The Taub Faculty of Computer Science Events and Talks

Cryptographic hash functions take a message of arbitrary length and generate a short fingerprint. Their main use are for digital signatures, due to their collision resistance property, i.e., that it is hard to find two different messages that have the same fingerprint. In this talk we present novel cryptanalysis techniques that we developed to attack hash functions. These techniques improve the functionality of differential attacks against the collision resistance property of the hash functions. We will briefly present the "neutral-bits" technique that enables an attacker to generate many messages that partially conform to a characteristic, and the "multi-block" technique that instead of directly attacking a single block for a collision, creates a path of near-collisions that can be found much more efficiently, and end with a collision. A major part of the talk is dedicated to the introduction of our recent work on the "second-order differential" technique. Our techniques are generic and we confirmed them by constructing attacks on SHA-0 and SHA-1.