A (Second) Preimage Attack on the GOST Hash Function

In this article, we analyze the security of the GOST hash function with respect to (second) preimage resistance. The GOST hash function, defined in the Russian standard GOST-R 34.11-94, is an iterated hash function producing a 256-bit hash value. As opposed to most commonly used hash functions such as MD5 and SHA-1, the GOST hash function defines, in addition to the common iterated structure, a checksum computed over all input message blocks. This checksum is then part of the final hash value computation. For this hash function, we show how to construct second preimages and preimages with a complexity of about 2 compression function evaluations and a memory requirement of about 2 bytes. First, we show how to construct a pseudo-preimage for the compression function of GOST based on its structural properties. Second, this pseudopreimage attack on the compression function is extended to a (second) preimage attack on the GOST hash function. The extension is possible by combining a multicollision attack and a meet-in-the-middle attack on the checksum.