You need to hash about 2^64 values to get a single collision among them, on average, if you don’t try to deliberately create collisions. Hash collisions are very similar to the Birthday problem. If you look at two arbitrary values, the collision probability is only 2-128. The problem with md5 is that it’s relatively easy … Read more
Assuming uniform spread in the range of MD5 and SHA-1 hashes for random strings (which isn’t the case), and assuming we’re only talking about two strings and not talking about a pool of strings (so we avoid birthday-paradox-type complexities): An MD5 hash is 128 bits wide, and SHA-1’s is 160. With the above assumptions, two … Read more
Update Ironically, a few weeks after I posted the previous answer, two Chinese researchers, Tao Xie and Dengguo Feng, published a new single-block collision for MD5. I was unaware of that paper until now. A single MD5 block means that the input size is 64 bytes or 512 bits. Note that the inputs are mostly … Read more
For a set of even billions of assets, the chances of random collisions are negligibly small — nothing that you should worry about. Considering the birthday paradox, given a set of 2^64 (or 18,446,744,073,709,551,616) assets, the probability of a single MD5 collision within this set is 50%. At this scale, you’d probably beat Google in … Read more
Python uses a random hash seed to prevent attackers from tar-pitting your application by sending you keys designed to collide. See the original vulnerability disclosure. By offsetting the hash with a random seed (set once at startup) attackers can no longer predict what keys will collide. You can set a fixed seed or disable the … Read more
Picking atoms on 10 Moons An SHA-1 hash is a 40 hex character string… that’s 4 bits per character times 40… 160 bits. Now we know 10 bits is approximately 1000 (1024 to be exact) meaning that there are 1 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 … Read more
I did an experiment to find out exactly how Git would behave in this case. This is with version 2.7.9~rc0+next.20151210 (Debian version). I basically just reduced the hash size from 160-bit to 4-bit by applying the following diff and rebuilding git: — git-2.7.0~rc0+next.20151210.orig/block-sha1/sha1.c +++ git-2.7.0~rc0+next.20151210/block-sha1/sha1.c @@ -246,6 +246,8 @@ void blk_SHA1_Final(unsigned char hashou blk_SHA1_Update(ctx, padlen, … Read more