The encryption template has structure similar 
	to the XML Encryption structure as it is described in 
	specification.
	The only difference is that some nodes (for example,
	<enc:CipherValue/>)
	are empty. The XML Security Library sets the content of these
	nodes after doing necessary calculations.
	
Example 2. Creating dynamic encrytion template.
/**
 * 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);
}
		
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