# Signing a dynamically created template

Signs an XML document using a dynamically created signature template.

## Source: `sign2.c`

```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>
 * \endcode
 *
 * Example:
 *
 * \code{.sh}
 *      ./sign2 sign2-doc.xml rsakey.pem > sign2-res.xml
 * \endcode
 *
 * The resulting signature can be validated using the verify1 example:
 *
 * \code{.sh}
 *      ./verify1 sign2-res.xml rsapub.pem
 * \endcode
 */
#include <stdlib.h>
#include <string.h>
#include <assert.h>

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

#ifndef XMLSEC_NO_XSLT
#include <libxslt/xslt.h>
#include <libxslt/security.h>
#endif /* XMLSEC_NO_XSLT */

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

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

int
main(int argc, char **argv) {
#ifndef XMLSEC_NO_XSLT
    xsltSecurityPrefsPtr xsltSecPrefs = NULL;
#endif /* XMLSEC_NO_XSLT */

    assert(argv);

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

    /* Init LibXML2 */
    xmlInitParser();
    LIBXML_TEST_VERSION

    /* Init LibXSLT */
#ifndef XMLSEC_NO_XSLT
    /* disable all XSLT file and network access */
    xsltSecPrefs = xsltNewSecurityPrefs();
    xsltSetSecurityPrefs(xsltSecPrefs,  XSLT_SECPREF_READ_FILE,        xsltSecurityForbid);
    xsltSetSecurityPrefs(xsltSecPrefs,  XSLT_SECPREF_WRITE_FILE,       xsltSecurityForbid);
    xsltSetSecurityPrefs(xsltSecPrefs,  XSLT_SECPREF_CREATE_DIRECTORY, xsltSecurityForbid);
    xsltSetSecurityPrefs(xsltSecPrefs,  XSLT_SECPREF_READ_NETWORK,     xsltSecurityForbid);
    xsltSetSecurityPrefs(xsltSecPrefs,  XSLT_SECPREF_WRITE_NETWORK,    xsltSecurityForbid);
    xsltSetDefaultSecurityPrefs(xsltSecPrefs);
#endif /* XMLSEC_NO_XSLT */

    /* Init XMLSec */
    if(xmlSecInit() < 0) {
        fprintf(stderr, "Error: xmlsec initialization failed.\n");
        return(-1);
    }

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

    /* 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");
        return(-1);
    }
#endif /* XMLSEC_CRYPTO_DYNAMIC_LOADING */

    /* Init crypto library */
    if(xmlSecCryptoAppInit(NULL) < 0) {
        fprintf(stderr, "Error: crypto initialization failed.\n");
        return(-1);
    }

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

    if(sign_file(argv[1], argv[2]) < 0) {
        return(-1);
    }

    /* Shutdown xmlsec-crypto library */
    xmlSecCryptoShutdown();

    /* Shutdown crypto library */
    xmlSecCryptoAppShutdown();

    /* Shutdown XMLSec */
    xmlSecShutdown();

    /* Shutdown LibXSLT / LibXML2*/
#ifndef XMLSEC_NO_XSLT
    xsltFreeSecurityPrefs(xsltSecPrefs);
    xsltCleanupGlobals();
#endif /* XMLSEC_NO_XSLT */
    xmlCleanupParser();

    return(0);
}

/**
 * @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-SHA1 enveloped signature */
    signNode = xmlSecTmplSignatureCreate(doc, xmlSecTransformExclC14NId, xmlSecTransformRsaSha1Id, NULL);
    if(signNode == NULL) {
        fprintf(stderr, "Error: failed to create signature template\n");
        return(NULL);
    }

    /* add <dsig:Signature/> node to the doc */
    xmlAddChild(xmlDocGetRootElement(doc), signNode);

    /* add <dsig:Reference/> node */
    refNode = xmlSecTmplSignatureAddReference(signNode, xmlSecTransformSha1Id, NULL, BAD_CAST "", NULL);
    if(refNode == NULL) {
        fprintf(stderr, "Error: failed to add reference to signature template\n");
        return(NULL);
    }

    /* adds <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.
 * @return 0 on success or a negative value if an error occurs.
 */
int
sign_file(const char* xml_file, const char* key_file) {
    xmlDocPtr doc = NULL;
    xmlNodePtr signNode = NULL;
    xmlSecDSigCtxPtr dsigCtx = NULL;
    int res = -1;

    assert(xml_file);
    assert(key_file);


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

    /* add signature template */
    signNode = create_signature_template(doc);
    if(signNode == NULL) {
        fprintf(stderr, "Error: failed to create signature template\n");
        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 to the file name; this is only an example */
    if(xmlSecKeySetName(dsigCtx->signKey, BAD_CAST 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, signNode) < 0) {
        fprintf(stderr,"Error: signature failed\n");
        goto done;
    }

    /* print signed document to stdout */
    xmlDocDump(stdout, signNode->doc);

    /* success */
    res = 0;

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

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

## Input Document: `sign2-doc.xml`

```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
<?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/2000/09/xmldsig#rsa-sha1"/>
<Reference URI="">
<Transforms>
<Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/>
</Transforms>
<DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/>
<DigestValue>HjY8ilZAIEM2tBbPn5mYO1ieIX4=</DigestValue>
</Reference>
</SignedInfo>
<SignatureValue>fUkinGC3hXEUrjJoq8Uc1Gtky7+4AumhtYV5804diUqbFh/SbQI5iPOnJojz0xZK
WFG9pbfsiWyiqTYlenqDng==</SignatureValue>
<KeyInfo>
<KeyName>rsakey.pem</KeyName>
</KeyInfo>
</Signature></Envelope>
```

