On Apr 14, 2009, at 11:57, Thomas Roessler wrote:
On 14 Apr 2009, at 10:27, Henri Sivonen wrote:
Wouldn't it be simpler to use jar signing instead of inventing a
new way of signing zip files with implementation dependencies on
XML signatures and spec dependencies on XSD? (Why does the spec
have dependencies on XSD?)
Which XSD dependency do you mean? The only XSD dependencies I could
think of right now are ones that say things like "the value of this
attribute is of type anyURI" or "the value space of this element is
a restriction on the base64Binary XSD type." XML Signature does not
require schema validation, or anything like that.
Hence, "spec dependencies".
I don't find the string anyURI in the spec, but anyURI is a great
example of why defining syntax in terms of XSD datatypes is a bad idea:
http://hsivonen.iki.fi/thesis/html5-conformance-checker#iri
XSD datatypes are too vague, allow whitespace where the spec writer
didn't mean to allow whitespace or allow surprising values (like "0"
and "1" when the spec writer though (s)he'd be allowing "true" and
"false"). It is much safer to define datatypes in precise English
prose like HTML5 does than to expect XSD to match what is really meant.
When you need to reserialize XML, you import all the troubles of
serializing XML (see e.g. https://issues.apache.org/bugzilla/buglist.cgi?query_format=advanced&product=Security&component=Canonicalization&cmdtype=doit
).
The only place where you actually need canonicalization is when
hashing the SignedInfo element inside the signature file (i.e., once
per signature verification).
Given that the signature format is profiled down pretty heavily in
the widget signing spec, I'd dare a guess that most of the
complexity isn't ever used, so a careful implementation might be
able to write a c14n implementation that bails out on anything that
doesn't look like a signature that follows the constraints in this
format.
If you need to do canonicalization even in one place, you need a
properly debugged implementation of it. If the signature format is
profiled heavily, doesn't it mean you can't even use an off-the-shelf
implementation of XML signatures?
--
Henri Sivonen
[email protected]
http://hsivonen.iki.fi/
