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<title>Decrypting an encrypted document</title>
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<br clear="all"><div class="SECT1">
<h1 class="SECT1"><a name="XMLSEC-NOTES-DECRYPT">Decrypting an encrypted document</a></h1>
<p>The typical decryption process includes following steps:
</p>
<p></p>
<ul>
<li><p> Load keys, X509 certificates, etc. in the <a href="xmlsec-keysmngr.html#XMLSECKEYSMNGR">keys manager</a> .
</p></li>
<li><p> Create encryption context <a href="xmlsec-xmlenc.html#XMLSECENCCTX">xmlSecEncCtx</a>
using <a href="xmlsec-xmlenc.html#XMLSECENCCTXCREATE">xmlSecEncCtxCreate</a> or
<a href="xmlsec-xmlenc.html#XMLSECENCCTXINITIALIZE">xmlSecEncCtxInitialize</a>
functions.
</p></li>
<li><p> Select start decryption <enc:EncryptedData> node.
</p></li>
<li><p> Decrypt by calling <a href="xmlsec-xmlenc.html#XMLSECENCCTXDECRYPT">xmlSecencCtxDecrypt</a>
function.
</p></li>
<li><p> Check returned value and if necessary consume encrypted data.
</p></li>
<li><p> Destroy encryption context <a href="xmlsec-xmlenc.html#XMLSECENCCTX">xmlSecEncCtx</a>
using <a href="xmlsec-xmlenc.html#XMLSECENCCTXDESTROY">xmlSecEncCtxDestroy</a> or
<a href="xmlsec-xmlenc.html#XMLSECENCCTXFINALIZE">xmlSecEncCtxFinalize</a>
functions.
</p></li>
</ul>
<p> </p>
<div class="EXAMPLE">
<a name="AEN333"></a><p><b>Example 2. Decrypting a document.</b></p>
<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->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;
}
/* decrypt the data */
if((xmlSecEncCtxDecrypt(encCtx, node) < 0) || (encCtx->result == NULL)) {
fprintf(stderr,"Error: decryption failed\n");
goto done;
}
/* print decrypted data to stdout */
if(encCtx->resultReplaced != 0) {
fprintf(stdout, "Decrypted XML data:\n");
xmlDocDump(stdout, doc);
} else {
fprintf(stdout, "Decrypted binary data (%d bytes):\n", xmlSecBufferGetSize(encCtx->result));
if(xmlSecBufferGetData(encCtx->result) != NULL) {
fwrite(xmlSecBufferGetData(encCtx->result),
1,
xmlSecBufferGetSize(encCtx->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 href="xmlsec-decrypt-with-signle-key.html#XMLSEC-EXAMPLE-DECRYPT1">Full Program Listing</a></p>
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