A Reddit user has posted scans of something that looks like a small codebook. It was found in a prison. Can a reader say more about it?
In 2016 several Brazilian newspapers reported on two encrypted letters sent by imprisoned members of the criminal organization PCC. Can my readers help to decipher the letter excerpts that are publicly available?
In 1934, an inmate of the Ohio State Penitentiary tried to hand an encrypted message to a visiting woman. A warden intercepted the message, a codebreaker in Washington could decipher it. Can a reader figure out what kind of cipher was used?