<?php
function str_auth($string, $operation = 'ENCODE', $key = '', $expiry = 0) { 
    $ckey_length = 4; 
    $key = md5($key!=''?$key:'www_uxuew_cn'); //加密秘钥
    $keya = md5(substr($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 = $operation == 'DECODE' ? base64_decode(strtr(substr($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 $keyc.rtrim(strtr(base64_encode($result), '+/', '-_'), '='); 
    } 
} 

var_dump(str_auth('jack'));

$string = '0494_qUPiWkv2NluPFEHdqqlimykBHNmnsXd9oTFultD';

var_dump(str_auth($string,'DECODE'));

?>