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

Encrypting data with a dynamically created template

Encrypts an XML document using a dynamically created encryption template.

Source: encrypt2.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: Encrypting an XML file with a dynamically created template.
 * @details Encrypts an XML file using a dynamically created template and a Triple DES key
 * from a binary file.
 *
 * Usage:
 *
 * \code{.sh}
 *      ./encrypt2 <xml-doc> <des-key-file>
 * \endcode
 *
 * Example:
 *
 * \code{.sh}
 *      ./encrypt2 encrypt2-doc.xml deskey.bin > encrypt2-res.xml
 * \endcode
 *
 * The result can be decrypted using the decrypt1 example:
 *
 * \code{.sh}
 *      ./decrypt1 encrypt2-res.xml deskey.bin
 * \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/xmlenc.h>
#include <xmlsec/templates.h>
#include <xmlsec/crypto.h>
#include <xmlsec/dl.h>

int encrypt_file(const char* xml_file, const char* key_file);
xmlNodePtr create_encryption_template(xmlDocPtr doc);

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

    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 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;

    /* encrypt file */
    if(encrypt_file(argv[1], argv[2]) < 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 Creates encryption template to encrypt the XML file.
 * @param doc the XML document.
 * @return pointer to the <enc:EncryptedData/> node or NULL if an error occurs.
 */
xmlNodePtr
create_encryption_template(xmlDocPtr doc) {
    xmlNodePtr encDataNode = NULL;
    xmlNodePtr keyInfoNode = NULL;

    assert(doc);

    /* add <enc:EncryptedData/> node to encrypt XML file and replace its content with encryption result */
    encDataNode = xmlSecTmplEncDataCreate(doc, xmlSecTransformDes3CbcId, NULL, xmlSecTypeEncElement, NULL, NULL);
    if(encDataNode == NULL) {
        fprintf(stderr, "Error: failed to create encryption template\n");
        return(NULL);
    }

    /* add <enc:CipherValue/> node */
    if(xmlSecTmplEncDataEnsureCipherValue(encDataNode) == NULL) {
        fprintf(stderr, "Error: failed to add CipherValue node\n");
        goto done;
    }

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

    /* success */
    return(encDataNode);

done:
    /* free the partially created template node and its subtree */
    xmlFreeNode(encDataNode);
    return(NULL);
}

/**
 * @brief Encrypts an XML file using a dynamically created template and Triple DES key.
 * @details Encrypts #xml_file using a dynamically created template and the Triple DES key
 * from #key_file.
 * @param xml_file the XML file name.
 * @param key_file the Triple DES key file.
 * @return 0 on success or a negative value if an error occurs.
 */
int
encrypt_file(const char* xml_file, const char* key_file) {
    xmlDocPtr doc = NULL;
    xmlNodePtr encDataNode = NULL;
    xmlSecEncCtxPtr encCtx = NULL;
    int res = -1;

    assert(xml_file);
    assert(key_file);

    /* load XML 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;
    }

    /* create encryption template */
    encDataNode = create_encryption_template(doc);
    if(encDataNode == NULL) {
        goto done;
    }

    /* create encryption context, we don't need keys manager in this example */
    encCtx = xmlSecEncCtxCreate(NULL);
    if(encCtx == NULL) {
        fprintf(stderr,"Error: failed to create encryption context\n");
        goto done;
    }

    /* load Triple DES key */
    encCtx->encKey = xmlSecKeyReadBinaryFile(xmlSecKeyDataDesId, key_file);
    if(encCtx->encKey == NULL) {
        fprintf(stderr,"Error: failed to load des key from binary file \"%s\"\n", key_file);
        goto done;
    }

    /* set the key name to the file name; this is only an example */
    if(xmlSecKeySetName(encCtx->encKey, BAD_CAST key_file) < 0) {
        fprintf(stderr,"Error: failed to set key name for key from \"%s\"\n", key_file);
        goto done;
    }

    /* encrypt the data */
    if(xmlSecEncCtxXmlEncrypt(encCtx, encDataNode, xmlDocGetRootElement(doc)) < 0) {
        fprintf(stderr,"Error: encryption failed\n");
        goto done;
    }

    /* the template is inserted into the document */
    encDataNode = NULL;

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

    /* success */
    res = 0;

done:

    /* cleanup */
    if(encCtx != NULL) {
        xmlSecEncCtxDestroy(encCtx);
    }

    if(encDataNode != NULL) {
        xmlUnlinkNode(encDataNode);
        xmlFreeNode(encDataNode);
    }

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

Input Document: encrypt2-doc.xml 

<?xml version="1.0" encoding="UTF-8"?>
<!-- 
XML Security Library example: Original XML doc file before encryption (encrypt2 example). 
-->
<Envelope xmlns="urn:envelope">
  <Data>
	Hello, World!
  </Data>
</Envelope>

Result: encrypt2-res.xml 

<?xml version="1.0" encoding="UTF-8"?>
<!-- 
XML Security Library example: Encrypted XML file (encrypt2 example). 
-->
<EncryptedData xmlns="http://www.w3.org/2001/04/xmlenc#" Type="http://www.w3.org/2001/04/xmlenc#Element">
<EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#tripledes-cbc"/>
<KeyInfo xmlns="http://www.w3.org/2000/09/xmldsig#">
<KeyName>deskey.bin</KeyName>
</KeyInfo>
<CipherData>
<CipherValue>WXlDyktaADlUe+PywKwS3KdKlahCteEKxi/hRlHcXNQlGwNGrYKy8aQ6dLtX1bKg
IgL/XoAQN3B27zD91b1ZLGh6QQ9CjnVD98+hYJ9TPp4piPnII4vGUA==</CipherValue>
</CipherData>
</EncryptedData>

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