Collision and Second Preimage Attacks on the HTBC Hash Function

A common way to build hash functions is combining a secure block cipher with an appropriate chaining structure. When the block cipher used has strong security properties such as AES, the security of this kind of hash functions mainly depends on the security of the certain chaining structure. HTBC is a hash function design which uses a special triple-block-chaining structure to be combined with a secure block cipher. The triple-block-chaining structure used by the HTBC hash function is not secure. Based on the serious flaws of the chaining structure, using particular properties of related operations, the collisions of the HTBC hash function can be directly constructed, and the time complexity to find a single collision is only 1. For the messages with certain length, a second preimage can be constructed as well. When AES-256 is used as the block cipher, the maximum time complexity to launch a second preimage attack is 2\+{112}, which is lower than the brute force attack bound 2\+{128}. For the particular weak messages, the overall time needed to find a second preimage is only 1. If the message is randomly chosen, the average time complexity to launch a successful second preimage attack is 2\+{46.56}.