French encrypted newspaper advertisements in the 19th century

Abstract

We present a ciphertext database created by one of the authors. It contains over 3700 encrypted newspaper advertisements published in the French newspaper Le Figaro between 1875 and 1897. The collection includes over 2300 solved messages, which have been encrypted in almost 90 different crypto systems, as well as over 1400 unsolved cryptograms. We introduce some of the most interesting solved and unsolved advertisements, including messages based on ciphers, codes, and steganography. It will become clear that in addition to the messages contained in the database so far, thousands more encrypted advertisements from French newspapers remain to be catalogued and deciphered.