Data-Depend Hash Algorithm
Hash algorithm is the algorithm that computes a fixed size message digest from arbitrary size messages. After SHA-0 was published, some technologys that analyse and attack hash algorithm are developed. The major technologys is differential attack. Papers[Wy05, Dau05] has explain the attack. Differential attack is the best technique to attack hash function. To attack hash function, it need do the work as follow: 1. Constitute a feasible difference path that has good possibility. 2. Constitute the adequate conditions for the difference path. 3. Find some technique to raise the possibility of the difference path. From mentioned above description of differential attack, it is easy to know that constituting a feasible difference path is the hinge. If it can make it hard to constitute a feasible difference path, it will be hard to attack the hash function. In appenix 1, we know that the data-depend circular shift has good defence feature. And we find a message expension function that make any difference path will has at least eight data-depend circular shift difference [appenix 2]. This make it hard to constitute a feasible difference path. At the same time, we study some technologys[1,2] that used to attack hash algorithm, DDHA use some ways to resist these attack technologys.