XML Security Library

LibXML2
LibXSLT
OpenSSL

Verifying a signed document

The typical signature verification process includes following steps:

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);
}
		

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