PHP生成唯一的激活码

<?php  
/** 
 * 生成永远唯一的激活码 
 * @return string 
 */  
function create_guid($namespace = null) {  
    static $guid = '';  
    $uid = uniqid ( "", true );  

    $data = $namespace;  
    $data .= $_SERVER ['REQUEST_TIME'];     // 请求那一刻的时间戳  
    $data .= $_SERVER ['HTTP_USER_AGENT'];  // 获取访问者在用什么操作系统  
    $data .= $_SERVER ['SERVER_ADDR'];      // 服务器IP  
    $data .= $_SERVER ['SERVER_PORT'];      // 端口号  
    $data .= $_SERVER ['REMOTE_ADDR'];      // 远程IP  
    $data .= $_SERVER ['REMOTE_PORT'];      // 端口信息  

    $hash = strtoupper ( hash ( 'ripemd128', $uid . $guid . md5 ( $data ) ) );  
    $guid = '{' . substr ( $hash, 0, 8 ) . '-' . substr ( $hash, 8, 4 ) . '-' . substr ( $hash, 12, 4 ) . '-' . substr ( $hash, 16, 4 ) . '-' . substr ( $hash, 20, 12 ) . '}';  

    return $guid;  
}  

//使用  
echo $key = create_guid ();  
?>  

 function make_coupon_card() {    
        $code = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';    
        $rand = $code[rand(0,25)]    
            .strtoupper(dechex(date('m')))    
            .date('d').substr(time(),-5)    
            .substr(microtime(),2,5)    
            .sprintf('%02d',rand(0,99));    
        for(    
            $a = md5( $rand, true ),    
            $s = '0123456789ABCDEFGHIJKLMNOPQRSTUV',    
            $d = '',    
            $f = 0;    
            $f < 8;    
            $g = ord( $a[ $f ] ),    
            $d .= $s[ ( $g ^ ord( $a[ $f + 8 ] ) ) - $g & 0x1F ],    
            $f++    
        );    
        return $d;    
    }    
    echo make_coupon_card();  

 function getRandomString($len, $chars=null)
    {
        if (is_null($chars)){
            $chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        }  
        mt_srand(10000000*(double)microtime());
        for ($i = 0, $str = '', $lc = strlen($chars)-1; $i < $len; $i++){
            $str .= $chars[mt_rand(0, $lc)];  
        }
        return $str;
    }

参考：http://stackoverflow.com/questions/3521621/php-code-for-generating-decent-looking-coupon-codes-mix-of-alphabets-and-number