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.

77 eliminations recorded.

Title	Configs	Best	Verdict	Tier
Physical strip cipher model from Sanborn oral history Physical strip cipher model from Sanborn oral history — using analysis of the internal key values the cipher would need to produce. 86.5 million key/p…	86,502,054	0/24 (0.0)	NOISE	N/A
Beaufort-focused K4 attack Beaufort-focused K4 attack — using a method that replaces each letter using a repeating keyword (Vigenère cipher). 25.1 million key/parameter combinat…	25,068,142	8/24 (0.0)	NOISE	N/A
Cipher Model Deep Structural Cipher Model Deep Structural — using analysis of the internal key values the cipher would need to produce. 11.9 million key/parameter combinations wer…	11,886,547	15/24 (0.0)	NOISE	N/A
Keystream generated by columnar transposition of periodic key Keystream generated by columnar transposition of periodic key — using a method that replaces each letter using a repeating keyword (Vigenère cipher). …	9,818,640	0/24 (0.0)	NOISE	N/A
Periodic cipher on null-extracted 80-char CT Periodic cipher on null-extracted 80-char CT — using a method that replaces each letter using a repeating keyword (Vigenère cipher). 5.8 million key/p…	5,833,230	7/24 (0.0)	NOISE	N/A
Cysquare cipher on Kryptos Vigenere tableau (26x26 body) Cysquare cipher on Kryptos Vigenere tableau (26x26 body) — using a method that replaces each letter using a repeating keyword (Vigenère cipher). 2.3 m…	2,339,030	8/24 (0.0)	NOISE	N/A
Autokey cipher with all variant combinations Autokey cipher with all variant combinations — structural ceiling proven at 21/24 — using a method that replaces each letter using a repeating keyword…	456,976	21/24 (0.0)	ELIMINATED	Tier 1
VIC key derivation + Beaufort/Vigenere substitution hybrid (no checkerboard) VIC key derivation + Beaufort/Vigenere substitution hybrid (no checkerboard) — using a method that replaces each letter using a repeating keyword (Vig…	254,720	6/24 (0.0)	NOISE	N/A
NDYAHR directional vectors coupled with consensus null mask + col-7 Beaufort NDYAHR directional vectors coupled with consensus null mask + col-7 Beaufort — using a method that replaces each letter using a repeating keyword with…	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) K0 Morse text (10+ variants) as running key for K4, all offsets, Beaufort/Vigenere/VarBeau, AZ/KA, Model A (CT97) + Model B (CT73) — using a method th…	28,140	5/24 (0.0)	NOISE	N/A
Keyword-derived transposition reveals periodic key Keyword-derived transposition reveals periodic key — using a method that replaces each letter using a repeating keyword (Vigenère cipher). 12 thousand…	11,684	17/24 (0.0)	NOISE	N/A
Hill cipher with YAR-derived matrix parameters (width 9) Hill cipher with YAR-derived matrix parameters (width 9, 2x2 and 3x3) — using a method that encrypts groups of letters using matrix multiplication (Hi…	2,000	0/24 (0.0)	ELIMINATED	Tier 1
Cipher Model Crosssweep Cipher Model Crosssweep — using analysis of the internal key values the cipher would need to produce. 2 thousand key/parameter combinations were teste…	1,872	15/24 (0.0)	NOISE	N/A
Proper autokey cross-validation (ENE↔BC, no transposition) Proper autokey cross-validation (ENE↔BC, no transposition) — using a method that replaces each letter using a repeating keyword (Vigenère cipher). 1 t…	1,080	0/24 (0.0)	ELIMINATED	N/A
Cipher Model Variations Cipher Model Variations — using analysis of the internal key values the cipher would need to produce. 969 key/parameter combinations were tested. Best…	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 Cipher Model Variations Ext — using analysis of the internal key values the cipher would need to produce. 421 key/parameter combinations were tested. …	421	15/24 (0.0)	NOISE	N/A
Z3 SMT proof of periodic key feasibility under Bean+crib constraints Z3 SMT proof of periodic key feasibility under Bean+crib constraints — using a method that replaces each letter using a repeating keyword (Vigenère ci…	82	0/24 (0.0)	NOISE	N/A
Autokey Vigenere bidirectional back-derivation from BERLINCLOCK Autokey Vigenere bidirectional back-derivation from BERLINCLOCK — using a method that replaces each letter using a repeating keyword (Vigenère cipher)…	45	0/24 (0.0)	NOISE	N/A
Date-derived key '04111922' (Carter tomb EU format) as vigenere Date-derived key '04111922' (Carter tomb EU format) as vigenere — using 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 Date-derived key '02161923' (Burial chamber opened) as vigenere — using 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 Date-derived key '11041922' (Carter tomb discovery date) as vigenere — using a method that replaces each letter using a repeating keyword (Vigenère ci…	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '3817N7709W' (CIA HQ coordinates) as vigenere Date-derived key '3817N7709W' (CIA HQ coordinates) as vigenere — using 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 Date-derived key '385709N0770706W' (Precise coords) as vigenere — using 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 Date-derived key '1990' (Kryptos installation year) as vigenere — using 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 Date-derived key '11031990' (Kryptos dedication Nov 3 1990) as vigenere — using a method that replaces each letter using a repeating keyword (Vigenère…	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 Vigenere with REVERSED Kryptos-keyed alphabet — using 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 Extended autokey bidirectional: all seed lengths 1-96, AZ+KA — using a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	ELIMINATED	N/A
Extend XOR Autokey Extend XOR Autokey — using a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Kasiski Kasiski — using a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Keyword Progressive Sweep Keyword Progressive Sweep — using a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	NOISE	N/A
Poly Poly — using a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	ELIMINATED	N/A
Poly Poly — using a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	ELIMINATED	N/A
Poly Poly — using a method that replaces each letter using a repeating keyword (Vigenère cipher).	N/A	0/24 (0.0)	ELIMINATED	N/A
Stego Cipher Brute Stego Cipher Brute — using 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 Running-key Vigenère/Beaufort from novel/speech text — using 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 Date-derived key '04111922' (Carter tomb EU format) as beaufort — using a method that replaces each letter using a repeating keyword with reversed ari…	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '02161923' (Burial chamber opened) as beaufort Date-derived key '02161923' (Burial chamber opened) as beaufort — using a method that replaces each letter using a repeating keyword with reversed ari…	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '02161923' (Burial chamber opened) as var_beaufort Date-derived key '02161923' (Burial chamber opened) as var_beaufort — using a method that replaces each letter using a repeating keyword with reversed…	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '11041922' (Carter tomb discovery date) as beaufort Date-derived key '11041922' (Carter tomb discovery date) as beaufort — using a method that replaces each letter using a repeating keyword with reverse…	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '11041922' (Carter tomb discovery date) as var_beaufort Date-derived key '11041922' (Carter tomb discovery date) as var_beaufort — using a method that replaces each letter using a repeating keyword with rev…	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '04111922' (Carter tomb EU format) as var_beaufort Date-derived key '04111922' (Carter tomb EU format) as var_beaufort — using a method that replaces each letter using a repeating keyword with reversed…	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '1990' (Kryptos installation year) as beaufort Date-derived key '1990' (Kryptos installation year) as beaufort — using a method that replaces each letter using a repeating keyword with reversed ari…	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '11031990' (Kryptos dedication Nov 3 1990) as beaufort Date-derived key '11031990' (Kryptos dedication Nov 3 1990) as beaufort — using a method that replaces each letter using a repeating keyword with reve…	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '11031990' (Kryptos dedication Nov 3 1990) as var_beaufort Date-derived key '11031990' (Kryptos dedication Nov 3 1990) as var_beaufort — using a method that replaces each letter using a repeating keyword with …	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '3817N7709W' (CIA HQ coordinates) as beaufort Date-derived key '3817N7709W' (CIA HQ coordinates) as beaufort — using a method that replaces each letter using a repeating keyword with reversed arit…	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '3817N7709W' (CIA HQ coordinates) as var_beaufort Date-derived key '3817N7709W' (CIA HQ coordinates) as var_beaufort — using a method that replaces each letter using a repeating keyword with reversed …	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '385709N0770706W' (Precise coords) as beaufort Date-derived key '385709N0770706W' (Precise coords) as beaufort — using a method that replaces each letter using a repeating keyword with reversed ari…	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '385709N0770706W' (Precise coords) as var_beaufort Date-derived key '385709N0770706W' (Precise coords) as var_beaufort — using a method that replaces each letter using a repeating keyword with reversed…	N/A	0/24 (0.0)	NOISE	N/A
Date-derived key '1990' (Kryptos installation year) as var_beaufort Date-derived key '1990' (Kryptos installation year) as var_beaufort — using a method that replaces each letter using a repeating keyword with reversed…	N/A	0/24 (0.0)	NOISE	N/A
Constrained keystream MCMC with SA for 73-char Beaufort Constrained keystream MCMC with SA for 73-char Beaufort — using a method that replaces each letter using a repeating keyword with reversed arithmetic …	N/A	0/24 (0.0)	NOISE	N/A
Ct Mutation Nullmask Beaufort Ct Mutation Nullmask Beaufort — using a method that replaces each letter using a repeating keyword with reversed arithmetic (Beaufort cipher). Best ma…	N/A	16/24 (0.0)	NOISE	N/A
Polybius grid walk analysis of Beaufort keystream Polybius grid walk analysis of Beaufort keystream — using a method that replaces each letter using a repeating keyword with reversed arithmetic (Beauf…	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 Brute-force PT[34]-PT[35] under Beaufort A=0, scoring extended keystream against confirmed properties — using a method that replaces each letter using…	N/A	0/24 (0.0)	NOISE	N/A
Sanborn Error Beaufort Sensitivity Sanborn Error Beaufort Sensitivity — using 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 Periodic Beaufort Keyword Sweep 73char — using 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 Null Mask Beaufort Deep 20260404 — using 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 Period13 Mixed Alphabet Beaufort — using 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 Agent K4 Keystream Language Scan — using analysis of the internal key values the cipher would need to produce.	N/A	0/24 (0.0)	NOISE	N/A
BCL Palette Keystream BCL Palette Keystream — using analysis of the internal key values the cipher would need to produce.	N/A	0/24 (0.0)	NOISE	N/A
Bean Keystream Bean Keystream — using analysis of the internal key values the cipher would need to produce.	N/A	3/24 (0.0)	NOISE	N/A
Digraph Anchored Search Digraph Anchored Search — using analysis of the internal key values the cipher would need to produce.	N/A	0/24 (0.0)	NOISE	N/A
Digraph Constrained SA Digraph Constrained SA — using analysis of the internal key values the cipher would need to produce.	N/A	0/24 (0.0)	NOISE	N/A
Digraph Running Key Digraph Running Key — using 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 Keystream structure analysis for width-7 orderings — using 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 Monoalphabetic affine cipher exhaustive disproof — using 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 Simple monoalphabetic substitution cipher — using 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) KA tableau gaps: Porta periods 15-26 (id+columnar all periods), Gronsfeld+columnar, structural proofs (two-square/four-square) — using a method that u…	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 Null palette {B,G,I,K,O,W,Z} as 7-digit Gromark primer on raw CT97 — using a method that generates key numbers using Fibonacci-like sequences (Gromark…	N/A	0/24 (0.0)	ELIMINATED	N/A
Hill cipher n=2,3 + columnar transposition widths 5-8 Hill cipher n=2,3 + columnar transposition widths 5-8 — using 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 Hill cipher + anomaly-inspired parameters — using 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 Exhaustive Gronsfeld (digit-only key) at period 7 — using 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 Mixed alphabet cipher + columnar transposition — using a method using a scrambled alphabet for substitution.	N/A	0/24 (0.0)	NOISE	N/A