1. RFC 9395
Internet Engineering Task Force (IETF)                   P. Wouters, Ed.
Request for Comments: 9395                                         Aiven
Updates: 8221, 8247                                           April 2023
Category: Standards Track                                               
ISSN: 2070-1721

Deprecation of the Internet Key Exchange Version 1 (IKEv1) Protocol and
                          Obsoleted Algorithms


   Internet Key Exchange Version 1 (IKEv1) has been deprecated, and RFCs
   2407, 2408, and 2409 have been moved to Historic status.  This
   document updates RFCs 8221 and 8247 to reflect the usage guidelines
   of old algorithms that are associated with IKEv1 and are not
   specified or commonly implemented for IKEv2.  This document further
   updates the IANA registries for IKEv2 "Transform Type Values" by
   adding a "Status" column where the deprecation status can be listed.

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

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Requirements Language
   3.  RFCs 2407, 2408, and 2409 Are Historic
   4.  IKEv1 Feature Equivalents for IKEv2
     4.1.  IKEv2 Post-Quantum Support
     4.2.  IKEv2 Labeled IPsec Support
     4.3.  IKEv2 Group SA and Multicast Support
   5.  Deprecating Obsolete Algorithms
   6.  Security Considerations
   7.  IANA Considerations
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Author's Address

1.  Introduction

   IKEv1 has been moved to Historic status.  IKEv1 [RFC2409] and its
   related documents for the Internet Security Association and Key
   Management Protocol (ISAKMP) [RFC2408] and IPsec DOI [RFC2407] were
   obsoleted by IKEv2 [RFC4306] in December 2005.  The latest version of
   IKEv2 at the time of writing was published in 2014 [RFC7296].  Since
   IKEv2 replaced IKEv1 over 15 years ago, IKEv2 has now seen wide
   deployment, and it provides a full replacement for all IKEv1
   functionality.  No new modifications or new algorithms have been
   accepted for IKEv1 for at least a decade.  IKEv2 addresses various
   issues present in IKEv1, such as IKEv1 being vulnerable to
   amplification attacks.

   Algorithm implementation requirements and usage guidelines for IKEv2
   [RFC8247] and Encapsulating Security Payload (ESP) and Authentication
   Header (AH) [RFC8221] gives guidance to implementors but limits that
   guidance to avoid broken or weak algorithms.  These two RFCs do not
   deprecate algorithms that have aged and are not in use.  Instead,
   they leave these algorithms in a state of "MAY be used" by not
   mentioning them.  This document deprecates those unmentioned
   algorithms that are no longer advised but for which there are no
   known attacks resulting in their earlier deprecation.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.  RFCs 2407, 2408, and 2409 Are Historic

   As IKEv1 is deprecated, systems running IKEv1 should be upgraded and
   reconfigured to run IKEv2.  Systems that support IKEv1 but not IKEv2
   are most likely also unsuitable candidates for continued operation
   for the following reasons:

   *  IKEv1 development ceased over a decade ago, and no new work will
      happen.  This poses the risk of unmaintained code in an otherwise
      supported product, which can result in security vulnerabilities.

   *  A number of IKEv1 systems have reached their End of Life and,
      therefore, will never be patched by the vendor if a vulnerability
      is found.

   *  There are vendors that still provide updates for their equipment
      that supports IKEv1 and IKEv2 but have "frozen" their IKEv1
      implementation.  Such users might not be aware that they are
      running unmaintained code with its associated security risks.

   *  IKEv1 systems can be abused for packet amplification attacks, as
      documented in the Security Bulletin [CVE-2016-5361].

   *  Great strides have been made in cryptography since IKEv1
      development ceased.  While some modern cryptographic algorithms
      were added to IKEv1, interoperability concerns mean that the
      defacto algorithms negotiated by IKEv1 will consist of dated or
      deprecated algorithms, like AES-CBC, SHA1, and Diffie-Hellman
      groups 1 or 2.  IKEv2 provides a state-of-the-art suite of
      cryptographic algorithms that IKEv1 lacks.

   IKEv2 is a more secure protocol than IKEv1.  For example, IKEv2
   offers more modern cryptographic primitives, proper defense against
   denial-of-service attacks, improved authentication via Extensible
   Authentication Protocol (EAP) methods, and password-authenticated key
   exchange (PAKE) support.  Also, IKEv2 is actively worked on with
   respect to defending against quantum-computer attacks.

   IKEv1-only systems should be upgraded or replaced by systems
   supporting IKEv2.  IKEv2 implementations SHOULD NOT directly import
   IKEv1 configurations without updating the cryptographic algorithms

4.  IKEv1 Feature Equivalents for IKEv2

   A few notable IKEv1 features are not present in the IKEv2 core
   specification [RFC7296] but are available for IKEv2 via an additional

4.1.  IKEv2 Post-Quantum Support

   IKEv1 and its way of using Preshared Keys (PSKs) protects against
   quantum-computer-based attacks.  IKEv2 updated its use of PSKs to
   improve the error reporting but at the expense of post-quantum
   security.  If post-quantum security is required, these systems should
   be migrated to use IKEv2 Post-quantum Preshared Keys (PPKs)

4.2.  IKEv2 Labeled IPsec Support

   Some IKEv1 implementations support Labeled IPsec, a method to
   negotiate an additional Security Context selector to the Security
   Policy Database (SPD), but this method was never standardized in
   IKEv1.  Those IKEv1 systems that require Labeled IPsec should migrate
   to an IKEv2 system supporting Labeled IPsec as specified in

4.3.  IKEv2 Group SA and Multicast Support

   The Group Domain of Interpretation (GDOI) protocol [RFC6407], which
   is based on IKEv1, defines the support for Multicast Group SAs.  For
   IKEv2, this work is currently in progress via [G-IKEV2].

5.  Deprecating Obsolete Algorithms

   This document deprecates the following algorithms:

   *  Encryption Algorithms: RC5, IDEA, CAST, Blowfish, and the
      unspecified 3IDEA, ENCR_DES_IV64, and ENCR_DES_IV32

   *  PRF Algorithms: the unspecified PRF_HMAC_TIGER

   *  Integrity Algorithms: HMAC-MD5-128

   *  Diffie-Hellman groups: none

6.  Security Considerations

   There are only security benefits if IKEv1 is deprecated and IKEv2 is

   The deprecated algorithms have long been in disuse and are no longer
   actively deployed or researched; this presents an unknown security
   risk that is best avoided.  Additionally, these algorithms not being
   supported in implementations simplifies those implementations and
   reduces the accidental use of deprecated algorithms through
   misconfiguration or downgrade attacks.

7.  IANA Considerations

   IANA has added the following line at the top of the Notes section of
   the "Internet Key Exchange (IKE) Attributes" and '"Magic Numbers" for
   ISAKMP Protocol' registries: "All registries listed below have been
   closed.  See RFC 9395."  In addition, this document has been added to
   the "Reference" column in these two registries, and their
   registration procedures have been changed to "Registry closed".

   IANA has added a "Status" column to the following IKEv2 "Transform
   Type Values" registries:

      Transform Type 1 - Encryption Algorithm Transform IDs
      Transform Type 2 - Pseudorandom Function Transform IDs
      Transform Type 3 - Integrity Algorithm Transform IDs
      Transform Type 4 - Key Exchange Method Transform IDs

   Also, the following entries have been marked as DEPRECATED:

            | Number | Name          | Status                |
            | 1      | ENCR_DES_IV64 | DEPRECATED (RFC 9395) |
            | 2      | ENCR_DES      | DEPRECATED [RFC8247]  |
            | 4      | ENCR_RC5      | DEPRECATED (RFC 9395) |
            | 5      | ENCR_IDEA     | DEPRECATED (RFC 9395) |
            | 6      | ENCR_CAST     | DEPRECATED (RFC 9395) |
            | 7      | ENCR_BLOWFISH | DEPRECATED (RFC 9395) |
            | 8      | ENCR_3IDEA    | DEPRECATED (RFC 9395) |
            | 9      | ENCR_DES_IV32 | DEPRECATED (RFC 9395) |

                  Table 1: Transform Type 1 - Encryption
                         Algorithm Transform IDs

            | Number | Name           | Status                |
            | 1      | PRF_HMAC_MD5   | DEPRECATED [RFC8247]  |
            | 3      | PRF_HMAC_TIGER | DEPRECATED (RFC 9395) |

                  Table 2: Transform Type 2 - Pseudorandom
                           Function Transform IDs

          | Number | Name               | Status                |
          | 1      | AUTH_HMAC_MD5_96   | DEPRECATED [RFC8247]  |
          | 3      | AUTH_DES_MAC       | DEPRECATED [RFC8247]  |
          | 4      | AUTH_KPDK_MD5      | DEPRECATED [RFC8247]  |
          | 6      | AUTH_HMAC_MD5_128  | DEPRECATED (RFC 9395) |
          | 7      | AUTH_HMAC_SHA1_160 | DEPRECATED (RFC 9395) |

              Table 3: Transform Type 3 - Integrity Algorithm
                               Transform IDs

     | Number | Name                         | Status               |
     | 1      | 768-bit MODP Group           | DEPRECATED [RFC8247] |
     | 22     | 1024-bit MODP Group with     | DEPRECATED [RFC8247] |
     |        | 160-bit Prime Order Subgroup |                      |

      Table 4: Transform Type 4 - Key Exchange Method Transform IDs

   All entries not mentioned here should receive no value in the new
   Status field.

8.  References

8.1.  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,

   [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>.

   [RFC8247]  Nir, Y., Kivinen, T., Wouters, P., and D. Migault,
              "Algorithm Implementation Requirements and Usage Guidance
              for the Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 8247, DOI 10.17487/RFC8247, September 2017,

8.2.  Informative References

              NIST National Vulnerability Database, "CVE-2016-5361
              Detail", 16 June 2016,

   [G-IKEV2]  Smyslov, V. and B. Weis, "Group Key Management using
              IKEv2", Work in Progress, Internet-Draft, draft-ietf-
              ipsecme-g-ikev2-09, 19 April 2023,

              Wouters, P. and S. Prasad, "Labeled IPsec Traffic Selector
              support for IKEv2", Work in Progress, Internet-Draft,
              draft-ietf-ipsecme-labeled-ipsec-11, 10 April 2023,

   [RFC2407]  Piper, D., "The Internet IP Security Domain of
              Interpretation for ISAKMP", RFC 2407,
              DOI 10.17487/RFC2407, November 1998,

   [RFC2408]  Maughan, D., Schertler, M., Schneider, M., and J. Turner,
              "Internet Security Association and Key Management Protocol
              (ISAKMP)", RFC 2408, DOI 10.17487/RFC2408, November 1998,

   [RFC2409]  Harkins, D. and D. Carrel, "The Internet Key Exchange
              (IKE)", RFC 2409, DOI 10.17487/RFC2409, November 1998,

   [RFC4306]  Kaufman, C., Ed., "Internet Key Exchange (IKEv2)
              Protocol", RFC 4306, DOI 10.17487/RFC4306, December 2005,

   [RFC6407]  Weis, B., Rowles, S., and T. Hardjono, "The Group Domain
              of Interpretation", RFC 6407, DOI 10.17487/RFC6407,
              October 2011, <https://www.rfc-editor.org/info/rfc6407>.

   [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>.

   [RFC8221]  Wouters, P., Migault, D., Mattsson, J., Nir, Y., and T.
              Kivinen, "Cryptographic Algorithm Implementation
              Requirements and Usage Guidance for Encapsulating Security
              Payload (ESP) and Authentication Header (AH)", RFC 8221,
              DOI 10.17487/RFC8221, October 2017,

   [RFC8784]  Fluhrer, S., Kampanakis, P., McGrew, D., and V. Smyslov,
              "Mixing Preshared Keys in the Internet Key Exchange
              Protocol Version 2 (IKEv2) for Post-quantum Security",
              RFC 8784, DOI 10.17487/RFC8784, June 2020,

Author's Address

   Paul Wouters (editor)
   Email: paul.wouters@aiven.io
  1. RFC 9395