Steganography & covert communications - Between Silk and Cyanide

Arnold G. Reinhold reinhold at
Mon Dec 31 12:32:44 EST 2001

At 2:59 PM -0800 12/30/01, John Gilmore wrote:
>Along these lines I can't help but recommend reading one of the best
>crypto books of the last few years:
>	Between Silk and Cyanide
>	Leo Marks, 1999

>This wonderful, funny, serious, and readable book was written by the
>chief cryptographer for the 'nefarious organization' in England which
>ran covert agents all over Europe during WW2 -- the Special 
>Operations Executive.

What makes this book so excellent is that Marks was not just the 
chief cryptographer at SOE, he was the *only* cryptographer. He got 
to do everything. A young amateur crypto enthusiast, he didn't make 
the cut for Bletchley after basic cryptanalysis training due to a bad 
case of smart ass and was sent down to SOE. He almost failed to get 
that job when it took him all day to decipher a test message. He 
didn't realize he had been supplied the key.

>... He taught the receiving code
>clerks in England how to decode even garbled messages, rather than
>asking agents to re-send them.  (Re-sends of the same text gave the
>enemy even more trivial ways to crack the codes.)

More important, it sharply increased their risk of being caught by 
German radio direction finders. Agents had been captured or shot in 
the middle of re-transmissions.

At 1:21 PM +0000 12/31/01, Ben Laurie wrote:
>David Honig wrote:
>> ....
> > Unbeknown to the latter, Marks had already cracked General de Gaulle's
>> private cypher in a spare moment on the lavatory. -from the obit of Leo
>> Marks, cryptographer
>But this was because it was, in fact, one of his own ciphers.

That's not quite fair to Mr. Marks. General de Gaulle used a double 
transposition cipher similar to the one the OSE had been using since 
before Marks got there, though Marks had to discover this on his own. 
Marks' codemaking efforts were directed toward improving that cipher 
and replacing it with a one-time pad. One advantage of the one time 
pad was that messages could be short, reducing the DF risk. Double 
transposition cipher required a minimum length, 200 letters, lest 
they simply be anagramed.

I have a review of the book at

Arnold Reinhold

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