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Aleksey Sanin edited this page Apr 11, 2026 · 2 revisions

Encrypting data with a session key

Encrypts an XML document using a session key wrapped with an RSA key from the keys manager.

Source: encrypt3.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 session key and a dynamically created template.
 * @details Encrypts an XML file using a dynamically created template and a session
 * DES key (encrypted with an RSA key).
 *
 * Usage:
 *
 * \code{.sh}
 *      ./encrypt3 <xml-doc> <rsa-pem-key-file>
 * \endcode
 *
 * Example (note: we are using the private key here instead of the public
 * key to make decrypt3 example work):
 *
 * \code{.sh}
 *      ./encrypt3 encrypt3-doc.xml rsakey.pem > encrypt3-res.xml
 * \endcode
 *
 * The result can be decrypted using the decrypt3 example:
 *
 * \code{.sh}
 *      ./decrypt3 encrypt3-res.xml
 * \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/xmlenc.h>
#include <xmlsec/templates.h>
#include <xmlsec/crypto.h>

xmlSecKeysMngrPtr load_rsa_keys(char* key_file);
int encrypt_file(xmlSecKeysMngrPtr mngr, const char* xml_file, const char* key_name);

int
main(int argc, char **argv) {
    xmlSecKeysMngrPtr mngr;
#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);
    }

    /* create keys manager and load keys */
    mngr = load_rsa_keys(argv[2]);
    if(mngr == NULL) {
        return(-1);
    }

    /* we use key filename as key name here */
    if(encrypt_file(mngr, argv[1], argv[2]) < 0) {
        xmlSecKeysMngrDestroy(mngr);
        return(-1);
    }

    /* destroy keys manager */
    xmlSecKeysMngrDestroy(mngr);

    /* 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 Creates a keys manager and loads an RSA key from a file.
 * @details Creates a simple keys manager and loads the RSA key from #key_file into it.
 * The caller is responsible for destroying returned keys manager using
 * #xmlSecKeysMngrDestroy.
 * @param key_file the key filename.
 * @return the pointer to newly created keys manager or NULL if an error
 * occurs.
 */
xmlSecKeysMngrPtr
load_rsa_keys(char* key_file) {
    xmlSecKeysMngrPtr mngr;
    xmlSecKeyPtr key;

    assert(key_file);

    /* create and initialize keys manager, we use a simple list based
     * keys manager, implement your own xmlSecKeysStore klass if you need
     * something more sophisticated
     */
    mngr = xmlSecKeysMngrCreate();
    if(mngr == NULL) {
        fprintf(stderr, "Error: failed to create keys manager.\n");
        return(NULL);
    }
    if(xmlSecCryptoAppDefaultKeysMngrInit(mngr) < 0) {
        fprintf(stderr, "Error: failed to initialize keys manager.\n");
        xmlSecKeysMngrDestroy(mngr);
        return(NULL);
    }

    /* load private RSA key */
    key = xmlSecCryptoAppKeyLoadEx(key_file, xmlSecKeyDataTypePublic | xmlSecKeyDataTypePrivate, xmlSecKeyDataFormatPem, NULL, NULL, NULL);
    if(key == NULL) {
        fprintf(stderr,"Error: failed to load rsa key from file \"%s\"\n", key_file);
        xmlSecKeysMngrDestroy(mngr);
        return(NULL);
    }

    /* set the key name to the file name; this is only an example */
    if(xmlSecKeySetName(key, BAD_CAST key_file) < 0) {
        fprintf(stderr,"Error: failed to set key name for key from \"%s\"\n", key_file);
        xmlSecKeyDestroy(key);
        xmlSecKeysMngrDestroy(mngr);
        return(NULL);
    }

    /* add key to keys manager, from now on keys manager is responsible
     * for destroying key
     */
    if(xmlSecCryptoAppDefaultKeysMngrAdoptKey(mngr, key) < 0) {
        fprintf(stderr,"Error: failed to add key from \"%s\" to keys manager\n", key_file);
        xmlSecKeyDestroy(key);
        xmlSecKeysMngrDestroy(mngr);
        return(NULL);
    }

    return(mngr);
}

/**
 * @brief Encrypts an XML file using a session DES key and RSA key transport.
 * @details Encrypts #xml_file using a dynamically created template, a session DES key,
 * and an RSA key from the keys manager.
 * @param mngr the pointer to keys manager.
 * @param xml_file the encryption template file name.
 * @param key_name the RSA key name.
 * @return 0 on success or a negative value if an error occurs.
 */
int
encrypt_file(xmlSecKeysMngrPtr mngr, const char* xml_file, const char* key_name) {
    xmlDocPtr doc = NULL;
    xmlNodePtr encDataNode = NULL;
    xmlNodePtr keyInfoNode = NULL;
    xmlNodePtr encKeyNode = NULL;
    xmlNodePtr keyInfoNode2 = NULL;
    xmlSecEncCtxPtr encCtx = NULL;
    int res = -1;

    assert(mngr);
    assert(xml_file);
    assert(key_name);

    /* load template */
    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;
    }

    /* create encryption template 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");
        goto done;
    }

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

    /* add <dsig:KeyInfo/> */
    keyInfoNode = xmlSecTmplEncDataEnsureKeyInfo(encDataNode, NULL);
    if(keyInfoNode == NULL) {
        fprintf(stderr, "Error: failed to add key info\n");
        goto done;
    }

    /* add <enc:EncryptedKey/> to store the encrypted session key */
    encKeyNode = xmlSecTmplKeyInfoAddEncryptedKey(keyInfoNode,
                                    xmlSecTransformRsaPkcs1Id,
                                    NULL, NULL, NULL);
    if(encKeyNode == NULL) {
        fprintf(stderr, "Error: failed to add key info\n");
        goto done;
    }

    /* we want to put encrypted key in the <enc:CipherValue/> node */
    if(xmlSecTmplEncDataEnsureCipherValue(encKeyNode) == NULL) {
        fprintf(stderr, "Error: failed to add CipherValue node\n");
        goto done;
    }

    /* add <dsig:KeyInfo/> and <dsig:KeyName/> nodes to <enc:EncryptedKey/> */
    keyInfoNode2 = xmlSecTmplEncDataEnsureKeyInfo(encKeyNode, NULL);
    if(keyInfoNode2 == NULL) {
        fprintf(stderr, "Error: failed to add key info\n");
        goto done;
    }

    /* set key name so we can lookup key when needed */
    if(xmlSecTmplKeyInfoAddKeyName(keyInfoNode2, BAD_CAST key_name) == NULL) {
        fprintf(stderr, "Error: failed to add key name\n");
        goto done;
    }

    /* create encryption context */
    encCtx = xmlSecEncCtxCreate(mngr);
    if(encCtx == NULL) {
        fprintf(stderr,"Error: failed to create encryption context\n");
        goto done;
    }

    /* generate a Triple DES key */
    encCtx->encKey = xmlSecKeyGenerate(xmlSecKeyDataDesId, 192, xmlSecKeyDataTypeSession);
    if(encCtx->encKey == NULL) {
        fprintf(stderr,"Error: failed to generate session des key\n");
        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 */
    xmlDocDump(stdout, doc);

    /* success */
    res = 0;

done:

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

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

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

Input Document: encrypt3-doc.xml 

<?xml version="1.0" encoding="UTF-8"?>
<!-- 
XML Security Library example: Original XML doc file before encryption (encrypt3 example). 
-->
<Envelope xmlns="urn:envelope">
  <Data>
	Hello, World!
  </Data>
</Envelope>

Result: encrypt3-res.xml 

<?xml version="1.0" encoding="UTF-8"?>
<!-- 
XML Security Library example: Original XML doc file before encryption (encrypt3 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#">
<EncryptedKey xmlns="http://www.w3.org/2001/04/xmlenc#">
<EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#rsa-1_5"/>
<KeyInfo xmlns="http://www.w3.org/2000/09/xmldsig#">
<KeyName>rsakey.pem</KeyName>
</KeyInfo>
<CipherData>
<CipherValue>pFfhaCpQfHTOJ+mRN919Ia3JimY2AS/8u9pimLEWGGjh3egy3pE2st4+YoVkpS4G
XyUU4Ps+KRzsdJcKI4moXQ==</CipherValue>
</CipherData>
</EncryptedKey>
</KeyInfo>
<CipherData>
<CipherValue>PMuoILFXjCmMg2pCzrmJYZcySLsTzgGYRX2ymYV9tLVrNSPhWV2mwMHWMchSWH9b
8pRgdaJ3msWmN3EqqElV1Y5wEDQjB5nMz7Tsz3+QmrAxGfxj7bCPyw==</CipherValue>
</CipherData>
</EncryptedData>

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