3 research outputs found
Improved Preimage Attack on One-block MD4
We propose an improved preimage attack on one-block MD4 with the
time complexity MD4 compression function operations, as
compared to in \cite{AokiS-sac08}. We research the attack
procedure in \cite{AokiS-sac08} and formulate the complexity for
computing a preimage attack on one-block MD4. We attain the result
mainly through the following two aspects with the help of the
complexity formula. First, we continue to compute two more steps
backward to get two more chaining values for comparison during the
meet-in-the-middle attack. Second, we search two more neutral words
in one independent chunk, and then propose the multi-neutral-word
partial-fixing technique to get more message freedom and skip ten
steps for partial-fixing, as compared to previous four steps. We
also use the initial structure technique and apply the same idea to
improve the pseudo-preimage and preimage attacks on Extended MD4
with and improvement factor, as compared to
previous attacks in \cite{SasakiA-acisp09}, respectively
Hash Gone Bad: Automated discovery of protocol attacks that exploit hash function weaknesses
Most cryptographic protocols use cryptographic hash functions as a building block. The security analyses of these protocols typically assume that the hash functions are perfect (such as in the random oracle model). However, in practice, most widely deployed hash functions are far from perfect -- and as a result, the analysis may miss attacks that exploit the gap between the model and the actual hash function used.
We develop the first methodology to systematically discover attacks on security protocols that exploit weaknesses in widely deployed hash functions. We achieve this by revisiting the gap between theoretical properties of hash functions and the weaknesses of real-world hash functions, from which we develop a lattice of threat models. For all of these threat models, we develop fine-grained symbolic models.
Our methodology's fine-grained models cannot be directly encoded in existing state-of-the-art analysis tools by just using their equational reasoning. We therefore develop extensions for the two leading tools, Tamarin and Proverif. In extensive case studies using our methodology, the extended tools rediscover all attacks that were previously reported for these protocols and discover several new variants