Christian Heimes wrote:
Gregory Ewing wrote:
Actually I gather it had a lot to do with the fact that the Germans
made some blunders in the way they used the Enigma that seriously
compromised its security. There was reportedly a branch of the
German forces that used their Enigmas differently, avoiding those
mistakes, and the British never managed to crack any of their
messages.
IIRC some versions of the Enigma weren't cracked because they used a
different setup and different daily keys.
The predecessor of the Enigma was cracked by Polish scientists years
before WW2 started. Some flaws in the instructions and a known plain
text attack made the crack of the Enigma practical. It took the
British scientists merely hours rather than days or weeks to decipher
the daily key with some smart tricks. For example they started fake
attacks on ships or cities just to have the names in some encrypted
reports.
>
In some cases the British had decoded the messages before the intended
recipient!
The Americans decoded Japanese messages about an planned attack on an
island, but didn't know which one because of the fake names, so they
instructed their bases to report certain problems in a way that the
Japanese could decode.
Midway reported a shortage of water, the Japanese decoded it and sent a
message about it, the Americans decoded their message and discovered
that island's fake name, and thus found out that Midway was the intended
target of the attack.
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