Fixed length random code generator

Question

I need to assign a random name to a PDF file of 20 digits (numbers). This code has to be generated from a unique person ID.

Example:

Person ID                                           File name
----------                                          ------------------------
40352142N ---------> random code generator -------> XXXXXXXXXXXXXXXXXXXX.pdf

It would be great if you could generate the person ID from the file name as well. It must be reversible but only if you know the formula.

What would be the best way to do it in PHP or ASP. Any ideas on how to elegantly implement this?

Thank you!

Answer 1

<?php
function randomNumber( $len) {
    $rand   = '';
    while( !( isset( $rand[$len-1] ) ) ) {
        $rand   .= mt_rand( );
    }
    return substr( $rand , 0 , $len );
}

echo randomNumber(20); ?>

use this code

Answer 2

Try this:-

$_rand = "0123456789abcdefghijklmnopqrstuvwxyz";
$str = '';
for( $i = 0; $i < 20; $i++ )
{
   $str .= substr( $_rand, rand( 0, ( strlen( $_rand ) - 1 ) ), 1 );
}

Answer 3

Using sha1 to get a unique hash, we then convert every char to number. Note: This decrease sha1 robustness because we only use a part of it. Plus the modulo isn't quite correct because it's apply on a range of 255.

<?php

$sha = sha1('test', 1);
$name = '';
for($i = 0; $i < 20; ++$i) {
    $name .= ord($sha[$i])%10;
}
echo $name;