<?php

function authcode($string, $operation = 'DECODE', $key = '', $expiry = 0) {

    $ckey_length = 4;

    $key = md5($key ? $key : UC_KEY);

    $keya = md5(substr($key, 0, 16));

    $keyb = md5(substr($key, 16, 16));

    $keyc = $ckey_length ? ($operation == 'DECODE' ? substr($string, 0, $ckey_length) : substr(md5(microtime()), -$ckey_length)) : '';

    $cryptkey = $keya . md5($keya . $keyc);

    $key_length = strlen($cryptkey);

    $string = $operation == 'DECODE' ? base64_decode(substr($string, $ckey_length)) : sprintf('%010d', $expiry ? $expiry + time() : 0) . substr(md5($string . $keyb), 0, 16) . $string;

    $string_length = strlen($string);

    $result = '';

    $box = range(0, 255);

    $rndkey = array();

    for ($i = 0; $i <= 255; $i++) {

        $rndkey[$i] = ord($cryptkey[$i % $key_length]);

    }

    for ($j = $i = 0; $i < 256; $i++) {

        $j = ($j + $box[$i] + $rndkey[$i]) % 256;

        $tmp = $box[$i];

        $box[$i] = $box[$j];

        $box[$j] = $tmp;

    }

    for ($a = $j = $i = 0; $i < $string_length; $i++) {

        $a = ($a + 1) % 256;

        $j = ($j + $box[$a]) % 256;

        $tmp = $box[$a];

        $box[$a] = $box[$j];

        $box[$j] = $tmp;

        $result .= chr(ord($string[$i]) ^ ($box[($box[$a] + $box[$j]) % 256]));

    }

    if ($operation == 'DECODE') {

        if ((substr($result, 0, 10) == 0 || substr($result, 0, 10) - time() > 0) && substr($result, 10, 16) == substr(md5(substr($result, 26) . $keyb), 0, 16)) {

            return substr($result, 26);

        } else {

            return '';

        }

    } else {

        return $keyc . str_replace('=', '', base64_encode($result));

    }

}

echo authcode($string = '5f04rJx7uHz25mDp4vUfC0JB4Nx5nMvyQzHwjRb6kN88N+T9RRipbwbHDIcRWtqXjemcJit26oE1Vu6lpdQPZ6St/obCAEc', $operation = 'DECODE', $key = 'ichunqiu105');

?>