Mark I

What would it be like?

Now, what are the features of such an enciphering system?

First of all, the number of ciphertext letters grows as opposed to the number of plaintext letters by a factor of about 2.5. (This is what we observe in the VM, if we take the entropy as a measure of “information content” of the plaintext.)

Repeated letters and sequences are frequent, which is also in accordance with the VM.

Depending on the alphabet chosen for the plaintext, something between a dozen and two dozen different ciphertext glyphs are required. This matches the VM roughly, where estimates are around 17 frequent and a large number of rarely and very rarely used characters.

The method is feasible, although a little cumbersome. One problem is that it is “lossy”, namely, the plaintext letter boundaries get blurred: In our example, the sequence “34434” should really be broken down into “34 43 4”, namely “b d o”, but the decipherer can’t know that. “34 4 34” (“b o b”) or “3 4 4 34” (“l o o d”) would de equally valid decipherments, and only context knowledge would show which interpretation is correct. (It is conceivable to introduce one special character to mark letter boundaries, but this letter alone would have to make up around 40% of all characters in the ciphertext. There is no single letter with that frequency in the VM.)

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