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1. WO1996006491 - QUANTUM CRYPTOGRAPHY

Publication Number WO/1996/006491
Publication Date 29.02.1996
International Application No. PCT/GB1995/001940
International Filing Date 16.08.1995
Chapter 2 Demand Filed 22.01.1996
IPC
G02F 1/141 2006.01
GPHYSICS
02OPTICS
FDEVICES OR ARRANGEMENTS, THE OPTICAL OPERATION OF WHICH IS MODIFIED BY CHANGING THE OPTICAL PROPERTIES OF THE MEDIUM OF THE DEVICES OR ARRANGEMENTS FOR THE CONTROL OF THE INTENSITY, COLOUR, PHASE, POLARISATION OR DIRECTION OF LIGHT, e.g. SWITCHING, GATING, MODULATING OR DEMODULATING; TECHNIQUES OR PROCEDURES FOR THE OPERATION THEREOF; FREQUENCY-CHANGING; NON-LINEAR OPTICS; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
1Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
01for the control of the intensity, phase, polarisation or colour
13based on liquid crystals, e.g. single liquid crystal display cells
137characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
139based on orientation effects in which the liquid crystal remains transparent
141using ferroelectric liquid crystals
H04L 9/08 2006.01
HELECTRICITY
04ELECTRIC COMMUNICATION TECHNIQUE
LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
9Arrangements for secret or secure communication
08Key distribution
CPC
G02F 1/141
GPHYSICS
02OPTICS
FDEVICES OR ARRANGEMENTS, THE OPTICAL OPERATION OF WHICH IS MODIFIED BY CHANGING THE OPTICAL PROPERTIES OF THE MEDIUM OF THE DEVICES OR ARRANGEMENTS FOR THE CONTROL OF THE INTENSITY, COLOUR, PHASE, POLARISATION OR DIRECTION OF LIGHT, e.g. SWITCHING, GATING, MODULATING OR DEMODULATING; TECHNIQUES OR PROCEDURES FOR THE OPERATION THEREOF; FREQUENCY-CHANGING; NON-LINEAR OPTICS; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
1Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating, or modulating; Non-linear optics
01for the control of the intensity, phase, polarisation or colour 
13based on liquid crystals, e.g. single liquid crystal display cells
137characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
139based on orientation effects in which the liquid crystal remains transparent
141using ferroelectric liquid crystals
G02F 2203/07
GPHYSICS
02OPTICS
FDEVICES OR ARRANGEMENTS, THE OPTICAL OPERATION OF WHICH IS MODIFIED BY CHANGING THE OPTICAL PROPERTIES OF THE MEDIUM OF THE DEVICES OR ARRANGEMENTS FOR THE CONTROL OF THE INTENSITY, COLOUR, PHASE, POLARISATION OR DIRECTION OF LIGHT, e.g. SWITCHING, GATING, MODULATING OR DEMODULATING; TECHNIQUES OR PROCEDURES FOR THE OPERATION THEREOF; FREQUENCY-CHANGING; NON-LINEAR OPTICS; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
2203Function characteristic
07Polarisation dependent
H04L 9/0858
HELECTRICITY
04ELECTRIC COMMUNICATION TECHNIQUE
LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
9Cryptographic mechanisms or cryptographic; arrangements for secret or secure communication
08Key distribution ; or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
0816Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
0852Quantum cryptography
0858Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding
Applicants
  • BRITISH TELECOMMUNICATIONS PUBLIC LIMITED COMPANY [GB/GB]; 81 Newgate Street London EC1A 7AJ, GB (AllExceptUS)
  • TOWNSEND, Paul, David [GB/GB]; GB (UsOnly)
Inventors
  • TOWNSEND, Paul, David; GB
Agents
  • GILL JENNINGS & EVERY; Broadgate House 7 Eldon Street London EC2M 7LH, GB
Priority Data
94306102.818.08.1994EP
95301050.120.02.1995EP
PCT/GB94/0195208.09.1994AT
Publication Language English (EN)
Filing Language English (EN)
Designated States
Title
(EN) QUANTUM CRYPTOGRAPHY
(FR) CRYPTOGRAPHIE QUANTIQUE
Abstract
(EN)
In a method of communication using quantum cryptography, single-photon signals from a highly attenuated source are modulated and subsequently detected. In the step of detecting the modulated signal, the signal is split between two branches according to its encoded state. Signals corresponding to different encoded states are detected independently in the respective branches and the rate of detection of coincident signals is determined. This rate is compared with a threshold to detect the presence of an eavesdropper.
(FR)
L'invention concerne un procédé de communication faisant appel à la cryptographie quantique. Dans ce procédé, des signaux monophotoniques provenant d'une source très atténuée sont modulés et ensuite détectés. Au stade de la détection du signal modulé, celui-ci est dédoublé en deux branches en fonction de son codage. On détecte indépendamment les signaux correspondants aux différents codages dans les branches respectives et on détermine la vitesse de détection des signaux coïncidents. On compare cette vitesse à un seuil pour repérer une écoute illicite.
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