Stripwire is a tool which demonstrates vulnerabilities in md5 checks described in this paper. Contains a perl script which proves that if md5(x) == md5(y), then md5(x+q) == md5(y+q) (assuming length(x) and length(y) are 0 mod 64, and q is any arbitrary data). This is true because once two blocks converge upon the same hash, the nature of them being different has thereafter been lost.
You can download it from the following link: https://packetstormsecurity.com/files/download/35125/stripwire-1.1.tar.gz
Source: https://packetstormsecurity.com/files/35125/stripwire-1.1.tar.gz.html