problem with encryption

[David Beck]

I finally resolved the issue with PHP and Rev encryption and I wanted to 
share the resolution with the list. I was able to get aes-128 bit 
working - 256 is still a mystery. (I think there is a problem with Rev 
only looking at the first 16 bytes of the IV value for 256 bit, as it 
appears bytes after #16 do not affect the resulting encrypted value with 
Rev. I will log this as a bug.)

The problem is that when the data being encrypted was not 16-byte 
aligned, meaning that the length of the data was not evenly divisible by 
16, the Rev and PHP mcrypt libraries would encrypt and dycrypt the 
values differently. I don't know if this is a bug in the mcrypt library 
or in Rev or a general lack of specification but that was the problem. 
Also PHP throws in some extra null characters when decrypting even 
16-byte aligned strings at the end, so what I am doing is including the 
length of the original data so that after the decryption is done with 
PHP just that data is used as the final decrypted string.

So to put all of this is technical terms, here is the Rev script to 
encrypt the data:

On encryptData theKey, @data
  -- first generate a random 16 byte IV value
  put getRandomSalt() into theIV
 
  put binaryEncode( "N", the number of chars in data ) into dataSize
  
  -- pad to size 16
  repeat while the number of chars in data mod 16 is not 0
    put numToChar( 0 ) after data
  end repeat
 
  encrypt data using "aes-128-cbc" with key theKey and iv theIV
  if the result is not empty then
    ci_NoteAlert "Error while encrypting:" && the result
    exit to top
  end if
 
  put dataSize & theIV & it into data

  return data
end encryptData

and the php to decode a chunk of data returned by the above script looks 
like:

function decryptData( $theKey, &$data )
{
    $dataLen = substr( $data, 0, 4 );
    $dataLenArr = unpack( "N*", $dataLen );
    $dataLen = $dataLenArr[1];
   
    $data = substr( $data, 4 );
   
    $iv = substr( $data, 0, 16 );
    $data = substr( $data, 16 );

    $td = mcrypt_module_open( MCRYPT_RIJNDAEL_128, '', 'cbc', '' );
    mcrypt_generic_init( $td, $theKey, $iv );
    $data = mdecrypt_generic( $td, $data );
    mcrypt_generic_deinit($td);
    mcrypt_module_close($td);

    $data = substr( $data, 0, $dataLen );
}

Hope this is helpful to somebody in the future!

David