These folks provide hash/tag directory for peer-to-peer file sharing. http://www.bitzi.com/

From http://www.bitzi.com/developer/code :

"Bitprint Definition Our distinctive bitprint is actually a combination of several nonproprietary cryptographic hash values. We take both the SHA1 hash of a file, and the "TigerTree" hash of a file. TigerTree is based on the Tiger hash algorithm, applied to each 1024-byte block of a file, then combined up through a binary hash tree to a final summary value. Such a composited hash tree value allows compact proofs that file fragments combine to form the full file - a useful quality for verifying or resuming downloads-in-progress from unreliable peers, among other applications. " __________________________________________________ Do You Yahoo!? Get personalized email addresses from Yahoo! Mail http://personal.mail.yahoo.com/