Straddling checkerboard digit-level attack on K4

In plain English: Straddling checkerboard digit-level attack on K4 — using a method that encodes letters as variable-length digit sequences. 86 thousand key/parameter combinations were tested. This approach is ruled out within the tested scope.

NOISE Tier 4

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: 86,066
Best Score: 0 / 24 known letters matched · no better than random guessing (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 4: Not properly tested. Fully open.
Date Tested: 2026-04-03
Script: scripts/analysis/e_straddling_checkerboard_k4.py

Reproduce

PYTHONPATH=src python3 -u scripts/analysis/e_straddling_checkerboard_k4.py

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

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