"The story of the seizure of the machine by Balme and his shipmates was kept secret until the mid-1970s". I've always been intrigued by this fact. Does anyone know why this was kept a secret for so long?
"An estimated 100,000 Enigma machines were constructed. After the end of World War II, the Allies sold captured Enigma machines, still widely considered secure, to developing countries".
I'm sure they were quite happy to sell Enigma and also decrypt their communications for nearly another 30 years.
If the Enigma machines were operated properly, they could never be broken. Breaking them were a result of German lack of discipline and irresponsibility, not machine's weakness (maybe a simple inscription on the cover of machine in the bold letters would help though, machine designers just expected too much from their enlisted, barely literate operators).
Not never. One of the "features" of the Enigma was that a plaintext letter could never be encrypted to itself. An 'A' going in could come out as any other letter, except 'A'. German information security policies were generally pretty good. There were lapses, of course, and some of these were used to form cribs for a known plaintext attack on encrypted messages. But Enigma was/is not invulnerable.
People found a couple encrypted Enigma messages after World War II. Here is a note from a group of people using modern computers and brute force to decrypt them:
Just as during WWII, during WWI, the British had a very sophisticated interception and decryption program[1]. Its capabilities were also kept secret for long after the war and the Germans remained largely ignorant of how thoroughly their codes had been broken. I think if the work during WWI had been revealed earlier, the Germans would have been more careful and would have avoided repeating some of the mistakes of WWI. It was shown to be a wise policy after WWI, so I'm not surprised that they continued it after WWII, especially with the start of the Cold War.
I can't speak about the relative sophistication of British cryptanalysis during WWI, but Bletchley owed much of its sophistication to the Poles. The Polish Cipher Bureau was responsible for bringing mathematical and computational techniques into cryptanalysis while the French and the British were still largely employing linguistic analysis. Few realize that the Enigma was actually broken and reverse engineered by the Cipher Bureau before two new rotors were added by the Germans less than a year before the War, or that Turing's bombe was developed from Rejewski's bomba.
The Poles certainly got the ball rolling (see http://www.codesandciphers.org.uk/virtualbp/poles/poles.htm), but the organization at Bletchley Park took decryption and analysis of Enigma traffic to an industrial scale. By the end of war Bletchley employed around 10,000 people. See Alan Turing's and Gordon Welchman's biographies for more details.
That sounds like the 30 year rule in action. At the time it was done, it would have been extremely secret, and secrecy was not abandoned simply because the war was over.
"An estimated 100,000 Enigma machines were constructed. After the end of World War II, the Allies sold captured Enigma machines, still widely considered secure, to developing countries".
I'm sure they were quite happy to sell Enigma and also decrypt their communications for nearly another 30 years.