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<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="xmlsec-decrypt-with-signle-key"></a>Decrypting data with a single key.</h2></div></div></div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="xmlsec-example-decrypt1"></a>decrypt1.c</h3></div></div></div>
<div class="informalexample"><pre class="programlisting">
/**
 * XML Security Library example: Decrypting an encrypted file using a single key.
 *
 * Decrypts encrypted XML file using a single DES key from a binary file
 *
 * Usage:
 *      ./decrypt1 &lt;xml-enc&gt; &lt;des-key-file&gt;
 *
 * Example:
 *      ./decrypt1 encrypt1-res.xml deskey.bin
 *      ./decrypt1 encrypt2-res.xml deskey.bin
 *
 * This is free software; see Copyright file in the source
 * distribution for preciese wording.
 *
 * Copyright (C) 2002-2024 Aleksey Sanin &lt;aleksey@aleksey.com&gt;. All Rights Reserved.
 */
#include &lt;stdlib.h&gt;
#include &lt;string.h&gt;
#include &lt;assert.h&gt;

#include &lt;libxml/tree.h&gt;
#include &lt;libxml/xmlmemory.h&gt;
#include &lt;libxml/parser.h&gt;

#ifndef XMLSEC_NO_XSLT
#include &lt;libxslt/xslt.h&gt;
#include &lt;libxslt/security.h&gt;
#endif /* XMLSEC_NO_XSLT */

#include &lt;xmlsec/xmlsec.h&gt;
#include &lt;xmlsec/xmltree.h&gt;
#include &lt;xmlsec/xmlenc.h&gt;
#include &lt;xmlsec/crypto.h&gt;

int decrypt_file(const char* enc_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 &lt;enc-file&gt; &lt;key-file&gt;\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() &lt; 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) &lt; 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) &lt; 0) {
        fprintf(stderr, "Error: crypto initialization failed.\n");
        return(-1);
    }

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

    if(decrypt_file(argv[1], argv[2]) &lt; 0) {
        return(-1);
    }

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

    /* Shutdown crypto library */
    xmlSecCryptoAppShutdown();

    /* Shutdown xmlsec library */
    xmlSecShutdown();

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

    return(0);
}

/**
 * decrypt_file:
 * @enc_file:           the encrypted XML  file name.
 * @key_file:           the Triple DES key file.
 *
 * Decrypts the XML file #enc_file using DES key from #key_file and
 * prints results to stdout.
 *
 * Returns 0 on success or a negative value if an error occurs.
 */
int
decrypt_file(const char* enc_file, const char* key_file) {
    xmlDocPtr doc = NULL;
    xmlNodePtr node = NULL;
    xmlSecEncCtxPtr encCtx = NULL;
    int res = -1;

    assert(enc_file);
    assert(key_file);

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

    /* find start node */
    node = xmlSecFindNode(xmlDocGetRootElement(doc), xmlSecNodeEncryptedData, xmlSecEncNs);
    if(node == NULL) {
        fprintf(stderr, "Error: start node not found in \"%s\"\n", enc_file);
        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 */
    encCtx-&gt;encKey = xmlSecKeyReadBinaryFile(xmlSecKeyDataDesId, key_file);
    if(encCtx-&gt;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-&gt;encKey, BAD_CAST key_file) &lt; 0) {
        fprintf(stderr,"Error: failed to set key name for key from \"%s\"\n", key_file);
        goto done;
    }

    /* decrypt the data */
    if((xmlSecEncCtxDecrypt(encCtx, node) &lt; 0) || (encCtx-&gt;result == NULL)) {
        fprintf(stderr,"Error: decryption failed\n");
        goto done;
    }

    /* print decrypted data to stdout */
    if(encCtx-&gt;resultReplaced != 0) {
        fprintf(stdout, "Decrypted XML data:\n");
        xmlDocDump(stdout, doc);
    } else {
        fprintf(stdout, "Decrypted binary data (" XMLSEC_SIZE_FMT " bytes):\n",
            xmlSecBufferGetSize(encCtx-&gt;result));
        if(xmlSecBufferGetData(encCtx-&gt;result) != NULL) {
            fwrite(xmlSecBufferGetData(encCtx-&gt;result),
                  1,
                  xmlSecBufferGetSize(encCtx-&gt;result),
                  stdout);
        }
    }
    fprintf(stdout, "\n");

    /* success */
    res = 0;

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

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

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