[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits] [IPR]

Versions: (draft-doherty-keyprov-dskpp) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 6063

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

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on July 28, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   DSKPP is a client-server protocol for initialization (and
   configuration) of symmetric keys to locally and remotely accessible
   cryptographic modules.  The protocol can be run with or without



Doherty, et al.           Expires July 28, 2008                 [Page 1]


Internet-Draft                    DSKPP                     January 2008


   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.

































Doherty, et al.           Expires July 28, 2008                 [Page 2]


Internet-Draft                    DSKPP                     January 2008


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



Doherty, et al.           Expires July 28, 2008                 [Page 3]


Internet-Draft                    DSKPP                     January 2008


     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



Doherty, et al.           Expires July 28, 2008                 [Page 4]


Internet-Draft                    DSKPP                     January 2008


     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





















Doherty, et al.           Expires July 28, 2008                 [Page 5]


Internet-Draft                    DSKPP                     January 2008


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".




Doherty, et al.           Expires July 28, 2008                 [Page 6]


Internet-Draft                    DSKPP                     January 2008


   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.







Doherty, et al.           Expires July 28, 2008                 [Page 7]


Internet-Draft                    DSKPP                     January 2008


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.




Doherty, et al.           Expires July 28, 2008                 [Page 8]


Internet-Draft                    DSKPP                     January 2008


   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.



























Doherty, et al.           Expires July 28, 2008                 [Page 9]


Internet-Draft                    DSKPP                     January 2008


   -----------          -------------
   | 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:





Doherty, et al.           Expires July 28, 2008                [Page 10]


Internet-Draft                    DSKPP                     January 2008


   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.





Doherty, et al.           Expires July 28, 2008                [Page 11]


Internet-Draft                    DSKPP                     January 2008


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








Doherty, et al.           Expires July 28, 2008                [Page 12]


Internet-Draft                    DSKPP                     January 2008


   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








Doherty, et al.           Expires July 28, 2008                [Page 13]


Internet-Draft                    DSKPP                     January 2008


   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








Doherty, et al.           Expires July 28, 2008                [Page 14]


Internet-Draft                    DSKPP                     January 2008


   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.





Doherty, et al.           Expires July 28, 2008                [Page 15]


Internet-Draft                    DSKPP                     January 2008


   +---------------+                            +---------------+
   |               |                            |               |
   |  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



Doherty, et al.           Expires July 28, 2008                [Page 16]


Internet-Draft                    DSKPP                     January 2008


       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>.






Doherty, et al.           Expires July 28, 2008                [Page 17]


Internet-Draft                    DSKPP                     January 2008


           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



Doherty, et al.           Expires July 28, 2008                [Page 18]


Internet-Draft                    DSKPP                     January 2008


   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



Doherty, et al.           Expires July 28, 2008                [Page 19]


Internet-Draft                    DSKPP                     January 2008


   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.










Doherty, et al.           Expires July 28, 2008                [Page 20]


Internet-Draft                    DSKPP                     January 2008


   +----------------------+    +-------+     +----------------------+
   |    +------------+    |    |       |     |                      |
   |    | 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



Doherty, et al.           Expires July 28, 2008                [Page 21]


Internet-Draft                    DSKPP                     January 2008


   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



Doherty, et al.           Expires July 28, 2008                [Page 22]


Internet-Draft                    DSKPP                     January 2008


   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.







Doherty, et al.           Expires July 28, 2008                [Page 23]


Internet-Draft                    DSKPP                     January 2008


   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>.









Doherty, et al.           Expires July 28, 2008                [Page 24]


Internet-Draft                    DSKPP                     January 2008


           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



Doherty, et al.           Expires July 28, 2008                [Page 25]


Internet-Draft                    DSKPP                     January 2008


   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.







Doherty, et al.           Expires July 28, 2008                [Page 26]


Internet-Draft                    DSKPP                     January 2008


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



Doherty, et al.           Expires July 28, 2008                [Page 27]


Internet-Draft                    DSKPP                     January 2008


   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



Doherty, et al.           Expires July 28, 2008                [Page 28]


Internet-Draft                    DSKPP                     January 2008


   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



Doherty, et al.           Expires July 28, 2008                [Page 29]


Internet-Draft                    DSKPP                     January 2008


   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



Doherty, et al.           Expires July 28, 2008                [Page 30]


Internet-Draft                    DSKPP                     January 2008


   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



Doherty, et al.           Expires July 28, 2008                [Page 31]


Internet-Draft                    DSKPP                     January 2008


   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:








Doherty, et al.           Expires July 28, 2008                [Page 32]


Internet-Draft                    DSKPP                     January 2008


   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:





Doherty, et al.           Expires July 28, 2008                [Page 33]


Internet-Draft                    DSKPP                     January 2008


      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.



Doherty, et al.           Expires July 28, 2008                [Page 34]


Internet-Draft                    DSKPP                     January 2008


   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)



Doherty, et al.           Expires July 28, 2008                [Page 35]


Internet-Draft                    DSKPP                     January 2008


   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.



Doherty, et al.           Expires July 28, 2008                [Page 36]


Internet-Draft                    DSKPP                     January 2008


   <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.




Doherty, et al.           Expires July 28, 2008                [Page 37]


Internet-Draft                    DSKPP                     January 2008


   <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.





Doherty, et al.           Expires July 28, 2008                [Page 38]


Internet-Draft                    DSKPP                     January 2008


   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).



Doherty, et al.           Expires July 28, 2008                [Page 39]


Internet-Draft                    DSKPP                     January 2008


   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.
















Doherty, et al.           Expires July 28, 2008                [Page 40]


Internet-Draft                    DSKPP                     January 2008


   <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]).














Doherty, et al.           Expires July 28, 2008                [Page 41]


Internet-Draft                    DSKPP                     January 2008


   <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.



















Doherty, et al.           Expires July 28, 2008                [Page 42]


Internet-Draft                    DSKPP                     January 2008


   <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.



Doherty, et al.           Expires July 28, 2008                [Page 43]


Internet-Draft                    DSKPP                     January 2008


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.





Doherty, et al.           Expires July 28, 2008                [Page 44]


Internet-Draft                    DSKPP                     January 2008


   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






















Doherty, et al.           Expires July 28, 2008                [Page 45]


Internet-Draft                    DSKPP                     January 2008


   <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.








Doherty, et al.           Expires July 28, 2008                [Page 46]


Internet-Draft                    DSKPP                     January 2008


   <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.





Doherty, et al.           Expires July 28, 2008                [Page 47]


Internet-Draft                    DSKPP                     January 2008


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.





Doherty, et al.           Expires July 28, 2008                [Page 48]


Internet-Draft                    DSKPP                     January 2008


   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.



Doherty, et al.           Expires July 28, 2008                [Page 49]


Internet-Draft                    DSKPP                     January 2008


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



Doherty, et al.           Expires July 28, 2008                [Page 50]


Internet-Draft                    DSKPP                     January 2008


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.




Doherty, et al.           Expires July 28, 2008                [Page 51]


Internet-Draft                    DSKPP                     January 2008


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



Doherty, et al.           Expires July 28, 2008                [Page 52]


Internet-Draft                    DSKPP                     January 2008


<?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">



Doherty, et al.           Expires July 28, 2008                [Page 53]


Internet-Draft                    DSKPP                     January 2008


    <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">



Doherty, et al.           Expires July 28, 2008                [Page 54]


Internet-Draft                    DSKPP                     January 2008


      <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">



Doherty, et al.           Expires July 28, 2008                [Page 55]


Internet-Draft                    DSKPP                     January 2008


    <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">



Doherty, et al.           Expires July 28, 2008                [Page 56]


Internet-Draft                    DSKPP                     January 2008


    <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>



Doherty, et al.           Expires July 28, 2008                [Page 57]


Internet-Draft                    DSKPP                     January 2008


    </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"



Doherty, et al.           Expires July 28, 2008                [Page 58]


Internet-Draft                    DSKPP                     January 2008


            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">



Doherty, et al.           Expires July 28, 2008                [Page 59]


Internet-Draft                    DSKPP                     January 2008


    <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" />



Doherty, et al.           Expires July 28, 2008                [Page 60]


Internet-Draft                    DSKPP                     January 2008


          <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])







Doherty, et al.           Expires July 28, 2008                [Page 61]


Internet-Draft                    DSKPP                     January 2008


   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.




Doherty, et al.           Expires July 28, 2008                [Page 62]


Internet-Draft                    DSKPP                     January 2008


   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



Doherty, et al.           Expires July 28, 2008                [Page 63]


Internet-Draft                    DSKPP                     January 2008


   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.




Doherty, et al.           Expires July 28, 2008                [Page 64]


Internet-Draft                    DSKPP                     January 2008


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.





Doherty, et al.           Expires July 28, 2008                [Page 65]


Internet-Draft                    DSKPP                     January 2008


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.






Doherty, et al.           Expires July 28, 2008                [Page 66]


Internet-Draft                    DSKPP                     January 2008


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



Doherty, et al.           Expires July 28, 2008                [Page 67]


Internet-Draft                    DSKPP                     January 2008


      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.




Doherty, et al.           Expires July 28, 2008                [Page 68]


Internet-Draft                    DSKPP                     January 2008


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:



Doherty, et al.           Expires July 28, 2008                [Page 69]


Internet-Draft                    DSKPP                     January 2008


   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,



Doherty, et al.           Expires July 28, 2008                [Page 70]


Internet-Draft                    DSKPP                     January 2008


              <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",



Doherty, et al.           Expires July 28, 2008                [Page 71]


Internet-Draft                    DSKPP                     January 2008


              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.





Doherty, et al.           Expires July 28, 2008                [Page 72]


Internet-Draft                    DSKPP                     January 2008


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





















Doherty, et al.           Expires July 28, 2008                [Page 73]


Internet-Draft                    DSKPP                     January 2008


   <?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










Doherty, et al.           Expires July 28, 2008                [Page 74]


Internet-Draft                    DSKPP                     January 2008


<?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









Doherty, et al.           Expires July 28, 2008                [Page 75]


Internet-Draft                    DSKPP                     January 2008


<?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






















Doherty, et al.           Expires July 28, 2008                [Page 76]


Internet-Draft                    DSKPP                     January 2008


   <?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.













Doherty, et al.           Expires July 28, 2008                [Page 77]


Internet-Draft                    DSKPP                     January 2008


   <?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

































Doherty, et al.           Expires July 28, 2008                [Page 78]


Internet-Draft                    DSKPP                     January 2008


<?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"



Doherty, et al.           Expires July 28, 2008                [Page 79]


Internet-Draft                    DSKPP                     January 2008


  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>



Doherty, et al.           Expires July 28, 2008                [Page 80]


Internet-Draft                    DSKPP                     January 2008


      </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>



Doherty, et al.           Expires July 28, 2008                [Page 81]


Internet-Draft                    DSKPP                     January 2008


          <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#"



Doherty, et al.           Expires July 28, 2008                [Page 82]


Internet-Draft                    DSKPP                     January 2008


     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>



Doherty, et al.           Expires July 28, 2008                [Page 83]


Internet-Draft                    DSKPP                     January 2008


       <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>



Doherty, et al.           Expires July 28, 2008                [Page 84]


Internet-Draft                    DSKPP                     January 2008


                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>



Doherty, et al.           Expires July 28, 2008                [Page 85]


Internet-Draft                    DSKPP                     January 2008


  <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>



Doherty, et al.           Expires July 28, 2008                [Page 86]


Internet-Draft                    DSKPP                     January 2008


    </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==



Doherty, et al.           Expires July 28, 2008                [Page 87]


Internet-Draft                    DSKPP                     January 2008


              </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,







Doherty, et al.           Expires July 28, 2008                [Page 88]


Internet-Draft                    DSKPP                     January 2008


       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.




Doherty, et al.           Expires July 28, 2008                [Page 89]


Internet-Draft                    DSKPP                     January 2008


       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.




Doherty, et al.           Expires July 28, 2008                [Page 90]


Internet-Draft                    DSKPP                     January 2008


       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:






Doherty, et al.           Expires July 28, 2008                [Page 91]


Internet-Draft                    DSKPP                     January 2008


   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)







Doherty, et al.           Expires July 28, 2008                [Page 92]


Internet-Draft                    DSKPP                     January 2008


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) ,
       ...



Doherty, et al.           Expires July 28, 2008                [Page 93]


Internet-Draft                    DSKPP                     January 2008


       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









Doherty, et al.           Expires July 28, 2008                [Page 94]


Internet-Draft                    DSKPP                     January 2008


   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


























Doherty, et al.           Expires July 28, 2008                [Page 95]


Internet-Draft                    DSKPP                     January 2008


Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





Doherty, et al.           Expires July 28, 2008                [Page 96]


Html markup produced by rfcmarkup 1.129b, available from https://tools.ietf.org/tools/rfcmarkup/