Improved Characteristics for Differential Cryptanalysis of Hash Functions Based on Block Ciphers

. In this paper we present an improvement of the differential attack on hash functions based on block ciphers. By using the specific properties of the collision attack on hash functions, we can greatly reduce the work factor to find a pair that follows the characteristic. We propose a new family of differential characteristics that is especially useful in combination with our improvement. Attacks on a hash function based on DES variants reduced to 12, 13 or 15 rounds become faster than brute force collision attacks. 1 Introduction Hash functions are functions that compress inputs of arbitrary length to an output of fixed length n. For cryptographic applications, we impose the following properties: 1. one-wayness: given Y , it is difficult to find an X such that h(X) = Y , and given X and h(X), it is difficult to find X 0 6= X such that h(X 0 ) = h(X) 2. collision resistance: it is difficult to find X and X 0 6= X such that h(X) = h(X 0 ). Most hash functions are iterated has..