TLS Working Group A. Zauner
Internet-Draft Independent
Intended status: Standards Track June 01, 2015
Expires: December 3, 2015
AES-OCB (Offset Codebook Mode) Ciphersuites for Transport Layer Security
(TLS)
draft-zauner-tls-aes-ocb-03
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 past IPR claims by various parties.
Status of This Memo
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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 Propery Rights Issues . . . . . . . . . . . . . 5
6.1. IPR Claims . . . . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8.1. (Perfect) Forward Secrecy . . . . . . . . . . . . . . . . 5
8.2. Static RSA Key-Transport . . . . . . . . . . . . . . . . 6
8.3. Nonce reuse . . . . . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . 6
10.2. Informative References . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
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].
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.
The nonce input to the AEAD is described above using the TLS
presentation language. All values are represented in big-endian form
when constructing the AEAD input.
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The sequence number of a message is always known to the receiver
through other means (either implicit protocol state or a per-message
header in the case of DTLS), so the nonce construction used does not
require any extra per-message information. Thus the record_iv_length
is zero (0) for all ciphersuites defined in this document.
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].
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 Propery Rights Issues
Historically OCB Mode has seen difficulty with deployment and
standardization because of pending patents and intellectual rights
claims on OCB itself. In preparation of this document all interested
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. 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
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.
8.1. (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.
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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.
9. Acknowledgements
This document borrows heavily from [RFC5288] and [RFC6655].
The author would like to thank Martin Thompson 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 and the
TLS Working Group in general for feedback and discussion on this
document.
10. References
10.1. 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.
10.2. Informative References
[AES] National Institute of Standards and Technology,
"Specification for the Advanced Encryption Standard
(AES)", NIST FIPS 197, November 2001.
[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 '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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