Meredith Gardner, who has died aged 89, was the American codebreaker responsible for breaking the ciphers that led to the arrests of the atom spies Julius and Ethel Rosenberg and the break-up of the Cambridge spy ring.During the late 1940s, Gardner was the main cryptanalyst working on the Venona material, messages sent between the KGB’s Moscow Centre and its agent handlers abroad using the theoretically unbreakable one-time pad system.Fluent in French, German, Greek, Italian, Japanese, Latin, Lithuanian, Russian and Spanish, Gardner joined the United States Army’s codebreaking organisation, the Signals Security Agency, early in the Second World War.He worked initially...