W3C home > Mailing lists > Public > public-xmlsec@w3.org > September 2008

more public feedback on canonicalization

From: Frederick Hirsch <frederick.hirsch@nokia.com>
Date: Thu, 25 Sep 2008 16:10:40 -0400
Message-Id: <7E443EE6-83ED-4DB1-9092-D50CD6D83624@nokia.com>
To: XMLSec WG Public List <public-xmlsec@w3.org>

fyi, from a public list, see item #3.

> 3. Canonicalization is difficult and typically 80% of digital  
> signature
>   failures derive from canonicalization bugs. Of those 95% are
>   XML namespace related (curse the inventor of XML namespaces), and
>   4% are whitespace related.

http://lists.oasis-open.org/archives/security-services/200809/msg00054.html

regards, Frederick

Frederick Hirsch
Nokia



Begin forwarded message:

> From: "ext sampo@symlabs.com" <sampo@symlabs.com>
> Date: September 25, 2008 3:27:06 PM EDT
> To: "Paul Madsen" <paulmadsen@rogers.com>
> Cc: "oasis sstc" <security-services@lists.oasis-open.org>
> Subject: Re: [security-services] Query submitted to saml.xml.org
> Reply-To: sampo@symlabs.com
>
> Paul Madsen wrote:
>> http://saml.xml.org/forum/calculating-digest-of-an-authentication-statement
>>
>> Dear Sirs, my name is Gianluca from Italy
>> I'm trying to calculate the Digest value of a SAML Authentication
>> STatement whith the SHA-1 algorithm. Let us suppose that we are  
>> dealing
>> with a string representing the following node:
>>
>> <saml:AuthenticationStatement>
>>    <saml:Subject>
>>        <saml:NameIdentifier>GIANLUCA</saml:NameIdentifier>
>>    </saml:Subject>
>> </saml:AuthenticationStatement>
>>
>> When I try to calculate SHA-1 with the function  b64_sha1(str2Digest)
>> what
>> exactly should the string str2Digest contain? I mean it should be  
>> equal to
>> "< 
>> saml:AuthenticationStatement 
>> ><saml:Subject><saml:NameIdentifier>GIANLUCA<
>> /saml:NameIdentifier></saml:Subject></saml:AuthenticationStatement>"
>> or only "GIANLUCA" or ....what else?
>
> Its a pity he did not provide email address, but lets hope this  
> reaches
> him anyway.
>
> 1. There is no univesally agreed way to digest Authentication  
> Statements
> 2. "Universally" agreed way to digest XML in general is exc-c14n  
> (exclusive
>   canonicalization) [XML-EXC-C14N]. This method is used by all  
> certified
>   SAML implementations. It is also the method used by digital
>   signatures [XMLDSIG].
> 3. Canonicalization is difficult and typically 80% of digital  
> signature
>   failures derive from canonicalization bugs. Of those 95% are
>   XML namespace related (curse the inventor of XML namespaces), and
>   4% are whitespace related.
> 4. For what you are apparently trying to do, it is important to
>   digest the entire canonicalized Authentication Statement.
>   If the question had been about canonicalizing the NameID, it
>   would still be important to digest the entire canonicalized
>   Name Identifier as the actual value in isolation is meaningless.
>   You need the identifier type and namespace qualification
>   for the digest to be meaningful.
>
> [XML-C14N] XML Canonicalization (non-exclusive),
> http://www.w3.org/TR/2001/REC-xml-c14n-20010315; J. Boyer:  
> "Canonical XML
> Version 1.0", W3C Recommendation, 15.3.2001,
> http://www.w3.org/TR/xml-c14n, RFC3076
>
> [XML-EXC-C14N] Exclusive XML Canonicalization,
> http://www.w3.org/TR/xml-exc-c14n/
>
> [XMLDSIG] "XML-Signature Syntax and Processing", W3C Recommendation,
> 12.2.2002, http://www.w3.org/TR/xmldsig-core, RFC3275
>
> Cheers,
> --Sampo
Received on Thursday, 25 September 2008 20:12:14 GMT

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