A 1542 Papal Cipher Cracked with Simulated Annealing
A 1542 letter from Cardinal Alessandro Farnese to the papal nuncio in Spain stayed unread for centuries, its digits hiding the key. By combining a beam-search decoder with a five-gram Italian language model and simulated annealing over possible keys, the cipher was broken. The recovered key assigns one or two digits per letter, with a single null; the opening reads 'Dopo la partita del Montepulciano', matching the cleartext on the same page.
The difficulty is deciding where each code ends. `73` is _d_, but `7 3` is also two letters, _n m_. Even with the key, a run of digits can be read more than one way.
- userbinator
Mentally autocorrected the title to "paypal cipher" and got enticed to click...
More seriously, this looks like the context modeling that advanced compression algorithms do, but in reverse.
Recovering the key does not settle the text.
That said, the Claudish in this article is only slightly annoying.
- raphlinus
I had a sense. Pangram identifies this as AI.
- esafak
I knew it was going to be cryptography. Everybody's cracking something these days. See also: https://news.ycombinator.com/item?id=49738551