Cryptography Reference
In-Depth Information
•
That gave the British an idea: weather ships often remain at sea for
months, so they have to carry code books with ground settings for the
entire period afloat. From the military viewpoint, they were weak adver-
saries. The only problem with their seizure could emerge if the Germans
became suspicious. But the Germans had other things to worry about at
the time, namely in the east. The coup was successful. The first victim
was the
Munchen
northeast of Iceland in May 1941. The British warships
fired intentionally past the ship. The crew panicked and abandoned the
ship, were taken prisoners by the British and taken below deck immedi-
ately for them to see that their ship wasn't sinking (yet). A later British
radio broadcast confirmed what the Germans thought, namely that all
secret papers sank together with the
Munchen
. And the British held the
basic keys for June 1941 in their hands.
•
Shortly after that event, the German submarine
U
-110, together with
extensive material, fell into the hands of British warships by chance.
Again, the Germans didn't become suspicious. The material was so exten-
sive that it had to be documented in photographs and shipped to Great
Britain in special containers. It included not only the basic keys for a
lengthy period, but also a large number of other code tables and the
'Kleine Signalbuch' (signal reference topic) for submarines, which was
of particular interest for plaintext attacks.
•
When the weather ship
Lauenburg
was fired at north of the Arctic Cir-
cle, the British used time-fuse missiles with black-powder charges, among
other things, which exploded above the ship without destroying it. The
system had an immediate effect; the conquerors again found highly inter-
esting documents on the ship abandoned in panic.
•
Those were true successes. Of course, all German crews were strictly
instructed to destroy secret documents before they could be captured by
the enemy. Code books were printed on absorbent paper with water-
soluble ink. Particularly with U-110 submarines, it was difficult to take
the material safely to a British warship.
•
We already know that the Germans sent encrypted weather reports from
submarines. It also transpired that they first compressed the meteorolog-
ical information using a secret dictionary. The British had such dictio-
naries. But only the submarines and one single land station possessed an
Enigma with four rotors. So when sending a weather report they held
the fourth rotor in place. That was a vulnerability for a plaintext attack
against the 3-rotor machine and eventually led to the breaking of the
