The Hashed Token SASL Mechanism
draft-schmaus-kitten-sasl-ht-03

Versions: 00 01 02 03                                                   
Common Authentication Technology Next Generation              F. Schmaus
Internet-Draft                                                  C. Egger
Intended status: Experimental           University of Erlangen-Nuremberg
Expires: April 2, 2018                                September 29, 2017


                    The Hashed Token SASL Mechanism
                    draft-schmaus-kitten-sasl-ht-01

Abstract

   This document specifies a SASL mechanism designed to be used with
   short-lived, exclusively ephemeral tokens.

Status of This Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions and Terminology . . . . . . . . . . . . . . .   3
     1.2.  Applicability . . . . . . . . . . . . . . . . . . . . . .   3
   2.  The HT-* Family of Mechanisms . . . . . . . . . . . . . . . .   3
   3.  The HT Mechanism  . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Initiator First Message . . . . . . . . . . . . . . . . .   4
     3.2.  Final Responder Message . . . . . . . . . . . . . . . . .   5
   4.  Compliance with SASL Mechanism Requirements . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   This section specifies the the family of Hashed Token (HT-*) SASL
   mechanisms.  It provides hash agility, mutual authentication and is
   secured by channel binding.

   This mechanism was designed to be used with short-lived tokens for
   quick, one round-trip, re-authentication of a previous session.
   Clients are supposed to request such tokens from the server after
   being authenticated using a "strong" SASL mechanism (e.g.  SCRAM).
   Hence a typical sequence of actions using SASL-HT may look like the
   following:

      A) Client authenticates using a strong mechanism (e.g., SCRAM)
      B) Client requests secret SASL-HT token
         <normal client-server interaction here>
      C) Connection between client and server gets interrupted
         (e.g., WiFi <-> GSM switch)
      D) Client resumes previous session using the token from B
      E) Client requests secret SASL-HT token
         [goto C]

   An example application protocol specific extension based on SASL-HT
   is [XEP-ISR-SASL2].

   Since the token is not salted, and only one hash iteration is used,
   the HT-* mechanism is not suitable to protect long-lived shared
   secrets (e.g. "passwords").  You may want to look at [RFC5802] for
   that.




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1.1.  Conventions and Terminology

   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 RFC 2119 [RFC2119].

   Additionally, the key words "*MIGHT*", "*COULD*", "*MAY WISH TO*",
   "*WOULD PROBABLY*", "*SHOULD CONSIDER*", and "*MUST (BUT WE KNOW YOU
   WON'T)*" in this document are to interpreted as described in RFC 6919
   [RFC6919].

1.2.  Applicability

   Because this mechanism transports information that should not be
   controlled by an attacker, the HT-* mechanism MUST only be used over
   channels protected by TLS, or over similar integrity-protected and
   authenticated channels.  In addition, when TLS is used, the client
   MUST successfully validate the server's certificate ([RFC5280],
   [RFC6125]).

   The family of HT-* mechanisms is not applicable for proxy
   authentication, since they can not carry a authorization identity
   string (authzid).

2.  The HT-* Family of Mechanisms

   Each mechanism in this family differs by the choice of the hash
   algorithm and the choice of the channel binding [RFC5929] type.

   A HT mechanism name is a string beginning with "HT-" followed by the
   capitalized name of the used hash, followed by "-", and suffixed by
   one of 'ENDP' and 'UNIQ'.

   Hence each HT mechanism has a name of the following form:

                          HT-<hash-alg>-<cb-type>

   Where <hash-alg> is the capitalized "Hash Name String" of the IANA
   "Named Information Hash Algorithm Registry" [iana-hash-alg] as
   specified in [RFC6920], and <cb-type> is one of 'ENDP' or 'UNIQ'
   denoting the channel binding type.  In case of 'ENDP', the tls-
   server-end-point channel binding type is used.  In case of 'UNIQ',
   the tls-unique channel binding type is used.  Valid channel binding
   types are defined in the IANA "Channel-Binding Types" registry
   [iana-cbt] as specified in [RFC5056].






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                      +------+----------------------+
                      | CBT  | Channel Binding Type |
                      +------+----------------------+
                      | ENDP | tls-server-end-point |
                      | UNIQ |      tls-unique      |
                      +------+----------------------+

                    Mapping of CBT to Channel Bindings

   The following table lists the HT-* SASL mechanisms registered this
   document.

   +------------------+----------------+-------------------------------+
   |  Mechanism Name  | Hash Algorithm | Channel-binding unique prefix |
   +------------------+----------------+-------------------------------+
   | HT-SHA-512-ENDP  |    SHA-512     |      tls-server-end-point     |
   | HT-SHA-512-UNIQ  |    SHA-512     |           tls-unique          |
   | HT-SHA3-512-ENDP |    SHA3-512    |      tls-server-end-point     |
   | HT-SHA-256-UNIQ  |    SHA-256     |           tls-unique          |
   +------------------+----------------+-------------------------------+

                       Defined HT-* SASL mechanisms

3.  The HT Mechanism

   The mechanism consists of a simple exchange of exactly two messages
   between the initiator and responder.

   The following syntax specifications use the Augmented Backus-Naur
   form (ABNF) notation as specified in [RFC5234].

3.1.  Initiator First Message

   The HT-* SASL mechanism starts with the initiator-msg, send by the
   initiator to the responder.

   initiator-msg = authcid-length authcid-data initiator-hashed-token

   authcid-length = 4OCTET

   authcid-data = 1*OCTET

   initiator-hashed-token = 1*OCTET

   The initiator message starts with an unsigned 32-bit integer in big
   endian.  It denotes length of the authcid-data, which contains the
   authentication identity.  Before sending the authentication identity




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   string the initiator SHOULD prepare the data with the
   UsernameCaseMapped profile of [RFC7613].

   The initiator-hashed-token value is defined as: HMAC(token,
   "Initiator" || cb-data)

   HMAC() is the function defined in [RFC2104] with H being the selected
   HT-* hash algorithm, 'cb-data' represents the data provided by the
   channel binding type, and 'token' are the UTF-8 encoded octets of the
   token string which acts as shared secret between initiator and
   responder.

   The initiator-msg MUST NOT be included in TLS 1.3 0-RTT early data
   (see [I-D.ietf-tls-tls13]).

   TODO: Add note why HMAC() is always involved, even if HMAC() is
   usually not required when modern hash algorithms are used.

3.2.  Final Responder Message

   This message is followed by a message from the responder to the
   initiator.  This 'responder-msg' is defined as follows:

   responder-msg = 1*OCTET

   The responder-msg value is defined as: HMAC(token, "Responder" || cb-
   data)

   The initiating entity MUST verify the responder-msg to achieve mutual
   authentication.

4.  Compliance with SASL Mechanism Requirements

   This section describes compliance with SASL mechanism requirements
   specified in Section 5 of [RFC4422].

   1.  "HT-SHA-256-ENDP", "HT-SHA-256-UNIQ", "HT-SHA-3-512-ENDP" and
       "HT-SHA-3-512-UNIQ".

   2.  Definition of server-challenges and client-responses:

       a  HT is a client-first mechanism.

       b  HT does not send additional data with success.

   3.  HT is capable of transferring authorization identities from the
       client to the server.




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   4.  HT does not offer any security layers (HT offers channel binding
       instead).

   5.  HT does not protect the authorization identity.

5.  Security Considerations

   To be secure, HT-* MUST be used over a TLS channel that has had the
   session hash extension [RFC7627] negotiated, or session resumption
   MUST NOT have been used.

6.  IANA Considerations

   IANA has added the following family of SASL mechanisms to the SASL
   Mechanism registry established by [RFC4422]:

      To: iana@iana.org
      Subject: Registration of a new SASL family HT

      SASL mechanism name (or prefix for the family): HT-*
      Security considerations:
        Section FIXME of draft-schmaus-kitten-sasl-ht-00
      Published specification (optional, recommended):
        draft-schmaus-kitten-sasl-ht-00 (TODO)
      Person & email address to contact for further information:
      IETF SASL WG <kitten@ietf.org>
      Intended usage: COMMON
      Owner/Change controller: IESG <iesg@ietf.org>
      Note: Members of this family MUST be explicitly registered
      using the "IETF Review" [@!RFC5226] registration procedure.
      Reviews MUST be requested on the Kitten WG mailing list
      <kitten@ietf.org> (or a successor designated by the responsible
      Security AD).

7.  References

7.1.  Normative References

   [I-D.ietf-tls-tls13]
              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-19 (work in progress),
              March 2017.

   [iana-cbt]
              Williams, N., "IANA Channel-Binding Types", 2010,
              <https://www.iana.org/assignments/channel-binding-types/
              channel-binding-types.xhtml>.




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   [iana-hash-alg]
              Williams, N., "IANA Named Information Hash Algorithm
              Registry", 2010, <https://www.iana.org/assignments/named-
              information/named-information.xhtml#hash-alg>.

   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              DOI 10.17487/RFC2104, February 1997,
              <https://www.rfc-editor.org/info/rfc2104>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4422]  Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
              Authentication and Security Layer (SASL)", RFC 4422,
              DOI 10.17487/RFC4422, June 2006,
              <https://www.rfc-editor.org/info/rfc4422>.

   [RFC5056]  Williams, N., "On the Use of Channel Bindings to Secure
              Channels", RFC 5056, DOI 10.17487/RFC5056, November 2007,
              <https://www.rfc-editor.org/info/rfc5056>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC5929]  Altman, J., Williams, N., and L. Zhu, "Channel Bindings
              for TLS", RFC 5929, DOI 10.17487/RFC5929, July 2010,
              <https://www.rfc-editor.org/info/rfc5929>.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <https://www.rfc-editor.org/info/rfc6125>.






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   [RFC6919]  Barnes, R., Kent, S., and E. Rescorla, "Further Key Words
              for Use in RFCs to Indicate Requirement Levels", RFC 6919,
              DOI 10.17487/RFC6919, April 2013,
              <https://www.rfc-editor.org/info/rfc6919>.

   [RFC6920]  Farrell, S., Kutscher, D., Dannewitz, C., Ohlman, B.,
              Keranen, A., and P. Hallam-Baker, "Naming Things with
              Hashes", RFC 6920, DOI 10.17487/RFC6920, April 2013,
              <https://www.rfc-editor.org/info/rfc6920>.

   [RFC7613]  Saint-Andre, P. and A. Melnikov, "Preparation,
              Enforcement, and Comparison of Internationalized Strings
              Representing Usernames and Passwords", RFC 7613,
              DOI 10.17487/RFC7613, August 2015,
              <https://www.rfc-editor.org/info/rfc7613>.

   [RFC7627]  Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A.,
              Langley, A., and M. Ray, "Transport Layer Security (TLS)
              Session Hash and Extended Master Secret Extension",
              RFC 7627, DOI 10.17487/RFC7627, September 2015,
              <https://www.rfc-editor.org/info/rfc7627>.

7.2.  Informative References

   [RFC5802]  Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams,
              "Salted Challenge Response Authentication Mechanism
              (SCRAM) SASL and GSS-API Mechanisms", RFC 5802,
              DOI 10.17487/RFC5802, July 2010,
              <https://www.rfc-editor.org/info/rfc5802>.

   [XEP-ISR-SASL2]
              Schmaus, F., "XEP-XXXX: Instant Stream Resumption", 2017,
              <http://geekplace.eu/xeps/xep-isr-sasl2/
              xep-isr-sasl2.html>.

Appendix A.  Acknowledgments

   Thanks to Thijs Alkemade.

Authors' Addresses

   Florian Schmaus
   University of Erlangen-Nuremberg

   Email: schmaus@cs.fau.de






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   Christoph Egger
   University of Erlangen-Nuremberg

   Email: egger@cs.fau.de















































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