Security of cryptographic hash functions: Difference between revisions

Revision as of 16:28, 19 March 2012

Revision as of 14:03, 9 April 2012

Line 19:

== Classical Hash Functions - Practical Approach to Security ==

Most hash functions are built on an ad hoc basis, where the bits of the message are nicely mixed to produce the hash. Various [[bitwise operation]]s (e.g. rotations), [[Modular arithmetic|modular additions]] and [[One-way compression function|compression functions]] are used in iterative mode to ensure high complexity and pseudo-randomness of the output. In this way, the security is very hard to prove and the proof is usually not done. Only a few years ago, one of the most popular hash functions, [[SHA-1]], was shown to be less secure than its length suggested: collisions could be found in only 2⁶³⁵¹<ref>http://eprint.iacr.org/2008/469.pdf</ref> tests, rather than the brute-force number of 2⁸⁰. The search for a "good" hash function has thus become a hot topic.

In other words, most of the hash functions in use nowadays, are not provably collision-resistant. These hashes are not based on purely mathematical functions. This approach results generally in more effective hashing functions, but with the risk that a weakness of such a function will be eventually used to find collisions. The famous case is [[MD5]].