Cryptology ePrint Archive: Report 2015/652

Modelling ciphersuite and version negotiation in the TLS protocol

Benjamin Dowling and Douglas Stebila

Abstract: Real-world cryptographic protocols such as the widely used Transport Layer Security (TLS) protocol support many different combinations of cryptographic algorithms (called ciphersuites) and simultaneously support different versions. Recent advances in provable security have shown that most modern TLS ciphersuites are secure authenticated and confidential channel establishment (ACCE) protocols, but these analyses generally focus on single ciphersuites in isolation. In this paper we extend the ACCE model to cover protocols with many different sub-protocols, capturing both multiple ciphersuites and multiple versions, and define a security notion for secure negotiation of the optimal sub-protocol. We give a generic theorem that shows how secure negotiation follows, with some additional conditions, from the authentication property of secure ACCE protocols. Using this framework, we analyse the security of ciphersuite and three variants of version negotiation in TLS, including a recently proposed mechanism for detecting fallback attacks.

Category / Keywords: cryptographic protocols / Transport Layer Security (TLS); ciphersuite negotiation; version negotiation; downgrade attacks

Original Publication (with major differences): 20th Australasian Conference on Information Security and Privacy (ACISP 2015)

Date: received 30 Jun 2015

Contact author: b1 dowling at qut edu au

Available format(s): PDF | BibTeX Citation

Note: A preliminary version of this paper appears in the proceedings of ACISP 2015. This is the full version.

Version: 20150701:011314 (All versions of this report)

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