Communication systems and communication methods

Abstract

The goal is to reduce data usage and storage capacity while also improving security. [Solution] The transmitting device of this communication system generates a plurality of first variance values ​​using a pseudo-random number generator based on a common key and random numbers, generates a distribution formula including the random numbers using an asymmetric ramp-type secret sharing scheme, generates a second variance value based on the distribution formula, and transmits the second variance value. The receiving device calculates at least a portion of the plurality of first variance values ​​using the common key, and recovers the secret information based on a portion of the plurality of first variance values ​​and the second variance value.

Description

[Technical Field]

[0001] The present invention relates to a communication system and a communication method. [Background technology]

[0002] In the field of data communications, there is a need for communication methods that can securely send and receive data while protecting the confidentiality of information. At the same time, there is a need to eliminate the need for complex procedures in data usage during transmission and reception, thereby increasing data availability. In other words, a balance between confidentiality and availability is required.

[0003] A long-established method for improving data confidentiality is encryption, where data is encrypted before transmission and decrypted upon receipt. Common methods include symmetric-key encryption, where the original data is encrypted using a pre-distributed shared key, and public-key cryptography, where confidential information is encrypted using a public key generated from a private key, and then decrypted using the private key. However, both symmetric-key and public-key encryption methods have complex encryption and decryption procedures, and there is a risk of confidential information being stolen if the shared or private key is leaked.

[0004] Secret sharing is a data communication method that enhances availability while protecting data confidentiality. A representative secret sharing method is the (k, n) threshold secret sharing method. The (k, n) threshold secret sharing method divides secret information into n distributed values, and the original secret information can be restored by collecting any k of these distributed values. Since the original secret information cannot be obtained from k-1 or fewer distributed values, the original secret information remains safe even if some of the distributed values ​​are leaked, and the original secret information can be restored even if nk or fewer of the distributed values ​​out of the n distributed values ​​are lost.

[0005] However, the (k, n) threshold secret sharing scheme has a problem in that it cannot make the data length of each of the n distributed values ​​smaller than the data length of the original secret information, resulting in poor encoding efficiency and large communication volume, as well as large storage capacity on transceivers and cloud servers.

[0006] As a method for improving this, the (k, L, n) lamp-type secret sharing method has been proposed. Since the lamp-type secret sharing method can transmit L pieces of information simultaneously, the data length of each shared value can be reduced to 1 / L of the original secret information. Therefore, the encoding efficiency is better than that of the ordinary secret sharing method, and the communication volume and storage capacity can also be suppressed.

[0007] However, even in the lamp-type secret sharing method, the communication volume and storage capacity are still large, and there are major problems in terms of power saving and cost.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention provides a communication system and a communication method capable of improving security while reducing communication volume and storage capacity.

Means for Solving the Problems

[0010] The communication system according to the present invention is composed of a transmission device and a reception device. The transmission device generates a plurality of first shared values using a pseudo-random number generator based on a common key and a random number, generates a distributed formula including the random number by an asymmetric lamp-type secret sharing method, generates a second shared value based on the distributed formula, and transmits the second shared value. The reception device calculates at least a part of the plurality of first shared values using the common key, and restores the secret information based on all of the plurality of first shared values and the second shared value. [[ID=4​​​ According to the communication system and method of the present invention, it is possible to reduce the amount of communication, storage capacity, and computational load of information sharing processing while also improving security. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram illustrating the communication system 1 according to the first embodiment. [Figure 2] This flowchart illustrates the pre-processing procedure for performing communication using an asymmetric ramp-type secret sharing scheme between a communication terminal 10 and a data server 20 of the communication system 1 of the first embodiment. [Figure 3] This flowchart illustrates the process (information sharing process) in which, after the pre-processing in the communication system 1 of the first embodiment is completed, the communication terminal 10 distributes confidential information to generate a distributed value, and sends a portion of it to the data server 20 to share the confidential information. [Figure 4] This is a flowchart illustrating the procedure for restoring confidential information in the data server 20 of the communication system 1 according to the first embodiment. [Figure 5] This is a flowchart illustrating the procedure for information sharing processing of the communication system 1 according to the second embodiment. [Figure 6] This is a flowchart illustrating the procedure for restoring confidential information in the data server 20 of the communication system 1 in the second embodiment. [Modes for carrying out the invention]

[0013] This embodiment will be described below with reference to the attached drawings. In the attached drawings, functionally identical elements may be indicated by the same number. The attached drawings show embodiments and implementation examples in accordance with the principles of this disclosure, but these are for the purpose of understanding this disclosure and are not to be used in any way to restrict the interpretation of this disclosure. The descriptions in this specification are merely typical examples and do not limit the claims or applications of this disclosure in any way. In each drawing, identical or substantially equivalent elements, members and parts are given the same reference numerals. Also, the dimensions and proportions in the drawings are exaggerated for illustrative purposes and may differ from actual proportions.

[0014] While this embodiment is described in sufficient detail for those skilled in the art to implement the disclosure, it is important to understand that other implementations and forms are possible, and that the configuration and structure can be modified and various elements replaced without departing from the scope and spirit of the technical idea of ​​this disclosure. Therefore, the following description should not be construed as limiting to this.

[0015] [First Embodiment] Referring to Figure 1, a communication system 1 according to the first embodiment will be described. This communication system 1 consists, for example, of a communication terminal (e.g., a smartphone) 10 owned by user Pi, a data server 20, and an aerial communication device (e.g., a drone) 30. In Figure 1, for the sake of simplicity, only one communication terminal 10 is shown, but in reality, multiple communication terminals 10 may exist in a single communication system 1. As will be described later, each of the multiple communication terminals 10 shares a shared key, distributed value ID, user identifier, etc. with the data server 20 through communication preprocessing based on an asymmetric ramp-type secret sharing scheme.

[0016] The communication terminal 10 transmits various information to the data server 20 via the network NW or the flight communication device 30. In the event of a disaster, the network NW may become unusable, in which case the flight communication device 30 relays communication between the communication terminal 10 and the data server 20 and functions as a temporary information communication network. The flight communication device 30 is connected to multiple aircraft (drones) D1-D m Each aircraft D1~D m In the event of a disaster, the aircraft can fly within the communication range of the communication terminal 10, receive the distributed value calculated by secret sharing from the communication terminal 10, and transmit it to the data server 20 via a different communication path. m Communication between the parties may be via Wi-Fi®, Bluetooth®, infrared communication, or other methods.

[0017] When transmitting data, the communication terminal 10 performs data transmission using an asymmetric ramp-type secret sharing scheme. By using an asymmetric ramp-type secret sharing scheme, only a portion (for example, one) of the distributed values ​​is sent from the communication terminal 10 to the data server 20, and the data server 20 can reconstruct the original secret information using a shared key or the like.

[0018] Asymmetric ramp-type secret sharing is a method based on ramp-type secret sharing that reduces the number of distributed values ​​transmitted by using a pseudo-random number generator (reduced communication volume). The sender (communication terminal 10) calculates and transmits only one distributed value and an identifier, enabling the transmission of confidential information with both confidentiality and availability through lightweight computation (reduced computational load: the overall computational load is almost the same, but by performing calculations related to random numbers in advance, the computational load during actual communication processing can be reduced).

[0019] By utilizing the characteristics of ramp-type secret sharing, two pieces of secret information can be transmitted simultaneously. Furthermore, by performing preprocessing, it is possible to pre-configure the information that will be leaked in ramp-type secret sharing. In addition, by performing randomization processing, the transmitted distribution values ​​can be randomized, thereby reducing the possibility of information inference (information inference prevention).

[0020] Furthermore, to utilize the asymmetric ramp-type secret sharing scheme, various identifiers (IDs), parameters, and shared keys are pre-configured and shared in advance between the sender (communication terminal 10) and the receiver (data server 20). This reduces the computational load on both the sender and receiver. Also, because it is a secret sharing scheme, securing a secure communication channel is unnecessary.

[0021] As an example, the communication terminal 10 is configured to include a pre-processing execution unit 11, a pseudo-random number generation unit 12, a variance value / hash value calculation unit 13, a time identification unit 14, and a transmission / reception control unit 15. As described later, the communication terminal 10 generates a plurality of first variance values ​​f(α0) to f(α2) by the pseudo-random number generation unit 12 based on a common key and time information as an example of a random number, and generates a distribution formula using an asymmetric ramp-type secret sharing scheme, generates a second variance value f(α3) based on that distribution formula, and transmits the second variance value f(α3) to the data server 20. These first and second variance values ​​constitute n variance values ​​calculated based on the ramp-type secret sharing scheme, and the secret information can be restored by generating or receiving these values ​​on the receiving side.

[0022] The pre-processing execution unit 11 is responsible for performing pre-processing for data communication using this asymmetric ramp-type secret sharing scheme. Pre-processing includes, as an example, generating a distributed value ID, generating a shared key, and setting a user identifier.

[0023] The pseudo-random number generation unit 12 generates pseudo-random numbers v0, v1, and v2 for executing an asymmetric ramp-type secret sharing method that is executed for information sharing processing for sharing secret information between the communication terminal 10 and the data server 20. The distributed value / hash value calculation unit 13 determines a distributed formula f(x) based on the generated pseudo-random numbers v0, v1, and v2, and further calculates a second distributed value f(α3) and a hash value according to the distributed formula. The transmission / reception control unit 15 transmits the thus generated second distributed value f(α3) and the hash value of the user identifier id[i] to the data server 20.

[0024] The data server 20 includes, as an example, a preprocessing execution unit 21, a drone information collection unit 22, a distributed value calculation unit 23, a time determination unit 24, a restoration processing unit 25, and a transmission / reception control unit 26. The data server 20 receives a distributed value from the communication terminal 10 via the flight communication device 30 according to the asymmetric ramp-type secret sharing method, and restores this to obtain secret information.

[0025] The preprocessing execution unit 21 executes the above-described preprocessing in cooperation with the preprocessing execution unit 11 of the communication terminal 10. The drone information collection unit 22 collects information from the flight communication device 30 received from the transmission / reception control unit 26.

[0026] The distributed value calculation unit 23 calculates the first distributed values f(α0), f(α2) using the common key key i , key i (C) corresponding to the hash value of the received user identifier id[i]. The time determination unit 24 determines the time t i at which the distributed value generation process was performed at the communication terminal 10 on the transmission side according to the ramp-type secret sharing method. The restoration processing unit 25 calculates the remaining first distributed value f(α1) using the obtained time t i and the common key key i , key i (C) and restores the secret information using the obtained four distributed values f(α0) to f(α3).

[0027] [Preprocessing] Next, referring to the flowchart in Figure 2, the pre-processing procedure for performing communication using the asymmetric ramp-type secret sharing method between the communication terminal 10 and the data server 20 of the communication system 1 of the first embodiment will be described.

[0028] The pre-processing execution unit 21 of the data server 20 calculates the 4x4 (4x4) Van der Mond matrix →X (step S11). The Van der Mond matrix →X is expressed as follows [number A]: Inverse matrix X -1 The following [number B] is expressed as, and element X -1 (1,j) It can be pre-set so that it becomes 0. [Math B] shows the case where j=1.

[0029]

number

number

[0030] From the obtained Van der Mond matrix →X, select (determine) the variance values ​​ID α0, α1, α2, and α3 (step S12). The inverse matrix of Van der Mond matrix X is →X -1 Ingredient X -1 (1,j) Since the matrix is ​​equal to 0, it becomes possible to obtain the secret information si from only three of the four variance values.

[0031] Furthermore, the pre-processing execution unit 21, corresponding to each of the multiple communication terminals 10, provides a unique user identifier id[i] and its hash value id[i]', and a common key key. i , key i (C) The following are determined (step S13). The distribution values ​​ID α0, α1, α2, α3 and the common key are determined in this way. i , key i (C) The user identifier id[i] is shared with the corresponding communication terminal 10 (step S14).

[0032] (Information sharing process) Next, referring to Figure 3, we will describe the process (information sharing process) in which, after the pre-processing in the communication system 1 of the first embodiment is completed, the communication terminal 10 distributes the secret information to generate distributed values, and sends a portion of these values ​​to the data server 20 to share the secret information. The distributed values ​​that were not sent are generated in the data server 20 according to the common key, distributed value ID, and user identifier in the manner described later.

[0033] In the information sharing process, first, the pseudo-random number generation unit 12 of the communication terminal 10 generates a common key i , key i (C) , and time information t i Using this, for example, pseudorandom numbers v0, v1, and v2 are generated as follows (step S31).

[0034]

number

[0035] Next, the communication terminal 10 uses the distribution formula f(x)=s i +t i x + a²x 2 +a3x 3 The coefficients a2 and a3 are determined by setting the predetermined variance values ​​ID α0, α1, and α2 into this distribution formula and setting the values ​​as pseudo-random numbers v0, v1, and v2 (step S32), and the distribution formula is determined (step S33). This distribution formula is determined by the time information t as one aspect of the random numbers. i The coefficient of the linear term is included, and the secret information s iIt includes as a constant term. The communication terminal 10 then calculates a second distribution value f(α3) using the pre-shared distribution value IDα3, and also calculates a hash value id[i]' = hash(id[i]), which it then transmits to the data server 20 via the flight communication device 30 (step S34). With this, the information sharing process between the communication terminal 10 and the data server 20 is completed.

[0036]

number

[0037] (Restoration process) Next, with reference to Figure 4, the procedure for recovering secret information in the data server 20 will be explained. First, the data server 20 collects the hash value id[i]' and the second distribution value f(α3) from the aerial communication device 30 (drone) as information generated at the communication terminal 10 according to the asymmetric ramp secret sharing scheme (step S41).

[0038] Next, the distributed value calculation unit 23 of the data server 20 calculates the common key corresponding to the hash value id[i]'. i , key i [C] The key is identified, and using this common key, the first variances f(α0) and f(α2), which are part of the first variance, are calculated as shown in [Equation 3] below (step S42). [Equation 3] corresponds to the calculation formulas for the pseudorandom numbers v0 and v2 in [Equation 1].

[0039]

number

[0040] Next, the time generation unit 24 of the data server 20 determines the time t when the communication terminal 10 generated the distribution value from the secret information, based on the distribution values ​​f(α0) and f(α2) as part of the calculated first distribution value, and the received second distribution value f(α3) (in other words, by taking advantage of the vulnerability of the ramp-type secret sharing scheme). i This can be calculated using the following formula (Step S43).

[0041]

number

[0042] And the time t i Based on this, the remaining first variance value f(α1) is calculated as shown in [Equation 5] below (step S44). This [Equation 5] corresponds to the calculation formula for the pseudorandom number v1 in [Equation 1].

[0043]

number

[0044] The three variance values ​​f(α0), f(α1), and f(α2) obtained in the manner described above, along with the variance value f(α3) received via the flight communication device 30, are combined to form four variance values, and the restoration processing unit 25 then processes the secret information (s i ) is restored (step S45).

[0045] As explained above, in the communication system 1 of the first embodiment, the communication terminal 10 generates a pseudorandom number based on a pre-shared common key and a random number (for example, time ti) according to an asymmetric ramp-type secret sharing scheme, generates a second variance value based on the generated pseudorandom number, and transmits it. The receiving data server 20 can then calculate the first variance value according to the common key and random number, in addition to the received information, and recover the secret information. Since the random number can be obtained on the receiving side by inversely utilizing the vulnerability of the ramp-type secret sharing scheme, it becomes possible to communicate information with high availability while ensuring the confidentiality of the information. In the above example, the time information t identified by the time identification unit 14 is used as an example of a random number. iWhile this method was used, it is not limited to this; for example, random numbers generated by a standard random number generator can also be used. The random numbers only need to provide information that can verify the validity of the second variance value.

[0046] [Second Embodiment] Next, the communication system 1 according to the second embodiment will be described with reference to Figures 5 and 6. The overall configuration of the communication system 1 in this second embodiment is substantially the same as that of the first embodiment, so redundant explanations will be omitted. The communication system 1 in this second embodiment differs from the first embodiment in the procedures for information sharing processing and restoration processing. This will be explained with reference to Figures 5 and 6.

[0047] (Information sharing process) Figure 5 shows the procedure for information sharing processing of the communication system 1 according to the second embodiment. First, the pseudo-random number generation unit 12 of the communication terminal 10 generates a common key i , key i (C) Using this, for example, pseudorandom numbers v0 and v2 are generated as follows (step S51). Unlike the first embodiment, time t i This information will not be used.

[0048]

number

[0049] Next, the communication terminal 10 outputs the distribution formula f(x) = R + s i x + a²x 2 +a3x 3 Set (R is a random number), input predetermined variance values ​​IDα0 and α2 into this distribution formula and set the values ​​as pseudorandom numbers v0 and v2 to determine the coefficients a2 and a3 (step S52), and determine the distribution formula (step S53). This distribution formula includes the random number R as a constant term, and the secret information s iIt includes as a coefficient of the first-order term. The communication terminal 10 then uses the pre-shared distribution value ID(α3) to calculate the second distribution value f(α3) and the hash value id[i]'=hash(id[i]), and transmits it to the data server 20 via the aerial communication device 30 (step S54). With this, the information sharing process between the communication terminal 10 and the data server 20 is completed. The random number R is a random number used to disrupt the second distribution value f(α3) after encryption, so that the same plaintext will have different values. The random number R does not need to be restored.

[0050]

number

[0051] In this second embodiment, it is preferable to share the matrix B shown in [Equation 8] below between the communication terminal 10 and the data server 20 in advance through preprocessing. By sharing matrix B in advance, it becomes possible to calculate the coefficients a2 and a3 without performing division as shown in [Equation 9].

[0052]

number

number

[0053] (Restoration process) Next, with reference to Figure 6, the procedure for recovering secret information in the data server 20 of the communication system 1 of the second embodiment will be described. First, the data server 20 collects the hash value id[i]' and the second distribution value f(α3) from the aerial communication device 30 (drone) as information generated at the communication terminal 10 according to the asymmetric ramp secret sharing scheme (step S61).

[0054] Next, the distributed value calculation unit 23 of the data server 20 calculates the common key corresponding to the hash value id[i]'. i , key i [C] The key is identified, and using this common key, the first variances f(α0) and f(α2), which are part of the first variance, are calculated as shown in [Equation 3] above (Step S62).

[0055] Next, the data server 20 processes the secret information (s) according to the calculated first distribution values ​​f(α0), f(α2), and the received second distribution value f(α3). i ) is calculated as follows (step S63). Note that X -1 (1、0) , X -1 (1、2) , X -1 (1、3) This is a 4x4 (0-3) Van der Mond matrix → the inverse of X → X -1 These are the (1,0) component, (1,2) component, and (1,3) component.

[0056]

number

[0057] According to the method of this second embodiment, if three of the four variance values ​​are obtained, the secret can be kept. i This can be determined. In the first embodiment, time t as a random number i (Step S43) find the value of the item t i It is necessary to calculate the variance value f(α1) based on (step S44), but according to the second embodiment, the secret information s can be obtained using only three of the four variance values. i Because it is possible to obtain the secret information s at a faster speed compared to the first embodiment. i It is possible to perform calculations on this.

[0058] This disclosure is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are described in detail for the purpose of explaining this disclosure clearly, and are not necessarily limited to having all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0059] 1…Communication system 10…Communication terminals 11…Pre-processing execution unit 12... Pseudo-random number generation unit 13...Distribution value / hash value calculation unit 14...Time identification section 15…Transmit / Receive Control Unit 20…Data Server 21…Pre-processing execution unit 22…Drone Information Gathering Department 23... Variance calculation unit 24…Time specification section 25…Restoration Processing Unit 26...Transmission / reception control unit 30... Flight communication equipment

Claims

1. A transmitting device that generates multiple first variance values ​​using a pseudo-random number generator based on a common key and random numbers, generates a distribution formula including the random numbers using an asymmetric ramp-type secret sharing scheme, generates a second variance value based on the distribution formula, and transmits the second variance value, A receiving device that calculates at least a portion of the plurality of first variance values ​​using the shared key, and recovers secret information based on the plurality of first variance values ​​and the second variance value. A communication system characterized by comprising the following features.

2. The communication system according to claim 1, wherein the random number is time information representing a time, or information for verifying the validity of a second variance value.

3. The transmitting device and the receiving device are The communication system according to claim 1, wherein a user identifier that identifies the user of the transmitting device, a distribution value ID relating to the first distribution value and the second distribution value, and the common key are shared in advance.

4. The communication system according to claim 3, wherein the aforementioned variance value ID is determined based on a van der Mond matrix in which one of the inverse matrices is 0.

5. The communication system according to claim 1, wherein the receiving device obtains a random number based on a portion of the first variance and the second variance using a ramp-type secret sharing scheme, calculates the remaining first variance using the random number, and restores the secret information based on all of the plurality of first and second variances.

6. The communication system according to claim 5, wherein the distribution formula includes the random numbers as coefficients of a first-order term and the confidential information as a constant term.

7. The communication system according to claim 1, wherein the receiving device reconstructs the secret information based on only a portion of the first variance and the second variance.

8. The communication system according to claim 7, wherein the distribution formula includes the random numbers as a constant term and the confidential information as a coefficient of the first-order term.

9. The transmitting device generates a plurality of first variance values ​​using a pseudo-random number generator based on a common key and random numbers, generates a distribution formula including the random numbers using an asymmetric ramp-type secret sharing scheme, generates a second variance value based on the distribution formula, and transmits the second variance value. The receiving device calculates at least a portion of the plurality of first variance values ​​using the common key, and recovers secret information based on the plurality of first variance values ​​and the second variance value. A communication method characterized by comprising:

10. The communication method according to claim 9, wherein the random number is time information representing a time, or information for verifying the validity of a second variance value.

11. The communication method according to claim 9, further comprising the step of sharing in advance a user identifier for identifying the user of the transmitting device, a distribution value ID relating to the first distribution value and the second distribution value, and the common key in the transmitting device and the receiving device.

12. The communication method according to claim 11, wherein the aforementioned variance value ID is determined based on a van der Mond matrix in which one of the inverse matrices is 0.

13. The communication method according to claim 9, wherein the receiving device obtains a random number based on a portion of the first variance and the second variance using a ramp-type secret sharing scheme, calculates the remaining first variance using the random number, and restores the secret information based on all of the plurality of first and second variances.

14. The communication method according to claim 13, wherein the distribution formula includes the random number as a coefficient of a first-order term and the secret information as a constant term.

15. The communication method according to claim 9, wherein the receiving device recovers secret information based on only a portion of the first variance and the second variance.

16. The communication method according to claim 15, wherein the distribution formula includes the random number as a constant term and the secret information as a coefficient of the first-order term.

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