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IPSECME                                                  D. Migault, Ed.
Internet-Draft                                                  Ericsson
Intended status: Standards Track                        T. Guggemos, Ed.
Expires: December 11, 2016                                    LMU Munich
                                                                  Y. Nir
                                                             Check Point
                                                            June 9, 2016


             Implicit IV for Counter-based Ciphers in IPsec
                 draft-mglt-ipsecme-implicit-iv-00.txt

Abstract

   IPsec ESP sends an initialization vector (IV) or nonce in each
   packet, adding 8 or 16 octets.  Some algorithms such as AES-GCM, AES-
   CCM, AES-CTR and ChaCha20-Poly1305 require a unique nonce but do not
   require an unpredictable nonce.  When using such algorithms the
   packet counter value can be used to generate a nonce, saving 8 octets
   per packet.  This document describes how to do this.

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 December 11, 2016.

Copyright Notice

   Copyright (c) 2016 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



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   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.  Requirements notation . . . . . . . . . . . . . . . . . . . .   2
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Implicit IV . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  Implicit IV Agreement . . . . . . . . . . . . . . . . . . . .   4
   6.  Initiator Behavior  . . . . . . . . . . . . . . . . . . . . .   5
   7.  Responder Behavior  . . . . . . . . . . . . . . . . . . . . .   5
   8.  Security Consideration  . . . . . . . . . . . . . . . . . . .   5
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Appendix A.  Document Change Log  . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Requirements notation

   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 [RFC2119].

2.  Introduction

   Counter-based AES modes of operation such as AES-CTR ([RFC3686]),
   AES-CCM ([RFC4309]), and AES-GCM ([RFC4104]) require the
   specification of an nonce for each ESP packet.  The same applies for
   ChaCha20-Poly1305 ([RFC7634].  Currently this nonce is sent in each
   ESP packet ([RFC4303]).  This practice is designated in this document
   as "explicit nonce".

   In some context, such as IoT, it may be preferable to avoid carrying
   the extra bytes associated to the IV and instead compute it locally
   on each peer.  The local generation of the nonce is designated in
   this document as "implicit IV".

   The size of this nonce depends on the specific algorithm, but all of
   the algorithms mentioned above take an 8-octet nonce.

   This document defines how to compute the nonce locally when it is
   implicit.  It also specifies how to negotiate this behavior within
   the Internet Key Exchange version 2 (IKEv2 - [RFC7296]).





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   This document limits its scope to the algorithms mentioned above.
   Other algorithms with similar properties may later be defined to use
   this extension.

   This document does not consider AES-CBC ([RFC3602])as AES-CBC
   requires the IV to be unpredictable.  Deriving it directly from the
   packet counter as described below is insecure.

3.  Terminology

   o  IoT: Internet of Things

   o  IV: Initialization Vector.  Although security requirements vary,
      the common usage of this term implies that the value is
      unpredictable.

   o  Nonce: a fixed-size octet string used only once.  This is similar
      to IV, except that in common usage there is no implication of non-
      predictability.

4.  Implicit IV

   With the algorithms listed in Section 2, the 8 byte nonce MUST NOT
   repeat.  The binding between a ESP packet and its nonce is provided
   using the Sequence Number or the Extended Sequence Number.  Figure 1
   and Figure 2 represent the IV with a regular 4-byte Sequence Number
   and with an 8-byte Extended Sequence Number respectively.

   0                   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              Zero                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Sequence Number                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 1: Implicit IV with a 4 byte Sequence Number

   o  Sequence Number: the 4 byte Sequence Number carried in the ESP
      packet.

   o  Zero: a 4 byte array with all bits set to zero.









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   0                   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Extended                              |
   |                      Sequence Number                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Figure 2: Implicit IV with an 8 byte Extended Sequence Number

   o  Extended Sequence Number: the 8 byte Extended Sequence Number of
      the Security Association.  The 4 byte low order bytes are carried
      in the ESP packet.

5.  Implicit IV Agreement

   NOTE: THIS SECTION SHOWS SEVERAL WAYS TO DO THE SAME THING.
   OBVIOUSLY THIS DOCUMENT WILL NOT BE PUBLISHED LIKE THAT.  WE EXPECT
   WG DISCUSSION TO PARE THIS DOWN TO JUST ONE WAY OF NEGOTIATING THE
   USE OF IMPLICIT IV (IIV).

   Negotiation of the use of implicit IV can be done in 3 different
   ways:

   o  An IMPLICIT IV Transform Type.  A proposal that contains this
      transform type requires (if accepted) that IPsec use the implicit
      IV and not include an explicit IV in the packets.  To facilitate
      backward compatibility with non-supporting implementations the
      Initiator SHOULD add another proposal that does not include this
      transform type as well as cryptographic suite the Initiator does
      not support the implicit IV.

   o  An IMPLICIT IV Transform ID.  This doubles the number of ENCR
      transform IDs by creating an ENCR_AES_CCM_16_IIV for each
      ENCR_AES_CCM_16.

   o  An IMPLICIT IV Transform Attribute, which would be associated to a
      Transform Type ID, specifying the use of an implicit IV. marks a
      particular ENCR transform as using implicit IVs.  To facilitate
      backward compatibility with non-supporting implementations the
      Initiator SHOULD add another ENCR transform for each algorithm so
      marked.  In other words, for each ENCR_AES_CCM_16 with
      keylength=256 and IIV=1, there will need to be an ENCR_AES_CCM_16
      with keylength=256 and no IIV attribute.








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6.  Initiator Behavior

   An initiator supporting this feature SHOULD propose implicit IV for
   all relevant algorithms.  To facilitate backward compatibility with
   non-supporting peers the initiator SHOULD also include those same
   algorithms without IIV.  Depending on the method chosen in Section 5
   this may require extra proposals or extra transforms.

7.  Responder Behavior

   An responder supporting this feature SHOULD accept implicit IV for
   all relevant algorithms.  It MUST NOT accept implicit IV for
   algorithms not specified to be safe for IIV in this or subsequent
   documents.  It SHOULD accept non-IIV proposals for all algorithms if
   IIV proposals were not included.

   The rules of SA payload processing ensure that the responder will
   never send an SA payload containing the IIV indicator to an initiator
   that does not support IIV.

8.  Security Consideration

   Nonce generation for these algorithms has not been explicitly
   defined.  It has been left to the implementation as long as certain
   security requirements are met.  This document provides an explicit
   and normative way to generate IVs.  The mechanism described in this
   document meets the IV security requirements of all relevant
   algorithms.

9.  IANA Considerations

   TBD: The content of this section depends on our decisions about
   Section 5.

   The following Transform Type is requested: IMPLICIT_IV Transform Type

   Values associated to IMPLICIT Transform Type are:

      False: 0 ===> Do we really need a negative value???

      True: 1

10.  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,
              <http://www.rfc-editor.org/info/rfc2119>.



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   [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,
              <http://www.rfc-editor.org/info/rfc3602>.

   [RFC3686]  Housley, R., "Using Advanced Encryption Standard (AES)
              Counter Mode With IPsec Encapsulating Security Payload
              (ESP)", RFC 3686, DOI 10.17487/RFC3686, January 2004,
              <http://www.rfc-editor.org/info/rfc3686>.

   [RFC4104]  Pana, M., Ed., Reyes, A., Barba, A., Moron, D., and M.
              Brunner, "Policy Core Extension Lightweight Directory
              Access Protocol Schema (PCELS)", RFC 4104,
              DOI 10.17487/RFC4104, June 2005,
              <http://www.rfc-editor.org/info/rfc4104>.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,
              <http://www.rfc-editor.org/info/rfc4303>.

   [RFC4309]  Housley, R., "Using Advanced Encryption Standard (AES) CCM
              Mode with IPsec Encapsulating Security Payload (ESP)",
              RFC 4309, DOI 10.17487/RFC4309, December 2005,
              <http://www.rfc-editor.org/info/rfc4309>.

   [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, <http://www.rfc-editor.org/info/rfc7296>.

   [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,
              <http://www.rfc-editor.org/info/rfc7634>.

Appendix A.  Document Change Log

Authors' Addresses

   Daniel Migault (editor)
   Ericsson
   8400 boulevard Decarie
   Montreal, QC H4P 2N2
   Canada

   Email: daniel.migault@ericsson.com





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   Tobias Guggemos (editor)
   LMU Munich
   Am Osteroesch 9
   87637 Seeg, Bavaria
   Germany

   Email: tobias.guggemos@gmail.com


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

   Email: ynir.ietf@gmail.com



































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