Editing Pseudo-Hadamard transform (section)

The '''pseudo-Hadamard transform''' is a reversible transformation of a bit string that provides [[diffusion (cryptography)|cryptographic diffusion]].  See [[Hadamard transform]].

The bit string must be of even length so that it can be split into two bit strings ''a'' and ''b'' of equal lengths, each of ''n'' bits. To compute the transform for Twofish algorithm, ''a''<nowiki>'</nowiki> and ''b''<nowiki>'</nowiki>, from these we use the equations:

:<math>a' = a + b \, \pmod{2^n}</math>

:<math>b' = a + 2b\, \pmod{2^n}</math>

To reverse this, clearly:

:<math>b = b' - a' \, \pmod{2^n}</math>

:<math>a = 2a' - b' \, \pmod{2^n}</math>

On the other hand, the transformation for '''SAFER+''' encryption is as follows:

:<math>a' = 2a + b \, \pmod{2^n}</math>

:<math>b' = a + b\, \pmod{2^n}</math>