Research Of Attack Methods On Hash Function BLAKE

As a tool in information security area, Cryptographic hash functions play an important role in date integrity, non-repudiation and so on. In recent years, security research on hash functions made great progress. A series of hash functions such as MD4, MD5 has been broken by Wang et al. Following with research in-depth and computer power improved, security of algorithms such as SHA-1 will also meet threat. So, The National Institute of Standards and Technology called for new standard hash function SHA-3 in 2007. There are fourteen candidates being selected for the second round evaluation in 2009, and BLAKE as one of five candidates which was finally selected for the third evaluation in December 2010, its security is worthy to study.In this thesis, characteristics of BLAKE is analyzed, its security is deeply researched by applying the following three attack methods:1. Characteristics of message permutation is analyzed and some flaws of permutation in round-reduced operations are explored. Applying compression operation rule and splice-and-subsection technology, three rounds of BLAKE is attacked by free-starting preimage attack. The computational complexity about resistance of preimage attack on BLAKE is reduced.2. Improved free-staring collision attack is proposed by applying characteristics of message permutation, this make further reduction of computational complexity for two rounds of operation. Applying differiential characteristics of input-output states and meet-in-the-middle technology, security of six and more rounds of BLAKE-32 is analyzed.3. By linearization of modular addition, the differential expansion caused by input differentials is found in each round of BLAKE-32.Finally, the efficiency of linearization differential attack on BLAKE is explored based on analysis of differential characteristics.Research shows that this method is the best one in analysis of BLAKE recently.