JP2011044768A - Communication equipment and communication control method in steganographic communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide communication equipment and a communication control method in a steganographic communication system, which can continue encryption communication even when a key consumption speed is larger than a key generation speed. <P>SOLUTION: The communication equipment in the steganographic communication system for using an encryption key to perform encryption communication includes: a key sharing part (10) for sharing an encryption key generated by opposite communication equipment therebetween; a key storing part (11) for storing the shared encryption key; an encryption communicating part (12) for using the stored encryption key to perform encryption communication with the opposite communication equipment; and a key consumption amount control part (13) for controlling the key consumption amount of the encryption key consumed by the encryption communicating part in accordance with the key storage amount of the key storing part. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a secret communication system, and more particularly to a communication device that performs secret communication using an encryption key shared between nodes and a communication control method thereof.

  The Internet is an economic and social infrastructure where various data come and go. Therefore, it is important to prepare preventive measures to protect data flowing on the Internet from the risk of eavesdropping in advance. One of the preventive measures is a secret communication system that encrypts data to be communicated. There are two types of encryption methods: common key encryption and public key encryption.

  Common key cryptography is capable of high-speed processing by a method using a common key for encryption and decryption, as represented by AES (Advanced Encryption Standard). Therefore, this method is used for encrypting the data body.

  On the other hand, public key cryptography is a scheme using a one-way function as represented by the RSA cryptosystem, which performs encryption with a public key and decrypts with a secret key. Since it is not suitable for high-speed processing, it is used for common key type cryptographic key distribution.

  What is important in order to ensure confidentiality by data encryption is that even if the encrypted data is wiretapped by an eavesdropper, the encrypted data cannot be decrypted. For that purpose, it is necessary not to continue using the same encryption key for encryption. This is because, if the same encryption key is continuously used for encryption, there is a high possibility that the encryption key is guessed from a large amount of data that has been wiretapped.

  Therefore, it is required to update the encryption key shared between the transmission side and the reception side. Since it is essential that the key to be updated is not eavesdropped / decrypted at the time of key update, it can be broadly divided into the following two methods: (1) a method of sending encrypted by public key encryption and (2) a key update beforehand. There is a method in which a master key, which is a common key, is encrypted and sent (for example, see Patent Documents 1 and 2). The security in these methods depends on the huge amount of calculation for decoding.

  However, in the method based on the huge amount of calculation for the security of information, there is a problem that the secrecy is lowered by the evolution of the computer and the decryption algorithm. For example, the 56-bit DES decryption contest for competing for the decryption time of DES, which is a common key cipher, was 96 days in 1997, but was shortened to 22 hours in 1999. As for public key cryptography, RSA public key decryption required 8 months for key length 429 bits in 1994, but in 2004, the decryption technology evolved to about 3 months for key length 576 bits. Yes.

  On the other hand, the quantum key distribution technique (QKD) is a technique for generating and sharing a secret key between transmission and reception by transmitting an average number of photons per bit of 1 or less unlike ordinary optical communication. (See Non-Patent Documents 1 and 2). QKD has not been proved to be wiretapped by quantum mechanics, rather than safety by calculation amount as in the past. Therefore, eavesdropping is achieved by using a secret key shared by QKD as an encryption key for a one-time pad (hereinafter referred to as “OTP”), which has been proved to be unbreakable by information theory. It is possible to realize impossible encryption key sharing and unencryptable encrypted communication.

  In addition, since the safety of the photon transmission part can be ensured by the QKD technology, not only one-to-one key generation / sharing but also one-to-many or many-to-many key generation / sharing is realized by the optical switching technology and the passive optical branching technology. (See Non-Patent Document 3). Furthermore, in a one-to-many network configuration, after a quantum key is shared between a center node and a plurality of remote nodes, it is also proposed to securely share a key for cryptographic communication between remote nodes using this quantum key. (See Patent Document 3).

  Furthermore, Patent Document 4 constantly secures the amount of encryption key by switching the connection between the center node and a plurality of remote nodes while monitoring the amount of shared random numbers in a one-to-many or many-to-many connection secret communication system. A control method is disclosed.

  Patent Document 5 discloses a cipher that selects one of a plurality of encryption methods in accordance with the security rank of information transmitted and received between the transmission side and the reception side, and generates a key corresponding to the selected encryption method. A communication system is disclosed.

JP 2002-344438 A Japanese Patent Laid-Open No. 2002-300158 JP 2008-306633 A JP 2007-288694 A Japanese Patent Laid-Open No. 9-18469

"QUANTUM CRYPTOGRAPHY: PUBLIC KEY DISTRIBUTION AND COIN TOSSING" C. H. Bennett and G. Brassard, IEEE Int. Conf. On Computers, Systems, and Signal Processing, Bangalore, India, December 10-12, 1984 pp.175-179 "Automated 'plug & play' quantum key distribution" G. Ribordy, J. Gauiter, N. Gisin, O. Guinnard and H. Zbinden, Electron. Lett., Vol. 34, No. 22 pp. 2116-2117, ( (1998) "Quantum cryptography on multiuser optical fiber Networks" P. D. Townsend, Nature vol. 385, 2 January 1997 pp. 47-49 “Temperature independent QKD system using alternative-shifted phase modulation method” A. Tanaka, A. Tomita, A. Tajima, T. Takeuchi, S. Takahashi, and Y. Nambu, Proc. Of ECOC 2004, Tu 4.5.3.

  As described above, by using the quantum key shared by QKD as the encryption key for One-time-pad encryption, it is possible to realize encryption key sharing that cannot be tapped and encrypted communication that cannot be decrypted.

  However, while the One-time-pad requires an encryption key with the same capacity (number of bits) as the data to be encrypted, the quantum key generation (sharing) speed is at most as shown in FIG. It is about 1 Mbps. For this reason, voice data such as VoIP (Voice Over IP) can be encrypted with a one-time-pad using a quantum key, but it can be used for data transmission at a speed exceeding Mbps, such as video data. On the other hand, the key generation speed is not sufficient.

  It is also possible to store the quantum key while not performing encryption and use the stored quantum key when there is a request for encrypted data transmission. However, since the key consumption rate is higher than the key generation rate in moving image data transmission, the key is depleted when the amount of data to be encrypted exceeds the stored key amount, and encrypted communication cannot be performed.

  Patent Document 4 discloses a technique for making the key amount uniform among a plurality of remote nodes and avoiding the depletion of the key amount of a specific remote node, but the key consumption rate is higher than the key generation rate. The problem that the amount of stored keys is depleted and encrypted communication cannot be performed when the password is large cannot be solved.

  Moreover, in the said patent document 5, although generation | occurrence | production of the key according to the selected encryption system is described using the difference in the length of a key for every encryption system, In this method, When the key consumption rate is higher than the key generation rate, the problem that the stored key amount is depleted and encrypted communication cannot be performed cannot be solved.

  Furthermore, when an encryption key cannot be generated when an abnormality occurs in the encrypted communication device or when there is an eavesdropping on the transmission path (when the key generation speed becomes zero), On the other hand, since it is impossible to take an effective countermeasure, communication is impossible even if there is a request for encrypted communication.

  Accordingly, an object of the present invention is to provide a communication device and a communication control method thereof in a secret communication system capable of continuing encrypted communication even when the key consumption rate is higher than the key generation rate. .

  A communication apparatus according to the present invention is a communication apparatus in a secret communication system that performs encrypted communication using an encryption key, and is shared with a key sharing unit that shares an encryption key generated with an opposite communication apparatus. Depending on the key storage amount of the key storage means, the key storage means for storing the encryption key, the encrypted communication means for performing encrypted communication with the opposing communication device using the stored encryption key, and the key storage amount of the key storage means And key consumption control means for controlling the key consumption of the encryption key consumed by the encrypted communication means.

  The communication control method according to the present invention is a communication control method in a secret communication system that performs encrypted communication using an encryption key, and stores an encryption key generated and shared with a facing communication device in a key storage means. Then, the encrypted communication means performs encrypted communication with the opposite communication device using the stored encryption key, and the encrypted communication means consumes according to the key storage amount of the key storage means. The key consumption of the encryption key to be controlled is controlled.

  A program according to the present invention is a program that causes a program control processor of a communication apparatus in a secret communication system that performs encrypted communication using an encryption key to function as a communication control apparatus, and is generated and shared with an opposite communication apparatus. A function of storing the encrypted encryption key in the key storage means, a function of the encrypted communication means performing encrypted communication with the opposing communication device using the stored encryption key, and a key of the key storage means The program control processor realizes a function of controlling a key consumption amount of an encryption key consumed by the encryption communication unit in accordance with an accumulation amount.

  According to the present invention, encrypted communication can be continued even when the key consumption rate is higher than the key generation rate.

It is a schematic block diagram which shows the functional structure of the secret communication apparatus by 1st Embodiment of this invention. It is a block diagram which shows the functional structure of the secret communication system by 1st Example of this invention. It is a block diagram which shows the more detailed structure of the encryption / decryption part in the secret communication apparatus shown in FIG. It is a graph which shows the change of the amount of stored keys for demonstrating the communication control method by a present Example. It is a schematic block diagram which shows the functional structure of the secret communication apparatus by 2nd Embodiment of this invention. It is a block diagram which shows the more detailed structure of the encryption / decryption part in the secret communication apparatus of the secret communication system by 2nd Example of this invention. It is a graph which shows the change of the amount of stored keys for demonstrating the communication control method by a present Example. It is a schematic block diagram which shows the functional structure of the secret communication apparatus by 3rd Embodiment of this invention. It is a block diagram which shows the more detailed structure of the encryption / decryption part in the secret communication apparatus of the secret communication system by 3rd Example of this invention. It is a graph which shows the change of the amount of stored keys for demonstrating the communication control method by a present Example. It is a block diagram which shows the functional structure of the secret communication system by 4th Example of this invention. It is a block diagram which shows the functional structure of the QKD transmission side communication apparatus which can be used for the secret communication system by this invention. It is a block diagram which shows the functional structure of the QKD receiving side communication apparatus which can be used for the secret communication system by this invention. It is a graph which shows the relationship between the transmission distance of a QKD system, and a key generation speed.

1. First Embodiment As shown in FIG. 1, a communication device according to a first embodiment of the present invention includes a key sharing unit 10, a key storage unit 11, an encrypted communication unit 12, and a key consumption control unit 13. The key storage unit 11 stores the key generated by the key sharing unit 11 and supplies the key used for encryption / decryption to the encryption communication unit 12. If the key generation rate input by the key storage unit 11 is V _G , and the key consumption rate consumed by the key storage unit 11 is V _C , the key storage amount of the key storage unit 11 increases when V _G > V _C. , V _G <V _C , the key storage amount of the key storage unit 11 decreases.

  The encryption communication unit 12 executes encryption of the transmission message or decryption of the reception message using the key input from the key storage unit 11. Further, the encrypted communication unit 12 can change the consumption amount of the key used for encryption / decryption. The key consumption can be changed, for example, by changing the key length used in the encryption method and / or changing the key update frequency. It is also possible to employ a method in which a plurality of encryption methods having different key consumption amounts are prepared in advance and one encryption method is selected in accordance with a change command from the key consumption amount control unit 12.

The key consumption control unit 13 compares the key storage amount S of the key storage unit 11 with the predetermined lower threshold value S _th1 and the upper threshold value S _th2 to thereby _issue a key consumption amount change command to the encrypted communication unit. 12 is output. Specifically, when the key accumulation amount S decreases to the lower threshold value S _th1 , the key consumption amount control unit 13 sets the encryption method of the encrypted communication unit 12 so that the key consumption rate V _C is lower than the key generation rate V _G. And / or the key length and / or update frequency is changed so that the key consumption of the current encryption method is V _G > V _C. In particular, by stopping the update of the encryption key, the key accumulation amount can be maintained as it is in exchange for a decrease in security. On the other hand, when the key accumulation amount S exceeds the upper threshold value S _th2 , the key consumption amount control unit 13 increases the key consumption amount (key length or update frequency) in the encrypted communication unit 12 and / or is safe. Change to an encryption method that has high performance and high key consumption.

The lower threshold value S _th1 and the upper threshold value S _th2 can be set as follows, for example.
S _th1 > (V _C −V _G ) * τ + S (rnd)
S _th2 > (V _C −V _G ) * Tp + S (rnd)
Here, τ is a time from detection of the key accumulation amount to switching of the encryption method, S (rnd) is a random number as a safety parameter, and Tp is a predicted communication time.

  By controlling in this way, even when the key consumption rate is higher than the key generation rate, it is possible to avoid the situation where the key is depleted and the encrypted communication becomes impossible, and the encrypted communication can be continued. It becomes possible. The key consumption control unit 13 can also realize an equivalent function by executing a computer program on a program control processor.

  Hereinafter, a case where a key is generated by the quantum key distribution technique (QKD) will be described in detail as an example.

1.1) First Embodiment FIG. 2 is a block diagram showing a schematic configuration of a secret communication system according to a first embodiment of the present invention. It is assumed that the encrypted communication nodes 100 and 200 are connected via an optical fiber 300 that is an optical transmission path. The encrypted communication node 100 includes a transmission side encryption key sharing unit (QKD Alice) 110, an encryption key file 120, an encryption key management unit 130, and an encryption / decryption unit 140. Similarly, the encrypted communication node 200 includes a receiving side encryption key sharing unit (QKD Bob) 210, an encryption key file 220, an encryption key management unit 230, and an encryption / decryption unit 240. Here, the encryption / decryption units 140 and 240 are connected to perform encrypted communication, but the physical interface is not particularly limited.

  The encryption keys shared by the encrypted communication nodes 100 and 200 are stored in the key files 120 and 220, respectively. For example, after synchronization is established, the encryption key sharing unit 110 on the transmission side performs single photon transmission to the encryption key sharing unit 210 on the reception side, and executes a predetermined key distillation process, whereby the shared key (quantum key) is obtained. Generated and stored respectively in the key files 120 and 220 (specific examples will be described later).

  The encryption / decryption units 140 and 240 correspond to the encryption communication unit 12 in FIG. 1, and encrypt the transmitted message or decrypt the received message using the encryption keys stored in the key files 120 and 220, respectively. . The key management units 130 and 230 correspond to the key consumption amount control unit 13 in FIG. 1 and monitor the encryption key accumulation amounts of the respective key files 120 and 220. As described below, the key management units 130 and 230 correspond to the key accumulation amounts. The amount of keys consumed by the encryption / decryption units 140 and 240 is controlled.

  In the encryption / decryption units 140 and 240 in this embodiment, two encryption methods with different key consumptions are prepared in advance, and the key consumption can be changed by switching between them. The key consumption can be changed by changing the length. Here, an OTP (One-time pad) encryption method and a block encryption method are exemplified as two encryption methods with different key consumptions, but the present invention is not limited to this. A stream cipher may be used instead of the block cipher, or two block ciphers or stream ciphers with different key consumptions may be used. As the block cipher, AES cipher is exemplified in the present embodiment, but DES cipher or Camellia cipher may be used.

  Since the basic configurations of the encryption / decryption units 140 and 240 are the same, the configuration of the encryption / decryption unit 140 will be described in detail below with reference to FIG.

1.2) Encryption / decryption unit (encrypted communication unit)
As shown in FIG. 3, the encryption / decryption unit 140 includes an encryption unit 400 and a decryption unit 500. The encryption unit 400 has a configuration in which either the OTP encryption unit 430 or the block encryption unit 440 is selected by the selectors 410 and 420. However, here, the block cipher is an AES cipher, and the key length can be selected. The transmission message is encrypted and transmitted by the encryption unit selected by the selectors 410 and 420 using the encryption key. The decoding unit 500 has a configuration in which either the OTP decoding unit 530 or the block decoding unit 540 is selected by the selectors 510 and 520. The received encrypted message is decrypted by the decryption unit selected by the selectors 510 and 520 using the decryption key.

  The OTP encryption unit 430 and the block encryption unit 440 are supplied with the encryption key from the key file 120, and the OTP decryption unit 530 and the block decryption unit 540 are supplied with the decryption key from the key file 120. As is well known, an encryption key having the same capacity (number of bits) as the data to be encrypted is consumed in the OTP encryption method, but the key length is selected in advance in the AES encryption method. Therefore, it is possible to reduce the key consumption by selecting the AES encryption unit / decryption unit.

  The selectors 410 and 420 select either the OTP encryption unit 430 or the block encryption unit 440 according to a control signal (Enc. Cont.) From the encryption method switching control unit 131 of the key management unit 130. The selectors 510 and 520 select either the OTP decryption unit 530 or the block decryption unit 540 in accordance with a control signal (Dec. Cont.) From the encryption method switching control unit 131.

While monitoring the key accumulation amount of the key file 120, the encryption method switching control unit 131 determines whether the key accumulation amount S has exceeded a predetermined upper threshold value S _th2 or has reached a lower threshold value S _th1. A control signal for encryption (Enc. Cont.) Or a control signal for decryption (Dec. Cont.) Is output according to the determination result. Hereinafter, the switching control of the encryption method will be described in detail.

1.3) Encryption method switching control (key consumption control)
As described above, since the encrypted communication nodes 100 and 200 have basically the same functional configuration except for the encryption key sharing unit 110 and the encryption key sharing unit 210, the encryption method switching control will be described below. This will be described based on the configuration of the encrypted communication node 100. The same applies to the encrypted communication node 200.

In FIG. 4, since the key is not consumed when there is no request for encrypted communication, the encryption key generated and shared by the encryption key sharing unit 110 is continuously stored in the key file 120, and the storage amount is as in the period 810. Will increase over time. Here, it is assumed that the key amount exceeding the upper threshold value S _{th2 at} which OTP encrypted communication is allowed is accumulated in the key file 120.

  When a request for encrypted communication occurs in this state, the encryption method switching control unit 131 of the key management unit 130 confirms that the key amount S stored in the key file 120 is a necessary amount for OTP encrypted communication. Then, the control signal (Enc. Cont.) Is output to the encryption unit 400 of the encryption / decryption unit 140, and the control signal (Dec. Cont.) Is output to the decryption unit 500, and the OTP encryption unit 430 is selected by the selectors 410 and 420. And the OTP decoder 530 is selected by the selectors 510 and 520. As a result, the transmission message is OTP encrypted by the OTP encryption unit 430 and transmitted. The received encrypted message is decrypted by the OTP decryption unit 530.

At the time of OTP encryption / decryption, if the key consumption rate V _C consumed by the OTP encryption is smaller than the key generation rate V _{G, the} key amount accumulated in the key file 120 gradually increases as in the period 820 of FIG. It will increase.

On the other hand, if the key consumption rate V _C consumed by the OTP encryption is larger than the key generation rate V _G , the key amount stored in the key file 120 decreases as in the period 830 in FIG. Encryption system switch control unit 131, the key monitors the stored key amounts of the file 120, the amount of accumulated lower threshold S _th1 and since the time T ₀ cryptographically an encryption method to switch from OTP to AES reduction / The control signal (Enc. Cont.) Is output to the encryption unit 400 of the decryption unit 140, and the control signal (Dec. Cont.) Is output to the decryption unit 500. Accordingly, at time T _th1 , the AES encryption unit 440 is selected by the selectors 410 and 420, the AES decryption unit 540 is selected by the selectors 510 and 520, and the transmission message is encrypted and transmitted by the AES encryption unit 440. The Since the received encrypted message is AES encrypted on the transmission side, it is decrypted by the AES decryption unit 540. The time lag from time T ₀ to time T _th1 is a circuit delay from when the key amount is monitored until switching, and the encryption method is switched at time T _th1 .

The AES encryption key is updated periodically, but its consumption rate V _C is considerably smaller than the key generation rate V _G. Therefore, when the encryption method is switched to AES, the key amount stored in the key file 120 increases rapidly as in the period 840 of FIG.

When the key amount S stored in the key file 120 exceeds the upper threshold value S _th2 , the encryption method switching control unit 131 encrypts the encryption unit of the encryption / decryption unit 140 so as to return the encryption method from AES to OTP. The control signal (Enc. Cont.) Is output to 400, and the control signal (Dec. Cont.) Is output to the decoding unit 500. As a result, the selectors 410 and 420 select the OTP encryption unit 430, and the selectors 510 and 520 select the OTP decryption unit 530. The transmission message is OTP encrypted by the OTP encryption unit 430 and transmitted. The received encrypted message is decrypted by the OTP decryption unit 530. It is at time T _th2 in FIG. 4 that the encryption method is actually switched due to a circuit delay from the monitoring of the key amount until the encryption method is switched.

When the encryption method is switched from AES to OTP, the operation is the same as in the above-described period 830. That is, as shown in a period 850 in FIG. 4, the key amount stored in the key file 120 decreases, and the encryption method is changed to OTP when the key storage amount S of the key file 120 reaches the lower threshold value S _th1. The control signal (Enc. Cont.) Is output to the encryption unit 400 of the encryption / decryption unit 140 and the control signal (Dec. Cont.) Is output to the decryption unit 500 so as to switch from AES to AES. Accordingly, at time T _th3 , the AES encryption unit 440 is selected by the selectors 410 and 420, the AES decryption unit 540 is selected by the selectors 510 and 520, and the transmission message is encrypted and transmitted by the AES encryption unit 440. The Since the received encrypted message is AES encrypted on the transmission side, it is decrypted by the AES decryption unit 540.

Even after the encryption method is switched to AES as shown in a period 860 in FIG. 4, if the amount of encrypted data is large and the key storage speed is not sufficient, the AES key update frequency is lowered at time T _th4 in FIG. The key accumulation rate can be increased (period 870) by shortening the AES key length (for example, changing from 256 bits to 128 bits).

1.4) Effect As described above, according to the present embodiment, when the key accumulation amount decreases to a predetermined level, the key accumulation amount is recovered by changing the encryption method to a method with a smaller key consumption amount. Even when the generation speed of the encryption key is lower than the consumption speed, it is possible to continue the encrypted communication without interruption.

2. Second Embodiment As shown in FIG. 5, a communication device according to a second embodiment of the present invention includes a key sharing unit 10, a key storage unit 11, an encrypted communication unit 12, a key consumption control unit 14, and a key consumption estimation. Part 15. Among these, since the key storage unit 11 and the encrypted communication unit 12 are the same as those in the first embodiment, the same reference numerals are given and the description thereof is omitted. Hereinafter, the key consumption control unit 14 and the key consumption estimation unit 15 will be described in detail.

  According to the present embodiment, the key consumption estimation unit 15 estimates the encryption key consumption rate when encrypting the transmission message from the transmission message, and outputs the estimated consumption rate to the key consumption control unit 14.

The key consumption amount control unit 14 compares the key accumulation amount S of the key accumulation unit 11 with a predetermined lower threshold value S _th1 and an upper threshold value S _th2 in consideration of the estimated consumption rate, thereby _obtaining a key. A consumption change command is output to the encrypted communication unit 12. By considering the estimated consumption speed, it is possible to predict the key accumulation amount S before reaching the predetermined lower threshold value S _th1, and the key accumulation amount due to the delay from time T ₀ to time T _th1 shown in FIG. A situation where S slightly falls below the lower threshold value S _th1 can be effectively avoided. Note that the key consumption control unit 14 can also realize an equivalent function by executing a computer program on a program control processor.

2.1) Second Embodiment Since the overall configuration of the secret communication system according to the second embodiment of the present invention is the same as that shown in FIG. 2, the description thereof is omitted. As shown in FIG. The encryption method switching control unit 132 of the management unit 130 and the encryption unit 401 of the encryption / decryption unit 140 will be described. Since other configurations and operations are the same as those of the first embodiment, the same reference numerals are given and description thereof is omitted.

  In FIG. 6, a data amount monitor 450 corresponding to the key consumption amount estimation unit 15 of FIG. 5 is provided in the preceding stage of the selector 410 of the encryption unit 401 to monitor the data amount of the transmission message, and the monitored transmission data amount Mon. is output to the encryption method switching control unit 132.

The encryption method switching control unit 132 compares the key accumulation amount S of the key file 120 with the predetermined lower threshold value S _th1 and upper threshold value S _th2 . At this time, the transmission data from the data amount monitor 450 is compared. The key amount that will be consumed is estimated based on the amount, the estimated consumed key amount is reduced from the current key accumulation amount S, and then compared with the lower threshold value S _th1 and the upper threshold value S _th2 . Therefore, the switching timing of the encryption method can be predicted before the actual key accumulation amount S reaches the lower threshold value S _th1 , and a delay from the monitoring of the key amount to the switching of the encryption method is avoided. be able to.

2.2) Effect By estimating the consumption key amount based on the transmission data amount from the data amount monitor 450 and predicting the switching timing of the encryption method in this way, as shown in FIG. The encryption method can be immediately switched at the time points T _th11 and T _th21 when the key accumulation amount S reaches the lower threshold value S _th1 or the upper threshold value S _th2 .

3. Third Embodiment As shown in FIG. 8, a communication device according to a third embodiment of the present invention includes a key sharing unit 10, a key storage unit 11, an encrypted communication unit 12, and a key consumption control unit 16. Among these, since the key storage unit 11 and the encrypted communication unit 12 are the same as those in the first embodiment, the same reference numerals are given and the description thereof is omitted. Hereinafter, the key sharing unit 10 and the key consumption control unit 16 will be described in detail.

  The key sharing unit 10 corresponds to the encryption key sharing unit (QKD Alice) 110 on the transmission side or the encryption key sharing unit (QKD Bob) 210 on the reception side and has a function of monitoring the operation state or performance thereof. Good. For example, when the encryption key sharing units 110 and 120 detect that the key generation / sharing cannot be performed due to a hardware failure or the optical fiber 300 is disconnected, the status monitor signal to that effect is sent to the key consumption control unit. 16 is output.

  When the key consumption control unit 16 knows that the encryption key generation / sharing process can no longer be performed based on the status monitor signal, the key consumption control unit 16 controls the encryption communication unit 12 so that the key consumption amount is reduced or becomes zero. For example, the encryption method is switched so that the key consumption is minimized, and the encryption key is fixed without being updated. Thereby, the key consumption can be made zero. The key consumption control unit 16 can also realize an equivalent function by executing a computer program on a program control processor.

3.1) Third Embodiment The overall configuration of the secret communication system according to the third embodiment of the present invention is the same as in FIG. 2, and the encryption / decryption unit 140 is also the same as in FIG. The description is omitted.

As shown in FIG. 9, the encryption method switching control unit 133 of the key management unit 130 in this embodiment sets the key accumulation amount S of the key file 120, the predetermined lower threshold value S _th1 and the upper threshold value S _th2 . The switching control is performed in the same manner as in the first embodiment, but in addition to this, the status monitor signal of the encryption key sharing unit 110 (120) is input. When the encryption method switching control unit 133 knows that the encryption key generation / sharing process cannot be performed by the status monitor signal, the encryption method of the encryption / decryption unit 140 is switched from OTP to AES here, or AES The encryption keys of the encryption unit 440 and the AES decryption unit 540 are fixed without being updated. As a result, the key consumption at the time of failure can be reduced or made zero, and encrypted communication can be continued.

As shown in FIG. 10, for example, at time T ₁₀ during execution of OTP encrypted communication in the period 830, QKD performance degradation occurs, or encryption key generation / sharing processing stops, and the initial key generation speed is increased. Suppose that it can no longer be maintained. When this situation is known from the status monitor signal, the encryption method switching control unit 133 switches the encryption method of the encryption / decryption unit 140 from OTP to AES and fixes the encryption key without updating it. Thereby, as shown in the period 842, the consumption amount of the key accumulated in the key file 120 (220) becomes zero, and the accumulated key can be continuously used. Alternatively, it is possible to continue using the stored keys for a certain period by executing only AES key update to reduce the key consumption.

When QKD recovers at time T ₂₀ and returns to the initial key generation rate, the encryption method switching control unit 133 periodically updates the AES encryption key. However, as described above, the consumption rate V _C is the key generation rate. Since it is considerably smaller than the speed V _G , the key amount stored in the key file 120 increases rapidly after the recovery of QKD (period 843).

When the key amount S stored in the key file 120 exceeds the upper threshold value S _th2 , the encryption method switching control unit 133 encrypts the encryption unit of the encryption / decryption unit 140 so as to return the encryption method from AES to OTP. The control signal (Enc. Cont.) Is output to 400 and the control signal (Dec. Cont.) Is output to the decoding unit 500 (time T ₃₀ ), and the control is performed in the same manner as in the first embodiment shown in FIG. .

3.2) Effect As described above, when the encryption key cannot be generated due to a failure of the encryption key sharing unit or the like, the encryption method is switched so that the key consumption is minimized or zero. As a result, as shown in a period 842 in FIG. 10, encrypted communication can be continued using the key stored in the key file 120.

4). Fourth Embodiment In the above-described embodiment, the encryption communication nodes 100 and 200 autonomously switch the encryption method according to the storage status of the encryption key, but it is up to the other party to determine from where the encryption method was actually changed. If you don't notify it, you won't know exactly. Therefore, in the secret communication system according to the fourth embodiment of the present invention, the other party is notified of switching of the encryption method.

  As shown in FIG. 11, when the encryption method is switched by the encryption unit 400, a message notifying the switching is transmitted to the opposite side. The encryption unit 400 on the transmission side transmits the switching message after OTP encryption so that the fact that the encryption method has been switched is not deciphered. A synchronization pattern may be inserted at the beginning of the switching message so that the decoding unit 500 on the receiving side can identify the switching message.

  In this way, the timing of switching between encryption and decryption can be accurately matched between the transmission side and the reception side, and data loss due to switching of the encryption method can be eliminated.

5). Application Example of QKD FIG. 12 is an example of the encryption key sharing unit 110 on the transmission side, and FIG. 13 is an example of the encryption key sharing unit 210 on the reception side. This application example is realized by a Plug & Play QKD system. In particular, the encryption key sharing unit 110 shown in FIG. 12 is based on the alternating shift phase modulation type Plug & Play method.

  In FIG. 12, the transmission-side quantum unit 30 includes a polarization beam splitter (PBS) 31, a phase modulation unit 32, a random number generation unit 33, a synchronization unit 34, and an optical demultiplexing unit 35. It is connected. The phase modulator 32 and the polarization beam sputter (PBS) 31 constitute a PBS loop. The PBS loop has a function similar to that of a Faraday mirror, and is transmitted with the polarization state of incident light rotated by 90 degrees (see Non-Patent Document 4).

  Here, the phase modulator 32 has four phase modulation depths (0, π / 2, π, 3π /) corresponding to the four combinations of the two random numbers RND0 and RND1 supplied from the random number generator 33, respectively. 2), phase modulation is performed at the timing when the optical pulse passes through the phase modulator 32. The random number generation unit 33 generates random numbers RND0 and RND1 according to the clock signal supplied from the synchronization unit 34, supplies the random numbers RND0 and RND1 to the phase modulator 32, and holds them in the key generation unit 51. The synchronization unit 34 synchronizes by exchanging clock signals with the synchronization unit 44 on the receiving side.

  In FIG. 13, a reception-side quantum unit 40 includes a polarization beam splitter (PBS) 41, a phase modulation unit 42, a random number generation unit 43, a synchronization unit 44, an optical demultiplexing unit 45, an optical coupler 46, an optical circulator 47, and photon detection. And a pulse light source 49 and connected to the optical fiber transmission line 300.

  The process of generating and sharing an encryption key between the encryption key sharing unit 110 on the transmission side and the encryption key sharing unit 210 on the reception side is described in Non-Patent Documents 1, 2, and 4. Is not limited to BB84, but can also be applied to B92, E91, and the like.

  In this way, the detection data obtained by the photon detector 48 of the reception-side quantum unit 40 in response to the single photon transmission from the transmission-side quantum unit 30 is held in the key generation unit 52, and between the transmission-side key generation unit 51 and Then, the key distillation process is performed, and the encryption key is shared between the transmission side and the reception side and stored in the key files 120 and 220.

  The failure of the encryption key sharing unit in the third embodiment described above is, for example, out-of-synchronization or in-synchronization state in the synchronization units 34 and 44, failure of the random number generators 33 and 43, abnormal detection rate of the photon detector 48, or key generation unit. This can be detected by increasing the error rate at 51 and 52.

  The present invention can be used for encrypted communication using a common encryption key distribution technique represented by a quantum encryption key distribution technique.

10 Key sharing part
11 Key file
12 Encrypted communication section
13, 14, 16 Key consumption controller
15 Key consumption estimation part
100, 200 Encrypted communication node
110, 210 Encryption key sharing part
120, 220 key file
130, 230 Key Management Department
140, 240 Encryption / decryption unit
300 optical fiber
400, 401 Encryption section
500 Decryption unit
410, 420, 510, 520 selector
430 OTP encryption unit
440 AES encryption unit
450 Data volume monitor
530 OTP decoder
540 AES decoder

Claims (24)

A communication device in a secret communication system that performs encrypted communication using an encryption key,
Key sharing means for sharing the generated encryption key with the opposing communication device;
Key storage means for storing a shared encryption key;
Encrypted communication means for performing encrypted communication with the opposing communication device using the stored encryption key;
A key consumption amount control means for controlling a key consumption amount of the encryption key consumed by the encrypted communication means according to a key accumulation amount of the key accumulation means;
A communication apparatus comprising:   The key consumption amount control means presets an upper threshold value and a lower threshold value of the key accumulation amount, and when the key accumulation amount of the key accumulation means decreases to the lower threshold value, the key consumption amount control means The amount of key consumption is increased when the key storage amount is changed to be equal to or less than the key storage amount, and the key storage amount of the key storage means exceeds the upper threshold value. The communication device described.   The communication apparatus according to claim 1, wherein the key consumption amount control unit controls the key consumption amount by changing an update rate of an encryption key consumed by the encrypted communication unit.   4. The key consumption control unit according to claim 1, wherein the key consumption control unit controls the key consumption by changing a key length of an encryption key consumed by the encrypted communication unit. Communication equipment.   The key consumption control means controls the key consumption by selecting a plurality of different encryption methods provided in advance in the encrypted communication means. The communication device according to item.   6. The communication apparatus according to claim 5, wherein the plurality of different encryption methods include a one-time pad encryption method, a block encryption method, and / or a stream encryption method.   The encrypted communication means has at least a one-time pad encryption method, and when the encryption method is changed by the key consumption control means, the change message is one-time pad encrypted and transmitted to the opposite communication device. The communication apparatus according to claim 5 or 6, wherein   The key consumption control means stops the update of the encryption key consumed by the encrypted communication means when the generation of the encryption key in the key sharing means stops. The communication device according to item.   The communication apparatus according to claim 1, wherein the key sharing unit generates and shares an encryption key with the opposing communication apparatus by quantum encryption key distribution. A communication control method in a secret communication system that performs encrypted communication using an encryption key,
The encryption key generated and shared with the opposing communication device is stored in the key storage means,
Encrypted communication means performs encrypted communication with the opposing communication device using the stored encryption key,
Controlling the key consumption amount of the encryption key consumed by the encrypted communication means according to the key accumulation amount of the key accumulation means;
A communication control method characterized by comprising:   An upper threshold value and a lower threshold value are set in advance, and when the key storage amount of the key storage means decreases to the lower threshold value, the key consumption amount is reduced below the key storage amount. The communication control method according to claim 10, wherein the key consumption amount is increased when the key accumulation amount of the key accumulation unit exceeds the upper threshold value.   12. The communication control method according to claim 10, wherein the key consumption is controlled by changing an update speed of an encryption key consumed by the encrypted communication unit.   The communication control method according to claim 10, wherein the key consumption is controlled by changing a key length of an encryption key consumed by the encrypted communication unit.   The communication control method according to any one of claims 10 to 13, wherein the key consumption is controlled by selecting a plurality of different encryption methods provided in advance in the encrypted communication means.   The communication control method according to claim 14, wherein the plurality of different encryption methods include a one-time pad encryption method, a block encryption method, and / or a stream encryption method.   The encrypted communication means has at least a one-time pad encryption method, and when the encryption method is changed, the change message is one-time pad encrypted and transmitted to the opposing communication device. The communication control method according to 14 or 15.   The communication control method according to any one of claims 10 to 16, wherein when the generation of the encryption key is stopped, the update of the encryption key consumed by the encrypted communication unit is stopped.   The communication control method according to any one of claims 10 to 17, wherein an encryption key is generated and shared with the opposing communication device by quantum encryption key distribution. A program that causes a program control processor of a communication device in a secret communication system that performs encrypted communication using an encryption key to function as a communication control device,
A function of storing the encryption key generated and shared with the opposing communication device in the key storage unit;
A function in which encrypted communication means performs encrypted communication with the opposing communication device using the stored encryption key;
A function for controlling a key consumption amount of an encryption key consumed by the encrypted communication unit according to a key storage amount of the key storage unit;
Is realized by the program control processor.   An upper threshold value and a lower threshold value are set in advance, and when the key storage amount of the key storage means decreases to the lower threshold value, the key consumption amount is reduced below the key storage amount. The program according to claim 19, wherein the key consumption amount is increased when the key accumulation amount of the key accumulation means exceeds the upper threshold value.   21. The program according to claim 19, wherein the key consumption is controlled by changing an update speed of an encryption key consumed by the encrypted communication unit.   The program according to any one of claims 19 to 21, wherein the key consumption is controlled by changing a key length of an encryption key consumed by the encrypted communication unit.   The program according to any one of claims 19 to 22, wherein the key consumption is controlled by selecting a plurality of different encryption methods provided in advance in the encrypted communication means.   The secret communication system which contains the communication apparatus of any one of Claims 1-9 as an encryption communication node.

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