How create an unique 20 single byte token/key/ID on php?

Answer 1

The question is not very clear as to what exactly you want. If you want to generate such a string randomly you can do something like:

$length = 20;
$characters = ‘0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ’;
$random_string = "";    
for ($p = 0; $p < $length; $p++) {
    $random_string .= $characters[mt_rand(0, strlen($characters))];
}

To ensure the newly generated token is unique, you'll have to keep track of all the previously generated tokens and perform a check.

Answer 2

if you want a short unique id you definitely need a database to keep all previous ids.

while (true)
{
    $prefix = "";
    $mid = $prefix . rand(100000,999999) . chr(rand(65, 90));
    $check = mysql_query("SELECT id FROM ids WHERE id = '$mid'");
    if (mysql_num_rows($check) != 0)
    {
        //duplicate
    }
    else
    {
        mysql_query("insert into ids VALUES('$mid')");
        break 1;
    }
}

Answer 3

i think you answered the question in your last comment, yes, generate UIDs directly from your database autoincrement ids + fill characters, for example

function uid($n) {
    $id_part = base_convert($n, 10, 36);
    $rand_part = str_shuffle('abcdefghijklmnopqrstuvwxyz0123456789');
    return sprintf("%05s%.15s", $id_part, $rand_part);
}

this creates an UID with 5 chars base-36 primary id + 15 rubbish chars