Page:Preliminary Historical Report on the Solution of the "B" Machine.pdf/8

 applying the principles of solution by homologs, guided by the aid of the reconstructed basic sequences. It was all the more gratifying that this could be done on the very day that announcement was made of the signing of the Tripartite Agreement among Germany, Italy, and Japan.

15. Much work remained to be done, however, since only the data applicable to but one out of the whole set of 120 indicators were at hand. Tc solve the remaining 119 indicators appeared still to present quite a large problem. These solutions consist of finding the initial settings of three 20-level rotary, electrical cryptographic elements of 25 points each, and finding the order in which these three elements are brought into play within each indicator system. With but little slackening of the pace set by the personnel themselves, work has progressed with vigor and at this moment solutions for over one-third of the 120 indicators are available.

16. As to the mechanics of the B-machine, naturally the basic principles of its construction and operation were deduced from the cryptographic phenomena observable in the messages, and immediately plans were initiated for the construction of an equivalent machine for our purposes. Orders for the materiel for 2 fully automatic machines were placed and expedited. 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. It has 150 cross-connections, which, as stated above, had been established long ago. As to the "20's", these are enciphered by means of 3 banks of 4 switches each, each bank having 500 cross-connections, making a total of 1,500 sub-circuits available for the encipherment of any given letter. The arrangements for advancing these switches is such that for a given indicator, say, bank number 3 steps continuously, bank number 2 steps once for every 25 steps of bank number 3, and bank number 1 steps once for every 625 steps of bank number 3. This type of motion has been designated as a "321" motion. For another indicator the order of this stepping may be different and in all there appear to be 6 different types of stepping: 1-2-3, 1-3-2, 2-1-3, 2-3-1, 3-1-2, and 3-2-1. Although there are 120 different indicators there are only 6 different types of motion or stepping of the three ciphering switches, so that it appears that each type of motion is represented by 20 different indicators. 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. 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