XML Security Library

LibXML2
LibXSLT
OpenSSL

Signing a document.

The typical signature process includes following steps:

Example 10. Signing a template.

/** 
 * sign_file:
 * @tmpl_file:		the signature template file name.
 * @key_file:		the PEM private key file name.
 *
 * Signs the #tmpl_file using private key from #key_file.
 *
 * Returns 0 on success or a negative value if an error occurs.
 */
int 
sign_file(const char* tmpl_file, const char* key_file) {
    xmlDocPtr doc = NULL;
    xmlNodePtr node = NULL;
    xmlSecDSigCtxPtr dsigCtx = NULL;
    int res = -1;
    
    assert(tmpl_file);
    assert(key_file);

    /* load template */
    doc = xmlParseFile(tmpl_file);
    if ((doc == NULL) || (xmlDocGetRootElement(doc) == NULL)){
	fprintf(stderr, "Error: unable to parse file \"%s\"\n", tmpl_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", tmpl_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 private key, assuming that there is not password */
    dsigCtx->signKey = xmlSecCryptoAppKeyLoad(key_file, xmlSecKeyDataFormatPem, NULL, NULL, NULL);
    if(dsigCtx->signKey == NULL) {
        fprintf(stderr,"Error: failed to load private 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;
    }

    /* sign the template */
    if(xmlSecDSigCtxSign(dsigCtx, node) < 0) {
        fprintf(stderr,"Error: signature failed\n");
	goto done;
    }
        
    /* print signed document to stdout */
    xmlDocDump(stdout, doc);
    
    /* success */
    res = 0;

done:    
    /* cleanup */
    if(dsigCtx != NULL) {
	xmlSecDSigCtxDestroy(dsigCtx);
    }
    
    if(doc != NULL) {
	xmlFreeDoc(doc); 
    }
    return(res);
}
		

Full program listing

Simple signature template file