



Internet Engineering Task Force (IETF)                          A. DeKok
Request for Comments: 8940                                    FreeRADIUS
Updates: 5247                                               October 2020
Category: Standards Track                                               
ISSN: 2070-1721


 Extensible Authentication Protocol (EAP) Session-Id Derivation for EAP
    Subscriber Identity Module (EAP-SIM), EAP Authentication and Key
             Agreement (EAP-AKA), and Protected EAP (PEAP)

Abstract

   RFC 5247 is updated to define and clarify EAP Session-Id derivation
   for multiple Extensible Authentication Protocol (EAP) methods.  The
   derivation of Session-Id was not given for EAP Subscriber Identity
   Module (EAP-SIM) or EAP Authentication and Key Agreement (EAP-AKA)
   when using the fast reconnect exchange instead of full
   authentication.  The derivation of Session-Id for full authentication
   is clarified for both EAP-SIM and EAP-AKA.  The derivation of
   Session-Id for Protected EAP (PEAP) is also given.  The definition
   for PEAP follows the definition for other TLS-based EAP methods.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8940.

Copyright Notice

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction
   2.  Updates to RFC 5247, Appendix A
     2.1.  EAP-AKA
     2.2.  EAP-SIM
     2.3.  Rationale for EAP-AKA and EAP-SIM Updates
   3.  Session-Id for PEAP
   4.  Security Considerations
   5.  IANA Considerations
   6.  References
     6.1.  Normative References
     6.2.  Informative References
   Acknowledgments
   Author's Address

1.  Introduction

   EAP [RFC3748] Session-Id derivation has not been defined for EAP-SIM
   and EAP-AKA when using the fast reconnect exchange instead of full
   authentication.  [RFC5247] defines the Session-Id for these EAP
   methods, but that derivation is only applicable for the full
   authentication case.  The Session-Id derivation was not defined for
   EAP-AKA', but [AKAP] now defines it, along with other updates.  As
   such, the definition for EAP-AKA' is not included here.

   Further, the derivation of Session-Id for full authentication is
   clarified, as the text in [RFC5247] is ambiguous.

   The IEEE has defined Fast Initial Link Setup (FILS) authentication
   [FILS], which needs the EAP Session-Id in order for the EAP Re-
   authentication Protocol (ERP) [RFC6696] to work.  It is therefore
   important to address the existing deficiencies in the definition of
   EAP Session-Id.

   Finally, [RFC5247] did not define Session-Id for PEAP [MS-PEAP]
   [PEAP].  We correct these deficiencies here by updating [RFC5247]
   with the Session-Id derivation during fast-reconnect exchange for
   EAP-SIM and EAP-AKA; clarifying the Session-Id derivation during full
   authentication for EAP-SIM and EAP-AKA; and defining the Session-Id
   derivation for PEAP, which is the same for both full authentication
   and fast reconnect.

2.  Updates to RFC 5247, Appendix A

   This section updates [RFC5247], Appendix A to define Session-Id for
   fast reconnect exchange for EAP-AKA and EAP-SIM.

2.1.  EAP-AKA

   For EAP-AKA, [RFC5247], Appendix A says:

   |  EAP-AKA
   |     EAP-AKA is defined in [RFC4187].  The EAP-AKA Session-Id is the
   |     concatenation of the EAP Type Code (0x17) with the contents of
   |     the RAND field from the AT_RAND attribute, followed by the
   |     contents of the AUTN field in the AT_AUTN attribute:
   |  
   |        Session-Id = 0x17 || RAND || AUTN

   It should say:

   |  EAP-AKA
   |     EAP-AKA is defined in [RFC4187].  When using full
   |     authentication, the EAP-AKA Session-Id is the concatenation of
   |     the EAP Type Code (0x17) with the contents of the RAND field
   |     from the AT_RAND attribute, followed by the contents of the
   |     AUTN field in the AT_AUTN attribute:
   |  
   |        Session-Id = 0x17 || RAND || AUTN
   |  
   |     When using fast reconnect, the EAP-AKA Session-Id is the
   |     concatenation of the EAP Type Code (0x17) with the contents of
   |     the NONCE_S field from the AT_NONCE_S attribute, followed by
   |     the contents of the MAC field from the AT_MAC attribute from
   |     EAP-Request/AKA-Reauthentication:
   |  
   |        Session-Id = 0x17 || NONCE_S || MAC

2.2.  EAP-SIM

   Similarly for EAP-SIM, [RFC5247], Appendix A says:

   |  EAP-SIM
   |     EAP-SIM is defined in [RFC4186].  The EAP-SIM Session-Id is the
   |     concatenation of the EAP Type Code (0x12) with the contents of
   |     the RAND field from the AT_RAND attribute, followed by the
   |     contents of the NONCE_MT field in the AT_NONCE_MT attribute:
   |  
   |        Session-Id = 0x12 || RAND || NONCE_MT

   It should say:

   |  EAP-SIM
   |     EAP-SIM is defined in [RFC4186].  When using full
   |     authentication, the EAP-SIM Session-Id is the concatenation of
   |     the EAP Type Code (0x12) with the contents of the RAND field
   |     from the AT_RAND attribute, followed by the contents of the
   |     NONCE_MT field in the AT_NONCE_MT attribute.  RFC 4186 says
   |     that the EAP server should obtain "n" GSM triplets where "n=2"
   |     or "n=3".
   |  
   |     For "n=2", the Session-Id is therefore defined as
   |  
   |        Session-Id = 0x12 || RAND1 || RAND2 || NONCE_MT
   |  
   |     which is 49 octets in length.
   |  
   |     For "n=3", the Session-Id is therefore defined as
   |  
   |        Session-Id = 0x12 || RAND1 || RAND2 || RAND3 || NONCE_MT
   |  
   |     which is 65 octets in length.
   |  
   |     RAND1, RAND2, and RAND3 correspond to the RAND value from the
   |     first, second, and third GSM triplet, respectively.
   |  
   |     When using fast reconnect, the EAP-SIM Session-Id is the
   |     concatenation of the EAP Type Code (0x12) with the contents of
   |     the NONCE_S field from the AT_NONCE_S attribute, followed by
   |     the contents of the MAC field from the AT_MAC attribute from
   |     EAP-Request/SIM/Reauthentication:
   |  
   |        Session-Id = 0x12 || NONCE_S || MAC
   |  
   |     which is 33 octets in length.

2.3.  Rationale for EAP-AKA and EAP-SIM Updates

   Appendix A of [RFC5247] was supposed to define exported parameters
   for existing EAP methods.  The way Session-Id was defined for EAP-AKA
   and EAP-SIM works only for the full authentication case, i.e., it
   cannot be used when the optional fast reconnect case is used since
   the used parameters (RAND, AUTN, NONCE_MT) are not used in the fast
   reconnect case.  Based on [RFC4187], Section 5.2 and similar text in
   [RFC4186], Section 5.2, NONCE_S corresponds to RAND and MAC in EAP-
   Request/AKA-Reauthentication, and EAP-Request/SIM/Reauthentication
   corresponds to AUTN.  That would seem to imply that the Session-Id
   could be defined using NONCE_S and MAC instead of RAND and AUTN/
   NONCE_MT.

   This derivation is done via a random value created by the server,
   along with a secret key and the peer's identity.  We believe that
   this derivation is secure, though no formal analysis has been done.

3.  Session-Id for PEAP

   [RFC5247] did not define Session-Id for Microsoft's Protected EAP
   (PEAP).  For consistency with the EAP-TLS definition given in
   [RFC5216], Section 2.3, we define it as:

      Session-Id = 0x19 || client.random || server.random

   This definition is that same for both full authentication and for
   fast reconnect.

   This definition is already in widespread use in all known PEAP
   implementations.

   Note that this definition for Session-Id only applies when TLS 1.2 or
   earlier is used.  A different derivation is defined for TLS 1.3 in
   [TLS-EAP-TYPES].

4.  Security Considerations

   This specification defines EAP Session-Ids for ERP with EAP-SIM and
   EAP-AKA.  It therefore enables ERP key hierarchy establishment using
   fast reconnect with EAP-SIM and EAP-AKA.

   The Session-Id definitions given here are unique per session,
   unforgeable, and unguessable by an outside party, as per the
   requirements of [RFC5247], Section 10.

   The definitions used here have been widely deployed for years in all
   major EAP implementations.  However, we acknowledge that very little
   security analysis has been done for these definitions.  As a result,
   any security issues would result in serious issues for the Internet
   as a whole.

   These updates do not modify the security considerations outlined in
   [RFC5247].

5.  IANA Considerations

   This document has no IANA actions.

6.  References

6.1.  Normative References

   [FILS]     IEEE, "IEEE Standard for Information technology--
              Telecommunications and information exchange between
              systems - Local and metropolitan area networks--Specific
              requirements - Part 11: Wireless LAN Medium Access Control
              (MAC) and Physical Layer (PHY) Specifications - Amendment
              1: Fast Initial Link Setup",
              DOI 10.1109/IEEESTD.2016.7792308, IEEE Std 802.11ai-2016,
              December 2016,
              <https://doi.org/10.1109/IEEESTD.2016.7792308>.

   [RFC3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
              Levkowetz, Ed., "Extensible Authentication Protocol
              (EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
              <https://www.rfc-editor.org/info/rfc3748>.

   [RFC5216]  Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS
              Authentication Protocol", RFC 5216, DOI 10.17487/RFC5216,
              March 2008, <https://www.rfc-editor.org/info/rfc5216>.

   [RFC5247]  Aboba, B., Simon, D., and P. Eronen, "Extensible
              Authentication Protocol (EAP) Key Management Framework",
              RFC 5247, DOI 10.17487/RFC5247, August 2008,
              <https://www.rfc-editor.org/info/rfc5247>.

6.2.  Informative References

   [AKAP]     Arkko, J., Lehtovirta, V., Torvinen, V., and P. Eronen,
              "Improved Extensible Authentication Protocol Method for
              3GPP Mobile Network Authentication and Key Agreement (EAP-
              AKA')", Work in Progress, Internet-Draft, draft-ietf-emu-
              rfc5448bis-07, 9 March 2020, <https://tools.ietf.org/html/
              draft-ietf-emu-rfc5448bis-07>.

   [Err5011]  RFC Errata, Erratum ID 5011, RFC 5247,
              <https://www.rfc-editor.org/errata/eid5011>.

   [MS-PEAP]  Microsoft, "[MS-PEAP]: Protected Extensible Authentication
              Protocol (PEAP)", <https://docs.microsoft.com/en-
              us/openspecs/windows_protocols/ms-peap/5308642b-90c9-4cc4-
              beec-fb367325c0f9>.

   [PEAP]     Palekar, A., Josefsson, S., Simon, D., and G. Zorn,
              "Protected EAP Protocol (PEAP) Version 2", Work in
              Progress, Internet-Draft, draft-josefsson-pppext-eap-tls-
              eap-10, 21 October 2004, <https://tools.ietf.org/html/
              draft-josefsson-pppext-eap-tls-eap-10>.

   [RFC4186]  Haverinen, H., Ed. and J. Salowey, Ed., "Extensible
              Authentication Protocol Method for Global System for
              Mobile Communications (GSM) Subscriber Identity Modules
              (EAP-SIM)", RFC 4186, DOI 10.17487/RFC4186, January 2006,
              <https://www.rfc-editor.org/info/rfc4186>.

   [RFC4187]  Arkko, J. and H. Haverinen, "Extensible Authentication
              Protocol Method for 3rd Generation Authentication and Key
              Agreement (EAP-AKA)", RFC 4187, DOI 10.17487/RFC4187,
              January 2006, <https://www.rfc-editor.org/info/rfc4187>.

   [RFC6696]  Cao, Z., He, B., Shi, Y., Wu, Q., Ed., and G. Zorn, Ed.,
              "EAP Extensions for the EAP Re-authentication Protocol
              (ERP)", RFC 6696, DOI 10.17487/RFC6696, July 2012,
              <https://www.rfc-editor.org/info/rfc6696>.

   [TLS-EAP-TYPES]
              DeKok, A., "TLS-based EAP types and TLS 1.3", Work in
              Progress, Internet-Draft, draft-ietf-emu-tls-eap-types-01,
              29 July 2020, <https://tools.ietf.org/html/draft-ietf-emu-
              tls-eap-types-01>.

Acknowledgments

   The issue corrected in this specification was first reported by Jouni
   Malinen in a technical erratum for RFC 5247 [Err5011].

   The text in this document follows Jouni's suggestions.

Author's Address

   Alan DeKok
   The FreeRADIUS Server Project

   Email: aland@freeradius.org
