[cryptography] New Hand Cipher - The Drunken Bishop

Aaron Toponce aaron.toponce at gmail.com
Thu Dec 26 14:05:24 EST 2013

I created a new hand cipher over the past few weeks, and announced it on my
blog yesterday. I'm curious what people on this list think.


The idea comes from taking an 8x8 chessboard, and assigning the values
0-63 randomly and uniquely to each square on the board. This gives a total
keyspace of 64!. The bishop takes a "random walk" around the board, based
on the square value he's landed on. Details are in the post.

The idea comes from wanting a hand cipher that wasn't a strenuous as the
Solitaire Cipher by Bruce Schneier, and takes the idea of the random walk
from the SSH key ASCII art.

The algorithm is a base-64 pseudorandom number generator which is applied
to the plain text, and added modulo 64. It's an output mode stream cipher.

I haven't done any cryptanalysis on the cipher yet. Lowest hanging fruit
seems to be frequency analysis with output biases and generating a "heat
map" of each square the bishop has landed on for a given key and plaintext
to discover any internal biases.

I'm not a professional cryptographer, just an amateur hobbyist. I think I
have a lot of my ducks in a row, but I would be interested in greater
feedback on how I can improve the cipher, and to discover any weaknesses.

If this list isn't appropriate for this sort of thing, my apologies. Please
point me the right direction to discuss this.


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