A Guide to Cryptography in PHP : Page 3

Building Hashes with MHash
MHash is a free library that lets developers choose from a large number of hash algorithms. These algorithms can be used to compute checksums, message digests, and create other signatures.

Installing Libmhash

1. Download libmhash.dll.
2. Copy the libmhash.dll file to {php_home}/ext and to {Windows_home}/System32.
3. In php.ini, activate the extension=php_mhash.dll line by deleting the comment mark (";").
4. Save the updated php.ini file.

Supported Hashes
The hashes currently supported by MHash are:

• MHASH_ADLER32
• MHASH_CRC32
• MHASH_CRC32B
• MHASH_GOST
• MHASH_HAVAL128
• MHASH_HAVAL160
• MHASH_HAVAL192
• MHASH_HAVAL256
• MHASH_MD4
• MHASH_MD5
• MHASH_RIPEMD160
• MHASH_SHA1
• MHASH_SHA256
• MHASH_TIGER
• MHASH_TIGER128
• MHASH_TIGER160

The following example uses MHash to encrypt the contents of texfile.txt and write the encrypted result to encrypted.txt:

   <?php
   
   $file = 'textfile.txt';
   $initial_contents = file_get_contents($file);
   
   if($initial_contents){
   
      //mhash() applies a hash function specified by MHASH_MD5 
      //to the $initial_contents 
      $encrypted = mhash(MHASH_MD5, $initial_contents);
      
      // get current Unix timestamp
      $current = time();
   
      $salt = $current;
      $password = "Octavia";
   
      //mhash_keygen_s2k generates a key according to the hash function 
      //given and the password provided by the user. 
      $hash = mhash_keygen_s2k(MHASH_GOST, $password, $salt, 20);
   
      //concatenate the $salt with the $hash 
      $key = $salt . "|" . bin2hex($hash);
   
      $encrypted_file = @fopen('encrypted.txt','w');
      $ok_encrypt = @fwrite($encrypted_file,
         'mhash: '.bin2hex($encrypted).'  mhash_keygen_s2k:   
         '.$key);
      
      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);
   }
   ?>

Secret Keys and Crypt_Blowfish
Secret-key cryptography uses a single key for both encryption and decryption—also called a symmetric key. For example, the commonly-used DES algorithm is a secret key algorithm. The Crypt_Blowfish PEAR package is based on the Blowfish block cipher and supports two-way encryption, either with or without a secret key. The package doesn't require MCrypt, but Crypt_Blowfish can use MCrypt if it's installed. The latest released version is 1.0.1 (stable), and you install it like any other PEAR package:

   > pear install pear_package_name

This package uses two classes defined in the Blowfish.php file, which you must include in all scripts that use the Crypt_Blowfish package:

        









                                

   require_once 'Crypt/Blowfish.php';

Here's the code for the by-now-familiar encryption example program using Crypt_Blowfish:

   <?php
   
   require_once 'Crypt/Blowfish.php';
   
   $file = 'textfile.txt';
   $initial_contents = file_get_contents($file);
   
   if($initial_contents){
      $bf = new Crypt_Blowfish('some secret key!');
   
      // Encrypts a string   
      $encrypted = $bf->encrypt($initial_contents); 
   
      $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);
   
      // Decrypts an encrypted string
      $plaintext = $bf->decrypt($encrypted); 
      $newfile = @fopen('newfile.txt','w');
      $ok_decrypt = @fwrite($newfile,$plaintext);
      if($ok_decrypt){
            echo 'The decrypted code was succesfully created '.
            'in newfile.txt!!!'.'<br />';
                 }
      else{
         echo ("The write of this file failed!");
         }
      
      @fclose($newfile);
      }
   ?> 

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