[cryptography] New Hand Cipher - The Drunken Bishop

Aaron Toponce aaron.toponce at gmail.com
Thu Dec 26 16:04:29 EST 2013

On Thu, Dec 26, 2013 at 05:57:11PM -0300, andrew cooke wrote:
> here's my suggestion on a possibly harder version.
> first, remove the complicated edge rules.  instead, imagine that the
> board repeats.  so something leaving nort from h4 will arrive at a7.
> this might help remove biases from the corners (where you can be stuck
> for one move). the drawback is that this almost removes the "drunken"
> switching from black to white, but see below.
> second, add a rook that moves in a similar way, but the directions are
> horizontal and vertical.  this starts at b3, say (see below).
> third, the moves are made alternately (bishop, rook, bishop, rook,
> bishop, rook), and if at any time one piece threatens the other, they
> change position.
> and maybe the plaintext is only added to one piece?
> and maybe the row number of the rook is a bit rotation applied to the
> output?

This is good. I'll take this advice, and see what comes as a result. I have
thought of a topological spheroid, where moving off the edges brings the
bishop to the other edge, similar to a pacman game. Or going out of corner
'h8' would bring you into corner 'a1', etc.

I also thought of two bishops, on their own color, but I couldn't think of
a clever way to avoid stream cycles repeating.

I need to introduce non-linearity into the system, which seems to be
allusive with this type of cipher. I'm afraid adding additional pieces
won't be enough, and that the requirement of a mathematical operation, such
as "new square = (current square)^2 * mod(64). But reversing it is going to
be tricky, and I'm not confident I'll get non-linearity into the algorithm.

Thanks very much for your feedback.

. o .   o . o   . . o   o . .   . o .
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o o o   . o .   . o o   o o .   o o o
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