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Listener No 4747, Transposition Cipher: A Setter’s Blog by Serpent

Posted by Listen With Others on 12 Feb 2023

Transposition Cipher was inspired by my previous Listener puzzle Impossible Construction. In that puzzle, a central panel in the completed grid contained a word square, will all grid entries outside the central panel being real words. I thought it would be interesting to see what other content could occupy a central region of the grid.

The message TRANSPOSITION CIPHER BY SERPENT has 28 characters which would fit nicely into a 4×7 panel that could be incorporated in a 10×13 grid. I was going to use a standard columnar transposition cipher but then thought it would be more interesting to use the Myzskowski variant with ANAGRAM as a rather natural keyword.

I used the approach of Impossible Construction of jumbling entries that intersected with the central region, with the constraint that the three letters of these jumbles outside that region should form real words. The excellent Qxw software confirmed that a grid-fill was possible. From there, I incrementally refined the grid in order to exclude as many obscurities and inflected word forms as possible.

The ambiguity in the grid-fill was irritating, but I realised the bug could be turned into a feature because it is disambiguated by (what is unambiguously) the correct plaintext.

As always, I must thank my test-solvers, David and Norman, and Shane and Roger at the Listener for their feedback and help in producing the final version of the puzzle. And many thanks to all the solvers who have been kind enough to send comments in with their solutions.

A number of solvers commented on the dimensions of the ciphertext panel being identical to the puzzle number (4747). That’s not something I’d noticed when checking the proof and Roger assures me that this is pure coincidence.


One Response to “Listener No 4747, Transposition Cipher: A Setter’s Blog by Serpent”

  1. Brock said

    Interesting that what started out as an annoying ambiguity could be turned into a thematic feature. That has been my experience on at least a few occasions for me too, most notably in Bunch of Fives where I’d put the puzzle aside for a long time due to that flaw before weaving it into the fabric of the puzzle.

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