Serial generation with PHP

Question

Throughout my days as a PHP Programmer and a beginner at C# programming I've always wondered of the best way to generate unique serials such as how Microsoft Office and Microsoft operating systems do.

Does anyone have a good guide to how to handle this, Like what are the important factors in generating the unique serial, prevent duplicates etc. small example on how to create / verify them.

Here is the RFC I'm talking about: http://tools.ietf.org/html/rfc1982.

Answer 1

Here's our solution. It generates a key with a configurable size/length and optional suffix based on a valid IPv4, Userid (or any meaningful integer), or text string. It also avoids ambiguous characters (i,1,l,0,o,O) in the standard result.

We append the Userid in the license, and can later convert that portion back to a base10 integer and check if it's valid against the user account that is using the license.

$license = generate_license();
// YF6G2-HJQEZ-8JZKY-8C8ZN

$license = generate_license(123456);
// ZJK82N-8GA5AR-ZSPQVX-2N9C

$license = generate_license($_SERVER['REMOTE_ADDR']);
// M9H7FP-996BNB-77Y9KW-ARUP4

$license = generate_license('my text suffix');
// Q98K2F-THAZWG-HJ8R56-MY-TEXT-SUFFIX

We do check uniqueness in the database when created, but using the IP/Userid in conjunction with the randomness, the likelihood of duplicates is virtually zero.

/**
* Generate a License Key.
* Optional Suffix can be an integer or valid IPv4, either of which is converted to Base36 equivalent
* If Suffix is neither Numeric or IPv4, the string itself is appended
*
* @param   string  $suffix Append this to generated Key.
* @return  string
*/
function generate_license($suffix = null) {
    // Default tokens contain no "ambiguous" characters: 1,i,0,o
    if(isset($suffix)){
        // Fewer segments if appending suffix
        $num_segments = 3;
        $segment_chars = 6;
    }else{
        $num_segments = 4;
        $segment_chars = 5;
    }
    $tokens = 'ABCDEFGHJKLMNPQRSTUVWXYZ23456789';
    $license_string = '';
    // Build Default License String
    for ($i = 0; $i < $num_segments; $i++) {
        $segment = '';
        for ($j = 0; $j < $segment_chars; $j++) {
            $segment .= $tokens[rand(0, strlen($tokens)-1)];
        }
        $license_string .= $segment;
        if ($i < ($num_segments - 1)) {
            $license_string .= '-';
        }
    }
    // If provided, convert Suffix
    if(isset($suffix)){
        if(is_numeric($suffix)) {   // Userid provided
            $license_string .= '-'.strtoupper(base_convert($suffix,10,36));
        }else{
            $long = sprintf("%u\n", ip2long($suffix),true);
            if($suffix === long2ip($long) ) {
                $license_string .= '-'.strtoupper(base_convert($long,10,36));
            }else{
                $license_string .= '-'.strtoupper(str_ireplace(' ','-',$suffix));
            }
        }
    }
    return $license_string;
}