Re: Blowfish Behaviour

On Tue, 02 Aug 2005 01:39:55 -0400, Wolfgang Keller <[email protected]> wrote:
>
> As to my extra testings, the Blowfish algorithm that I use for my Java
> Pws library (Markus Hahn 2.13) has the same transformative funtion than
> any other Blowfish algorithm (on other environments). This means that
> all test-vector qualifying Blowfish implementations behave identical in
> respect to byte arrays regardless of platform or endianness differences.
>
> Still I have to swap byte order in a 4-byte pattern in order to make
> things running. _I am interested to obtain confirmation if this
> procedure has been introduced by Pws itself_ and is not a consequence of
> platform or language specific circumstance.
>

Check out the definition of the "aword" structure in corelib/BlowFish.h:

   union aword
   {
      unsigned long word;
      unsigned char byte [4];
      struct
      {
         unsigned int byte3:8;
         unsigned int byte2:8;
         unsigned int byte1:8;
         unsigned int byte0:8;
      } w;
   };

As you see, the "w" structure assumes big-endian byte order, thus,
on a little-endian architecture, eventually interpreting integers the
wrong way around.

To compensate for this using a "correct" implementation of the blowfish
algorithm, you have to byte-swap all inputs and outputs to the encrypt
and decrypt operations.

Frank

-- 
Frank Pilhofer, [email protected]


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