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The Pseudo-Hadamard transform is a reversible transformation of a bit string that provides cryptographic diffusion.
The bit string must be of even length, so it can be split into two bit strings of equal length, a and b, each of n bits. To compute the transform, a' and b', 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 = a' - b \pmod{2^n}<math>
See also
References
- Bruce Schneier, John Kelsey, Doug Whiting, David Wagner, Chris Hall, "Twofish: A 128-Bit Block Cipher", 1998. [1] (http://www.schneier.com/paper-twofish-paper.html)
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