Autokey cipher with all variant combinations

Autokey cipher with all variant combinations — structural ceiling proven at 21/24

In plain English: 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 impossible — no key or setting can make it work. Best match: 21/24 known letters (statistically expected at this key length, not a real signal). This approach is ruled out within the tested scope.

ELIMINATED Tier 1

How to read this record

Verdict – NOISE (no better than random guessing), INTERESTING (slightly above random, almost certainly coincidence), SIGNAL (statistically unusual, warrants investigation), or FULL MATCH (all 24 known letters correct).
Confidence Tier – Tier 1 = mathematical proof (permanent). Tier 2 = every possibility tested. Tier 3 = partially tested. Tier 4 = not yet tested.
Configs Tested – How many different key/parameter combinations were tried.
Best Score – How many of the 24 known plaintext letters the best attempt matched (out of 24).
Keystream Consistency (Bean) – Whether the key values at different positions are mathematically consistent with each other.
Scope Limitations – What this elimination does not rule out.

Configs Tested: 456,976
Best Score: 21 / 24 known letters matched · worth investigating (random guess would score: 0.0)
Keystream Consistency (Bean): FAIL
Checks whether the key values at different positions are mathematically consistent with each other.
Confidence: Tier 1: Mathematical proof. Permanently valid unless cribs or CT are wrong.
Date Tested: 2026-02-19
Script: scripts/polyalphabetic/e_chart_02_autokey.py

Scope Limitations

This elimination does not rule out:

Does not test autokey as one layer of multi-layer. Structural ceiling proven: autokey max 21/24.

Assumptions

Direct positional correspondence
All autokey seed lengths tested

Reproduce

PYTHONPATH=src python3 -u scripts/polyalphabetic/e_chart_02_autokey.py

Requires the kryptos repo, Python 3.11+, PYTHONPATH=src.

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