3 ms·

TIL. My understanding is based on the Navy procedures. I didn't realize the Army's procedures were so different. I thought the only difference between Navy a

by mulmen 5y ago

TIL. My understanding is based on the Navy procedures. I didn't realize the Army's procedures were so different. I thought the only difference between Navy and Army Enigma was the plugboard and number of available rotors but that procedures were the same. Thanks for the great resource. E: Reading this transcript I see: > Since they knew the Enigma would never duplicate a letter in the original, if any pairs of letters did match, the phrase must be in the wrong position. They slid the crib along the message until they found a point where none of the letters were the same. This could be where the phrase was located. If successful, they could then work out the Enigma settings for the next 24 hours. I wonder if Enigma could have been cracked based on this frequency analysis alone. Presumably the Navy replaced the codebooks after they were compromised, but AFAIK Bletchley Park was able to decipher messages through the end of the war.

shadowgovt 5y ago
In the case of the navy, the beauty of their randomized code book solution was the Achilles heel. Once the code book was compromised, there wasn't any easy way to replace it that didn't involve recalling every ship at sea. A one-time pad is completely worthless if the enemy has the pad, and the code book was essentially a sequence of one time pad entries (sort of; technically, just a sequence of random seeds for an algorithmic encryptor... Point is, if you're compromise would break a one-time pad it will break everything else too). But hilariously, I'm pretty sure the main thing that dragged out the length of time that the navy codes were broken was the fact that the German admiralty spent more time executing high ranking officers suspected of espionage after the codes were broken than coming up with an actual solution ;)
- mulmen 5y ago
  For some reason I thought the codebooks had a limited life. Something like a month. And that there was a mechanism for distributing these books along with supplies like food and fuel. But I also thought the Army was using them.
ncmncm 5y ago
The Friedmans in the US routinely decrypted Enigma messages (mostly from South America) without assistance from any bombes or Colossus. Just good old fashioned cryptanalysis.

by mulmen 5y ago

shadowgovt 5y ago

In the case of the navy, the beauty of their randomized code book solution was the Achilles heel. Once the code book was compromised, there wasn't any easy way to replace it that didn't involve recalling every ship at sea. A one-time pad is completely worthless if the enemy has the pad, and the code book was essentially a sequence of one time pad entries (sort of; technically, just a sequence of random seeds for an algorithmic encryptor... Point is, if you're compromise would break a one-time pad it will break everything else too). But hilariously, I'm pretty sure the main thing that dragged out the length of time that the navy codes were broken was the fact that the German admiralty spent more time executing high ranking officers suspected of espionage after the codes were broken than coming up with an actual solution ;)

mulmen 5y ago
For some reason I thought the codebooks had a limited life. Something like a month. And that there was a mechanism for distributing these books along with supplies like food and fuel. But I also thought the Army was using them.

ncmncm 5y ago

The Friedmans in the US routinely decrypted Enigma messages (mostly from South America) without assistance from any bombes or Colossus. Just good old fashioned cryptanalysis.