Patent GB-1120031-A (GB)
Title: Device for stepping a group of key elements of cryptographic apparatus having an irregular sequence of steps
IPC: G09C1/10
Filed: 1962-12-28
Abstract: 1,120,031. Random number generators; ciphering. PHILIPS USFA N.V. 28 Dec., 1962 [29 Dec., 1961], No. 48961/62. Headings G4D and G5X. In a device for the stepping of a group of key elements 1, 2, 3 and 4 of a cryptographic apparatus, which elements are stepped according to a cyclic stepping scheme with an irregular sequence of steps and each of which elements can occupy a number of active or " one " positions and a number of passive or " zero " positions, the total number of positions of each element being preferably a prime number, the elements not all simultaneously reaching the starting position again until a predetermined number of stepping operations has been effected, each element 1, 2, 3 or 4 is provided with a driving means 5, 6, 7 or 8, respectively and a means 9, 10, 11 or 12, respectively for reading the position of the element, the device further comprising a common driving mechanism 17 which drives the driving means 5 of the first element 1 directly and the driving means 6, 7 and 8 of the following elements 2, 3 and 4, respectively via couplings 38, 39 and 40, respectively in the form of " AND " gate circuits, in dependency on the read positions of the preceding elements, wherein the driving means of a key element is connected to the common driving mechanism 17 by the coupling belonging to it, in dependency on a control signal obtained by the modulo-two addition of the position read on the preceding key element and the control signal of the preceding key element. In the embodiment shown in Fig. 1, this addition is effected by modulo-two adders 41 42 and 43, respectively, and a control signal source 44 supplies to the first of these adders, i.e. adder 41, a signal which may be a one or a zero. When the device is operating, the driving mechanism 17 emits pulses, preferably evenly distributed as to time, and the first element 1 is advanced by one step under the control of each of these pulses. The device 9 reads the position of the element 1, which position consists of a one or a zero, and supplies it in the form of a pulse to the modulo-two adder 41. Either a one or a zero appears at the output of the adder 41, which is connected to the " AND " gate 38 and the modulo-two adder 42. The gate 38 will open only if a one appears at the output of the adder 41 and the driving mechanism 17 is then connected to the driving means 6 of the element 2. The stepping of the element 3 is in a similar way under the control of the adder 42. A particular element steps only if the number of elements before it which are in the one-position is either exclusively even or exclusively odd, depending on the nature of the signal supplied by the source 44 and whether or not inverters such as 45, 46 are included in the couplings between the reading means and the modulo-two adders. In alternative embodiments, the elements are connected to the driving mechanism via a commutator in such a way that the elements can be stepped one after another only, or the elements are connected to each other by double transmissions in which there are change-over switches, which switches comprise the couplings between the driving means of the elements and the driving mechanism.