Following up on yesterday’s discussion about new attacks on cryptographic hashfunctions, Eric Rescorla points to a new paper from Chinese computer scientists, which claims to have found a collision in MD5. MD5 is a cousin of the SHA-1 function discussed yesterday; MD5 is believed to be the weaker of the two.

The paper is odd, in that it includes two values that it claims have the same MD5 value, but it doesn’t explain *how* the claimed collision was generated. And it turns out that the authors made an error, so that the two values don’t in fact generate the same MD5 value. Eric and the commenters on his site did some clever detective work to determine that the two published values generate a collision for a slightly different function, which Eric dubbed MD5′. MD5′ is very similar to MD5 so it seems very likely that the new attack can be extended to the real MD5.

Report from Crypto 2004Here’s the summary of events from last night’s work-in-progress session at the Crypto conference. [See previous entries for backstory.] (I’ve reordered the sequence of presentations to simplify the explanation.) Antoine Joux re-announced the collision …

There’s a new version of the paper that fixes the previous bug. You can verify the collision easily yourself too,

using this data, which I extracted from the paper.

Cheers,

– mjos

There’s a new version of the paper that fixes the previous bug. You can verify the collision easily yourself too,

using this data, which I extracted from the paper.

Cheers,

– mjos