加密与解密

function lock_url($txt,$key='www')
{
    $txt = $txt.$key;
    $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(base64_encode($ch.$tmp));
}
//解密函数
function unlock_url($txt,$key='www')
{
    $txt = base64_decode(urldecode($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 trim(base64_decode($tmp),$key);
}