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Re: [vox] MD5 Checksums and Public Downloading
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Re: [vox] MD5 Checksums and Public Downloading



> > I should think that such things as PGP signatures would be infinitely
> > more valuable to ensuring the integrity of data.
> 
> 1.  You mean GnuPG.  PGP is a dead proprietary product.

No, I don't.  I mean a PGP signature, as described by the RFC 1991. 
Actually, though, if I'd wanted to be *really* accurate, I'd have said
"OpenPGP" signature (RFC 2440, which is more up-to-date and open).  I'm
referring to an open message format. I specifically avoided "GnuPG"
because that would restrict me to only one implementation.  Despite the
fact that GnuPG happens to be the only real implementation around these
days, the format is open, and there can be any number of implementations
(not to mention that there are still people who use the "dead" Network
Associates product).

> 2.  PGP/GnuPG isn't designed for signing of large files.  I'm not even
> sure what happens if you try that.  I'm not sure it hashes the entire
> file.  MD5 was designed to do exactly all of that, and is fast for what
> it does.

Please justify this statement.  I am *quite* sure that it was designed
for signing of any size of file - otherwise it's pointless.  What good
is a signature if I can only be certain that a *portion* of it is
certified to have come from the person it claims to have come from?

In fact, a signature is nothing more or less than an encrypted hash
(with the PUBLIC key).  The hash proves (mostly) that it corresponds to
the data you think it does, and the encryption proves that it came from
the person you think it did. MD5 is frequently the algorithm used for
the hash, so anything you say about MD5 is generally true for an OpenPGP
signature (the other possible hash algorithms are MD2, SHA-1 and
RIPEMD-160).

The one thing you can say about a signature that you *can't* say about a
generic hash, is that it also helps to prove who signed it, whereas
anyone can generate an MD5 checksum.

> 3.  For those GnuPG signatures to be useful for authentication requires
> a raft of other things, including reliable distribution of public keys
> and/or an extensive web of trust.

Not necessarily.  Without those things, it is true that verifying a
signature provides no guarantee that it has not been tampered with (you
can't be certain you hold the right key); however, it makes it much
easier to know for *certain* that it *has* been tampered with.  This in
itself is at least *some* added security.

However, the web of trust need not be extensive to provide the former
guarantee - a single signature by a widely-trusted key is really all
that's necessary.

At any rate, little guarantee is still better than none at all.

-Micah

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