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INTERNET-DRAFT                                 Editor: Stephen Farrell
expires in six months                           Trinity College Dublin
                                                             June 2003

                  Securely Available Credentials Protocol

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 10 of [RFC2026].
   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

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at


   This document describes a protocol whereby a user can acquire
   cryptographic credentials (e.g., private keys, PKCS #15 structures)
   from a credential server, using a workstation that has locally
   trusted software installed, but with no user-specific configuration.
   The protocol's payloads are described in XML. This memo also
   specifies a BEEP profile of the protocol. Security requirements are
   met by mandating support for TLS and/or DIGEST-MD5 (through BEEP).

Table Of Contents

    Status of this Memo.............................................1
    Table Of Contents...............................................1
    1. Introduction.................................................2
    2. The protocol.................................................3
    3. BEEP Profile for SACRED......................................8
    4. IANA Considerations.........................................11
    5. Security Considerations.....................................11
    Editor's Address...............................................14
    Full Copyright Statement.......................................14
    Appendix A: XML Schema.........................................15
    Appendix B: An Example of Tuning with BEEP.....................19

Editor: Farrell                                               [Page 1]

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    Appendix C: Provision SACRED using other Protocols.............22
    Appendix D: Changes & Open Issues..............................22

1. Introduction

   Many user-chosen passwords are vulnerable to dictionary attacks. So
   the SACRED protocol is designed to give no information with which an
   attacker can acquire information for launching a dictionary attack,
   whether by eavesdropping or by impersonating either the client or

   The protocol also allows a user to create or delete an account,
   change her account password and/or credentials and upload the new
   values to the server. The protocol ensures that only someone that
   knew the old account password is able to modify the credentials as
   stored on the credential server. The protocol does not preclude
   configuring a server to disallow some operations (e.g. credential
   upload) for some users. The account management operations as a whole
   are optional to implement for both credential servers and clients.

   Note that there are potentially two "passwords" involved when using
   this protocol - the first used to authenticate the user to the
   credential server, and the second to decrypt (parts of) the
   credential following a download operation. Where the context
   requires it, we refer to the former as the account password and the
   latter as the credential password.

   Using a protocol such as this is somewhat less secure than using a
   smart card, but can be used until smart cards and smart card readers
   on workstations become ubiquitous, and can be useful even after
   smart cards are ubiquitous, as a backup strategy when a user's smart
   card is lost or malfunctioning.

   The protocol sets out to meet the requirements in [REQS].
   Cryptographic credentials may take the form of private keys, PKCS
   #15 [PKCS15] or structures. As stated, a profile based on BEEP
   [BEEP] is specified for message transport and security
   (confidentiality, authentication, etc.). In particular, in that
   case, the security requirements are met by mandating support (via
   BEEP) for TLS [TLS] and/or DIGEST-MD5 [DIGEST-MD5].

   We assume the only authentication information available to the user
   is a username and password.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   this document are to be interpreted as described in [RFC2119].

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2. The protocol

   This section defines the account management and "run-time"
   operations for the SACRED protocol.

   It also describes the message formats used, which are described in
   XML [XMLSCHEMA]. Appendix A provides an XML schema for these

   The approach taken here is to define SACRED elements that are
   compatible with the elements used in [XKMS] and [XMLDSIG], so that
   an implementation of this protocol can easily also support XKMS, and
   vice versa.

   It is also intended that other SACRED protocol instances (e.g. using
   a different authentication scheme, credential format or transport
   protocol) could re-use many of the definitions here.

2.1 Account management operations

   These operations MAY be implemented, that is, they are OPTIONAL.

2.1.1   Information Request

   This operation does NOT REQUIRE authentication.

   The purpose of this operation is to provide to the client the values
   required for account creation.

   The client sends an InfoRequest message (which has no content).

   The server responds with an InfoResponse message which contains the
   authentication mechanism parameters for the server and the list of
   supported ProcessInfo types. For DIGEST-MD5 this consists of the
   list of realms (each as an XML element named "Realm") which the
   server supports. There MUST be at least one realm specified. Clients
   MUST be able to select one from a list of Realms and MUST be able to
   disregard any other information present (allowed for extensibility).

2.1.2   Create Account

   This operation REQUIRES server authentication.

   The purpose of this operation is to setup a new account on the
   server.  The information required for a "new" account will depend on
   the SASL [SASL] mechanism used.

   The client sends a CreateAccountRequest, which contains the account
   name (e.g. username). It also contains the elements required to
   create an account for a particular authentication mechanism.  The
   actual information is defined according to the authentication
   mechanism. For DIGEST-MD5 this consists of the password verifier
   (the hashed username, password and realm) and the chosen realm.

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   Although more than one set of such data is allowed by the data
   structures defined in the appendix, clients SHOULD only include one

   The server responds with an error or acknowledgement message.

2.1.3   Remove Account

   This operation REQUIRES mutual authentication.

   The purpose of this operation is to delete the entire account.

   The client sends a RemoveAccountRequest message (which has no
   content) to the server.

   The server MUST delete all information relating to the account and
   respond with an error or acknowledgement message.

2.1.4   Modify Account

   This operation REQUIRES mutual authentication.

   The purpose of this operation is to allow the client to change the
   information required for authentication.  The information required
   will depend on the authentication method used.

   The client sends a ModifyAccountRequest message which contains the
   elements required to change the authentication information for the
   account, for a particular authentication mechanism.  The actual
   information is defined according to the authentication mechanism.
   For [DIGEST-MD5] it will consist of a realm and password verifier

   Once the account information has been changed, the server will
   respond with an error or acknowledgement message.

2.2 "Run-time" operations

   These operations MUST be supported by all conformant

2.2.1   Credential Upload

   This operation REQUIRES mutual authentication.

   The purpose of this operation is to allow the client to deposit a
   credential with the server.

   The client sends an UploadRequest message to the server which MUST
   contain one Credential.

   If a credential with the same credential selector field as in the
   UploadRequest, (a "matching" credential), already exists for the

Editor: Farrell                                               [Page 4]

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   account, then that credential is replaced with the new credential
   from the UploadRequest. Otherwise a "new" credential is associated
   with that account. If a new credential is being uploaded then the
   client SHOULD include (in LastModified) its local concept of the
   time (if it has one) or else an indicator that it has no clock. The
   actual value of LastModified can be anything, (but the element has
   to be present) since this will be overwritten by the server in any

   If any change is made to the stored credentials associated with the
   account then the server MUST update the corresponding LastModified
   value (returned in DownloadResponse messages) to the current time
   (at the server).

   The LastModified value in the UploadRequest MUST be the value which
   was most recently received in a corresponding DownloadResponse for
   that credential. This means the clients are strongly RECOMMENDED to
   only produce an UploadRequest based on recently downloaded
   credentials, since otherwise the LastModified value may be out of

   The LastModified value can also be of use in detecting conflicts.
   For example, download to platform A, download to platform B, update
   from B, update from A.  The server could detect a conflict on the
   second upload. In this case the server MUST respond with a BEEP
   error (which SHOULD be StaleCredential).

   The server replaces the provided LastModified value with the current
   time at the server before storing the credential. (Note that this
   means that it would be unwise for a client to include the
   LastModified field in a ClientInfo digital signature which is
   calculated over the CredentialType.)

   The server responds with an error or acknowledgement message.

2.2.2   Credential Download

   This operation REQUIRES mutual authentication.

   The purpose of this operation is to allow a client to get one or
   more credentials from a server (the purpose of the entire protocol

   The client sends a DownloadRequest message to the server which MAY
   contain a credential selector string for the credential. No, or an
   enmpty, credential selector means the request is for all credentials
   associated with the account.

   The server responds with a DownloadResponse or an error message. A
   DownloadResponse contains one or more credential payloads including
   the LastModified time which represents the time (at the server) when
   the last change was made to each credential associated with the
   account (e.g. subsequent to an UploadRequest).

Editor: Farrell                                               [Page 5]

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2.2.3   Credential Delete

   This operation REQUIRES mutual authentication.

   The purpose of this operation is to allow the client to delete one
   or all credentials associated with the account.

   The client sends an DeleteRequest message to the server which can
   contain either a CredentialSelector or an All element.

   If the DeleteRequest contains an All element then all of the
   credentials associated with that account are deleted.

   If the DeleteRequest contains a CredentialSelector then the request
   MAY include a LastModified value.  If the LastModified value is
   present in the DeleteRequest then it MUST be the value which was
   most recently received in a corresponding DownloadResponse for that
   credential. If the value does not match then the server MUST NOT
   delete the credentials.

   If no "matching" credential exists, the server returns an error.

   The server responds to this request with an error or acknowledgement

2.3 Miscellaneous

2.3.1   Session security

   Six SACRED operations are defined above. In this section we specify
   the requirements for security for each of the operations (where

        Operation                 Security REQUIRED
        ---------                 -----------------
        Information request       NONE
        Create account            Server authentication,
                                  Privacy, Integrity
        Remove account            Mutual authentication,
                                  Privacy, Integrity
        Modify account            Mutual authentication,
                                  Privacy, Integrity
        Credential upload         Mutual authentication,
                                  Privacy, Integrity
        Credential download       Mutual authentication,
                                  Privacy, Integrity
        Credential delete         Mutual authentication,
                                  Privacy, Integrity

   The security requirements can be met by several mechanisms. This
   document REQUIRES credential servers to support TLS and DIGEST-MD5.
   Clients MUST support DIGEST-MD5 and TLS with server authentication.

Editor: Farrell                                               [Page 6]

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   The mandatory-to-implement TLS cipher suite for SACRED is
   TLS_RSA_WITH_3DES-EDE_CBC_SHA. Implementations SHOULD also support

   When performing mutual authentication using DIGEST-MD5 for the
   client, DIGEST-MD5 MUST only be used "within" a TLS server-
   authenticated "pipe", and MUST only be used only for client
   authentication. That is, we do not use the DIGEST-MD5 security
   services (confidentiality, integrity etc.).

2.3.2   Handling multiple credentials for an account

   When more than one credential is stored under a single account, the
   client can select a single credential using the optional credential
   selector string.

   There is no concept of a "default credential" - all credentials MUST
   have an associated selector unique for that account.  The selector
   is REQUIRED for upload requests and OPTIONAL for download requests.
   If the selector is omitted in a download request it MUST be
   interpreted as a request for all the stored credentials.

   An empty selector string value (i.e. "") in a credential download
   request, is to be interpreted as if the selector string were
   omitted, i.e. a download request containing this is a request for
   all credentials.

   It is an error to have more than one credential stored under the
   same account where both have the same credential selector string.

2.3.3   Common fields

   All messages sent to the server MAY contain ProcessInfo values. This
   field MAY be used by other specifications or for vendor extensions.
   For example, a server might require clients to include a phone
   number in this field. The information response message contains a
   list of the types of ProcessInfo that the server supports. This
   extensibility scheme is similar to that used in [XKMS] and [XBULK].

   Where no specific response message is defined for an operation (e.g.
   for UploadRequest) then the transport will indicate success or

   All of the response messages defined here MAY contain a Status
   string, containing a value intended for human consumption.

2.3.4   Credential Format

   A number of messages involve the Credential element. It has the
   following fields (all optional fields may occur exactly zero or one
   times unless otherwise stated):

Editor: Farrell                                               [Page 7]

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   - CredentialSelector contains a string by which this particular
     credential (for this account) can be identified.
   - PayLoad contains either a ds:KeyInfo or some other form of
     credential. Implementations MUST support the PKCS #15 form of
     ds:KeyInfo defined below (the SacredPKCS15 element).
   - LastModified is a string containing the time (at the server) at
     which this credential was last modified.
   - TimeToLive (optional) is a hint which clients SHOULD honor, which
     specifies the number of seconds for which the downloaded
     credential is to be usable.
   - ProcessInfo (optional) MAY contain any (typed) information that
     the server is intended to process. If the server doesn't support
     any of the ProcessInfo data, it MAY ignore that data.
   - ClientInfo (optional) MAY contain any (typed) information that the
     client is intended to process, but which the server MUST ignore.
     If the client doesn't support any of the ClientInfo data, it MAY
     ignore that data (e.g. if the ClientInfo is device specific).

3. BEEP Profile for SACRED

   The protocol described in this memo is realized as a [BEEP] profile.

   Future memos may define alternative versions of the BEEP profile for
   SACRED. When a BEEP peer sends its greeting, it indicates which
   profiles it is willing to support. Accordingly, when the BEEP client
   asks to start a channel, it indicates the versions it supports, and
   if any of these are acceptable to the BEEP server, the latter
   specifies which profile it is starting.

   Profile Identification: http://iana.org/beep/transient/sacred/bss

   This profile URI is consistent with [TRANS].

   Messages Exchanged during Channel Creation:

   Messages starting one-to-one exchanges:

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   Messages in positive replies:

   Messages in negative replies: error

   Messages in one-to-many changes: none

   Message Syntax: c.f.,Section 3

   Message Semantics: c.f., Section 2

   Contact Information: c.f., the editor's address section of this memo

3.1 Profile Initialization

   Because all but one of the operations of the SACRED profile have
   security requirements (cf., Section 2.3.1), before starting the
   SACRED profile, the BEEP session will likely be tuned using either



          http://iana.org/beep/TLS followed by

   Appendix B gives an example of tuning a BEEP session using DIGEST-
   MD5 (i.e. it shows how to turn on BEEP security).

   Regardless, upon completion of the negotiation process, a tuning
   reset occurs in which both BEEP peers issue a new greeting. Consult
   Section 3 of [BEEP] for an example of how a BEEP peer may choose to
   issue different greetings based on whether privacy is in use.

   Any of the messages listed in section 3.2 below may be exchanged
   during channel initialization (c.f., Section of [BEEP]),

        C: <start number='1'>
        C:   <profile uri='http://iana.org/beep/transient/sacred/bss'>
        C:             <![CDATA[<DownloadRequest ...>]]>
        C:     </profile>
        C: </start>

        S: <profile uri='http://iana.org/beep/transient/sacred/bss'>
        S:   <![CDATA[<DownloadResponse ...>]]>
        S: </profile>

Editor: Farrell                                               [Page 9]

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   Note that BEEP imposes both encoding and length limitations on the
   messages that are piggybacked during channel initialization.

3.2 Profile Exchange

   All messages are exchanged as "application/beep+xml" (c.f., Section
   6.4 of [BEEP]):

   Role         MSG                   RPY                     ERR
   ----         ---                   ---                     ---
   I            InfoRequest           InfoResponse            error
   I            CreateAccountRequest  ok                      error
   I            RemoveAccountRequest  ok                      error
   I            ModifyAccountRequest  ok                      error
   I            DownloadRequest       DownloadResponse        error
   I            UploadRequest         ok                      error
   I            DeleteRequest         Ok                      error

3.3 Error handling

   The "error" message from Section of [BEEP] is used to convey
   error information. Typically, after flagging an error, a peer will
   initiate a graceful release of the BEEP session.

   The following BEEP error reply codes from [BEEP] are to be used:

    code  Meaning
    ====  =======
    421   service not available
    450   requested action not taken (e.g., lock already in
    451   requested action aborted (e.g., local error in
    454   temporary authentication failure
    500   general syntax error (e.g., poorly-formed XML)
    501   syntax error in parameters (e.g., non-valid XML)
    504   parameter not implemented
    530   authentication required
    534   authentication mechanism insufficient (e.g., too
          weak, sequence exhausted, etc.)
    535   authentication failure
    537   action not authorized for user
    538   authentication mechanism requires encryption
    550   requested action not taken (e.g., no requested
          profiles are acceptable)
    553   parameter invalid
    554   transaction failed (e.g., policy violation)

   The following SACRED-specific error reply codes can also be used:

    code  Meaning
    ====  =======
    555   Extension (ProcessInfo) used not supported

Editor: Farrell                                              [Page 10]

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    556   Required extension (ProcessInfo) not present
    557   StaleCredential (A bad LastModified value was
          contained in an UploadRequest.)

3.4 SASL authorization identity

   The use of the SASL authorization identity in this protocol is
   implementation-specific.  If used, the authorization identity is not
   a substitute for the credential selector field, but may be used to
   affect authorization for access to credentials.

4. IANA Considerations

   If the IANA approves this memo for standards-track publication, then
   the IANA registers the BEEP profile specified in Section 4, and
   selects an appropriate standards-track URI, e.g.,


   The sacred protocol SHOULD be run over port <<TBD>>.

   The GSSAPI service name (required when using SASL) for this protocol
   SHALL be "sacred".

5. Security Considerations

   [REQS] calls for specifications to state how they address the
   vulnerabilities listed below.

     V1.   A passive attacker can watch all packets on the network and
           later carry out a dictionary attack.
            - The use of DIGEST-MD5 and/or TLS counters this
     V2.   An attacker can attempt to masquerade as a credential server
           in an attempt to get a client to reveal information on line
           that allows for a later dictionary attack.
            - The use of server or mutual authentication counters this
     V3.   An attacker can attempt to get a client to decrypt a chosen
           "ciphertext" and get the client to make use of the resulting
           plaintext - the attacker may then be able to carry out a
           dictionary attack (e.g. if the plaintext resulting from
           "decryption" of a random string is used as a DSA private
            - The use of server or mutual authentication counters this
     V4.   An attacker could overwrite a repository entry so that when
           a user subsequently uses what they think is a good
           credential, they expose information about their password
           (and hence the "real" credential).
            - Server implementations SHOULD take measures to protect the
            database. Clients MAY use the ClientInfo field to store e.g.

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            a signature over the Credential, which they then verify
            before using the private component.
     V5.   An attacker can copy a credential server's repository and
           carry out a dictionary attack.
            - Server implementations SHOULD take measures to protect the
     V6.   An attacker can attempt to masquerade as a client in an
           attempt to get a server to reveal information that allows
           for a later dictionary attack.
            - The mutual authentication requirements of this protocol
            counter this to a great extent. Additionally, credential
            servers MAY choose to provide mechanisms that protect
            against online dictionary attacks against user account
            passwords, either by repeated access attempts to a single
            user account (varying the password) or by attempting to
            access many user accounts using the same password.
     V7.   An attacker can persuade a server that a successful login
           has occurred, even if it hasn't.
            - Client authentication prevents this.
     V8.   (Upload) An attacker can overwrite someone else's
           credentials on the server.
            - Only if they know the account password already (thanks to
            mutual authentication).
     V9.   (When using password-based authentication) An attacker can
           force a password change to a known (or "weak") password.
            - Client authentication counters this.
     V10.  An attacker can attempt a man-in-the-middle attack for lots
           of reasons...
            - Mutual authentication plus the encryption of subsequent
            messages prevents this.
     V11.  User enters password instead of name.
            - Since the DIGEST-MD5 mechanism is only used after TLS
            tuning, the user's name is also protected.
     V12.  An attacker could attempt various denial-of-service attacks.
            - No specific countermeasures against DoS are proposed.

   If the CreateAccountRequest message were sent over a cleartext
   channel (or otherwise exposed) then an attacker could mount a
   dictionary attack and recover the account password. This is why the
   server authenticated TLS transport is REQUIRED for this operation.

   If someone steals the server database they can launch a dictionary
   attack.  If the dictionary attack is successful, the attacker can
   decrypt the user's credentials. An attacker that has learned the
   user's account password can also upload new credentials, assuming
   the user is authorized to modify the credentials, because someone
   who knows the user's account password is assumed to be the user.
   However, if someone steals the server database and is unsuccessful
   at obtaining the user's account password through a dictionary
   attack, they will be unable to upload new credentials.

   Credential servers SHOULD incorporate measures that act to counter
   denial of service attacks. In particular, they SHOULD drop inactive

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   connections and minimize the use of resources by un-authenticated
   connections. A number of recommendations are listed at [DDOS].

   Various operations in the SACRED protocol depend upon server
   authentication being provided by server authenticated TLS. SACRED
   clients SHOULD take care that the correct server is at the far end
   of the TLS "pipe" by performing the checks which are listed in
   section 3.1 of RFC2818 [RFC2818]. Clients SHOULD also include the
   optional BEEP serverName field in their "start" message and SHOULD
   then ensure that the BEEP serverName is consistent with the checks
   on the TLS server described in RFC2818. Failure to carry out these
   checks could allow a spoof server access a user's credential.

   If the SACRED account password were to be used in some other, less
   secure protocol using DIGEST-MD5, then it might appear to be the
   case that a man-in-the-middle (MITM) attack could be mounted.
   However, this is not the case since the DIGEST-MD5 client hash
   includes a client-selected "digest-uri-value" which in SACRED's case
   will be  "sacred/<serverName>". In a MITM attack, those values will
   be something else. A MITM attack as described is therefore thwarted
   because digest-uri-value wouldn't match what the SACRED server is



        [BEEP]     Rose, M., "The Blocks Extensible Exchange Protocol
                    Core", RFC 3080.
        [DIGEST-MD5]    "Using Digest Authentication as a SASL
                    Mechanism", Leach, P., Newman, C., RFC 2831.
        [PKCS15]   "PKCS #15 v1.1: Cryptographic Token Information
                    Syntax Standard," RSA Laboratories, June 2000.
        [REQS]     Arsenault, A., Farrell, S., "Securely Available
                    Credentials - Requirements", RFC 3157.
        [RFC2026]  Bradner, S., "The Internet Standards Process --
                    Revision 3", RFC 2026.
        [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
                    Requirement Levels", RFC 2119.
        [SASL]     Myers, J., "Simple Authentication and Security Layer
                    (SASL)", RFC 2222.
        [TLS]      Dierks, T., "The TLS Protocol - Version 1.0", RFC
        [TLSAES]   Chown, P., "Advanced Encryption Standard (AES)
                    Ciphersuites for Transport Layer Security (TLS)",
                    RFC 3268.
        [XMLDSIG]  Eastlake, D., et al. "XML-Signature Syntax and
                    Processing", RFC 3075.
        [XMLSCHEMA] "XML Schema Part 1: Structures", D. Beech, M.
                    Maloney, N. Mendelsohn, and H. Thompson. W3C
                    Recommendation, May 2001.  Available at

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        [DDOS]     "Recommendations for the Protection against
                    Distributed Denial-of-Service Attacks in the
        [RFC2818]  Rescorla, E., "HTTP over TLS", RFC 2818.
        [TRANS]    Rose, M., "A Transient Prefix for Identifying
                    Profiles under Development by the Working Groups of
                    the IETF", RFC 3349.
        [XKMS]     Hallam-Baker, P. (ed), "XML Key Management
                    Specification", http://www.w3.org/TR/xkms2/
        [XBULK]    Hughes, M (ed), "XML Key Management Specification -
                    Bulk Operation", http://www.w3.org/TR/xkms2-xbulk/


   Radia Perlman (radia.perlman@sun.com) and Charlie Kaufman
   (ckaufman@iris.com) co-authored earlier versions of this document.
   Michael Zolotarev (mzolotar@tpg.com.au) did much of the initial work
   adapting an earlier draft to the use of SRP (though SRP was
   subsequently dropped, much of the framework survives). Marshall Rose
   (mrose@dbc.mtview.ca.us) helped out a lot, in particular, with the
   BEEP profile. And the following people were actively involved in the
   mailing list discussions leading to this draft:

        David Chizmadia (vze2729k@verizon.net),
        Dave Crocker (dcrocker@brandenburg.com),
        Lawrence Greenfield (leg+@andrew.cmu.edu),
        Dale Gustafson (dale.gustafson@bpsi.net),
        Mike Just (Mike.Just@entrust.com),
        John Linn (jlinn@rsasecurity.com),
        Neal McBurnett (neal@bcn.boulder.co.us),
        Keith Moore (moore@cs.utk.edu),
        Bob Morgan (rlmorgan@washington.edu),
        Magnus Nystrom (magnus@rsasecurity.com),
        Eamon O'Tuathail (eamon.otuathail@clipcode.com),
        Gareth Richards (grichards@rsasecurity.com)

   Of course, any and all errors remain the editor's responsibility.

Editor's Address

   Stephen Farrell,
   Distributed Systems Group,
   Computer Science Department,
   Trinity College Dublin,
   Phone: +353-1-608-3070
   Email: stephen.farrell@cs.tcd.ie

Full Copyright Statement

Editor: Farrell                                              [Page 14]

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   Copyright (C) The Internet Society (date).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works.  In addition,
   the ASN.1 module presented in Appendix B may be used in whole or in
   part without inclusion of the copyright notice.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process shall be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.  This
   document and the information contained herein is provided on an "AS

Appendix A: XML Schema

   <?xml version="1.0" encoding="UTF-8"?>
        <import namespace="http://www.w3.org/2000/09/xmldsig#"
        <!-- extensibility holes -->
        <complexType name="ProcessInfoType">
         <sequence maxOccurs="unbounded">
          <any namespace="##other"/>
        <element name="ProcessInfo" type="sacred:ProcessInfoType"/>
        <complexType name="ClientInfoType">
         <sequence maxOccurs="unbounded">
          <any namespace="##other"/>
        <element name="ClientInfo" type="sacred:ClientInfoType"/>
        <!-- Where to put authenentication information -->
        <complexType name="AuthInfoType">
         <choice maxOccurs="unbounded">

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          <element name="DigestMD5AuthInfo">
             <element name="PasswordVerifier" type="base64Binary"/>
             <element name="Realm" type="string" />
          <any namespace="##other"/>
        <element name="AuthInfo" type="sacred:AuthInfoType"/>
        <!-- authentication mechanism parameters -->
        <complexType name="AuthParamsType">
         <choice maxOccurs="unbounded">
          <element name=" DigestMD5AuthParams">
             <element name="Realm" type="string"
               minOccurs="1" maxOccurs="unbounded"/>
          <any namespace="##other"/>
        <element name="AuthParams" type="sacred:AuthParamsType"/>
        <!-- Protocol messsages -->
        <!-- "account handling" operations -->
        <!-- Information request -->
        <element name="InfoRequest"/>
        <element name="InfoResponse">
           <element name="Status" type="string" minOccurs="0"/>
           <element name="ServerId" type="string"/>
           <element ref="sacred:AuthParams"/>
           <element ref="sacred:ProcessInfo" minOccurs="0"/>
        <!-- Create Account Request -->
        <element name="CreateAccountRequest">
           <element name="UserId" type="string"/>
           <element ref="sacred:AuthInfo"/>
           <element ref="sacred:ProcessInfo" minOccurs="0"/>
        <!-- reomve account request -->
        <element name="RemoveAccountRequest">

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           <element ref="sacred:ProcessInfo" minOccurs="0"/>
        <!-- password change request -->
        <element name="ModifyAccountRequest">
           <element ref="sacred:AuthInfo"/>
           <element ref="sacred:ProcessInfo" minOccurs="0"/>
        <!-- "run-time" operations -->
        <!-- DownLoad Request -->
        <element name="DownloadRequest">
           <element name="CredentialSelector" type="string"
           <element ref="sacred:ProcessInfo" minOccurs="0"/>
        <!-- Download Response -->
        <element name="DownloadResponse">
           <element name="Status" type="string" minOccurs="0"/>
           <element name="Credential" type="sacred:CredentialType"
        <!-- Upload request -->
        <element name="UploadRequest">
           <element name="Credential" type="sacred:CredentialType"/>
        <element name="DeleteRequest">
                  <element name="CredentialSelector" type="string"/>
                  <element name="LastModified" type="dateTime"

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                <element name="All"/>
              <element ref="sacred:ProcessInfo" minOccurs="0"/>
        <!-- Credential related structures -->
        <!-- A new ds:KeyInfo thing -->
        <element name="SacredPKCS15" type="base64Binary"/>
        <!-- credential -->
        <complexType name="CredentialType">
          <element name="CredentialSelector" type="string"/>
          <element name="LastModified" type="dateTime"/>
          <element name="Payload" type="ds:KeyInfoType" minOccurs="0"/>
          <element name="TimeToLive" type="string" minOccurs="0"/>
          <element ref="sacred:ProcessInfo" minOccurs="0"/>
          <element ref="sacred:ClientInfo" minOccurs="0"/>


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Appendix B: An Example of Tuning with BEEP

   Here is what tuning BEEP for authentication and privacy looks like
   using TLS and SASL's DIGEST-MD5:

   L: <wait for incoming connection>
   I: <open connection>

   ... each peer sends a greeting indicating the services that
       it offers ...

   L: RPY 0 0 . 0 233
   L: Content-Type: application/beep+xml
   L: <greeting>
   L:    <profile uri='http://iana.org/beep/SASL/DIGEST-MD5' />
   L:    <profile uri='http://iana.org/beep/TLS' />
   L:    <profile uri='http://iana.org/beep/transient/sacred/bss' />
   L: </greeting>
   L: END
   I: RPY 0 0 . 0 52
   I: Content-Type: application/beep+xml
   I: <greeting />
   I: END

   ... the initiator starts a channel for TLS and piggybacks a request
       to start the TLS negotiation ...

   I: MSG 0 1 . 52 149
   I: Content-Type: application/beep+xml
   I: <start number='1' serverName="sacred.example.org">
   I:    <profile uri='http://iana.org/beep/TLS'>
   I:        &lt;ready />
   I:    </profile>
   I: </start>
   I: END

   ... the listener creates the channel and piggybacks its readiness to
       start TLS ...

   L: RPY 0 1 . 233 112
   L: Content-Type: application/beep+xml
   L: <profile uri='http://iana.org/beep/TLS'>
   L:     &lt;proceed />
   L: </profile>
   L: END

   ... upon receiving the reply, the initiator starts up TLS ...

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   ... successful transport security negotiation ...

   ... a new greeting is sent (cf., Section 9 of RFC 3080), note that
       the listener no longer advertises TLS (we're already running

   L: RPY 0 0 . 0 186
   L: Content-Type: application/beep+xml
   L: <greeting>
   L:    <profile uri='http://iana.org/beep/SASL/DIGEST-MD5' />
   L:    <profile uri='http://iana.org/beep/transient/sacred/bss' />
   L: </greeting>
   L: END
   I: RPY 0 0 . 0 52
   I: Content-Type: application/beep+xml
   I: <greeting />
   I: END

   ... the initiator starts a channel for DIGEST-MD5 and piggybacks
       initialization information for the mecdhanism ...

   I: MSG 0 1 . 52 178
   I: Content-Type: application/beep+xml
   I: <start number='1'>
   I:    <profile uri='http://iana.org/beep/SASL/DIGEST-MD5'>
   I:        &lt;blob> ... &lt;/blob>
   I:    </profile>
   I: </start>
   I: END

   ... the listener creates the channel and piggybacks a challenge ...

   L: RPY 0 1 . 186 137
   L: Content-Type: application/beep+xml
   L: <profile uri='http://iana.org/beep/SASL/DIGEST-MD5'>
   L:     &lt;blob> ... &lt;/blob>
   L: </profile>
   L: END

   ... the initiator sends a response to the challenge ...

   I: MSG 1 0 . 0 58
   I: Content-Type: application/beep+xml
   I: <blob> ... </blob>
   I: END

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   ... the listener accepts the challenge and tells the initiator
       that it is now authenticated ...

   L: RPY 1 0 . 0 66
   L: Content-Type: application/beep+xml
   L: <blob status='complete' />
   L: END

   ... the initiator starts a channel for SACRED and piggybacks its
       initial SACRED request ...

   I: MSG 0 2 . 230 520
   I: Content-Type: application/beep+xml
   I: <start number='3'>
   I:    <profile uri='http://iana.org/beep/transient/sacred/bss' />
   I:        &lt;?xml version="1.0" encoding="UTF-8"?>
   I:        &lt;sacred:DownloadRequest
   I:          xmlns:sacred="urn:sacred-2002-11-20"
   I:          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   I:          xsi:schemaLocation="urn:sacred-2002-11-20 sacred.xsd">
   I:          &lt;CredentialSelector>
   I:                      magnus-credentials&lt;/CredentialSelector>
   I:        &lt;/sacred:DownloadRequest>
   I: </start>
   I: END

   ... the listener creates the channel and piggybacks the response to
       initial SACRED request

   L: RPY 0 2 . 323 805
   L: Content-Type: application/beep+xml
   L: <profile uri='http://iana.org/beep/transient/sacred/bss' />
   L:     &lt;?xml version="1.0" encoding="UTF-8"?>
   L:     &lt;sacred:DownloadResponse
   L:       xmlns:sacred="urn:sacred-2002-11-20"
   L:       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   L:       xsi:schemaLocation="urn:sacred-2002-11-20 sacred.xsd">
   L:       &lt;Status>Success&lt;/Status>
   L:       &lt;Credential>
   L:         &lt;CredentialSelector>
   L:              magnus-credential&lt;/CredentialSelector>
   L:         &lt;LastModified>2002-11-22T00:00:08Z&lt;/LastModified>
   L:         &lt;Payload>
   L:             &lt;sacred:SacredPKCS15
   L:               xmlns:sacred="urn:sacred-2002-11-20">GpM7
   L:             &lt;/sacred:SacredPKCS15>
   L:         &lt;/Payload>

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   L:       &lt;/Credential>
   L:     &lt;/sacred:DownloadResponse>
   L: </profile>
   L: END

Appendix C: Provision SACRED using other Protocols

   SACRED may be implemented in a non-BEEP environment, providing that
   before any SACRED PDUs are sent, the application protocol must be
   protected according to the security mandates provided in Section

   For example, if SACRED is provisioned as the payload of an
   application protocol that supports SASL and TLS, then the
   appropriate SASL and/or TLS negotiation must successfully occur
   before exchanging Sacred PDUs.

   Alternatively, if the application protocol doesn't support SASL,
   then one or more PDUs are defined to facilitate a SASL negotiation,
   and the appropriate negotiation must occur before exchanging Sacred

Appendix D: Changes & Open Issues

   <<Note to RFC editor. Please remove this appendix and its TOC entry
   prior to RFC publication.>>

   -08 (Couple of pre-IESG nits and AD issues):
        - Re-worded abstract (and consequently a bit of the intro too)
           as per AD advice
        - Removed contradictory sentence from 2.2.1 ("If no "matching"
           credential exists, the server returns an error.")
        - Added TLS_RSA_WITH_AES_128_CBC_SHA as a SHOULD and associated
           reference to RFC 3268, again as per AD advice.
        - Added a clarification about what's in LastModified for an
           initial upload (at end of fourth paragraph of 2.2.1)
        - Editor affiliation change

   -07 (WG Last-Call Issues):
        - Added explicit credential delete message
        - Updated appendix B with Marshall's latest text (but including
           the serverName attribute in the initiator's first start
           message, as in -05)
        - Otherwise no change
        - Credential payload element -> minOccurs="0"
        - Added security considerations for the compound authentication
        - Gratefully added rlbob SASL authorization id text
        - Extended Appendix B with Magnus' samples
        - Applied changes in "More editorials" mail

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        - Clarified that we're using BEEP for security and what
           "tuning" means
        - Replaced schema with equivalent that "compiles"
        - Replaced SASL-MD5 with DIGEST-MD5 everywhere
        - Updated appendix B and other BEEP issues according to
           Marshall Rose's Oct 6th recommendations
        - Applied all but three "editorial corrections" raised on list,
        - Added a recommendation to download prior to modify
        - Fixed AuthXXXType extensibility as suggested by Gareth
        - Should the DTD or schema be normative? I'd usually go for the
           schema, but in this case the DTD seems much simpler.
           - Deleted DTD
        - Should we apply for a port number? (probably)
           - Mailed IANA and added IANA considerations section.
        - Multiple substrates issue
           - Decided at Minneapolis (Spring 2002) not to change.
        - Should we specify a max value where "unbounded" is in the
           schema or "+"/"*" in the DTD?
           - Nope.
        - Remove SASL-SRP and replace with something else
           - Done - changed to DIGEST-MD5 (rfc 2831).
        - SASL authorization identity issue
           - Waited some time for text that didn't arrive and so leaving
             current text as is.
        - Changed away from having a request with an empty sequence
           representing an implicit delete to where an explicit deletion
           request indicator (an XML attribute) is required
        - Added a service name: "The GSSAPI service name (required when
           using SASL) for this protocol SHALL be "SACRED"." (Note: I
           don't understand this and don't want to, but do let me know
           if its wrong:-)
         - Changes as per mailing list discussion:
           - deleted (previous) section 2.4: session mgt & added sec.
              cons about DoS
           - Applied changes from the following threads:
              - "BEEP adjustments"
              - "MultipleCredentials"
              - "SRP adjustments"
              - "LastModified"
        - Other changes:
           - clarified how UploadRequest can delete one or more
             credential payloads
           - merged sections 2 and 3 since its much clearer that way
           - changed Credential structure about a bit due to moving
   -01: Changes as per mailing list discussion:
        - Change from authors to editor + acks
        - Included resolved comments from list:

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           - password -> account pwd or cred pwd as appropriate
           - account mgt separated and optional
           - added example beep tuning
           - selector: no default, omit in d/l means all
           - changed LastModified scheme as per list comments
        - Excluded administrative operations (was an open issue)
        - Demoted hashed(username) concept to a note under security
           considerations (see V11).
        - Dropped idea of specifying a mapping between SRP id and cTLS
        - Dropped xkms & xbulk as normative references, but copied some
           stuff from them.
   -00: This version is adapted from draft-ietf-SACRED-protocol-beep-
   pdm-00.txt, the main changes are:
        - PDM -> SRP &/or TLS
        - Payload security -> SASL or TLS
        - Dropped username hashing
        - Dropped away-from-home

Editor: Farrell                                              [Page 24]

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