William Frederick Friedman

“ 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. ”

“ In this case an enemy cryptoanalytic staff would not know the wiring of the commutators, the positions of the pins on the program device, or the settings of the keying dials. Nevertheless, it can be stated that one day's traffic, if it consisted of say 40 - 50 messages, can be solved, although this solution might require one or two weeks by a well organized cryptoanalytic staff. Its purpose would be not so much to learn the contents of these messages as to reconstruct the cam positions on the discs of program device and wiring of the commutator. ”