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In this paper, we examine the resistance of the popular hash function SHA-1 and its predecessor SHA-0 against dedicated preimage attacks. In order to assess the security margin of these hash functions against these attacks, two new cryptanalytic techniques are developed: Reversing the inversion problem: the idea is to start with an impossible expanded message that would lead to the required digest, and then to correct this message until it becomes valid without destroying the preimage property. P 3 graphs : an algorithm based on the theory of random graphs that allows the conversion of preimage attacks on the compression function to attacks on the hash function with less effort than traditional meet-in-the-middle approaches. Combining these techniques, we obtain preimage-style shortcuts attacks for up to 45 steps of SHA-1, and up to 50 steps of SHA-0 (out of 80). [ABSTRACT FROM AUTHOR]

In this article, we analyze the security of the GOST hash function. The GOST hash function, defined in the Russian standard GOST 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 iterative structure, a checksum computed over all input message blocks. This checksum is then part of the final hash value computation. As a result of our security analysis of the GOST hash function, we present the first collision attack with a complexity of about 2105 evaluations of the compression function. Furthermore, we are able to significantly improve upon the results of Mendel et al. with respect to preimage and second preimage attacks. Our improved attacks have a complexity of about 2192 evaluations of the compression function. [ABSTRACT FROM AUTHOR]