Cipher challenge platform
Appears in 1 story · Last updated Sep 19, 2026
As of September 2026: Hosted Vatican Challenge Part 5 since July 2019; showed zero solves as of September 16, 2026
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
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