It sounds like you're using MD5 to generate unique identifiers for the cache. If you're looking to generate unique identifiers, you should really use a UUID generator for this (see RFC 4412). OTOH, If you really do need a one-way hash function, I'd highly recommend SHA1 over MD5 due to serious security flaws in MD5. Disclaimer: I haven't looked at the code to see what you're doing. I'm a security guy, so the word MD5 always makes me uneasy. Matt