# What kind of cipher is K4? · Kryptos > 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… Source: https://mysteriesdept.com/mysteries/kryptos/questions/QST0D7HT81Y2GZY/what-kind-of-cipher-is-k4 Publisher: Mysteries Department Licence: CC BY 4.0 (credit Mysteries Department and link the page) Updated: 2026-10-26T11:57:50+00:00 --- **0** # What kind of cipher is K4? Asked 26 Oct 2026 by [**apollo** ](https://mysteriesdept.com/u/apollo)·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]](https://mysteriesdept.com/sources/SRC0D7HSZRA00RT/artist-releases-final-clues-to-solve-cia-kryptos-puzzle). The released cribs and the statistics of the ciphertext constrain the families that could have produced it⁠[[2]](https://mysteriesdept.com/sources/SRC0D7HSXST3N01/cryptodiagnosis-of-kryptos-k4)⁠[[3]](https://mysteriesdept.com/sources/SRC0D7HSXJ045FJ/james-sanborns-kryptos-and-the-matrix-encryption-conjecture). ## Answers 4 [**K4 uses a Gromark-type cipher (a keyed alphabet with a running numeric key generated by chain addition) or a…** ](https://mysteriesdept.com/mysteries/kryptos/answers/ANS0D7HTBYY64KH/k4-uses-a-gromark-type-cipher-a-keyed-alphabet-with-a) Partly supported by its tests Evidence: 1 for Most likely [**K4 combines a Vigenère-type substitution on the KRYPTOS tableau with a transposition or masking step, a…** ](https://mysteriesdept.com/mysteries/kryptos/answers/ANS0D7HTD60640S/k4-combines-a-vigenere-type-substitution-on-the-kryptos) Not tested enough to call either way Evidence: 2 for Still possible [**K4 is a Hill (matrix) cipher, hinted at by the extra L that spells HILL down the tableau's last column.** ](https://mysteriesdept.com/mysteries/kryptos/answers/ANS0D7HTCEJ6D8G/k4-is-a-hill-matrix-cipher-hinted-at-by-the-extra-l-that) Tested, but the results don't decide it Evidence: 1 for, 1 against Disputed [**None of these.** ](https://mysteriesdept.com/mysteries/kryptos/answers/ANS0D7HTDXE1BY6/none-of-these) Not tested enough to call either way Evidence: none yet Still possible ## History 1. 2016[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.](https://mysteriesdept.com/sources/SRC0D7HSXJ045FJ/james-sanborns-kryptos-and-the-matrix-encryption-conjecture) 1. 2016[Bauer et al.: bauer, Link and Molle tested the matrix conjecture; it has not produced a solution.](https://mysteriesdept.com/sources/SRC0D7HSXJ045FJ/james-sanborns-kryptos-and-the-matrix-encryption-conjecture)Against: K4 is a Hill (matrix) cipher, hinted at by the extra L that spells HILL down the tableau's last column. 1. 2021[Bean puts forward: k4 uses a Gromark-type cipher (a keyed alphabet with a running numeric key generated by chain addition) or a…](https://mysteriesdept.com/sources/SRC0D7HSXST3N01/cryptodiagnosis-of-kryptos-k4) 1. 2021[Bean: monte Carlo permutation tests show a strong one-to-one relation between corresponding plaintext and…](https://mysteriesdept.com/sources/SRC0D7HSXST3N01/cryptodiagnosis-of-kryptos-k4)For: K4 uses a Gromark-type cipher (a keyed alphabet with a running numeric key generated by chain addition) or a… 1. 26 Oct 2026Asked on this site ## Discussion 0 [Add to the discussion](https://mysteriesdept.com/signin?next=/mysteries/kryptos/questions/QST0D7HT81Y2GZY/what-kind-of-cipher-is-k4%23discussion) Help with this question [ **Propose an answer** Something the evidence could support or rule out ] [ **Propose an answer** Something the evidence could support or rule out ](https://mysteriesdept.com/signin?next=/mysteries/kryptos/questions/QST0D7HT81Y2GZY/what-kind-of-cipher-is-k4%23add-answer) [ **Add evidence** A result for or against an answer ] [ **Add evidence** A result for or against an answer ](https://mysteriesdept.com/signin?next=/mysteries/kryptos/questions/QST0D7HT81Y2GZY/what-kind-of-cipher-is-k4%23add-evidence) [ **Ask a sub-question** A smaller question that would help settle this one ] [ **Ask a sub-question** A smaller question that would help settle this one ](https://mysteriesdept.com/signin?next=/mysteries/kryptos/questions/QST0D7HT81Y2GZY/what-kind-of-cipher-is-k4%23add-question) [ **Add a source** A paper, archive record or image ] [ **Add a source** A paper, archive record or image ](https://mysteriesdept.com/signin?next=/mysteries/kryptos/questions/QST0D7HT81Y2GZY/what-kind-of-cipher-is-k4%23add-source) Where it fits Kryptos **What kind of cipher is K4?** Key question · you're here [How far do the 24 released letters constrain K4?](https://mysteriesdept.com/mysteries/kryptos/questions/QST0D7HT89R1MSZ/how-far-do-the-24-released-letters-constrain-k4)Open · 3 answers, inconclusive [ Ask a question under this one ]