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docs/api/xmlsec-notes-decrypt.html
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Docs update (#869)
29 янв 2025, 20:55
29 янв 2025, 20:55c61a4a9
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<title>Decrypting an encrypted document: XML Security Library Reference Manual</title>
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<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="xmlsec-notes-decrypt"></a>Decrypting an encrypted document</h2></div></div></div>
<p>The typical decryption process includes following steps:
	  </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>
		Load keys, X509 certificates, etc. in the <a class="link" href="xmlsec-keysmngr.html#xmlSecKeysMngr" title="struct xmlSecKeysMngr">keys manager</a> .
	    </p></li>
<li class="listitem"><p>
		Create encryption context <a class="link" href="xmlsec-xmlenc.html#xmlSecEncCtx" title="struct xmlSecEncCtx">xmlSecEncCtx</a>
		using <a class="link" href="xmlsec-xmlenc.html#xmlSecEncCtxCreate" title="xmlSecEncCtxCreate ()">xmlSecEncCtxCreate</a> or
		<a class="link" href="xmlsec-xmlenc.html#xmlSecEncCtxInitialize" title="xmlSecEncCtxInitialize ()">xmlSecEncCtxInitialize</a>
		functions.
	    </p></li>
<li class="listitem"><p>
		Select start decryption &lt;enc:EncryptedData&gt; node.
	    </p></li>
<li class="listitem"><p>
		Decrypt by calling <a class="link" href="xmlsec-xmlenc.html#xmlSecEncCtxDecrypt" title="xmlSecEncCtxDecrypt ()">xmlSecencCtxDecrypt</a> 
		function.
	    </p></li>
<li class="listitem"><p>
		Check returned value and if necessary consume encrypted data.
	    </p></li>
<li class="listitem"><p>
		Destroy encryption context <a class="link" href="xmlsec-xmlenc.html#xmlSecEncCtx" title="struct xmlSecEncCtx">xmlSecEncCtx</a>
		using <a class="link" href="xmlsec-xmlenc.html#xmlSecEncCtxDestroy" title="xmlSecEncCtxDestroy ()">xmlSecEncCtxDestroy</a> or
		<a class="link" href="xmlsec-xmlenc.html#xmlSecEncCtxFinalize" title="xmlSecEncCtxFinalize ()">xmlSecEncCtxFinalize</a>
		functions.
	    </p></li>
</ul></div>
<p>
	</p>
<p>
	     </p>
<div class="example">
<a name="id-1.2.8.4.3.1"></a><p class="title"><b>Example 15. Decrypting a document.</b></p>
<div class="example-contents">
<pre class="programlisting">
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 = xmlParseFile(enc_file);
    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, 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 (%d 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);
}
		</pre>
<p><a class="link" href="xmlsec-decrypt-with-signle-key.html#xmlsec-example-decrypt1" title="decrypt1.c">Full Program Listing</a></p>
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