Could one use three different disks set at different positions and encrypt a strong message?

For example:

  • Wheel 1: A = J
  • Wheel 2: A = E
  • Wheel 3: A = B

The first letter is encrypted using 1, and then that wheel is rotated (possibly according to a key). Then letter 2 is encrypted using wheel 2, and it is then rotated (possibly according to a different key than in the first wheel), and so forth.

  • 4
    $\begingroup$ A more sophisticated Enigma was broken in 1940s. $\endgroup$
    – DannyNiu
    May 29 '19 at 2:21
  • $\begingroup$ @DannyNiu it was broken mainly on the basis of cribs, security faults and the plugboard. If the Enigma didn't have these faults, would it be stronger? $\endgroup$
    – Neo1009
    Jun 27 '19 at 22:21
  • $\begingroup$ Yet, those things you listed are the basis a strong cipher must be secure against. $\endgroup$
    – DannyNiu
    Jun 28 '19 at 1:12

You have described the Alberti cipher, outlined in Leon Battista Alberti's 1467 treatise on encipherment, De Cifris (Alberti, Leon Battista, A Treatise on Ciphers, trans. A. Zaccagnini. Foreword by David Kahn, Galimberti, Torino 1997). The original Italian version, with illustrations, is De componendis cifris.

Alberti's work marked an important innovation in Western cryptography, the polyalphabetic system. Whitfield Diffie often talks about this, by the way.

Whitfield Diffie points out that Alberti's notable advance for cryptography clarified the distinction between a cryptographic key and a cryptographic system. Before the Renaissance, this distinction was difficult to make because the systems were very simple. For example, in using a codebook, all of the expense is put into the codebook, the secret piece, not into the system of looking up plaintext and writing ciphertext. Alberti's cipher resisted cryptanalysis by advancing from the current monoalphabetic systems to a polyalphabetic system. Importantly, it shifted the expense to the public piece, the system, making the secret part cheap.

This story is important in the history of cryptography, but we cannot use Alberti's cipher to secure communications today. It would be trivial to very rapidly break such messages with a modern computer.

In short, classical cryptography is useless against today's computers (excluding codebooks and one-time pads, two methods very rarely used, it seems).

For more detail on Alberti's fascinating work, see: Williams, K., March, L., Wassell, S. R. (Eds.). (2010). The Mathematical Works of Leon Battista Alberti. Springer Basel AG . pp. 189-200.


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