Electrical computers: arithmetic processing and calculating – Electrical digital calculating computer – Particular function performed
Reexamination Certificate
2000-05-09
2003-08-19
Mai, Tan V. (Department: 2187)
Electrical computers: arithmetic processing and calculating
Electrical digital calculating computer
Particular function performed
C708S255000
Reexamination Certificate
active
06609139
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for generating a random number on a quantum-mechanical mechanical basis using a beam splitter.
RELATED TECHNOLOGY
Binary random numbers are the backbone of many encryption techniques for the secret and secure exchange of messages. Especially well known is the sole secure cryptography method in which the key is composed of a random sequence of binary zeros and ones which is as long as the binary message itself and which is only used once (“one time pad” method). It may be that a spy who, for example, tries out all the possible keys will at some stage or other also use the correct key and decrypt the message with it. However, with the same probability, he will also obtain all manner of other possible messages of the same length, and he will not be able to discover the correct one, apart from the fact that, in the case of longer messages, the number of possible keys is astronomical and exceeds the capacity of any computer.
Random numbers are also needed for scientific and technical purposes (Monte Carlo method), but especially for games of chance. For lottery games and gambling machines, the quality of these numbers is the basis for the confidence of the players in the equipment and, therefore, is prerequisite for its economic operation. Consequently, cryptography and games of chance are dependent to a very considerable extent on the quality of random series of numbers.
Moreover, the trustworthy generation of random numbers is one of the primary tasks of a company involved in the transmission of messages.
Till now, basically two different classes of methods have been used for generating random numbers:
In algorithmic methods, a short starting sequence (seed) is used to generate a considerably longer pseudo-random sequence with the aid of mathematical operations which can be executed in software or in hardware. These pseudo-random numbers have been produced by deterministic processes in the computer, and are therefore basically not random. For many applications, however, such as for use in simulations according to the Monte Carlo method, they are sufficient and even have advantages, because they can be repeatedly generated in the same sequence. However, random-number generators designed on the basis of algorithmic methods frequently fail to satisfy the requirements of cryptography because, in the generation of the random number, there are a certain number of unusable sequences (weak keys) from the beginning, and it can be expected that there will be correlations between the random numbers.
The second class of methods for generating random numbers are physical methods. In these methods, use is made of the statistical character of certain physical processes. Generally, physical methods can be further subdivided into:
statistical processes which, although they obey deterministic equations of motion, are not predictable because of the high complexity and lack of knowledge of the initial state. Random-number generators on this basis are, for instance, the tossing of a coin “heads” or “tails”, or lottery machines. Such methods produce a deterministic chaos which can be considered random because, when each individual random number is generated, the starting conditions of the generator are always slightly different, without such difference being quantifiable;
fundamentally random processes (elementary processes) of the kind described by quantum mechanics. According to the present status of science, such processes cannot be attributed to hypothetical deterministic mechanisms (hidden variables), and are therefore fundamentally random by nature.
Bit sequences generated by physical processes, especially by fundamentally random quantum processes, come closer to the concept of a random sequence than algorithmically generated sequences.
The decay of radioactive atoms is a random elementary event which, owing to the high energy of the particles produced, can be easily detected and has been proposed for the generation of a random number (M. Gude: Ein quasiidealer Gleichverteilungsgenerator basierend auf physikalischen Zufallsphänomenen [A quasi-ideal uniform-distribution generator based on random physical phenomena], dissertation RWTH Aachen, 1987). A disadvantage in this connection, however, is the potentially harmful effect of radioactive radiation on humans and on sensitive electronic equipment.
Other physical random-number generators use physical noise sources, such as the electromagnetic noise of a resistor or diode, in order to generate random bit sequences (e.g. M. Richter: Ein Rauschgenerator zur Gewinnung von quasiidealen Zufallszahlenfür die stochastische Simulation [A noise generator for obtaining quasi-ideal random numbers for stochastic simulation], dissertation RWTH Aachen, 1992). With these methods, however, it is often difficult for the decision threshold between bit value 1 and bit value 0 to be set precisely and invariably with respect to time. Furthermore, such random-number generators can be manipulated from outside, in that an arbitrarily selected “noise”, such as that from the irradiation of electromagnetic waves, can be superimposed on the quantum noise. Since it is not easy to separate the quantum noise from this extraneous pseudo-noise, such methods are considered unsafe.
An elementary random process which has undergone careful quantum-mechanical investigation is the path selection of an individual quantum of light (photon) at a beam splitter. It is fundamentally random into which of the output channels a photon will be transferred after it strikes the beam splitter. In order to generate a random sequence, the quantum of light is reflected or transmitted, for example, at a semi-transmitting mirror, the output channels of the beam splitter each being assigned a detector which registers the quantum and whose indicator represents—depending on the detector—the bit value 0 or 1 of the random sequence. Methods for generating random numbers on an optical basis and for the tap-proof transmission of the random code have been described, for example, in J. G. Rarity et al.: Quantum random-number generation and key-sharing, J. Mod. Opt. 41, p. 2435 (1994).
Problematic with the methods for generating a random sequence based on the individual-photon statistics at an optical beam splitter, however, are interference pulses of the detectors stemming, for instance, from cosmic radiation or other extraneous electromagnetic effects, and the low response probability of a detector to individual photons.
To date, there has been no light source which generates individual photons at identical time intervals. Previous light sources generate the photons in a random time sequence, so that it is impossible to foresee when a photon will strike the beam splitter of the optical random-number generator. This, combined with the detector noise, leads to interference pulses which are incorporated into the formation of the random sequence. In order to reduce the interference German Patent Document No. extraneous effects, it is described from DE 196 41 754.6 to employ a two-photon source as the light source in which the two photons of a photon pair are always generated approximately simultaneously. The two photons are spatially separated, one of the photons striking a trigger detector, and the other photon striking the beam splitter of the optical random-number generator. Only if the trigger responds, is the response of the detectors of the random-number generator registered. Consequently, the background due to the dark current of the detectors is reduced and the probability is increased that only those events attributable to the random-number-generating mechanism at the beam splitter will be included in the random sequence.
Basically, however, there is still the problem of the inadequate efficiency of detection of individual photons. One disadvantage of known optical random-number generators is the relatively low quantum efficiency of the detectors which are used to count the individual photons at the outputs o
Dultz Gisela
Dultz Wolfgang
Hildebrandt Eric
Schmitzer Heidrun
Deutsche Telekom AG
Kenyon & Kenyon
Mai Tan V.
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