xmldsig.md

dsigsample.xml

<?xml version="1.0" encoding="UTF-8"?>
<Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
<SignedInfo>
  <CanonicalizationMethod Algorithm="http://www.w3.org/TR/2001/REC-xml-c14n-20010315" />
  <SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1" />
  <Reference URI="#object">
    <DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" />
    <DigestValue>OPnpF/ZNLDxJ/I+1F3iHhlmSwgo=</DigestValue>
  </Reference>
</SignedInfo>
<SignatureValue>nihUFQg4mDhLgecvhIcKb9Gz8VRTOlw+adiZOBBXgK4JodEe5aFfCqm8WcRIT8GL
LXSk8PsUP4//SsKqUBQkpotcAqQAhtz2v9kCWdoUDnAOtFZkd/CnsZ1sge0ndha4
0wWDV+nOWyJxkYgicvB8POYtSmldLLepPGMz+J7/Uws=</SignatureValue>
<KeyInfo>
  <KeyValue>
    <RSAKeyValue>
      <Modulus>4IlzOY3Y9fXoh3Y5f06wBbtTg94Pt6vcfcd1KQ0FLm0S36aGJtTSb6pYKfyX7PqC
      UQ8wgL6xUJ5GRPEsu9gyz8ZobwfZsGCsvu40CWoT9fcFBZPfXro1Vtlh/xl/yYHm
      +Gzqh0Bw76xtLHSfLfpVOrmZdwKmSFKMTvNXOFd0V18=</Modulus>
      <Exponent>AQAB</Exponent>
    </RSAKeyValue>
  </KeyValue>
</KeyInfo>
<Object Id="object">some text
  with spaces and CR-LF.</Object>
</Signature>

xmldsig.md

Procedure

Algorithm: XMLDSIG of simple text string.

INPUT:

T, text-to-be-signed, a byte string;

Ks, RSA private key;

OUTPUT: XML file, xml

• Canonicalize* the text-to-be-signed, C = C14n(T).

• Compute the message digest of the canonicalized text, m = Hash(C).

• Encapsulate the message digest in an XML element, SI, in canonicalized form.

• Compute the RSA signatureValue of the canonicalized element, SV = RsaSign(Ks, SI).

• Compose the final XML document including the signatureValue, this time in non-canonicalized form.

• Strictly, what we are doing here is encapsulating the text string T inside an element, then canonicalizing that element.

  CANONICALIZATION

  This is the official (2001) outline of the procedure for c14n, taken from [XML-C14N]:

  • The document is encoded in UTF-8
  • Line breaks normalized to #xA on input, before parsing
  • Attribute values are normalized, as if by a validating processor
  • Character and parsed entity references are replaced
  • CDATA sections are replaced with their character content
  • The XML declaration and document type declaration (DTD) are removed
  • Empty elements are converted to start-end tag pairs
  • Whitespace outside of the document element and within start and end tags is normalized
  • All whitespace in character content is retained (excluding characters removed during line feed normalization)
  • Attribute value delimiters are set to quotation marks (double quotes)
  • Special characters in attribute values and character content are replaced by character references
  • Superfluous namespace declarations are removed from each element
  • Default attributes are added to each element
  • Lexicographic order is imposed on the namespace declarations and attributes of each element