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<title>Verifying a signed document: XML Security Library Reference Manual</title>
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<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="xmlsec-notes-verify"></a>Verifying a signed document</h2></div></div></div>
<p>The typical signature verification process includes following steps:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>
Load keys, X509 certificates, etc. in the <a class="link" href="xmlsec-keysmngr.html#xmlSecKeysMngr" title="struct xmlSecKeysMngr">keys manager</a> .
</p></li>
<li class="listitem"><p>
Create signature context <a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtx" title="struct xmlSecDSigCtx">xmlSecDSigCtx</a>
using <a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtxCreate" title="xmlSecDSigCtxCreate ()">xmlSecDSigCtxCreate</a> or
<a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtxInitialize" title="xmlSecDSigCtxInitialize ()">xmlSecDSigCtxInitialize</a>
functions.
</p></li>
<li class="listitem"><p>
Select start verification
<a class="ulink" href="" target="_top"><dsig:Signature/></a>
node in the signed XML document.
</p></li>
<li class="listitem"><p>
Verify signature by calling <a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtxVerify" title="xmlSecDSigCtxVerify ()">xmlSecDSigCtxVerify</a>
function.
</p></li>
<li class="listitem"><p>
Check returned value and verification status (<em class="structfield"><code>status</code></em>
member of <a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtx" title="struct xmlSecDSigCtx">xmlSecDSigCtx</a> structure).
If necessary, consume returned data from the <a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtx" title="struct xmlSecDSigCtx">context</a>.
</p></li>
<li class="listitem"><p>
Destroy signature context <a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtx" title="struct xmlSecDSigCtx">xmlSecDSigCtx</a>
using <a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtxDestroy" title="xmlSecDSigCtxDestroy ()">xmlSecDSigCtxDestroy</a> or
<a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtxFinalize" title="xmlSecDSigCtxFinalize ()">xmlSecDSigCtxFinalize</a>
functions.
</p></li>
</ul></div>
<p>
</p>
<p>
</p>
<div class="example">
<a name="id-1.2.8.3.3.1"></a><p class="title"><b>Example 14. Verifying a document.</b></p>
<div class="example-contents">
<pre class="programlisting">
/**
* verify_file:
* @xml_file: the signed XML file name.
* @key_file: the PEM public key file name.
*
* Verifies XML signature in #xml_file using public key from #key_file.
*
* Returns 0 on success or a negative value if an error occurs.
*/
int
verify_file(const char* xml_file, const char* key_file) {
xmlDocPtr doc = NULL;
xmlNodePtr node = NULL;
xmlSecDSigCtxPtr dsigCtx = NULL;
int res = -1;
assert(xml_file);
assert(key_file);
/* load file */
doc = xmlParseFile(xml_file);
if ((doc == NULL) || (xmlDocGetRootElement(doc) == NULL)){
fprintf(stderr, "Error: unable to parse file \"%s\"\n", xml_file);
goto done;
}
/* find start node */
node = xmlSecFindNode(xmlDocGetRootElement(doc), xmlSecNodeSignature, xmlSecDSigNs);
if(node == NULL) {
fprintf(stderr, "Error: start node not found in \"%s\"\n", xml_file);
goto done;
}
/* create signature context, we don't need keys manager in this example */
dsigCtx = xmlSecDSigCtxCreate(NULL);
if(dsigCtx == NULL) {
fprintf(stderr,"Error: failed to create signature context\n");
goto done;
}
/* load public key */
dsigCtx->signKey = xmlSecCryptoAppKeyLoad(key_file,xmlSecKeyDataFormatPem, NULL, NULL, NULL);
if(dsigCtx->signKey == NULL) {
fprintf(stderr,"Error: failed to load public pem key from \"%s\"\n", key_file);
goto done;
}
/* set key name to the file name, this is just an example! */
if(xmlSecKeySetName(dsigCtx->signKey, key_file) < 0) {
fprintf(stderr,"Error: failed to set key name for key from \"%s\"\n", key_file);
goto done;
}
/* Verify signature */
if(xmlSecDSigCtxVerify(dsigCtx, node) < 0) {
fprintf(stderr,"Error: signature verify\n");
goto done;
}
/* print verification result to stdout */
if(dsigCtx->status == xmlSecDSigStatusSucceeded) {
fprintf(stdout, "Signature is OK\n");
} else {
fprintf(stdout, "Signature is INVALID\n");
}
/* success */
res = 0;
done:
/* cleanup */
if(dsigCtx != NULL) {
xmlSecDSigCtxDestroy(dsigCtx);
}
if(doc != NULL) {
xmlFreeDoc(doc);
}
return(res);
}
</pre>
<p><a class="link" href="xmlsec-verify-with-key.html#xmlsec-example-verify1" title="verify1.c">Full Program Listing</a></p>
</div>
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<p><br class="example-break">
</p>
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