fpaq

> Again, hashes are by definition, insecure. I.e. you don't have a guarantee that the hash references the same commit, just a (very, very strong) probability that it does.

This doesn't seem to be a useful definition. Would you classify every computable algorithm as insecure, because by generating a random bitstring, there is a (very, very low) probability of guessing the hash/secret key/solution/signature?

> However, if I see that you pushed commit abcd134, and then I can build and push a colliding commit...

You cannot do that. This is called a second-preimage attack, which has not been demonstrated even against MD5, let alone SHA1.