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Aleksey Sanin edited this page Oct 12, 2026 · 3 revisions

Signing a dynamically created template

Signs an XML document using a dynamically created signature template.

Source: sign2.c 

/**
 * XML Security Library (http://www.aleksey.com/xmlsec).
 *
 * This is free software; see the Copyright file in the source distribution for precise wording.
 *
 * Copyright (C) 2002-2026 Aleksey Sanin <aleksey@aleksey.com>. All Rights Reserved.
 */
/**
 * @brief XML Security Library example: Signing a file with a dynamically created template.
 * @details Signs a file using a dynamically created template and a key from a PEM file.
 * The signature has one reference with one enveloped transform to sign
 * the whole document except the <dsig:Signature/> node itself.
 *
 * Usage:
 *
 * \code{.sh}
 *      sign2 <xml-doc> <pem-key> [key-name]
 * \endcode
 *
 * Example:
 *
 * \code{.sh}
 *      ./sign2 sign2-doc.xml rsakey.pem test-key-name > sign2-res.xml
 * \endcode
 *
 * The resulting signature can be validated using the verify1 example with the
 * public key file:
 *
 * \code{.sh}
 *      ./verify1 sign2-res.xml rsapub.pem test-key-name
 * \endcode
 */
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include <libxml/tree.h>
#include <libxml/xmlmemory.h>
#include <libxml/parser.h>

#include <xmlsec/xmlsec.h>
#include <xmlsec/xmltree.h>
#include <xmlsec/xmldsig.h>
#include <xmlsec/templates.h>
#include <xmlsec/crypto.h>
#include <xmlsec/dl.h>

int sign_file(const char* xml_file, const char* key_file, const char* key_name);
xmlNodePtr create_signature_template(xmlDocPtr doc);

int
main(int argc, char **argv) {
    int xmlsec_initialized = 0;
    int res = -1;
    const char* key_name;

    assert(argv);

    if((argc != 3) && (argc != 4)) {
        fprintf(stderr, "Error: wrong number of arguments.\n");
        fprintf(stderr, "Usage: %s <xml-file> <key-file> [key-name]\n", argv[0]);
        return(1);
    }

    /* Init LibXML2 */
    xmlInitParser();
    LIBXML_TEST_VERSION

    /* Init XMLSec */
    if(xmlSecInit() < 0) {
        fprintf(stderr, "Error: xmlsec initialization failed.\n");
        goto done;
    }

    /* Check loaded library version */
    if(xmlSecCheckVersion() != 1) {
        fprintf(stderr, "Error: loaded xmlsec library version is not compatible.\n");
        goto done;
    }

    /* Load default crypto engine if we are supporting dynamic
     * loading for xmlsec-crypto libraries. Use the crypto library
     * name ("openssl", "nss", etc.) to load corresponding
     * xmlsec-crypto library.
     */
#ifdef XMLSEC_CRYPTO_DYNAMIC_LOADING
    if(xmlSecCryptoDLLoadLibrary(NULL) < 0) {
        fprintf(stderr, "Error: unable to load default xmlsec-crypto library. Make sure\n"
                        "that you have it installed and check shared libraries path\n"
                        "(LD_LIBRARY_PATH and/or LTDL_LIBRARY_PATH) environment variables.\n");
        goto done;
    }
#endif /* XMLSEC_CRYPTO_DYNAMIC_LOADING */

    /* Init crypto library */
    if(xmlSecCryptoAppInit(NULL) < 0) {
        fprintf(stderr, "Error: crypto initialization failed.\n");
        goto done;
    }

    /* Init xmlsec-crypto library */
    if(xmlSecCryptoInit() < 0) {
        fprintf(stderr, "Error: xmlsec-crypto initialization failed.\n");
        goto done;
    }
    xmlsec_initialized = 1;

    /* use the key name from the command line, or default to the key file name */
    key_name = (argc == 4) ? argv[3] : argv[2];

    /* sign file */
    if(sign_file(argv[1], argv[2], key_name) < 0) {
        goto done;
    }
    res = 0; /* success */

done:
    /* shutdown xmlsec-crypto library and xmlsec itself */
    if (xmlsec_initialized != 0) {
        xmlSecCryptoShutdown();
        xmlSecCryptoAppShutdown();
        xmlSecShutdown();
    }

    /* shutdown LibXML2 */
    xmlCleanupParser();

    return(res);
}

/**
 * @brief Adds enveloped signature template to the XML document.
 * @param doc the XML document.
 * @return pointer to the dsig:Signature node or NULL if an error occurs.
 */
xmlNodePtr
create_signature_template(xmlDocPtr doc) {
    xmlNodePtr signNode = NULL;
    xmlNodePtr refNode = NULL;
    xmlNodePtr keyInfoNode = NULL;

    assert(doc);

    /* create signature template for RSA-SHA256 enveloped signature */
    signNode = xmlSecTmplSignatureCreate(doc, xmlSecTransformExclC14NId, xmlSecTransformRsaSha256Id, NULL);
    if(signNode == NULL) {
        fprintf(stderr, "Error: failed to create signature template\n");
        return(NULL);
    }

    /* add <dsig:Signature/> node to the doc */
    if(xmlAddChild(xmlDocGetRootElement(doc), signNode) == NULL) {
        fprintf(stderr, "Error: failed to add signature node to the document\n");
        xmlFreeNode(signNode);
        return(NULL);
    }

    /* add <dsig:Reference/> node */
    refNode = xmlSecTmplSignatureAddReference(signNode, xmlSecTransformSha256Id, NULL, BAD_CAST "", NULL);
    if(refNode == NULL) {
        fprintf(stderr, "Error: failed to add reference to signature template\n");
        return(NULL);
    }

    /* add <dsig:Transform/> node with enveloped transform */
    if(xmlSecTmplReferenceAddTransform(refNode, xmlSecTransformEnvelopedId) == NULL) {
        fprintf(stderr, "Error: failed to add enveloped transform to reference\n");
        return(NULL);
    }

    /* add <dsig:KeyInfo/> and <dsig:KeyName/> nodes to put key name in the signed document */
    keyInfoNode = xmlSecTmplSignatureEnsureKeyInfo(signNode, NULL);
    if(keyInfoNode == NULL) {
        fprintf(stderr, "Error: failed to add key info\n");
        return(NULL);
    }
    if(xmlSecTmplKeyInfoAddKeyName(keyInfoNode, NULL) == NULL) {
        fprintf(stderr, "Error: failed to add key name\n");
        return(NULL);
    }

    /* done */
    return(signNode);
}

/**
 * @brief Signs an XML file using a dynamically created enveloped signature template.
 * @details Signs #xml_file using the private key from #key_file and a
 * dynamically created enveloped signature template.
 * @param xml_file the XML file name.
 * @param key_file the PEM private key file name.
 * @param key_name the name to assign to the key (used in the signature KeyName).
 * @return 0 on success or a negative value if an error occurs.
 */
int
sign_file(const char* xml_file, const char* key_file, const char* key_name) {
    xmlDocPtr doc = NULL;
    xmlNodePtr signNode = NULL;
    xmlSecDSigCtxPtr dsigCtx = NULL;
    int res = -1;

    assert(xml_file);
    assert(key_file);
    assert(key_name);


    /* load doc file */
#if LIBXML_VERSION >= 21300
    doc = xmlReadFile(xml_file, NULL, XML_PARSE_PEDANTIC | XML_PARSE_NONET | XML_PARSE_NOENT | XML_PARSE_NO_XXE);
#else /* LIBXML_VERSION >= 21300 */
    doc = xmlReadFile(xml_file, NULL, XML_PARSE_PEDANTIC | XML_PARSE_NONET | XML_PARSE_NOENT);
#endif /* LIBXML_VERSION >= 21300 */
    if ((doc == NULL) || (xmlDocGetRootElement(doc) == NULL)){
        fprintf(stderr, "Error: unable to parse file \"%s\"\n", xml_file);
        goto done;
    }

    /* add signature template (create_signature_template() reports the error) */
    signNode = create_signature_template(doc);
    if(signNode == NULL) {
        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 no password */
    dsigCtx->signKey = xmlSecCryptoAppKeyLoadEx(key_file,
        xmlSecKeyDataTypePrivate,
        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 the key name */
    if(xmlSecKeySetName(dsigCtx->signKey, BAD_CAST key_name) < 0) {
        fprintf(stderr,"Error: failed to set key name for key from \"%s\"\n", key_file);
        goto done;
    }

    /* sign the template */
    if(xmlSecDSigCtxSign(dsigCtx, signNode) < 0) {
        fprintf(stderr,"Error: signature failed\n");
        goto done;
    }

    /* print signed document to stdout */
    if(xmlDocDump(stdout, doc) < 0) {
        fprintf(stderr, "Error: failed to write the signed document to stdout\n");
        goto done;
    }

    /* success */
    res = 0;

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

    if(doc != NULL) {
        xmlFreeDoc(doc);
    }
    return(res);
}

Input Document: sign2-doc.xml 

<?xml version="1.0" encoding="UTF-8"?>
<!-- 
XML Security Library example: Original XML doc file for sign2 example. 
-->
<Envelope xmlns="urn:envelope">
  <Data>
	Hello, World!
  </Data>
</Envelope>

Result: sign2-res.xml 

<?xml version="1.0" encoding="UTF-8"?>
<!-- 
XML Security Library example: Original XML doc file for sign2 example. 
-->
<Envelope xmlns="urn:envelope">
  <Data>
	Hello, World!
  </Data>
<Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
<SignedInfo>
<CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/>
<SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"/>
<Reference URI="">
<Transforms>
<Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/>
</Transforms>
<DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
<DigestValue>POwWY1qUxMsC7dZaqXVlSZDaQataXRNFAt+aa0eIlKw=</DigestValue>
</Reference>
</SignedInfo>
<SignatureValue>DJYNbr1OEGCXWZHDzQrfVp7HRnb03SstZTLZR00WJTrPINNB3H93LEgz/zGOHjTm
4key8cVFQJn9/pBC26j6Tw==</SignatureValue>
<KeyInfo>
<KeyName>test-key-name</KeyName>
</KeyInfo>
</Signature></Envelope>

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