/**对字符串进行加密。
 * @param $txt
 * @param string $key
 * @return string
 */
public static function lockString($txt,$key='xxx')
{
    $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);
}

/**对字符串进行解密。
 * @param $txt
 * @param string $key
 * @return bool|string
 */
public static function unlockString($txt,$key='xxx')
{
    $txt = urldecode($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);
}