Newsgroups: comp.risks
X-issue: 6.64
Date: Mon, 18 Apr 88 06:02:29 EDT
From: mnetor!utzoo!henry@uunet.UU.NET
Subject: Re: More evidence for an old risk -- Enigma 

Those interested in this should probably also read Patrick Beesly's book
"Very Special Intelligence" (1977).  It's the story from the user end:
an account of the British Admiralty's Operational Intelligence Centre,
which was charged with putting intelligence information together into a
useful form for naval operations.  In particular, it was effectively the
nerve center for the Battle of the Atlantic.  It had a dedicated teletype
link to the Bletchley Park cryptanalysts.  Apart from the inherent interest
of the user's-eye view, most of what OIC did is declassified, unlike a lot
of the detailed doings of the cryptanalysts.

Concerning "probable word" attacks on ciphers, Beesly observes that a
possible factor in the success of the cryptanalysts was that situation
reports from weather aircraft were often sent to shore in relatively low-
security ciphers and then rebroadcast verbatim in the high-security naval
ciphers.  Later in the war the Admiralty had to make a substantial effort to
discourage the RAF from shooting down those aircraft, without revealing why!

He also sheds some light on the question of why the cryptanalysis was not
discovered.  The Germans did persistently suspect either treachery or
cryptanalysis.  Against the former they took increasingly elaborate
precautions.  The possibility of the latter was investigated not once but
several times.  Unfortunately, the investigation was always run by the
signals people themselves, and the conclusion invariably was that they
were not at fault, i.e. the ciphers were unbreakable.

The situation wasn't as obvious as people might think, also.  Encryption
keys changed daily, and the cryptanalysts were often two or three days
behind in finding the new ones.  Cryptanalysis was often incomplete. And
the Germans used increasingly-elaborate map codes for geographic locations,
meaning that a message was often hard to interpret even if cryptanalysis
was complete.  The result was that OIC had to work hard to put things
together with other intelligence reports (e.g. direction-finding and actual
sightings), and errors did creep in.  These errors showed, and made it
harder to see that cryptanalysis was involved.

(For the same reasons, Beesly has a low opinion of some of the popular
books on wartime cryptanalysis.  Some of them make it sound like the Allies
knew everything the Germans were doing, and if any Allied ships were lost,
it was because of Machiavellian scheming by Allied commanders.  Beesly
makes it clear that it just wasn't that simple.)

A contributing factor may have been something that Beesly mentions as a
problem with OIC:  because there were few people qualified, cleared, and
available to do the work, and the workload was heavy, and the atmosphere was
one of constant crisis, nobody ever really got a chance to stand back for a
while and think about the deeper implications of events.  Nobody was charged
with looking for things like signs of hostile cryptanalysis.  Only a lucky
hunch by a senior man would reveal such a situation.  The British got lucky:
early in 1943 the head of OIC, Rodger Winn, noted for his lucky hunches,
concluded (correctly) that the *Germans* were reading the *Allied* naval
ciphers, and made enough of a stink to get things done about it.  Evidently
none of his German counterparts ever had a similar stroke of insight.

Beesly's account also has something to say about the perils of becoming
obviously dependent on one information source.  OIC had little cryptanalytic
intelligence for most of 1942, because the Germans had changed ciphers
and the cryptanalysts took a long time to solve the new one.  The OIC
people decided to try to continue detailed tracking of all U-boats,
recognizing that there would be many more errors.  Many people thought that
this was silly and wasn't going to work.  In fact it worked moderately
well, and the skeptics were proved wrong, but only because Winn and others
insisted that this "obviously" ridiculous scheme was worth trying.

Henry Spencer @ U of Toronto Zoology   {ihnp4,decvax,uunet!mnetor}!utzoo!henry