lambda: resilient.systems

azet@azet.org

General TLS Working Group Internet-Draft 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.

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 for 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 , 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 and the AES-OCB-based AEAD algorithms defined in and . 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 . 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.

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 .

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 . The following forward-secret ciphersuites are defined:

These ciphersuites make use of the AEAD capability in TLS 1.2 . Because this document makes use of an AEAD construct, use of HMAC truncation in TLS (as specified in ) 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: The 64-bit record sequence number is serialized as an 8-byte, big-endian value and padded on the left with four 0x00 bytes. 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. 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 , 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 .

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

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

These ciphersuites make use of the authenticated encryption with associated data (AEAD) defined in TLS 1.2 . 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.

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 .

The following parties have made IPR claims in the past: US Patent No. 7,093,126 (Issued Aug 15, 2006) - Filed Apr 14, 2000. Inventor Name: Charanjit S. Jutla, Assignee: IBM US Patent No. 6,963,976 (Issued Nov 8, 2005) - Filed Nov 3, 2000. Inventor Name: Charanjit S. Jutla, Assignee: IBM US Patent No. 7,046,802 (Issued May 16, 2006) - Filed 30 Jul 2001. Inventor Name: Phillip W. Rogaway, Assignee: Rogaway Phillip W US Patent No. 7,200,227 (Issued Apr 3, 2007) - Filed 18 Jul 2005. Inventor Name: Phillip Rogaway, Assignee: Phillip Rogaway 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.

IANA is requested to assign the values for the ciphersuites defined in and 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.

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

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

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

AES-OCB security requires that the “nonce” (number used once) is never reused. The IV construction in 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.

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 .

This document borrows heavily from , 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.

This document specifies OCB, a shared-key blockcipher-based encryption scheme that provides confidentiality and authenticity for plaintexts and authenticity for associated data. This document is a product of the Crypto Forum Research Group (CFRG). This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol. The TLS protocol provides communications security over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. [STANDARDS-TRACK] This document provides specifications for existing TLS extensions. It is a companion document for RFC 5246, "The Transport Layer Security (TLS) Protocol Version 1.2". The extensions specified are server_name, max_fragment_length, client_certificate_url, trusted_ca_keys, truncated_hmac, and status_request. [STANDARDS-TRACK] This document defines algorithms for Authenticated Encryption with Associated Data (AEAD), and defines a uniform interface and a registry for such algorithms. The interface and registry can be used as an application-independent set of cryptoalgorithm suites. This approach provides advantages in efficiency and security, and promotes the reuse of crypto implementations. [STANDARDS-TRACK] This document specifies three sets of new ciphersuites for the Transport Layer Security (TLS) protocol to support authentication based on pre-shared keys (PSKs). These pre-shared keys are symmetric keys, shared in advance among the communicating parties. The first set of ciphersuites uses only symmetric key operations for authentication. The second set uses a Diffie-Hellman exchange authenticated with a pre-shared key, and the third set combines public key authentication of the server with pre-shared key authentication of the client. [STANDARDS-TRACK] In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This memo describes the use of the Advanced Encryption Standard (AES) in Galois/Counter Mode (GCM) as a Transport Layer Security (TLS) authenticated encryption operation. GCM provides both confidentiality and data origin authentication, can be efficiently implemented in hardware for speeds of 10 gigabits per second and above, and is also well-suited to software implementations. This memo defines TLS cipher suites that use AES-GCM with RSA, DSA, and Diffie-Hellman-based key exchange mechanisms. [STANDARDS-TRACK] This document specifies version 1.2 of the Datagram Transport Layer Security (DTLS) protocol. The DTLS protocol provides communications privacy for datagram protocols. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. The DTLS protocol is based on the Transport Layer Security (TLS) protocol and provides equivalent security guarantees. Datagram semantics of the underlying transport are preserved by the DTLS protocol. This document updates DTLS 1.0 to work with TLS version 1.2. [STANDARDS-TRACK] This memo describes the use of the Advanced Encryption Standard (AES) in the Counter with Cipher Block Chaining - Message Authentication Code (CBC-MAC) Mode (CCM) of operation within Transport Layer Security (TLS) and Datagram TLS (DTLS) to provide confidentiality and data origin authentication. The AES-CCM algorithm is amenable to compact implementations, making it suitable for constrained environments. [STANDARDS-TRACK] National Institute of Standards and Technology