Vatican Apostolic Archive

New Capabilities

As of September 2026: Holds the Spagna 1A correspondence containing the Farnese letter

A 484-year-old papal letter written in a numeric cipher has been cracked using simulated annealing, an optimization algorithm that accepts worse solutions to escape dead ends. The cipher used variable-length codes and decoy nulls; the recovered key, 18 letters plus one null, held up when each half was solved independently.

Updated Sep 19