AES-OCB (Offset Codebook Mode) Ciphersuites for Transport Layer Security (TLS)
draft-zauner-tls-aes-ocb-00

TLS Working Group                                              A. Zauner
Internet-Draft                                               Independent
Intended status: Standards Track                        January 20, 2015
Expires: July 24, 2015

AES-OCB (Offset Codebook Mode) Ciphersuites for Transport Layer Security
                                 (TLS)
                      draft-zauner-tls-aes-ocb-00

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.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on July 24, 2015.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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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.  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.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
     7.1.  (Perfect) Forward Secrecy . . . . . . . . . . . . . . . .   5
     7.2.  RSA as key-exchange . . . . . . . . . . . . . . . . . . .   5
     7.3.  Nonce reuse . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

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.

   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].  Additional AEAD
   algorithms are defined, which use AES-OCB but which have shorter
   authentication tags, and therefore are more suitable for use across
   networks in which bandwidth is constrained and message sizes may be
   small.

   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

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   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].

   Use of HMAC truncation in TLS (as specified in [RFC6066]) has no
   effect on the ciphersuites defined in this document.

   The "nonce" input to the AEAD algorithm is exactly that of [RFC5288]:
   the "nonce" SHALL be 12 bytes long and is constructed as follows:

     struct {
        case client:
           uint32 client_write_IV;  // low order 32-bits
        case server:
           uint32 server_write_IV;  // low order 32-bits
        uint64 seq_num;
     } OCBNonce.

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

   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].

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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
   additional 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.  Because
   TLS has no way for the client to indicate that it supports TLS 1.2
   but not earlier, a non-compliant server might potentially negotiate
   TLS 1.1 or earlier and select one of the cipher suites in this
   document.  Clients MUST check the TLS version and generate a fatal
   "illegal_parameter" alert if they detect an incorrect version.

6.  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.

7.  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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7.1.  (Perfect) Forward Secrecy

   With the exception of two Pre-Shared-Key (PSK) ciphersuites, defined
   in Section 4, this document deals exclusively with ciphersuites that
   are inherently forward-secret.

7.2.  RSA as key-exchange

   No ciphersuite is defined in this document that makes use of RSA as
   key-exchange.

7.3.  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.

8.  Acknowledgements

   This document borrows heavily from [RFC5288] and [RFC6655].

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4279]  Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites
              for Transport Layer Security (TLS)", RFC 4279, December
              2005.

   [RFC5116]  McGrew, D., "An Interface and Algorithms for Authenticated
              Encryption", RFC 5116, January 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5288]  Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
              Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
              August 2008.

   [RFC6066]  Eastlake, D., "Transport Layer Security (TLS) Extensions:
              Extension Definitions", RFC 6066, January 2011.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

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   [RFC6655]  McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for
              Transport Layer Security (TLS)", RFC 6655, July 2012.

9.2.  Informative References

   [AES]      National Institute of Standards and Technology,
              "Specification for the Advanced Encryption Standard
              (AES)", NIST FIPS 197, November 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 '01), ACM Press, pp. 196-205,
              2001.

   [RFC7253]  Krovetz, T. and P. Rogaway, "The OCB Authenticated-
              Encryption Algorithm", RFC 7253, May 2014.

Author's Address

   Aaron Zauner
   Independent

   Email: azet@azet.org

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