Php change a number into another number that can be changed back to the original

Question

Using PHP, I\'m trying to encode a number into another number that I can decode back to the original number. The encoded string needs to be only numbers and should not contain a

Answer 1

Why not using a mathematicat operation on the original number? like x becomes x * y + z. you would only have to make the reverse operation to get the original number. consider using large enough prime numbers for y and/or z

Answer 2

Quite heavy, but very good encryption, by using ord & chr a bit. While this works, consider other options: just being able to use strings rather then numbers already makes it a lot simpler (base64_encode etc.):

<?php
class Crypter {
  private $key = '';
  private $iv = '';
  function __construct($key,$iv){
    $this->key = $key;
    $this->iv  = $iv;
  }
  protected function getCipher(){
     $cipher = mcrypt_module_open(MCRYPT_BLOWFISH,'','cbc','');
     mcrypt_generic_init($cipher, $this->key, $this->iv);
     return $cipher;
  }
  function encrypt($string){
     $binary = mcrypt_generic($this->getCipher(),$string);
     $string = '';
     for($i = 0; $i < strlen($binary); $i++){
        $string .=  str_pad(ord($binary[$i]),3,'0',STR_PAD_LEFT);
     }
     return $string;
  }
  function decrypt($encrypted){
     //check for missing leading 0's
     $encrypted = str_pad($encrypted, ceil(strlen($encrypted) / 3) * 3,'0', STR_PAD_LEFT);
     $binary = '';
     $values = str_split($encrypted,3);
     foreach($values as $chr){
        $chr = ltrim($chr,'0');
        $binary .= chr($chr);
     }
     return mdecrypt_generic($this->getCipher(),$binary);
  }
}

$crypt = new Crypter('secret key','12348765');
$encrypted = $crypt->encrypt(1234);
echo $encrypted.PHP_EOL;
//fake missing leading 0
$encrypted = ltrim($encrypted,'0');
echo $encrypted.PHP_EOL;
$decrypted = $crypt->decrypt($encrypted);
echo $decrypted.PHP_EOL;

Result:

057044206104214236155088
57044206104214236155088
1234