The Copiale cipher

The decipherment is established and independently checkable. The cipher is a homophonic substitution for German: each plaintext letter can be written by one of several symbols, common letters having more alternatives, which flattens the frequency distribution that a simple substitution would leave; the unaccented Roman letters stand for nothing and mark the spaces between words; some symbols stand for common digraphs or suffixes⁠[4]⁠[5]. The German is of the eighteenth century and the content is the "Gesetzbuch" of the Oculists: the degrees of membership, the ceremony of admission with its blindfold, eye tests and oaths, the signs and words of recognition, and the duties of officers⁠[5]⁠[1]. The society was based at Wolfenbüttel; a separate Oculist archive in the Staatsarchiv Wolfenbüttel contains material in the same cipher, which the team transcribed and deciphered in 2012 and published alongside the Copiale text⁠[1]. Önnerfors's reading of the society's insignia, cats watching mice, and of its interest in Masonic ritual suggests an order that observed Freemasonry from inside, whether as a rival, an offshoot or an intelligence operation⁠[6].

The method is the point. The team began with no knowledge of the language. Their first hypothesis, that the Roman letters were the cipher text and the other symbols decoration, was tested by treating the Roman letters as a substitution cipher for German and failed. They then considered the abstract symbols as the carrier and used expectation-maximisation decipherment against language models for some eighty candidate languages, scoring how well each language explained the symbol sequence under an unknown substitution; German scored best. Treating the Roman letters as spaces and allowing several symbols per letter produced readable German, and the first clear phrases confirmed the hypothesis⁠[4]⁠[2]. The reading was then checked the way a decipherment should be: every page was read, the German was grammatical throughout, the content was coherent and historically specific, and a second corpus in the same cipher from Wolfenbüttel read correctly with the same key⁠[5]⁠[1].

No rival reading exists. The questions that remain are historical. The date of the manuscript is bracketed between about 1730 and 1780 by paper and hand, and the "Copiales 3" note implies it is a copy, so the original composition may be earlier than the manuscript⁠[1]⁠[3]. The Oculists' purpose is argued between a Masonic lodge under another name, a society that collected and recorded Masonic secrets, and an ophthalmological fraternity whose eye imagery was more than metaphor; the ritual's eye tests and the Wolfenbüttel archive are the evidence⁠[6]⁠[5]. The identity of the owner "Philipp" of 1866 and the route from Wolfenbüttel to the Berlin academy are not documented⁠[1].

The cipher is settled. The historical questions would be settled by the Wolfenbüttel archive, which names members and dates, and by the Academy's accession records for the manuscript's provenance⁠[1]⁠[5]. For the site's purposes the case shows the tests a claimed decipherment of any of the unsolved documents must pass: a stated method, a published key, a reading of the whole text rather than selected passages, grammatical output in an identified language, and confirmation from an independent text or source⁠[4].