Nasour BAgheri

  Oral Defense Notice

  In this thesis we conceder the designing and analysis of cryptographic hash functions. Our analysis leads to variety of successful attacks for the known hash functions, includes:

  In addition, we study the relationship between information theoretic attack costs and real costs. We show that in the information theoretic model, many well-known and commonly used hash functions such as MD5 and SHA-256 fail to be preimage resistant.

  We propose a generic n -bit iterated hash function framework based on n -bit compression function called Suffix-free-Prefix-free (SFPF) which works for arbitrary IV s and does not possess MD strengthening. We formally prove that SFPF is indifferentiable from the random oracle (RO) when the compression function is viewed as a fixed input-length random oracle (FIL-RO). We also design a concrete hash constriction which fits the SFPF. A hash function with free IV has many benefits such as speedup for the short messages up to two times and applications in randomized hashing.

  We propose a permutation based compression function and prove its security with respect to collision and (second) preimage attacks in the ideal permutation model. The proposed compression function can be seen as a generalization of the compression function of MD6 hash function.

  Date: Monday July 12, 2010 Time: 5:00PM

  Location: The seminar room of E.E. Dept