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What kind of cipher is K4?

Asked 26 Oct 2026 by ·4 answers·0·0 following
Most likely: k4 uses a Gromark-type cipher (a keyed alphabet with a running numeric key generated by chain addition) or a…Ahead on the evidence, not yet confirmed. It needs two reviews to be accepted.

Where it stands

Four answers have been proposed. K4 uses a Gromark-type cipher (a keyed alphabet with a running numeric key generated by chain addition) or a… leads, with evidence 1 for: partly supported by its tests. Three are still possible. Of the one narrower question under it, none is answered yet.

Why it matters

Even with the plaintext held privately, the method is what the puzzle was set to test, and it is what K5 is said to share⁠[1]. The released cribs and the statistics of the ciphertext constrain the families that could have produced it⁠[2]⁠[3].

Answers 4

Evidence: 1 for
Most likely
Evidence: 2 for
Still possible
Evidence: 1 for, 1 against
Disputed
None of these.
Not tested enough to call either way
Evidence: none yet
Still possible

History

  1. Bauer et al. puts forward: k4 is a Hill (matrix) cipher, hinted at by the extra L that spells HILL down the tableau's last column.
  2. Bauer et al.: bauer, Link and Molle tested the matrix conjecture; it has not produced a solution.Against: K4 is a Hill (matrix) cipher, hinted at by the extra L that spells HILL down the tableau's last column.
  3. Bean puts forward: k4 uses a Gromark-type cipher (a keyed alphabet with a running numeric key generated by chain addition) or a…
  4. Bean: monte Carlo permutation tests show a strong one-to-one relation between corresponding plaintext and…For: K4 uses a Gromark-type cipher (a keyed alphabet with a running numeric key generated by chain addition) or a…
  5. Asked on this site
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