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Network Working Group                                         V. Smyslov
Internet-Draft                                                ELVIS-PLUS
Intended status: Standards Track                       September 9, 2020
Expires: March 13, 2021


          Announcing Supported Authentication Methods in IKEv2
              draft-smyslov-ipsecme-ikev2-auth-announce-02

Abstract

   This specification defines a mechanism that allows the Internet Key
   Exchange version 2 (IKEv2) implementations to indicate the list of
   supported authentication methods to their peers while establishing
   IKEv2 Security Association (SA).  This mechanism improves
   interoperability when IKEv2 partners are configured with multiple
   different credentials to authenticate each other.

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 https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 March 13, 2021.

Copyright Notice

   Copyright (c) 2020 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
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   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of




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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology and Notation  . . . . . . . . . . . . . . . . . .   3
   3.  Protocol Details  . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Exchanges . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  SUPPORTED_AUTH_METHODS Notify . . . . . . . . . . . . . .   4
       3.2.1.  2-octet Announcement  . . . . . . . . . . . . . . . .   5
       3.2.2.  3-octet Announcement  . . . . . . . . . . . . . . . .   6
       3.2.3.  Multi-octet Announcement  . . . . . . . . . . . . . .   7
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   The Internet Key Exchange version 2 (IKEv2) protocol, defined in
   [RFC7296], performs authenticated key exchange in IPsec.  IKEv2,
   unlike its predecessor IKEv1, defined in [RFC2409], doesn't include a
   mechanism to negotiate an authentication method that the peers would
   use to authenticate each other.  It is assumed that each peer selects
   whatever authentication method it thinks is appropriate, depending on
   authentication credentials it has.

   This approach generally works well when there is no ambiguity in
   selecting authentication credentials.  The problem may arise when
   there are several credentials of different type configured on one
   peer, while only some of them are supported on the other peer.
   Another problem situation is when a single credential may be used to
   produce different types of authentication tokens (e.g. signatures of
   different formats).  Emerging post-quantum signature algorithms may
   bring additional challenges for implementations, especially if so
   called hybrid schemes are used (e.g. see
   [I-D.ounsworth-pq-composite-sigs]).

   This specification defines an extension to the IKEv2 protocol that
   allows peers to announce their supported authentication methods, thus
   decreasing risks of SA establishment failure in situations when there
   are several ways for the peers to authenticate themselves.






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2.  Terminology and Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Protocol Details

   The idea is that each party sends a list of authentication methods it
   supports to its peer.  In addition, the sending party may optionally
   specify that some of the authentication methods are only to be used
   with particular trust anchors.  Upon receiving this information the
   peer may take it into account while selecting an algorithm for its
   authentication if several methods are available.

3.1.  Exchanges

   If the responder is willing to use this extension, it includes a new
   notification SUPPORTED_AUTH_METHODS in a response message of the
   IKE_SA_INIT exchange.  This notification contains a list of
   authentication methods supported by the responder.

   Initiator                              Responder
   -----------                            -----------
   HDR, SAi1, KEi, Ni -->
                                      <-- HDR, SAr1, KEr, Nr, [CERTREQ,]
                                             [N(SUPPORTED_AUTH_METHODS)]

                      Figure 1: IKE_SA_INIT Exchange

   If the initiator doesn't support this extension, it will ignore the
   received notification as an unknown status notify.  Otherwise, it MAY
   send the SUPPORTED_AUTH_METHODS notification in the IKE_AUTH request
   message, with a list of authentication methods supported by the
   initiator.

   Initiator                              Responder
   -----------                            -----------
   HDR, SK {IDi, [CERT,] [CERTREQ,]
   [IDr,] AUTH, SAi2, TSi, TSr,
   [N(SUPPORTED_AUTH_METHODS)] }  -->
                                      <-- HDR, SK {IDr, [CERT,]
                                               AUTH, SAr2, TSi, TSr }

                        Figure 2: IKE_AUTH Exchange




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   Since the responder sends the SUPPORTED_AUTH_METHODS notification in
   the IKE_SA_INIT exchange, it must take care that the size of the
   response message wouldn't grow too much so that IP fragmentation
   takes place.  If the following conditions are met:

   o  the SUPPORTED_AUTH_METHODS notification to be included is so
      large, that the responder suspects that IP fragmentation of the
      resulting IKE_SA_INIT response message may happen;

   o  both peers support the IKE_INTERMEDIATE exchange, defined in
      [I-D.ietf-ipsecme-ikev2-intermediate] (i.e.  the responder has
      received and is going to send the INTERMEDIATE_EXCHANGE_SUPPORTED
      notification);

   then the responder may choose not to send actual list of the
   supported authentication methods in the IKE_SA_INIT exchange and
   instead ask the initiator to start the IKE_INTERMEDIATE exchange for
   the list to be sent in.  In this case the responder includes
   SUPPORTED_AUTH_METHODS notification containing no data in the
   IKE_SA_INIT response.

   If the initiator receives the empty SUPPORTED_AUTH_METHODS
   notification in the IKE_SA_INIT exchange, it means that the responder
   is going to send the list of the supported authentication methods in
   the IKE_INTERMEDIATE exchange.  If this exchange is to be initiated
   anyway for some other reason, then the responder MUST use it to send
   the SUPPORTED_AUTH_METHODS notification.  Otherwise, the initiator
   MAY start the IKE_INTERMEDIATE exchange just for this sole purpose by
   sending an empty request message.

   Initiator                              Responder
   -----------                            -----------
   HDR, SK {...}  -->
                                      <-- HDR, SK {...
                                          [N(SUPPORTED_AUTH_METHODS)] }

                    Figure 3: IKE_INTERMEDIATE Exchange

   Note, that sending the SUPPORTED_AUTH_METHODS notification and using
   information obtained from it is optional for both the initiator and
   the responder.

3.2.  SUPPORTED_AUTH_METHODS Notify

   The format of the SUPPORTED_AUTH_METHODS notification is shown below.






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                       1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Protocol ID  |   SPI Size    |      Notify Message Type      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~          List of Supported Auth Methods Announcements         ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 4: SUPPORTED_AUTH_METHODS Notify

   The Notify payload format is defined in Section 3.10 of [RFC7296].
   When a Notify payload of type SUPPORTED_AUTH_METHODS is sent, the
   Protocol ID field is set to 0, the SPI Size is set to 0, meaning
   there is no SPI field, and the Notify Message Type is set to <TBA by
   IANA>.

   The Notification Data field contains the list of supported
   authentication methods announcements.  Each individual announcement
   is a variable-size data blob, which format depends on the announced
   authentication method.  The blob always starts with an octet
   containing the length of the blob followed by an octet containing the
   authentication method.  Authentication methods are represented as
   values from the "IKEv2 Authentication Method" registry defined in
   [IKEV2-IANA].  The meaning of the remaining octets of the blob, if
   any, depends on the authentication method and is defined below.
   Note, that for the currently defined authentication methods the
   length octet fully defines both the format and the semantics of the
   blob.

   If more authentication methods are defined in future, the
   corresponding documents must describe the semantics of the
   announcements for these methods.  Implementations MUST skip
   announcements which semantics they don't understand.

3.2.1.  2-octet Announcement

   If the announcement contains an authentication method that is not
   concerned with public key cryptography, then the following format is
   used.








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                       1
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Length (=2)  |  Auth Method  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 5: Supported Authentication Method

   o  Length - Length of the blob, must be 2 for this case.

   o  Auth Method - Announced authentication method.

   This format is applicable for the authentication methods "Shared Key
   Message Integrity Code" (2) and "NULL Authentication" (13).  Note,
   that authentication method "Generic Secure Password Authentication
   Method" (12) would also fall in this category, however it is
   negotiated separately (see [RFC6467] and for this reason there is no
   point to announce it via this mechanism.

3.2.2.  3-octet Announcement

   If the announcement contains an authentication method that is
   concerned with public key cryptography, then the following format is
   used.  This format allows to link the announcement with a particular
   trust anchor from the Certificate Request payload.

                       1                   2
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Length (=3)  |  Auth Method  |   Cert Link   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 6: Supported Authentication Method

   o  Length - Length of the blob, must be 3 for this case.

   o  Auth Method - Announced authentication method.

   o  Cert Link - Link this announcement to a particular CA.

   If the Cert Link field contains non-zero value N, it means that the
   announced authentication method is intended to be used only with the
   N-th trust anchor (CA certificate) from the Certificate Request
   payload(s) sent by this peer.  If it is zero, then this
   authentication method may be used with any of CAs, that are not
   linked to any other announcement.  If multiple CERTREQ payloads were
   sent, the CAs from all of them are treated as a single list for the
   purpose of the linking.  If no Certificate Request payload were



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   receives, the content of this field MUST be ignored and treated as
   zero.

   This format is applicable for the authentication methods "RSA Digital
   Signature" (1), "DSS Digital Signature" (3), "ECDSA with SHA-256 on
   the P-256 curve" (9), "ECDSA with SHA-384 on the P-384 curve" (10)
   and "ECDSA with SHA-512 on the P-512 curve" (11).  Note however, that
   these authentication methods are currently superseded by the "Digital
   Signature" (14) authentication method, which has a different
   announcement format, described below.

3.2.3.  Multi-octet Announcement

   The following format is currently used only with the "Digital
   Signature" (14) authentication method.

                       1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Length (>3)  |  Auth Method  |   Cert Link   |               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +
   |                                                               |
   ~                AlgorithmIdentifier ASN.1 object               ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 7: Supported Authentication Method

   o  Length - Length of the blob, must be greater than 3 for this case.

   o  Auth Method - Announced authentication method, currently may only
      be 14 ("Digital Signature").

   o  Cert Link - Link this announcement to a particular CA; see
      Section 3.2.2 for details.

   o  AlgorithmIdentifier ASN.1 object - DER-encoded ASN.1 object
      AlgorithmIdentifier.

   The "Digital Signature" authentication method, defined in [RFC7427],
   supersedes previously defined signature authentication methods.  In
   this case the real authentication algorithm is identified via
   AlgorithmIdentifier ASN.1 object.  Appendix A in [RFC7427] contains
   examples of Commonly Used ASN.1 Objects.







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4.  Security Considerations

   Security considerations for IKEv2 protocol are discussed in
   [RFC7296].  It is assumed that this extension of the IKEv2 doesn't
   add new vulnerabilities to the protocol.

5.  IANA Considerations

   This document defines a new Notify Message Types in the "Notify
   Message Types - Status Types" registry:

     <TBA>       SUPPORTED_AUTH_METHODS

6.  References

6.1.  Normative References

   [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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
              2014, <https://www.rfc-editor.org/info/rfc7296>.

   [RFC7427]  Kivinen, T. and J. Snyder, "Signature Authentication in
              the Internet Key Exchange Version 2 (IKEv2)", RFC 7427,
              DOI 10.17487/RFC7427, January 2015,
              <https://www.rfc-editor.org/info/rfc7427>.

   [I-D.ietf-ipsecme-ikev2-intermediate]
              Smyslov, V., "Intermediate Exchange in the IKEv2
              Protocol", draft-ietf-ipsecme-ikev2-intermediate-04 (work
              in progress), June 2020.

   [IKEV2-IANA]
              IANA, "Internet Key Exchange Version 2 (IKEv2)
              Parameters", <http://www.iana.org/assignments/ikev2-
              parameters/ikev2-parameters.xhtml#ikev2-parameters-7>.






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6.2.  Informative References

   [RFC2409]  Harkins, D. and D. Carrel, "The Internet Key Exchange
              (IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998,
              <https://www.rfc-editor.org/info/rfc2409>.

   [RFC6467]  Kivinen, T., "Secure Password Framework for Internet Key
              Exchange Version 2 (IKEv2)", RFC 6467,
              DOI 10.17487/RFC6467, December 2011,
              <https://www.rfc-editor.org/info/rfc6467>.

   [I-D.ounsworth-pq-composite-sigs]
              Ounsworth, M. and M. Pala, "Composite Keys and Signatures
              For Use In Internet PKI", draft-ounsworth-pq-composite-
              sigs-03 (work in progress), July 2020.

Author's Address

   Valery Smyslov
   ELVIS-PLUS
   PO Box 81
   Moscow (Zelenograd)  124460
   RU

   Phone: +7 495 276 0211
   Email: svan@elvis.ru

























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