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

Versions: 00 01 02 03 04 05 06 07

Network Working Group                                          L. Howard
Internet-Draft                                                      PADL
Intended status: Experimental                                N. Williams
Expires: October 27, 2013                                   Cryptonector
                                                          April 25, 2013


 A SASL and GSS-API Mechanism for the BrowserID Authentication Protocol
                   draft-howard-gss-browserid-04.txt

Abstract

   This document defines protocols, procedures and conventions for a
   Generic Security Service Application Program Interface (GSS-API)
   security mechanism based on the BrowserID authentication mechanism.
   Through the GS2 family of mechanisms defined in RFC 5801, these
   protocols also define how Simple Authentication and Security Layer
   (SASL, RFC 4422) applications may use BrowserID.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on October 27, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



Howard & Williams       Expires October 27, 2013                [Page 1]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.      Introduction . . . . . . . . . . . . . . . . . . . . . . .  4
   1.1.    Discovery and Negotiation  . . . . . . . . . . . . . . . .  5
   1.2.    Authentication . . . . . . . . . . . . . . . . . . . . . .  5
   1.3.    Message protection services  . . . . . . . . . . . . . . .  6
   2.      Requirements notation  . . . . . . . . . . . . . . . . . .  7
   3.      Naming . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   3.1.    GSS name types . . . . . . . . . . . . . . . . . . . . . .  8
   3.1.1.  GSS_C_NT_BROWSERID_PRINCIPAL . . . . . . . . . . . . . . .  8
   3.1.2.  GSS_C_NT_USER_NAME . . . . . . . . . . . . . . . . . . . .  8
   3.1.3.  GSS_C_NT_HOSTBASED_SERVICE . . . . . . . . . . . . . . . .  8
   3.1.4.  GSS_C_NT_DOMAINBASED_SERVICE . . . . . . . . . . . . . . .  9
   3.1.5.  GSS_C_NT_ANONYMOUS . . . . . . . . . . . . . . . . . . . .  9
   3.2.    Audience encoding  . . . . . . . . . . . . . . . . . . . .  9
   3.3.    Name canonicalization  . . . . . . . . . . . . . . . . . .  9
   3.4.    Exported name token format . . . . . . . . . . . . . . . .  9
   3.5.    Naming extensions  . . . . . . . . . . . . . . . . . . . . 10
   4.      Context tokens . . . . . . . . . . . . . . . . . . . . . . 11
   4.1.    Base protocol  . . . . . . . . . . . . . . . . . . . . . . 11
   4.1.1.  Initial context token  . . . . . . . . . . . . . . . . . . 11
   4.1.2.  Acceptor context token . . . . . . . . . . . . . . . . . . 12
   4.1.3.  Initiator context completion . . . . . . . . . . . . . . . 13
   4.2.    Mutual authentication  . . . . . . . . . . . . . . . . . . 13
   4.2.1.  Initiator mutual authentication context token  . . . . . . 14
   4.2.2.  Acceptor mutual authentication context token . . . . . . . 14
   4.2.3.  Initiator mutual authentication context completion . . . . 14
   4.2.4.  Acceptor certificate advertisement . . . . . . . . . . . . 15
   4.3.    Fast re-authentication . . . . . . . . . . . . . . . . . . 16
   4.3.1.  Ticket generation  . . . . . . . . . . . . . . . . . . . . 16
   4.3.2.  Initiator re-authentication context token  . . . . . . . . 16
   4.3.3.  Acceptor re-authentication context token . . . . . . . . . 17
   4.3.4.  Interaction with mutual authentication . . . . . . . . . . 18
   4.3.5.  Ticket renewal . . . . . . . . . . . . . . . . . . . . . . 18
   4.4.    Extra round-trip (XRT) option  . . . . . . . . . . . . . . 18
   4.4.1.  Initiator XRT advertisement  . . . . . . . . . . . . . . . 18
   4.4.2.  Acceptor XRT advertisement . . . . . . . . . . . . . . . . 19
   4.4.3.  Initiator XRT context token  . . . . . . . . . . . . . . . 19
   4.4.4.  Acceptor XRT context token validation  . . . . . . . . . . 19
   4.4.5.  Interaction with message protection services . . . . . . . 19
   5.      Validation . . . . . . . . . . . . . . . . . . . . . . . . 20
   5.1.    Expiry times . . . . . . . . . . . . . . . . . . . . . . . 20
   5.2.    Audience . . . . . . . . . . . . . . . . . . . . . . . . . 20
   5.3.    Channel bindings . . . . . . . . . . . . . . . . . . . . . 20



Howard & Williams       Expires October 27, 2013                [Page 2]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   5.4.    Key agreement  . . . . . . . . . . . . . . . . . . . . . . 20
   5.5.    Signatures . . . . . . . . . . . . . . . . . . . . . . . . 21
   5.6.    Replay detection . . . . . . . . . . . . . . . . . . . . . 21
   5.7.    Return flags . . . . . . . . . . . . . . . . . . . . . . . 21
   6.      Assertion claims . . . . . . . . . . . . . . . . . . . . . 22
   6.1.    Request (initiator/UA) assertion . . . . . . . . . . . . . 22
   6.1.1.  "aud" (Audience) . . . . . . . . . . . . . . . . . . . . . 22
   6.1.2.  "exp" (Expiry time)  . . . . . . . . . . . . . . . . . . . 23
   6.1.3.  "iat" (Issued at time) . . . . . . . . . . . . . . . . . . 23
   6.1.4.  "nbf" (Not before time)  . . . . . . . . . . . . . . . . . 23
   6.1.5.  "ecdh" (Elliptic Curve Diffie-Hellman key agreement) . . . 23
   6.1.6.  "cb" (Channel binding) . . . . . . . . . . . . . . . . . . 23
   6.1.7.  "nonce" (Mutual authentication nonce)  . . . . . . . . . . 23
   6.1.8.  "tkt" (Ticket) . . . . . . . . . . . . . . . . . . . . . . 24
   6.1.9.  "opts" (Options) . . . . . . . . . . . . . . . . . . . . . 24
   6.2.    Response (acceptor/RP) assertion . . . . . . . . . . . . . 24
   6.2.1.  "iat" (Issued at time) . . . . . . . . . . . . . . . . . . 25
   6.2.2.  "ecdh" (Elliptic Curve Diffie-Hellman key agreement) . . . 25
   6.2.3.  "exp" (Expiry time)  . . . . . . . . . . . . . . . . . . . 26
   6.2.4.  "nonce" (Mutual authentication nonce)  . . . . . . . . . . 26
   6.2.5.  "tkt" (Ticket) . . . . . . . . . . . . . . . . . . . . . . 26
   6.2.6.  "jti" (JWT ID) . . . . . . . . . . . . . . . . . . . . . . 26
   6.3.    Error (acceptor/RP) assertion  . . . . . . . . . . . . . . 26
   6.3.1.  "gss-maj" (GSS major status code)  . . . . . . . . . . . . 26
   6.3.2.  "gss-min" (GSS minor status code)  . . . . . . . . . . . . 26
   6.4.    XRT assertion  . . . . . . . . . . . . . . . . . . . . . . 29
   7.      Key derivation . . . . . . . . . . . . . . . . . . . . . . 30
   7.1.    Diffie-Hellman Key (DHK) . . . . . . . . . . . . . . . . . 30
   7.2.    Context Master Key (CMK) . . . . . . . . . . . . . . . . . 30
   7.3.    RP Response Key (RRK)  . . . . . . . . . . . . . . . . . . 30
   7.4.    Context Root Key (CRK) . . . . . . . . . . . . . . . . . . 30
   7.5.    Authenticator Root Key (ARK) . . . . . . . . . . . . . . . 31
   7.6.    Authenticator Session Key (ASK)  . . . . . . . . . . . . . 31
   7.6.1.  Extra Round Trip Key (XRTK)  . . . . . . . . . . . . . . . 31
   7.7.    GSS Pseudo-Random Function (PRF) . . . . . . . . . . . . . 31
   8.      Example  . . . . . . . . . . . . . . . . . . . . . . . . . 32
   9.      Security Considerations  . . . . . . . . . . . . . . . . . 40
   9.1.    Host certificates for mutual authentication  . . . . . . . 40
   9.2.    Error statuses . . . . . . . . . . . . . . . . . . . . . . 40
   10.     IANA Considerations  . . . . . . . . . . . . . . . . . . . 41
   10.1.   OID Registry . . . . . . . . . . . . . . . . . . . . . . . 41
   10.2.   SASL Registry  . . . . . . . . . . . . . . . . . . . . . . 42
   11.     References . . . . . . . . . . . . . . . . . . . . . . . . 43
   11.1.   Normative References . . . . . . . . . . . . . . . . . . . 43
   11.2.   Informative References . . . . . . . . . . . . . . . . . . 44
           Authors' Addresses . . . . . . . . . . . . . . . . . . . . 46





Howard & Williams       Expires October 27, 2013                [Page 3]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


1.  Introduction

   [BrowserID] is a web-based three-party security protocol by which
   user agents can present to a Relying Party (RP) a signed assertion of
   e-mail address ownership.  BrowserID was intended to be used for web
   authentication.  We find BrowserID to be useful in general, therefore
   we define herein how to use it in many more applications.

   The Simple Authentication and Security Layer (SASL) [RFC4422] is a
   framework for providing authentication and message protection
   services via pluggable mechanisms.  Protocols that support it include
   IMAP, SMTP, and XMPP.

   The Generic Security Service Application Program Interface (GSS-API)
   [RFC2743] provides a framework for authentication and message
   protection services through a common programming interface.  This
   document conforms to the SASL and GSS-API bridge specified in
   [RFC5801], so it defines both a SASL and GSS-API mechanism.

   The BrowserID mechanism described in this document reuses the
   existing web-based BrowserID protocol, but profiles it for use in
   applications that support SASL or GSS-API, adding features such as
   key agreement, mutual authentication, and fast re-authentication.

   The following diagram illustrates the interactions between the three
   parties in the GSS BrowserID protocol.  Note that the terms client,
   initiator and user agent (UA) are used interchangeably in this
   document, as are server, acceptor and relying party (RP).























Howard & Williams       Expires October 27, 2013                [Page 4]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


                       +------------+
                       | BrowserID  |
                       | identity   |
                       | provider   |
                       +------------+
                         //      \\
                        //        \\
                       //          \\
                      //            \\
      make signed    //              \\    fetch IdP public
      certificate   //                \\   key over HTTPS
      for user's   //                  \\  (RP may cache)
      public key  //                    \\
                 //                      \\
                //                        \\
               //                          \\
              |/                            \|
       +-------------+                     +-------------+
       | SASL or GSS |    GSS BrowserID    | SASL or GSS |
       | client/UA   |<------------------->| server/RP   |
       | (initiator) |                     | (acceptor)  |
       +-------------+                     +-------------+


                    Figure 1: Interworking Architecture

1.1.  Discovery and Negotiation

   The means of discovering GSS-API peers and their supported mechanisms
   is out of this specification's scope.  They may use SASL [RFC4422] or
   the Simple and Protected Negotiation mechanism (SPNEGO) [RFC4178].

   Discovery of a BrowserID identity provider (IdP) for a user is
   described in the BrowserID specification.  A domain publishes a
   document containing their public key and URIs for authenticating and
   provisioning users, or pointer to an authority containing such a
   document.

1.2.  Authentication

   The GSS-API protocol involves a client, known as the initiator,
   sending an initial security context token of a chosen GSS-API
   security mechanism to a peer, known as the acceptor.  The two peers
   subsequently exchange, synchronously, as many security context tokens
   as necessary to complete the authentication or fail.  The specific
   number of context tokens exchanged varies by security mechanism: in
   the case of the BrowserID mechanism, it is typically two (i.e. a
   single round trip), however it can be more in some cases.  Once



Howard & Williams       Expires October 27, 2013                [Page 5]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   authentication is complete, the initiator and acceptor share a
   security context which identifies the peers and can optionally be
   used for integrity or confidentiality protecting subsequent
   application messages.

   The original BrowserID protocol, as defined outside this document,
   specifies a bearer token authentication protocol for web
   applications.  The user agent generates a short-term key pair, the
   public key of which is signed by the user's IdP.  (The user must have
   already authenticated to the IdP; how this is done is not specified
   by BrowserID, but forms-based authentication is common.)  The IdP
   returns a certificate for the user which may be cached by the user's
   browser.  When authenticating to a Relying Party (RP), the browser
   generates an identity assertion containing the RP domain and an
   expiration time.  The user agent signs this and presents both the
   assertion and certificate to the RP.  (The combination of an
   assertion and zero or more certificates is termed a "backed
   assertion".)  The RP fetches the public key for the IdP, validates
   the user's certificate (and those of any intermediate certifying
   parties) and then verifies the assertion.

   The GSS BrowserID protocol extends this by having the RP always send
   back a response to the user agent, which at a minimum provides key
   confirmation (this is needed for some key agreement methods) and
   indicates the lifetime of the established security context.  The key
   confirmation token is also required for mutual authentication, when
   the initiator application requests that feature.

1.3.  Message protection services

   GSS-API provides a number of a message protection services:

   GSS_Wrap()  integrity and optional confidentiality for a message

   GSS_GetMIC()  integrity for a message sent separately

   GSS_Pseudo_random()  shared key derivation (e.g., for keying external
      confidentiality+integrity layers)

   These services may be used with security contexts that have a shared
   session key, to protect application-layer messages.










Howard & Williams       Expires October 27, 2013                [Page 6]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


2.  Requirements notation

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

   The reader is assumed to be familiar with the terms used in the
   BrowserID specification.











































Howard & Williams       Expires October 27, 2013                [Page 7]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


3.  Naming

   The GSS-API provides a rich security principal naming model.  At its
   most basic the query forms of names consist of a user-entered/
   displayable string and a "name-type".  Name-types are constants with
   names prefixed with "GSS_C_NT_" in the GSS-API.  Names may also have
   attributes [RFC6680].

3.1.  GSS name types

3.1.1.  GSS_C_NT_BROWSERID_PRINCIPAL

   This name may contain an e-mail address, or a service principal name
   identifying an acceptor.  The encoding of service principal names is
   intended to be somewhat compatible with the Kerberos [RFC4120]
   security protocol (without the realm name).

   The following ABNF defines the 'name' rule that names of this type
   must match.

   [[anchor1: Should we reference RFC2822 here?  The Mozilla BrowserID
   docs sure don't.]]

       char-normal = %x00-2E/%x30-3F/%x41-5B/%x5D-FF
       char-escaped = "\" %x2F / "\" %x40 / "\" %x5C
       name-char = char-normal / char-escaped
       name-string = 1*name-char
       user = name-string
       domain = name-string
       email = user "@" domain
       service-name = name-string
       service-host = name-string
       service-specific = name-string
       service-specifics = service-specific 0*("/" service-specifics)
       spn = service-name ["/" service-host [ "/" service-specifics]]
       name = email / spn

3.1.2.  GSS_C_NT_USER_NAME

   This name is implicitly converted to a GSS_C_NT_BROWSERID_PRINCIPAL.
   A default domain may be appended when importing names of this type.

3.1.3.  GSS_C_NT_HOSTBASED_SERVICE

   This name is transformed by replacing the "@" symbol with a "/", and
   then implicitly converted to a GSS_C_NT_BROWSERID_PRINCIPAL.





Howard & Williams       Expires October 27, 2013                [Page 8]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


3.1.4.  GSS_C_NT_DOMAINBASED_SERVICE

   [RFC5178] domain-based service names are transformed into a
   GSS_C_NT_BROWSERID_PRINCIPAL as follows:

   o  the <service> name becomes the first component of the BrowserID
      principal name (service-name in ABNF)

   o  the <hostname> becomes the second component (service-host)

   o  the <domain> name becomes the third component (service-specific)

3.1.5.  GSS_C_NT_ANONYMOUS

   If the initiator principal's leaf certificate does not contain a
   "principal" claim, then the initiator name has this name type.

3.2.  Audience encoding

   A GSS-API service name is encoded into a BrowserID audience URL with
   the following syntax, where spn is defined above:

                         audience = "urn:x-gss:" spn

   [[anchor2: Can we request assignment of a URN?]]

3.3.  Name canonicalization

   The BrowserID GSS-API mechanism performs no name canonicalization.
   The mechanism's GSS_Canonicalize_name() returns an MN whose display
   form is the same as the query form.  Of course, the principal named
   obtained from a CREDENTIAL HANDLE may be canonical in that the IdP
   might only issue credentials for canonical names, but credential
   acquisition is out of scope here.

3.4.  Exported name token format

   The exported name token format for the BrowserID GSS-API mechanism is
   the same as the query form, plus the standard exported name token
   format header mandated by the GSS-API [RFC2743].

   [[anchor3: Do we wish to say anything about the exported composite
   name token format?  It should be an encoding of the initiator's leaf
   certificate.]]







Howard & Williams       Expires October 27, 2013                [Page 9]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


3.5.  Naming extensions

   The acceptor MAY surface attributes from the assertion and any
   certificates using GSS_Get_name_attribute() (see [RFC6680]).  The URN
   prefix is "urn:<TBD>:params:gss:jwt".  If a SAML assertion is present
   in the "saml" parameter of the leaf certificate, it may be surfaced
   using the URN prefix "urn:<TBD>:params:gss:federated-saml-attribute".

   Attributes from the assertion MUST be marked as unauthenticated
   unless otherwise validated by the acceptor (e.g. the audience).

   Attributes from certificates SHOULD be marked as authenticated.







































Howard & Williams       Expires October 27, 2013               [Page 10]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


4.  Context tokens

   All context tokens include a two-byte token identifier followed by a
   backed BrowserID assertion.  This document defines the following
   token IDs:

         +---------+----------+-------+--------------------------+
         | Section | Token ID | ASCII |        Description       |
         +---------+----------+-------+--------------------------+
         |  4.1.1  |  0x632C  |   c,  |  Initiator context token |
         |         |          |       |                          |
         |  4.1.2  |  0x432C  |   C,  |  Acceptor context token  |
         |         |          |       |                          |
         |         |  0x442C  |   D,  |  Context deletion token  |
         |         |          |       |                          |
         |  4.2.4  |  0x6D2C  |   m,  | Initiator metadata token |
         |         |          |       |                          |
         |  4.2.4  |  0x4D2C  |   M,  |  Acceptor metadata token |
         +---------+----------+-------+--------------------------+

   The token ID has a human-readable ASCII encoding for the benefit of
   pure SASL implementations of this mechanism.

4.1.  Base protocol

4.1.1.  Initial context token

   The initial context token is framed per Section 1 of [RFC2743]:

                GSS-API DEFINITIONS ::=
                    BEGIN

                    MechType ::= OBJECT IDENTIFIER
                    -- representing BrowserID mechanism
                    GSSAPI-Token ::=
                    [APPLICATION 0] IMPLICIT SEQUENCE {
                        thisMech MechType,
                        innerToken ANY DEFINED BY thisMech
                            -- token ID and backed assertion
                    }
                    END

   Unlike many other GSS-API mechanisms such as Kerberos, this token
   framing is not used by subsequent context or by [I-D.zhu-negoex]
   metadata tokens.  As such, pure SASL implementations of this
   mechanism do not need to deal with DER encoding the mechanism object
   identifier.




Howard & Williams       Expires October 27, 2013               [Page 11]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   GSS BrowserID is a family of mechanisms, where the last element in
   the OID arc indicates the [RFC4121] encryption type supported for
   message protection services.  The OID prefix is
   1.3.6.1.4.1.5322.24.1.  The NULL encryption type is valid, in which
   case services that require a key are not available.

   The innerToken consists of the initiator context token ID
   concatenated with a backed assertion for the audience corresponding
   to the target name passed into GSS_Init_sec_context().  In addition,
   the assertion MAY contain the additional claims, which are described
   later in this document:

   o  ECDH key agreement parameters (see Section 6.1.5)

   o  Channel binding information (see Section 6.1.6)

   o  A nonce for binding the request to a response signed with a
      private key for mutual authentication (see Section 6.1.7)

   o  A ticket identifier for fast re-authentication using an
      established session key rather than a BrowserID certificate (see
      Section 6.1.8)

   The call to GSS_Init_sec_context() returns GSS_C_CONTINUE_NEEDED to
   indicate that a subsequent context token from the acceptor is
   expected.

4.1.2.  Acceptor context token

   Upon receiving a context token from the initiator, the acceptor
   validates that the token is well formed and contains a valid
   BrowserID mechanism OID and the initiator context token ID.

   The acceptor then verifies the backed identity assertion per the
   BrowserID specification.  This includes validating the expiry times,
   audience, certificate chain, and assertion signature.  The acceptor
   then verifies the channel binding token, if present, and any other
   GSS-specific claims in the assertion.  In case of failure, a response
   assertion containing GSS major and minor status codes SHOULD be
   returned.

   If the [RFC3961] encryption type for the selected mechanism is not
   ENCTYPE_NULL, the acceptor generates a ECDH public key using the
   parameters received from the client (see Section 6.2.2), and from it
   derives the RP Response Key (RRK) (see Section 7.3).  The acceptor
   then generates a response assertion containing its ECDH public key
   and context expiration time (note that the context expiration time is
   a purely informational quantity).  The response assertion will be:



Howard & Williams       Expires October 27, 2013               [Page 12]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   o  signed in the acceptor's private key, if mutual authentication was
      requested, and the acceptor has a key (see Section 4.2);

   o  signed in the RRK, if the encryption type for the selected
      mechanism is not ENCTYPE_NULL;

   o  not signed in all other cases.

   The response assertion is encoded as a backed assertion, prefixed
   with the acceptor context token ID.  It SHALL have a certificate
   count of zero.

   Finally, the Context Root Key (CRK) (see Section 7.4) is derived from
   the ECDH shared secret (if present) and GSS_S_COMPLETE is returned,
   along with the initiator name from the verified assertion.  If the
   CRK is available, the replay_det_state (GSS_C_REPLAY_FLAG),
   sequence_state (GSS_C_SEQUENCE_FLAG), conf_avail (GSS_C_CONF_FLAG)
   and integ_avail (GSS_C_INTEG_FLAG) security context flags are set to
   TRUE.

   Other assertion/certificate claims MAY be made available via
   GSS_Get_name_attribute().

4.1.3.  Initiator context completion

   Upon receiving the acceptor context token, the initiator unpacks the
   response assertion and, if applicable, computes the ECDH shared
   secret and RRK.  The RRK is used to verify the response assertion
   unless mutual authentication is available, in which case the
   acceptor's public key will be used.

   The initiator sets the context expiry time with that received in the
   response assertion, if present; otherwise, the context expires when
   the initiator principal's certificate expires.

   The CRK is derived from the ECDH shared secret and GSS_S_COMPLETE is
   returned to indicate the initiator is authenticated and the context
   is ready for use.  No output token is emitted.  Security context
   flags are set as for the acceptor context.

4.2.  Mutual authentication

   Mutual authentication allows the acceptor to be authenticated to the
   initiator.  The mechanism SHALL set the mutual_state security context
   flag (GSS_C_MUTUAL_FLAG) to TRUE if mutual authentication succeeded.
   Support for mutual authentication is OPTIONAL.

   The base protocol is extended as follows to support this:



Howard & Williams       Expires October 27, 2013               [Page 13]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


4.2.1.  Initiator mutual authentication context token

   If the initiator requested the mutual_state flag, it sends in its
   request assertion an "opts" claim (see Section 6.1.9) containing the
   "ma" value.  It also includes a nonce (see Section 6.1.7) in order to
   bind the initiator and acceptor assertions.

4.2.2.  Acceptor mutual authentication context token

   If the acceptor has a private key and certificate available and the
   initiator indicated it desired mutual authentication by including the
   "ma" protocol option, the acceptor signs the response using a private
   key rather than the RP Response Key (RRK).  The response includes the
   nonce from the initiator's assertion.  The acceptor MUST reject
   requests for mutual authentication lacking a nonce.

   While the response is a backed assertion, in order to take advantage
   of existing keying infrastructures BrowserID certificates MUST NOT be
   included in the backed assertion.  Rather, an X.509 certificate SHALL
   be included as a value for the "x5c" header parameter in the
   assertion (see [I-D.ietf-jose-json-web-signature] 4.1.6).  The
   certificate MUST be valid for signing.

   [[anchor4: We don't want to burden the initiator with having to
   implement both methods of authenticating acceptors, and given that
   initiators and acceptors both will generally need a PKIX
   implementation, and given that acceptors will need a PKIX credential
   for TLS, and that there is as yet no standard protocol for automatic
   provisioning of BrowserID credentials for servers, using PKIX to
   authenticate the server seems to be the easiest way to go.]]

4.2.3.  Initiator mutual authentication context completion

   The initiator verifies the assertion signature and that the nonce
   matches, and validates the certificate chain according to [RFC5280].

   Initiators MUST authenticate the service name using the matching
   rules below:

   o  A service-name EKU from the registry defined by [I-D.zhu-pku2u];
      id-kpServerAuth maps to the "http" service

   o  A spn expressed as a KRB5PrincipalName in the id-pkinit-san
      otherName SAN (see [RFC4556] Section 3.2.2; the realm is ignored)

   o  A BrowserID audience URN containing the spn, encoded in a URI SAN
      (see Section 3.2)




Howard & Williams       Expires October 27, 2013               [Page 14]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   o  An out-of-band binding to the certificate

   If there are no EKUs, or a single EKU containing id-kp-
   anyExtendedKeyUsage, and no SAN containing the service name is
   present, then all service names match.  If a SAN containing the
   service name is present, then any EKUs are ignored.

   If the the host component of the service name (service-host) is not
   expressed in a SAN as specified above, it MUST be present as a value
   for the dNSName SAN or as the least significant Common Name RDN.

   Note only the id-pkinit-san or URI SANs provide the ability to
   authenticate the a service name containing a service-specific
   component.

4.2.4.  Acceptor certificate advertisement

   [I-D.zhu-negoex] may be used to advertise acceptor certificates.

   If the acceptor supports mutual authentication, it MAY include its
   certificate and any additional certificates inside a backed assertion
   with an empty payload as output for GSS_Query_meta_data().  The
   "assertion" is prefixed with the two byte token identifier "M,".

   Upon receiving this, the initiator MAY validate the certificate or
   fingerprint, or present either to the initiator before committing to
   authenticate.

   The NegoEx signing key is the output of GSS_Pseudo_random() (see
   Section 7.7) with an input of GSS_C_PRF_KEY_FULL and "gss-browserid-
   negoex-initiator" or "gss-browserid-negoex-acceptor" (without
   quotes), depending on the party generating the signature.

   The NegoEx authentication scheme is the binary encoding of the
   following hexadecimal string:

   535538008647F5BC624BD8076949F0

   where the third byte (zero above) is set to the [RFC3961] encryption
   type for the selected mechanism.  The authentication scheme for
   encryption types greater than 255 is not specified here.

   There is currently no initiator-sent metadata defined and acceptors
   should ignore any sent.  The metadata is advisory and the initiator
   is free to ignore it.

   [[anchor5: Delete this section as NegoEx will likely not be
   progressed.]]



Howard & Williams       Expires October 27, 2013               [Page 15]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


4.3.  Fast re-authentication

   Fast re-authentication allows a security context to be established
   using a secret key derived from the initial certificate-signed ECDH
   key agreement.

   The re-authentication assertion is signed with a HMAC using the
   Authenticator Root Key (ARK) (see Section 7.5), rather than a
   initiator principal's BrowserID certificate.

   Support for fast re-authentication is OPTIONAL and is indicated by
   the acceptor returning a ticket in the response assertion.

4.3.1.  Ticket generation

   If the acceptor supports re-authentication, the following steps are
   added to Section 4.1.2:

   1.  A unique, opaque ticket identifier is generated.

   2.  The acceptor creates a JSON object containing the ticket
       identifier and expiry time and returns it in the response to the
       initiator (see Section 6.2.5).

   The acceptor must be able to use the ticket identifier to securely
   retrieve the subject, issuer, audience, expiry time, ARK and any
   other relevant properties of the original security context.  One
   implementation choice may be to use the ticket identifier as a key
   into a dictionary containing this information.  Another would be to
   encrypt this information in a long-term secret only known to the
   acceptor and encode the resulting cipher-text in the opaque ticket
   identifier.

   The ticket expiry time by default SHOULD match the initiator's
   certificate expiry, however it MAY be configurable so the ticket
   expires before or after the certificate.

   The initiator MAY cache tickets, along with the ARK, received from
   the acceptor in order to re-authenticate to it at a future time.

4.3.2.  Initiator re-authentication context token

   The initiator looks in its ticket cache for an unexpired ticket for
   the desired acceptor.  If none is found, the normal certificate-based
   authentication flow is performed, otherwise:






Howard & Williams       Expires October 27, 2013               [Page 16]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   1.  The initiator generates a re-authentication assertion containing:
       the name of the acceptor (see Section 6.1.1), an expiry time (see
       Section 6.1.2) and/or the current time (see Section 6.1.3),
       optional channel binding information (see Section 6.1.6), a
       random nonce (see Section 6.1.7), and the ticket identifier (see
       Section 6.1.8).

   2.  The initiator signs the re-authentication assertion with the ARK,
       using the hash algorithm associated with the original context key
       (see Section 10.1; HS256 is specified for the encryption types
       referenced in this document).

   3.  The re-authentication assertion is packed into a backed
       assertion.  The certificate count is zero as the assertion is
       signed with an established symmetric key.

   4.  The initiator generates an Authenticator Session Key (ASK) (see
       Section 7.6) which is used to verify the response and derive the
       CRK.

   [[anchor6: Question: do we want an option to do an ECDH session key
   exchange in the fast re-auth case?  If we had a GSS req_flag for
   requesting perfect forward security (PFS) then we would want to have
   this option.]]

4.3.3.  Acceptor re-authentication context token

   1.  The acceptor unpacks the re-authentication assertion and
       retrieves the ARK, ticket expiry time, mutual authentication
       state and any other properties (such as the initiator name)
       associated with the ticket identifier.

   2.  The acceptor validates that the ticket and re-authentication
       assertion have not expired.

   3.  The acceptor verifies the assertion using the ARK.

   4.  The acceptor generates the ASK (see Section 7.6) and derives the
       RRK and CRK from this (see Section 7.3 and Section 7.4,
       respectively).

   5.  The acceptor generates a response and signs and returns it.  Note
       that, unlike the certificate-based mutual authentication case,
       the nonce need not be echoed back as the ASK (and thus the RRK)
       is cryptographically bound to the nonce.

   If the ticket cannot be found, or the authentication fails, the
   acceptor SHOULD return a REAUTH_FAILED error, permitting the



Howard & Williams       Expires October 27, 2013               [Page 17]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   initiator to recover and fallback to generating a BrowserID
   assertion.  It MAY also include its local timestamp (see
   Section 6.2.1) so that the initiator can perform clock skew
   compensation.

4.3.4.  Interaction with mutual authentication

   The mutual authentication state of a re-authenticated context is
   transitive.  The initiator and acceptor MUST NOT set the mutual_state
   flag for a re-authenticated context unless the original context was
   mutually authenticated.

   As such, the mutual authentication state of the original context must
   be associated with the ticket.

4.3.5.  Ticket renewal

   Normally, re-authentication tickets are only issued when the
   initiator authenticated with a certificate-signed assertion.
   Acceptors MAY issue a new ticket with an expiry beyond the ticket
   lifetime when the initiator used a re-authentication assertion.  The
   issuing of new tickets MUST be subject to a policy that prevents them
   from being renewed indefinitely.

4.4.  Extra round-trip (XRT) option

   The extra round-trip (XRT) option adds an additional round trip to
   the context token exchange.  It allows the initiator to prove
   knowledge of the Context Master Key (CMK) (see Section 7.2) by
   sending an additional token signed in a key derived from the CMK and
   an acceptor-issued challenge.  Support for the XRT option is OPTIONAL
   in the acceptor and REQUIRED in the initiator.  The initiator is
   allowed to not request it, but MUST perform XRT if the acceptor
   requires it.

   (Note that the term "extra round trip" is something of a misnomer; it
   only adds an additional token to the context token exchange.  It is
   anticipated however that this mechanism will most commonly be used
   with pseudo-mechanisms or application protocols that require an even
   number of tokens.)

4.4.1.  Initiator XRT advertisement

   The initiator may advertise to the acceptor that it desires the XRT
   option by sending in its request assertion an "opts" claim (see
   Section 6.1.9) containing the "xrt" value.  This option MUST be set
   if the caller requested GSS_C_DCE_STYLE (see [RFC4757]).  Otherwise,
   the setting of this option is implementation dependent.



Howard & Williams       Expires October 27, 2013               [Page 18]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


4.4.2.  Acceptor XRT advertisement

   If the initiator requested the XRT option and the acceptor supports
   it, or the acceptor requires it, the acceptor sends a "jti" claim
   (see Section 6.2.6) in the response assertion containing a random
   base 64 URL encoded value.  This value MUST be at least 64 bits in
   length.  The acceptor then returns GSS_C_CONTINUE_NEEDED to indicate
   that an additional context token is expected from the initiator.

4.4.3.  Initiator XRT context token

   If the acceptor indicated support for the XRT option by including a
   "jti" claim in its response, then the initiator sends an additional
   context token to the acceptor.  This token contains the initiator
   context token ID concatenated with a backed assertion with zero
   certificates and an empty payload, signed using the XRTK (see
   Section 7.6.1).

4.4.4.  Acceptor XRT context token validation

   The acceptor MUST validate the XRT context token by first validating
   the context token ID, and then verifying the assertion signature with
   the XRTK.  The acceptor SHOULD reject XRT context tokens with a
   certificate count greater than zero.  Unknown claims in the assertion
   payload MUST be ignored.  The acceptor then returns GSS_C_COMPLETE to
   the caller.

   The acceptor MAY avoid using a replay cache when this option is in
   effect.

4.4.5.  Interaction with message protection services

   When the XRT option is in effect, the XRTK is used instead of the CMK
   to derive the Context Root Key (CRK) (see Section 7.4).  Per-message
   tokens MUST have the AcceptorSubkey flag set (see [RFC4121] Section
   4.2.2).















Howard & Williams       Expires October 27, 2013               [Page 19]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


5.  Validation

5.1.  Expiry times

   The expiry and, if present, issued-at and not-before times of all
   elements in a backed assertion, MUST be validated.  This applies
   equally to re-authentication assertions, public key assertions, and
   the entire certificate chain.  If the expiry time is absent, the
   issued-at time MUST be present, and the JWT implicitly expires a
   short, implementation-defined interval after the issued-at time.  (A
   suggested interval is five minutes.)

   The GSS context lifetime SHOULD NOT exceed the lifetime of the
   initiator principal's certificate.

   The lifetime of a re-authentication ticket SHOULD NOT exceed the
   lifetime of the initiator principal's certificate.  The acceptor MUST
   validate the ticket expiry time when performing re-authentication.

   Message protections services such as GSS_Wrap() SHOULD be available
   beyond the GSS context lifetime for maximum application
   compatibility.

5.2.  Audience

   If the credential passed to GSS_Accept_sec_context() is not for
   GSS_C_NO_NAME, then its string representation as a BrowserID
   principal MUST match the unencoded audience (that is, the audience
   without the URN prefix defined in Section 3.2).

5.3.  Channel bindings

   GSS-API channel binding is a protected facility for naming an
   enclosing channel between the initiator and acceptor.  If the
   acceptor passed in channel bindings to GSS_Accept_sec_context(), the
   assertion MUST contain a matching channel binding claim.  (Only the
   application_data component is validated.)

   The acceptor SHOULD accept any channel binding provided by the
   initiator if NULL channel bindings are passed to
   GSS_Accept_sec_context().

5.4.  Key agreement

   The initiator MUST choose an ECDH curve with an equivalent strength
   to the negotiated [RFC4121] encryption type.  Appropriate curves are
   given in Section 10.1.




Howard & Williams       Expires October 27, 2013               [Page 20]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   The curve strength MUST be verified by the acceptor.  A stronger than
   required curve MAY be selected by the initiator.

5.5.  Signatures

   Signature validation on assertions is the same as for the web usage
   of BrowserID, with the addition that response assertions may and re-
   authentication assertions must be signed with a symmetric key.  In
   this case the HMAC algorithm associated with the mechanism OID is
   used, and there are no certificates in the backed assertion.

5.6.  Replay detection

   If the XRT option is not in effect, the acceptor MUST maintain a
   cache of received assertions in order to guard against replay
   attacks.

5.7.  Return flags

   The initiator and acceptor should set the returned flags as follows:

   deleg_state  never set

   mutual_state  set if the initiator requested mutual authentication
      and mutual authentication succeeded

   replay_det_state  set if message protection services are available

   sequence_state  set if message protection services are available

   anon_state  set if the initiator principal's leaf certificate lacks a
      "principal" claim

   trans_state  set if the implementation supports importing and
      exporting of security contexts

   prot_ready_state  may be set when or after the RP Response Token is
      produced or consumed

   conf_avail  set if message protection services are available

   integ_avail  set if message protection services are available









Howard & Williams       Expires October 27, 2013               [Page 21]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


6.  Assertion claims

6.1.  Request (initiator/UA) assertion

   These claims are included in the assertion sent to the acceptor and
   are authenticated by the initiator's private key and certificate
   chain (directly, or in the case of re-authentication assertions,
   transitively).  Claims not specified here MUST be ignored by the
   acceptor.

   Here is an example assertion containing Elliptic Curve Diffie-Hellman
   parameters, along with options and nonce claims indicating that
   mutual authentication is desired:

         {
             "opts": [
                 "ma"
             ],
             "exp": 1360158396188,
             "ecdh": {
                 "crv": "P-256",
                 "x": "JR5UPDgMLFPZwOGaKKSF24658tB1DccM1_oHPbCHeZg",
                 "y": "S45Esx_6DfE5-xdB3X7sIIJ16MwO0Y_RiDc-i5ZTLQ8"
             },
             "nonce": "bbqT10Gyx3s",
             "aud": "urn:x-gss:imap/mail.example.com"
         }

   The following claims are permitted in the request assertion:

6.1.1.  "aud" (Audience)

   The audience, formatted as a URN containing the acceptor's principal
   name (see Section 3.2).  This claim is REQUIRED.

   [[anchor7: Note that if the initiator application specified a
   target_name of GSS_C_NO_NAME then we could omit this (although this
   may not be permitted by the base protocol).  If the initiator wanted
   mutual authentication then we could find out the acceptor's name and
   provide it via GSS_Inquire_context().  This is only really useful and
   secure with mechanisms like this one where the initiator credential
   is based on a public/private key pair and either we use key agreement
   and per-message tokens or channel binding to a secure channel.  This
   really should [have] be[en] explained in RFC2743.]]







Howard & Williams       Expires October 27, 2013               [Page 22]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


6.1.2.  "exp" (Expiry time)

   This contains the time when the assertion expires, in milliseconds
   since January 1, 1970.  At least one of "exp" or "iat" MUST be
   present.

6.1.3.  "iat" (Issued at time)

   This contains the time the assertion was issued (in milliseconds
   since January 1, 1970).  If present, the acceptor MUST validate that
   the assertion was recently issued.  At least one of "exp" or "iat"
   MUST be present.

6.1.4.  "nbf" (Not before time)

   This contains the time, in milliseconds since January 1, 1970, from
   which the assertion begins to be valid.  This claim is OPTIONAL.

6.1.5.  "ecdh" (Elliptic Curve Diffie-Hellman key agreement)

   These contain ECDH key parameters for deriving a shared session key
   with the relying party: "crv" contains the curve, "x" the X
   coordinate and "y" the Y coordinate (see
   [I-D.ietf-oauth-json-web-token] Section 5.2).

   The "ecdh" claim is REQUIRED unless the associated encryption type is
   ENCTYPE_NULL, or there is already a prior session key (as is the case
   for re-authentication assertions).

6.1.6.  "cb" (Channel binding)

   This contains channel binding information for binding the GSS context
   to an outer channel (e.g. see [RFC5929]).  Its value is the base64
   URL encoding of the application-specific data component of the
   channel bindings passed to GSS_Init_sec_context() or
   GSS_Accept_sec_context().  This claim is OPTIONAL.

6.1.7.  "nonce" (Mutual authentication nonce)

   This is a random quantity of at least 64 bits, base 64 URL encoded,
   which is used to bind the request and response assertions in the case
   a freshly agreed key is not used to sign the response assertion.
   This claim is REQUIRED if mutual authentication is desired and the
   assertion is signed using a certificate, or if re-authentication is
   being performed.






Howard & Williams       Expires October 27, 2013               [Page 23]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


6.1.8.  "tkt" (Ticket)

   When the assertion is being used for fast re-authentication, this
   contains a JSON object with a single parameter, "tid".  The "tid"
   parameter matches the "tid" parameter from the initial response
   assertion ticket (see Section 6.2.5).  This claim is REQUIRED for re-
   authentication assertions, otherwise it the assertion MUST be
   rejected.  Other parameters SHOULD NOT be present in the "tkt"
   object.

6.1.9.  "opts" (Options)

   This contains a JSON array of string values indicating various
   protocol options that are supported by the initiator.  Unknown
   options MUST be ignored by the acceptor.  This document defines the
   following extensions:

   +------+------------------------------------------------------------+
   | Name |                         Description                        |
   +------+------------------------------------------------------------+
   |  ma  |          The initiator requested GSS_C_MUTUAL_FLAG         |
   |      |                                                            |
   |  xrt |   The initiator supports the extra round trip option (see  |
   |      |                        Section 4.4)                        |
   |      |                                                            |
   |  dce |    The initiator requested GSS_C_DCE_STYLE (see RFC4757    |
   |      |                        Section 7.1)                        |
   |      |                                                            |
   |  ify |  The initiator requested GSS_C_IDENTIFY_FLAG (see RFC4757  |
   |      |                        Section 7.1)                        |
   +------+------------------------------------------------------------+

6.2.  Response (acceptor/RP) assertion

   The response assertion is sent from the acceptor to the initiator to
   provide key agreement, and either key confirmation or mutual
   authentication.  It is formatted as a backed assertion, however in
   the current specification it consists of a single assertion with zero
   certificates; that is, it is "unbacked".  (It is encoded as a backed
   assertion in order to provide future support for mutual
   authentication using native BrowserID certificates.  Such support is
   not specified here.)

   In the case of a key successfully being negotiated, the response
   assertion is signed with the RP Response Key (RRK) (see Section 7.3).
   Alternatively, it may be signed with the acceptor's private RSA or
   DSA key.  In this case, the acceptor's X.509 certificate is included
   in the "x5c" claim of the JWT header.



Howard & Williams       Expires October 27, 2013               [Page 24]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   The HMAC-SHA256 (HS256) algorithm MUST be supported by implementors
   of this specification.

   If the [RFC3961] encryption type for the mechanism is ENCTYPE_NULL,
   then the signature is absent and the value of the "alg" header
   parameter is "none".  No signature verification is required in this
   case.

   Claims not specified here MUST be ignored by the initiator.

   Here is an example response assertion:

       {
           "exp": 1362960258000,
           "nonce": "bbqT10Gyx3s",
           "ecdh": {
               "x": "bvNF6V1rpMeQyGOKCj0kBaOaSh3tlhUcbffaji4uCEI",
               "y": "Iuqs650FXzXFUD9kHknETfbqiB8XBbCHlJXoysx3rvw"
           },
           "tkt": {
               "tid": "Jgg7vKX2sEKlCWBfmLTg_n4qz3NVZxOU-a2B4qYMkXI",
               "exp": 1362992660000
           }
       }

   The following claims are permitted in the response assertion:

6.2.1.  "iat" (Issued at time)

   The current acceptor time, in milliseconds since January 1, 1970.
   This allows the initiator to compensate for clock differences when
   generating assertions.  This claim is OPTIONAL.

6.2.2.  "ecdh" (Elliptic Curve Diffie-Hellman key agreement)

   This contains a JSON object containing the coordinates of the
   acceptor's ECDH public key: "x" contains the X coordinate and "y" the
   Y coordinate (see [I-D.ietf-oauth-json-web-token] Section 5.2).  This
   claim is REQUIRED unless the associated encryption type is
   ENCTYPE_NULL, or there is already an established session key, as is
   the case for re-authentication assertions.

   The "crv" claim MUST NOT be present; it is determined by the
   initiator.







Howard & Williams       Expires October 27, 2013               [Page 25]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


6.2.3.  "exp" (Expiry time)

   This contains the time when the context expires, in milliseconds
   since January 1, 1970.  This claim is OPTIONAL; the initiator should
   use the certificate or ticket expiry time if absent.

6.2.4.  "nonce" (Mutual authentication nonce)

   The nonce as received from the initiator.  This MUST NOT be present
   unless a nonce was received from the initiator, and the acceptor is
   signing the assertion with a private key.

6.2.5.  "tkt" (Ticket)

   This contains a JSON object that may be used for re-authenticating to
   the acceptor without acquiring an assertion.  It has two parameters:
   "tid", an opaque identifier to be presented in a re-authentication
   assertion (this need not be a string); and "exp", the expiry time of
   the ticket.  This claim is OPTIONAL.

6.2.6.  "jti" (JWT ID)

   This contains a base64 URL encoded random value of at least 64 bits
   that is used to uniquely identify the acceptor response, in the case
   that the extra round trip option is used.  It SHOULD not be present
   unless the initiator requested the extra round trip option.

6.3.  Error (acceptor/RP) assertion

   Error assertions are backed assertions containing any or all of the
   following claims.  In addition, they MUST have the "iat" claim, for
   initiator clock skew correction.  All other response assertion claims
   are OPTIONAL or not applicable in error assertions.  Conversely, the
   claims listed below MUST NOT be present in a non-error response
   assertion.

   The error assertion MAY be signed if a key is available, otherwise
   the signature is absent and the value of the "alg" header parameter
   is "none".

6.3.1.  "gss-maj" (GSS major status code)

   This contains a GSS major status code represented as a number.

6.3.2.  "gss-min" (GSS minor status code)

   This contains a GSS minor status code represented as a number.




Howard & Williams       Expires October 27, 2013               [Page 26]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   If REAUTH_FAILED is received, the initiator SHOULD attempt to send
   another initial context token containing a fresh assertion.

   The following protocol minor status codes are defined.  Note that the
   API representation of these status codes is implementation dependent.
   Status codes with the high bit set are GSS BrowserID protocol errors;
   the remainder are BrowserID protocol errors.

   +---------------------------+------------+--------------------------+
   |           Error           |  Protocol  |        Description       |
   +---------------------------+------------+--------------------------+
   |        INVALID_JSON       |      8     |   Invalid JSON encoding  |
   |                           |            |                          |
   |       INVALID_BASE64      |      9     |  Invalid Base64 encoding |
   |                           |            |                          |
   |     INVALID_ASSERTION     |     10     |     Invalid assertion    |
   |                           |            |                          |
   |       TOO_MANY_CERTS      |     13     |   Too many certificates  |
   |                           |            |                          |
   |      UNTRUSTED_ISSUER     |     14     |     Untrusted issuer     |
   |                           |            |                          |
   |       INVALID_ISSUER      |     15     |      Invalid issuer      |
   |                           |            |                          |
   |       MISSING_ISSUER      |     16     |      Missing issuer      |
   |                           |            |                          |
   |      MISSING_AUDIENCE     |     17     |     Missing audience     |
   |                           |            |                          |
   |        BAD_AUDIENCE       |     18     |       Bad audience       |
   |                           |            |                          |
   |     EXPIRED_ASSERTION     |     19     |     Assertion expired    |
   |                           |            |                          |
   |  ASSERTION_NOT_YET_VALID  |     20     |  Assertion not yet valid |
   |                           |            |                          |
   |        EXPIRED_CERT       |     21     |    Certificate expired   |
   |                           |            |                          |
   |     CERT_NOT_YET_VALID    |     22     |    Certificate not yet   |
   |                           |            |           valid          |
   |                           |            |                          |
   |     INVALID_SIGNATURE     |     23     |     Invalid signature    |
   |                           |            |                          |
   |     MISSING_ALGORITHM     |     24     |   Missing JWS algorithm  |
   |                           |            |                          |
   |     UNKNOWN_ALGORITHM     |     25     |   Unknown JWS algorithm  |
   |                           |            |                          |
   |     MISSING_PRINCIPAL     |     34     |     Missing principal    |
   |                           |            |         attribute        |
   |                           |            |                          |
   |   UNKNOWN_PRINCIPAL_TYPE  |     35     |  Unknown principal type  |



Howard & Williams       Expires October 27, 2013               [Page 27]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   |        MISSING_CERT       |     36     |    Missing certificate   |
   |                           |            |                          |
   |  MISSING_CHANNEL_BINDINGS |     38     | Missing channel bindings |
   |                           |            |                          |
   | CHANNEL_BINDINGS_MISMATCH |     39     |  Channel bindings do not |
   |                           |            |           match          |
   |                           |            |                          |
   |    NOT_REAUTH_ASSERTION   |     70     |  Not a re-authentication |
   |                           |            |         assertion        |
   |                           |            |                          |
   |        BAD_SUBJECT        |     71     |     Bad subject name     |
   |                           |            |                          |
   |   MISMATCHED_RP_RESPONSE  |     72     |  Mismatched RP response  |
   |                           |            |           token          |
   |                           |            |                          |
   |   REFLECTED_RP_RESPOSNE   |     73     |   Reflected RP response  |
   |                           |            |           token          |
   |                           |            |                          |
   |      UNKNOWN_EC_CURVE     |     77     |     Unknown ECC curve    |
   |                           |            |                          |
   |      INVALID_EC_CURVE     |     78     |     Invalid ECC curve    |
   |                           |            |                          |
   |       MISSING_NONCE       |     79     |       Missing nonce      |
   |                           |            |                          |
   |         WRONG_SIZE        | 0x80000001 | Buffer is incorrect size |
   |                           |            |                          |
   |         WRONG_MECH        | 0x80000002 |     Mechanism OID is     |
   |                           |            |         incorrect        |
   |                           |            |                          |
   |       BAD_TOK_HEADER      | 0x80000003 |      Token header is     |
   |                           |            |   malformed or corrupt   |
   |                           |            |                          |
   |         TOK_TRUNC         | 0x80000004 |   Token is missing data  |
   |                           |            |                          |
   |       BAD_DIRECTION       | 0x80000005 |  Packet was replayed in  |
   |                           |            |      wrong direction     |
   |                           |            |                          |
   |        WRONG_TOK_ID       | 0x80000006 |  Received token ID does  |
   |                           |            |    not match expected    |
   |                           |            |                          |
   |      KEY_UNAVAILABLE      | 0x80000007 |      Key unavailable     |
   |                           |            |                          |
   |       KEY_TOO_SHORT       | 0x80000008 |       Key too weak       |
   |                           |            |                          |
   |    CONTEXT_ESTABLISHED    | 0x80000009 |      Context already     |
   |                           |            |        established       |
   |                           |            |                          |
   |     CONTEXT_INCOMPLETE    | 0x8000000A |    Context incomplete    |



Howard & Williams       Expires October 27, 2013               [Page 28]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   |     BAD_CONTEXT_TOKEN     | 0x8000000B |  Context token malformed |
   |                           |            |        or corrupt        |
   |                           |            |                          |
   |      BAD_ERROR_TOKEN      | 0x8000000C | Error token malformed or |
   |                           |            |          corrupt         |
   |                           |            |                          |
   |     BAD_CONTEXT_OPTION    | 0x8000000D |    Bad context option    |
   |                           |            |                          |
   |       REAUTH_FAILED       | 0x8000000E |     Re-authentication    |
   |                           |            |          failure         |
   +---------------------------+------------+--------------------------+

6.4.  XRT assertion

   No claims are presently defined for the extra round trip assertion.
   Unknown claims MUST be ignored by the acceptor.



































Howard & Williams       Expires October 27, 2013               [Page 29]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


7.  Key derivation

   The following function is used as the base algorithm for deriving
   keys:

   browserid-derive-key(K, usage) = HMAC(K, "BrowserID" || K || usage ||
   0x01)

   The HMAC hash algorithm for all currently specified key lengths is
   SHA-256.  Note that the inclusion of K in the HMAC input is for
   interoperability with some crypto implementations.

7.1.  Diffie-Hellman Key (DHK)

   This key is the shared secret resulting from the ECDH exchange.  Its
   length corresponds to the selected EC curve.  It is never used
   without derivation and thus may be used with implementations that do
   not expose the ECDH value directly.

7.2.  Context Master Key (CMK)

   This is the Diffie-Hellman Key (DHK) for all initially authenticated
   contexts and the Authenticator Session Key (ASK) for re-authenticated
   contexts.

7.3.  RP Response Key (RRK)

   If mutual authentication without a fast re-authentication ticket is
   performed then the response assertion will be signed with a public
   key signature using the private key for the acceptor's certificate.

   Otherwise a symmetric RP Response Key (RRK) is derived as follows:

   RRK = browserid-derive-key(CMK, "RRK")

7.4.  Context Root Key (CRK)

   The Context Root Key (CRK) is used for [RFC4121] message protection
   services, e.g.  GSS_Wrap() and GSS_Get_MIC().  If the extra round-
   trip option is in effect, it is derived as follows:

   CRK = random-to-key(browserid-derive-key(XRTK, "CRK"))

   Otherwise, the CMK is used:

   CRK = random-to-key(browserid-derive-key(CMK, "CRK"))

   The random-to-key function is defined in [RFC3961].



Howard & Williams       Expires October 27, 2013               [Page 30]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


7.5.  Authenticator Root Key (ARK)

   The Authenticator Root Key (ARK) is used to sign assertions used for
   fast re-authentication.  (The term "authenticator" is equivalent to
   "re-authentication assertion" and exists for historical reasons.)  It
   is derived as follows:

   ARK = browserid-derive-key(CMK, "ARK")

7.6.  Authenticator Session Key (ASK)

   The Authenticator Session Key (ASK) is used instead of the DHK for
   re-authenticated contexts.  It is derived as follows:

   ASK = browserid-derive-key(ARK, nonce-binary)

   The usage (nonce-binary) is the base64 URL decoding of the initiator
   "nonce" claim.

7.6.1.  Extra Round Trip Key (XRTK)

   The Extra Round Trip Key (XRTK) is used to sign the extra round trip
   token, and also as the master key for the CRK when the extra round
   trip option is used.

   XRTK = browserid-derive-key(CMK, acceptor-jti-binary)

   The usage (acceptor-jti-binary) is the base64 URL decoding of the
   acceptor "jti" claim.

7.7.  GSS Pseudo-Random Function (PRF)

   The BrowserID mechanism shares the same Pseudo-Random Function (PRF)
   as the Kerberos GSS mechanism, defined in [RFC4402].
   GSS_C_PRF_KEY_FULL and GSS_C_PRF_KEY_PARTIAL are equivalent.  The
   protocol key to be used for GSS_Pseudo_random() SHALL by the Context
   Root Key (CRK).

   [[anchor8: Can we replace this with a function that imports less of
   RFC3962?  We arguably should, because otherwise the only things we
   import from RFC3962 (and 3961) are random-to-key (the identity
   function in RFC3962) and the crypto bits needed for RFC4121 per-
   message tokens.]]








Howard & Williams       Expires October 27, 2013               [Page 31]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


8.  Example

   Suppose a mail user agent for the principal lukeh@lukktone.com wishes
   to authenticate to an IMAP server rand.mit.de.padl.com.  They do not
   have a re-authentication ticket.  The mail user agent would display a
   dialog box in which the principal would sign in to their IdP and
   request a fresh assertion be generated.

     C: <connects to IMAP port>
     S: * OK
     C: C1 CAPABILITY
     S: * CAPABILITY IMAP4rev1 SASL-IR SORT [...] AUTH=BROWSERID-AES128
     S: C1 OK Capability Completed
     C: C2 AUTHENTICATE BROWSERID-AES128
        biwsYyxleUpoYkdjaU9pSlNVekkxTmlKOS5leUp3ZFdKc2FXTXRhMlY
        1SWpwN0ltRnNaMjl5YVhSb2JTSTZJa1JUSWl3aWVTSTZJak01TVRObE
        9EZ3laRGhqTXpWa01qSm1ObVEwTURZNVkyVTJNREJrWW1OallqTTVOR
        0ZqWVdGaFl6WTBPV1prTjJZNVptTmtObU0wTVRJME5tWTFOakk1TUdW
        bU1HTmpNemMwTnpaaE1EUmhOREU0WXpGbE9ETXhPV0kxTkdJeFpXTml
        ObVkyWTJWaE56VTBOR1kyWlRFMU5qTmxaR05sWkdNNU1EWmtOamcwTT
        JRd01XSmpaVFJtTjJFMVpqY3dOMk5tWVRZd1lXTTVNVE0yWm1GbU5qS
        m1aR0ZtTkRoa09HRTVPRGxoWVdGbE5EUXdOMlZrTmpjeU56ZGhNVGM0
        TW1WallXRXhOVFppWkdOaFpXRXhOamRtTWpZek56STFaR1UyTTJWa09
        HWXlPR0UyTUROaU5tWm1OVEV3WmpRNE1ESmtOelJrTjJWaFpUZGhZbU
        15WldJaUxDSndJam9pWm1ZMk1EQTBPRE5rWWpaaFltWmpOV0kwTldWa
        FlqYzROVGswWWpNMU16TmtOVFV3WkRsbU1XSm1NbUU1T1RKaE4yRTRa
        R0ZoTm1Sak16Um1PREEwTldGa05HVTJaVEJqTkRJNVpETXpOR1ZsWld
        GaFpXWmtOMlV5TTJRME9ERXdZbVV3TUdVMFkyTXhORGt5WTJKaE16ST
        FZbUU0TVdabU1tUTFZVFZpTXpBMVlUaGtNVGRsWWpOaVpqUmhNRFpoT
        XpRNVpETTVNbVV3TUdRek1qazNORFJoTlRFM09UTTRNRE0wTkdVNE1t
        RXhPR00wTnprek16UXpPR1k0T1RGbE1qSmhaV1ZtT0RFeVpEWTVZemh
        tTnpWbE16STJZMkkzTUdWaE1EQXdZek5tTnpjMlpHWmtZbVEyTURRMk
        16aGpNbVZtTnpFM1ptTXlObVF3TW1VeE55SXNJbkVpT2lKbE1qRmxNR
        FJtT1RFeFpERmxaRGM1T1RFd01EaGxZMkZoWWpOaVpqYzNOVGs0TkRN
        d09XTXpJaXdpWnlJNkltTTFNbUUwWVRCbVpqTmlOMlUyTVdaa1pqRTR
        OamRqWlRnME1UTTRNelk1WVRZeE5UUm1OR0ZtWVRreU9UWTJaVE5qT0
        RJM1pUSTFZMlpoTm1ObU5UQTRZamt3WlRWa1pUUXhPV1V4TXpNM1pUQ
        TNZVEpsT1dVeVlUTmpaRFZrWldFM01EUmtNVGMxWmpobFltWTJZV1l6
        T1Rka05qbGxNVEV3WWprMllXWmlNVGRqTjJFd016STFPVE15T1dVME9
        ESTVZakJrTUROaVltTTNPRGsyWWpFMVlqUmhaR1UxTTJVeE16QTROVG
        hqWXpNMFpEazJNalk1WVdFNE9UQTBNV1kwTURreE16WmpOekkwTW1Fe
        k9EZzVOV001WkRWaVkyTmhaRFJtTXpnNVlXWXhaRGRoTkdKa01UTTVP
        R0prTURjeVpHWm1ZVGc1TmpJek16TTVOMkVpZlN3aWNISnBibU5wY0d
        Gc0lqcDdJbVZ0WVdsc0lqb2liSFZyWldoQWJIVnJhM1J2Ym1VdVkyOX
        RJbjBzSW1saGRDSTZNVE0yTWprMk1UQTVOakV5TWl3aVpYaHdJam94T
        XpZeU9UWTBOamsyTVRJeUxDSnBjM01pT2lKc2IyZHBiaTV3WlhKemIy
        NWhMbTl5WnlKOS5mT3V5ZlZkNWFZZ285ckJncmdHVDJHYjkzUUoxVnp
        LSE9rNjdFUXBEeU9pUENPdXFweUw5a2tVVDdxcGNZaWZsb0NTWjlPej



Howard & Williams       Expires October 27, 2013               [Page 32]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


        UtVWRrcldlcTZXUkRLcUdOeXg0OFdyVGduVkoyRlM3MU1Mbl9DeWhGM
        Go1Y1ZsQ0E5WWh3YVlWTHhsbW9YU01uWTdyRzFWa0VSdjRtaWtCM3FD
        cFB2NXJtSEswbkNiRlpiN1dXR3JkVEdkcmNHTkRkZHlDQkQ5a1dpUUd
        VbkktenN3WXdiZXJUTmQ3Nmc1Z2N1c1MtbWxjVk5jbzNMTG4zMlNhbG
        x0eDBCUHAtVTAyMXpvR00wWEhibm1Sa2VRdGVtblVXZGloYzRVbVpNR
        EJJZ05nSFFCSmdXMGhBcTlHWVFmYzVObFNzZW5RX0p5MGR4anE1bHdE
        Wll3SExsUXlmYnVYbGFtRTNDZ3ZkZUF+ZXlKaGJHY2lPaUpFVXpFeU9
        DSjkuZXlKdWIyNWpaU0k2SW1nMVVEUkxja2M0ZVc1bklpd2laV05rYU
        NJNmV5SjRJam9pWm1wYVRuQnpRbXBIYmw5WVFVTnRaMkpPZDBGemRuS
        TRPR2MwUmxkNmRHOWljWEExVkUxaVgxbEdNQ0lzSW1OeWRpSTZJbEF0
        TWpVMklpd2llU0k2SWxKTFJYWktlalU1WTNOaGRqaExZM2RsVlhZMVd
        IRkdaM1E0UVZkRFFXdHlTa0o2TTFCUWNVeEtkSE1pZlN3aVkySjBJam
        9pWW1sM2N5SXNJbVY0Y0NJNk1UTTJNamsyTVRJeE5qRTBPU3dpWVhWa
        0lqb2lkWEp1T25ndFozTnpPbWx0WVhBdmNtRnVaQzV0YVhRdVpHVXVj
        R0ZrYkM1amIyMGlmUS51ZHRvSTNVNUMtM3BwNHhJSloxbWstQ3o0Ymh
        sQkxlSzAyNlVhbWRhMjhwTFk4c013Tk50Y0E=
     S: + Qyx
        +ZXlKaGJHY2lPaUpTVXpJMU5pSXNJbmcxWXlJNld5Sk5TVWxFZW1wRF
        EwRnlZV2RCZDBsQ1FXZEpRa0o2UVU1Q1oydHhhR3RwUnpsM01FSkJVV
        lZHUVVSQ1pFMVJjM2REVVZsRVZsRlJSMFYzU2tKV1ZFVmxUVUozUjBF
        eFZVVkRaM2RXVlVWR1JWUkRRbFJpTWxvd1pESkdlVnBUUWxGa1NHdG5
        WRWhTYTAxVE5IZE1RVmxFVmxGUlJFUkRWbEZSVlZKTlNVWk9kbHB1VW
        pOWldFcHNTVVZPYkdOdVVuQmFiV3hxV1ZoU2NHSXlOR2RSV0ZZd1lVY
        zVlV0ZZVWpWTlFqUllSRlJGZWsxRVJYaE5WRUV4VFhwUmVVMUdiMWhF
        VkVVeVRVUkZlRTFVUVRGTmVsRjVUVVp2ZDFSRVJVeE5RV3RIUVRGVlJ
        VSm9UVU5SVmxWNFNHcEJZMEpuVGxaQ1FXOU5SbFpDUWxKRmQyZFZNam
        x0WkVoa2FHTnRWV2RWU0ZJMVNVVjRNRnBFUldSTlFuTkhRVEZWUlVGM
        2QxVmpiVVoxV2tNMWRHRllVWFZhUjFWMVkwZEdhMkpETldwaU1qQjNa
        MmRGYVUxQk1FZERVM0ZIVTBsaU0wUlJSVUpCVVZWQlFUUkpRa1IzUVh
        kblowVkxRVzlKUWtGUlJFSm9la1p3Wmt3MmRraDRjM2d5UkhaR1dsQX
        JSMUl3Vlc5dFJIQXZRMFZsSzA5SVRqQmFNR00yT1RGWlp6bG5WMWh0V
        lROdVVIRldWR0pCU1hGWVNEaEJWWFIyWmpkTmVtSlpNamh2Vm14d1ds
        UXdOWHB0TW1NdmRFVXpaMnRvVkhodFdFOVNaMUZ5WTNWMVozVnFUMWh
        OUm1oSk5ITjJSVm9yUTJKSVVHeGFhVm92VkhwcldFeElVREk1UlhvM2
        QwNWFiakZJTlRkQlRIRnRVMEZ2TlZRMGNYaE5SbWRDV1hWa2R5OWFlR
        kJTZWtSMFZXOUpWakJ6TWpOWlp6UjRWRGxoZDBwdWNqRkhaMDFWVW1s
        aVZVSnFSamQ1WW1OdE1FczRjMHBVSzFWSFpVSTNjbTFNYkZCM0syWkJ
        hMDltTjFwcVdqbDBjRlJyUlUxcE9IVk1SVTF4WTNoaFIxTkJTeThyYT
        FjM05YRlBlR1JCUmtrNGVsbGFXRFV6WjNCbk5HMXBLMUZYWmtkWk1Wc
        E9VVXBOZFVoSFVWaG5MM1ZtZUUxNllYaE9UalJvTVdGUGJHMWFXbGxy
        UWtod05USkJPWGxKVFZWaVFXZE5Ra0ZCUjJwbllXdDNaMkZaZDBOUld
        VUldVakJVUWtGSmQwRkVRWE5DWjJ4bmFHdG5RbWgyYUVOQlVUQkZTSG
        haWkZRelFteGliRTVVVkVOQ1NGcFhOV3hqYlVZd1dsZFJaMUV5Vm5sa
        1IyeHRZVmRPYUdSSFZYZElVVmxFVmxJd1QwSkNXVVZHUzFOemRXSkZS
        SFZpVWtsSFNFTkNkSFJCYkZSMk1rWlhSMllyVFVJNFIwRXhWV1JKZDF
        GWlRVSmhRVVpNYVhwYWJFMVhia3RMTVZCWllXZGtTbXByVm5WU2FFVl
        JTbXBOUVd0SFFURlZaRVZSVVVOTlFVRjNRM2RaUkZaU01GQkNRVkZFU
        VdkWVowMUNUVWRCTVZWa1NsRlJUVTFCYjBkRFEzTkhRVkZWUmtKM1RV



Howard & Williams       Expires October 27, 2013               [Page 33]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


        Uk5RVEJIUTFOeFIxTkpZak5FVVVWQ1FsRlZRVUUwU1VKQlVVSkVNVUo
        2VVZBcmNrNHhWVlY2TjBFMmVpdExSRkJoY1Roek1tbENSekJHZWxwNG
        MxZ3lVVlZQZFhCQ1JVbGlkVnB3TUV0S1lYVnFWazFuTURGbVpHcHpkV
        WRITUhWWVlrMW1aVkpIZVU1c1ZYTk5UaXRhUkhrNEwwMUpUMmd4WVZW
        SGRqQlRWWGRMZEVOMFRIUlhja3AyTmpWMWQwaEhSM1ExZFVaTGVFMUZ
        OakZXVkRRcmNYQkpNa0ZIY1hoNE5XUnljM2hGVEVKUFpIbFFibVYxUV
        dsTVVIaEdkV0pTUm0xNmRXaFdVMGszUVZCTmJEYzVUMnN6TUc5WGRXU
        kJORGxzVlZnNWQzb3paemx4T1haa2JEbDVhR2RsWlZWVFZYQk5hR3hh
        TWpSVll6bFFkVXg2Y2pFMWFqWjJOak5ZZW5KVFpGZDBUbnAyTUVZeE1
        HVkViRFI1VkZWT1YxTkthRGR4UW1obmNURkpiMWc1UVZCUFQzVk1Zaz
        FPY25BMlltVkZaVzkzYURNMGNGWlhabFJoVTNoSk4yNUxOVGRyU3pKN
        GFGSlZORE5sZDFscU1ta3ZVM0o2T0VkelRWTTVNWFZ5TWpWSmRDSmRm
        US5leUowYTNRaU9uc2lhblJwSWpvaVlXVmhlVEJIU21sNlJIZzNPVUZ
        uTFMxWFRDMTJkelpaT1VKWWVGSjFRekZZYzFwNGNuazFNVk5WU1NJc0
        ltVjRjQ0k2TVRNMk1qazVOekE1T0RBd01IMHNJbVZqWkdnaU9uc2llQ
        0k2SWtveFNWZGlTREpCTlVNelkyaFBWVWx4YldaWWNGQmZVbEZGUlU5
        dFpESkZlRmh2UzNKeFVWRllURTBpTENKNUlqb2lYekpGZEhoaWVsOTJ
        TbVZsVlZWaWVUSnlabVJsYTFSVVVGVlNjR0pIU2tnM2EzbEpWM0Z0YT
        BsRlp5SjlMQ0p1YjI1alpTSTZJbWcxVURSTGNrYzRlVzVuSWl3aVpYa
        HdJam94TXpZeU9UWTBOamsyTURBd2ZRLnFaaFVxdXBWUHgzRTdNSTBH
        dnNIZjZER3pzc3ByMkJsdUVUMFNwMERxdkpFS1F4S3BiOG9faVZsWHZ
        Qa2p2SXp0Qm5JajNNb084UlZMUWJwdE9QZDFrN3FoTUVwRkhOVGI1WF
        pKYWVJTlBpQUNSSzA5dUZpVE5ud1cxanMxQ3pPY2FMakxsSTN4bFdkL
        Ul1em8zODhyTUxsSXVkbmkxak5uRS0yOXZfc1NUTnRxLUMwQmNoNUMw
        T3drbDcxQk54eHgzaFVxeEcxT0w0UHQyZ0JKWUFQX3NOVk12aDFwWDl
        hRzd0Vms0S2sxS2NjaXRqUFdGN0dXc3JGeld4ekRSMHU2REZ0RmFjaE
        NPYmVmcmZnZkUxOXFlWnJLcnpJMFVkQ3JEUHpZazlYb1dKR2twRlNPd
        1dhY192Q0N1dXY1VjNHZF9MTlNJM3JCaS1GYWVoWUhBRjFJUQ==

   Unpacking the mail user agent's AUTHENTICATE message reveals the
   following:




















Howard & Williams       Expires October 27, 2013               [Page 34]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


        n,,c,eyJhbGciOiJSUzI1NiJ9.eyJwdWJsaWMta2V5Ijp7ImFsZ29yaXRob
        SI6IkRTIiwieSI6IjM5MTNlODgyZDhjMzVkMjJmNmQ0MDY5Y2U2MDBkYmNj
        YjM5NGFjYWFhYzY0OWZkN2Y5ZmNkNmM0MTI0NmY1NjI5MGVmMGNjMzc0NzZ
        hMDRhNDE4YzFlODMxOWI1NGIxZWNiNmY2Y2VhNzU0NGY2ZTE1NjNlZGNlZG
        M5MDZkNjg0M2QwMWJjZTRmN2E1ZjcwN2NmYTYwYWM5MTM2ZmFmNjJmZGFmN
        DhkOGE5ODlhYWFlNDQwN2VkNjcyNzdhMTc4MmVjYWExNTZiZGNhZWExNjdm
        MjYzNzI1ZGU2M2VkOGYyOGE2MDNiNmZmNTEwZjQ4MDJkNzRkN2VhZTdhYmM
        yZWIiLCJwIjoiZmY2MDA0ODNkYjZhYmZjNWI0NWVhYjc4NTk0YjM1MzNkNT
        UwZDlmMWJmMmE5OTJhN2E4ZGFhNmRjMzRmODA0NWFkNGU2ZTBjNDI5ZDMzN
        GVlZWFhZWZkN2UyM2Q0ODEwYmUwMGU0Y2MxNDkyY2JhMzI1YmE4MWZmMmQ1
        YTViMzA1YThkMTdlYjNiZjRhMDZhMzQ5ZDM5MmUwMGQzMjk3NDRhNTE3OTM
        4MDM0NGU4MmExOGM0NzkzMzQzOGY4OTFlMjJhZWVmODEyZDY5YzhmNzVlMz
        I2Y2I3MGVhMDAwYzNmNzc2ZGZkYmQ2MDQ2MzhjMmVmNzE3ZmMyNmQwMmUxN
        yIsInEiOiJlMjFlMDRmOTExZDFlZDc5OTEwMDhlY2FhYjNiZjc3NTk4NDMw
        OWMzIiwiZyI6ImM1MmE0YTBmZjNiN2U2MWZkZjE4NjdjZTg0MTM4MzY5YTY
        xNTRmNGFmYTkyOTY2ZTNjODI3ZTI1Y2ZhNmNmNTA4YjkwZTVkZTQxOWUxMz
        M3ZTA3YTJlOWUyYTNjZDVkZWE3MDRkMTc1ZjhlYmY2YWYzOTdkNjllMTEwY
        jk2YWZiMTdjN2EwMzI1OTMyOWU0ODI5YjBkMDNiYmM3ODk2YjE1YjRhZGU1
        M2UxMzA4NThjYzM0ZDk2MjY5YWE4OTA0MWY0MDkxMzZjNzI0MmEzODg5NWM
        5ZDViY2NhZDRmMzg5YWYxZDdhNGJkMTM5OGJkMDcyZGZmYTg5NjIzMzM5N2
        EifSwicHJpbmNpcGFsIjp7ImVtYWlsIjoibHVrZWhAbHVra3RvbmUuY29tI
        n0sImlhdCI6MTM2Mjk2MTA5NjEyMiwiZXhwIjoxMzYyOTY0Njk2MTIyLCJp
        c3MiOiJsb2dpbi5wZXJzb25hLm9yZyJ9.fOuyfVd5aYgo9rBgrgGT2Gb93Q
        J1VzKHOk67EQpDyOiPCOuqpyL9kkUT7qpcYifloCSZ9Oz5-UdkrWeq6WRDK
        qGNyx48WrTgnVJ2FS71MLn_CyhF0j5cVlCA9YhwaYVLxlmoXSMnY7rG1VkE
        Rv4mikB3qCpPv5rmHK0nCbFZb7WWGrdTGdrcGNDddyCBD9kWiQGUnI-zswY
        wberTNd76g5gcusS-mlcVNco3LLn32Salltx0BPp-U021zoGM0XHbnmRkeQ
        temnUWdihc4UmZMDBIgNgHQBJgW0hAq9GYQfc5NlSsenQ_Jy0dxjq5lwDZY
        wHLlQyfbuXlamE3CgvdeA~eyJhbGciOiJEUzEyOCJ9.eyJub25jZSI6Img1
        UDRLckc4eW5nIiwiZWNkaCI6eyJ4IjoiZmpaTnBzQmpHbl9YQUNtZ2JOd0F
        zdnI4OGc0Rld6dG9icXA1VE1iX1lGMCIsImNydiI6IlAtMjU2IiwieSI6Il
        JLRXZKejU5Y3NhdjhLY3dlVXY1WHFGZ3Q4QVdDQWtySkJ6M1BQcUxKdHMif
        SwiY2J0IjoiYml3cyIsImV4cCI6MTM2Mjk2MTIxNjE0OSwiYXVkIjoidXJu
        OngtZ3NzOmltYXAvcmFuZC5taXQuZGUucGFkbC5jb20ifQ.udtoI3U5C-3p
        p4xIJZ1mk-Cz4bhlBLeK026Uamda28pLY8sMwNNtcA

   The initial "n,," is the GS2 header (indicating that there are no
   channel bindings).  The "c," denotes the token as being a BrowserID
   initial context token.  The remaining base64 URL encoded data is a
   BrowserID backed assertion, containing the following certificate (for
   clarity, the payload has been reformatted and JWT header and
   signature omitted):









Howard & Williams       Expires October 27, 2013               [Page 35]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


        {
            "public-key": {
                "algorithm": "DS",
                "y": "3913e882d8c35d22f6d4069ce600dbccb394acaaac649
                      fd7f9fcd6c41246f56290ef0cc37476a04a418c1e8319
                      b54b1ecb6f6cea7544f6e1563edcedc906d6843d01bce
                      4f7a5f707cfa60ac9136faf62fdaf48d8a989aaae4407
                      ed67277a1782ecaa156bdcaea167f263725de63ed8f28
                      a603b6ff510f4802d74d7eae7abc2eb",
                "p": "ff600483db6abfc5b45eab78594b3533d550d9f1bf2a9
                      92a7a8daa6dc34f8045ad4e6e0c429d334eeeaaefd7e2
                      3d4810be00e4cc1492cba325ba81ff2d5a5b305a8d17e
                      b3bf4a06a349d392e00d329744a5179380344e82a18c4
                      7933438f891e22aeef812d69c8f75e326cb70ea000c3f
                      776dfdbd604638c2ef717fc26d02e17",
                "q": "e21e04f911d1ed7991008ecaab3bf775984309c3",
                "g": "c52a4a0ff3b7e61fdf1867ce84138369a6154f4afa929
                      66e3c827e25cfa6cf508b90e5de419e1337e07a2e9e2a
                      3cd5dea704d175f8ebf6af397d69e110b96afb17c7a03
                      259329e4829b0d03bbc7896b15b4ade53e130858cc34d
                      96269aa89041f409136c7242a38895c9d5bccad4f389a
                      f1d7a4bd1398bd072dffa896233397a"
            },
            "principal": {
                "email": "lukeh@lukktone.com"
            },
            "iat": 1362961096122,
            "exp": 1362964696122,
            "iss": "login.persona.org"
        }

   and assertion:

        {
            "nonce": "h5P4KrG8yng",
            "ecdh": {
                "x": "fjZNpsBjGn_XACmgbNwAsvr88g4FWztobqp5TMb_YF0",
                "crv": "P-256",
                "y": "RKEvJz59csav8KcweUv5XqFgt8AWCAkrJBz3PPqLJts"
            },
            "cb": "biws",
            "exp": 1362961216149,
            "aud": "urn:x-gss:imap/rand.mit.de.padl.com"
        }

   Note the channel binding token that protects the GS2 header.

   [[anchor9: The encoded example needs to be regenerated to reflect



Howard & Williams       Expires October 27, 2013               [Page 36]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   that "cb" is now used for channel bindings.]]

   Turning to the response backed assertion sent from the IMAP server to
   the mail user agent, we have the following after base64 decoding:

        eyJhbGciOiJSUzI1NiIsIng1YyI6WyJNSUlEempDQ0FyYWdBd0lCQWdJQkJ
        6QU5CZ2txaGtpRzl3MEJBUVVGQURCZE1Rc3dDUVlEVlFRR0V3SkJWVEVlTU
        J3R0ExVUVDZ3dWVUVGRVRDQlRiMlowZDJGeVpTQlFkSGtnVEhSa01TNHdMQ
        VlEVlFRRERDVlFRVVJNSUZOdlpuUjNZWEpsSUVObGNuUnBabWxqWVhScGIy
        NGdRWFYwYUc5eWFYUjVNQjRYRFRFek1ERXhNVEExTXpReU1Gb1hEVEUyTUR
        FeE1UQTFNelF5TUZvd1RERUxNQWtHQTFVRUJoTUNRVlV4SGpBY0JnTlZCQW
        9NRlZCQlJFd2dVMjltZEhkaGNtVWdVSFI1SUV4MFpERWRNQnNHQTFVRUF3d
        1VjbUZ1WkM1dGFYUXVaR1V1Y0dGa2JDNWpiMjB3Z2dFaU1BMEdDU3FHU0li
        M0RRRUJBUVVBQTRJQkR3QXdnZ0VLQW9JQkFRREJoekZwZkw2dkh4c3gyRHZ
        GWlArR1IwVW9tRHAvQ0VlK09ITjBaMGM2OTFZZzlnV1htVTNuUHFWVGJBSX
        FYSDhBVXR2ZjdNemJZMjhvVmxwWlQwNXptMmMvdEUzZ2toVHhtWE9SZ1FyY
        3V1Z3VqT1hNRmhJNHN2RVorQ2JIUGxaaVovVHprWExIUDI5RXo3d05abjFI
        NTdBTHFtU0FvNVQ0cXhNRmdCWXVkdy9aeFBSekR0VW9JVjBzMjNZZzR4VDl
        hd0pucjFHZ01VUmliVUJqRjd5YmNtMEs4c0pUK1VHZUI3cm1MbFB3K2ZBa0
        9mN1pqWjl0cFRrRU1pOHVMRU1xY3hhR1NBSy8ra1c3NXFPeGRBRkk4ellaW
        DUzZ3BnNG1pK1FXZkdZMVpOUUpNdUhHUVhnL3VmeE16YXhOTjRoMWFPbG1a
        WllrQkhwNTJBOXlJTVViQWdNQkFBR2pnYWt3Z2FZd0NRWURWUjBUQkFJd0F
        EQXNCZ2xnaGtnQmh2aENBUTBFSHhZZFQzQmxibE5UVENCSFpXNWxjbUYwWl
        dRZ1EyVnlkR2xtYVdOaGRHVXdIUVlEVlIwT0JCWUVGS1NzdWJFRHViUklHS
        ENCdHRBbFR2MkZXR2YrTUI4R0ExVWRJd1FZTUJhQUZMaXpabE1XbktLMVBZ
        YWdkSmprVnVSaEVRSmpNQWtHQTFVZEVRUUNNQUF3Q3dZRFZSMFBCQVFEQWd
        YZ01CTUdBMVVkSlFRTU1Bb0dDQ3NHQVFVRkJ3TURNQTBHQ1NxR1NJYjNEUU
        VCQlFVQUE0SUJBUUJEMUJ6UVArck4xVVV6N0E2eitLRFBhcThzMmlCRzBGe
        lp4c1gyUVVPdXBCRUlidVpwMEtKYXVqVk1nMDFmZGpzdUdHMHVYYk1mZVJH
        eU5sVXNNTitaRHk4L01JT2gxYVVHdjBTVXdLdEN0THRXckp2NjV1d0hHR3Q
        1dUZLeE1FNjFWVDQrcXBJMkFHcXh4NWRyc3hFTEJPZHlQbmV1QWlMUHhGdW
        JSRm16dWhWU0k3QVBNbDc5T2szMG9XdWRBNDlsVVg5d3ozZzlxOXZkbDl5a
        GdlZVVTVXBNaGxaMjRVYzlQdUx6cjE1ajZ2NjNYenJTZFd0Tnp2MEYxMGVE
        bDR5VFVOV1NKaDdxQmhncTFJb1g5QVBPT3VMYk1OcnA2YmVFZW93aDM0cFZ
        XZlRhU3hJN25LNTdrSzJ4aFJVNDNld1lqMmkvU3J6OEdzTVM5MXVyMjVJdC
        JdfQ.eyJ0a3QiOnsianRpIjoiYWVheTBHSml6RHg3OUFnLS1XTC12dzZZOU
        JYeFJ1QzFYc1p4cnk1MVNVSSIsImV4cCI6MTM2Mjk5NzA5ODAwMH0sImVjZ
        GgiOnsieCI6IkoxSVdiSDJBNUMzY2hPVUlxbWZYcFBfUlFFRU9tZDJFeFhv
        S3JxUVFYTE0iLCJ5IjoiXzJFdHhiel92SmVlVVVieTJyZmRla1RUUFVScGJ
        HSkg3a3lJV3Fta0lFZyJ9LCJub25jZSI6Img1UDRLckc4eW5nIiwiZXhwIj
        oxMzYyOTY0Njk2MDAwfQ.qZhUqupVPx3E7MI0GvsHf6DGzsspr2BluET0Sp
        0DqvJEKQxKpb8o_iVlXvPkjvIztBnIj3MoO8RVLQbptOPd1k7qhMEpFHNTb
        5XZJaeINPiACRK09uFiTNnwW1js1CzOcaLjLlI3xlWd-Iuzo388rMLlIudn
        i1jNnE-29v_sSTNtq-C0Bch5C0Owkl71BNxxx3hUqxG1OL4Pt2gBJYAP_sN
        VMvh1pX9aG7tVk4Kk1KccitjPWF7GWsrFzWxzDR0u6DFtFachCObefrfgfE
        19qeZrKrzI0UdCrDPzYk9XoWJGkpFSOwWac_vCCuuv5V3Gd_LNSI3rBi-Fa
        ehYHAF1IQ




Howard & Williams       Expires October 27, 2013               [Page 37]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


   Here we show the JWT header for the response assertion, as it
   includes an ASN.1 encoded X.509 certificate, which is used to
   mutually authenticate the IMAP server to the UA:

        {
            "alg": "RS256",
            "x5c": [
                "MIIDzjCCAragAwIBAgIBBzANBgkqhkiG9w0BAQUFADBdMQswCQ
                 YDVQQGEwJBVTEeMBwGA1UECgwVUEFETCBTb2Z0d2FyZSBQdHkg
                 THRkMS4wLAYDVQQDDCVQQURMIFNvZnR3YXJlIENlcnRpZmljYX
                 Rpb24gQXV0aG9yaXR5MB4XDTEzMDExMTA1MzQyMFoXDTE2MDEx
                 MTA1MzQyMFowTDELMAkGA1UEBhMCQVUxHjAcBgNVBAoMFVBBRE
                 wgU29mdHdhcmUgUHR5IEx0ZDEdMBsGA1UEAwwUcmFuZC5taXQu
                 ZGUucGFkbC5jb20wggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwgg
                 EKAoIBAQDBhzFpfL6vHxsx2DvFZP+GR0UomDp/CEe+OHN0Z0c6
                 91Yg9gWXmU3nPqVTbAIqXH8AUtvf7MzbY28oVlpZT05zm2c/tE
                 3gkhTxmXORgQrcuugujOXMFhI4svEZ+CbHPlZiZ/TzkXLHP29E
                 z7wNZn1H57ALqmSAo5T4qxMFgBYudw/ZxPRzDtUoIV0s23Yg4x
                 T9awJnr1GgMURibUBjF7ybcm0K8sJT+UGeB7rmLlPw+fAkOf7Z
                 jZ9tpTkEMi8uLEMqcxaGSAK/+kW75qOxdAFI8zYZX53gpg4mi+
                 QWfGY1ZNQJMuHGQXg/ufxMzaxNN4h1aOlmZZYkBHp52A9yIMUb
                 AgMBAAGjgakwgaYwCQYDVR0TBAIwADAsBglghkgBhvhCAQ0EHx
                 YdT3BlblNTTCBHZW5lcmF0ZWQgQ2VydGlmaWNhdGUwHQYDVR0O
                 BBYEFKSsubEDubRIGHCBttAlTv2FWGf+MB8GA1UdIwQYMBaAFL
                 izZlMWnKK1PYagdJjkVuRhEQJjMAkGA1UdEQQCMAAwCwYDVR0P
                 BAQDAgXgMBMGA1UdJQQMMAoGCCsGAQUFBwMDMA0GCSqGSIb3DQ
                 EBBQUAA4IBAQBD1BzQP+rN1UUz7A6z+KDPaq8s2iBG0FzZxsX2
                 QUOupBEIbuZp0KJaujVMg01fdjsuGG0uXbMfeRGyNlUsMN+ZDy
                 8/MIOh1aUGv0SUwKtCtLtWrJv65uwHGGt5uFKxME61VT4+qpI2
                 AGqxx5drsxELBOdyPneuAiLPxFubRFmzuhVSI7APMl79Ok30oW
                 udA49lUX9wz3g9q9vdl9yhgeeUSUpMhlZ24Uc9PuLzr15j6v63
                 XzrSdWtNzv0F10eDl4yTUNWSJh7qBhgq1IoX9APOOuLbMNrp6b
                 eEeowh34pVWfTaSxI7nK57kK2xhRU43ewYj2i/Srz8GsMS91ur
                 25It"]
        }

   The assertion payload is below (again, for clarity the actual JWT
   signature has been omitted):













Howard & Williams       Expires October 27, 2013               [Page 38]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


       {
           "tkt": {
               "tid": "aeay0GJizDx79Ag--WL-vw6Y9BXxRuC1XsZxry51SUI",
               "exp": 1362997098000
           },
           "ecdh": {
               "x": "J1IWbH2A5C3chOUIqmfXpP_RQEEOmd2ExXoKrqQQXLM",
               "y": "_2Etxbz_vJeeUUby2rfdekTTPURpbGJH7kyIWqmkIEg"
           },
           "nonce": "h5P4KrG8yng",
           "exp": 1362964696000
       }

   Note the fast re-authentication ticket and the nonce echoed back from
   the initiator.




































Howard & Williams       Expires October 27, 2013               [Page 39]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


9.  Security Considerations

   This document defines a GSS-API security mechanism, and therefore
   deals in security and has security considerations text embedded
   throughout.  This section only addresses security considerations
   associated with the BrowserID GSS mechanism described in this
   document.  It does not address security considerations associated
   with the BrowserID protocol or the GSS-API themselves.

   This mechanism provides for authentication of initiator principals
   using private keys to public key crypto-systems, using the BrowserID
   specification for user certificates (which are NOT PKIX [RFC5280]
   certificates).  Authentication of the acceptor principal is optional.
   Fast re-authentication is supported via acceptor-issued fast re-
   authentication tickets.

   All cryptography for per-message tokens is imported from the Kerberos
   GSS-API mechanism [RFC4121].

   This mechanism actually has several mechanism OIDs, composed of a
   prefix identifying this family of mechanisms followed by an arc
   identifying the [RFC3961] encryption type for use with per-message
   tokens and the GSS_Pseudo_random() function.  The NULL encryption
   type is supported, and when it is used then the GSS-API per-message
   tokens and GSS_Pseudo_random() function are not available, but
   channel binding and mutual authentication may be available.  Also,
   when using the NULL encryption type the fast re-authentication
   feature is not available because key exchange is only performed the
   initiator application uses the variant of this mechanism that
   supports per-message tokens and the GSS_Pseudo_random() function.

   Acceptor credentials are PKIX [RFC5280] certificates and their
   private keys.

9.1.  Host certificates for mutual authentication

   Allowing a match on only the DNS subjectAltName in an acceptor's
   X.509 certificate permits different services on the same host to
   impersonate each other.  This should be subject to local policy.

9.2.  Error statuses

   Returning rich error information in the clear (see Section 6.3.2) may
   leak information.  Implementations may squash status codes and/or
   avoid returning minor statuses entirely.  Indeed, applications may
   even not send back error tokens at all, instead closing the
   connection or whatever might be appropriate for the application.
   (This is a generic GSS-API security consideration.)



Howard & Williams       Expires October 27, 2013               [Page 40]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


10.  IANA Considerations

   This specification creates a number of IANA registries.

10.1.  OID Registry

   Prefix: iso.org.dod.internet.private.enterprise.padl.gssBrowserID
   (1.3.6.1.4.1.5322.24)

   +---------+------------+-------------------------------------------+
   | Decimal |    Name    |                Description                |
   +---------+------------+-------------------------------------------+
   |    0    |  Reserved  |                  Reserved                 |
   |         |            |                                           |
   |    1    | mechanisms | A sub-arc containing BrowserID mechanisms |
   |         |            |                                           |
   |    2    |  nametypes | A sub-arc containing BrowserID name types |
   +---------+------------+-------------------------------------------+

   Prefix:
   iso.org.dod.internet.private.enterprise.padl.gssBrowserID.mechanisms
   (1.3.6.1.4.1.5322.24.1)

   +-------+------------------+---------------------+-------+----------+
   | Decim |       Name       |     Description     |  ECDH | Symmetri |
   |   al  |                  |                     | curve |  c hash  |
   +-------+------------------+---------------------+-------+----------+
   |   0   | gss-browserid-nu |  The NULL security  |  N/A  |    N/A   |
   |       |        ll        |      mechanism      |       |          |
   |       |                  |                     |       |          |
   |   17  | gss-browserid-ae |         The         | P-256 |   HS256  |
   |       |       s128       | aes128-cts-hmac-sha |       |          |
   |       |                  |    1-96 mechanism   |       |          |
   |       |                  |                     |       |          |
   |   18  | gss-browserid-ae |         The         | P-521 |   HS256  |
   |       |       s256       | aes256-cts-hmac-sha |       |          |
   |       |                  |    1-96 mechanism   |       |          |
   +-------+------------------+---------------------+-------+----------+

   Prefix:
   iso.org.dod.internet.private.enterprise.padl.gssBrowserID.nametypes
   (1.3.6.1.4.1.5322.24.2)









Howard & Williams       Expires October 27, 2013               [Page 41]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


         +---------+------------------------------+-------------+
         | Decimal |             Name             | Description |
         +---------+------------------------------+-------------+
         |    0    |           Reserved           |   Reserved  |
         |         |                              |             |
         |    1    | GSS_C_NT_BROWSERID_PRINCIPAL |    3.1.1    |
         +---------+------------------------------+-------------+

10.2.  SASL Registry

   Subject: Registration of SASL mechanisms BROWSERID-AES128 and
   BROWSERID-AES128-PLUS

   SASL mechanism names: BROWSERID-AES128 and BROWSERID-AES128-PLUS

   Security considerations: See RFC 5801 and draft-howard-gss-browserid

   Published specification (recommended): draft-howard-gss-browserid

   Person & email address to contact for further information:

   Luke Howard lukeh@padl.com

   Intended usage: common

   Owner/Change controller: iesg@ietf.org

   Note: This mechanism describes the GSS BrowserID mechanism used with
   the aes128-cts-hmac-sha1-96 encryption type.  The GSS-API OID for
   this mechanism is 1.3.6.1.4.1.5322.24.1.17.  As described in RFC 5801
   a PLUS variant of this mechanism is also required.

   [[anchor10: We could use the NULL encryption type variant for SASL,
   as the GS2 bridge does not use message protection services.  However,
   because that mechanisms is unkeyed, re-authentication would not be
   available.  Defining a single AES128 mechanism is consistent with GSS
   EAP.]]














Howard & Williams       Expires October 27, 2013               [Page 42]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2743]  Linn, J., "Generic Security Service Application Program
              Interface Version 2, Update 1", RFC 2743, January 2000.

   [RFC3961]  Raeburn, K., "Encryption and Checksum Specifications for
              Kerberos 5", RFC 3961, February 2005.

   [RFC4402]  Williams, N., "A Pseudo-Random Function (PRF) for the
              Kerberos V Generic Security Service Application Program
              Interface (GSS-API) Mechanism", RFC 4402, February 2006.

   [RFC4121]  Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
              Version 5 Generic Security Service Application Program
              Interface (GSS-API) Mechanism: Version 2", RFC 4121,
              July 2005.

   [RFC4178]  Zhu, L., Leach, P., Jaganathan, K., and W. Ingersoll, "The
              Simple and Protected Generic Security Service Application
              Program Interface (GSS-API) Negotiation Mechanism",
              RFC 4178, October 2005.

   [RFC4422]  Melnikov, A. and K. Zeilenga, "Simple Authentication and
              Security Layer (SASL)", RFC 4422, June 2006.

   [RFC4556]  Zhu, L. and B. Tung, "Public Key Cryptography for Initial
              Authentication in Kerberos (PKINIT)", RFC 4556, June 2006.

   [RFC4757]  Jaganathan, K., Zhu, L., and J. Brezak, "The RC4-HMAC
              Kerberos Encryption Types Used by Microsoft Windows",
              RFC 4757, December 2006.

   [RFC4985]  Santesson, S., "Internet X.509 Public Key Infrastructure
              Subject Alternative Name for Expression of Service Name",
              RFC 4985, August 2007.

   [RFC5178]  Williams, N. and A. Melnikov, "Generic Security Service
              Application Program Interface (GSS-API)
              Internationalization and Domain-Based Service Names and
              Name Type", RFC 5178, May 2008.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key



Howard & Williams       Expires October 27, 2013               [Page 43]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5801]  Josefsson, S. and N. Williams, "Using Generic Security
              Service Application Program Interface (GSS-API) Mechanisms
              in Simple Authentication and Security Layer (SASL): The
              GS2 Mechanism Family", RFC 5801, July 2010.

   [RFC5929]  Altman, J., Williams, N., and L. Zhu, "Channel Bindings
              for TLS", RFC 5929, July 2010.

   [RFC6680]  Williams, N., Johansson, L., Hartman, S., and S.
              Josefsson, "Generic Security Service Application
              Programming Interface (GSS-API) Naming Extensions",
              RFC 6680, August 2012.

   [I-D.ietf-jose-json-web-algorithms]
              Jones, M., "JSON Web Algorithms (JWA)",
              draft-ietf-jose-json-web-algorithms-09 (work in progress),
              April 2013.

   [I-D.ietf-jose-json-web-signature]
              Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", draft-ietf-jose-json-web-signature-09
              (work in progress), April 2013.

   [I-D.ietf-oauth-json-web-token]
              Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", draft-ietf-oauth-json-web-token-07 (work in
              progress), April 2013.

   [I-D.zhu-negoex]
              Short, M., Zhu, L., Damour, K., and D. McPherson, "SPNEGO
              Extended Negotiation (NEGOEX) Security Mechanism",
              draft-zhu-negoex-04 (work in progress), January 2011.

   [I-D.zhu-pku2u]
              Zhu, L., Altman, J., and N. Williams, "Public Key
              Cryptography Based User-to-User Authentication - (PKU2U)",
              draft-zhu-pku2u-09 (work in progress), November 2008.

   [BrowserID]
              Adida, B., "BrowserID Specification", February 2013.

11.2.  Informative References

   [RFC4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
              Kerberos Network Authentication Service (V5)", RFC 4120,



Howard & Williams       Expires October 27, 2013               [Page 44]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


              July 2005.


















































Howard & Williams       Expires October 27, 2013               [Page 45]

Internet-Draft          BrowserID SASL & GSS-API              April 2013


Authors' Addresses

   Luke Howard
   PADL Software
   PO Box 59
   Central Park, VIC  3145
   Australia

   Email: lukeh@padl.com


   Nicolas Williams
   Cryptonector, LLC

   Email: nico@cryptonector.com




































Howard & Williams       Expires October 27, 2013               [Page 46]


Html markup produced by rfcmarkup 1.109, available from https://tools.ietf.org/tools/rfcmarkup/