[ufo]

Low-level crypto stuff such as block cyphers and hashing functions is usually done in C or assembly language. One of the biggest reasons is that its very hard to avoid timing attacks on higher level languages (when a computation takes a different time to run depending on the inputs an attacker can extract some info about secrets you control). Performance is also really important because the bad guys will use whatever means necessary to speed up their brute-forcing and you don't want to give them too much of an edge.

Another reason for C and assembly is that when everything your algorithm manipulates is a bunch of bytes you don't get much advantage from a type system.