Substitution

Methods that replace each letter with a different letter using a key or pattern, like a secret alphabet. Includes Vigenère, Beaufort, Quagmire, Hill, and more.

What we tested: Every possible repeating keyword at every possible length has been mathematically proven impossible for K4 — not just searched, but proven with algebra. This includes Vigenère, Beaufort, and all their variants with any keyword. Even a specific keyword you have in mind cannot work as a simple repeating-key cipher on K4.

79 eliminations recorded.

Title	Configs	Best	Verdict	Tier
Physical strip cipher model from Sanborn oral history Tested analysis of the internal key values the cipher would need to produce. 86.5 million key/parameter combinations were tested.	86,502,054	0/24 (0.0)	NOISE	N/A
Beaufort-focused K4 attack Tested a method that replaces each letter using a repeating keyword (Vigenère cipher). 25.1 million key/parameter combinations were tested.	25,068,142	8/24 (0.0)	NOISE	N/A
Cipher Model Deep Structural Tested analysis of the internal key values the cipher would need to produce. 11.9 million key/parameter combinations were tested. Best match: 15/24 kn…	11,886,547	15/24 (0.0)	NOISE	N/A
Keystream generated by columnar transposition of periodic key Tested a method that replaces each letter using a repeating keyword (Vigenère cipher). 9.8 million key/parameter combinations were tested.	9,818,640	0/24 (0.0)	NOISE	N/A
Periodic cipher on null-extracted 80-char CT Tested a method that replaces each letter using a repeating keyword (Vigenère cipher). 5.8 million key/parameter combinations were tested.	5,833,230	7/24 (0.0)	NOISE	N/A
Cysquare cipher on Kryptos Vigenere tableau (26x26 body) Tested a method that replaces each letter using a repeating keyword (Vigenère cipher). 2.3 million key/parameter combinations were tested.	2,339,030	8/24 (0.0)	NOISE	N/A
Autokey cipher with all variant combinations Structural ceiling proven at 21/24 — using a method that replaces each letter using a repeating keyword (Vigenère cipher). Mathematically proven impos…	456,976	21/24 (0.0)	ELIMINATED	Tier 1
VIC key derivation + Beaufort/Vigenere substitution hybrid (no checkerboard) Tested a method that replaces each letter using a repeating keyword (Vigenère cipher). 255 thousand key/parameter combinations were tested.	254,720	6/24 (0.0)	NOISE	N/A
NDYAHR directional vectors coupled with consensus null mask + col-7 Beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher). 64 thousand key/parameter combinations…	63,684	7/24 (0.0)	NOISE	N/A
Autokey cipher on 73-char column mask extract (all variants) Tested autokey (PT/CT feedback × Vig/Beau/VBeau × AZ/KA), progressive key, running key on 73-char column mask extracts from the 28×31 native grid null…	46,170	6/24 (0.0)	NOISE	Tier 2
K0 Morse text (10+ variants) as running key for K4, all offsets, Beaufort/Vigenere/VarBeau, AZ/KA, Model A (CT97) + Model B (CT73) Tested a method that replaces each letter using a repeating keyword (Vigenère cipher). 28 thousand key/parameter combinations were tested.	28,140	5/24 (0.0)	NOISE	N/A
Keyword-derived transposition reveals periodic key Tested a method that replaces each letter using a repeating keyword (Vigenère cipher). 12 thousand key/parameter combinations were tested. Best match:…	11,684	17/24 (0.0)	NOISE	N/A
Hill cipher with YAR-derived matrix parameters (width 9) 2x2 and 3x3) — using a method that encrypts groups of letters using matrix multiplication (Hill cipher). Mathematically proven impossible — no key or …	2,000	0/24 (0.0)	ELIMINATED	Tier 1
Cipher Model Crosssweep Tested analysis of the internal key values the cipher would need to produce. 2 thousand key/parameter combinations were tested. Best match: 15/24 know…	1,872	15/24 (0.0)	NOISE	N/A
Proper autokey cross-validation (ENE↔BC, no transposition) Tested a method that replaces each letter using a repeating keyword (Vigenère cipher). 1 thousand key/parameter combinations were tested.	1,080	0/24 (0.0)	ELIMINATED	N/A
Cipher Model Variations Tested analysis of the internal key values the cipher would need to produce. 969 key/parameter combinations were tested. Best match: 15/24 known lette…	969	15/24 (0.0)	NOISE	N/A
Autokey chain propagation from crib bootstrap. Phase 4 scores 24/24 circularly (cribs used to derive key, then checked against same cribs). Phase 5 cross-validation scored 0/24 — not a real signal. All variants (Vig/Beau/VarBeau), AZ+KA, primers 1-29. Autokey chain propagation from crib bootstrap — using a method that replaces each letter using a repeating keyword (Vigenère cipher). 480 key/paramete…	480	0/24 (0.0)	ELIMINATED	N/A
Cipher Model Variations Ext Tested analysis of the internal key values the cipher would need to produce. 421 key/parameter combinations were tested. Best match: 15/24 known lette…	421	15/24 (0.0)	NOISE	N/A
Z3 SMT proof of periodic key feasibility under Bean+crib constraints Tested a method that replaces each letter using a repeating keyword (Vigenère cipher). 82 key/parameter combinations were tested.	82	0/24 (0.0)	NOISE	N/A
Autokey Vigenere bidirectional back-derivation from BERLINCLOCK Tested a method that replaces each letter using a repeating keyword (Vigenère cipher). 45 key/parameter combinations were tested.	45	0/24 (0.0)	NOISE	N/A
Date-derived key '04111922' (Carter tomb EU format) as vigenere Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '02161923' (Burial chamber opened) as vigenere Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '11041922' (Carter tomb discovery date) as vigenere Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '3817N7709W' (CIA HQ coordinates) as vigenere Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '385709N0770706W' (Precise coords) as vigenere Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '1990' (Kryptos installation year) as vigenere Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '11031990' (Kryptos dedication Nov 3 1990) as vigenere Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Coordinates as fractional key values 'The point' = decimal point: coordinates as fractional key values — using a method that replaces each letter using a repeating keyword (Vigenère ciphe…	N/A	0/24 (0.0)	NOISE	N/A
Vigenere with REVERSED Kryptos-keyed alphabet Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Extended autokey bidirectional: all seed lengths 1-96, AZ+KA Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	ELIMINATED	N/A
Extend XOR Autokey Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Kasiski Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Keyword Progressive Sweep Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Poly Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	ELIMINATED	N/A
Poly Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	ELIMINATED	N/A
Poly Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	ELIMINATED	N/A
Stego Cipher Brute Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Running-key Vigenère/Beaufort from novel/speech text Tested a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '04111922' (Carter tomb EU format) as beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '02161923' (Burial chamber opened) as beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '02161923' (Burial chamber opened) as var_beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '11041922' (Carter tomb discovery date) as beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '11041922' (Carter tomb discovery date) as var_beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '04111922' (Carter tomb EU format) as var_beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '1990' (Kryptos installation year) as beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '11031990' (Kryptos dedication Nov 3 1990) as beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '11031990' (Kryptos dedication Nov 3 1990) as var_beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '3817N7709W' (CIA HQ coordinates) as beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '3817N7709W' (CIA HQ coordinates) as var_beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '385709N0770706W' (Precise coords) as beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '385709N0770706W' (Precise coords) as var_beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '1990' (Kryptos installation year) as var_beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Constrained keystream MCMC with SA for 73-char Beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Ct Mutation Nullmask Beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher). Best match: 16/24 known letters — slig…	N/A	16/24 (0.0)	NOISE	N/A
Polybius grid walk analysis of Beaufort keystream Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Brute-force PT[34]-PT[35] under Beaufort A=0, scoring extended keystream against confirmed properties Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Sanborn Error Beaufort Sensitivity Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	6/24 (0.0)	NOISE	N/A
Periodic Beaufort Keyword Sweep 73char Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Null Beaufort Exhaustive Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Null Mask Beaufort Deep 20260404 Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Period13 Mixed Alphabet Beaufort Tested a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher).	N/A	0/24 (0.0)	NOISE	N/A
Agent K4 Keystream Language Scan Tested analysis of the internal key values the cipher would need to produce.	N/A	0/24 (0.0)	NOISE	N/A
BCL Palette Keystream Tested analysis of the internal key values the cipher would need to produce.	N/A	0/24 (0.0)	NOISE	N/A
Bean Keystream Tested analysis of the internal key values the cipher would need to produce.	N/A	3/24 (0.0)	NOISE	N/A
Digraph Anchored Search Tested analysis of the internal key values the cipher would need to produce.	N/A	0/24 (0.0)	NOISE	N/A
Digraph Constrained SA Tested analysis of the internal key values the cipher would need to produce.	N/A	0/24 (0.0)	NOISE	N/A
Digraph Running Key Tested analysis of the internal key values the cipher would need to produce.	N/A	0/24 (0.0)	NOISE	N/A
Keystream structure analysis for width-7 orderings Tested analysis of the internal key values the cipher would need to produce.	N/A	0/24 (0.0)	NOISE	N/A
Monoalphabetic affine cipher exhaustive disproof Tested a simple letter-shifting method (Caesar/ROT cipher or affine substitution).	N/A	0/24 (0.0)	ELIMINATED	N/A
Structural impossibility proof (direct correspondence) Homophonic substitution partition analysis — structural impossibility proof — using a method that replaces each letter with a fixed substitute (simple…	N/A	0/24 (0.0)	ELIMINATED	Tier 1
Structural impossibility proof (pure model) Nomenclator (code+cipher) model — structural analysis of repeated word EAST — using a method that replaces each letter with a fixed substitute (simple…	N/A	0/24 (0.0)	ELIMINATED	Tier 1
Simple monoalphabetic substitution cipher Tested a method that replaces each letter with a fixed substitute (simple substitution).	N/A	0/24 (0.0)	NOISE	N/A
KA tableau gaps: Porta periods 15-26 (id+columnar all periods), Gronsfeld+columnar, structural proofs (two-square/four-square) Tested a method that uses 13 paired-letter alphabets selected by a keyword (Porta cipher).	N/A	0/24 (0.0)	NOISE	N/A
Null palette {B,G,I,K,O,W,Z} as 7-digit Gromark primer on raw CT97 Tested a method that generates key numbers using Fibonacci-like sequences (Gromark/Vimark cipher).	N/A	0/24 (0.0)	ELIMINATED	N/A
Hill cipher n=2,3 + columnar transposition widths 5-8 Tested a method that encrypts groups of letters using matrix multiplication (Hill cipher).	N/A	0/24 (0.0)	ELIMINATED	N/A
Hill cipher + anomaly-inspired parameters Tested a method that encrypts groups of letters using matrix multiplication (Hill cipher).	N/A	0/24 (0.0)	NOISE	N/A
Exhaustive Gronsfeld (digit-only key) at period 7 Tested a method that uses a numeric key (digits only) to shift letters (Gronsfeld cipher).	N/A	0/24 (0.0)	NOISE	N/A
Mixed alphabet cipher + columnar transposition Tested a method using a scrambled alphabet for substitution.	N/A	0/24 (0.0)	NOISE	N/A
Quagmire III (K2 canonical: ABSCISSA + KRYPTOS alphabet) on the 4 w10 Bean-surviving column orders from f_archive_col_notation_v1; bin D3 follow-on. Quagmire III (K2 canonical: ABSCISSA + KRYPTOS alphabet) on the 4 w10 Bean-surviving column orders from f_archive_col_notation_v1 — using a method tha…	N/A	0/24 (0.0)	NOISE	N/A