
of the <KeyProvClientHello> message in the case of 2-pass DSKPP) 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 protection method in the
<KeyProvClientHello> message that triggered the response. The
<CarriedKeyName> element MAY be present, and MUST, when present,
contain the same value as the <KeyID> element of the
<KeyProvServerFinished> message. The Type attribute of the xenc:
EncryptedKeyType MUST be present and MUST identify the type of the
wrapped key. The type MUST be one of the types supported by the
DSKPP client (as reported in the <SupportedKeyTypes> of the preceding
<KeyProvClientHello> message in the case of 2-pass DSKPP). 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
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length of K_TOKEN (and hence also the length of K_MAC) is determined
by the type of K_TOKEN.
DSKPP servers and cryptographic modules supporting this profile MUST
support the http://www.w3.org/2001/04/xmlenc#kw-aes128 key-wrapping
mechanism defined in [XMLENC].
When this profile is used, the MacAlgorithm attribute of the <Mac>
element of the <KeyProvServerFinished> message MUST be present and
MUST identify the selected MAC algorithm. The selected MAC algorithm
MUST be one of the MAC algorithms supported by the DSKPP client (as
indicated in the <SupportedMacAlgorithms> element of the
<KeyProvClientHello> message in the case of 2-pass DSKPP). The MAC
MUST be calculated as described in Section 3.2.
In addition, DSKPP servers MUST include the AuthenticationDataType
element in their <KeyProvServerFinished> messages whenever a
successful protocol run will result in an existing K_TOKEN being
replaced.
3.2.2.3. Passphrase-Based Key Wrap Profile
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_PROV from which two keys, K_TOKEN and K_MAC
are derived MUST be wrapped.
This profile MUST be identified with the following URI:
urn:ietf:params:xml:schema:keyprov:protocol#passphrase-wrap
In the 2-pass version of DSKPP, the client MUST send a payload
associated with this key protection 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 protection method MUST be
of type xenc:EncryptedKeyType ([XMLENC]), and only those encryption
methods utilizing a passphrase to derive the key-wrapping key that
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are supported by the DSKPP client (as indicated in the
<SupportedEncryptionAlgorithms> element of the <KeyProvClientHello>
message in the case of 2-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 protection method in the <KeyProvClientHello> message
that triggered the response. The <CarriedKeyName> element MAY be
present, and MUST, when present, contain the same value as the
<KeyID> element of the <KeyProvServerFinished> message. The Type
attribute of the xenc:EncryptedKeyType MUST be present and MUST
identify the type of the wrapped key. The type MUST be one of the
types supported by the DSKPP client (as reported in the
<SupportedKeyTypes> of the preceding <KeyProvClientHello> message in
the case of 2-pass DSKPP). The wrapped key MUST consist of two parts
of equal length. The first half constitutes K_MAC and the second
half constitutes K_TOKEN. The length of K_TOKEN (and hence also the
length of K_MAC) is determined by the type of K_TOKEN.
DSKPP servers and cryptographic modules supporting this profile MUST
support the PBES2 password based encryption scheme defined in
[PKCS-5] (and identified as
http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbes2 in
[PKCS-5-XML]), the PBKDF2 passphrase-based key derivation function
also defined in [PKCS-5] (and identified as
http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbkdf2 in
[PKCS-5-XML]), and the http://www.w3.org/2001/04/xmlenc#kw-aes128
key-wrapping mechanism defined in [XMLENC].
When this profile is used, the MacAlgorithm attribute of the <Mac>
element of the <KeyProvServerFinished> message MUST be present and
MUST identify the selected MAC algorithm. The selected MAC algorithm
MUST be one of the MAC algorithms supported by the DSKPP client (as
indicated in the <SupportedMacAlgorithms> element of the
<KeyProvClientHello> message in the case of 2-pass DSKPP). The MAC
MUST be calculated as described in Section 3.2.
In addition, DSKPP servers MUST include the AuthenticationDataType
element in their <KeyProvServerFinished> messages whenever a
successful protocol run will result in an existing K_TOKEN being
replaced.
3.2.3. MAC Calculations
3.2.3.1. Key Confirmation
In two-pass DSKPP, the client MUST include a nonce R in the
<KeyProvClientHello> message. Further, the DSKPP server MUST include
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its identifier, ServerID, in the <KeyProvServerFinished> message (via
the Key Container). The MAC value in the <KeyProvServerFinished>
message MUST be computed on the (ASCII) string "MAC 1 computation",
the server identifier ServerID, and R using a MAC key K_MAC. This
key MUST be provided together with K_TOKEN to the cryptographic
module.
If DSKPP-PRF is used as the MAC algorithm, then the input parameter s
MUST consist of the concatenation of the (ASCII) string "MAC 1
computation" and R, and the parameter dsLen MUST be set to the length
of R:
dsLen = len(R)
MAC = DSKPP-PRF (K_MAC, "MAC 1 computation" || ServerID || R, dsLen)
3.2.3.2. Server Authorization
A MAC MUST be present in the <KeyProvServerFinished> message as proof
that the DSKPP server is authorized to provide a new key to the
cryptographic module. In 2-pass DSKPP, servers include this MAC
value in the AuthenticationDataType element of
<KeyProvServerFinished>. The MAC value in the AuthenticationDataType
element MUST be computed on the (ASCII) string "MAC 1 computation",
the server identifier ServerID, 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" ServerID, 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" || ServerID || R, dsLen)
3.3. User Authentication
The DSKPP server MUST ensure that a generated key is associated with
the correct cryptographic module, and if applicable, the correct
user. If the user has not been authenticated by some out-of-band
means, then the user SHOULD be authenticated within the DSKPP. For a
further discussion of this, and threats related to man-in-the-middle
attacks in this context, see Section 9.
When relying on DSKPP for user authentication, the DSKPP server
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SHOULD explicitly:
o Bind the user to the device (see Section 3.3.1, below)
o Rely on client-provided Authentication Data (AD) to verify that a
legitimate user is behind the wheel (see Section 3.3.2, below)
NOTE: Device authentication can be handled implicitly by either
relying on the device certificate for wrapping the key in the two-
pass DSKPP Key Wrap Profile (seeSection 3.2.2), or by coupling the
device certificate with the Authentication Code (see below).
3.3.1. Device Identifier
The DSKPP server MAY be pre-configured with a unique device
identifier corresponding to a particular cryptographic module. The
DSKPP server MAY then include this identifier in the DSKPP
initialization trigger, in which case the DSKPP client MUST 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.
3.3.2. Authentication Data
As described in the message flows above (see Section 3.1.1 and
Section 3.2.1), the DSKPP client MAY include Authentication Data (AD)
in its request(s). Note that AD MAY be omitted if client certificate
authentication has been provided by the transport channel such as
TLS. Nonetheless, when AD is provided, the DSKPP server MUST verify
the data before continuing with the protocol run. The DSKPP client
generates AD through derivation of an Authentication Code (AC) as
follows (see Section 3.3.2.2 for details):
AD = HMAC(AC, K)
AC is a one-time use value that is a special form of a shared secret
between a user and the DSKPP server. This secret MUST be made
available to the client before or during DSKPP initiation. Two ways
in which this MAY be done are:
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a. A key issuer may deliver an AC to the user or device in response
to a key request, which the user enters into an application
hosted on their device. For example, a user runs an application
that is resident on their device, e.g., a mobile phone. The
application cannot proceed without a new symmetric key. The user
is redirected to an issuer's Web site from where the user
requests a key. The issuer's Web application processes the
request, and returns an AC, which then appears on the user's
display. The user then invokes a symmetric key-based application
hosted on the device, which asks the user to input the AC using a
keypad. The application invokes the DSKPP client, providing it
with the AC.
b. The provisioning server may send a trigger message,
<KeyProvTrigger>, to the DSKPP client, which and set the value of
the trigger nonce, R_TRIGGER, to AC. When this method is used, a
transport providing privacy and integrity MUST be used to deliver
the DSKPP initialization trigger from the DSKPP server to the
DSKPP client, e.g. HTTPS.
Note that 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.
A description of the AC and how it is used to derive AD is contained
in the sub-sections below.
3.3.2.1. Authentication Code Format
At a minimum, the AC MUST contain the following parameters:
identifier: A globally unique identifier that represents the user's
key request. The MAY be generated as a sequence number.
password: A unique value that SHOULD be generated by the system as a
random number to make AC more difficult to guess.
checksum: The checksum SHOULD be calculated from the remaining
digits in the AC.
The Issuer MUST rely on a Tag-Length-Value (TLV) format to represent
the AC, such as:
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Tag = 0x01 = password
Tag = 0x02 = identifier
Tag = 0x03 = checksum
where one (or two) byte(s) MAY be used to indicate the L(ength) of
the V(alue) field.
3.3.2.2. MAC Calculation
The Authentication Data is a MAC that is derived from AC as follows
(refer to Section 3.4 for a description of DSKPP-PRF in general and
Appendix C for a description of DSKPP-PRF-AES):
MAC = DSKPP-PRF-AES(K_AC, AC->Identifier||URL_S||R_C||[R_S], 16)
In four-pass DSKPP, the cryptographic module uses R_C, R_S, and
URL_S, to calculate the MAC. In two-pass DSKPP, the cryptographic
module does not have access to R_S, therefore only R_C is used in
combination with URL_S to produce the MAC. In either case, K_AC MAY
be derived from AC>password as follows [PKCS-5]:
K_AC = PBKDF2(AC->password, R_C || [K], c, 16)
K MAY be one of the following:
K_CLIENT: The device public key when a device certificate is
available and used for key transport in 2-pass
K_SHARED: The shared key between the client and the server when it
is used for key wrap in two-pass or for R_C protection in four-
pass
K_DERIVED: When a passphrase-derived key is used for key wrap in
two-pass DSKPP.
Finally, c is iteration count between 10 and 1000.
3.4. The DSKPP One-Way Pseudorandom Function, DSKPP-PRF
3.4.1. Introduction
All of the protocol variations depend on DSKPP-PRF. The general
requirements on DSKPP-PRF are the same as on keyed hash functions: It
MUST take an arbitrary length input, and be one-way and collision-
free (for a definition of these terms, see, e.g., [FAQ]). Further,
the DSKPP-PRF function MUST be capable of generating a variable-
length output, and its output MUST be unpredictable even if other
outputs for the same key are known.
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It is assumed that any realization of DSKPP-PRF takes three input
parameters: A secret key k, some combination of variable data, and
the desired length of the output. The combination of variable data
can, without loss of generalization, be considered as a salt value
(see PKCS#5 Version 2.0 [PKCS-5], Section 4), and this
characterization of DSKPP-PRF SHOULD fit all actual PRF algorithms
implemented by cryptographic modules. From the point of view of this
specification, DSKPP-PRF is a "black-box" function that, given the
inputs, generates a pseudorandom value.
Separate specifications MAY define the implementation of DSKPP-PRF
for various types of cryptographic modules. Appendix C contains two
example realizations of DSKPP-PRF.
3.4.2. Declaration
DSKPP-PRF (k, s, dsLen)
Input:
k secret key in octet string format
s octet string of varying length consisting of variable data
distinguishing the particular string being derived
dsLen desired length of the output
Output:
DS pseudorandom string, dsLen-octets long
For the purposes of this document, the secret key k MUST be at least
16 octets long.
3.5. 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)
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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:
E(DS, R_C) = DS ^ R_C
The DSKPP server will then perform the reverse operation to extract
R_C from E(DS, R_C).
4. DSKPP Message Formats
The message formats from the DSKPP XML schema, found in Section 7,
are explained in this section. Examples can be found in Appendix A.
The XML format for DSKPP messages have been designed to be
extensible. However, it is possible that the use of extensions will
harm interoperability; therefore, any use of extensions SHOULD be
carefully considered. For example, if a particular implementation
relies on the presence of a proprietary extension, then it may not be
able to interoperate with independent implementations that have no
knowledge of this extension.
4.1. General XML Schema Requirements
Some DSKPP elements rely on the parties being able to compare
received values with stored values. Unless otherwise noted, all
elements in this document that have the XML Schema "xs:string" type,
or a type derived from it, MUST be compared using an exact binary
comparison. In particular, DSKPP implementations MUST NOT depend on
case-insensitive string comparisons, normalization or trimming of
white space, or conversion of locale-specific formats such as
numbers.
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.
4.2. Components of the <KeyProvTrigger> Message
The DSKPP server MAY initialize the DSKPP protocol by sending a
<KeyProvTrigger> message. This message MAY, e.g., be sent in
response to a user requesting key initialization in a browsing
session.
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<xs:element name="KeyProvTrigger" type="dskpp:KeyProvTriggerType">
</xs:element>
<xs:complexType name="KeyProvTriggerType">
<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>
<xs:complexType name="InitializationTriggerType">
<xs:sequence>
<xs:element minOccurs="0" name="DeviceIdentifierData"
type="dskpp:DeviceIdentifierDataType" />
<xs:element minOccurs="0" name="KeyID" type="xs:base64Binary" />
<xs:element minOccurs="0" name="TokenPlatformInfo"
type="dskpp:TokenPlatformInfoType" />
<xs:element name="TriggerNonce" type="dskpp:NonceType" />
<xs:element minOccurs="0" name="ServerUrl" type="xs:anyURI" />
<xs:any minOccurs="0" namespace="##other"
processContents="strict" />
</xs:sequence>
</xs:complexType>
The <KeyProvTrigger> element is intended for the DSKPP client and MAY
inform the DSKPP client about the identifier for the device that
houses the cryptographic module to be initialized, and optionally of
the identifier for the key on that module. The latter would apply to
key renewal. The trigger always contains a nonce to allow the DSKPP
server to couple the trigger with a later DSKPP <KeyProvClientHello>
request. Finally, the trigger MAY contain a URL to use when
contacting the DSKPP server. The <xs:any> elements are for future
extensibility. Any provided <DeviceIdentifierData> or <KeyID> values
MUST be used by the DSKPP client in the subsequent
<KeyProvClientHello> request. The OPTIONAL <TokenPlatformInfo>
element informs the DSKPP client about the characteristics of the
intended cryptographic module platform, and applies in the public-key
variant of DSKPP in situations when the client potentially needs to
decide which one of several modules to initialize.
4.3. Components of the <KeyProvClientHello> Request
This message is the initial message sent from the DSKPP client to the
DSKPP server in both variants of the DSKPP.
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<xs:element name="KeyProvClientHello"
type="dskpp:KeyProvClientHelloPDU">
</xs:element>
<xs:complexType name="KeyProvClientHelloPDU">
<xs:complexContent mixed="false">
<xs:extension base="dskpp:AbstractRequestType">
<xs:sequence>
<xs:element minOccurs="0" name="DeviceIdentifierData"
type="dskpp:DeviceIdentifierDataType" />
<xs:element minOccurs="0" name="KeyID"
type="xs:base64Binary" />
<xs:element minOccurs="0" name="ClientNonce"
type="dskpp:NonceType" />
<xs:element minOccurs="0" name="TriggerNonce"
type="dskpp:NonceType" />
<xs:element name="SupportedKeyTypes"
type="dskpp:AlgorithmsType" />
<xs:element name="SupportedEncryptionAlgorithms"
type="dskpp:AlgorithmsType" />
<xs:element name="SupportedMacAlgorithms"
type="dskpp:AlgorithmsType" />
<xs:element minOccurs="0" name="SupportedProtocolVariants"
type="dskpp:ProtocolVariantsType" />
<xs:element minOccurs="0" name="SupportedKeyContainers"
type="dskpp:KeyContainersFormatType" />
<xs:element minOccurs="0" name="AuthenticationData"
type="dskpp:AuthenticationDataType" />
<xs:element minOccurs="0" name="Extensions"
type="dskpp:ExtensionsType" />
</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 3.3 above. The identifier MUST only be
present if such shared secrets exist or if the identifier was
provided by the server in a <KeyProvTrigger> element (see
Section 6.2.7). In the latter case, it MUST have the same value
as the identifier provided in that element.
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o <KeyID>: An identifier for the key that will be overwritten if the
protocol run is successful. The identifier MUST only be present
if the key exists or if the identifier was provided by the server
in a <KeyProvTrigger> element, in which case, it MUST have the
same value as the identifier provided in that element (see a
(Section 4.2) and Section 6.2.7).
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 <KeyProvTrigger> message
(see Section 6.2.7), and MUST, in that case, have the same value
as the <TriggerNonce> child of that message. A server using
nonces in this way MUST verify that the nonce is valid and that
any device or key identifier values provided in the
<KeyProvTrigger> message match the corresponding identifier values
in the <KeyProvClientHello> message.
o <SupportedKeyTypes>: A sequence of URLs indicating the key types
for which the cryptographic module is willing to generate keys
through DSKPP.
o <SupportedEncryptionAlgorithms>: A sequence of URLs 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 URLs 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.,
http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes, which is defined
in Appendix C).
o <SupportedProtocolVariants>: This OPTIONAL element is used by the
DSKPP client to indicate support for four-pass or two-pass DSKPP.
If two-pass support is specified, then <KeyProvClientNonce> MUST
be set to nonce R in the <KeyProvClientHello> message unless
<TriggerNonce> is already present.
o <SupportedKeyContainers>: This OPTIONAL element is a sequence of
URLs 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.ietf.org/keyprov/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 3.3.
o <Extensions>: A sequence of extensions. One extension is defined
for this mesolsage in this version of DSKPP: the ClientInfoType
(see Section 5).
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Some of the core elements of the message are described below.
4.3.1. The DeviceIdentifierDataType Type
The DeviceIdentifierDataType type is used to uniquely identify the
device that houses the cryptographic module, e.g., a mobile phone.
The device identifier allows the DSKPP server to find, e.g., a pre-
shared transport key for 2-pass DSKPP and/or the correct shared
secret for MAC'ing purposes. The default DeviceIdentifierDataType is
defined in [PSKC].
<xs:complexType name="DeviceIdentifierDataType">
<xs:choice>
<xs:element name="DeviceId" type="pskc:DeviceIdType" />
<xs:any namespace="##other" processContents="strict" />
</xs:choice>
</xs:complexType>
4.3.2. The ProtocolVariantsType Type
The ProtocolVariantsType type is OPTIONAL for a DSKPP client, who MAY
use it to indicate the number of passes of the DSKPP protocol that it
supports. The ProtocolVariantsType MAY be used to indicate support
for 4-pass or 2-pass DSKPP. If the ProtocolVariantsType is not used,
then the DSKPP server will proceed with ordinary 4-pass DSKPP.
However, if it does not support 4-pass DSKPP, then the server MUST
find a suitable two-pass variation or else the protocol run will
fail.
Selecting the "TwoPass" element signals client support for the 2-pass
version of DSKPP, informs the server of supported two-pass key
protection methods, 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 thekey
protection method with which the payload is associated.
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<xs:complexType name="ProtocolVariantsType">
<xs:sequence>
<xs:element minOccurs="0" name="FourPass" />
<xs:element minOccurs="0" name="TwoPass"
type="dskpp:KeyProtectionDataType"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="KeyProtectionDataType">
<xs:complexContent mixed="false">
<xs:sequence maxOccurs="unbounded">
<xs:element name="SupportedKeyProtectionMethod" type="xs:anyURI"/>
<xs:element name="Payload" type="dskpp:PayloadType"
</xs:sequence>
</xs:complexContent>
</xs:complexType>
The elements of this type have the following meaning:
o <SupportedKeyProtectionMethod>: A two-pass key protection 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
protection method.
A DSKPP client that indicates support for two-pass DSKPP MUST also
include the nonce R in its <KeyProvClientHello> message (this will
enable the client to verify that the DSKPP server it is communicating
with is alive).
4.3.3. The KeyContainersFormatType Type
The OPTIONAL KeyContainersFormatType type is a list of type-value
pairs that a DSKPP client or server MAY use to define key container
formats it supports. Key container formats are identified through
URLs, e.g., the PSKC KeyContainer URL
"http://www.ietf.org/keyprov/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>
4.3.4. The AuthenticationDataType Type
The OPTIONAL AuthenticationDataType type is used by DSKPP clients and
server to carry authentication values in DSKPP messages. The element
MAY contain a MAC derived from an authentication code as follows:
a. A DSKPP client MAY include a one-time use AuthenticationCode that
was given by the issuer to the user for acquiring a symmetric
key. An AuthenticationCode MAY contain alphanumeric characters
in addition to numeric digits depending on the device type and
policy of the issuer. For example, if the device is a mobile
phone, a code that the user enters on the keypad would typically
be restricted to numeric digits for ease of use. An
authentication code MAY be sent to the DSKPP server as MAC data
calculated according to section Section 3.3.2.
b. A DSKPP server MAY use the AuthenticationDataType element
AuthenticationCodeMac to carry a MAC for authenticating itself to
the client. For example, when a successful 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 minOccurs="0" name="ClientID"
type="dskpp:IdentifierType" />
<xs:element name="AuthenticationCodeMac"
type="dskpp:AuthenticationCodeMacType" />
</xs:sequence>
</xs:complexType>
<xs:complexType name="AuthenticationCodeMacType">
<xs:sequence>
<xs:element minOccurs="0" name="Nonce" type="dskpp:NonceType" />
<xs:element minOccurs="0" name="IterationCount" type="xs:int" />
<xs:element name="Mac" type="dskpp:MacType" />
</xs:sequence>
</xs:complexType>
The elements of the AuthenticationDataType type have the following
meaning:
o <ClientID>: A requester's identifier. The value MAY be a user ID,
a device ID, or a keyID associated with the requester's
authentication value. Ifa <KeyProvTrigger> message was provided
by the server to initiate the DSKPP protocol run, <ClientID> can
be omitted, as the DeviceID, KeyID, and/or nonce provided in the
<InitializationTriggerType> element ought to be sufficient to
identify the requester.
o <AuthenticationCodeMac>: An authentication MAC and additional
information (e.g., MAC algorithm). This MAC MAY be derived as
follows:
* User Authentication: 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 contain
alphanumeric characters in addition to numeric digits depending
on the device type and policy of the issuer. For example, if
the device is a mobile phone, a code that the user enters on
the keypad would typically be restricted to numeric digits for
ease of use. An authentication code MAY be sent to the DSKPP
server as MAC data calculated as described in section
Section 3.3.2.
* Server Authorization (two-pass DSKPP only): A DSKPP server MUST
include a MAC in its <KeyProvServerFinished> message as proof
that the DSKPP server is authorized to provide a new key to the
cryptographic module. For example, when a successful 2-pass
DSKPP protocol run will result in an existing key being
replaced, then the DSKPP server MUST include the
AuthenticationDataType element's AuthenticationCodeMac in its
<KeyProvServerFinished> message. For more information, refer
to Section 3.2.3.2.
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4.4. Components of the <KeyProvServerHello> Response (Used Only in
Four-Pass DSKPP)
In a four-pass exchange, this message is the first message sent from
the DSKPP server to the DSKPP client (assuming a trigger message has
not been sent to initiate the protocol, in which case, this message
is the second message sent from the DSKPP server to the DSKPP
client). It is sent upon reception of a <KeyProvClientHello>
message.
<xs:element name="KeyProvServerHello"
type="dskpp:KeyProvServerHelloPDU">
</xs:element>
<xs:complexType name="KeyProvServerHelloPDU">
<xs:complexContent mixed="false">
<xs:extension base="dskpp:AbstractResponseType">
<xs:sequence minOccurs="0">
<xs:element name="KeyType" type="dskpp:AlgorithmType" />
<xs:element name="EncryptionAlgorithm"
type="dskpp:AlgorithmType" />
<xs:element name="MacAlgorithm" type="dskpp:AlgorithmType" />
<xs:element name="EncryptionKey" type="ds:KeyInfoType" />
<xs:element name="KeyContainerFormat"
type="dskpp:KeyContainerFormatType" />
<xs:element name="Payload" type="dskpp:PayloadType" />
<xs:element minOccurs="0" name="Extensions"
type="dskpp:ExtensionsType" />
<xs:element minOccurs="0" name="Mac" type="dskpp:MacType" />
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
The components of this message have the following meaning:
o Version: (attribute inherited from the AbstractResponseType type)
The version selected by the DSKPP server. MAY be lower than the
version indicated by the DSKPP client, in which case, local policy
at the client MUST determine whether or not to continue the
session.
o SessionID: (attribute inherited from the AbstractResponseType
type) An identifier for this session.
o Status: (attribute inherited from the AbstractResponseType type)
Return code for the <KeyProvClientHello>. If Status is not
"Continue", only the Status and Version attributes will be
present; otherwise, all the other element MUST be present as well.
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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 5).
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.
4.5. Components of a <KeyProvClientNonce> Request (Used Only in Four-
Pass DSKPP)
In a four-pass DSKPP exchange, this message contains the nonce R_C
that was chosen by the cryptographic module, and encrypted by the
negotiated encryption key and encryption algorith
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<xs:element name="KeyProvClientNonce"
type="dskpp:KeyProvClientNoncePDU">
</xs:element>
<xs:complexType name="KeyProvClientNoncePDU">
<xs:complexContent mixed="false">
<xs:extension base="dskpp:AbstractRequestType">
<xs:sequence>
<xs:element name="EncryptedNonce" type="xs:base64Binary" />
<xs:element minOccurs="0" name="AuthenticationData"
type="dskpp:AuthenticationDataType" />
<xs:element minOccurs="0" name="Extensions"
type="dskpp:ExtensionsType" />
</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 <KeyProvServerHello> message.
o <SessionID>: (attribute inherited from the AbstractResponseType
type) MUST have the same value as the SessionID attribute in the
received <KeyProvServerHello> message.
o <EncryptedNonce>: The nonce generated and encrypted by the
cryptographic module. The encryption MUST be made using the
selected encryption algorithm and identified key, and as specified
in Section 3.4.
o <AuthenticationData>: The authentication data value MUST be set as
specified in Section 3.3 and Section 4.3.4.
o <Extensions>: A list of extensions. Two extensions are defined
for this message in this version of DSKPP: the ClientInfoType and
the ServerInfoType (see Section 5)
4.6. Components of a <KeyProvServerFinished> Response
This message is the last message of the DSKPP protocol run. In a
4-pass exchange, the DSKPP server sends this message in response to a
<KeyProvClientNonce> message, whereas in a 2-pass exchange, the DSKPP
server sends this message in response to a <KeyProvClientHello>
message.
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<xs:element name="KeyProvServerFinished"
type="dskpp:KeyProvServerFinishedPDU">
</xs:element>
<xs:complexType name="KeyProvServerFinishedPDU">
<xs:complexContent mixed="false">
<xs:extension base="dskpp:AbstractResponseType">
<xs:sequence minOccurs="0">
<xs:element name="KeyContainer"
type="dskpp:KeyContainerType" />
<xs:element minOccurs="0" name="Extensions"
type="dskpp:ExtensionsType" />
<xs:element name="Mac" type="dskpp:MacType" />
<xs:element minOccurs="0" name="AuthenticationData"
type="dskpp:AuthenticationDataType" />
</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 <KeyProvServerFinished> message. If Status is not
"Success", only the Status, SessionID, and Version attributes will
be present (the presence of the SessionID attribute is dependent
on the type of reported error); otherwise, all the other elements
MUST be present as well. In this latter case, the
<KeyProvServerFinished> message can be seen as a "Commit" message,
instructing the cryptographic module to store the generated key
and associate the given key identifier with this key.
o <KeyContainer>: The key container containing symmetric key values
(in the case of a 2-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 5).
o <Mac>: To avoid a false "Commit" message causing the cryptographic
module to end up in an initialized state for which the server does
not know the stored key, <KeyProvServerFinished> messages MUST
always be authenticated with a MAC. The MAC MUST be made using
the already established MAC algorithm.
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4.7. The StatusCode Type
The StatusCode type enumerates all possible return codes:
<xs:simpleType name="StatusCode">
<xs:restriction base="xs:string">
<xs:enumeration value="Continue" />
<xs:enumeration value="Success" />
<xs:enumeration value="Abort" />
<xs:enumeration value="AccessDenied" />
<xs:enumeration value="MalformedRequest" />
<xs:enumeration value="UnknownRequest" />
<xs:enumeration value="UnknownCriticalExtension" />
<xs:enumeration value="UnsupportedVersion" />
<xs:enumeration value="NoSupportedKeyTypes" />
<xs:enumeration value="NoSupportedEncryptionAlgorithms" />
<xs:enumeration value="NoSupportedMacAlgorithms" />
<xs:enumeration value="NoProtocolVariants" />
<xs:enumeration value="NoSupportedKeyContainers" />
<xs:enumeration value="AuthenticationDataMissing" />
<xs:enumeration value="AuthenticationDataInvalid" />
<xs:enumeration value="InitializationFailed" />
</xs:restriction>
</xs:simpleType>
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.
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o "Abort" indicates that the DSKPP server rejected the DSKPP
client's request for unspecified reasons.
o "AccessDenied" indicates that the DSKPP client is not authorized
to contact this DSKPP server.
o "MalformedRequest" indicates that the DSKPP server failed to parse
the DSKPP client's request.
o "UnknownRequest" indicates that the DSKPP client made a request
that is unknown to the DSKPP server.
o "UnknownCriticalExtension" indicates that a critical DSKPP
extension (see below) used by the DSKPP client was not supported
or recognized by the DSKPP server.
o "UnsupportedVersion" indicates that the DSKPP client used a DSKPP
protocol version not supported by the DSKPP server. This error is
only valid in the DSKPP server's first response message.
o "NoSupportedKeyTypes" indicates that the DSKPP client only
suggested key types that are not supported by the DSKPP server.
This error is only valid in the DSKPP server's first response
message.
o "NoSupportedEncryptionAlgorithms" indicates that the DSKPP client
only suggested encryption algorithms that are not supported by the
DSKPP server. This error is only valid in the DSKPP server's
first response message.
o "NoSupportedMacAlgorithms" indicates that the DSKPP client only
suggested MAC algorithms that are not supported by the DSKPP
server. This error is only valid in the DSKPP server's first
response message.
o "NoProtocolVariants" indicates that the DSKPP client only
suggested a protocol variation (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.
o "NoSupportedKeyContainers" indicates that the DSKPP client only
suggested key container formats that are not supported by the
DSKPP server. This error is only valid in the DSKPP server's
first response message.
o "AuthenticationDataMissing" indicates that the DSKPP client didn't
provide authentication data that the DSKPP server required.
o "AuthenticationDataInvalid" indicates that the DSKPP client
supplied user authentication data that the DSKPP server failed to
validate.
o "InitializationFailed" indicates that the DSKPP server could not
generate a valid key given the provided data. When this status
code is received, the DSKPP client SHOULD try to restart DSKPP, as
it is possible that a new run will succeed.
o "ProvisioningPeriodExpired" indicates that the provisioning period
set by the DSKPP server has expired. When the status code is
received, the DSKPP client SHOULD report the reason for key
initialization failure to the user and the user MUST register with
the DSKPP server to initialize a new key.
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5. Extensibility
5.1. The ClientInfoType Type
Present in a <KeyProvClientHello> or a <KeyProvClientNonce> message,
the OPTIONAL ClientInfoType extension contains DSKPP client-specific
information. DSKPP servers MUST support this extension. DSKPP
servers MUST NOT attempt to interpret the data it carries and, if
received, MUST include it unmodified in the current protocol run's
next server response. Servers need not retain the ClientInfoType's
data after that response has been generated.
5.2. The ServerInfoType Type
When present, the OPTIONAL ServerInfoType extension contains DSKPP
server-specific information. This extension is only valid in
<KeyProvServerHello> messages for which Status = "Continue". DSKPP
clients MUST support this extension. DSKPP clients MUST NOT attempt
to interpret the data it carries and, if received, MUST include it
unmodified in the current protocol run's next client request (i.e.,
the <KeyProvClientNonce> message). DSKPP clients need not retain the
ServerInfoType's data after that request has been generated. This
extension MAY be used, e.g., for state management in the DSKPP
server.
6. Protocol Bindings
6.1. General Requirements
DSKPP assumes a reliable transport.
6.2. HTTP/1.1 Binding for DSKPP
6.2.1. 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.
6.2.2. Identification of DSKPP Messages
The MIME-type for all DSKPP messages MUST be
application/vnd.ietf.keyprov.dskpp+xml
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6.2.3. 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 6.2.2.
6.2.4. 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.
6.2.5. HTTP Status Codes
A DSKPP HTTP responder that refuses to perform a message exchange
with a DSKPP HTTP requester SHOULD return a 403 (Forbidden) response.
In this case, the content of the HTTP body is not significant. In
the case of an HTTP error while processing a DSKPP request, the HTTP
server MUST return a 500 (Internal Server Error) response. This type
of error SHOULD be returned for HTTP-related errors detected before
control is passed to the DSKPP processor, or when the DSKPP processor
reports an internal error (for example, the DSKPP XML namespace is
incorrect, or the DSKPP schema cannot be located). If the type of a
DSKPP request cannot be determined, the DSKPP responder MUST return a
400 (Bad request) response.
In these cases (i.e., when the HTTP response code is 4xx or 5xx), the
content of the HTTP body is not significant.
Redirection status codes (3xx) apply as usual.
Whenever the HTTP POST is successfully invoked, the DSKPP HTTP
responder MUST use the 200 status code and provide a suitable DSKPP
message (possibly with DSKPP error information included) in the HTTP
body.
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6.2.6. HTTP Authentication
No support for HTTP/1.1 authentication is assumed.
6.2.7. Initialization of DSKPP
The DSKPP server MAY initialize the DSKPP protocol by sending an HTTP
response with Content-Type set according to Section 6.2.2 and
response code set to 200 (OK). This message MAY, e.g., be sent in
response to a user requesting key initialization in a browsing
session. The initialization message MAY carry data in its body. If
this is the case, the data MUST be a valid instance of a
<KeyProvTrigger> element.
6.2.8. 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>
DSKPP data in XML form (server random nonce, server public key,
...)
7. DSKPP Schema
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<?xml version="1.0" encoding="utf-8"?>
<xs:schema
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container:1.0"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
elementFormDefault="qualified" attributeFormDefault="unqualified"
targetNamespace="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
version="1.0">
<xs:import namespace="http://www.w3.org/2000/09/xmldsig#"
schemaLocation="http://www.w3.org/TR/2002/REC-xmldsig-core-20020212/
xmldsig-core-schema.xsd"/>
<xs:import namespace="urn:ietf:params:xml:ns:keyprov:container:1.0"
schemaLocation="keyprov-pskc-1.0.xsd"/>
<xs:complexType name="AbstractRequestType" abstract="true">
<xs:annotation>
<xs:documentation> Basic types </xs:documentation>
</xs:annotation>
<xs:attribute name="Version" type="dskpp:VersionType"
use="required"/>
</xs:complexType>
<xs:complexType name="AbstractResponseType" abstract="true">
<xs:annotation>
<xs:documentation> Basic types </xs:documentation>
</xs:annotation>
<xs:attribute name="Version" type="dskpp:VersionType"
use="required"/>
<xs:attribute name="SessionID" type="dskpp:IdentifierType" />
<xs:attribute name="Status" type="dskpp:StatusCode" use="required"/>
</xs:complexType>
<xs:simpleType name="VersionType">
<xs:restriction base="xs:string">
<xs:pattern value="\d{1,2}\.\d{1,3}" />
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="IdentifierType">
<xs:restriction base="xs:string">
<xs:maxLength value="128" />
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="StatusCode">
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<xs:restriction base="xs:string">
<xs:enumeration value="Continue" />
<xs:enumeration value="Success" />
<xs:enumeration value="Abort" />
<xs:enumeration value="AccessDenied" />
<xs:enumeration value="MalformedRequest" />
<xs:enumeration value="UnknownRequest" />
<xs:enumeration value="UnknownCriticalExtension" />
<xs:enumeration value="UnsupportedVersion" />
<xs:enumeration value="NoSupportedKeyTypes" />
<xs:enumeration value="NoSupportedEncryptionAlgorithms" />
<xs:enumeration value="NoSupportedMacAlgorithms" />
<xs:enumeration value="NoProtocolVariants" />
<xs:enumeration value="NoSupportedKeyContainers" />
<xs:enumeration value="AuthenticationDataMissing" />
<xs:enumeration value="AuthenticationDataInvalid" />
<xs:enumeration value="InitializationFailed" />
</xs:restriction>
</xs:simpleType>
<xs:complexType name="DeviceIdentifierDataType">
<xs:choice>
<xs:element name="DeviceId" type="pskc:DeviceIdType" />
<xs:any namespace="##other" processContents="strict" />
</xs:choice>
</xs:complexType>
<xs:simpleType name="PlatformType">
<xs:restriction base="xs:string">
<xs:enumeration value="Hardware" />
<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">
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<xs:element name="Algorithm" type="dskpp:AlgorithmType" />
</xs:sequence>
</xs:complexType>
<xs:simpleType name="AlgorithmType">
<xs:restriction base="xs:anyURI" />
</xs:simpleType>
<xs:complexType name="ProtocolVariantsType">
<xs:sequence>
<xs:element minOccurs="0" name="FourPass" />
<xs:element minOccurs="0" name="TwoPass"
type="dskpp:KeyProtectionDataType"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="KeyProtectionDataType">
<xs:annotation>
<xs:documentation xml:lang="en">
This element is only valid for two-pass DSKPP.
</xs:documentation>
</xs:annotation>
<xs:complexContent mixed="false">
<xs:sequence maxOccurs="unbounded">
<xs:element name="SupportedKeyProtectionMethod" type="xs:anyURI"/>
<xs:element name="Payload" type="dskpp:PayloadType" />
</xs:sequence>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="PayloadType">
<xs:choice>
<xs:element name="Nonce" type="dskpp:NonceType" />
<xs:any namespace="##other" processContents="strict" />
</xs:choice>
</xs:complexType>
<xs:complexType name="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">
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<xs:annotation>
<xs:documentation xml:lang="en">
Authentication data contains a MAC.
</xs:documentation>
</xs:annotation>
<xs:sequence>
<xs:element minOccurs="0" name="ClientID"
type="dskpp:IdentifierType" />
<xs:element name="AuthenticationCodeMac"
type="dskpp:AuthenticationCodeMacType" />
</xs:sequence>
</xs:complexType>
<xs:complexType name="AuthenticationCodeMacType">
<xs:annotation>
<xs:documentation xml:lang="en">
An authentication MAC calculated from an authentication code and
optionally server information as well as nonce value if they are
available.
</xs:documentation>
</xs:annotation>
<xs:sequence>
<xs:element minOccurs="0" name="Nonce" type="dskpp:NonceType" />
<xs:element minOccurs="0" name="IterationCount" type="xs:int" />
<xs:element name="Mac" type="dskpp:MacType" />
</xs:sequence>
</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:sequence>
<xs:element minOccurs="0" name="ServerID" type="xs:anyURI" />
<xs:element minOccurs="0" name="KeyProtectionMethod" type="xs:anyURI" />
<xs:choice>
<xs:element name="KeyContainer" type="pskc:KeyContainerType" />
<xs:any namespace="##other" processContents="strict" />
</xs:choice>
</xs:sequence>
</xs:complexType>
<xs:complexType name="InitializationTriggerType">
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<xs:sequence>
<xs:element minOccurs="0" name="DeviceIdentifierData"
type="dskpp:DeviceIdentifierDataType" />
<xs:element minOccurs="0" name="KeyID" type="xs:base64Binary" />
<xs:element minOccurs="0" name="TokenPlatformInfo"
type="dskpp:TokenPlatformInfoType" />
<xs:element name="TriggerNonce" type="dskpp:NonceType" />
<xs:element minOccurs="0" name="ServerUrl" type="xs:anyURI" />
<xs:any minOccurs="0" namespace="##other"
processContents="strict" />
</xs:sequence>
</xs:complexType>
<xs:complexType name="ExtensionsType">
<xs:annotation>
<xs:documentation> Extension types </xs:documentation>
</xs:annotation>
<xs:sequence maxOccurs="unbounded">
<xs:element name="Extension" type="dskpp:AbstractExtensionType" />
</xs:sequence>
</xs:complexType>
<xs:complexType name="AbstractExtensionType" abstract="true">
<xs:attribute name="Critical" type="xs:boolean" />
</xs:complexType>
<xs:complexType name="ClientInfoType">
<xs:complexContent mixed="false">
<xs:extension base="dskpp:AbstractExtensionType">
<xs:sequence>
<xs:element name="Data" type="xs:base64Binary" />
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="ServerInfoType">
<xs:complexContent mixed="false">
<xs:extension base="dskpp:AbstractExtensionType">
<xs:sequence>
<xs:element name="Data" type="xs:base64Binary" />
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:element name="KeyProvTrigger" type="dskpp:KeyProvTriggerType">
<xs:annotation>
<xs:documentation> DSKPP PDUs </xs:documentation>
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</xs:annotation>
</xs:element>
<xs:complexType name="KeyProvTriggerType">
<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>
<xs:element name="KeyProvClientHello"
type="dskpp:KeyProvClientHelloPDU">
<xs:annotation>
<xs:documentation> KeyProvClientHello PDU </xs:documentation>
</xs:annotation>
</xs:element>
<xs:complexType name="KeyProvClientHelloPDU">
<xs:annotation>
<xs:documentation xml:lang="en">
Message sent from DSKPP client to DSKPP server to initiate a
DSKPP session.
</xs:documentation>
</xs:annotation>
<xs:complexContent mixed="false">
<xs:extension base="dskpp:AbstractRequestType">
<xs:sequence>
<xs:element minOccurs="0" name="DeviceIdentifierData"
type="dskpp:DeviceIdentifierDataType" />
<xs:element minOccurs="0" name="KeyID"
type="xs:base64Binary" />
<xs:element minOccurs="0" name="ClientNonce"
type="dskpp:NonceType" />
<xs:element minOccurs="0" name="TriggerNonce"
type="dskpp:NonceType" />
<xs:element name="SupportedKeyTypes"
type="dskpp:AlgorithmsType" />
<xs:element name="SupportedEncryptionAlgorithms"
type="dskpp:AlgorithmsType" />
<xs:element name="SupportedMacAlgorithms"
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type="dskpp:AlgorithmsType" />
<xs:element minOccurs="0" name="SupportedProtocolVariants"
type="dskpp:ProtocolVariantsType" />
<xs:element minOccurs="0" name="SupportedKeyContainers"
type="dskpp:KeyContainersFormatType" />
<xs:element minOccurs="0" name="AuthenticationData"
type="dskpp:AuthenticationDataType" />
<xs:element minOccurs="0" name="Extensions"
type="dskpp:ExtensionsType" />
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:element name="KeyProvServerHello"
type="dskpp:KeyProvServerHelloPDU">
<xs:annotation>
<xs:documentation> KeyProvServerHello PDU </xs:documentation>
</xs:annotation>
</xs:element>
<xs:complexType name="KeyProvServerHelloPDU">
<xs:annotation>
<xs:documentation xml:lang="en">
Response message sent from DSKPP server to DSKPP client
in four-pass DSKPP.
</xs:documentation>
</xs:annotation>
<xs:complexContent mixed="false">
<xs:extension base="dskpp:AbstractResponseType">
<xs:sequence minOccurs="0">
<xs:element name="KeyType" type="dskpp:AlgorithmType" />
<xs:element name="EncryptionAlgorithm"
type="dskpp:AlgorithmType" />
<xs:element name="MacAlgorithm" type="dskpp:AlgorithmType" />
<xs:element name="EncryptionKey" type="ds:KeyInfoType" />
<xs:element name="KeyContainerFormat"
type="dskpp:KeyContainerFormatType" />
<xs:element name="Payload" type="dskpp:PayloadType" />
<xs:element minOccurs="0" name="Extensions"
type="dskpp:ExtensionsType" />
<xs:element minOccurs="0" name="Mac" type="dskpp:MacType" />
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:element name="KeyProvClientNonce"
type="dskpp:KeyProvClientNoncePDU">
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<xs:annotation>
<xs:documentation> KeyProvClientNonce PDU </xs:documentation>
</xs:annotation>
</xs:element>
<xs:complexType name="KeyProvClientNoncePDU">
<xs:annotation>
<xs:documentation xml:lang="en">
Response message sent from DSKPP client to
DSKPP server in a four-pass DSKPP session.
</xs:documentation>
</xs:annotation>
<xs:complexContent mixed="false">
<xs:extension base="dskpp:AbstractRequestType">
<xs:sequence>
<xs:element name="EncryptedNonce" type="xs:base64Binary" />
<xs:element minOccurs="0" name="AuthenticationData"
type="dskpp:AuthenticationDataType" />
<xs:element minOccurs="0" name="Extensions"
type="dskpp:ExtensionsType" />
</xs:sequence>
<xs:attribute name="SessionID" type="dskpp:IdentifierType"
use="required" />
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:element name="KeyProvServerFinished"
type="dskpp:KeyProvServerFinishedPDU">
<xs:annotation>
<xs:documentation> KeyProvServerFinished PDU </xs:documentation>
</xs:annotation>
</xs:element>
<xs:complexType name="KeyProvServerFinishedPDU">
<xs:annotation>
<xs:documentation xml:lang="en">
Final message sent from DSKPP server to DSKPP client in a DSKPP
session. A MAC value serves for key confirmation, and optional
AuthenticationData serves for server authentication.
</xs:documentation>
</xs:annotation>
<xs:complexContent mixed="false">
<xs:extension base="dskpp:AbstractResponseType">
<xs:sequence minOccurs="0">
<xs:element name="KeyContainer"
type="dskpp:KeyContainerType" />
<xs:element minOccurs="0" name="Extensions"
type="dskpp:ExtensionsType" />
<xs:element name="Mac" type="dskpp:MacType" />
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<xs:element minOccurs="0" name="AuthenticationData"
type="dskpp:AuthenticationDataType" />
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
</xs:schema>
8. Conformance Requirements
In order to assure that all implementations of DSKPP can
interoperate, there are the following "MUST support" requirements"
The conformance requirements for the DSKPP server consist of the
following:
a. MUST implement the four-pass variant of the protocol
(Section 3.1)
b. MUST implement the two-pass variant of the protocol (Section 3.2)
c. MUST support user authentication (Section 3.3)
d. MUST support the Key Transport, Key Wrap, and Passphrase-Based
Key Wrap Protection Profiles (Section 3.2.2)
e. MUST support the DSKPP-PRF-AES DSKPP-PRF realization (Appendix C)
f. MUST support the DSKPP-PRF-SHA256 DSKPP-PRF realization
(Appendix C)
g. MAY support the RSA Encryption Scheme ([PKCS-1])
h. MAY support DSKPP-PRF with XOR (Section 3.5)
i. SHOULD support integration with PKCS #11 in four-pass DSKPP
(Appendix B)
The conformance requirements for the DSKPP client consist of the
following:
a. MUST implement the four-pass variant of the protocol
(Section 3.1)
b. MUST implement the two-pass variant of the protocol (Section 3.2)
c. MUST support user authentication (Section 3.3)
d. MUST support the Key Transport, Key Wrap, and Passphrase-Based
Key Wrap Protection Profiles (Section 3.2.2)
e. MUST support the DSKPP-PRF-AES DSKPP-PRF realization (Appendix C)
f. MUST support the DSKPP-PRF-SHA256 DSKPP-PRF realization
(Appendix C)
g. MAY support the RSA Encryption Scheme ([PKCS-1])
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h. MAY support DSKPP-PRF with XOR (Section 3.5)
i. SHOULD support integration with PKCS #11 in four-pass DSKPP
(Appendix B)
Of course, DSKPP is a security protocol, and one of its major
functions is to allow only authorized parties to successfully
initialize a cryptographic module with a new symmetric key.
Therefore, a particular implementation may be configured with any of
a number of restrictions concerning algorithms and trusted
authorities that will prevent universal interoperability.
9. Security Considerations
9.1. General
DSKPP is designed to protect generated key material from exposure.
No other entities than the DSKPP server and the cryptographic module
will have access to a generated K_TOKEN if the cryptographic
algorithms used are of sufficient strength and, on the DSKPP client
side, generation and encryption of R_C and generation of K_TOKEN take
place as specified in the cryptographic module. This applies even if
malicious software is present in the DSKPP client. However, as
discussed in the following, DSKPP does not protect against certain
other threats resulting from man-in-the-middle attacks and other
forms of attacks. DSKPP SHOULD, therefore, be run over a transport
providing privacy and integrity, such as HTTP over Transport Layer
Security (TLS) with a suitable ciphersuite, when such threats are a
concern. Note that TLS ciphersuites with anonymous key exchanges are
not suitable in those situations.
9.2. Active Attacks
9.2.1. Introduction
An active attacker MAY attempt to modify, delete, insert, replay, or
reorder messages for a variety of purposes including service denial
and compromise of generated key material. Section 9.2.2 through
Section 9.2.7.
9.2.2. Message Modifications
Modifications to a <DSKPPTrigger> message will either cause denial-
of-service (modifications of any of the identifiers or the nonce) or
will cause the DSKPP client to contact the wrong DSKPP server. The
latter is in effect a man-in-the-middle attack and is discussed
further in Section 9.2.7.
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An attacker may modify a <KeyProvClientHello> message. This means
that the attacker could indicate a different key or device than the
one intended by the DSKPP client, and could also suggest other
cryptographic algorithms than the ones preferred by the DSKPP client,
e.g., cryptographically weaker ones. The attacker could also suggest
earlier versions of the DSKPP protocol, in case these versions have
been shown to have vulnerabilities. These modifications could lead
to an attacker succeeding in initializing or modifying another
cryptographic module than the one intended (i.e., the server
assigning the generated key to the wrong module), or gaining access
to a generated key through the use of weak cryptographic algorithms
or protocol versions. DSKPP implementations MAY protect against the
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
variation. Therefore, DSKPP servers MUST NOT accept unilaterally
provided device identifiers in the public-key variation. This is
also indicated in the protocol description. In the shared-key
variation, 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 9.5 for a discussion of this threat and possible
countermeasures.
An attacker may also modify a <KeyProvServerHello> message. This
means that the attacker could indicate different key types,
algorithms, or protocol versions than the legitimate server would,
e.g., cryptographically weaker ones. The attacker may also provide a
different nonce than the one sent by the legitimate server. Clients
MAY protect against the former through strict adherence to policies
regarding permissible algorithms and protocol versions. The latter
(wrong nonce) will not constitute a security problem, as a generated
key will not match the key generated on the legitimate server. Also,
whenever the DSKPP run would result in the replacement of an existing
key, the <Mac> element protects against modifications of R_S.
Modifications of <KeyProvClientNonce> messages are also possible. If
an attacker modifies the SessionID attribute, then, in effect, a
switch to another session will occur at the server, assuming the new
SessionID is valid at that time on the server. It still will not
allow the attacker to learn a generated K_TOKEN since R_C has been
wrapped for the legitimate server. Modifications of the
<EncryptedNonce> element, e.g., replacing it with a value for which
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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 9.5
below. Note that use of TLS does not protect against this attack if
the attacker has access to the DSKPP client (e.g., through malicious
software, "trojans").
Finally, attackers may also modify the <KeyProvServerFinished>
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.
9.2.3. Message Deletion
Message deletion will not cause any other harm than denial-of-
service, since a cryptographic module MUST NOT change its state
(i.e., "commit" to a generated key) until it receives the final
message from the DSKPP server and successfully has processed that
message, including validation of its MAC. A deleted
<KeyProvServerFinished> message will not cause the server to end up
in an inconsistent state vis-a-vis the cryptographic module if the
server implements the suggestions in Section 9.5.
9.2.4. Message Insertion
An active attacker may initiate a DSKPP run at any time, and suggest
any device identifier. DSKPP server implementations MAY receive some
protection against inadvertently initializing a key or inadvertently
replacing an existing key or assigning a key to a cryptographic
module by initializing the DSKPP run by use of the <KeyProvTrigger>.
The <TriggerNonce> element allows the server to associate a DSKPP
protocol run with, e.g., an earlier user-authenticated session. The
security of this method, therefore, depends on the ability to protect
the <TriggerNonce> element in the DSKPP initialization message. If
an eavesdropper is able to capture this message, he may race the
legitimate user for a key initialization. DSKPP over a transport
providing privacy and integrity, coupled with the recommendations in
Section 9.5, 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.
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9.2.5. Message Replay
During 4-pass DSKPP, attempts to replay a previously recorded DSKPP
message will be detected, as the use of nonces ensures that both
parties are live. For example, a DSKPP client knows that a server it
is communicating with is "live" since the server MUST create a MAC on
information sent by the client.
The same is true for 2-pass DSKPP thanks to the requirement that the
client sends R in the <KeyProvClientHello> message and that the
server includes R in the MAC computation.
9.2.6. 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-pass DSKPP since each party
sends at most one message each.
9.2.7. 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 3.1. 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 9.3.
9.3. Passive Attacks
Passive attackers may eavesdrop on DSKPP runs to learn information
that later on may be used to impersonate users, mount active attacks,
etc.
If DSKPP is not run over a transport providing privacy, a passive
attacker may learn:
o What cryptographic modules a particular user is in possession of;
o The identifiers of keys on those cryptographic modules and other
attributes pertaining to those keys, e.g., the lifetime of the
keys; and
o DSKPP versions and cryptographic algorithms supported by a
particular DSKPP client or server.
Whenever the above is a concern, DSKPP SHOULD be run over a transport
providing privacy. If man-in-the-middle attacks for the purposes
described above are a concern, the transport SHOULD also offer
server-side authentication.
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9.4. 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 3.5
and Section 3 contain discussions of this threat and steps
RECOMMENDED to protect against it.
9.5. 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 variation or the shared-secret
variation 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-pass DSKPP as the client
does not provide any entropy to K_TOKEN. The attack as such (and its
countermeasures) still applies to 2-pass DSKPP, however, as it
essentially is a man-in-the-middle attack.
Another threat arises when an attacker is able to trick a user to
authenticate to the attacker rather than to the legitimate service
before the DSKPP protocol run. If successful, the attacker will then
be able to impersonate the user towards the legitimate service, and
subsequently receive a valid DSKPP trigger. If the public-key
variant of DSKPP is used, this may result in the attacker being able
to (after a successful DSKPP protocol run) impersonate the user.
Ordinary precautions MUST, therefore, be in place to ensure that
users authenticate only to legitimate services.
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9.6. Additional Considerations
9.6.1. 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 2-pass DSKPP
version 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 variation. Server implementations SHOULD therefore take
extreme care to ensure that this situation does not occur.
9.6.2. Key Confirmation
4-pass DSKPP servers provide key confirmation through the MAC on R_C
in the <KeyProvServerFinished> message. In the 2-pass DSKPP
variation described herein, key confirmation is provided by the MAC
including R, using K_MAC.
9.6.3. Server Authentication
DSKPP servers MUST authenticate themselves whenever a successful
DSKPP 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 2-pass DSKPP, servers authenticate by including the
AuthenticationDataType extension containing a MAC as described in
Section 3.2 for Two-Pass DSKPP.
9.6.4. User Authentication
A DSKPP server MUST authenticate a client to ensure that K_TOKEN is
delivered to the intended device. The following measures SHOULD be
considered:
o When an Authentication Code is used for client authentication, a
password dictionary attack on the authentication data is possible.
o The length of the Authentication Code when used over a non-secure
channel SHOULD be longer than what is used over a secure channel.
When a device, e.g., some mobile phones with small screens, cannot
handle a long Authentication Code in a user-friendly manner, DSKPP
SHOULD rely on a secure channel for communication.
o In the case that a non-secure channel has to be used, the
Authentication Code SHOULD be sent to the server MAC'd as
specified in Section 3.3. The Authentication Code and nonce value
MUST be strong enough to prevent offline brute-force recovery of
the Authentication Code from the HMAC data. Given that the nonce
value is sent in plaintext format over a non-secure transport, the
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cryptographic strength of the AuthenticationData depends more on
the quality of the AuthenticationCode.
o When the AuthenticationCode is sent from the DSKPP server to the
device in a DSKPP initialization trigger message, an eavesdropper
may be able to capture this message and race the legitimate user
for a key initialization. To prevent this, the transport layer
used to send the DSKPP trigger MUST provide privacy and integrity
e.g. secure browser session.
9.6.5. Key Protection in the Two-Pass Passphrase Profile
The passphrase-based key wrap profile uses the PBKDF2 function from
[PKCS-5] to generate an encryption key from a passphrase and salt
string. The derived key, K_DERIVED is used by the server to encrypt
K_TOKEN and by the cryptographic module to decrypt the newly
delivered K_TOKEN. It is important to note that passphrase-based
encryption is generally limited in the security that it provides
despite the use of salt and iteration count in PBKDF2 to increase the
complexity of attack. Implementations SHOULD therefore take
additional measures to strengthen the security of the passphrase-
based key wrap profile. The following measures SHOULD be considered
where applicable:
o The passphrase SHOULD be selected well, and usage guidelines such
as the ones in [NIST-PWD] SHOULD be taken into account.
o A different passphrase SHOULD be used for every key initialization
wherever possible (the use of a global passphrase for a batch of
cryptographic modules SHOULD be avoided, for example). One way to
achieve this is to use randomly-generated passphrases.
o The passphrase SHOULD be protected well if stored on the server
and/or on the cryptographic module and SHOULD be delivered to the
device's user using secure methods.
o User pre-authentication SHOULD be implemented to ensure that
K_TOKEN is not delivered to a rogue recipient.
o The iteration count in PBKDF2 SHOULD be high to impose more work
for an attacker using brute-force methods (see [PKCS-5] for
recommendations). However, it MUST be noted that the higher the
count, the more work is required on the legitimate cryptographic
module to decrypt the newly delivered K_TOKEN. Servers MAY use
relatively low iteration counts to accommodate devices with
limited processing power such as some PDA and cell phones when
other security measures are implemented and the security of the
passphrase-based key wrap method is not weakened.
o Transport level security (e.g. TLS) SHOULD be used where possible
to protect a 2-pass protocol run. Transport level security
provides a second layer of protection for the newly generated
K_TOKEN.
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10. Internationalization Considerations
The DSKPP protocol is mostly meant for machine-to-machine
communications; as such, most of its elements are tokens not meant
for direct human consumption. If these tokens are presented to the
end user, some localization may need to occur. DSKPP exchanges
information using XML. All XML processors are required to understand
UTF-8 and UTF-16 encoding, and therefore all DSKPP clients and
servers MUST understand UTF-8 and UTF-16 encoded XML. Additionally,
DSKPP servers and clients MUST NOT encode XML with encodings other
than UTF-8 or UTF-16.
11. 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"
12. 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.
13. Contributors
This work is based on information contained in [RFC4758], authored by
Magnus Nystrom, with enhancements (esp. Client Authentication, and
support for multiple key container formats) from an individual
Internet-Draft co-authored by Mingliang Pei and Salah Machani.
We would like to thank Shuh Chang for contributing the DSKPP object
model, and Philip Hoyer for his work in aligning DSKPP and PSKC
schemas.
We would also like to thank Hannes Tschofenig for his draft reviews,
feedback, and text contributions.
14. Acknowledgements
We would like to thank the following for review of previous DSKPP
document versions:
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o Lakshminath Dondeti (Review December 2007)
o Dr. Ulrike Meyer (Review June 2007)
o Niklas Neumann (Review June 2007)
o Shuh Chang (Review June 2007)
o Hannes Tschofenig (Review June 2007 and again in August 2007)
o Sean Turner (Review August 2007)
o John Linn (Review August 2007)
o Philip Hoyer (Review September 2007)
We would also like to thank the following for their input to selected
design aspects of the DSKPP protocol:
o Anders Rundgren (Key Container Format and Client Authentication
Data)
o Hannes Tschofenig (HTTP Binding)
o Phillip Hallam-Baker (Registry for Algorithms)
Finally, we would like to thank Robert Griffin for opening
communication channels for us with the IEEE P1619.3 Key Management
Group, and facilitating our groups in staying informed of potential
areas (esp. key provisioning and global key identifiers of
collaboration) of collaboration.
15. References
15.1. Normative references
[UNICODE] Davis, M. and M. Duerst, "Unicode Normalization Forms",
March 2001,
<http://www.unicode.org/unicode/reports/tr15/
tr15-21.html>.
[XMLDSIG] W3C, "XML Signature Syntax and Processing",
W3C Recommendation, February 2002,
<http://www.w3.org/TR/2002/REC-xmldsig-core-20020212/>.
[XMLENC] W3C, "XML Encryption Syntax and Processing",
W3C Recommendation, December 2002,
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<http://www.w3.org/TR/2002/REC-xmldsig-core-20020212/>.
15.2. 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>.
[PKCS-1] RSA Laboratories, "RSA Cryptography Standard", PKCS #1
Version 2.1, June 2002,
<http://www.rsasecurity.com/rsalabs/pkcs/>.
[PKCS-11] RSA Laboratories, "Cryptographic Token Interface
Standard", PKCS #11 Version 2.20, June 2004,
<http://www.rsasecurity.com/rsalabs/pkcs/>.
[PKCS-12] "Personal Information Exchange Syntax Standard", PKCS #12
Version 1.0, 2005,
<ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-12/
pkcs-12v1.pdf>.
[PKCS-5] RSA Laboratories, "Password-Based Cryptography Standard",
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PKCS #5 Version 2.0, March 1999,
<http://www.rsasecurity.com/rsalabs/pkcs/>.
[PKCS-5-XML]
RSA Laboratories, "XML Schema for PKCS #5 Version 2.0",
PKCS #5 Version 2.0 Amd.1 (FINAL DRAFT), October 2006,
<http://www.rsasecurity.com/rsalabs/pkcs/>.
[PSKC] "Portable Symmetric Key Container", 2005, <http://
www.ietf.org/internet-drafts/
draft-hoyer-keyprov-portable-symmetric-key-container-
00.txt>.
[RFC2104] Krawzcyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
February 1997.
[RFC2119] "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997,
<http://www.ietf.org/rfc/rfc2119.txt>.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999,
<http://www.ietf.org/rfc/rfc2616.txt>.
[RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.
[RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
IETF URN Sub-namespace for Registered Protocol
Parameters", RFC 3553, BCP 73, June 2003.
[RFC4758] RSA, The Security Division of EMC, "Cryptographic Token
Key Initialization Protocol (CT-KIP)", November 2006,
<http://www.ietf.org/rfc/rfc4758.txt>.
Appendix A. Examples
This appendix contains example messages that illustrate parameters,
encoding, and semantics in four-and two- pass DSKPP exchanges. The
examples are written using XML, and are syntactically correct. MAC
and cipher values are fictitious however.
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A.1. Trigger Message
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvTrigger Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container:1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:protocol:1.0
keyprov-dskpp-1.0.xsd">
<dskpp:InitializationTrigger>
<dskpp:DeviceIdentifierData>
<dskpp:DeviceId>
<pskc:Manufacturer>ManufacturerABC</pskc:Manufacturer>
<pskc:SerialNo>XL0000000001234</pskc:SerialNo>
<pskc:Model>U2</pskc:Model>
</dskpp:DeviceId>
</dskpp:DeviceIdentifierData>
<dskpp:KeyID>SE9UUDAwMDAwMDAx</dskpp:KeyID>
<dskpp:TokenPlatformInfo KeyLocation="Hardware"
AlgorithmLocation="Software"/>
<dskpp:TriggerNonce>112dsdfwf312asder394jw==</dskpp:TriggerNonce>
<dskpp:ServerUrl>https://www.somekeyprovservice.com/
</dskpp:ServerUrl>
</dskpp:InitializationTrigger>
</dskpp:KeyProvTrigger>
A.2. Four-Pass Protocol
A.2.1. <KeyProvClientHello> Without a Preceding Trigger
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<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvClientHello Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container:1.0"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:protocol:1.0
keyprov-dskpp-1.0.xsd">
<dskpp:DeviceIdentifierData>
<dskpp:DeviceId>
<pskc:Manufacturer>ManufacturerABC</pskc:Manufacturer>
<pskc:SerialNo>XL0000000001234</pskc:SerialNo>
<pskc:Model>U2</pskc:Model>
</dskpp:DeviceId>
</dskpp:DeviceIdentifierData>
<dskpp:SupportedKeyTypes>
<dskpp:Algorithm>http://www.ietf.org/keyprov/pskc#hotp
</dskpp:Algorithm>
<dskpp:Algorithm>http://www.rsa.com/rsalabs/otps/schemas/2005/09/
otps-wst#SecurID-AES</dskpp:Algorithm>
</dskpp:SupportedKeyTypes>
<dskpp:SupportedEncryptionAlgorithms>
<dskpp:Algorithm>http://www.w3.org/2001/05/xmlenc#rsa_1_5
</dskpp:Algorithm>
<dskpp:Algorithm>http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
</dskpp:Algorithm>
</dskpp:SupportedEncryptionAlgorithms>
<dskpp:SupportedMacAlgorithms>
<dskpp:Algorithm>http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
</dskpp:Algorithm>
</dskpp:SupportedMacAlgorithms>
<dskpp:SupportedProtocolVariants><dskpp:FourPass/>
</dskpp:SupportedProtocolVariants>
<dskpp:SupportedKeyContainers>
<dskpp:KeyContainerFormat>
http://www.ietf.org/keyprov/pskc#KeyContainer
</dskpp:KeyContainerFormat>
</dskpp:SupportedKeyContainers>
</dskpp:KeyProvClientHello>
A.2.2. <KeyProvClientHello> Assuming a Preceding Trigger
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<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvClientHello Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container:1.0"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:protocol:1.0
keyprov-dskpp-1.0.xsd">
<dskpp:DeviceIdentifierData>
<dskpp:DeviceId>
<pskc:Manufacturer>ManufacturerABC</pskc:Manufacturer>
<pskc:SerialNo>XL0000000001234</pskc:SerialNo>
<pskc:Model>U2</pskc:Model>
</dskpp:DeviceId>
</dskpp:DeviceIdentifierData>
<dskpp:KeyID>SE9UUDAwMDAwMDAx</dskpp:KeyID>
<dskpp:TriggerNonce>112dsdfwf312asder394jw==</dskpp:TriggerNonce>
<dskpp:SupportedKeyTypes>
<dskpp:Algorithm>http://www.ietf.org/keyprov/pskc#hotp</dskpp:Algorithm>
<dskpp:Algorithm>http://www.rsa.com/rsalabs/otps/schemas/2005/09/
otps-wst#SecurID-AES</dskpp:Algorithm>
</dskpp:SupportedKeyTypes>
<dskpp:SupportedEncryptionAlgorithms>
<dskpp:Algorithm>http://www.w3.org/2001/05/xmlenc#rsa_1_5
</dskpp:Algorithm>
<dskpp:Algorithm>http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
</dskpp:Algorithm>
</dskpp:SupportedEncryptionAlgorithms>
<dskpp:SupportedMacAlgorithms>
<dskpp:Algorithm>http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
</dskpp:Algorithm>
</dskpp:SupportedMacAlgorithms>
<dskpp:SupportedProtocolVariants><dskpp:FourPass/>
</dskpp:SupportedProtocolVariants>
<dskpp:SupportedKeyContainers>
<dskpp:KeyContainerFormat>
http://www.ietf.org/keyprov/pskc#KeyContainer
</dskpp:KeyContainerFormat>
</dskpp:SupportedKeyContainers>
</dskpp:KeyProvClientHello>
A.2.3. <KeyProvServerHello> Without a Preceding Trigger
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<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvServerHello Version="1.0" SessionID="4114" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container:1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:protocol:1.0
keyprov-dskpp-1.0.xsd">
<dskpp:KeyType>
http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES
</dskpp:KeyType>
<dskpp:EncryptionAlgorithm>
http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
</dskpp:EncryptionAlgorithm>
<dskpp:MacAlgorithm>
http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
</dskpp:MacAlgorithm>
<dskpp:EncryptionKey>
<ds:KeyName>KEY-1</ds:KeyName>
</dskpp:EncryptionKey>
<dskpp:KeyContainerFormat>
http://www.ietf.org/keyprov/pskc#KeyContainer
</dskpp:KeyContainerFormat>
<dskpp:Payload>
<dskpp:Nonce>qw2ewasde312asder394jw==</dskpp:Nonce>
</dskpp:Payload>
</dskpp:KeyProvServerHello>
A.2.4. <KeyProvServerHello> Assuming a Preceding Trigger
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<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvServerHello Version="1.0" SessionID="4114"
Status="Success"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container:1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:protocol:1.0
keyprov-dskpp-1.0.xsd">
<dskpp:KeyType>
urn:ietf:params:xml:schema:keyprov:otpalg#SecurID-AES
</dskpp:KeyType>
<dskpp:EncryptionAlgorithm>
http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
</dskpp:EncryptionAlgorithm>
<dskpp:MacAlgorithm>
http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
</dskpp:MacAlgorithm>
<dskpp:EncryptionKey>
<ds:KeyName>KEY-1</ds:KeyName>
</dskpp:EncryptionKey>
<dskpp:KeyContainerFormat>
http://www.ietf.org/keyprov/pskc#KeyContainer
</dskpp:KeyContainerFormat>
<dskpp:Payload>
<dskpp:Nonce>qw2ewasde312asder394jw==</dskpp:Nonce>
</dskpp:Payload>
<dskpp:Mac
MacAlgorithm="http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes">
cXcycmFuZG9tMzEyYXNkZXIzOTRqdw==
</dskpp:Mac>
</dskpp:KeyProvServerHello>
A.2.5. <KeyProvClientNonce> Using Default Encryption
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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<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvClientNonce Version="1.0" SessionID="4114"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:protocol:1.0
keyprov-dskpp-1.0.xsd">
<dskpp:EncryptedNonce>VXENc+Um/9/NvmYKiHDLaErK0gk=
</dskpp:EncryptedNonce>
<dskpp:AuthenticationData>
<dskpp:ClientID>31300257</dskpp:ClientID>
<dskpp:AuthenticationCodeMac>
<dskpp:IterationCount>512</dskpp:IterationCount>
<dskpp:Mac>4bRJf9xXd3KchKoTenHJiw==</dskpp:Mac>
</dskpp:AuthenticationCodeMac>
</dskpp:AuthenticationData>
</dskpp:KeyProvClientNonce>
A.2.6. <KeyProvServerFinished> Using Default Encryption
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<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvServerFinished Version="1.0" SessionID="4114" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container:1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:protocol:1.0
keyprov-dskpp-1.0.xsd">
<dskpp:KeyContainer>
<dskpp:KeyContainer Version="1.0">
<pskc:DigestMethod
Algorithm="http://www.w3.org/2000/09/xmldsig#hmac-sha1"/>
<pskc:Device>
<pskc:Key
KeyAlgorithm="http://www.rsa.com/rsalabs/otps/schemas/2005/09/
otps-wst#SecurID-AES"
KeyId="XL0000000001234">
<pskc:Issuer>CredentialIssuer</pskc:Issuer>
<pskc:Usage OTP="true">
<pskc:ResponseFormat Format="DECIMAL" Length="6"/>
</pskc:Usage>
<pskc:FriendlyName>MyFirstToken</pskc:FriendlyName>
<pskc:Data Name="TIME">
<pskc:Value>AAAAADuaygA=</pskc:Value>
</pskc:Data>
<pskc:Expiry>10/30/2012</pskc:Expiry>
</pskc:Key>
</pskc:Device>
</dskpp:KeyContainer>
</dskpp:KeyContainer>
<dskpp:Mac
MacAlgorithm="http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes">
miidfasde312asder394jw==
</dskpp:Mac>
</dskpp:KeyProvServerFinished>
A.3. Two-Pass Protocol
A.3.1. Example Using the Key Transport Profile
The client indicates support all the Key Transport, Key Wrap, and
Passphrase-Based Key Wrap profiles (see Section 3.2.2):
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvClientHello Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container:1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:protocol:1.0
keyprov-dskpp-1.0.xsd">
<dskpp:DeviceIdentifierData>
<dskpp:DeviceId>
<pskc:Manufacturer>ManufacturerABC</pskc:Manufacturer>
<pskc:SerialNo>XL0000000001234</pskc:SerialNo>
<pskc:Model>U2</pskc:Model>
</dskpp:DeviceId>
</dskpp:DeviceIdentifierData>
<dskpp:ClientNonce>xwQzwEl0CjPAiQeDxwRJdQ==</dskpp:ClientNonce>
<dskpp:SupportedKeyTypes>
<dskpp:Algorithm>http://www.ietf.org/keyprov/pskc#hotp
</dskpp:Algorithm>
<dskpp:Algorithm>
http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES
</dskpp:Algorithm>
</dskpp:SupportedKeyTypes>
<dskpp:SupportedEncryptionAlgorithms>
<dskpp:Algorithm>http://www.w3.org/2001/05/xmlenc#rsa_1_5
</dskpp:Algorithm>
<dskpp:Algorithm>http://www.w3.org/2001/04/xmlenc#kw-aes128
</dskpp:Algorithm>
<dskpp:Algorithm>http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
</dskpp:Algorithm>
</dskpp:SupportedEncryptionAlgorithms>
<dskpp:SupportedMacAlgorithms>
<dskpp:Algorithm>http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
</dskpp:Algorithm>
</dskpp:SupportedMacAlgorithms>
<dskpp:SupportedProtocolVariants>
<dskpp:TwoPass>
<dskpp:SupportedKeyProtectionMethod>
urn:ietf:params:xml:schema:keyprov:protocol#wrap
</dskpp:SupportedKeyProtectionMethod>
<dskpp:Payload xsi:type="ds:KeyInfoType">
<ds:KeyName>Key_001</ds:KeyName>
</dskpp:Payload>
<dskpp:SupportedKeyProtectionMethod>
urn:ietf:params:xml:schema:keyprov:protocol#transport
</dskpp:SupportedKeyProtectionMethod>
<dskpp:SupportedKeyProtectionMethod>
urn:ietf:params:xml:schema:keyprov:protocol#passphrase-wrap
</dskpp:SupportedKeyProtectionMethod>
<dskpp:Payload xsi:type="ds:KeyInfoType">
<ds:X509Data>
<ds:X509Certificate>miib</ds:X509Certificate>
</ds:X509Data>
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</dskpp:Payload>
</dskpp:TwoPass>
</dskpp:SupportedProtocolVariants>
<dskpp:SupportedKeyContainers>
<dskpp:KeyContainerFormat>
http://www.ietf.org/keyprov/pskc#KeyContainer
</dskpp:KeyContainerFormat>
</dskpp:SupportedKeyContainers>
<dskpp:AuthenticationData>
<dskpp:ClientID>31300257</dskpp:ClientID>
<dskpp:AuthenticationCodeMac>
<dskpp:IterationCount>512</dskpp:IterationCount>
<dskpp:Mac>4bRJf9xXd3KchKoTenHJiw==</dskpp:Mac>
</dskpp:AuthenticationCodeMac>
</dskpp:AuthenticationData>
</dskpp:KeyProvClientHello>
In this example, the server responds to the previous request using
the key transport profile.
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvServerFinished Version="1.0" SessionID="4114"
Status="Success"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container:1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:protocol:1.0
keyprov-dskpp-1.0.xsd">
<dskpp:KeyContainer>
<dskpp:KeyContainer Version="1.0">
<dskpp:ServerID>https://www.somedskppservice.com/</dskpp:ServerID>
<dskpp:KeyProtectionMethod>
urn:ietf:params:xml:schema:keyprov:protocol#transport
</dskpp:KeyProtectionMethod>
<pskc:EncryptionMethod
Algorithm="http://www.w3.org/2001/05/xmlenc#rsa_1_5">
<pskc:KeyInfo>
<ds:X509Data>
<ds:X509Certificate>miib</ds:X509Certificate>
</ds:X509Data>
</pskc:KeyInfo>
</pskc:EncryptionMethod>
<pskc:DigestMethod
Algorithm="http://www.w3.org/2000/09/xmldsig#hmac-sha1"/>
<pskc:Device>
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<pskc:Key KeyAlgorithm="http://www.ietf.org/keyprov/pskc#hotp"
KeyId="SDU312345678">
<pskc:Issuer>CredentialIssuer</pskc:Issuer>
<pskc:Usage OTP="true">
<pskc:ResponseFormat Format="DECIMAL" Length="6"/>
</pskc:Usage>
<pskc:FriendlyName>MyFirstToken</pskc:FriendlyName>
<pskc:Data Name="SECRET">
<pskc:Value>
7JHUyp3azOkqJENSsh6b2vxXzwGBYypzJxEr+ikQAa229KV/BgZhGA==
</pskc:Value>
<pskc:ValueDigest>
i8j+kpbfKQsSlwmJYS99lQ==
</pskc:ValueDigest>
</pskc:Data>
<pskc:Data Name="COUNTER">
<pskc:Value>AAAAAAAAAAA=</pskc:Value>
</pskc:Data>
<pskc:Expiry>10/30/2012</pskc:Expiry>
</pskc:Key>
</pskc:Device>
</dskpp:KeyContainer>
</dskpp:KeyContainer>
<dskpp:Mac
MacAlgorithm="http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes">
miidfasde312asder394jw==
</dskpp:Mac>
<dskpp:AuthenticationData>
<dskpp:AuthenticationCodeMac>
<dskpp:Mac>4bRJf9xXd3KchKoTenHJiw==</dskpp:Mac>
</dskpp:AuthenticationCodeMac>
</dskpp:AuthenticationData>
</dskpp:KeyProvServerFinished>
A.3.2. Example Using the Key Wrap Profile
The client sends a request that specifies a shared key to protect the
K_TOKEN, and the server responds using the Key Wrap Profile.
Authentication data in this example is basing on an authentication
code rather than a device certificate.
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvClientHello Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container:1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
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xmlns:pkcs-5=
"http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:protocol:1.0
keyprov-dskpp-1.0.xsd">
<dskpp:DeviceIdentifierData>
<dskpp:DeviceId>
<pskc:Manufacturer>ManufacturerABC</pskc:Manufacturer>
<pskc:SerialNo>XL0000000001234</pskc:SerialNo>
<pskc:Model>U2</pskc:Model>
</dskpp:DeviceId>
</dskpp:DeviceIdentifierData>
<dskpp:ClientNonce>xwQzwEl0CjPAiQeDxwRJdQ==</dskpp:ClientNonce>
<dskpp:SupportedKeyTypes>
<dskpp:Algorithm>http://www.ietf.org/keyprov/pskc#hotp
</dskpp:Algorithm>
<dskpp:Algorithm>http://www.rsa.com/rsalabs/otps/schemas/2005/09/
otps-wst#SecurID-AES</dskpp:Algorithm>
</dskpp:SupportedKeyTypes>
<dskpp:SupportedEncryptionAlgorithms>
<dskpp:Algorithm>http://www.w3.org/2001/05/xmlenc#rsa_1_5
</dskpp:Algorithm>
<dskpp:Algorithm>http://www.w3.org/2001/04/xmlenc#kw-aes128
</dskpp:Algorithm>
<dskpp:Algorithm>http://www.rsasecurity.com/rsalabs/pkcs/schemas/
pkcs-5#pbes2</dskpp:Algorithm>
<dskpp:Algorithm>http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
</dskpp:Algorithm>
</dskpp:SupportedEncryptionAlgorithms>
<dskpp:SupportedMacAlgorithms>
<dskpp:Algorithm>http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
</dskpp:Algorithm>
</dskpp:SupportedMacAlgorithms>
<dskpp:SupportedProtocolVariants>
<dskpp:TwoPass>
<dskpp:SupportedKeyProtectionMethod>
urn:ietf:params:xml:schema:keyprov:protocol#wrap
</dskpp:SupportedKeyProtectionMethod>
<dskpp:Payload xsi:type="ds:KeyInfoType">
<ds:KeyName>Key_001</ds:KeyName>
</dskpp:Payload>
</dskpp:TwoPass>
</dskpp:SupportedProtocolVariants>
<dskpp:SupportedKeyContainers>
<dskpp:KeyContainerFormat>
http://www.ietf.org/keyprov/pskc#KeyContainer
</dskpp:KeyContainerFormat>
</dskpp:SupportedKeyContainers>
<dskpp:AuthenticationData>
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<dskpp:ClientID>31300257</dskpp:ClientID>
<dskpp:AuthenticationCodeMac>
<dskpp:IterationCount>512</dskpp:IterationCount>
<dskpp:Mac>4bRJf9xXd3KchKoTenHJiw==</dskpp:Mac>
</dskpp:AuthenticationCodeMac>
</dskpp:AuthenticationData>
</dskpp:KeyProvClientHello>
In this example, the server responds to the previous request using
the key wrap profile.
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvServerFinished Version="1.0" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container:1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:protocol:1.0
keyprov-dskpp-1.0.xsd">
<dskpp:KeyContainer>
<dskpp:KeyContainer Version="1.0">
<dskpp:ServerID>https://www.somedskppservice.com/</dskpp:ServerID>
<dskpp:KeyProtectionMethod>
urn:ietf:params:xml:schema:keyprov:protocol#wrap
</dskpp:KeyProtectionMethod>
<pskc:EncryptionMethod
Algorithm="http://www.w3.org/2001/04/xmlenc#kw-aes128">
<pskc:KeyInfo>
<ds:KeyName>Key-001</ds:KeyName>
</pskc:KeyInfo>
</pskc:EncryptionMethod>
<pskc:DigestMethod
Algorithm="http://www.w3.org/2000/09/xmldsig#hmac-sha1"/>
<pskc:Device>
<pskc:Key KeyAlgorithm="http://www.ietf.org/keyprov/pskc#hotp"
KeyId="SDU312345678">
<pskc:Issuer>CredentialIssuer</pskc:Issuer>
<pskc:Usage OTP="true">
<pskc:ResponseFormat Format="DECIMAL" Length="6"/>
</pskc:Usage>
<pskc:FriendlyName>MyFirstToken</pskc:FriendlyName>
<pskc:Data Name="SECRET">
<pskc:Value>
JSPUyp3azOkqJENSsh6b2hdXz1WBYypzJxEr+ikQAa22M6V/BgZhRg==
</pskc:Value>
<pskc:ValueDigest>
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i8j+kpbfKQsSlwmJYS99lQ==
</pskc:ValueDigest>
</pskc:Data>
<pskc:Data Name="COUNTER">
<pskc:Value>AAAAAAAAAAA=</pskc:Value>
</pskc:Data>
<pskc:Expiry>10/30/2012</pskc:Expiry>
</pskc:Key>
</pskc:Device>
</dskpp:KeyContainer>
</dskpp:KeyContainer>
<dskpp:Mac
MacAlgorithm="http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes">
miidfasde312asder394jw==
</dskpp:Mac>
<dskpp:AuthenticationData>
<dskpp:AuthenticationCodeMac>
<dskpp:Mac>4bRJf9xXd3KchKoTenHJiw==</dskpp:Mac>
</dskpp:AuthenticationCodeMac>
</dskpp:AuthenticationData>
</dskpp:KeyProvServerFinished>
A.3.3. Example Using the Passphrase-Based Key Wrap Profile
The client sends a request similar to that in Appendix A.3.1 with
authentication data basing on an authentication code, and the server
responds using the Passphrase-Based Key Wrap Profile. The
authentication data is set in clear text when it is sent over a
secure transport channel such as TLS.
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvClientHello Version="1.0"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container:1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:pkcs-5=
"http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5v2-0#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:protocol:1.0
keyprov-dskpp-1.0.xsd">
<dskpp:DeviceIdentifierData>
<dskpp:DeviceId>
<pskc:Manufacturer>ManufacturerABC</pskc:Manufacturer>
<pskc:SerialNo>XL0000000001234</pskc:SerialNo>
<pskc:Model>U2</pskc:Model>
</dskpp:DeviceId>
</dskpp:DeviceIdentifierData>
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<dskpp:ClientNonce>xwQzwEl0CjPAiQeDxwRJdQ==</dskpp:ClientNonce>
<dskpp:SupportedKeyTypes>
<dskpp:Algorithm>http://www.ietf.org/keyprov/pskc#hotp
</dskpp:Algorithm>
<dskpp:Algorithm>
http://www.rsa.com/rsalabs/otps/schemas/2005/09/otps-wst#SecurID-AES
</dskpp:Algorithm>
</dskpp:SupportedKeyTypes>
<dskpp:SupportedEncryptionAlgorithms>
<dskpp:Algorithm>http://www.w3.org/2001/05/xmlenc#rsa_1_5
</dskpp:Algorithm>
<dskpp:Algorithm>http://www.w3.org/2001/04/xmlenc#kw-aes128
</dskpp:Algorithm>
<dskpp:Algorithm>
http://www.rsasecurity.com/rsalabs/pkcs/schemas/pkcs-5#pbes2
</dskpp:Algorithm>
<dskpp:Algorithm>
http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
</dskpp:Algorithm>
</dskpp:SupportedEncryptionAlgorithms>
<dskpp:SupportedMacAlgorithms>
<dskpp:Algorithm>
http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
</dskpp:Algorithm>
</dskpp:SupportedMacAlgorithms>
<dskpp:SupportedProtocolVariants>
<dskpp:TwoPass>
<dskpp:SupportedKeyProtectionMethod>
urn:ietf:params:xml:schema:keyprov:protocol#wrap
</dskpp:SupportedKeyProtectionMethod>
<dskpp:Payload xsi:type="ds:KeyInfoType">
<ds:KeyName>Key_001</ds:KeyName>
</dskpp:Payload>
<dskpp:SupportedKeyProtectionMethod>
urn:ietf:params:xml:schema:keyprov:protocol#passphrase-wrap
</dskpp:SupportedKeyProtectionMethod>
</dskpp:TwoPass>
</dskpp:SupportedProtocolVariants>
<dskpp:SupportedKeyContainers>
<dskpp:KeyContainerFormat>
http://www.ietf.org/keyprov/pskc#KeyContainer
</dskpp:KeyContainerFormat>
</dskpp:SupportedKeyContainers>
<dskpp:AuthenticationData>
<dskpp:ClientID>31300257</dskpp:ClientID>
<dskpp:AuthenticationCodeMac>
<dskpp:IterationCount>512</dskpp:IterationCount>
<dskpp:Mac>4bRJf9xXd3KchKoTenHJiw==</dskpp:Mac>
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</dskpp:AuthenticationCodeMac>
</dskpp:AuthenticationData>
</dskpp:KeyProvClientHello>
In this example, the server responds to the previous request using
the Passphrase-Based Key Wrap Profile.
<?xml version="1.0" encoding="UTF-8"?>
<dskpp:KeyProvServerFinished Version="1.0"
SessionID="4114" Status="Success"
xmlns:dskpp="urn:ietf:params:xml:ns:keyprov:protocol:1.0"
xmlns:pskc="urn:ietf:params:xml:ns:keyprov:container:1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
xsi:schemaLocation="urn:ietf:params:xml:ns:keyprov:protocol:1.0
keyprov-dskpp-1.0.xsd">
<dskpp:KeyContainer>
<dskpp:KeyContainer Version="1.0">
<dskpp:ServerID>https://www.somedskppservice.com/</dskpp:ServerID>
<dskpp:KeyProtectionMethod>
urn:ietf:params:xml:schema:keyprov:protocol#passphrase-wrap
</dskpp:KeyProtectionMethod>
<pskc:EncryptionMethod
Algorithm="http://www.rsasecurity.com/rsalabs/pkcs/schemas/
pkcs-5#pbes2">
<pskc:PBEEncryptionParam
EncryptionAlgorithm=
"http://www.w3.org/2001/04/xmlenc#kw-aes128-cbc">
<pskc:PBESalt>y6TzckeLRQw=</pskc:PBESalt>
<pskc:PBEIterationCount>1024</pskc:PBEIterationCount>
</pskc:PBEEncryptionParam>
<pskc:IV>c2FtcGxlaXY=</pskc:IV>
</pskc:EncryptionMethod>
<pskc:DigestMethod
Algorithm="http://www.w3.org/2000/09/xmldsig#hmac-sha1"/>
<pskc:Device>
<pskc:Key KeyAlgorithm="http://www.ietf.org/keyprov/pskc#hotp"
KeyId="SDU312345678">
<pskc:Issuer>CredentialIssuer</pskc:Issuer>
<pskc:Usage OTP="true">
<pskc:ResponseFormat Format="DECIMAL" Length="6"/>
</pskc:Usage>
<pskc:FriendlyName>MyFirstToken</pskc:FriendlyName>
<pskc:Data Name="SECRET">
<pskc:Value>
JSPUyp3azOkqJENSsh6b2hdXz1WBYypzJxEr+ikQAa22M6V/BgZhRg==
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</pskc:Value>
<pskc:ValueDigest>
i8j+kpbfKQsSlwmJYS99lQ==
</pskc:ValueDigest>
</pskc:Data>
<pskc:Data Name="COUNTER">
<pskc:Value>AAAAAAAAAAA=</pskc:Value>
</pskc:Data>
<pskc:Expiry>10/30/2012</pskc:Expiry>
</pskc:Key>
</pskc:Device>
</dskpp:KeyContainer>
</dskpp:KeyContainer>
<dskpp:Mac
MacAlgorithm="http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes">
miidfasde312asder394jw==
</dskpp:Mac>
<dskpp:AuthenticationData>
<dskpp:AuthenticationCodeMac>
<dskpp:Mac>4bRJf9xXd3KchKoTenHJiw==</dskpp:Mac>
</dskpp:AuthenticationCodeMac>
</dskpp:AuthenticationData>
</dskpp:KeyProvServerFinished>
Appendix B. Integration with PKCS #11
A DSKPP client that needs to communicate with a connected
cryptographic module to perform a DSKPP exchange MAY use PKCS #11
[PKCS-11]as a programming interface.
B.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.
B.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,
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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_PROV = 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_PROV
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_PROV by calling
C_DeriveKey using the CKM_EXTRACT_KEY_FROM_KEY mechanism,
this time setting CK_EXTRACT_PARAMS to the length of K_PROV
(in bits) divided by two.
2. The server wraps K_PROV 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.
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 ServerID 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.
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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 ServerID 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_PROV 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 ServerID
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.
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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.
Appendix C. Example of DSKPP-PRF Realizations
C.1. Introduction
This example appendix defines DSKPP-PRF in terms of AES [FIPS197-AES]
and HMAC [RFC2104].
C.2. DSKPP-PRF-AES
C.2.1. Identification
For cryptographic modules supporting this realization of DSKPP-PRF,
the following URL MAY be used to identify this algorithm in DSKPP:
http://www.ietf.org/keyprov/dskpp#dskpp-prf-aes
When this URL is used to identify the encryption algorithm to use,
the method for encryption of R_C values described in Section 3.5 MUST
be used.
C.2.2. Definition
DSKPP-PRF-AES (k, s, dsLen)
Input:
k Encryption key to use
s Octet string consisting of randomizing material. The
length of the string s is sLen.
dsLen Desired length of the output
Output:
DS A pseudorandom string, dsLen-octets long
Steps:
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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
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.
C.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)
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C.3. DSKPP-PRF-SHA256
C.3.1. Identification
For cryptographic modules supporting this realization of DSKPP-PRF,
the following URL MAY be used to identify this algorithm in DSKPP:
http://www.ietf.org/keyprov/dskpp#dskpp-prf-sha256
When this URL is used to identify the encryption algorithm to use,
the method for encryption of R_C values described in Section 3.5 MUST
be used.
C.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) ,
...
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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:
DS = B1 || B2 || ... || Bn<0..j-1>
Output the derived data DS.
C.3.3. Example
If we assume that sLen = 256 (two 128-octet long values) and dsLen =
16, then:
n = ROUND ( 16 / 32 ) = 1
j = 16 - (1 - 1) * 32 = 16
B1 = F (k, s, 1) = HMAC-SHA256 (k, INT (1) || s)
DS = B1<0 ... 15>
That is, the result will be the first 16 octets of the HMAC output.
Authors' Addresses
Andrea Doherty
RSA, The Security Division of EMC
174 Middlesex Tpk.
Bedford, MA 01730
USA
Email: adoherty@rsa.com
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Mingliang Pei
Verisign, Inc.
487 E. Middlefield Road
Mountain View, CA 94043
USA
Email: mpei@verisign.com
Salah Machani
Diversinet Corp.
2225 Sheppard Avenue East, Suite 1801
Toronto, Ontario M2J 5C2
Canada
Email: smachani@diversinet.com
Magnus Nystrom
RSA, The Security Division of EMC
Arenavagen 29
Stockholm, Stockholm Ln 121 29
SE
Email: mnystrom@rsa.com
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