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Thesis Defense - Cochran

Cryptographic Hash Functions
Computer Science PhD Candidate

Cryptographic hash functions have grown to be some of the most widely-used objects from cryptography. Typically they are built from smaller, well-defined primitives known as compression functions using the celebrated result from Merkle and Damgard to extend the domain. This research takes a comprehensive look at these primitives, providing new results on ways they should, and should not, be constructed, in addition to making contributions to the exciting recent cryptanalysis of MD5 and other hashes.

Specifically, we show the impossibility of using blockciphers, another ubiquitous cryptographic object, in desirable configurations to build collision-resistant hash functions, and suggest a novel way to structure compression functions to increase their utility, efficiency, and security bounds when used in modes of operation, and with regard to differing security goals. Finally, we provide the first reasonably complete analysis for the meta-methods used in the recent spectacular collision attacks announced for, among others, MD4, MD5, and SHA-0, reducing the complexity of the best-known attack in the case of MD5.

Committee: John Black, Assistant Professor (Chair)
Harold (Hal) Gabow, Professor
Andrzej Ehrenfeucht, Distinguished Professor
David Grant, Department of Mathematics
Phillip Rogaway, University of California, Davis
Department of Computer Science
University of Colorado Boulder
Boulder, CO 80309-0430 USA
May 5, 2012 (14:20)