> you have to be able to also edit the size field in the header.” As I read the OP [1] a chosen-prefix collision attack such as this allows you to “edit the si

> you have to be able to also edit the size field in the header.” As I read the OP [1] a chosen-prefix collision attack such as this allows you to “edit the size field in the header”. Or am I missing something? 1. “A chosen-prefix collision is a more constrained (and much more difficult to obtain) type of collision, where two message prefixes P and P’ are first given as challenge to the adversary, and his goal is then to compute two messages M and M’ such that H(P || M) = H(P’ || M’), where || denotes concatenation.” EDIT: On second thought I was missing something: the adversary is further constrained in the git case because it must find M and M’ of correct length (specified in P and P’). Linus is right (as usual), this probably makes it much harder.