Columnar transposition × periodic substitution on 73-char column mask extract

Meet-in-the-Middle attack on 73-char column mask extract: columnar transposition (w7-9 exhaustive, 408,240 permutations) × periodic sub (p1-13) × Vig/Beau/VBeau × key-at-CT and key-at-PT models. Also tested rail fence (depths 2-15) and route ciphers (serpentine, spiral, colwise for widths 7-14). 31.8M total configs. Best: 18/24 at w9/p11/vigenere. Monte Carlo verification (100K random w9 perms at p11) shows ~3.6 expected hits in full 362,880 search = MARGINAL NOISE. Decrypted texts: IC 0.035-0.044 (random), zero crib matches at expected positions.

In plain English: Meet-in-the-Middle attack on 73-char column mask extract: columnar transposition (w7-9 exhaustive, 408,240 permutations) × periodic sub (p1-13) × Vig/Beau/VBeau × key-at-CT and key-at-PT models — using a combined approach: scramble the letter order AND replace each letter. Every possible combination was tested (31.8 million configurations) — none produced a valid solution. Best match: 18/24 known letters (statistically expected at this key length, not a real signal). This approach is ruled out within the tested scope.

NOISE: best 18/24 at w9/p11 ≈ expected by chance (Monte Carlo: ~3.6 hits expected) Tier 2

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: 31,800,000
Best Score: 18 / 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 2: Exhaustive search under stated assumptions. Does not eliminate multi-layer variants.
Truth Tag: [INTERNAL RESULT]
Date Tested: 2026-03-12

Scope Limitations

This elimination does not rule out:

Only columnar, rail fence, and route transpositions. Other transposition types (double columnar, Myszkowski, turning grille) untested on 73-char extract.

Assumptions

Column mask null removal
Columnar/route transposition
Periodic substitution
Shifted crib positions (ENE 13-25, BC 47-57)

Reproduce

PYTHONPATH=src python3 -u scripts/grille/e_mitm_trans_sub_73_01.py

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

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