Network Working Group                                         D. Migault
Internet-Draft                                               J. Mattsson
Obsoletes: 7321 (if approved)                                   Ericsson
Intended status: Standards Track                              P. Wouters
Expires: March 13, 2017                                          Red Hat
                                                                  Y. Nir
                                                             Check Point
                                                              T. Kivinen
                                                           INSIDE Secure
                                                       September 9, 2016

 Cryptographic Algorithm Implementation Requirements and Usage Guidance
for Encapsulating Security Payload (ESP) and Authentication Header (AH)


   This document updates the Cryptographic Algorithm Implementation
   Requirements for ESP and AH.  The goal of these document is to enable
   ESP and AH to benefit from cryptography that is up to date while
   making IPsec interoperable.

   This document obsoletes RFC 7321 on the cryptographic recommendations

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

   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, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( 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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Updating Algorithm Implementation Requirements and Usage
           Guidance  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Updating Algorithm Requirement Levels . . . . . . . . . .   3
     1.3.  Document Audience . . . . . . . . . . . . . . . . . . . .   4
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  ESP Encryption Algorithms . . . . . . . . . . . . . . . . . .   5
   4.  ESP and AH Authentication Algorithms  . . . . . . . . . . . .   7
   5.  ESP and AH Compression Algorithms . . . . . . . . . . . . . .   8
   6.  Summary of Changes from RFC 7321  . . . . . . . . . . . . . .   9
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The Encapsulating Security Payload (ESP) [RFC4303] and the
   Authentication Header (AH) [RFC4302] are the mechanisms for applying
   cryptographic protection to data being sent over an IPsec Security
   Association (SA) [RFC4301].

   This document provides guidance and recommendations so that ESP and
   AH can be used with a cryptographic algorithms that are up to date.
   The challenge of such document is to make sure that over the time
   IPsec implementations can use secure and up-to-date cryptographic
   algorithms while keeping IPsec interoperable.

1.1.  Updating Algorithm Implementation Requirements and Usage Guidance

   The field of cryptography evolves continuously.  New stronger
   algorithms appear and existing algorithms are found to be less secure
   then originally thought.  Therefore, algorithm implementation

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   requirements and usage guidance need to be updated from time to time
   to reflect the new reality.  The choices for algorithms must be
   conservative to minimize the risk of algorithm compromise.
   Algorithms need to be suitable for a wide variety of CPU
   architectures and device deployments ranging from high end bulk
   encryption devices to small low-power IoT devices.

   The algorithm implementation requirements and usage guidance may need
   to change over time to adapt to the changing world.  For this reason,
   the selection of mandatory-to-implement algorithms was removed from
   the main IKEv2 specification and placed in a separate document.

1.2.  Updating Algorithm Requirement Levels

   The mandatory-to-implement algorithm of tomorrow should already be
   available in most implementations of AH/ESP by the time it is made
   mandatory.  This document attempts to identify and introduce those
   algorithms for future mandatory-to-implement status.  There is no
   guarantee that the algorithms in use today may become mandatory in
   the future.  Published algorithms are continuously subjected to
   cryptographic attack and may become too weak or could become
   completely broken before this document is updated.

   This document only provides recommendations for the mandatory-to-
   implement algorithms or algorithms too weak that are recommended not
   to be implemented.  As a result, any algorithm listed at the IPsec
   IANA registry not mentioned in this document MAY be implemented.  As
   [RFC7321] omitted most of the algorithms mentioned by the IPsec IANA
   repository, which makes it difficult to define whether non mentioned
   algorithms are optional to implement or must not be implemented as
   they are too weak.  This document provides explicit guidance for all
   of them.  It is expected that this document will be updated over time
   and next versions will only mention algorithms which status has
   evolved.  For clarification when an algorithm has been mentioned in
   [RFC7321], this document states explicitly the update of the status.

   Although this document updates the algorithms to keep the AH/ESP
   communication secure over time, it also aims at providing
   recommendations so that AH/ESP implementations remain interoperable.
   AH/ESP interoperability is addressed by an incremental introduction
   or deprecation of algorithms.  In addition, this document also
   considers the new use cases for AH/ESP deployment, such as Internet
   of Things (IoT).

   It is expected that deprecation of an algorithm is performed
   gradually.  This provides time for various implementations to update
   their implemented algorithms while remaining interoperable.  Unless
   there are strong security reasons, an algorithm is expected to be

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   downgraded from MUST to MUST- or SHOULD, instead of MUST NOT.
   Similarly, an algorithm that has not been mentioned as mandatory-to-
   implement is expected to be introduced with a SHOULD instead of a

   The current trend toward Internet of Things and its adoption of AH/
   ESP requires this specific use case to be taken into account as well.
   IoT devices are resource constrained devices and their choice of
   algorithms are motivated by minimizing the footprint of the code, the
   computation effort and the size of the messages to send.  This
   document indicates "[IoT]" when a specified algorithm is specifically
   listed for IoT devices.  Requirement levels that are marked as "IoT"
   apply to IoT devices and to server-side implementations that might
   presumably need to interoperate with them, including any general-
   purpose VPN gateways.

1.3.  Document Audience

   The recommendations of this document mostly target AH/ESP
   implementers as implementations need to meet both high security
   expectations as well as high interoperability between various vendors
   and with different versions.  Interoperability requires a smooth move
   to more secure cipher suites.  This may differ from a user point of
   view that may deploy and configure AH/ESP with only the safest cipher

   This document does not give any recommendations for the use of
   algorithms, it only gives implementation recommendations for
   implementations.  The use of algorithms by users is dictated by the
   security policy requirements for that specific user, and are outside
   the scope of this document.

   The algorithms considered here are listed by the IANA as part of the
   IKEv2 parameters.  IKEv1 is out of scope of this document.  IKEv1 is
   deprecated and the recommendations of this document must not be
   considered for IKEv1, nor IKEv1 parameters be considered by this

   The IANA registry for Internet Key Exchange Version 2 (IKEv2)
   Parameters contains some entries that are not for use with ESP or AH.
   This document does not modify the status of those algorithms.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in

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   Following [RFC4835], we define some additional key words:

   MUST-  This term means the same as MUST.  However, we expect that at
      some point in the future this algorithm will no longer be a MUST.
   SHOULD+  This term means the same as SHOULD.  However, it is likely
      that an algorithm marked as SHOULD+ will be promoted at some
      future time to be a MUST.

3.  ESP Encryption Algorithms

    | Name                    | Status     | AEAD    | Comment       |
    | ENCR_DES_IV64           | MUST NOT   | No      | UNSPECIFIED   |
    | ENCR_DES                | MUST NOT   | No      | [RFC2405]     |
    | ENCR_3DES               | SHOULD NOT | No      | [RFC2451]     |
    | ENCR_BLOWFISH           | MUST NOT   | No      | [RFC2451]     |
    | ENCR_3IDEA              | MUST NOT   | No      | UNSPECIFIED   |
    | ENCR_DES_IV32           | MUST NOT   | No      | UNSPECIFIED   |
    | ENCR_NULL               | MUST       | No      | [RFC2410]     |
    | ENCR_AES_CBC            | MUST       | No      | [RFC3602][1]  |
    | ENCR_AES_CCM_8          | SHOULD     | Yes     | [RFC4309]IoT] |
    | ENCR_AES_GCM_16         | MUST       | Yes     | [RFC4106][1]  |
    | ENCR_CHACHA20_POLY1305  | SHOULD     | Yes     | [RFC7634]     |

       [1] - This requirement level is for 128-bit and 256-bit keys.
    192-bit keys remain at MAY level.  [IoT] - This requirement is for
     interoperability with IoT.  Only 128-bit keys are at MUST level.
              192-bit and 256-bit keys are at the MAY level.

   IPsec sessions may have very long life time, and carry multiple
   packets, so there is a need to move 256-bit keys in the long term.
   For that purpose requirement level is for 128 bit keys and 256 bit
   keys are at SHOULD (when applicable).  In that sense 256 bit keys
   status has been raised from MAY in RFC7321 to SHOULD.

   IANA has allocated codes for cryptographic algorithms that have not
   been specified by the IETF.  Such algorithms are noted as
   UNSPECIFIED.  Usually, the use of theses algorithms is limited to
   specific cases, and the absence of specification makes
   interoperability difficult for IPsec communications.  These
   algorithms were not been mentioned in [RFC7321] and this document
   clarify that such algorithms MUST NOT be implemented for IPsec

   Similarly IANA also allocated code points for algorithms that are not
   expected to be used to secure IPsec communications.  Such algorithms

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   are noted as Non IPsec.  As a result, these algorithms MUST NOT be

   Various older and not well tested and never widely implemented
   ciphers have been changed to MUST NOT.

   ENCR_3DES status has been downgraded from MAY in RFC7321 to SHOULD
   NOT.  ENCR_CHACHA20_POLY1305 is a more modern approach alternative
   for ENCR_3DES than ENCR_AES_CBC and so it expected to be favored to
   replace ENCR_3DES.

   ENCR_BLOWFISH has been downgraded to MUST NOT as it has been
   deprecated for years by TWOFISH, which is not standarized for ESP and
   therefor not listed in this document.  Some implementations support
   TWOFISH using a private range number.

   ENCR_NULL status was set to MUST in [RFC7321] and remains a MUST to
   enable the use of ESP with only authentication which is preferred
   over AH due to NAT traversal.  ENCR_NULL is expected to remain MUST
   by protocol requirements.

   ENCR_AES_CBC status remains to MUST.  ENCR_AES_CBC MUST be
   implemented in order to enable interoperability between
   implementation that followed RFC7321.  However, there is a trend for
   the industry to move to AEAD encryption, and the overhead of
   ENCR_AES_CBC remains quite large so it is expected to be replaced by
   AEAD algorithms in the long term.

   ENCR_AES_CCM_8 status was set to MAY in [RFC7321] and has been raised
   from MAY to SHOULD in order to interact with Internet of Things
   devices.  As this case is not a general use case for VPNs, its status
   is expected to remain as SHOULD.

   ENCR_AES_GCM_16 status has been updated from SHOULD+ to MUST in order
   to favor the use of authenticated encryption and AEAD algorithms.
   ENCR_AES_GCM_16 has been widely implemented for ESP due to its
   increased performance and key longevity compared to ENCR_AES_CBC.

   ENCR_CHACHA20_POLY1305 was not ready to be considered at the time of
   RFC7321.  It has been recommended by the CRFG and others as an
   alternative to ENCR_AES_XCBC and ENCR_AES_GCM_*. It is also being
   standardized for ESP for the same reasons.  At the time of writing,
   there are not enough ESP implementations of ENCR_CHACHA20_POLY1305 to
   be able to introduce it at the SHOULD+ level.  Its status has been
   set to SHOULD and is expected to become MUST in the long term.

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4.  ESP and AH Authentication Algorithms

   Encryption without authentication MUST NOT be used.  As a result,
   authentication algorithm recommendations in this section are
   targeting two types of communications: Firstly authenticated only
   communications without encryption.  Such communications can be ESP
   with NULL encryption or AH communications.  Secondly, communications
   that are encrypted with non AEAD encryption algorithms mentioned
   above.  In this case, they MUST be combined with an authentication

   | Name                   | Status           | Comment               |
   | AUTH_NONE              | MUST / MUST NOT  | [RFC7296]  AEAD       |
   | AUTH_HMAC_MD5_96       | MUST NOT         | [RFC2403][RFC7296]    |
   | AUTH_HMAC_SHA1_96      | MUST-            | [RFC2404][RFC7296]    |
   | AUTH_DES_MAC           | MUST NOT         | [UNSPECIFIED]         |
   | AUTH_KPDK_MD5          | MUST NOT         | [UNSPECIFIED]         |
   | AUTH_AES_XCBC_96       | SHOULD           | [RFC3566][RFC7296]    |
   |                        |                  | [IoT]                 |
   | AUTH_AES_128_GMAC      | MAY              | [RFC4543]             |
   | AUTH_AES_256_GMAC      | MAY              | [RFC4543]             |
   | AUTH_HMAC_SHA2_256_128 | MUST             | [RFC4868]             |
   | AUTH_HMAC_SHA2_512_256 | SHOULD           | [RFC4868]             |

         [IoT] - This requirement is for interoperability with IoT

   AUTH_NONE has been downgraded from MAY in RFC7321 to MUST NOT.  The
   only reason NULL is acceptable is when authenticated encryption
   algorithms are selected from Section 3.  In all other case, NULL MUST
   NOT be selected.  As ESP and AH provides both authentication, one may
   be tempted to combine these protocol to provide authentication.  As
   mentioned by RFC7321, it is NOT RECOMMENDED to use ESP with NULL
   authentication - with non authenticated encryption - in conjunction
   with AH; some configurations of this combination of services have
   been shown to be insecure [PD10].  In addition, NULL authentication
   cannot be combined with ESP NULL encryption.

   AUTH_HMAC_MD5_96 and AUTH_KPDK_MD5 were not mentioned in RFC7321.  As
   MD5 is known to be vulnerable to collisions, these algorithms MUST
   NOT be used.

   AUTH_HMAC_SHA1_96 has been downgraded from MUST in RFC7321 to MUST-
   as there is an industry-wide trend to deprecate its usage.

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   AUTH_DES_MAC was not mentioned in RFC7321.  As DES is known to be
   vulnerable, it MUST NOT be used.

   AUTH_AES_XCBC_96 is only recommended in the scope of IoT, as Internet
   of Things deployments tend to prefer AES based HMAC functions in
   order to avoid implementing SHA2.  For the wide VPN deployment, as it
   has not been widely adopted, it has been downgraded from SHOULD to

   AUTH_AES_128_GMAC status has been downgraded from SHOULD+ to MAY.
   Along with AUTH_AES_192_GMAC and AUTH_AES_256_GMAC, these algorithms
   should only be used for AH not for ESP.  If using ENCR_NULL,
   AUTH_HMAC_SHA2_256_128 is recommended for integrity.  If using GMAC
   without authentication, ENCR_NULL_AUTH_AES_GMAC is recommended.
   Therefore, these ciphers are kept at MAY.

   AUTH_HMAC_SHA2_256_128 was not mentioned in RFC7321, as no SHA2 based
   authentication was mentioned.  AUTH_HMAC_SHA2_256_128 MUST be
   implemented in order to replace AUTH_HMAC_SHA1_96.  Note that due to
   a long standing common implementation bug of this algorithm that
   truncates the hash at 96-bits instead of 128-bits, it is recommended
   that implementations prefer AUTH_HMAC_SHA2_512_256 over
   AUTH_HMAC_SHA2_256_128 if they implement AUTH_HMAC_SHA2_512_256.

   AUTH_HMAC_SHA2_512_256 SHOULD be implemented as a future replacement
   of AUTH_HMAC_SHA2_256_128 or when stronger security is required.
   This value has been preferred to AUTH_HMAC_SHA2_384, as the
   additional overhead of AUTH_HMAC_SHA2_512 is negligible.

5.  ESP and AH Compression Algorithms

                | Name           | Status   | Comment     |
                | IPCOMP_OUI     | MUST NOT | UNSPECIFIED |
                | IPCOMP_DEFLATE | MAY      | [RFC2393]   |
                | IPCOMP_LZS     | MAY      | [RFC2395]   |
                | IPCOMP_LZJH    | MAY      | [RFC3051]   |

         [IoT] - This requirement is for interoperability with IoT

   Compression was not mentioned in RFC7321.  As it is not widely
   deployed, it remains optional and at the MAY-level.

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6.  Summary of Changes from RFC 7321

   The following table summarizes the changes from RFC 7321.


            | Algorithm         | RFC 7321 |     RFC XXXX    |
            | ENCR_AES_GCM_16   | SHOULD+  |       MUST      |
            | ENCR_AES_CCM_8    |   MAY    |      SHOULD     |
            | ENCR_AES_CTR      |   MAY    |       (*)       |
            | ENCR_3DES         |   MAY    |    SHOULD NOT   |
            | AUTH_HMAC_SHA1_96 |   MUST   |      MUST-      |
            | AUTH_AES_128_GMAC | SHOULD+  |       MAY       |
            | AUTH_NONE         |   MAY    | MUST / MUST NOT |

     (*) This algorithm is not mentioned in the above sections, so it
                             defaults to MAY.

7.  Acknowledgements

   Some of the wording in this document was adapted from [RFC7321], the
   document that this one obsoletes, which was written by D.  McGrew and
   P.  Hoffman.

8.  IANA Considerations

   This document has no IANA actions.

9.  Security Considerations

   The security of a system that uses cryptography depends on both the
   strength of the cryptographic algorithms chosen and the strength of
   the keys used with those algorithms.  The security also depends on
   the engineering and administration of the protocol used by the system
   to ensure that there are no non-cryptographic ways to bypass the
   security of the overall system.

   This document concerns itself with the selection of cryptographic
   algorithms for the use of ESP and AH, specifically with the selection
   of mandatory-to-implement algorithms.  The algorithms identified in
   this document as "MUST implement" or "SHOULD implement" are not known
   to be broken at the current time, and cryptographic research to date
   leads us to believe that they will likely remain secure into the
   foreseeable future.  However, this is not necessarily forever.

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   Therefore, we expect that revisions of that document will be issued
   from time to time to reflect the current best practice in this area.

10.  References

10.1.  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,

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <>.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              DOI 10.17487/RFC4302, December 2005,

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,

   [RFC7321]  McGrew, D. and P. Hoffman, "Cryptographic Algorithm
              Implementation Requirements and Usage Guidance for
              Encapsulating Security Payload (ESP) and Authentication
              Header (AH)", RFC 7321, DOI 10.17487/RFC7321, August 2014,

   [RFC7634]  Nir, Y., "ChaCha20, Poly1305, and Their Use in the
              Internet Key Exchange Protocol (IKE) and IPsec", RFC 7634,
              DOI 10.17487/RFC7634, August 2015,

10.2.  Informative References

   [PD10]     Paterson, K. and J. Degabriele, "On the (in)security of
              IPsec in MAC-then-encrypt configurations (ACM Conference
              on Computer and Communications Security, ACM CCS)", 2010.

   [RFC2393]  Shacham, A., Monsour, R., Pereira, R., and M. Thomas, "IP
              Payload Compression Protocol (IPComp)", RFC 2393,
              DOI 10.17487/RFC2393, December 1998,

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   [RFC2395]  Friend, R. and R. Monsour, "IP Payload Compression Using
              LZS", RFC 2395, DOI 10.17487/RFC2395, December 1998,

   [RFC2403]  Madson, C. and R. Glenn, "The Use of HMAC-MD5-96 within
              ESP and AH", RFC 2403, DOI 10.17487/RFC2403, November
              1998, <>.

   [RFC2404]  Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96 within
              ESP and AH", RFC 2404, DOI 10.17487/RFC2404, November
              1998, <>.

   [RFC2405]  Madson, C. and N. Doraswamy, "The ESP DES-CBC Cipher
              Algorithm With Explicit IV", RFC 2405,
              DOI 10.17487/RFC2405, November 1998,

   [RFC2410]  Glenn, R. and S. Kent, "The NULL Encryption Algorithm and
              Its Use With IPsec", RFC 2410, DOI 10.17487/RFC2410,
              November 1998, <>.

   [RFC2451]  Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher
              Algorithms", RFC 2451, DOI 10.17487/RFC2451, November
              1998, <>.

   [RFC3051]  Heath, J. and J. Border, "IP Payload Compression Using
              ITU-T V.44 Packet Method", RFC 3051, DOI 10.17487/RFC3051,
              January 2001, <>.

   [RFC3566]  Frankel, S. and H. Herbert, "The AES-XCBC-MAC-96 Algorithm
              and Its Use With IPsec", RFC 3566, DOI 10.17487/RFC3566,
              September 2003, <>.

   [RFC3602]  Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC Cipher
              Algorithm and Its Use with IPsec", RFC 3602,
              DOI 10.17487/RFC3602, September 2003,

   [RFC4106]  Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
              (GCM) in IPsec Encapsulating Security Payload (ESP)",
              RFC 4106, DOI 10.17487/RFC4106, June 2005,

   [RFC4309]  Housley, R., "Using Advanced Encryption Standard (AES) CCM
              Mode with IPsec Encapsulating Security Payload (ESP)",
              RFC 4309, DOI 10.17487/RFC4309, December 2005,

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   [RFC4543]  McGrew, D. and J. Viega, "The Use of Galois Message
              Authentication Code (GMAC) in IPsec ESP and AH", RFC 4543,
              DOI 10.17487/RFC4543, May 2006,

   [RFC4835]  Manral, V., "Cryptographic Algorithm Implementation
              Requirements for Encapsulating Security Payload (ESP) and
              Authentication Header (AH)", RFC 4835,
              DOI 10.17487/RFC4835, April 2007,

   [RFC4868]  Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA-
              384, and HMAC-SHA-512 with IPsec", RFC 4868,
              DOI 10.17487/RFC4868, May 2007,

   [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, <>.

Authors' Addresses

   Daniel Migault
   8400 boulevard Decarie
   Montreal, QC   H4P 2N2

   Phone: +1 514-452-2160

   John Mattsson
   Ericsson AB
   SE-164 80 Stockholm


   Paul Wouters
   Red Hat


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   Yoav Nir
   Check Point Software Technologies Ltd.
   5 Hasolelim st.
   Tel Aviv  6789735


   Tero Kivinen
   INSIDE Secure
   Eerikinkatu 28
   HELSINKI  FI-00180


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