MD5 Collision Source Code Released

SiliconEntity writes "The crypto world was shaken to its roots last year with the announcement of a new algorithm to find collisions in the still widely-used MD5 hash algorithm. Despite considerable work and commentary since then, no source code for finding such collisions has been published. Until today! Patrick Stach has announced the availability of his source code for finding MD5 collisions and MD4 collisions (Coral cache links provided to prevent slashdotting). MD4 collisions can be found in a few seconds (but nobody uses that any more), while MD5 collisions (still being used!) take 45 minutes on a 1.6 GHz P4. At last we will be able to implement various attacks which have been purely hypothetical until now. This more than anything should be the final stake in the heart of MD5, now that anyone can generate collisions whenever they want."

Comments

Re:Q and A

[CodeRx]

sha1(md5($password . '¥1i9k') . 'a-thirty-five-ch4racter-l0ng-str1ng' . md5($password))

This is a very bad password salting scheme and vulnerable to a dictionary attack. Once I have your database and salts, I can run a dictionary of common passwords through your scheme and crack any weak passwords.

You can make things much harder by having your salt change for each password - include the username for example. Now I have to run my entire dictionary through the sha/md5 function for each user. By doing this, you make the attack O(m*n) instead of O(m) (where m = the number of words in my dictionary and n = the number of users).

And as you mentioned in a follow up post, this code only generates documents with identical md5 sums, it does not generate a document with a given sum. So MD5 is broken for document signing and the like, but secure for password hashing for the time being.