William F. Friedman

“ First, the basic law underlying the B-machine was of such character that the ciphering mechanisms seemed to start from certain initial settings and to progress absolutely methodically without cyclic repetition of any sort, straight through to the end of the messages, the longest of which for which plain text had been recovered comprised over 1,500 letters. Secondly, two identical plain-text letters in sequence could never be represented by two identical cipher-text letters; nor could two identical plain text letters 26 letters apart be identically enciphered. ”

“ Once these factors concerning all indicators have been established, and our machine is in operation, the reading of B-machine messages resolves itself into the establishment of the daily plugboard arrangement, that is, the order and identity of the wires leading from the keyboard into the cryptograph and thence out of the cryptograph into the printing unit. Cryptanalytic procedures for this purpose have already been established and tested so that this should not be a serious problem. ”

“ While awaiting the arrival of this materiel a hand-operated machine was designed by personnel of the J-B section, constructed by them, and is at this writing being used to assist in the decipherment of messages. Basically, the B-machine consists of 13 rotary, 6-level, 25-point, switches of the type employed in automatic telephony. One of these 13 switches controls the encipherment of the "6's" and it goes through the same 25-point cycle over and over again as many times as is necessary to encipher the messages. ”

“ What differentiates one indicator from another within such a set of 20 indicators are the relative starting points within the three banks of switches. These starting points appear to have been very carefully selected so as to preclude or reduce the possibility of "overlaps," that is, the production of two messages which in whole or in part have been enciphered by identical keying elements in identical sequence. ”

“ The excellent work of Tabulating Machine Supervisor Ulrich J. Kropfl end Cryptanalytic Aide Mary J. Dunning in performing countless tabulating machine operations deserves mention, as well as the painstaking work of the various card punch operators under their supervision. Miss Dronenburg performed and assisted in many clerical jobs of routine and special nature in connection with these studies. The work of Research Analysts John B. Hurt and Paul S. Cate must be mentioned in connection with our efforts to reconstruct the texts of messages in Japanese. ”

“ These 25 alphabets were merely a carefully selected set of 25 of the possible 720 permutations or transpositions of 6 elements taken 6 at a time, and a
1Washington, Berlin, London, Paris, Moscow, Rome, Geneva, Brussels, Ankara, Shanghai, and Peking. deciphering chart or "development" was constructed to correspond with these 25 permutations. ”