Encrypting data with a session key.: XML Security Library Reference Manual

## Encrypting data with a session key.

### encrypt3.c

    /**
     * XML Security Library example: Encrypting XML file with a session key and dynamicaly created template.
     *
     * Encrypts XML file using a dynamicaly created template file and a session
     * DES key (encrypted with an RSA key).
     *
     * Usage:
     *      ./encrypt3 <xml-doc> <rsa-pem-key-file>
     *
     * Example:
     *      ./encrypt3 encrypt3-doc.xml rsakey.pem > encrypt3-res.xml
     *
     * The result could be decrypted with decrypt3 example:
     *      ./decrypt3 encrypt3-res.xml
     *
     * This is free software; see Copyright file in the source
     * distribution for preciese wording.
     *
     * Copyright (C) 2002-2024 Aleksey Sanin <aleksey@aleksey.com>. All Rights Reserved.
     */
    #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 libxml and libxslt libraries */
        xmlInitParser();
        LIBXML_TEST_VERSION
        xmlLoadExtDtdDefaultValue = XML_DETECT_IDS | XML_COMPLETE_ATTRS;
        xmlSubstituteEntitiesDefault(1);
    #ifndef XMLSEC_NO_XSLT
        xmlIndentTreeOutput = 1;
    #endif /* XMLSEC_NO_XSLT */

        /* Init libxslt */
    #ifndef XMLSEC_NO_XSLT
        /* disable everything */
        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 library */
        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 library */
        xmlSecShutdown();

        /* Shutdown libxslt/libxml */
    #ifndef XMLSEC_NO_XSLT
        xsltFreeSecurityPrefs(xsltSecPrefs);
        xsltCleanupGlobals();
    #endif /* XMLSEC_NO_XSLT */
        xmlCleanupParser();

        return(0);
    }

    /**
     * load_rsa_keys:
     * @key_file:           the key filename.
     *
     * Creates simple keys manager and load RSA key from #key_file in it.
     * The caller is responsible for destroying returned keys manager using
     * @xmlSecKeysMngrDestroy.
     *
     * Returns 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 = xmlSecCryptoAppKeyLoad(key_file, 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 key name to the file name, this is just 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);
    }

    /**
     * encrypt_file:
     * @mngr:               the pointer to keys manager.
     * @xml_file:           the encryption template file name.
     * @key_name:           the RSA key name.
     *
     * Encrypts #xml_file using a dynamicaly created template, a session DES key
     * and an RSA key from keys manager.
     *
     * Returns 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 = xmlParseFile(xml_file);
        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;
        }

        /* we template is inserted in the doc */
        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);
    }

### 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>

### 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>QYYKljhcX20QyP20hYmq8CSES875oIdbrsjMOxnb0VnYDn01Jk00OIPpb9gdIdZg
    MLOtSy26mWrQ+XqfPGuyaA==</CipherValue>
    </CipherData>
    </EncryptedKey>
    </KeyInfo>
    <CipherData>
    <CipherValue>+UiDv73SE8K8KwXuOmHLHK7N2hNWDakTAEu6NprbCdULC1w/LXT9FLtNRJetmwwO
    XpBqTY56AAMeMgpxPWN3SPO0ETeQw7pR+bp0IjUvcGlFSXz6yE1qgQ==</CipherValue>
    </CipherData>
    </EncryptedData>