+/**
+ * Decrypt file.
+ * @param $fp_src file path to the file to decrypt.
+ * @param $fp_dst file path to the file to write decrypted file (could be the same).
+ * @param $k string composed of the key and the iv separated by a point ('.')
+ * @return key used to decrypt. a string of length 0 is returned if failed.
+ */
+function
+jirafeau_decrypt_file ($fp_src, $fp_dst, $k)
+{
+ $fs = filesize ($fp_src);
+ if ($fs === false || $fs == 0 || !(extension_loaded('mcrypt') == true))
+ return false;
+
+ /* Init module */
+ $m = mcrypt_module_open('rijndael-256', '', 'ofb', '');
+ /* Extract key and iv. */
+ $crypt_key = $k;
+ $md5_key = md5($crypt_key);
+ $iv = jirafeau_crypt_create_iv ($md5_key, mcrypt_enc_get_iv_size($m));
+ /* Decrypt file. */
+ $r = fopen ($fp_src, 'r');
+ $w = fopen ($fp_dst, 'c');
+ while (!feof ($r))