Cryptology ePrint Archive: Report 2012/630

On the Security of TLS Renegotiation

Florian Giesen and Florian Kohlar and Douglas Stebila

Abstract: The Transport Layer Security (TLS) protocol is the most widely used security protocol on the Internet. It supports negotiation of a wide variety of cryptographic primitives through different cipher suites, various modes of client authentication, and additional features such as renegotiation. Despite its widespread use, only recently has the full TLS protocol been proven secure, and only then a single ciphersuite family (TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA) with no additional features. These additional features have been the cause of practical attacks on TLS. In 2009, Ray and Dispensa demonstrated how TLS renegotiation allows an attacker to splice together its own session with that of a victim, resulting in a man-in-the-middle attack on TLS-reliant applications such as HTTP. TLS was subsequently patched with two defence mechanisms for protection against this attack.

We present the first formal treatment of renegotiation in secure channel establishment protocols. We add optional renegotiation to the authenticated and confidential channel establishment model of Jager et al., an adaptation of the Bellare--Rogaway authenticated key exchange model. We describe the attack of Ray and Dispensa on TLS within our model. We show generically that the proposed fixes for TLS offer good protection against renegotiation attacks, and give a simple new countermeasure that provides renegotiation security for TLS even in the face of stronger adversaries.

Category / Keywords: cryptographic protocols / Transport Layer Security (TLS), renegotiation, security models, key exchange

Date: received 5 Nov 2012, last revised 1 Mar 2013

Contact author: stebila at qut edu au

Available format(s): PDF | BibTeX Citation

Note: Revised with generic result.

Version: 20130302:055856 (All versions of this report)

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