Digital signatures have a big problem with meaning

[Anne & Lynn Wheeler]

Peter Gutmann wrote:
> That cuts both ways though.  Since so many systems *do* screw with data (in
> insignificant ways, e.g. stripping trailing blanks), anyone who does massage
> data in such a way that any trivial change will be detected is going to be
> inundated with false positives.  Just ask any OpenPGP implementor about
> handling text canonicalisation.

this was one of the big issues in the asn.1 encoding vis-a-vis xml 
encoding wars.

asn.1 encoding provided deterministic encoding for signed material, 
although some of the more common applications of digital signature have 
what is transmitted is the original encoded material along with the 
signature of that encoded material.

fstc/e-check project wanted to digital sign stuff that was xml encoded 
... but not transmit the xml encoded fields. they wanted to take 
standard financial transaction fields ... momentarily xml encode the 
standard fields, digitally sign the encoded material ... and then append 
the resulting digital signature to the (original) standard transaction 
for transmission.

the problem was that xml didn't have a deterministic definition for 
encoding fields. when the recipient/relying party received the 
transmission ... they had to take the standard transaction fields and 
re-encode in xml in order to verifiy the digital signature. fstc/e-check 
came up with fsml for deterministic encoding of fields ... so that the 
encoding done by the originator (of the digital signature) and the 
encoding done by the relying party (for verifying the digital signature) 
would have identical bit patterns.

fsml was subsequently contributed to the xml digital signature project.

xml is descendent of gml invented by "G", "M", and "L" in 1969 at the 
science center
http://www.garlic.com/~lynn/subtopic.html#545tech
and then standardized at ISO in the 70s
http://www.garlic.com/~lynn/subtopic.html#sgml

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