<chapter id="xmlsec-notes-verify-decrypt">
    <title>Verifing and decrypting documents.</title>
    <sect1 id="xmlsec-notes-verify-decrypt-overview">
        <title>Overview.</title>
        <para>Since the template is just an XML file, it might be created in advance 
	and saved in a file. It's also possible for application to create 
	templates without using XML Security Library functions. Also in some 
	cases template should be inserted in the signed or encrypted data 
	(for example, if you want to create an enveloped or enveloping 
	signature).</para>
	<para>Signature verification and data decryption do not require template 
	because all the necessary information is provided in the signed or 
	encrypted document.
    	  <figure>
	    <title>The verification or decryption processing model.</title>
	    <graphic fileref="images/verif-dec-model.png" align="center"></graphic>
	  </figure>	 
	</para>
    </sect1>
    
    <sect1 id="xmlsec-notes-verify" >
	<title>Verifying a signed document</title>
	<para>The typical siganture verification process includes following steps:
	  <itemizedlist>
	    <listitem><para>
		Load keys, X509 certificates, etc. in the <link linkend="xmlSecKeysMngr">keys manager</link> .
	    </para></listitem>
	    <listitem><para>
		Create signature context <link linkend="xmlSecDSigCtx">xmlSecDSigCtx</link>
		using <link linkend="xmlSecDSigCtxCreate">xmlSecDSigCtxCreate</link> or
		<link linkend="xmlSecDSigCtxInitialize">xmlSecDSigCtxInitialize</link>
		functions.
	    </para></listitem>
	    <listitem><para>
		Select start verification 
    		<ulink URL="http://www.w3.org/TR/xmldsig-core/#sec-Signature">&lt;dsig:Signature/&gt;</ulink>
		node in the signed XML document.
	    </para></listitem>
	    <listitem><para>
		Verify signature by calling <link linkend="xmlSecDSigCtxVerify">xmlSecDSigCtxVerify</link> 
		function.
	    </para></listitem>
	    <listitem><para>
		Check returned value and verification status (<structfield>status</structfield>
		member of <link linkend="xmlSecDSigCtx">xmlSecDSigCtx</link> structure).
		If necessary, consume returned data from the <link linkend="xmlSecDSigCtx">context</link>.
	    </para></listitem>
	    <listitem><para>
		Destroy signature context <link linkend="xmlSecDSigCtx">xmlSecDSigCtx</link>
		using <link linkend="xmlSecDSigCtxDestroy">xmlSecDSigCtxDestroy</link> or
		<link linkend="xmlSecDSigCtxFinalize">xmlSecDSigCtxFinalize</link>
		functions.
	    </para></listitem>
	  </itemizedlist>
	</para>
	<para>
	     <example>
		<title>Verifying a document.</title>
		<programlisting><![CDATA[
/** 
 * verify_file:
 * @xml_file:		the signed XML file name.
 * @key_file:		the PEM public key file name.
 *
 * Verifies XML signature in #xml_file using public key from #key_file.
 *
 * Returns 0 on success or a negative value if an error occurs.
 */
int 
verify_file(const char* xml_file, const char* key_file) {
    xmlDocPtr doc = NULL;
    xmlNodePtr node = NULL;
    xmlSecDSigCtxPtr dsigCtx = NULL;
    int res = -1;
    
    assert(xml_file);
    assert(key_file);

    /* load file */
    doc = xmlParseFile(xml_file);
    if ((doc == NULL) || (xmlDocGetRootElement(doc) == NULL)){
	fprintf(stderr, "Error: unable to parse file \"%s\"\n", xml_file);
	goto done;	
    }
    
    /* find start node */
    node = xmlSecFindNode(xmlDocGetRootElement(doc), xmlSecNodeSignature, xmlSecDSigNs);
    if(node == NULL) {
	fprintf(stderr, "Error: start node not found in \"%s\"\n", xml_file);
	goto done;	
    }

    /* create signature context, we don't need keys manager in this example */
    dsigCtx = xmlSecDSigCtxCreate(NULL);
    if(dsigCtx == NULL) {
        fprintf(stderr,"Error: failed to create signature context\n");
	goto done;
    }

    /* load public key */
    dsigCtx->signKey = xmlSecCryptoAppKeyLoad(key_file,xmlSecKeyDataFormatPem, NULL, NULL, NULL);
    if(dsigCtx->signKey == NULL) {
        fprintf(stderr,"Error: failed to load public pem key from \"%s\"\n", key_file);
	goto done;
    }

    /* set key name to the file name, this is just an example! */
    if(xmlSecKeySetName(dsigCtx->signKey, key_file) < 0) {
    	fprintf(stderr,"Error: failed to set key name for key from \"%s\"\n", key_file);
	goto done;
    }

    /* Verify signature */
    if(xmlSecDSigCtxVerify(dsigCtx, node) < 0) {
        fprintf(stderr,"Error: signature verify\n");
	goto done;
    }
        
    /* print verification result to stdout */
    if(dsigCtx->status == xmlSecDSigStatusSucceeded) {
	fprintf(stdout, "Signature is OK\n");
    } else {
	fprintf(stdout, "Signature is INVALID\n");
    }    

    /* success */
    res = 0;

done:    
    /* cleanup */
    if(dsigCtx != NULL) {
	xmlSecDSigCtxDestroy(dsigCtx);
    }
    
    if(doc != NULL) {
	xmlFreeDoc(doc); 
    }
    return(res);
}
		]]></programlisting>
	    <simpara><link linkend="xmlsec-example-verify1">Full Program Listing</link></simpara>
	    </example>
	</para>
    </sect1>

    <sect1 id="xmlsec-notes-decrypt" >
	<title>Decrypting an encrypted document</title>
	<para>The typical decryption process includes following steps:
	  <itemizedlist>
	    <listitem><para>
		Load keys, X509 certificates, etc. in the <link linkend="xmlSecKeysMngr">keys manager</link> .
	    </para></listitem>
	    <listitem><para>
		Create encryption context <link linkend="xmlSecEncCtx">xmlSecEncCtx</link>
		using <link linkend="xmlSecEncCtxCreate">xmlSecEncCtxCreate</link> or
		<link linkend="xmlSecEncCtxInitialize">xmlSecEncCtxInitialize</link>
		functions.
	    </para></listitem>
	    <listitem><para>
		Select start decryption &lt;enc:EncryptedData&gt; node.
	    </para></listitem>
	    <listitem><para>
		Decrypt by calling <link linkend="xmlSecEncCtxDecrypt">xmlSecencCtxDecrypt</link> 
		function.
	    </para></listitem>
	    <listitem><para>
		Check returned value and if necessary consume encrypted data.
	    </para></listitem>
	    <listitem><para>
		Destroy encryption context <link linkend="xmlSecEncCtx">xmlSecEncCtx</link>
		using <link linkend="xmlSecEncCtxDestroy">xmlSecEncCtxDestroy</link> or
		<link linkend="xmlSecEncCtxFinalize">xmlSecEncCtxFinalize</link>
		functions.
	    </para></listitem>
	  </itemizedlist>
	</para>
	<para>
	     <example>
		<title>Decrypting a document.</title>
		<programlisting><![CDATA[
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);
}
		]]></programlisting>
	    <simpara><link linkend="xmlsec-example-decrypt1">Full Program Listing</link></simpara>
	    </example>
	</para>
    </sect1>
</chapter>