Ah. That's a tough one. Digests can help, but since two very different sets of data can share a digest... well, it won't be unique. You could do something like a digest prepended with the nth 10 bytes from the file, or something, but even that wouldn't be a guarantee.

It comes down to finding something that's unique enough about the data that when it's combined with a digest, you have a "pretty much guaranteed" unique key. MIME type, maybe? Combined with a longer digest (say, SHA-256), that would be pretty good.

Two different digests (say, MD5().SHA256()) would be a likely candidate, too -- the chance that data "A" will have a digest collision with data "B" in two different digest systems is fanstastically small.

<-radiant.matrix->
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In reply to Re^3: Simple Digests? by radiantmatrix
in thread Simple Digests? by pileofrogs

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