Collision Attacks on Variant of OCB Mode and Its Series

摘要

Three versions of OCB appeared in the literature: OCB1, OCB2 and OCB3. Ferguson pointed out that OCB1 could not resist against collision attacks, which was improved by Mathiassen. Zhang, Xing and Yang made the first attempt to improve OCB1 against this prevailing attack in blockcipher modes of operation, and proposed a new authenticated encryption mode OCB-ZXY, using offset dependent plaintext block transformation (ODPBT) technique. Our research shows that: 1) OCB-ZXY still cannot resist against collision attacks. 2) OCB2 and OCB3 also suffer from collision attacks, even more severely than OCB1. 3) Even if OCB2 and OCB3 adopt the ODPBT technique, collision attacks still exist.