Re: the FBI and 1 time pads

From: Benjamin Goldberg (ben.goldberg_at_hotpop.com)
Date: 08/30/03 

Date: Fri, 29 Aug 2003 21:11:40 -0400

"Arthur J. O'Dwyer" wrote:
>
> On Wed, 27 Aug 2003, Alex Flanagan wrote:
[snip]
>> Organizations using OTPs deal with this is by having lots of pads. In
>> World War II, for example, they apparently had rooms full of clerks
>> drawing numbers from hats, from bingo machines, from any source of
>> random numbers that had no pattern (or, to be precise, a pattern so
>> complex that no one could predict it) and writing those numbers down to
>> make one time pads.
>
> Neal Stephenson's _Cryptonomicon_ contains a brief anecdote somewhere
> about how the Allies ended up having to change around their codes
> sometime in the middle of WWII just because some little old lady got
> lazy picking her bingo numbers. See, the Bletchley Park people had
> hired a lot of women to pick letters out of bingo tumblers for their
> one-time pads, and this woman eventually, subconsciously, realized that
> the letters she was drawing "weren't random enough" -- you know,
> sometimes she'd get two E's in a row, or three T's, and we all know that
> really *random* letter arrangements won't repeat that often, and will
> contain a lot of Q's and X's (because it's not just plain English; it's
> random!). So she must have started putting a ball or two back into the
> machine every so often,

I think you mean, *not* putting the balls back into the machine.

That is to say, drawing without replacement, instead of drawing with
replacement.

> and of course that didn't make the pads more random -- it made them
> *less* random. The Germans eventually managed to exploit this
> irregularity, and broke one of the British pads. And then some other
> stuff happened.
> Anyway, moral of the story was: Don't mess with randomness.
>
> :-)
> -Arthur 

-- 
$a=24;split//,240513;s/\B/ => /for@@=qw(ac ab bc ba cb ca
);{push(@b,$a),($a-=6)^=1 for 2..$a/6x--$|;print "$@[$a%6
]\n";((6<=($a-=6))?$a+=$_[$a%6]-$a%6:($a=pop @b))&&redo;}

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