Digital signatures are widely used as security tokens, not just in XML. In this article, we look at how to create a digital signature and the way that digital signatures are constructed. We examine the current W3C XML digital signature and consider the effects of the structure of this XML-specific tool. The chapter concludes by finding where this construct fits into overall XML security and its potential uses.

The signature is generated from a hash over the canonical form of the manifest, which can reference multiple XML documents. To canonicalize something is to put it in a standard format that everyone generally uses. Because the signature is dependent on the content it is signing, a signature produced from a noncanonicalized document could possibly be different from that produced from a canonicalized document. Remember that this specification is about defining digital signatures in general, not just those involving XML documents. The manifest may also contain references to any digital content that can be addressed or even to part of an XML document.

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