digital signatures

Frank Tobin
Sat Feb 16 06:01:01 2002

Lee Roberts, at 20:48 -0700 on 2002-02-15, wrote:

> Why is this necessary? What's wrong with PGP/GPG signatures?

xmldsig is not an actual cryptographic protocol, but more of a means of
using helping defining what has been signed in an XML document.  The idea
is that an xmldsig document "I'm running a signature over these elements,
but not these, (they're part of form data)".  The actual cryptographic
signature comes from OpenPGP, S/MIME, or similar, and inserted into the
xmldsig document.

Part of the whole mess is the important concept of canonicalization; the
xmldsig-signed documents are canonicalized first before a signature is run
over them, so that the XML document can be transmitted in a variety of
different manners.  Once the message needs to be verified, the message is
re-canonicalized, and the signature verified.  This helps eliminate the
many problems of whitespace, etc, that have been a thorn in OpenPGP's side
for quite some time regarding textmode signatures.

Frank Tobin