According to various sources, attacks looking for sha-1 collisions have been improved to 2^52 operations:
http://www.secureworks.com/research/blog/index.php/2009/6/3/sha-1-collision-attacks-now-252/
What I’d like to know is the implication of these discoveries on systems that are not under attack. Meaning if I hash random data, what are the statistical odds of a collision? Said another way, does the recent research indicate that a brute-force birthday attack has a higher chance of finding collisions that originally proposed?
Some writeups, like the one above, say that obtaining a SHA-1 collision via brute force would require 2^80 operations. Most sources say that 2^80 is a theoretical number (I assume because no hash function is really distributed perfectly even over its digest space).
So are any of the announced sha1 collision weaknesses in the fundamental hash distribution? Or are the increased odds of collision only the result of guided mathematical attacks?
I realize that in the end it is just a game of odds, and that their is an infinitesimally small change that your first and second messages will result in a collision. I also realize that even 2^52 is a really big number, but I still want to understand the implications for a system not under attack. So please don’t answer with “don’t worry about it”.
The result announced in your link is an attack, a sequence of careful, algorithmically-chosen steps that generate collisions with greater probability than would a random attack. It is not a weakness in the hash function’s distribution. Well, ok, it is, but not of the sort that makes a random attack likely on the order of 2^52 to succeed.
If no one is trying to generate collisions in your hash outputs, this result does not affect you.