Ever Better Cryptanalytic Results Against SHA-1

The SHA family (which, I suppose, should really be called the MD4 family) of cryptographic hash functions has been under attack for a long time. In 2005, we saw the first cryptanalysis of SHA-1 that was faster than brute force: collisions in 269 hash operations, later improved to 263 operations. A great result, but not devastating. But remember the great truism of cryptanalysis: attacks always get better, they never get worse. Last week, devastating got a whole lot closer. A new attack can, at least in theory, find collisions in 252 hash operations — well within the realm of computational possibility. Assuming the cryptanalysis is correct, we should expect to see an actual SHA-1 collision within the year.

Note that this is a collision attack, not a pre-image attack. Most uses of hash functions don’t care about collision attacks. But if yours does, switch to SHA-2 immediately. (This has more information on this, written for the 269 attack.)

This is why NIST is administering a SHA-3 competition for a new hash standard. And whatever algorithm is chosen, it will look nothing like anything in the SHA family (which is why I think it should be called the Advanced Hash Standard, or AHS).

Posted on June 16, 2009 at 12:21 PM • 50 Comments