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Home Page Hebern's machines The 5 rotors machine home page
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IntroductionIn 1924, the US Navy was ready to adopt Hebern's cipher machine equipped with 5 rotors as a means of high level encryption. However, the Navy asks William Friedman, the Army's chief cryptanalyst, to test the security of the machine by trying to decipher a set of ten messages. Friedman achieved the feat of deciphering all of the messages. In all, Friedman took two months to complete! The first six weeks allowed him to find a method of attack. The remaining two weeks were spent deciphering the 10 messages. It must be remembered that at the time he was no machine to help him. Following Friedman's exploit, the US Navy abandoned the idea of order this version of Hebern's cipher machine. W. Friedman's storyIn a declassified document (ID: A38378), Friedman tells us the genesis of this Challenge. "I got the War Department to purchase one of these machines from Mr Hebern. I sat and studied that thing for some weeks--three or four weeks. The whole of my outfit consisted of myself and a veteran, an ex-prize fighter with cauliflower ears and the only thing he could do was to type, he could copy from draft letters or cipher text with absolute accuracy but that's all he could do. The rest of it was up to me. As I say, I studied the thing for sometime until an idea came and then I went over to the Navy Section, it was in charge then of a Lt Struble, who now is Vice Admiral Struble, he may be retired. I said to Struble,"Lieutenant, I don't think that machine is quite as safe as you think it is," He said, "oh, you're crazy". I said, "does this mean that you challenge me?" and he said, "yes" and I said, "I accept" and he said "well, what do you want" and I said "Oh, I'll take ten messages if you will put them up on your machine". He gave me the ten messages and I worked on those messages and I got to a place one day at the close of business when I had reduced the text of one of those messages to monoalphabetic terms--by this I mean I knew in the first line of the text of one of the messages, let us say, the first, the seventh, the ninth letters were the same letters, whatever they were in the second, the seventeenth and the twenty-third were the same and so on. That's all. I had when I left for home that evening. We were going out to some sort of a party and I had these letters in my mind, at least the identities and their positions, and as I was tieing a black tie, it suddenly came to me and I can't tell you to this day just how or from where but the whole line of text fell into place with all the identities in the proper place. "President of the United States." I could hardly wait to get to the office in the morning--it was correct. I reconstructed the ten messages, turned them over to Lt Struble, and there was considerable amount of excitement. The Navy Department cancelled the order that they had placed, the Hebern Company, which had been selling stock on the basis of great prospects, went to pieces, the lady who joined from the Navy lost her Job and came back [1]. Mr Hebern, trying to recesitate what he could from his fortunes, bought stock in the Southerm part of California at 40 cent and sold it in the northern part of California at about $2.00 and the California blue sky laws didn't like that so Mr. Hebern was trid and he spent a year in prison. " [1] Note: Without a doubt, this lady is Agnes Driscoll. A complement from Mrs FriedmanMrs Friedman said [cf. R.W. Clark]: "He told me many times that he sat before those messages for about six weeks, becomming discouraged almost to the point of break-down, before he even thought of a method of tackling them. Then he did tackle them, he did solve them". ConclusionWhen the Navy challenged Friedman they thought Hebern's cipher machine was unbreakable. In fact, all cryptologists professionals reacted in the same way when the first encryption machines appeared. Indeed, through the mechanization of encryption, not only we had fast and reliable encryption but apparently very secure: the length of the keys exceeded anything we had known and most of the cryptanalytic methods of the time were ineffective. In short, the appearance of number machines was a real revolution. Friedman's victory demonstrated that we had to be a little disillusioned: encryption machines can be attacked. On the other hand, enormous resources are required, with the limits of manual methods. Ultimately, the mechanization of encryption will lead to the mechanization of attacks. In the particular case of the machine studied by Friedman, we can identify several weaknesses:
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