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==Symmetric Decryption==



   
  <!-- start source code -->
   
    <source lang="html4strict">
 
<?
    srand((double)microtime( )*1000000 );
    $td = mcrypt_module_open(MCRYPT_RIJNDAEL_256, "", MCRYPT_MODE_CFB, "");
    $iv = mcrypt_create_iv(mcrypt_enc_get_iv_size($td), MCRYPT_RAND);
    $ks = mcrypt_enc_get_key_size($td);
    $key = substr(sha1("Your Secret Key Here"), 0, $ks);
    mcrypt_generic_init($td, $key, $iv);
    $ciphertext = mcrypt_generic($td, "This is very important data");
    mcrypt_generic_deinit($td);
    mcrypt_generic_init($td, $key, $iv);
    $plaintext = mdecrypt_generic($td, $ciphertext);
    mcrypt_generic_deinit($td);
    mcrypt_module_close($td);
    print $iv . "\n";
    print trim($ciphertext) . "\n";
    print trim($plaintext) . "\n";
?>
  
  </source>