[jgrahamc]

Agreed. And also everyone talks about Enigma but in many ways it was the end of the line of cryptosystems.

The Lorenz cipher that Tutte broke is much closer to today's ciphers. It was a pseudo-random number generator whose output was XORed with the message to be enciphered (which had been converted to Baudot code): http://en.wikipedia.org/wiki/Lorenz_cipher

Very similar to RC4, for example.

And Lorenz worked by exploiting co-primality to achieve a long key stream.