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.
