KR20170133245A - Method, apparatus and system for code based quantum key distribution - Google Patents

Abstract

The present invention relates to a quantum encryption key distribution method, apparatus, and system, and more specifically, to a quantum encryption key distribution method, apparatus, and system which distribute a quantum encryption key by dividing a single photon pulse signal into a plurality of chips, each having a period shorter than a pulse width, through fast phase modulation in a complex plane and coding a phase of each chip, in implementation of a multi-qubit quantum encryption key distribution system. According to an embodiment of the present invention, the quantum encryption key distribution method, apparatus, and system perform quantum encryption key distribution between a transmitter and a receiver (Bob) by dividing a light pulse into a plurality of chips and phase-modulating each chip on the basis of predetermined codes. Therefore, it is possible to increase data transmission efficiency and improve security while simplifying structures of the receiver (Bob) and the like, and in addition, it is also possible to improve detection efficiency at a receiving end.

Description

METHOD AND APPARATUS FOR DISTRIBUTING CODE-BASED QUANTITATIVE CYPRUS KEYS,

The present invention relates to a quantum cryptographic key distribution method, apparatus, and system, and more particularly, to a multi-cue bit quantum cryptography key distribution system, in which a single photon pulse signal is transmitted through a fast phase modulation on a complex plane, The present invention relates to a quantum cryptographic key distribution method, apparatus, and system for dividing a plurality of chips having a period and coding the phase of each chip to distribute a quantum cryptographic key.

In recent years, there has been a lot of interest in security due to the leakage of information due to eavesdropping. However, the security communication according to the related art has a considerable risk that communication contents can be exposed by an external attack, and as a next generation security technology to complement it, the quantum cryptographic communication that can secure theoretically very high security, .

In this regard, research on quantum cryptography key distribution among quantum cryptography communication technologies is actively being carried out. The quantum cryptography key distribution technique is a technique for distributing and sharing cryptographic keys among remote users using the quantum mechanical properties of photons. At this time, when the eavesdropper attempts to acquire the cryptographic key information distributed among the users due to the quantum mechanical properties, the cryptographic key information may be altered, and thus, users receiving the cryptographic key can detect the presence of the eavesdropper .

As a quantum cryptography key distribution technique, a technique of distributing a quantum cryptographic key by modulating the frequency or phase of optical pulses has been proposed. However, in this case, a modulating circuit must be provided not only in the sender (Alice) but also in the receiver (Bob) The back structure may be complicated, and the loss of the optical pulse may occur.

In addition, there is a continuing demand for improving the security of the quantum cryptographic key distribution while improving the data transmission efficiency due to the complicated structure of the recipient Bob and loss of optical pulses.

Accordingly, there is a continuing need for a quantum cryptography key distribution scheme that can simplify the structure of a receiver Bob and the like, improve data transmission efficiency and improve security, and further increase detection efficiency at the receiving end However, there is still no adequate solution to this problem.

Korean Patent Publication No. 10-2009-0124679

Disclosure of Invention Technical Problem [8] The present invention has been made in order to solve the problems of the related art as described above, and it is an object of the present invention to provide a method and apparatus for modulating a frequency or phase of an optical pulse, A structure such as a circuit must be provided, and a loss of optical pulses may occur. In this case, it is possible to simplify the structure of a receiver Bob and improve data transmission efficiency and security, And an object of the present invention is to provide a quantum cryptographic key distribution method, apparatus, and system capable of increasing detection efficiency in a quantum cryptography key distribution system.

According to an aspect of the present invention, there is provided a system for distributing a quantum cryptographic key using a series of optical pulses, wherein a transmitter and a receiver respectively divide one optical pulse into ^2N chips a transmitter for transmitting an optical pulse containing data of N qubits by applying a first base of a plurality of predetermined bases to the 2 ^N chips to perform phase modulation, wherein N is a natural number of 1 or more ; And a receiver for receiving an optical pulse transmitted by the sender and for detecting a light pulse by applying a second base of the plurality of bases and restoring a part or all of the data, Characterized in that the first base and the second base are collated and a cryptographic key is distributed to each other using part or all of the data.

Here, the receiver may include a light splitter for dividing the received optical pulse at a predetermined probability and transmitting the divided optical pulse to the first path and the second path; A delay and summing filter for dividing the optical pulse into a first optical pulse and a second optical pulse, delaying the first optical pulse by a predetermined chip interval, and summing the delayed optical pulse and the second optical pulse, ; And a photon detector for detecting optical pulses output from the delay and summation filter.

The delay and sum filter may include a phase modulator for modulating the phase of the first optical pulse or the second optical pulse according to the second basis.

The receiver may further include a 1-chip delay and a sum filter when N = 1, a 2-chip delay and sum filter and a 1-chip delay and summation filter when N = 2, Chip delay and summation filter, ..., 2 ^{n -1} - chip delay and summing filter, where n is a natural number greater than or equal to 3, where N = n, ; At this time, the optical pulse received by the receiver may be divided into a plurality of paths while passing through one or two optical splitters, and may be detected by the optical detector after sequentially passing through the delay and sum filters of the respective types.

The optical splitter may include a switch for dividing a plurality of chips in the optical pulse and transmitting the selected chips to the first path and the remaining chips to the second path.

Further, the switch may divide the plurality of chips into a leading half and a trailing half chip, respectively, so as to transfer the chips to the first path and the second path, respectively.

A quantum cryptography key distribution method according to another aspect of the present invention is a method of distributing a quantum cryptographic key using a series of optical pulses by a sender and a receiver, wherein a sender divides one optical pulse into ^2N chips And phase-modulating the first base of a plurality of predetermined bases to the 2 ^N chips to transmit optical pulses containing data of N cubes (where N is a natural number of 1 or more) , The receiver receives an optical pulse transmitted by the sender and detects a light pulse by applying a second base of the plurality of bases to recover a part or all of the data, Characterized in that the first base and the second base are collated and a cryptographic key is distributed to each other using a part or the whole of the data.

Quantum cryptography key distribution method, the sender and the receiver, a series of a method of distributing a quantum cryptographic key by using the optical pulse, the receiver, a single light pulse 2 ^N chips from the sender in accordance with a further aspect of the present invention ( chip, applying the first base of a plurality of predetermined bases to the ^2N chips, performing phase modulation on the first base, receiving data of the transmitted N pulses, wherein N is 1 Above natural number); And recovering a part or all of the data by detecting a light pulse by applying a second base of the plurality of bases to the received optical pulse by the receiver, Characterized in that the first base and the second base are collated and a cryptographic key is distributed to each other using a part or the whole of the data.

The restoring may include dividing the received optical pulse into a predetermined probability and transmitting the divided optical pulse to a plurality of paths; And a control unit configured to divide the optical pulses into a first optical pulse and a second optical pulse, delay the first optical pulse by a predetermined wavelength, Delay and summing steps; And a photon detection step of detecting optical pulses output from the delay and summation filter.

In the delay and summation step, the phase of the first optical pulse or the second optical pulse may be modulated according to the second basis.

The receiver may further include a 1-chip delay and a sum filter when N = 1, a 2-chip delay and sum filter and a 1-chip delay and summation filter when N = 2, Chip delay and summation filter, ..., 2 ^{n -1} - chip delay and summing filter, where n is a natural number greater than or equal to 3, where N = n, ; At this time, the optical pulse received by the receiver may be divided into a plurality of paths while passing through one or two optical splitters, and may be detected by the optical detector after sequentially passing through the delay and sum filters of the respective types.

Also, the light splitting step may be implemented using a switch that divides a plurality of chips in the optical pulse, transfers some chips to a first path, and transmits the remaining chips to a second path.

In addition, the switch may divide the plurality of chips into a preceding half and a following half chip, and transfer the same to the first path and the second path, respectively.

According to another aspect of the present invention, there is provided a transmitting apparatus for distributing a quantum cryptographic key to a receiving apparatus using a series of optical pulses, comprising: an optical pulse generating unit for generating optical pulses; And one of the divided optical pulses with 2 ^N chips (chip), and to it the phase modulation applied to the first base of the plurality of ground (basis) predetermined in the 2 ^N of the chip the light pulse actually the data of the N qubits Wherein N is a natural number greater than or equal to 1, and the receiving apparatus receives the optical pulse transmitted by the transmitting apparatus, and applies the second base of the plurality of bases to the optical pulse modulating unit And the transmitting device and the receiving device collate the first base and the second base and distribute the cipher key to each other using a part or the whole of the data .

The receiving device according to another aspect of the invention, a set of a reception apparatus for distributing a quantum cryptographic key by using the optical pulse, a light pulse is 2 ^N chips from the sender from the sender (chip) for receiving from the transmitter An optical pulse receiving section for receiving the transmitted optical pulse by applying N-qubit data by phase-modulating the first base of a plurality of predetermined bases to the ^2N chips, wherein N is 1 Above natural number; And a light pulse detector for detecting a light pulse by applying a second base of the plurality of bases to the received light pulse to recover a part or all of the data, Characterized in that the first base and the second base are collated and a cryptographic key is distributed to each other using part or all of the data.

A quantum cryptographic key distribution method and apparatus system according to an embodiment of the present invention divides an optical pulse into a plurality of chips and phase modulates each chip based on a predetermined code to distribute a quantum cryptographic key between a sender and a receiver, It is possible to improve the data transmission efficiency, improve the security, and further improve the detection efficiency at the receiving end.

1 is a block diagram of a quantum cryptography key distribution system according to an embodiment of the present invention.
2 is a flowchart of a quantum cryptography key distribution method according to an embodiment of the present invention.
3 is a diagram illustrating a process of generating a plurality of chips in an optical pulse according to an embodiment of the present invention.
4 is a diagram illustrating a structure of a two-chip coding quantum cryptographic key distribution system according to an embodiment of the present invention.
5 is a diagram illustrating modulation (a) of a single photon signal and a chip signal (b) after delayed interference according to an embodiment of the present invention.
6 is a diagram illustrating a structure of a two-chip quantum cryptography key distribution system maximizing detection efficiency according to an embodiment of the present invention.
7 is a diagram for explaining an attack model of an eavesdropper using a two-chip switching and delay interferometer according to an embodiment of the present invention.
8 is a diagram illustrating a structure of a 4-chip-coded quantum cryptographic key distribution system according to an embodiment of the present invention.
9 is a view for explaining a structure of a 4-chip quantum cryptographic key distribution system maximizing detection efficiency according to an embodiment of the present invention.
10 is a configuration diagram of a transmitting apparatus according to an embodiment of the present invention.
11 is a configuration diagram of a receiving apparatus according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments will be described in detail below with reference to the accompanying drawings.

The following examples are provided to aid in a comprehensive understanding of the methods, apparatus, and / or systems described herein. However, this is merely an example and the present invention is not limited thereto.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. The following terms are defined in consideration of the functions of the present invention, and may be changed according to the intention or custom of the user, the operator, and the like. Therefore, the definition should be based on the contents throughout this specification. The terms used in the detailed description are intended only to describe embodiments of the invention and should in no way be limiting. Unless specifically stated otherwise, the singular form of a term includes plural forms of meaning. In this description, the expressions "comprising" or "comprising" are intended to indicate certain features, numbers, steps, operations, elements, parts or combinations thereof, Should not be construed to preclude the presence or possibility of other features, numbers, steps, operations, elements, portions or combinations thereof.

It is also to be understood that the terms first, second, etc. may be used to describe various components, but the components are not limited by the terms, and the terms may be used to distinguish one component from another .

Hereinafter, a quantum cryptography key distribution technique will be described in brief for an understanding of the present invention, followed by a more detailed description of various embodiments according to the present invention.

In designing a quantum key distribution (QKD) system, the allowable error rate limit (Error Tolerance Bound) is an indicator of the security of the protocol. A new protocol has been proposed to increase the limit of allowable error rate in many previous researches. Among them, limit value of permissible error rate in multi-cubic quantum cryptographic key distribution protocol which encodes multi-cubit information in one quantum state is the number of qubits , Respectively. In the present invention, focusing on a method of implementing a multi-cubic quantum cryptographic key distribution system, a single photon pulse signal is divided into optical pulses of a chip unit shorter than a pulse width by high-speed phase modulation in a complex plane, Lt; RTI ID = 0.0 > a < / RTI > multi-cubit quantum cryptography protocol.

,

와 기저 2의 양자상태

,

로 표현된다. 송신자(Alice)는 4가지 양자상태 중 임의의 하나를 수신자(Bob)에게 전송하고 수신자(Bob)은 기저 1과 기저 2 중 임의의 기저를 선택하여 측정을 한다. 수신자(Bob)은 송신한 양자상태의 기저와 동일한 기저로 측정을 한 경우에만 올바른 비밀키 정보를 얻을 수 있다. 이와 같은 이유로 양자 채널에서 모든 전송이 끝난 후 고전 채널을 통해 송신자(Alice)와 수신자(Bob)은 각자의 기저 정보를 공개하고 동일한 기저를 사용한 결과 값만을 비밀키 추출에 사용한다. 이 과정을 시프팅(Sifting)이라고 하는데, 시프팅이 끝난 후 유효한 결과 값의 일부를 취해 도청자의 공격에 의해 발생한 오류를 계산하여 결과 값을 비밀키로 사용할지 여부를 판단한다. 이 때, 허용 가능한 오류율의 한계값을 정하여 이 값보다 오류율이 큰 경우 결과 값 전부를 버리고 오류율이 한계 값보다 작을 경우 추가적인 과정을 통해 성공적으로 비밀키를 생성할 수 있다. Quantum cryptographic key distribution is one of the cryptographic key distribution methods used to distribute keys for modulating or demodulating information for communication between two authenticated users. The conventional cryptographic key distribution scheme provides security based on mathematical complexity Unlike quantum cryptography key distribution, it allows the sharing of secret keys in the presence of eavesdroppers based on physical laws at the quantum level. In the BB84 protocol proposed by Bennett and Breassard in 1984, it was shown that quantum key distribution is possible using the four quantum states constituting the two bases. The four quantum states are the quantum states of base 1

,

And the quantum state of base 2

,

Lt; / RTI > The sender (Alice) transmits any one of the four quantum states to the receiver (Bob), and the receiver (Bob) selects and measures any base of the base 1 and base 2. The receiver Bob can obtain the correct secret key information only when the measurement is performed on the basis of the base of the transmitted quantum state. For this reason, after all transmissions in the quantum channel are completed, the sender (Alice) and the receiver (Bob) disclose their respective base information through the classical channel and use only the result using the same basis for the secret key extraction. This process is called shifting. After shifting, it takes some of the valid result values to calculate the error caused by the attack of the eavesdropper and judges whether to use the result value as the secret key. In this case, if the error rate is larger than the allowable error rate limit, the entire resultant value is discarded and if the error rate is smaller than the threshold value, the secret key can be successfully generated through the additional process.

The permissible error rate limits are used as a good indicator for designing a more secure quantum key distribution system. Therefore, a protocol for increasing the allowable error rate limit has been studied, and a protocol using six quantum states has been proposed. In recent years, quantum key distribution has been proposed in which a single photon is not a single qubit but a "single photon multiple qubit" In the protocol, when the symbols are grouped into several qubits, the permissible error rate limits are increased according to the number of qubits as shown in Equation 1 below.

 The present invention proposes a new implementation method applicable to the multi-qubit protocol based on the BB84 protocol. Various implementations such as phase modulation or frequency modulation have been proposed to implement the existing BB84 protocol and two qubit single photon quantum key distribution systems using polarization modulation and phase modulation have been proposed. The quantum key distribution system proposed in the present invention uses a quantum state in which phase coding is modulated on optical pulses of a plurality of chips by performing phase modulation of a single single pulse on a high-speed complex plane.

In the present invention, a code-based quantum cryptographic key distribution system is proposed and a photon transmission system composed of two chips capable of transmitting one qubit information and four chips capable of transmitting two qubit information is described We propose a multi - cubic quantum cryptographic key distribution system that can transmit N qubit information by extending it to 2 ^N chips.

Hereinafter, exemplary embodiments of a code-based quantum cryptography key distribution method, apparatus, and system according to an embodiment of the present invention will be described in turn with reference to the accompanying drawings.

FIG. 1 illustrates a block diagram of a code-based quantum cryptography key distribution system 100 according to an embodiment of the present invention. 1, the quantum cryptographic key distribution system 100 according to an exemplary embodiment of the present invention may include a sender 110 and a receiver 120. The sender 110 and the receiver 120 may be coupled using an optical communication network 130 that includes optical channels capable of transmitting optical pulses.

FIG. 2 illustrates a flowchart of a quantum cryptography key distribution method according to an embodiment of the present invention.

As can be seen in Figure 2, the quantum cryptography key distribution method according to an embodiment of the present invention, the sender 110 to divide the one light pulse with 2 ^N chips (chip), the second ^N chips (Where N is a natural number equal to or greater than 1) (S110) of applying a first base of a plurality of predetermined bases and transmitting the optical pulse containing data of N cubes by phase modulation, and the receiver 120 Receiving an optical pulse sent by the sender 110 and detecting a light pulse by applying a second base of the plurality of bases to the received optical pulse to recover some or all of the data S120).

More specifically, the quantum cryptography key distribution method in terms of the sender 110 according to an embodiment of the present invention is a method in which the sender 110 and the receiver 120 distribute a quantum cryptographic key using a series of optical pulses , The transmitter 110 divides one optical pulse into 2 ^N chips and applies the first base of a plurality of predetermined bases to the 2 ^N chips to perform phase modulation to form N cubes (N is a natural number equal to or greater than 1) S110, and the receiver 120 receives the optical pulses transmitted by the sender 110, the transmitter 110 and the receiver 120 collate the first base and the second base, and detect the first base and the second base, respectively, Using a part or all of the encryption keys. It is. At this time, the data may be data for generating a quantum cryptographic key distributed between the sender 110 and the receiver 120.

The method for distributing a quantum cryptographic key in terms of a receiver 120 according to an embodiment of the present invention is a method in which a sender 110 and a receiver 120 distribute a quantum cryptographic key using a series of optical pulses , receiver 120, to from a sender (110) to apply one of being light pulse is divided into 2 ^N chips (chip), the two first base of the ^N plurality of ground a predetermined in-chip (basis) phase (Where N is a natural number equal to or greater than 1) S120a of receiving the optical pulses by modulating the data of N qubits and transmitting the optical pulses to the receiver 120, (S120b) of detecting a light pulse by applying a first base and a second base to recover a part or all of the data, wherein the sender (110) and the receiver (120) compare the first base and the second base And uses a part or the whole of the data to encrypt keys Distribution.

Further, the restoring step (S120b) may include dividing the received optical pulse into a predetermined probability and transmitting the divided optical pulse to the first path and the second path; A delay and summing step of dividing the optical pulse into a first optical pulse and a second optical pulse, delaying the first optical pulse by a predetermined chip interval, and summing the delayed first optical pulse and the second optical pulse, ; And a photon detection step of detecting optical pulses output from the delay and summation filter.

In particular, the receiver has a 1-chip delay and a sum filter when N = 1 and a 2-chip delay and sum filter and a 1-chip delay and sum filter when N = 2, Chip delay and summation filter, ..., 2 ^{n -1} - chip delay and summing filter, where n is a natural number greater than or equal to 3, where N = n, ; At this time, the optical pulse received by the receiver may be divided into a plurality of paths while passing through one or two optical splitters, and may be detected by the optical detector after sequentially passing through the delay and sum filters of the respective types.

Herein, the 1-chip delay and summation filter means a filter for delaying and summing the optical pulses including a plurality of chips by one chip, more generally, the 2 ^{< n >} Is delayed by 2 ^{< n &gt}; -chip and then summed.

Hereinafter, a method and system for distributing a quantum cryptographic key according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2. FIG.

First, the sender 110 divides one optical pulse into a plurality of chips, phase-modulates the plurality of chips according to a predetermined plurality of codes on a basis, 130 to the recipient 120.

The receiver 120 receives the optical pulses transmitted from the sender 110 and transmits a plurality of delay and sum filters (hereinafter referred to as " add " and " And then the optical pulse is detected using a single photon detector.

Subsequently, the sender 110 informs the receiver 120 of the basis used to modulate the optical pulse, that is, the basis of the code comprising the chips constituting the phase-modulated optical pulse, The receiver 120 informs the sender 110 of the basis used to detect the optical pulse, i.e., the phase delay value in the delay and add filter, After determining the attack, the quantum cryptographic key is calculated by applying an error correction technique and a privacy amplification technique.

Accordingly, the quantum cryptographic key distribution system 100 according to an embodiment of the present invention can simplify the structure of the receiver 120 without modulating the modulator, improve data transmission efficiency, The attack of the eavesdropper 140 can be effectively suppressed.

FIG. 3 is a diagram illustrating optical pulse modulation in the transmitter 110 according to an embodiment of the present invention. 3, a light source such as a laser diode of the transmitter 110 or an optical pulse (photon) generated by the optical pulse generating unit 112 is input to an optical pulse modulating unit 114 such as an IQ modulator, And may be divided into a plurality of chips. Further, the optical pulse modulator 114 such as the IQ modulator may phase-modulate and output the respective chips.

That is, optical pulses generated from a light source such as a laser diode have one phase (for example, 0 DEG). In an IQ modulator, the optical pulses are divided into a plurality of chips, Can be modulated at intervals of a predetermined phase so that a plurality of chips having a series of phase values can be formed.

FIG. 4 illustrates a diagram for explaining an implementation example of a quantum cryptography key distribution system 100 according to an embodiment of the present invention. 4, the quantum cryptographic key distribution system 100 according to an exemplary embodiment of the present invention may include a sender 110 and a receiver 120. As shown in FIG.

Hereinafter, the structure of a two-chip coding quantum cryptographic key distribution system 100 according to an embodiment of the present invention will be described in more detail with reference to FIG.

In the BB84 protocol employing a phase modulation qubit, the sender (Alice) 110 generates a signal divided into two chips of a single photon pulse through high-speed phase modulation of the complex plane. The modulated phase of each chip has a value of {0 DEG, 90 DEG, 180 DEG, 270 DEG}. FIG. 4 illustrates a system model using the above-described modulation scheme. 5 (a) shows a signal obtained by modulating a single photon pulse transmitted in a period T with two chips. When the phase of the first chip is referenced to 0 ° in the complex plane, all four possible quantum states are determined by the phase modulation value of chip 2.

Bob 120 divides the incoming signal into two paths using a 50:50 beam splitter and generates delay and sum filters DAF 1 and DAF 2 with a delay path of one- ). The delay and sum filters DAF 1 and DAF 2 have a phase path difference of 0 ° and 90 ° in the delay path, respectively.

5 (b) shows the interference signal generated by the interference of the two chips transmitted by the sender (Alice) at the constructive interference port and the destructive interference port of the delay and sum filter. The interference signal from each port appears as chips on the time axis at t ₁ , t ₂ = t ₁ + t and t ₃ = t ₁ + 2t and is measured through a single photon detector (SPD) connected. Recipients 120 is the sender 110 may have to determine the two-chip one quantum state received over the interference signals sent and detected at time t _2, because the chip of the actual interference takes place is located within a time t ₂ the interference signal Only results can be used to extract key information.

Accordingly, the secret key can be generated through the system structure of FIG. 4 as follows. The sender 110 modulates the single photon pulse into two chips and sends it to the receiver 120. The time t ₂ = 0 is taken, and the modulated signal can be expressed as Equation 2 below based on the single photon state.

: 큐빗생성 연산

: Qubit generation operation

Where | 1> _t represents the single photon state and the subscripts represent the time position of the chip. If the phase of the first chip signal is 0 ° and the phase of the second chip signal is modulated by θ∈ {0 °, 90 °, 180 °, 270 °}, then four quantum states can be made according to θ . The four quantum states are defined as Equation (3) by the qubit generating operation of Equation (2).

The orthogonality of the four quantum states defined in Equation (3) is expressed as Equation (4).

,

}, 기저{

,

}로 나눌 수 있다. 따라서 BB84 프로토콜에서와 마찬가지로 아래의 수학식 5와 같이 하나의 양자상태는 다른 기저에 속한 두 개의 양자상태의 superposition으로 나타낼 수 있으며 동일한 기저를 사용하지 않을 경우 정확한 양자상태를 알아낼 수 없음을 알 수 있다.According to Equation (4), the four quantum states defined in Equation (3) are divided into two basis, base {

,

}, Base {

,

}. Thus, as in the BB84 protocol, one quantum state can be expressed as a superposition of two quantum states belonging to different bases as shown in Equation (5) below, and it can be understood that an accurate quantum state can not be obtained without using the same basis .

를 보내는 경우를 예로 들어 설명한다. One of the four quantum states received from the sender 110 passes through the beam splitter of the receiver 120 and the delay and sum filters DAF1 and DAF2 and then passes through the delay and interference filters DAF1 and DAF2 2, 3, 4 (SPD1, SPD2, SPD3, SPD4) connected to the constructive interference port and the destructive interference port. The detection probability of the detector is determined by the sender 110

Is described as an example.

을 보낸 경우 지연 간섭계를 지나 단일 광자 검출기 i 로 들어가는 신호를

라 하였을 때 다음과 같이 수학식 6으로 나타내어 진다.If the sender 110

A single photon detector < RTI ID = 0.0 > Signal to i

(6) " (6) "

를 보낸 경우, 각 단일 광자 검출기(SPD)에서 신호가 측정될 확률은 다음의 수학식 7과 같다.By the state of Equation (6), the sender 110

, The probability that a signal is measured in each single photon detector (SPD) is given by Equation (7).

에 대해서 단일 광자 검출기 1, 2, 3, 4(SPD1, SPD2, SPD3, SPD4)에서의 검출 확률 비는 1:0:1/2:1/2이 되며 마찬가지로

의 경우에는 0:1:1/2:1/2,

의 경우에는 1/2:1/2:1:0,

의 경우에는 1/2:1/2:0:1의 비율로 각 검출기에서 검출이 일어난다. 정리하면 송신자(110)가 보낸 양자상태의 집합{

,

}의 기저를 X라 하고 집합{

,

}의 기저를 Z라 하면, 수신자(120)의 측정 기저는 검출기 1, 2(SPD1, SPD2)에서 검출이 된 경우는 기저 X에 해당하며 검출기 3, 4(SPD3, SPD4)에서 검출이 된 경우 기저 Z에 해당한다.

The detection probability ratio in the single photon detectors 1, 2, 3 and 4 (SPD1, SPD2, SPD3, SPD4) is 1: 0: 1/2:

0: 1: 1/2: 1/2,

1/2: 1/2: 1: 0,

Detection is performed in each detector at a ratio of 1/2: 1/2: 0: 1. In summary, the set of quantum states {

,

} Is X and the set {

,

} Is Z, the measurement base of the receiver 120 corresponds to the base X when detected by the detectors 1 and 2 (SPD1 and SPD2) and detected by the detectors 3 and 4 (SPD3 and SPD4) It corresponds to base Z.

After the transmission of all the signals to the same base for the measurement of the chip signal for the receiver 120 transmitter 110 is a base (X or Z), and the public time t _{t -t} a time and the measurement of the detected photon to It is used as key information only when it is used.

0 "if measured at the single photon detector 1 (SPD1) and a bit" 1 "if measured at the detector 2 (SPD2) when the originator 110 uses the base X, Z generates bit "0" if measured at detector 3 (SPD3) and bit "1" if measured at detector 4 (SPD4).

For the structure previously described Fig. 5 (b) that the optical signal yirwojin two chip signal as shown in the equivalent to t _1, t _2, t ₃ time when arriving at the detector (SPD) via a delay and summing filter (DAF) all chip signal gatneunde the probability that the photon detection signal containing the actual useful information, since time is because the chip signal at t ₂ chip signal corresponding to a time t _1, t ₃ other than t ₂ does not contain valid information, The detection efficiency is reduced by 50% and thus the absolute secure transmission distance is reduced by 3-dB. This corresponds to a shortening of the transmission distance of 20 km when using a general communication optical fiber (SMF-28). Therefore, a new structure using a high-speed switch is proposed in Fig. 6 in order to prevent unnecessary signals from being removed to reduce the detection efficiency.

In Fig. 6, a high-speed switch and an interferometer are used instead of the delay and sum filter (DAF) (or delay interferometer). At this time, it is known that the quantum phase interference in the interferometer of this structure can achieve the same result as the classical interference. The high-speed switch divides the chip signal constituting the transmission pulse into upper and lower paths. The divided chip signal has a 1-chip time delay when passing the upper path, and the chip signal of the lower path is 0 ° or 90 ° phase- And enters the single photon detector through the interferometer. In this structure, detection efficiency is not reduced because detection is performed in one time differently from the previous structure.

Similarly, the sender 110 and the receiver 120 can generate a secret key using the structure of FIG.

1. The sender 110 randomly selects one of the quantum states of equation (2) and transmits it to the receiver 120. [

2. The receiver 120 uses the switch to divide the incoming chip signal into the upper path and the next incoming chip signal into the lower path. At this time, the chip signal entering the upper path experiences a delay of one chip time without changing the phase, and the chip signal entering the lower path is phase-modulated with any value of {0 °, 90 °} (PM).

3. The signal due to the constructive interference of the chip signal in the upper path and the lower path enters the single photon detector 1 (SPD1) and the canceling interference signal enters the single photon detector 2 (SPD2).

4. If the receiver 120 does not perform phase modulation, it corresponds to the base X measurement, and if it is detected by phase modulation of 90 degrees, it corresponds to the base Z measurement.

5. The receiver 120 discloses the measured basis to the sender 110 and generates a bit "0" or "1" according to the quantum state.

Furthermore, the four-chip coding system modulates one single photon pulse into four chip signals. As with the two-chip coding system, each chip signal is phase modulated to one of {0 °, 90 °, 180 °, 270 °}. In order to apply the 4-chip coding system to the general BB84 protocol, four quantum states satisfying Equation (4) can be formed. When the phase value of the chip signal is expressed as a complex number,

Generally, in the BB84 protocol, a single photon pulse carries one bit of information. As shown in the above two-chip coding system, one bit information can be transmitted with only two chip signals. If four quantum states are used as 4-chip coding and the four quantum states are used as quantum information, So as to have redundant information. The chip signal having redundant information increases the amount of information exposed to the eavesdropper 140, so that the security can not be guaranteed.

FIG. 7 is an example of an attack of a possible eavesdropper 140 when transmitting one bit of information to four chips. The eavesdropper 140 intercepts the signal sent by the sender 110 and interferes by dividing the two chip signals into an upper path and a lower path through a two-chip delay switch. In this case, only the quantum states {(1,1,1,1), (1, -1,1, -1)} in the constructive interference port have detection probabilities and the quantum states { 1, -i), (1, -i, -1, i)} has a detection probability. Therefore, the base of the signal is automatically classified according to the constructive interference port and the destructive interference port, and when the single photon detection corresponding to each base is performed, the eavesdropper 140 can accurately detect the signal sent from the sender 110, The same signal is regenerated and sent to the receiver 120 so that all the key information can be obtained.

In the present invention, the number of transmitted quantum states is increased in order to avoid duplication of transmitted information while increasing the number of chip signals, and accordingly, The amount of information to be transmitted to the quantum state of FIG. The four-chip coding quantum cryptography key distribution system 100 transmits two qubit information to one quantum state using a total of sixteen quantum states.

The method of generating sixteen quantum states can be represented by a qubit generating operation as shown in Equation (9) below.

의 조합으로 만들어 지는 16개의 양자상태는 아래와 같다. here

The following 16 quantum states are produced.

인 경우 첫 번째 큐빗의 기저는 X,

인 경우 첫 번째 큐빗의 기저는 Z에 매치된다. 마찬가지로

인 경우 두 번째 큐빗의 기저는 X,

인 경우 두 번째 큐빗의 기저는 Z로 매치되어 모든 양자상태 는 {XX, XZ, ZX, ZZ} 기저에 포함된다. Each quantum state is determined based on the value of the qubit generating operation.

, The basis of the first qubit is X,

, The basis of the first qubit is matched to Z. Likewise

, The basis of the second qubit is X,

, The basis of the second qubit is matched to Z and all quantum states are contained in {XX, XZ, ZX, ZZ} basis.

In the case of the four-chip coding quantum cryptographic key distribution system 100 having sixteen quantum states, the inner product between quantum states is calculated as shown in Equation (4), so that the quantum states of the same base are orthogonal to each other, (The quantum state information of the 4-chip coded quantum cryptographic key distribution system 100) shown in Table 1 below when the sender 110 and the receiver 120 use different bases, As shown in the superposition set column, the quantum state of a certain base can be expressed as a superposition of quantum states of other bases, and it is impossible to find the correct quantum state unless the same base is used.

FIG. 8 illustrates an operation structure of a 4-chip coding quantum key distribution system 100 according to an embodiment of the present invention. In FIG. 8, the sender 110 sends one of the sixteen quantum states to the recipient 120. The signal received at the receiver 120 passes through a two-chip delay interferometer and passes through a one-chip delay interferometer (DAF) and is measured with a single photon detector (SPD). The receiver 120 determines the measurement basis according to the phase path difference of the two-chip delay interferometer (DAF) and the one-chip delay interferometer (DAF). 2, 5, and 6 (corresponding to 0 °, 0 °) expressed as (phase path difference of the 2-chip delay interferometer DAF, phase path difference of the 1-chip delay interferometer DAF) SPD1, SPD2, SPD5, and SPD6) correspond to the base XX and detectors 9, 10, 13, and 14 (SPD9, SPD10, SPD13, SPD14) corresponding to (90 degrees, 0 degrees) correspond to the base XZ, The detector 3, 4, 7, 8 (SPD3, SPD4, SPD7, SPD8) corresponding to the angle of 90 degrees corresponds to the base ZX and the detectors 11, 12, 15, 16 (SPD11, SPD12, SPD15, SPD16) correspond to the base ZZ.

After the communication of the quantum channel is completed, the sender 110 and the receiver 120 disclose the basis of each other and use only the signal when the same base is used for the secret key extraction. In this case, the same basis refers to the case where both the base of the first qubit and the base of the second qubit are the same, and the two qubits are shifted and symbolized in a symbol unit as in the quadrature phase shifting key Go ahead. When the shifting process and the post-process are applied in the symbol unit, the allowable error rate limit value of the system increases.

8, the measurement efficiency of a signal is reduced and the number of single photon detectors (SPD) increases as the number of chip signals increases. As in the two-chip quantum cryptographic key distribution system 100, By using the two-chip switching and delay interferometer (DAF) and the one-chip switching and delay interferometer (DAF) of FIG. 9, the detection efficiency can be prevented from decreasing and the number of single photon detectors (SPD) can be reduced.

If we increase the number of chip signals to 2 ^N , we use 4 ^N total quantum states, which can be expressed by a qubit generating operation as shown in Equation 10 below.

의 조합이 가능하므로 아래의 수학식 11과 같이 N 큐빗에 대하여 4^N 개의 양자상태를 생성할 수 있게 된다. As before

It is possible to generate 4 ^N quantum states with respect to N qubits as shown in Equation (11) below.

은 독립적인 큐빗들을 생성시킬 수 있고, 따라서 커뮤테이터

이다. 앞서 표 1과 같이 양자상태들이 비직교적 양자상태들의 양자 중첩을 통해 생성되어 질 수 도 있다. One qubit generation operation encodes one qubit information. Qubit generation operation

Lt; / RTI > can generate independent cubits,

to be. Quantum states can be generated by quantum superposition of non-orthonormal quantum states as shown in Table 1 above.

에 따라 하나의 큐빗의 기저를 X와 Z로 매치하여 XXX...X, ZZZ...Z까지 총 2^N개의 기저가 존재하고 송신자(110)와 수신자(120)는 4-칩 양자 암호키 분배 시스템(100)에서 사용한 방법과 동일하게 송신자(110)가 보낸 양자상태의 기저와 수신자(120)의 측정 기저가 동일한 경우의 신호로부터 비밀키 정보를 추출한다.The basis of each quantum state is

A total of 2 ^N bases exist from XXX ... X to ZZZ ... Z, and the sender 110 and the receiver 120 have a 4-chip quantum cryptographic key Extracts the secret key information from the signal when the base of the quantum state sent by the sender 110 and the measurement basis of the receiver 120 are the same as the method used in the distribution system 100. [

Further, the structure of FIG. 9 is a two-chip coding system. The present invention can be applied not only to the 4-chip coding system but also to the ^2N -chip coding system as described above.

In the present invention, one single photon pulse is subjected to high-speed phase modulation on a complex plane to divide it into chips of small time units to form one quantum state. Chip coding system having one classical bit information and a 4-chip system having two pieces of bit information, a ^2N -chip coding system capable of having ^N classical bit information in one photon through the corresponding modulation scheme As a generalization. More specifically, the method of encoding a multi-qubit according to the present invention is simple and the structure of the receiving unit is also composed of a switch, a delay interferometer, and a single photon detector, thereby realizing an actual quantum cryptography key distribution protocol.

FIG. 10 illustrates a configuration of a transmitting apparatus 110 according to an embodiment of the present invention, and FIG. 11 illustrates a configuration diagram of a receiving apparatus 120 according to an embodiment of the present invention.

The transmitting apparatus 110 and the receiving apparatus 120 can be easily implemented by referring to the description of the quantum cryptographic key distribution system 100 and method according to the present invention. .

First, a transmitting apparatus 110 according to an embodiment of the present invention includes a transmitting apparatus 110 for distributing a quantum cryptographic key to a receiving apparatus 120 using a series of optical pulses, generator 112 and by dividing the my pulse with 2 ^N chips (chip), and the phase by applying the first base of the plurality of ground (basis) predetermined in the 2 ^N-chip modulation data of N qubits (N is a natural number equal to or greater than 1), and the receiving apparatus 120 receives the optical pulse transmitted from the transmitting apparatus 110 , And detects a light pulse by applying a second base of the plurality of bases and restores a part or all of the data so that the transmitting device 110 and the receiving device 120 can detect the optical pulse, The second base is collated and a part or the whole of the data is used The encryption keys can be distributed to each other.

A receiving apparatus 120 according to an embodiment of the present invention includes a receiving apparatus 120 for distributing a quantum cryptographic key using a series of optical pulses received from a transmitting apparatus 110, from one of the optical pulse is divided into 2 ^N chips (chip), the 2 ^N of applying a first base of the plurality of baseband predetermined (basis) on the chip to the phase modulation carries the transmission light data of the N qubits (N is a natural number equal to or greater than 1) receiving a pulse and a second base of the plurality of bases to the received optical pulse to detect a part of the data, The transmitting device 110 and the receiving device 120 may be configured to collate the first base and the second base and to transmit a part or all of the data To distribute the encryption key to each other It can be so.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments described in the present invention are not intended to limit the technical spirit of the present invention but to illustrate the present invention. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents thereof should be construed as being included in the scope of the present invention.

100: Quantum cryptographic key distribution system
110: sender
112: Optical pulse generator
114: Optical pulse modulation section
120: Recipient
122: optical pulse receiver
124: Optical pulse detector
130: Optical communication network
140: Interceptor

Claims (15)

In a system in which a sender and a receiver distribute a quantum cryptographic key using a series of optical pulses,
Dividing the one light pulse with 2 ^N chips (chip), said 2 ^N different to the chip applying the first base of the plurality of ground (basis) predetermined by the phase modulation actually the data of the N qubits transmitted light pulses Where N is a natural number greater than or equal to 1; And
And a receiver for receiving the optical pulse transmitted by the transmitter and detecting a light pulse by applying a second base of the plurality of bases to recover a part or all of the data,
Wherein the sender and the receiver match the first base and the second base and distribute the cryptographic keys to each other using part or all of the data. The method according to claim 1,
The receiver,
A light splitter for dividing a received optical pulse at a predetermined probability and transmitting the divided optical pulse to a first path and a second path;
A delay and summing filter for dividing the optical pulse into a first optical pulse and a second optical pulse, delaying the first optical pulse by a predetermined chip interval, and summing the delayed optical pulse and the second optical pulse, ; And
And a photon detector for detecting optical pulses output from the delay and summation filter. 3. The method of claim 2,
Wherein the delay and summation filter comprises:
And a phase modulator for modulating the phase of the first optical pulse or the second optical pulse according to the second basis. 3. The method of claim 2,
The receiver,
Chip delay and a summation filter when N = 1,
Chip delay and summation filter and a 1-chip delay and summation filter when N = 2,
Chip delay and summation filter, ..., 2 ^{n -1} - chip delay and summing filter, where n is a natural number greater than or equal to 3, where N = n, ;
At this time, the optical pulses received by the receiver,
Is divided into a plurality of paths while passing through one or more optical splitters,
After sequentially passing through the delay and sum filter of each kind,
Wherein the quantum cryptographic key distribution system is detected by the photodetector. 3. The method of claim 2,
The optical splitter comprises:
And a switch for dividing the plurality of chips in the optical pulse and transmitting the selected chips to the first path and the remaining chips to the second path. 6. The method of claim 5,
Wherein the switch comprises:
Wherein the plurality of chips are divided into a leading half and a trailing half of chips, and are transmitted to the first path and the second path, respectively. In a method in which a sender and a receiver distribute a quantum cryptographic key using a series of optical pulses,
The transmitter divides one optical pulse into ^2N chips, phase-modulates the optical signal by applying a first base of a plurality of predetermined bases to the ^2N chips, (Where N is a natural number equal to or greater than 1)
The receiver receives an optical pulse transmitted by the sender, detects a light pulse by applying a second base of the plurality of bases, restores a part or all of the data,
Wherein the sender and the receiver match the first base and the second base and distribute the cryptographic keys to each other using part or all of the data. In a method in which a sender and a receiver distribute a quantum cryptographic key using a series of optical pulses,
The receiver receives the data of the ^N -cubes by dividing one optical pulse from the sender into ^2N chips, applying the first base of a plurality of predetermined bases to the ^2N chips, Receiving light pulses emitted (here, N is a natural number of 1 or more); And
And applying a second base of the plurality of bases to the received optical pulse to detect a light pulse to recover a part or all of the data,
Wherein the sender and the receiver match the first base and the second base and distribute the cryptographic keys to each other using part or all of the data. 9. The method of claim 8,
Wherein,
A light splitting step of splitting the received optical pulses at a predetermined probability and transmitting the divided optical pulses to a first path and a second path;
A delay and summing step of dividing the optical pulse into a first optical pulse and a second optical pulse, delaying the first optical pulse by a predetermined chip interval, and summing the delayed first optical pulse and the second optical pulse, ; And
And a photon detection step of detecting an optical pulse output from the delay and summation filter. 10. The method of claim 9,
In the delay and summation step,
Wherein the phase of the first optical pulse or the phase of the second optical pulse is modulated according to the second basis. 10. The method of claim 9,
The receiver,
Chip delay and a summation filter when N = 1,
Chip delay and summation filter and a 1-chip delay and summation filter when N = 2,
Chip delay and summation filter, ..., 2 ^{n -1} - chip delay and summing filter, where n is a natural number greater than or equal to 3, where N = n, ;
At this time, the optical pulses received by the receiver,
Is divided into a plurality of paths while passing through one or more optical splitters,
After sequentially passing through the delay and sum filter of each kind,
Wherein the quantum cryptographic key distribution is detected by the photodetector. 10. The method of claim 9,
The light splitting step includes:
Wherein the optical pulse is implemented using a switch that divides a plurality of chips into a plurality of chips, transfers the chips to a first path, and transmits the remaining chips to a second path. 13. The method of claim 12,
Wherein the switch comprises:
And dividing the plurality of chips into a preceding half and a following half chip, and delivering the quantum cipher key to the first path and the second path, respectively. A transmitting apparatus for distributing a quantum cryptographic key to a receiving apparatus using a series of optical pulses,
An optical pulse generator for generating optical pulses; And
Dividing the one light pulse with 2 ^N chips (chip), said 2 ^N different to the chip applying the first base of the plurality of ground (basis) predetermined by the phase modulation actually the data of the N qubits transmitted light pulses , Where N is a natural number greater than or equal to 1,
The receiving apparatus receives an optical pulse transmitted by the transmitting apparatus, detects a light pulse by applying a second base of the plurality of bases and restores a part or all of the data,
Wherein the transmitting device and the receiving device collate the first base and the second base and distribute the cipher key to each other using part or all of the data. A receiving apparatus for distributing a quantum cryptographic key using a series of optical pulses received from a transmitting apparatus,
One optical pulse is divided into ^2N chips from the transmitting apparatus. The ^2N chips are subjected to phase modulation by applying a first base of a predetermined plurality of bases to the ^N chips, Wherein N is a natural number of 1 or more; And
And an optical pulse detector for detecting a light pulse by applying a second base of the plurality of bases to the received optical pulse to recover a part or all of the data,
Wherein the transmitting apparatus and the receiving apparatus collate the first base and the second base and distribute the cipher key to each other using part or all of the data.

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