Password interception in a SSL/TLS channel

Abstract

Simple password authentication is often used e.g. from an email software application to a remote IMAP server. This is frequently done in a protected peer-to-peer tunnel, e.g. by SSL/TLS. At Eurocrypt'02, Vaudenay presented vulnerabilities in padding schemes used for block ciphers in CBC mode. He used a side channel, namely error information in the padding verification. This attack was not possible against SSL/TLS due to both unavailability of the side channel (errors are encrypted) and premature abortion of the session in case of errors. In this paper we extend the attack and optimize it. We show it is actually applicable against latest and most popular implementations of SSL/TLS (at the time this paper was written) for password interception. We demonstrate that a password for an IMAP account can be intercepted when the attacker is not too far from the server in less than an hour in a typical setting. We conclude that these versions of the SSL/TLS implementations are not secure when used with block ciphers in CBC mode and propose ways to strengthen them. We also propose to update the standard protocol. © International Association for Cryptologic Research 2003.