Recommended Movie: "Sebastian" 1968.

Peter Fairbrother peter at
Tue Aug 18 23:52:56 PDT 2015

On 18/08/15 19:23, jim bell wrote:
> *From:* Peter Fairbrother <peter at>
> *Subject:* Re: Recommended Movie: "Sebastian" 1968.
> On 18/08/15 03:46, jim bell wrote:
>  >> Since people seem to be recommending things, I recommend the movie
>  >> "Sebastian".  Dirk Bogarde, Susannah York.
>  >>
>  >> Out of date even when it was made, I think it really represents the
>  >> cryptography situation as of the 1930's.
>  >Based on a screenplay by Leo Marks - author of Between Silk and Cyanide:
>  >A Codemaker's War 1941-1945.
>  >Essential reading. Leo was the codemaker for SOE. All hand ciphers and
>  >agents.
>  >He wasn't at Bletchley - who called him "the one who got away" - though,
>  >and so no machine ciphers.
>  >The Silk in the title was for OTPs which could be hidden in clothing
>  >from Gestapo/SS searches.
>  >As I said, essential reading.
> The tv show 60 Minutes spilled the beans about Enigma in 1975.

Not sure that was the one to spill the beans. I thought it was 
Winterbotham's 1974 book of the same name which first got the idea 
across to the public; though there was a French book in 1973 as well.

Like Winterbotham's book, which the TV show seems to be based on, it's 
also a bit confused and/or inaccurate. Much of what they tell - the 
conversations between Hitler and his generals, "knowing Hitler's most 
secret thoughts", and Hitler's message re Anzio which Gen Clark read - 
came from the breaking of the Lorentz SZ40, not the Enigma. Colossus, 
not Bombe.

And the Coventry story is fiction [1]. Churchill could not have been 
told the target from ULTRA decrypts. The ULTRA decrypts are now 
available in public records, and they do not mention Coventry.

[1] My theory: Probably it began as a story made up to impress the need 
to keep the ULTRA secret - "hey if the man at the door with the revolver 
who just threatened to shoot you doesn't impress you, Churchill allowed 
[2] the bombing of Coventry in order to keep the secret".

Later the story became an accusation, then a rumour, then a play - 
though by the time it became a play it was becoming obvious that ULTRA 
wasn't involved, and the motive for allowing the bombing changed to 
"Impressing the Americans" [3].

I can easily imagine someone telling Winterbotham the story 
(Winterbotham was the one who first told the Coventry story in public).

I can also imagine Winterbotham repeating the story, in confidence, in 
order to impress the listener with the need to keep the secret (and with 
W himself) so often that he didn't know whether it was true or not (he 
didn't claim to be personally involved).

Good story, and Churchill was probably capable of it - but it ain't true.

[2] not that there was anything he could have done to stop the bombing, 
but for the sake of the narrative ..

[3] requiring an even wilder suspension of belief, IME

> What most people didn't realize was that the controversy was due to the
> fact that rotor-driven cipher machines had been continued to be sold in
> the post-WWII era, without their weakness being recognized.  This
> allowed the CIA/GCHQ to continue to decrypt enciphered messages for
> decades afterwards.

Yes - but Leo Marks wasn't involved in that. He ~ stopped being a 
cryptographer when SOE was broken up at the end of the war.

What he did was hand ciphers, for agents in occupied countries - they 
couldn't carry cipher machines.

There is nothing else like Between Silk and Cyanide in the crypto 
literature. Crypto at the cutting edge, where a mistake is a painful 
death, and likely worse.

More, it is about how a cryptographer and his work interact with the world.

I would not like to have been Leo (I met him once), but hell if I don't 
respect him.

There is a TV documentary about him, called "A Very British Psycho" - an 
apt title.

-- Peter Fairbrother

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