The first cipher was simple—a substitution code containing 26 symbols, each of which stood in for a letter in the English alphabet. Donald Harden, a high school teacher, and his wife, Bettye ...

“This cipher was first submitted to the FBI Laboratory on November 13, 1969, but not successfully decrypted,” the statement continued. “Over the past 51 years CRRU [the FBI Cryptanalysis and ...

First published in newspapers on November 12, 1969, the 340-character cipher (often referred to as “Z340”) baffled amateur and professional cryptographers alike for years.