JPH07202880A - Quantum ciphering system - Google Patents

Abstract

PURPOSE:To improve the utilizing efficiency of pulses by enabling an intercept check by only 45 deg. polarized pulses so as to reduce number of pulses used for quantum ciphering. CONSTITUTION:A sender selects a parameter (q) and selects a random sequence comprising a straight line base of N(1-q) (N is the number of transmission pulses) and upper right 45 deg. slant line base of Nq and allocates a random bit string to the straight line base and sends the pulse string. A recipient uses a detector 40 or 50 to measure the straight line base by establishment of 1-q for the pulse sting at random and to measure the slant line base with the establishment of the (q), compares the slant line base with that of the sender and estimates no intercept, when no correlation is found out. When the (q) is set to, e.g. 1/4, 9/16 of photons are used for information bits and 1/16 of them is used for intercept check as the slant line base to facilitate the intercept check and the bits are effectively utilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an enemy-safe quantum cryptography system having excellent technology and powerful computing power.

[0002]

2. Description of the Related Art Quantum cryptography is a method for communicating while monitoring whether or not wiretapping has been performed on the basis of the uncertainty principle. (Science Technical Report vol.92, No.134, p33, ISE
92-5, "Principles and Problems of Quantum Cryptography") That is, the information in the storage medium to be stored does not leak to the outside, but if the transmitted information is eavesdropped, some quantum mechanical change occurs in the transmission medium. Therefore, if this change can be monitored, it is possible to monitor whether or not wiretapping has occurred. This is the basic principle of quantum cryptography. However, it is too late to know that there was eavesdropping after sending important information, so monitor work to confirm safety and actual information transmission are appropriately mixed and communicated. That is, communication is performed by mixing useless bits for actual communication monitoring.

As a specific means therefor, there is a secret key encryption method. The problem with this method is how to securely exchange the private key between the sender and the receiver. The key protects confidential information from eavesdroppers.

The current encryption method is Ben netta
first developed by C. H. Bennett, G. Brassar (BB).
d, in processeds of IEEE
international Conference o
n Computers, Systems, and Si
general Processing, Bangalor
e, India, IEEE, New York, 198.
4, p. 175). First of all, the notation used below is defined. Linear pulses are polarized along either the horizontal or vertical axis, and diagonal pulses are polarized at 135 ° or 45 ° with respect to the horizontal axis. With a horizontally polarized pulse or a 45 ° polarized pulse,
Represents a binary 1 and is a vertically polarized pulse or 1
A binary 0 is represented by a pulse polarized at 35 °.

In the BB cryptosystem (FIGS. 3 and 4), sender A chooses a linear and diagonal based N random sequence (where N is the number of pulses A attempts to send to receiver B). ) (Step 1). Next, sender A assigns a random bit string (consisting of 0s and 1s with a probability of 0.5) to all straight and diagonal bases (step 2). A then sends a pulse train to B. Each pulse represents one bit of the bit string of the base selected for that bit position (step 3). B makes linear and diagonal-based measurements with random probability of 0.5 pulses (of course independent of the choice made by A. That is, at this point,
(A's choice is unknown to B) (step 4). B then, based on the results of the corresponding measurements,
Interpret each result as a binary 1 or 0 (step 5). Next, B publicly informs (step 6) whether or not a diagonal or straight line-based pulse has been measured (not the measurement result of B). A publicly informs B which base was correctly estimated (step 7). They are
Example of B measuring a linear-based pulse when A sends a diagonal-based pulse to B, or example of B measuring a diagonal-based pulse when A sends a linear-based pulse to B Agree to discard (step 8). A and B then openly compare both measurements on a random subset of the pulses, which subset has about p ² N pulses (step 9). If A and B find that their examined results are perfectly correlated, then A and B can be presumed to have not been eavesdropped (step 1).
0). Therefore, the remaining unchecked subset is also fully correlated and is a suitable source for key generation (step 11).

The summary of FIG. 4 is as follows.

(1) base selected by A (2) random bits of A (3) pulse transmitted by A (4) bit selected by B (5) bit received by B public Discussion (6) B informs the base on which the received pulse was examined.

(7) A says which base was correctly estimated.

(8) B discards all false bases.

(9) B informs all the bits on the diagonal line basis.

(10) If there is no eavesdropping, A confirms these bits.

Result (11) A key can be generated using the remaining bits.

[0013]

After discarding the incorrect measurement example, A and B must be able to hold about 0.5N pulses (assuming the detector is perfect). A and B then examine a random subset of the remaining data (p ² N) they agree with, if not eavesdropping. Therefore, A and B are approximately (0.5-
p ² ) N pulses can be used to generate the key distribution. The efficiency of this current cryptosystem (A and B are proportional to the number of pulses that can be used to generate the key distribution) is low and empirically difficult to improve.
This is because A must prepare pulses for horizontal polarization, vertical polarization, 135 ° polarization, and 45 ° polarization.

[0014]

SUMMARY OF THE INVENTION The present invention uses a 0 ° polarized or 90 ° polarized pulse to generate a key distribution and a 45 ° polarized pulse to check for general eavesdropping by an eavesdropper. It is a method.

[0015]

First, the notation used below will be defined. Linear pulses are polarized along the horizontal or vertical axis and diagonal pulses are polarized 45 ° with respect to the horizontal axis. A binary 1 is represented by a horizontally polarized pulse or a 45 ° polarized pulse, and a binary 0
Is represented by a vertically polarized pulse.

In the encryption scheme of the present invention (FIGS. 1 and 2), A generates horizontal and vertical pulses, namely |
> And | ↑> are mainly used to check for general eavesdropping by eavesdroppers using a 45 ° diagonal pulse or

[0017]

Is used.

A selects the parameter 0 <q <1 and announces it publicly. A then selects a random sequence consisting of N (1-q) linear bases and Nq diagonal bases, where N is the number of pulses A tries to send to B (step 1). . A then assigns a binary 1 to all diagonal bases and a random bit string (consisting of 0s and 1s with a probability of 0.5) to all linear bases (step 2). A then sends a pulse train to B, each pulse representing one bit of the base bit train selected for that bit position (step 3). B makes a pulse-based linear-based measurement with random probability (1-q), and q
A diagonal-based measurement with a probability of (independent of the choice made by A, of course, because the choice by A is unknown to B at this point) (step 4). B then interprets each result as a binary 0 or 1 based on the result of the corresponding measurement (step 5). Next, B publicly informs (step 6) whether or not a diagonal or straight line-based pulse has been measured (not the measurement result of B). A publicly informs B which base was correctly estimated (step 7). They are A to B

[0020]

Agree to discard the example in which B measures a linear-based pulse when transmitting B or the example in which B measures a diagonal-based pulse when A transmits a linear pulse to B. (Step 8). Then A and B are
A is

[0022]

, And publicly compare their measurements for the subset B measures on a diagonal basis, which subset has about q ² N pulses. If A and B find that their examined results are perfectly correlated, they can presume that they were not eavesdropping (step 10). Therefore, the remaining unchecked subset is also fully correlated and is a suitable source for key generation (step 11).

[0024]

EXAMPLE Consider the case of q = 1/4. In this case, 9/16 of the photons are transmitted and received along the horizontal and vertical axes, producing bits of information between A and B. 1/16 of the photons are transmitted and received diagonally, allowing eavesdropping inspection (the remaining 3/8 of the photons are discarded).
The important point is that this method has the following 3
It is excellent in two respects. (I) 9/16 is greater than 1/2. Therefore, A and B are exchanging more bits with the same photon. (Ii) The BB scheme is inefficient because A and B have to sacrifice some bit checking (percentage p ² ) for eavesdropping. On the other hand, in the method of the present invention, A and B have already finished the wiretapping inspection by the photons with diagonal lines. (Iii) In the BB system, A and B are 45 for eavesdropping inspection.
While the ° and 135 ° pulses are used, in the scheme of the present invention, A and B use only 45 ° pulses. Therefore, the present invention can be easily realized.

[0025]

In the system of the present invention, A and B use only 45 ° pulse for eavesdropping inspection, but in the BB system, both 45 ° pulse and 135 ° pulse must be used. The invention can be realized more easily.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a quantum cryptography system of the present invention.

FIG. 2 is a diagram illustrating steps of the quantum cryptography method of the present invention.

FIG. 3 is a diagram for explaining a conventional quantum cryptography system.

FIG. 4 is a diagram illustrating steps of a conventional quantum cryptography system.

[Explanation of symbols]

 10, 30 Quantum channel 15, 25, 35, 45 Polarizer 40, 60 First detector 50, 70 Second detector

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H04B 10/02 10/18 H04K 1/08

Claims (1)

[Claims] 1. A quantum cryptography scheme, wherein horizontal and vertical pulses are used to generate the key distribution and 45 ° polarized pulses are used to check for eavesdropping.