No. 16, 1918. “Methods for the Solution of Running-key Ciphers.”
No. 17, 1918. “An Introduction to Methods for the Solution of Ciphers.”
No. 18, 1918. “Synoptic Tables for the Solution of Ciphers, and a Bibliography of Cipher Literature.”
No. 19, 1918. “Formulae for the Solution of Geometrical Transposition Ciphers,” by Captain Lenox R. Lohr, with an introduction by W. F. Friedman.
No. 20, 1918. “Several Machine Ciphers and Methods for Their Solution.”
No. 21, 1918. “Methods for the Reconstruction of Primary Alphabets.”
No. 22, 1922. “The Index of Coincidence and Its Applications in Cryptographic Analysis.”
Sacco, Luigi (General). Manuale di crittografia. Rome, 2nd edition, revised and enlarged, 1936. (The first edition was privately printed under the title Nozioni di crittografia. Rome, 1930.)
Zanotti, Mario. Crittografia. Milan, 1928.