REF ID:A4127215
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settings, were requested for study. It was thought that possibly the cam positions on the program device and the wirings of the commutators were the same as had been found from a previous study of the machine, before the addition of the plug-board. Had this been true, the subsequent study would have required less time, but it was soon noted that at least the cam positions had been changed, if not the wirings of the commutators. Upon request, and in order to conform with the assumptions set forth in Par. 1 above, the cipher equivalents of 9,000 consecutive AIs were furnished and from this text the affective cam positions were readily reconstructed. It also developed that the commutator wirings were unchanged and that the internal period for the checking circuit, namely 180 letters, coincided with the external check shown at the end of every 4th line. This indicated that the program device made a complete revolution in 180 letters, whereas before this period was 360.
6. Having the cam positions and the commutator wirings, only one of the 12 messages was selected for detailed study. This was the longest in the set, namely "No. 1130 from Paris August 9, Section One." It contains 9 periods of 180 letters. Applying the principles of solution devised to meet the situation, the plain-text of the first period was recovered and is attached hereto. In this process, some time was lost because of unfamiliarity with necessary procedure. This is always to be expected of an initial solution, but it can now be stated definitely that a second trial would undoubtedly yield solution of such a first period within the time indicated in Par. 2 above. This is hardly sufficient for confidential or secret messages.
7. The following conclusions seem warranted:
a. As regards its mechanico-electrical functioning, the machine appears to be highly reliable, speedy, and efficient.
b. The degree of cryptographic security afforded by the machine is relatively low, and certainly not sufficient for governmental confidential or secret messages.
c. The cryptographic principle upon which this machine is based is quite weak. In a final analysis, it consists of but three primary mixed, reciprocal sequences. It is true that these sequences are brought into play in an irregular manner for an irregular number of sequent letters, and that the complete period is 19,000 letters. But this period is a resultant period; it is relatively very short compared as cryptographic periods go; and even then it is composed of but 18 different types of primary periods of only 180 letters each. The fact that there are two dial settings for each message, one with 25 different positions and the other with 50, is of no serious consequence from a cryptoanalytic viewpoint.
