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INTERNET-DRAFT                                 Editor: Stephen Farrell
expires in six months                           Baltimore Technologies
                                                        September 2002

                  Securely Available Credentials Protocol
                  <draft-ietf-sacred-protocol-bss-03.txt>

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   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
   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.

Abstract

   This document describes a protocol the secure up- and down-load of
   cryptographic credentials. Discussion of this draft is taking place
   on the SACRED mailing list of the IETF SACRED working group (see
   http://www.imc.org/ietf-sacred for subscription information).

Table Of Contents

   Status of this Memo.............................................1
   Abstract........................................................1
   Table Of Contents...............................................1
   1. Introduction.................................................2
   2. The protocol.................................................2
   3. BEEP Profile for SACRED......................................8
   4. IANA Considerations.........................................10
   5. Security Considerations.....................................11
   References.....................................................12
   Acknowledgements...............................................13
   Editor's Address...............................................14
   Full Copyright Statement.......................................14
   Appendix A: XML Schema.........................................14
   Appendix B: An Example of Tuning with BEEP.....................17
   Appendix C: Provision SACRED using other Protocols.............19
   Appendix D: Changes & Open Issues..............................19


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1. Introduction

   We describe a protocol whereby a user can acquire cryptographic
   credentials (e.g., private keys, PKCS#15 structures) from a
   workstation that has locally trusted software installed, but with no
   user-specific configuration. This is somewhat less secure than 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's payloads are described in XML. This memo also
   specifies a BEEP [BEEP] profile of the protocol. The protocol sets
   out to meet the requirements in [REQS]. In particular, security
   requirements in [REQS] are met by mandating support for TLS [TLS]
   and/or SASL-MD5 [SASL-MD5].

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

   Many user-chosen passwords are vulnerable to dictionary attacks. So
   this 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
   server.

   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.

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 based on XML.
   Appendix A provides an XML schema for these elements.

   The approach taken here is to define SACRED elements that are
   compatible with the elements used in [XKMS] and [XMLDSIG], so that

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   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 REQUIRES no 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 SASL-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.

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 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 SASL-MD5 this consists of the password verifier (the
   hashed username, password and realm) and the chosen realm.

   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.



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   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 [SASL-MD5] it will consist of a realm and password verifier
   value.

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

   The server responds with an error or acknowledgement message.

2.2 "Run-time" operations

   These operations MUST be supported by all conformant
   implementations.

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, or to delete one or more credentials
   associated with the account.

   The client sends an UploadRequest message to the server which can
   contain zero or one Credential. If the UploadRequest contains no
   Credential and the UploadRequest contains a "Delete="yes""
   attribute, then the all the credentials associated with that account
   are deleted.

   If a credential with the same credential selector field as in the
   UploadRequest, (a "matching" credential), already exists for the
   account, then that credential is replaced with the new credential
   from the UploadRequest. Otherwise a "new" credential is associated
   with that account.

   If the new credential from the UploadRequest contains no PayLoad
   field and the new credential has a "Delete="yes"" attribute, then
   the (one and only) "matching" credential is deleted.



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   The processing of the "Delete" attribute MUST be strict û that is,
   this attribute MUST be ignored unless it is set on a data structure
   (either UploadRequest or Credential) which contains no useful value,
   and the value of the attribute MUST be precisely "yes", any other
   string value MUST be ignored.

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

   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.

   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).

   In the case of the upload of a new credential the client SHOULD
   include its best idea of the LastModified value in the credential.
   The server MUST replace this with the current time at the server
   before storing the credential however. (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
   really!).

   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).



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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
   supported).

        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

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

   The mandatory-to-implement TLS cipher suite for SACRED is
   TLS_RSA_WITH_3DES-EDE_CBC_SHA.

   When performing mutual authentication using SASL-MD5 for the client,
   SASL-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 SASL-MD5 cryptographic 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.



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   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

   The type "ds:CryptoBinary" (inherited from [XMLDSIG]) is used for
   almost all binary values. The value in such elements MUST be the
   base64 encoding of the binary value in network byte order. See
   [XMLDSIG] for further details and example. The exception to this is
   the "salt" field, which is of type base64Binary instead. The reason
   for this is that leading zeros are stripped from ds:CryptoBinary,
   which is correct in most cases, but since the salt is a direct input
   to a hash function, leading zeros are significant and so have to be
   preserved.

   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 like 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
   failure.

   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):

   - 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).


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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:
        InfoRequest,
        CreateAccountRequest,
        RemoveAccountRequest,
        ModifyAccountRequest,
        DownloadRequest,
        UploadRequest,
        InfoResponse,
        DownloadResponse,
        error,
        ok

   Messages starting one-to-one exchanges:
        InfoRequest,
        CreateAccountRequest,
        RemoveAccountRequest,
        ModifyAccountRequest,
        DownloadRequest,
        UploadRequest

   Messages in positive replies:
        ok,
        InfoResponse,
        DownloadResponse

   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





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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
       or
       http://iana.org/SASL/SASL-MD5

   (Appendix B gives an example of tuning a BEEP session using SASL-
   MD5).

   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 2.3.1.2 of [BEEP]),
   e.g.,

        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>

   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






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3.3 Error handling

   The "error" message from Section 2.3.1.5 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
         use)
   451   requested action aborted (e.g., local error in
         processing)
   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
   556   Required extension (ProcessInfo) not present
   557   StaleCredential (A bad LastModified value was
         contained in an UploadRequest.)

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.,

        http://iana.org/beep/sacred/bss

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

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



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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 SASL-MD5 and/or TLS counters this
           vulnerability.
    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
           vulnerability.
    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
          key).
           - The use of server or mutual authentication counters this
           vulnerability.
    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.
           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
           database.
    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).



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

References

   Normative:

       [BEEP]     Rose, M., "The Blocks Extensible Exchange Protocol
                  Core", RFC 3080.
       [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.
       [SASL-MD5] "Using Digest Authentication as a SASL Mechanism",
                  Leach, P., Newman, C., RFC 2831.
       [TLS]      Dierks, T., "The TLS Protocol - Version 1.0", RFC
                  2246.

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       [XMLDSIG]  Eastlake, D., et al. "XML-Signature Syntax and
                  Processing", RFC 3075.

   Informative:

       [DDOS]     "Recommendations for the Protection against
                  Distributed Denial-of-Service Attacks in the
                  Internet",
                  http://www.iwar.org.uk/comsec/resources/dos/ddos_en.
                  htm
       [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/

Acknowledgements

   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),
        Eamon O'Tuathail (eamon.otuathail@clipcode.com),
        Magnus Nystrom (magnus@rsasecurity.com),
        Gareth Richards (grichards@rsasecurity.com)

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











Editor: Farrell                                              [Page 13]

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Editor's Address

   Stephen Farrell,
   Baltimore Technologies,
   39 Parkgate Street,
   Dublin 8,
   IRELAND
   Phone: +353-1-881-6000
   Email: stephen.farrell@baltimore.ie

Full Copyright Statement

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   FORCE DISCLAIMS 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.

Appendix A: XML Schema

   <?xml version="1.0"?>
   <!--DOCTYPE schema PUBLIC "-//W3C//DTD XMLSchema 200102//EN"
      "XMLSchema.dtd" [
       <!ATTLIST schema
       xmlns:sacred CDATA #FIXED "sacred-2002-09-27"
      >
       <!ENTITY sacred 'sacred-2002-09-27'>
       <!ENTITY % p ''>
       <!ENTITY % s ''>
      ] -->
   <schema
     targetNamespace="sacred-2002-09-27"

Editor: Farrell                                              [Page 14]

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     xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
     xmlns:sacred="sacred-2002-09-27"
     xmlns="http://www.w3.org/2000/10/XMLSchema">
     <!-- extensibility holes -->
     <complexType name="ProcessInfoType">
      <sequence maxOccurs="unbounded">
       <any namespace="##other"/>
      </sequence>
     </complexType>
     <element name="ProcessInfo" type="sacred:ProcessInfoType"/>
     <complexType name="ClientInfoType">
      <sequence maxOccurs="unbounded">
       <any namespace="##other"/>
      </sequence>
     </complexType>
     <element name="ClientInfo" type="sacred:ClientInfoType"/>
     <!-- Where to put authenentication information -->
     <complexType name="AuthInfoType">
      <choice>
       <element name="DigestMD5AuthInfo">
        <complexType>
         <sequence>
          <element name="PasswordVerifier"type="ds:CryptoBinary"/>
          <element name="Realm" type="string" />
         </sequence>
        </complexType>
       </element>
       <sequence maxOccurs="unbounded">
        <any namespace="##other"/>
       </sequence>
      </choice>
     </complexType>
     <element name="AuthInfo" type="sacred:AuthInfoType"/>
     <!-- authentication mechanism parameters -->
     <complexType name="AuthParamsType">
      <choice>
       <element name=" DigestMD5AuthParams">
        <complexType>
         <sequence>
          <element name="Realm" type="string"
            minOccurs="1" maxOccurs="unbounded"/>
         </sequence>
        </complexType>
       </element>
       <sequence maxOccurs="unbounded">
        <any namespace="##other"/>
       </sequence>
      </choice>
     </complexType>
     <element name="AuthParams" type="sacred:AuthParamsType"/>
     <!-- Protocol messsages -->
     <!-- "account handling" operations -->
     <!-- Information request -->

Editor: Farrell                                              [Page 15]

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     <element name="InfoRequest"/>
     <element name="InfoResponse">
      <complexType>
       <sequence>
        <element name="Status" type="string" minOccurs="0"/>
        <element name="ServerId" type="string"/>
        <element ref="sacred:AuthParams"/>
        <element ref="sacred:ProcessInfo" minOccurs="0"/>
       </sequence>
      </complexType>
     </element>
     <!-- Create Account Request -->
     <element name="CreateAccountRequest">
      <complexType>
       <sequence>
        <element name="UserId" type="string"/>
        <element ref="sacred:AuthInfo"/>
        <element ref="sacred:ProcessInfo" minOccurs="0"/>
       </sequence>
      </complexType>
     </element>
     <!-- reomve account request -->
     <element name="RemoveAccountRequest">
      <complexType>
       <sequence>
        <element ref="sacred:ProcessInfo" minOccurs="0"/>
       </sequence>
      </complexType>
     </element>
     <!-- password change request -->
     <element name="ModifyAccountRequest">
      <complexType>
       <sequence>
        <element ref="sacred:AuthInfo"/>
        <element ref="sacred:ProcessInfo" minOccurs="0"/>
       </sequence>
      </complexType>
     </element>
     <!-- "run-time" operations -->
     <!-- DownLoad Request -->
     <element name="DownloadRequest">
      <complexType>
       <sequence>
        <element name="CredentialSelector" type="string"
   minOccurs="0"/>
        <element ref="sacred:ProcessInfo" minOccurs="0"/>
       </sequence>
      </complexType>
     </element>
     <!-- Download Response -->
     <element name="DownloadResponse">
      <complexType>
       <sequence>

Editor: Farrell                                              [Page 16]

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        <element name="Status" type="string" minOccurs="0"/>
        <element name="Credential" type="sacred:CredentialType"
         maxOccurs="unbounded"/>
       </sequence>
      </complexType>
     </element>
     <!-- Upload request -->
     <element name="UploadRequest">
      <complexType>
       <sequence>
        <element name="Credential" type="sacred:CredentialType"
         minOccurs="0" maxOccurs="1" />
       </sequence>
       <attribute name=öDeleteö type=östringö use=öoptionalö/>
      </complexType>
     </element>
     <!-- Credential related structures -->
     <!-- A new ds:KeyInfo thing -->
     <element name="SacredPKCS15" type="ds:CryptoBinary"/>
     <!-- credential -->
     <complexType name="CredentialType">
      <sequence>
       <element name="CredentialSelector" type="string"/>
       <element name="LastModified" type="dateTime"/>
       <element name="Payload" type="ds:KeyInfoType"/>
       <element name="TimeToLive" type="string" minOccurs="0"/>
       <element ref="sacred:ProcessInfo" minOccurs="0"/>
       <element ref="sacred:ClientInfo" minOccurs="0"/>
      </sequence>
      <attribute name=öDeleteö type=östringö use=öoptionalö/>
     </complexType>
     <!-- if base64Binary isn't in your schema editor then add this -->
     <simpleType name="base64Binary">
      <restriction base="string"/>
     </simpleType>
   </schema>

Appendix B: An Example of Tuning with BEEP

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

       L: <wait for incoming connection>
       I: <open connection>
       L: RPY 0 0 . 0 170
       L: Content-Type: application/beep+xml
       L:
       L: <greeting>
       L:    <profile uri='http://iana.org/beep/TLS' />
       L:    <profile uri='http://iana.org/beep/SASL/SASL-MD5' />
       L: </greeting>
       L: END
       I: RPY 0 0 . 0 52

Editor: Farrell                                              [Page 17]

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       I: Content-Type: application/beep+xml
       I:
       I: <greeting />
       I: END
       I: MSG 0 1 . 52 184
       I: Content-Type: application/beep+xml
       I:
       I: <start number='1'>
       I:    <profile uri='http://iana.org/beep/SASL/SASL-MD5'>
       I:        <![CDATA[<blob>...</blob>]]>
       I:    </profile>
       I: </start>
       I: END
       L: RPY 0 1 . 170 783
       L: Content-Type: application/beep+xml
       L:
       L: <profile uri='http://iana.org/beep/SASL/SASL-MD5'>
       L:     <![CDATA[<blob>...</blob>]]>
       L: </profile>
       L: END
       I: MSG 1 0 . 0 559
       I: Content-Type: application/beep+xml
       I:
       I: <blob>...</blob>
       I: END
       L: RPY 1 0 . 0 429
       L: Content-Type: application/beep+xml
       L:
       L: <blob>...</blob>
       L: END
       I: MSG 1 1 . 559 82
       I: Content-Type: application/beep+xml
       I:
       I: <blob>...</blob>
       I: END
       L: RPY 1 2 . 429 66
       L: Content-Type: application/beep+xml
       L:
       L: <blob status='complete' />
       L: END

           ... successful transport security negotiation ...

       L: RPY 0 0 . 0 127
       L: Content-Type: application/beep+xml
       L:
       L: <greeting>
       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:

Editor: Farrell                                              [Page 18]

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       I: <greeting />
       I: 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
   2.3.

   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
   PDUs.

Appendix D: Changes & Open Issues

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

   Open Issues:


   -03:
        - 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 û changed to SASL-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:-)



Editor: Farrell                                              [Page 19]

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   -02:
        - 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
             LastModified

   -01: Changes as per mailing list discussion:
        - Change from authors to editor + acks
        - Included resolved comments from list:
          - 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
          certificate.
        - 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 20]


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