php 之 字符加密解密

<?php 
//加密函数 
function lock_url($txt,$key='liiu'){ 
    $chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-=+"; 
    $nh = rand(0,64); 
    $ch = $chars[$nh]; 
    $mdKey = md5($key.$ch); 
    $mdKey = substr($mdKey,$nh%8, $nh%8+7); 
    $txt = base64_encode($txt); 
    $tmp = ''; 
    $i=0;$j=0;$k = 0; 
    for ($i=0; $i<strlen($txt); $i++) { 
        $k = $k == strlen($mdKey) ? 0 : $k; 
        $j = ($nh+strpos($chars,$txt[$i])+ord($mdKey[$k++]))%64; 
        $tmp .= $chars[$j]; 
    } 
    return urlencode($ch.$tmp); 
} 
//解密函数 
function unlock_url($txt,$key='liiu'){ 
    $txt = urldecode($txt); 
    $chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-=+"; 
    $ch = $txt[0]; 
    $nh = strpos($chars,$ch); 
    $mdKey = md5($key.$ch); 
    $mdKey = substr($mdKey,$nh%8, $nh%8+7); 
    $txt = substr($txt,1); 
    $tmp = ''; 
    $i=0;$j=0; $k = 0; 
    for ($i=0; $i<strlen($txt); $i++) { 
        $k = $k == strlen($mdKey) ? 0 : $k; 
        $j = strpos($chars,$txt[$i])-$nh - ord($mdKey[$k++]); 
        while ($j<0) $j+=64; 
        $tmp .= $chars[$j]; 
    } 
    return base64_decode($tmp); 
} 

echo lock_url('123');//H58Fc
echo "<br>";
echo unlock_url('x22fF');
?>