XML Digital Signatures • Chapter 5
157
A Detached Signature Example
As a final basic example, let’s consider a detached signature.This form can be
used when it is undesirable or impractical to physically merge the digital signa-
ture and its data (see Figure 5.7).
Figure 5.7 Canonical Detached XML Digital Signature
<?xml version="1.0" encoding="UTF-8"?>
<Envelope xmlns="urn:envelope">
<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#dsa-sha1" />
<Reference URI="file:///home/skip/xml/weather.xml">
<Transforms>
</Transforms>
<DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1" />
<DigestValue></DigestValue>
</Reference>
</SignedInfo>
<SignatureValue/>
<KeyInfo>
<KeyValue/>
</KeyInfo>
</Signature>
</Envelope>
The only thing new about this canonical form is that the Reference URI is
now filled in.This URI can be anything that both the signer and the verifier will
have read access authorization to. In this example, we used a local file, but it could
have easily been a remote file accessible through HTTP, FTP, or other protocols.
For our example file, we use an XML file that contains some weather reports
(see Figure 5.8).
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