php - Check if a generated license is valid -

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i have php script generates strings used license keys:

function keygen(){      $key = md5(microtime());      $new_key = '';      for($i=1; $i <= 25; $i ++ ){                $new_key .= $key[$i];                if ( $i%5==0 && $i != 25) $new_key.='-';      }   return strtoupper($new_key);   } $x = 0; while($x <= 10) {   echo keygen();   echo "<br />"; $x++;  }

after running script once, got these:

8b041-ec7d2-0b9e3-09846-e8c71 c8d82-514b9-068bc-8bf80-05061 a18a3-e05e5-7ded7-d09ed-298c4 fb1ec-c9844-b9b20-ade2f-0858f e9aed-945c8-4baaa-6938d-713ed 4d284-c5a3b-734df-09bd6-6a34c ef534-3bae4-860b5-d3260-1cef8 d84db-b8c72-5bdee-1b4fe-24e90 93af2-80813-cd66e-e7a5e-bf0ae c3397-93aa3-6239c-28d9f-7a582 d83b8-697c6-58cd1-56f1f-58180

what trying change have function check if key has been generated using script. currently, thinking setting $key md5 of 1 specific string (for example, test) but, of course, returns strings same.

can help?

note:

this solution on assumption want licence key in fixed format (see below) , still self authenticated

  format : xxxxx-xxxxx-xxxxx-xxxxx-xxxx

if not case refer @ircmaxell better solution

introduction

self authenticated serial tricky solution because:

  • limited size of serial
  • it need authenticate self without database or storage
  • if private key leaked .. can reversed

example 

$option = new checkprofile(); $option->name = "my application"; // application name $option->version = 0.9; // application version $option->username = "benedict lewis"; // can limit key per user $option->uniqid = null; // add if   $checksum = new checksum($option); $key = $checksum->generate(); var_dump($key, $checksum->check($key));

output 

string '40b93-c7fd6-ab5e6-364e2-3b96f' (length=29) boolean true

please note modification in options change key , make invalid;

checking collision

i ran simple test 

set_time_limit(0);  $checksum = new checksum($option); $cache = array(); $collision = $error = 0; for($i = 0; $i < 100000; $i ++) {     $key = $checksum->generate();     isset($cache[$key]) , $collision ++;     $checksum->check($key) or $error ++;     $cache[$key] = true; }  printf("fond %d collision , %d errors  in 100000 entries", $collision, $error);

output 

  fond 0 collision , 0 errors in 100000 entries

better security

by default script uses sha1 php has lot of better hash functions can following code 

print_r(hash_algos());

example 

$checksum = new checksum($option, null, "sha512");

class used 

class checksum {     // used used binaray in hex format     private $privatekey = "ec340029d65c7125783d8a8b27b77c8a0fcdc6ff23cf04b576063fd9d1273257"; // default     private $keysize = 32;     private $profile;     private $hash = "sha1";      function __construct($option, $key = null, $hash = "sha1") {         $this->profile = $option;         $this->hash = $hash;          // use default binary key or generate yours         $this->privatekey = ($key === null) ? pack('h*', $this->privatekey) : $key;         $this->keysize = strlen($this->privatekey);     }      private function randstring($length) {         $r = 0;         switch (true) {             case function_exists("openssl_random_pseudo_bytes") :                 $r = bin2hex(openssl_random_pseudo_bytes($length));                 break;             case function_exists("mcrypt_create_ivc") :             default :                 $r = bin2hex(mcrypt_create_iv($length, mcrypt_dev_urandom));                 break;         }         return strtoupper(substr($r, 0, $length));     }      public function generate($keys = false) {         // 10 ramdom char         $keys = $keys ?  : $this->randstring(10);         $keys = strrev($keys); // reverse string          // add keys options         $this->profile->keys = $keys;          // serialise convert string         $data = json_encode($this->profile);          // simple random chr authentication         $hash = hash_hmac($this->hash, $data, $this->privatekey);         $hash = str_split($hash);          $step = floor(count($hash) / 15);         $i = 0;          $key = array();         foreach ( array_chunk(str_split($keys), 2) $v ) {             $i = $step + $i;             $key[] = sprintf("%s%s%s%s%s", $hash[$i ++], $v[1], $hash[$i ++], $v[0], $hash[$i ++]);             $i ++; // increment position         }         return strtoupper(implode("-", $key));     }      public function check($key) {         $key = trim($key);         if (strlen($key) != 29) {             return false;         }         // exatact ramdom keys         $keys = implode(array_map(function ($v) {             return $v[3] . $v[1];         }, array_map("str_split", explode("-", $key))));          $keys = strrev($keys); // important         return $key === $this->generate($keys);     } }

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