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TLS Working Group                                              A. Zauner
Internet-Draft                                 lambda: resilient.systems
Intended status: Standards Track                          April 04, 2016
Expires: October 6, 2016


AES-OCB (Offset Codebook Mode) Ciphersuites for Transport Layer Security
                                 (TLS)
                      draft-zauner-tls-aes-ocb-04

Abstract

   This memo describes the use of the Advanced Encryption Standard (AES)
   in the Offset Codebook Mode (OCB) of operation within Transport Layer
   Security (TLS) and Datagram TLS (DTLS) to provide confidentiality and
   data origin authentication.  The AES-OCB algorithm is highly
   parallelizable, provable secure and can be efficiently implemented in
   software and hardware providing high performance.  Furthermore, use
   of AES-OCB in TLS is exempt from former IPR claims by various
   parties.

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
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   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 October 6, 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.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
   3.  Forward-secret AES-OCB Ciphersuites . . . . . . . . . . . . .   3
   4.  Pre-Shared-Key (PSK) AES-OCB Ciphersuites . . . . . . . . . .   4
   5.  Applicable TLS Versions . . . . . . . . . . . . . . . . . . .   4
   6.  Intellectual Property Rights  . . . . . . . . . . . . . . . .   5
     6.1.  Resolved IPR Claims . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
     8.1.  (Perfect) Forward Secrecy . . . . . . . . . . . . . . . .   6
     8.2.  Static RSA Key-transport  . . . . . . . . . . . . . . . .   6
     8.3.  Nonce reuse . . . . . . . . . . . . . . . . . . . . . . .   6
     8.4.  Data volume limit under a single key  . . . . . . . . . .   6
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     10.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   This document describes the use of the Advanced Encryption Standard
   (AES) in the Offset Codebook Mode (OCB) of operation within Transport
   Layer Security (TLS) and Datagram TLS (DTLS) to provide
   confidentiality and data origin authentication.  The AES-OCB
   algorithm is highly parallelizable, provable secure and can be
   efficiently implemented in software and hardware providing high
   performance.

   Furthermore OCB Mode [OCB] for AES [AES] provides a high performance,
   single-pass, constant-time AEAD alternative to existing and deployed
   block-cipher modes without the need for special platform specific
   instructions.

   Authenticated encryption, in addition to providing confidentiality
   for the plaintext that is encrypted, provides a way to check its
   integrity and authenticity.  Authenticated Encryption with Associated
   Data, or AEAD [RFC5116], adds the ability to check the integrity and
   authenticity of some associated data that is not encrypted.  This
   document utilizes the AEAD facility within TLS 1.2 [RFC5246] and the
   AES-OCB-based AEAD algorithms defined in [RFC5116] and [RFC7253].



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   The ciphersuites defined in this document use ECDHE, DHE or Pre-
   Shared-Key (PSK) as their key establishment mechanism; these
   ciphersuites can be used with DTLS [RFC6347].  Since the abiltiy to
   use AEAD ciphers was introduced in DTLS version 1.2, the ciphersuites
   defined in this document cannot be used with earlier versions of that
   protocol.

2.  Conventions Used in This Document

   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].

3.  Forward-secret AES-OCB Ciphersuites

   The ciphersuites defined in this document are based on the AES-OCB
   authenticated encryption with associated data (AEAD) algorithms
   AEAD_AES_128_OCB_TAGLEN96 and AEAD_AES_256_OCB_TAGLEN96 described in
   [RFC7253].  The following forward-secret ciphersuites are defined:

     CipherSuite TLS_DHE_RSA_WITH_AES_128_OCB = {TBD1, TBD1}
     CipherSuite TLS_DHE_RSA_WITH_AES_256_OCB = {TBD2, TBD2}
     CipherSuite TLS_ECDHE_RSA_WITH_AES_128_OCB = {TBD3, TBD3}
     CipherSuite TLS_ECDHE_RSA_WITH_AES_256_OCB = {TBD4, TBD4}
     CipherSuite TLS_ECDHE_ECDSA_WITH_AES_128_OCB = {TBD5, TBD5}
     CipherSuite TLS_ECDHE_ECDSA_WITH_AES_256_OCB = {TBD6, TBD6}

   These ciphersuites make use of the AEAD capability in TLS 1.2
   [RFC5246].

   Because this document makes use of an AEAD construct, use of HMAC
   truncation in TLS (as specified in [RFC6066]) has no effect on the
   ciphersuites defined herein.

   The "nonce" construction is identical to that of draft-ietf-tls-
   chacha20-poly1305-04:

   AES-OCB requires a 96-bit nonce, which is formed as follows:

   1.  The 64-bit record sequence number is serialized as an 8-byte,
       big-endian value and padded on the left with four 0x00 bytes.

   2.  The padded sequence number is XORed with the client_write_IV
       (when the client is sending) or server_write_IV (when the server
       is sending).

   In DTLS, the 64-bit seq_num is the 16-bit epoch concatenated with the
   48-bit seq_num.



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   This nonce construction is different from the one used with AES-GCM
   in TLS 1.2 but matches the scheme expected to be used in TLS 1.3.
   The nonce is constructed from the record sequence number and shared
   secret, both of which are known to the recipient.  The advantage is
   that no per-record, explicit nonce need be transmitted, which saves
   eight bytes per record and prevents implementations from mistakenly
   using a random nonce.  Thus, in the terms of [RFC5246],
   SecurityParameters.fixed_iv_length is twelve bytes and
   SecurityParameters.record_iv_length is zero bytes.

   These ciphersuites make use of the default TLS 1.2 Pseudorandom
   Function (PRF), which uses HMAC with the SHA-256 hash function.  The
   ECDSA-ECDHE, RSA-ECDHE and RSA-DHE key exchanges are performed as
   defined in [RFC5246].

4.  Pre-Shared-Key (PSK) AES-OCB Ciphersuites

   As in Section 3, these ciphersuites follow [RFC7253].  The PSK,
   ECDHE_PSK and DHE_PSK key exchanges are performed as specified in
   [RFC4279].  The following Pre-Shared-Key (PSK) ciphersuites are
   defined:

     CipherSuite TLS_PSK_WITH_AES_128_OCB = {TBD7, TBD7}
     CipherSuite TLS_PSK_WITH_AES_256_OCB = {TBD8, TBD8}
     CipherSuite TLS_DHE_PSK_WITH_AES_128_OCB = {TBD9, TBD9}
     CipherSuite TLS_DHE_PSK_WITH_AES_256_OCB = {TBD10, TBD10}
     CipherSuite TLS_ECDHE_PSK_WITH_AES_128_OCB = {TBD11, TBD11}
     CipherSuite TLS_ECDHE_PSK_WITH_AES_256_OCB = {TBD12, TBD12}

   The "nonce" input to the AEAD algorithm is identical to the one
   defined in Section 3.  These ciphersuites make use of the default TLS
   1.2 Pseudorandom Function (PRF), which uses HMAC with the SHA-256
   hash function.

5.  Applicable TLS Versions

   These ciphersuites make use of the authenticated encryption with
   associated data (AEAD) defined in TLS 1.2 [RFC5288].  Earlier
   versions of TLS do not have support for AEAD; for instance, the
   TLSCiphertext structure does not have the "aead" option in TLS 1.1.
   Consequently, these ciphersuites MUST NOT be negotiated in older
   versions of TLS.  Clients MUST NOT offer these cipher suites if they
   do not offer TLS 1.2 or later.  Servers which select an earlier
   version of TLS MUST NOT select one of these ciphersuites.  A client
   MUST treat the selection of these cipher suites in combination with a
   version of TLS that does not support AEAD (i.e., TLS 1.1 or earlier)
   as an error and generate a fatal 'illegal_parameter' TLS alert.




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6.  Intellectual Property Rights

   Historically Offset Codebook Mode has seen difficulty with
   implementation, deployment and standardization because of pending
   patents and intellectual rights claims on OCB itself.  In preparation
   of this document all involved parties have declared they will issue
   IPR statements exempting use of OCB Mode in TLS from these claims.
   Specifically - OCB Mode as described in this document for use in TLS
   - is based, and strongly influenced, by earlier work from Charanjit
   Jutla on [IAPM].

6.1.  Resolved IPR Claims

   The following parties have made IPR claims in the past:

   o  US Patent No. 7,093,126 (Issued Aug 15, 2006) - Filed Apr 14,
      2000.  Inventor Name: Charanjit S.  Jutla, Assignee: IBM

   o  US Patent No. 6,963,976 (Issued Nov 8, 2005) - Filed Nov 3, 2000.
      Inventor Name: Charanjit S.  Jutla, Assignee: IBM

   o  US Patent No. 7,046,802 (Issued May 16, 2006) - Filed 30 Jul 2001.
      Inventor Name: Phillip W.  Rogaway, Assignee: Rogaway Phillip W

   o  US Patent No. 7,200,227 (Issued Apr 3, 2007) - Filed 18 Jul 2005.
      Inventor Name: Phillip Rogaway, Assignee: Phillip Rogaway

   o  US Patent No. 7,949,129 (Issued May 24, 2011) - Filed 23 Mar 2007.
      Inventor Name: Phillip W.  Rogaway, Assignee: Rogaway Phillip W

   Use of technology described by these patents, when used with TLS, has
   been explicitly exempted from any previous claims by the original
   authors and patent holders.

7.  IANA Considerations

   IANA is requested to assign the values for the ciphersuites defined
   in Section 3 and Section 4 from the TLS and DTLS Ciphersuite
   registries.  IANA, please note that the DTLS-OK column should be
   marked as "Y" for each of these algorithms.

8.  Security Considerations

   The security considerations in [RFC5246] apply to this document as
   well.  The remainder of this section describes security
   considerations specific to the ciphersuites described in this
   document.




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8.1.  (Perfect) Forward Secrecy

   With the exception of two Pre-Shared-Key (PSK) ciphersuites intended
   for use in constrained environments and embedded devices (IoT),
   defined in Section 4, this document deals exclusively with
   ciphersuites that are inherently forward-secret.

8.2.  Static RSA Key-transport

   No ciphersuite is defined in this document that makes use of RSA as
   Key-Transport.

8.3.  Nonce reuse

   AES-OCB security requires that the "nonce" (number used once) is
   never reused.  The IV construction in Section 3 is designed to
   prevent nonce reuse.  Specifically, if there is any error in the
   nonce construction implementation, it will simply be non-
   interoperable with conforming implementations.

8.4.  Data volume limit under a single key

   There is a limitation on the total number of bytes that can be
   transmitted under one set of keys.  For the AES-OCB ciphersuites,
   implementations MUST NOT transmit more than 2^36 bytes encrypted
   under a single key: they MUST rekey or close the connection before
   2^36 bytes are reached.  These limitations are based on limitations
   introduced in the TLS 1.3 draft for AES-GCM, this document adheres to
   the same constraints.  A detailed analysis can be found in [AELIMIT].

9.  Acknowledgements

   This document borrows heavily from [RFC5288], [RFC6655] and draft-
   ietf-tls-chacha20-poly1305-04.

   The author would like to thank Martin Thomson for his suggested
   change on the client negotiation paragraph, Nikos Mavrogiannopoulos
   and Peter Gutmann for the discussion on PSK ciphersuites, Jack Lloyd
   for content on the clarification of the TLS Record IV length, Samuel
   Neves for suggesting the data-limitation paragraph from the TLS 1.3
   draft and the TLS Working Group in general for feedback and
   discussion on this document.

10.  References







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

   [RFC4279]  Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
              Ciphersuites for Transport Layer Security (TLS)", RFC
              4279, DOI 10.17487/RFC4279, December 2005,
              <http://www.rfc-editor.org/info/rfc4279>.

   [RFC5116]  McGrew, D., "An Interface and Algorithms for Authenticated
              Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
              <http://www.rfc-editor.org/info/rfc5116>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/
              RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

   [RFC5288]  Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
              Counter Mode (GCM) Cipher Suites for TLS", RFC 5288, DOI
              10.17487/RFC5288, August 2008,
              <http://www.rfc-editor.org/info/rfc5288>.

   [RFC6066]  Eastlake 3rd, D., "Transport Layer Security (TLS)
              Extensions: Extension Definitions", RFC 6066, DOI
              10.17487/RFC6066, January 2011,
              <http://www.rfc-editor.org/info/rfc6066>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <http://www.rfc-editor.org/info/rfc6347>.

   [RFC7253]  Krovetz, T. and P. Rogaway, "The OCB Authenticated-
              Encryption Algorithm", RFC 7253, DOI 10.17487/RFC7253, May
              2014, <http://www.rfc-editor.org/info/rfc7253>.

10.2.  Informative References

   [AELIMIT]  Luykx, A. and K. Paterson, "Limits on Authenticated
              Encryption Use in TLS", date 2016-03-08, n.d..

   [AES]      National Institute of Standards and Technology,
              "Specification for the Advanced Encryption Standard
              (AES)", NIST FIPS 197, November 2001.




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   [IAPM]     Jutla, C., "Encryption Modes with Almost Free Message
              Integrity", EUROCRYPT01 Proc. Eurocrypt 2001, pp. 529-544,
              2001.

   [OCB]      Rogaway, P., Bellare, M., and J. Black, "OCB: A Block-
              Cipher Mode of Operation for Efficient Authenticated
              Encryption", CCS01 ACM Conference on Computer and
              Communications Security (CCS 2001), ACM Press, pp.
              196-205, date 2001, n.d..

   [RFC6655]  McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for
              Transport Layer Security (TLS)", RFC 6655, DOI 10.17487/
              RFC6655, July 2012,
              <http://www.rfc-editor.org/info/rfc6655>.

Author's Address

   Aaron Zauner
   lambda: resilient.systems

   Email: azet@azet.org






























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