Advances in Cryptology — EUROCRYPT 2002

Volume 2332 of the series Lecture Notes in Computer Science pp 534-545


Security Flaws Induced by CBC Padding — Applications to SSL, IPSEC, WTLS...

  • Serge VaudenayAffiliated withSwiss Federal Institute of Technology (EPFL)


In many standards, e.g. SSL/TLS, IPSEC, WTLS, messages are first pre-formatted, then encrypted in CBC mode with a block cipher. Decryption needs to check if the format is valid. Validity of the format is easily leaked from communication protocols in a chosen ciphertext attack since the receiver usually sends an acknowledgment or an error message. This is a side channel.

In this paper we show various ways to perform an efficient side channel attack. We discuss potential applications, extensions to other padding schemes and various ways to fix the problem.