Practical Padding Oracle Attacks

At Eurocrypt 2002, Vaudenay introduced a powerful side-channel attack, which is called padding oracle attack, against CBC-mode encryption with PKCS#5 padding (See [6]). If there is an oracle which on receipt of a ciphertext, decrypts it and then replies to the sender whether the padding is correct or not, Vaudenay shows how to use that oracle to e ciently decrypt data without knowing the encryption key. In this paper, we turn the padding oracle attack into a new set of practical web hacking techniques. We also introduce a new technique that allows attackers to use a padding oracle to encrypt messages of any length without knowing the secret key. Finally, we show how to use that technique to mount advanced padding oracle exploits against popular web development frameworks.