Security of cryptographic hash functions: Difference between revisions

Revision as of 20:15, 26 August 2024

Latest revision as of 18:28, 7 January 2025

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{{Main article|Cryptographic hash function}}

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{{When|date=August 2024}}, 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 2⁵¹<ref>{{Cite web| title=Classification and Generation of Disturbance Vectors for Collision Attacks against SHA-1 | url=http://eprint.iacr.org/2008/469.pdf {{Bare| URLarchive-url=https://web.archive.org/web/20090115213127/http://eprint.iacr.org/2008/469.pdf PDF| archive-date=March 20222009-01-15}}</ref> tests, rather than the brute-force number of 2⁸⁰.

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. One famous case is [[MD5]].