[cryptography] New Hand Cipher - The Drunken Bishop

Kevin kevinsisco61784 at gmail.com
Thu Dec 26 14:35:13 EST 2013


On 12/26/2013 2:28 PM, andrew cooke wrote:
> the way that you use the plaintext to avoid short cycles (the "output number"
> etc) is worrying - it might open you up to a chosen plaintext attack in some
> way.
>
> and thinking about chosen plaintexts - if you encode a message that is all
> zeroes, what does that reveal?  it seems like it might leak information about
> the board you are using.
>
> these aren't attacks, but they are obvious places where i (with, admittedly,
> very little experience of attacking ciphers) would start.
>
> andrew
>
>
>
> On Thu, Dec 26, 2013 at 12:05:24PM -0700, Aaron Toponce wrote:
>> 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.
>>
>>      https://pthree.org/2013/12/25/the-drunken-bishop-cipher/
>>
>> 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.
>>
>> Thanks,
>>
>> -- 
>> . o .   o . o   . . o   o . .   . o .
>> . . o   . o o   o . o   . o o   . . o
>> o o o   . o .   . o o   o o .   o o o
>
>
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A valid point.  However this is a hand cipher which probably would not 
see its way into a system.


-- 
Kevin



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