X.509 certificate serial number format

As far as I can tell, X509 certificates all seem to contain a hexadecimal serial number. However, the schema definition in section 4.4.4 (The X509Data element) of the XML Signature Syntax and Processing document at http://www.w3.org/TR/2002/REC-xmldsig-core-20020212/#sec-X509Data <http://www.w3.org/TR/2002/REC-xmldsig-core-20020212/#sec-X509Data>  states that the X509SerialNumber element should be of type "integer" (presumably this also means it should be in decimal format), and SHOULD be compliant with
RFC2253.
 
Unfortunately, RFC2253 doesn't give any indication of format for a serial number, and as far as I can see, only gives instructions on how to convert attribute values from ASN.1 to a string.
 
This is giving me significant problems as I urgently need to find out how to do this conversion, and I feel like I am going round in circles chasing through RFCs!
 
It would be great if someone could give me some advice on how a hex X509 serial number should be converted to an integer for use in XML digital signatures, or point me towards some code or app that might do the job.
 
Regards,
Graham

Graham Simpson
UNIPASS Technical Lead, MCSE
http://www.unipass.co.uk
mailto:technical@unipass.co.uk <mailto:technical@unipass.co.uk>  


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