Common Authentication Technology Next Generation F. Schmaus Internet-Draft C. Egger Intended status: Experimental University of Erlangen-Nuremberg Expires: January 7, 2018 July 6, 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 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 January 7, 2018. Copyright Notice Copyright (c) 2017 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 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Schmaus & Egger Expires January 7, 2018 [Page 1] Internet-Draft July 2017 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 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. Schmaus & Egger Expires January 7, 2018 [Page 2] Internet-Draft July 2017 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-- Where is the capitalized "Hash Name String" of the IANA "Named Information Hash Algorithm Registry" [iana-hash-alg] as specified in [RFC6920], and 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]. Schmaus & Egger Expires January 7, 2018 [Page 3] Internet-Draft July 2017 +------+----------------------+ | 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 Schmaus & Egger Expires January 7, 2018 [Page 4] Internet-Draft July 2017 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 used even if it is 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. Schmaus & Egger Expires January 7, 2018 [Page 5] Internet-Draft July 2017 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 Intended usage: COMMON Owner/Change controller: IESG 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 (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, . Schmaus & Egger Expires January 7, 2018 [Page 6] Internet-Draft July 2017 [iana-hash-alg] Williams, N., "IANA Named Information Hash Algorithm Registry", 2010, . [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- Hashing for Message Authentication", RFC 2104, DOI 10.17487/RFC2104, February 1997, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple Authentication and Security Layer (SASL)", RFC 4422, DOI 10.17487/RFC4422, June 2006, . [RFC5056] Williams, N., "On the Use of Channel Bindings to Secure Channels", RFC 5056, DOI 10.17487/RFC5056, November 2007, . [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, . [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, . [RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings for TLS", RFC 5929, DOI 10.17487/RFC5929, July 2010, . [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, . Schmaus & Egger Expires January 7, 2018 [Page 7] Internet-Draft July 2017 [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, . [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, . [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, . [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, . 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, . [XEP-ISR-SASL2] Schmaus, F., "XEP-XXXX: Instant Stream Resumption", 2017, . Appendix A. Acknowledgments Thanks to Thijs Alkemade. Authors' Addresses Florian Schmaus University of Erlangen-Nuremberg Email: schmaus@cs.fau.de Schmaus & Egger Expires January 7, 2018 [Page 8] Internet-Draft July 2017 Christoph Egger University of Erlangen-Nuremberg Email: egger@cs.fau.de Schmaus & Egger Expires January 7, 2018 [Page 9]