Finding partial hash collisions by brute force parallel programming

Abstract

A hash function maps an arbitrary length of (longer) message into a fixed length of shorter string, called message digest. Inevitably there will be a lot of different messages being hashed to the same or similar digest. We call this collision or partial collision. By utilizing multiple processors from the CUNY High Performance Computing Center's facility, we locate partial collisions for MD5 and SHA-1 by brute force parallel programming in C with MPI library. The brute force method of finding a second preimage collision entails systematically computing all of the permutations, digests, and Hamming distances of the target preimage. We explore varying size target strings and the number of processors allocation and examine the effect these variables have on finding partial collisions. The results show that for the same message space the search time for the partial collisions is roughly halved for each doubling of the number of processors; and the longer the message is the better partial collisions are produced.