Internet DRAFT - draft-zauner-tls-aes-ocb
draft-zauner-tls-aes-ocb
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.
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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
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to this document. Code Components extracted from this document must
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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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