Cryptography – Particular algorithmic function encoding – Nbs/des algorithm
Patent
1995-08-15
1997-10-07
Buczinski, Stephen C.
Cryptography
Particular algorithmic function encoding
Nbs/des algorithm
359112, 359118, 380 44, 380 59, H04L 900, H04B 1000, H04J 1400
Patent
active
056756488
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system for communicating encrypted data. In particular, it relates to the technique known as quantum cryptography.
2. Related Art
In quantum cryptography, data is encoded at the transmitter and decoded at the receiver using some specified algorithm which is assumed to be freely available to all users of the system, whether authorised or otherwise. The security of the system depends upon the key to the algorithm being available only to the authorised users. To this end, the key is distributed over a secure quantum channel. The transmitter and receiver then communicate over a separate channel, known as the public channel, to compare the transmitted and received data. The presence of any eavesdropper intercepting the transmitted key results in a change in the statistics of the received data, which can be detected. Accordingly, in the absence of any such change in the statistics of the data, the key is known to be secure.
In general, a communication system using quantum cryptography includes the steps of: to different, non-commuting quantum mechanical operators and encoding a signal for transmission on the quantum channel using the selected operator; and using that operator in detecting the signal transmitted in step (a); signals; the encryption alphabets to determine for which of the transmitted signals common operators were selected for transmitting and detecting; detect any discrepancy resulting from the presence of an eavesdropper; and, least some of the data transmitted in steps (a) and (b) as a key for encryption/decryption of subsequent transmissions.
SUMMARY OF THE INVENTION
According to the present invention, a method of communication using quantum cryptography is characterised in that a quantum channel and public channel are transmitted over a common transmission medium, and in that a calibration signal is transmitted over the public channel to calibrate the system for the transmission of a key on the quantum channel.
Hitherto, different transmission media have generally been used for the public channel and the quantum channel. The quantum channel has typically been carried over an optical fibre link, while for the public channel a standard telephony link has typically been used. The present invention by contrast achieves significant advantages by both using a common transmission medium and using transmissions over the public channel to calibrate the system prior to subsequent transmissions over the quantum channel. The calibration step can be used, for example, to counter the effect of any shifts in polarization, phase or timing across the transmission medium from the transmitter to the receiver. This makes it possible to maintain the quantum channel effectively over far greater distances than would otherwise be possible.
Preferably the step of calibrating the system includes comparing the phase and/or polarization of a signal communicated over the public channel and received at the transmitter with predetermined values of phase and/or polarization, and controlling phase or polarization compensation means connected in line with the transmission medium so as to produce a predetermined relationship between the phase or polarization of the transmitter and receiver.
The calibration step preferably includes transmitting a clock from the transmitter to the receiver on the public channel to provide timing information for the subsequent decoding of a key transmitted on the quantum channel.
Preferably the transmission system comprises an optical fibre link, and the public channel is encoded on a multiple-photon optical signal, and the quantum channel is encoded on a single-photon optical signal.
Preferably separate source outputs are used for the multiple photons and for the single photons and the transmitter switches between the different outputs. Preferably the single-photon and multiple photon outputs are derived from a common source.
According to a second aspect of the present invention there is provided a method
REFERENCES:
patent: 4965856 (1990-10-01), Swanic
patent: 5243649 (1993-09-01), Franson
patent: 5307410 (1994-04-01), Bennett
patent: 5339182 (1994-08-01), Kimble et al.
patent: 5418905 (1995-05-01), Rarity et al.
patent: 5515438 (1996-05-01), Bennett et al.
C. H. Bennett; Physical Rev. Let.; vol. 68, No. 21, 25 May '92, pp. 3121-3124.
IBM Tech. Discl. Bul.; vol. 26, No. 8, Jan. 1984, pp. 4363-4366.
IBM Tech. Discl. Bul.; vol. 28, No. 7, Dec. 1985, pp. 3153-3163.
British Telecommunications public limited company
Buczinski Stephen C.
LandOfFree
System and method for key distribution using quantum cryptograph does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System and method for key distribution using quantum cryptograph, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and method for key distribution using quantum cryptograph will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2363728