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The typical signature verification process includes following steps:
Load keys, X509 certificates, etc. in the keys manager .
Create signature context xmlSecDSigCtx using xmlSecDSigCtxCreate or xmlSecDSigCtxInitialize functions.
Select start verification <dsig:Signature/> node in the signed XML document.
Verify signature by calling xmlSecDSigCtxVerify function.
Check returned value and verification status (status
member of xmlSecDSigCtx structure).
If necessary, consume returned data from the context.
Destroy signature context xmlSecDSigCtx using xmlSecDSigCtxDestroy or xmlSecDSigCtxFinalize functions.
Example 14. Verifying a document.
/**
* 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);
}