Method · cryptanalysis

Naibbe-structured key search with held-out check

Takes the Naibbe system as known (Greshko's unigram, prefix and suffix inventories, a fixed number of symbols per letter in each class) and searches for the key by class-preserving swaps under a 5-gram letter model, on the training quires only; the key is then read unchanged on the held-out quires. Validated on planted Naibbe keys for Latin and Italian.

CryptanalysisVersion 1.0Licence MIT4 runsUsed on 1 mystery

Questions it answers

Is it a cipher of a known language?

Code

Download module (.c)solver2.cView source

Runs and results 4 runs

Run	Mystery	Measured	Result	Against
RUN0DC7QP36PPPB	Voynich	Tokens that are a unigram type or split into prefix + suffix / of which unigram types / word types that parse	whole book 78.2 % (41.7 % unigram), types 36.5 %; Currier B 81.3 % (47.0 %); Currier A 72.4 % (30.8 %)	Naibbe ciphertext 100 % (about 47 % unigram) · plain Latin 2 %
RUN0DC7QXZNFBJF	Voynich	Held-out letters decoded correctly / held-out gap (nats/letter) / dict5 / restart agreement	Latin: 98.0 % / -0.018 / 0.543 / 0.997. Italian: 99.1 % / 0.069 / 0.443 / 1.000	Same key with letters permuted within each class: gap 2.93 (Latin), 3.31 (Italian) · dict5 0.003, 0.001
RUN0DC7QYS5KSXZ	Voynich	Held-out gap (nats/letter) / dict5 / restart agreement, manuscript vs its words shuffled across the book	manuscript: gap 1.231, 1.222, 1.259; dict5 0.040, 0.038, 0.042; agreement 0.40, 0.38, 0.45. Shuffled: gap 1.299, 1.279, 1.242; dict5 0.033, 0.030, 0.040; agreement 0.44, 0.36, 0.36	Planted-key control: gap -0.018, dict5 0.543, agreement 0.997 · permuted fitted key: gap 2.79-3.06
RUN0DC7QZ6DA6J4	Voynich	Held-out gap (nats/letter) / dict5	whole book, Italian: 1.622 / 0.009 (shuffled 1.618 / 0.013). Currier B only: Latin 1.389 / 0.034; Italian 1.709 / 0.012	Italian control: 0.069 / 0.443

Applied to

Voynich Manuscript

3 datasetsLatin genre texts, Naibbe cipher tables and example plaintexts (greshko/naibbe-cipher, commit 719f2f4c), ZL3b transcription