A Guide to Cryptography in PHP : Page 4

Encrypt Data Using an Arbitrary Key Length with the Crypt_RSA PEAR Package
This package supports two-way encryption; it's based on the RSA block cipher. Crypt_RSA supports encryption and decryption using an arbitrary key length. You can download the latest version (1.0.0, stable) and install it like any other PEAR package:

   > pear install pear_package_name

Crypt_RSA performs intensive math calculations, for which it uses one of the following extensions:

• PECL big_int extension—(requires a version greater than or equal to 1.0.3)
• PHP GMP extension
• PHP BCMath extension for PHP4/PHP5. Required because libbcmath was bundled with PHP 4.0.4.

Here's an example of using this package:

   <?php
   
   require_once 'Crypt/RSA.php';
   
   //Generates the pair keys
   function generate_key_pair()
   {
      global $public_key,$private_key;
   
      $key_pair = new Crypt_RSA_KeyPair(32);
   
      //Returns public key from the pair
      $public_key = $key_pair->getPublicKey();
   
      //Returns private key from the pair
      $private_key = $key_pair->getPrivateKey();
   }
   
   //Check runtime errors
   function check_error(&$obj)
   {
      if ($obj->isError()){
         $error = $obj->getLastError();
         switch ($error->getCode()) {
         case CRYPT_RSA_ERROR_WRONG_TAIL :
            // nothing to do
            break;
         default:
            // echo error message and exit
            echo 'error: ', $error->getMessage();
            exit;
         }
      }
   }
      
   $file = 'textfile.txt';
   
   generate_key_pair();  
   $plain_text = file_get_contents($file);
      
   //get string represenation of the public key
   $key = Crypt_RSA_Key::fromString($public_key->toString()); 
      
   $rsa_obj = new Crypt_RSA;
   check_error($rsa_obj);
      
   //Ecnrypts $plain_text by the key $key.
   $encrypted = $rsa_obj->encrypt($plain_text, $key);
      
   $encrypted_file = @fopen('encrypted.txt','w');
   $ok_encrypt = fwrite($encrypted_file,$encrypted);
   if($ok_encrypt){
      echo 'The encrypted code was succesfully created '.
      'in encrypted_file.txt!!!'.'<br />';
   }
   else{
      echo ("The write of this file failed!");
   }
   @fclose($encrypted_file);
      
   $enc_text = $encrypted;
     
   //Get string represenation of the private key
   $key2 = Crypt_RSA_Key::fromString($private_key->toString());
   check_error($key2);
      
   //Check encrypting/decrypting function's behaviour
   $rsa_obj->setParams(array('dec_key' => $key2));
   check_error($rsa_obj);
   
   //Decrypts $enc_text
   $decrypted = $rsa_obj->decrypt($enc_text);
      
   $newfile = @fopen('newfile.txt','w');
   $ok_decrypt = @fwrite($newfile,$decrypted);
   if($ok_decrypt){
      echo 'The decrypted code was succesfully created '.
      'in newfile.txt!!!'.'<br />';
   }
   else{
       echo ("The write of this file failed!");
   }
   @fclose($newfile);
    
   ?>   

Generating Hashes with Crypt_HMAC
The Crypt_HMAC PEAR package contains a class you can use to calculate RFC 2104-compliant hashes. Crypt_HMAC is easy to use; you need only provide your secret key, the hash method you want to use, and the plaintext string. Crypt_HMAC supports both MD5 and SHA-1 algorithms. The latest stable released version is 1.0.0. You install it just like any other PEAR package:

   > pear install pear_package_name

And here's a simple example that creates a hash using Crypt_HMAC:

   <?php
      
   require_once 'Crypt/HMAC.php';
   
   //Creating a key by repeating the "0x0b" character for 20 times 
   $key = str_repeat(chr(0x0b), 20);
   
   //Creating an instance of the Crypt_HMAC class
   //$crypt = new Crypt_HMAC($key, 'md5');
   $crypt = new Crypt_HMAC($key, 'md5');
     
   //Hashing function
   echo $crypt->hash('Hello')."<br />";
   
   $key = str_repeat(chr(0xaa), 10);
   $data = str_repeat(chr(0xdd), 50);
   
   //Sets key to use with hash
   $crypt->setKey($key);
   echo $crypt->hash($data)."\n";
   ?>

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