> At first I decided to use CRC32, but some people pointed out that
> it's too weak to be used as hash.  If CRC32 was used, could you
> explain how to avoid hash collision between files?  Although
> collision would very rarely occur, but people want a perfect one.

Actually, with a 32-bit hash, collisions become expected somewhere
around 64K entries - plausible for many types of system (especially
those involving a lot of developer activity, meaning running many
different executables, even though most of them only a few times).

If you're concerned about accident, why not use a 128-bit CRC?  It
can't be that hard to find an appropriate polynomial of degree 128.
(No, I don't have one on tap, but I know there are books that explain
how to find one; I've seen them.)

Of course, CRCs (of any length) are worthless against malice; if you
are concerned about people deliberately provoking collisions, you will
need something stronger in that regard.

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