A Bribe and a Verdict: Wilhelm von Fürstenberg's Ciphered Letter from Vienna, 10 July 1659

Landesarchiv NRW, Abteilung Westfalen (Münster), W 004 (Manuskripte VI) Nr. 52 contains a letter from Wilhelm von Fürstenberg in Vienna to Jobst Edmund von Brabeck in Münster, dated 10 July 1659, with six passages in a letter cipher. The file is catalogued as "Geheime Schrift nebst Schlüssel", but the numerical key filed with it does not fit the passages, which had remained unread. This preprint shows that the passages use a two-alphabet periodic (Bellaso/Vigenère-type) cipher with the key BI over a 24-letter alphabet, restarted at each passage, and gives the decipherment, a provisional edition, an English translation and a commentary. Fürstenberg learns from the president of the Imperial Aulic Council (Reichshofrat), Count Ernst of Oettingen-Wallerstein, that a decision is due; reports that the Emperor will keep the word he gave in writing at Frankfurt; and, in a postscript, that everything "was concluded today in the secret council in favour of the prince, with no condition attached". The letter also arranges a bill of exchange for 700 Reichsthaler promised to the case's referent, the Aulic councillor Georg Ludwig von Lindenspür. Files: the preprint (PDF), a letter-by-letter transcription of the cipher passages with direct decipherment, and a Python script reproducing the decipherment and the index-of-coincidence statistics. Version 1: decipherment and provisional edition; the clear text of the letter is paraphrased and will be transcribed in full in a later version. The archive's images are not reproduced; they are viewable on Archivportal-D. AI assistance (Claude, Anthropic) was used in transcription, analysis and drafting and is disclosed in the text.