How to generate an Activation Key (or Serial Key)

My problem is this : I have a user id : 0001 And Expiration code : 2015-10-10 12:00

What I need is to encrypt the two value so that I can have some like : TRE-3DR-SER-WER-67J-AX3 (something like this), and also can be decrypted to its original values.

What I did was to jumble the two value, remove spaces and dashes and create a letter or number equivalent to a single character.

My problem is I want the generated kay to be more secure and harder to decode and if possible shorter string.

2 Answers

You should keep the activation key seperate, and irrelevant to expiry date and user ID. It's literally creating a method to decrypt your own keys. Instead; have your table similar to the below.

+----------------------------------------+ | UserID | Key | Expiry | +----------------------------------------+ 

Than you can generate the ID:

<?php function sernum() { $template = 'XX99-XX99-99XX-99XX-XXXX-99XX'; $k = strlen($template); $sernum = ''; for ($i=0; $i<$k; $i++) { switch($template[$i]) { case 'X': $sernum .= chr(rand(65,90)); break; case '9': $sernum .= rand(0,9); break; case '-': $sernum .= '-'; break; } } return $sernum; } // try it, lets generate 4 serial numbers echo '<pre>'; for ($i=0; $i < 4; $i++) echo sernum(), '<br/>'; echo '</pre>'; ?> 

Output:

WS41-IZ91-55XO-23WA-WVZS-20VK

SJ42-CV50-79DA-55UV-TERR-28IJ

LY80-CN84-69LV-73EW-ZZEU-09AI

IS86-RG15-39CG-38HK-XLUG-86FO

Then check to see if the generated key is in use (1/1,000,000 chance~)

Encoding:

 $user = "0001"; //Solution only works if this value is always 4 characters. $datetime = "2015-10-10 12:00"; $reps = array("-", " ", ":"); $unencoded = $user . str_replace($reps, "", $datetime); //gives: 001201510101200 $encoded = strtoupper(base64_encode($unencoded)); //This will always be 20 characters long //Result: MDAXMJA5OTK5OTAXMJAW $finalCode = substr($encoded, 0, 5) . "-" .substr($encoded, 4, 5) . "-" .substr($encoded, 9, 5) . "-" .substr($encoded, 14, 5) . "-" //result: MDAXM-JA5OT-K5OTA-XMJAW 

Decode:

 $input = "MDAXM-JA5OT-K5OTA-XMJAW"; $encoded = str_replace("-", "", $input ); $decoded = base64_decode($encoded); $year = substr($decoded, 4, 4); $month = substr($decoded, 8, 2); $day = substr($decoded, 10, 2); $hour = substr($decoded, 12, 2); $min = substr($decoded, 14, 2); $userid = substr($decoded, 0, 4); $date = new DateTime($year . "-". $month . "-" .$day. " ".$hour.":".$min); 

Note: I would not recommend doing this, it is very insecure. I would follow the advice of some of the other answers and keep your code random and seperate to the user ID and date/time.