[kakwa_]

Enigma security didn't rely on security through obscurity. Having the machine didn't enable the allies to decrypt the messages. It relied on the secret of the... secret keys and the monthly key books.

It's also quite interesting to see that the Polish cryptanalists were able to reproduce the enigma machine used by the german army without even having seen one. They were able to deduce the number of rotors, the wiring, etc.

What in the end doomed the Enigma was the fact it was more a kitchen recipe than cryptography based on solid principles. It was a smart recipe for the time, but it had flaws (like the fact a letter could not be the same letter once encrypted). In some regards, most of our symetric encryption algorithms today feel a bit that way (with a lot more external scrutiny from experts however).

Even in WWII, I don't think that security through obscurity was considered as an absolute barrier. It's more in line with a "defense in depth" pattern. It gives a little more work to your adversary as he now has to figure out how your encryption works before breaking it, but it's not expected to last for long.