Re: Nonlinear combination of streams

On Mar 13, 9:16 pm, Maaartin <grajc...@xxxxxxxxx> wrote:
You could do something multiplication in
a field with a prime of the form 2^k + 1 [e.g. p=257] then just
promote all values into 1..256, then multiplication is a BBM,

How? The multiplication returns one result, but you need two, don'tyou? Ritter writes:

"Balanced Block Mixing: An orthogonal pair of Latin squares which
reversibly mix two input blocks or values of some power-of-2 size into
two output blocks of the original size.".
Or do you mean computing
(X, Y) -> (a*X+b*Y, c*X+d*Y)
in a GF where a, b, c, d, and a*d-b*c are all co-prime to the
characteristic of the field? In the latter case, it's clear.

No, it's not. In GF(256) or GF(257) it would work, but with your
"values promotion" you have only the multiplicative group of GF(257)
and no field. So I'm confused in both cases.