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As the article some days ago about SHA1 got a lot of interest, I thought I'll write some more background info about this, especially for people thinking that collisions aren't a big problem.

Cryptographic hash functions are functions where you can put a string of any length and get a fixed-size result. E. g. with SHA1, you get 160 bit, with MD5 128 bit. The hash-function has to fulfill some requirements:
- It should be hard to get two strings with the same hash (collision-resistant).
- It should be hard to get a string to a given hash (one-way-function).
To be more precise: In an optimal case, hard means that it shouldn't be possible with all hardware on earth in the timeframe that your cryptography needs to be secure. Some examples where cryptographic hashes are used are shadown-passwords, digital signatures or verification of file downloads.

Xiaoyun Wang, chinese cryptographer and well known for her analysis of the SHA1 function, was not allowed to travel to the US to attend the Crypto conference starting today (via Bruce Schneier).

Too bad, because she discovered some new results on the attacks on SHA1, which reduce it to a complexity of 2^63 to generate a collission. Adi Shamir, well known cryptographer and one of the RSA-inventors, presented these results.
These news are important, because 2^63 is a complexity that can be broken with todays hardware if you invest enough money and time. This would be an interesting project for distributed computing, although I don't know if the attack can be implemented on common hardware (maybe someone with cryptographic experiences wants to comment if this is possible).

Too bad that most software devs have not noticed the recent results on hash-functions. Most of them still use MD5 (which has been broken about a year ago), SHA-1 is widely used. The GNU Coreutils don't have any tools for modern hash-functions, same goes with most programming languages (PHP, Python), while they implement some sort of md5sum or sha1sum, no sha256sum or whirlpoolsum at all.