Encrypting data with a dynamicaly created template.

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# Encrypting data with a dynamicaly created template. ## encrypt2.c
    /**
     * XML Security Library example: Encrypting XML file with a dynamicaly created template.
     *
     * Encrypts XML file using a dynamicaly created template file and a DES key
     * from a binary file
     *
     * Usage:
     *      ./encrypt2 <xml-doc> <des-key-file>
     *
     * Example:
     *      ./encrypt2 encrypt2-doc.xml deskey.bin > encrypt2-res.xml
     *
     * The result could be decrypted with decrypt1 example:
     *      ./decrypt1 encrypt2-res.xml deskey.bin
     *
     * This is free software; see Copyright file in the source
     * distribution for preciese wording.
     *
     * Copyright (C) 2002-2016 Aleksey Sanin <aleksey@aleksey.com>
     */
    #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>

    int encrypt_file(const char* xml_file, const char* key_file);

    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 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(BAD_CAST XMLSEC_CRYPTO) < 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) envornment variable.\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(encrypt_file(argv[1], argv[2]) < 0) {
            return(-1);
        }

        /* 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);
    }

    /**
     * encrypt_file:
     * @xml_file:           the encryption template file name.
     * @key_file:           the Triple DES key file.
     *
     * Encrypts #xml_file using a dynamicaly created template and DES key from
     * #key_file.
     *
     * Returns 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;
        xmlNodePtr keyInfoNode = NULL;
        xmlSecEncCtxPtr encCtx = NULL;
        int res = -1;

        assert(xml_file);
        assert(key_file);

        /* 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/> and <dsig:KeyName/> nodes to put key name in the signed 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;
        }

        /* 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 DES key, assuming that there is not password */
        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 key name to the file name, this is just an example! */
        if(xmlSecKeySetName(encCtx->encKey, 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;
        }

        /* 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);
    }
## 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>
## 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>