A CHALLENGING BUT FEASIBLE BLOCKWISE-ADAPTIVE CHOSEN-PLAINTEXT ATTACK ON SSL

Gregory V. Bard

2006

Abstract

This paper introduces a chosen-plaintext vulnerability in the Secure Sockets Layer (SSL) and Trasport Layer Security (TLS) protocols which enables recovery of low entropy strings such as can be guessed from a likely set of 2–1000 options. SSL and TLS are widely used for securing communication over the Internet. When utilizing block ciphers for encryption, the SSL and TLS standards mandate the use of the cipher block chaining (CBC) mode of encryption which requires an initialization vector (IV) in order to encrypt. Although the first IV used by SSL is a (pseudo)random string which is generated and shared during the initial handshake phase, subsequent IVs used by SSL are chosen in a deterministic, predictable pattern; in particular, the IV of a message is taken to be the final ciphertext block of the immediately-preceding message, and is therefore known to the adversary. The one-channel nature of web proxies, anonymizers or Virtual Private Networks (VPNs), results in all Internet traffic from one machine traveling over the same SSL channel. We show this provides a feasible “point of entry” for this attack. Moreover, we show that the location of target data among block boundaries can have a profound impact on the number of guesses required to recover that data, especially in the low-entropy case. The attack in this paper is an application of the blockwise-adaptive chosen-plaintext attack paradigm, and is the only feasible attack to use this paradigm with a reasonable probability of success. The attack will work for all versions of SSL, and TLS version 1.0. This vulnerability and others are closed in TLS 1.1 (which is still in draft status) and OpenSSL after 0.9.6d. It is hoped this paper will encourage the deprecation of SSL and speed the adoption of OpenSSL or TLS 1.1/1.2 when they are finially released.

Paper Citation

in Harvard Style

V. Bard G. (2006). A CHALLENGING BUT FEASIBLE BLOCKWISE-ADAPTIVE CHOSEN-PLAINTEXT ATTACK ON SSL . In Proceedings of the International Conference on Security and Cryptography - Volume 1: SECRYPT, (ICETE 2006) ISBN 978-972-8865-63-4, pages 99-109. DOI: 10.5220/0002104100990109

in Bibtex Style

@conference{secrypt06,
author={Gregory V. Bard},
title={A CHALLENGING BUT FEASIBLE BLOCKWISE-ADAPTIVE CHOSEN-PLAINTEXT ATTACK ON SSL},
booktitle={Proceedings of the International Conference on Security and Cryptography - Volume 1: SECRYPT, (ICETE 2006)},
year={2006},
pages={99-109},
publisher={SciTePress},
organization={INSTICC},
doi={10.5220/0002104100990109},
isbn={978-972-8865-63-4},
}

in EndNote Style

TY - CONF
JO - Proceedings of the International Conference on Security and Cryptography - Volume 1: SECRYPT, (ICETE 2006)
TI - A CHALLENGING BUT FEASIBLE BLOCKWISE-ADAPTIVE CHOSEN-PLAINTEXT ATTACK ON SSL
SN - 978-972-8865-63-4
AU - V. Bard G.
PY - 2006
SP - 99
EP - 109
DO - 10.5220/0002104100990109