CI_Encryption::decrypt PHP Method

    public function decrypt($data, array $params = NULL)
    {
        if (($params = $this->_get_params($params)) === FALSE) {
            return FALSE;
        }
        if (isset($params['hmac_digest'])) {
            // This might look illogical, but it is done during encryption as well ...
            // The 'base64' value is effectively an inverted "raw data" parameter
            $digest_size = $params['base64'] ? $this->_digests[$params['hmac_digest']] * 2 : $this->_digests[$params['hmac_digest']];
            if (self::strlen($data) <= $digest_size) {
                return FALSE;
            }
            $hmac_input = self::substr($data, 0, $digest_size);
            $data = self::substr($data, $digest_size);
            isset($params['hmac_key']) or $params['hmac_key'] = $this->hkdf($this->_key, 'sha512', NULL, NULL, 'authentication');
            $hmac_check = hash_hmac($params['hmac_digest'], $data, $params['hmac_key'], !$params['base64']);
            // Time-attack-safe comparison
            $diff = 0;
            for ($i = 0; $i < $digest_size; $i++) {
                $diff |= ord($hmac_input[$i]) ^ ord($hmac_check[$i]);
            }
            if ($diff !== 0) {
                return FALSE;
            }
        }
        if ($params['base64']) {
            $data = base64_decode($data);
        }
        isset($params['key']) or $params['key'] = $this->hkdf($this->_key, 'sha512', NULL, self::strlen($this->_key), 'encryption');
        return $this->{'_' . $this->_driver . '_decrypt'}($data, $params);
    }