Cryptography – Particular algorithmic function encoding – Nbs/des algorithm
Patent
1996-03-07
1998-06-16
Barron, Jr., Gilberto
Cryptography
Particular algorithmic function encoding
Nbs/des algorithm
380112, 380157, H04L 908
Patent
active
057683786
DESCRIPTION:
BRIEF SUMMARY
RELATED APPLICATIONS
This application is related to the following copending commonly assigned applications:
______________________________________ 08/464,710 filed August 15, 1995 entitled "SYSTEM AND
METHOD FOR KEY DISTRIBUTION USING
QUANTUM CRYPTOGRAPHY" naming
Townsend as inventor (now U.S. Pat. No.
5,675,648);
08/612,881 filed April 22, 1996 entitled "METHOD FOR
KEY DISTRIBUTION USING QUANTUM
CRYPTOGRAPHY" naming Messrs. Phoenix
and Barnett as inventors;
08/612,880 filed March 8, 1996 entitled "SYSTEM AND
METHOD FOR KEY DISTRIBUTION USING
QUANTUM CRYPTOGRAPHY" naming
Messrs. Townsend and Blow as inventors;
08/617,848 filed March 8, 1996 entitled "SYSTEM AND
METHOD FOR QUANTUM CRYPTOGRAPHY"
naming Mr. Blow as inventor; and
08/776,296 filed January 30, 1997 entitled "QUANTUM
CRYPTOGRAPHY" naming Townsend as
inventor.
______________________________________
BACKGROUND TO THE INVENTION
The present invention relates to a system for the communication of encrypted data. In particular, it relates to the technique known as quantum cryptography.
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, that is a channel carried by single-photon signals and exhibiting non-classical behaviour, as further discussed below. The transmitter and the receiver then communicate over a separate channel, known as the public channel, to compare the transmitted and the 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. The secret key thus established is used in the encryption and decryption of subsequent communications between the transmitter and receiver. For added security, the existing key may periodically be replaced by a newly generated key.
In general, a communication method using quantum cryptography includes the steps of: corresponding 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 by the transmitter and receiver, 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 data transmissions between the two users of the channel. This scheme is described in detail in C. H. Bennett, G. Brassard, S. Breidbart and S. Wiesner, in "Advances in cryptology: Proceedings of Crypto'82, (Plenum, N.Y., 1983); C. H. Bennett and G. Brassard, IBM Technical Disclosure Bulletin, 28 3153, (1985).
In the term "encryption alphabet" as used herein, "encryption" refers to the coding of the single-photon pulses during the key distribution phase rather than to the subsequent encryption of text for transmission once a key has been established.
SUMMARY OF THE INVENTION
According to the present invention, a method of communication using quantum cryptography is characterised in that a transmitter communicates on a quantum channel over a common communications network with a plurality of receivers located on the common communications network and establishes a different respective secret key for each receiver.
Hitherto, quantum cryptography has only been used for communication between a single transmitter and receiver pair operating over a dedicated communication link. Typically the link has been provided by an optical fibre. The present invention b
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C.H. Bennett; Physical Rev. Let.; vol. 68, No. 21, 25 May 1992, pp. 3121-3124.
IBM Technical Disclosure Bulletin; vol. 26, No. 8, Jan. 1984, pp. 4363-4366.
IBM Technical Disclosure Bulletin, vol. 28, No. 7, Dec. 1985, pp. 3153-3163 .
Smith David W.
Townsend Paul D.
Barron Jr. Gilberto
British Telecommunications public limited company
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