Secret and urgent
Subtitle: the story of codes and ciphers
By: by Fletcher Pratt.
Publisher: Blue Ribbon Books
Published: 1982
Place of publication: Garden City, N.Y
Language: eng
Number of pages: 282
Subjects: Cryptography.; Cyphers.
Notes: Photocopy. Ann Arbor, Mich. : University Microfilms International, 1982.