JP2014197839A - Communication system, client terminal, server, data communication method, and data communication program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce damage due to spoofing in network communication.SOLUTION: A data communication method of a data communication system including a server (10) which transmits data and a client terminal (20) which receives the data transmitted from the server via a network (50) prevents spoofing by performing the steps of: encrypting present communication time and previous communication time using the previous communication time with the server as an encryption key and transmitting the encrypted data to the server (transmission step); and receiving the encrypted data transmitted from the client terminal by the server and decrypting the received encrypted data using the previous communication time taken out from storage means and relating to the client terminal as a decryption key (decryption step).

Description

  The present invention relates to a communication system including a server and a client terminal connected via a network, and a technique for preventing information leakage and so-called “spoofing” in a communication method executed by them.

  In a network environment where an unspecified number of people such as the Internet participate, a server that has a function that provides a service only to a user who has the right to receive a service, does the connected user have the right to receive the service? First of all, make a decision. At this time, the user authentication is performed based on whether or not the user ID or password composed of characters, symbols, and numbers transmitted by the user via the client terminal 20 is valid. The problem here is so-called “spoofing”. “Impersonation” means that someone else's user ID, password, etc. are stolen and pretending to be someone else, acting on the network. If a malicious third party steals a user ID or password by means of wiretapping or social engineering, it is impersonated and connected to the server system. As a result, the server is illegally provided with a service by a malicious third party, thereby incurring a disadvantage to the user (client). Similarly, the service provider also loses the provision of the service to the malicious third party who does not pay a legitimate price. For example, if the server system is online banking of a financial institution, cash is illegally withdrawn from a user (client) account. Moreover, if it is a membership system online game, it will suffer damage that the rare item and in-game currency possessed by the user (client) are stolen. In addition to changing the password regularly and in a short period of time as a “common sense” for using the network, it is recommended that the password be set to a type that cannot be easily guessed. Is annoying and not easy to implement in practice.

  Patent Document 1 generates identification information (for example, anonymity of a user properly used for each site) to be included in an email when the person who obtained the personal information sends an email to the user who is the principal personal information However, a technique for preventing spoofing by determining whether or not the identification information matches is disclosed. In Patent Documents 2 and 3, an authentication code is generated by encrypting the current communication time, and an access request attached with the authentication code is transmitted to a www server. In order to determine whether or not the authentication is permitted, the authenticator is decrypted and the time is extracted, and it is verified whether the time is within the allowable range, thereby preventing impersonation. ing.

JP 2003-67524 A JP 2002-132730 A WO2011 / 052671 Publication

  However, since the technique disclosed in Patent Document 1 is based on the premise that mail is transmitted and received and cannot be used for communications other than mail, it is effective only in a limited range. Furthermore, if the identification information itself is stolen by a third party, there is a problem that the third party can easily impersonate the user. In addition, the techniques proposed in Patent Documents 2 and 3 have a problem that it is impossible for the impersonated person to know the fact or it takes time to know the fact. Therefore, the present invention aims to reduce damage caused by impersonation by a method in which a user cannot easily steal the above-described problem.

  In order to solve the above problems, the present invention has the following configuration. It should be noted that the definitions of terms used to describe the invention described in any claim are applicable to the invention described in other claims as far as possible, regardless of the category of the invention, the description order, etc. To do.

(Characteristics of the invention of claim 1)
A data communication system according to the invention of claim 1 (hereinafter referred to as “system of claim 1” as appropriate) includes a server that transmits data, a client terminal that receives the data transmitted by the server via a network, Is a data communication system. Here, the client terminal stores, for each communication, the previous identification code transmitted to the server in the previous communication, and the previous identification code extracted from the storage means using the previous identification code as an encryption key. Encryption means for encrypting at least including the current identification code different from the previous identification code and a transmission means for transmitting the encrypted data encrypted by the encryption means to the server. On the other hand, the server stores receiving means for receiving encrypted data transmitted from the client terminal, and storage means for storing the current identification code transmitted from the client terminal as a previous identification code at a predetermined timing for each communication. And decrypting means for decrypting the encrypted data received by the receiving means using the previous identification code relating to the client terminal extracted from the storage means as a decryption key.

  According to the system of claim 1, first, the client terminal transmits the encrypted data including the previous identification code and the current identification code acquired or generated by the client to the server using the previous identification code as an encryption key. The server decrypts the received identification data from the previous identification code transmitted before the current communication with the client (may be immediately before or a predetermined second or more times before). Decrypt as The decrypted current identification code is stored in the storage means as a previous identification code as a decryption key for decrypting the encrypted data transmitted from the client by subsequent communication (next time or after the second predetermined time). . In this way, the previous identification code, which is the common encryption key, is used between the encrypted data and the server by determining the agreement between the client terminal and the server at the time of communication before the present time (immediately before or the second time before the predetermined time). It is possible to shift the transmission / reception timing of the encrypted key between the client terminal and the server, and the content of the encryption key is changed / updated for each communication, so that the transmitted / received data is decrypted by interception on the network. Becomes extremely difficult, and as a result, an effect of effectively preventing impersonation by a third party is brought about.

(Characteristics of the invention described in claim 2)
The data communication system according to the invention of claim 2 (hereinafter referred to as “system of claim 2” as appropriate) is the system of claim 1, wherein the current identification code is between the client terminal and the server. Current communication time indicating the current communication time, and the previous identification code is a previous communication time indicating a communication time communicated immediately before the current communication time between the client terminal and the server. And

  According to the system of claim 2, the operation effect of the system of claim 1 is realized by the communication time. In other words, the previous communication time between the client terminal and the server is used as an encryption key, and the encryption key and the current communication time are transmitted as encrypted data. The server that receives the encrypted data decrypts using the previous communication time as the decryption key. The current communication time transmitted from the client terminal is used as a decryption key for subsequent communication. Therefore, the previous communication time here means that the communication already performed between the client terminal and the server is completed normally and successfully, and this is mutually approved between the client terminal and the server. If the time is.

(Characteristics of Claim 3)
A data communication system according to the invention described in claim 3 (hereinafter referred to as “system of claim 3” as appropriate) includes a server for transmitting data, a client terminal for receiving data transmitted by the server via a network, Is a data communication system. Here, the client terminal stores the previous communication time with the server for each communication, and the current communication time and the previous communication time with the previous communication time retrieved from the storage means as an encryption key. Encryption means for encrypting at least, and transmission means for transmitting the encrypted data encrypted by the encryption means to the server. On the other hand, the server stores receiving means for receiving the encrypted data transmitted from the client terminal, and storage means for storing the current communication time transmitted from the client terminal as the previous communication time at a predetermined timing for each communication. And decrypting means for decrypting the encrypted data received by the receiving means using the previous communication time associated with the client terminal extracted from the storage means as a decryption key.

  According to the communication system of the third aspect, first, encrypted data including the previous communication time and the current communication time is transmitted from the client terminal to the server using the previous communication time as an encryption key. The server decrypts the received encrypted data using the previous communication time with the client terminal as a decryption key. The decrypted current communication time is stored in the storage unit as a decryption key for decrypting the encrypted data transmitted from the client by the next communication as the previous communication time after the authentication is normally completed. In this way, the previous communication time, which is the common encryption key, is determined between the client terminal and the server at the time of communication before the current time (immediately before or the second time or more previously determined), so that the encrypted data and its use are used. It is possible to shift the transmission / reception timing of the encrypted key between the client terminal and the server, and the content of the encryption key is changed / updated for each communication, so that the transmitted / received data is decrypted by interception on the network. Becomes extremely difficult, and as a result, an effect of effectively preventing impersonation by a third party is brought about.

(Feature of the invention of claim 4)
The data communication system according to the invention of claim 4 (hereinafter referred to as “system of claim 4” as appropriate) is the system of claim 2, wherein the server further decrypts by the decrypting means. The current communication time and the previous communication time are compared with the current communication time (received data from the client on the server side) and the previous communication time concerning the client terminal taken out from the storage means to determine whether authentication is possible. The determination means includes a determination means, and the determination means determines that authentication is possible only when both current communication times are within a predetermined range (including coincidence) and both previous communication times are completely coincident. Is configured to do.

  According to the system of claim 4, in addition to the operational effect of the system of claim 3, the determination means determines that authentication is possible only when at least the following two requirements are satisfied, thereby impersonating by a third party: Try to prevent effectiveness. That is, the first requirement is whether the current communication time of the client terminal is compared with the current communication time of the server, and whether or not the two are within a predetermined range. The reason why the value is within the predetermined range is theoretically the time difference due to the time required for computer processing with communication, and realistically and technically, the time generated by the communication status such as traffic and the performance difference of the computer equipment. This is a result of taking each measurement error into consideration. In general, if this range is narrowed, it is proof that the time between the start of access by the client terminal and its acceptance at the server is close in time, but it is the responsibility of the client terminal and server such as communication line congestion. Authentication is rejected due to external reasons that cannot be attributed, and the possibility of hindering smooth operation increases. How to determine this predetermined range quantitatively must be determined according to the specific operational status. On the other hand, if this error deviates from the above-mentioned reasonable range, that is, the current communication time on the client terminal side that requested the authentication and the current communication time on the server side that received the request separated from each other beyond a predetermined range. In such a case, it may be assumed that there is a reasonable reason to suspect that data transmitted from the client terminal to the server on the network has been compromised or modified by a third party, and a countermeasure may be taken. The second requirement is a perfect match of the previous communication time. Here, the concept of error does not exist because the last communication time of the server is the one that was transmitted as the current communication time in the last successful communication with the client terminal, that is, the authentication that was successfully completed. As the last communication time used in the next authentication in the process was synchronized with the agreement of both the server and the client, and since the server was not obtained independently, no error could occur, so it became a perfect match Yes.

(Feature of the invention of claim 5)
A client terminal for a data communication system according to the invention described in claim 5 (hereinafter referred to as “terminal of claim 5” as appropriate) stores storage means for storing the previous communication time with the server for each communication, and from the storage means Encryption means for encrypting at least the current communication time and the previous communication time with the taken out previous communication time as an encryption key, and a transmission means for transmitting the encrypted data encrypted by the encryption means to the server And.

  According to the terminal of claim 5, first, using the previous communication time as an encryption key, the client transmits encrypted data including the previous communication time and the current communication time to the server. The server decrypts the transmitted encrypted data using the previous communication time with the client as a decryption key. In this way, the previous communication time, which is the common encryption key, is determined between the client terminal and the server at the time of communication before the current time (immediately before or the second time or more previously determined), so that the encrypted data and its use are used. It is possible to shift the transmission / reception timing of the encrypted key between the client terminal and the server, and the content of the encryption key is changed / updated for each communication, so that the transmitted / received data is decrypted by interception on the network. Becomes extremely difficult, and as a result, an effect of effectively preventing impersonation by a third party is brought about.

(Characteristics of the invention described in claim 6)
A server for a data communication system according to a sixth aspect of the invention (hereinafter referred to as “the server of the sixth aspect” as appropriate) is a receiving means for receiving encrypted data transmitted from a client terminal, and is transmitted from the client terminal. Storage means for storing the current communication time as the previous communication time at a predetermined timing for each communication degree, and the encryption data received by the reception means before updating the client terminal extracted from the storage means. Decrypting means for decrypting the previous communication time as a decryption key.

  According to the server of claim 6, the server that has received the encrypted data encrypted with the previous communication time as the encryption key decrypts the encrypted data with the previous communication time with the client as the decryption key. The decrypted current communication time is stored in the storage means as a previous communication time as a decryption key for decrypting encrypted data transmitted from the client by the next communication. In this way, the previous communication time, which is the common encryption key, is determined between the client terminal and the server at the time of communication before the current time (immediately before or the second time or more previously determined), so that the encrypted data and its use are used. It is possible to shift the transmission / reception timing of the encrypted key between the client terminal and the server, and the content of the encryption key is changed / updated for each communication, so that the transmitted / received data is decrypted by interception on the network. Becomes extremely difficult, and as a result, an effect of effectively preventing impersonation by a third party is brought about.

(Feature of the invention of claim 7)
A data communication method according to the invention of claim 7 (hereinafter referred to as “method of claim 7” as appropriate) includes a server for transmitting data, a client terminal for receiving data transmitted by the server via a network, Is a data communication method of a data communication system including: Here, the client terminal encrypts at least the current communication time and the previous communication time with the previous communication time with the server taken out from the storage means as an encryption key, and the encrypted encrypted data A transmitting step for transmitting to the server, and a decryption for receiving the encrypted data transmitted from the client terminal and decrypting the previous communication time related to the client terminal extracted from the storage means by using the decryption key And a storage step of storing the current communication time transmitted from the client terminal in the storage unit as the previous communication time at a predetermined timing for the communication degree.

  According to the communication method of the seventh aspect, first, using the previous communication time as an encryption key, the client transmits encrypted data including the previous communication time and the current communication time to the server. The server decrypts the received encrypted data using the previous communication time with the client as a decryption key. The decrypted current communication time is stored in the storage means as a previous communication time as a decryption key for decrypting encrypted data transmitted from the client by the next communication. In this way, the previous communication time, which is the common encryption key, is determined between the client terminal and the server at the time of communication before the current time (immediately before or the second time or more previously determined), so that the encrypted data and its use are used. It is possible to shift the transmission / reception timing of the encrypted key between the client terminal and the server, and the content of the encryption key is changed / updated for each communication, so that the transmitted / received data is decrypted by interception on the network. Becomes extremely difficult, and as a result, an effect of effectively preventing impersonation by a third party is brought about.

(Characteristics of the invention described in claim 8)
The data communication method according to the invention of claim 8 (hereinafter referred to as “method of claim 8” as appropriate) is the communication method of claim 7, wherein the server further performs the decrypted current communication time. The previous communication time is compared with the current communication time and the previous communication time of the client terminal taken out from the storage means, and the both current communication times are within a predetermined range. A determination step of determining that the comparison result is coincident is performed on the assumption that the two coincide completely.

  According to the system of claim 8, in addition to the function and effect of the system of claim 3, according to the system of claim 4, in addition to the function and effect of the system of claim 3, the server satisfies at least the following two requirements: In such a case, it is determined that authentication is possible, thereby preventing the spoofing by a third party. That is, the first requirement is whether the current communication time of the client terminal is compared with the current communication time of the server, and whether or not the two are within a predetermined range. The reason why the value is within the predetermined range is theoretically the time difference due to the time required for computer processing with communication, and realistically and technically, the time generated by the communication status such as traffic and the performance difference of the computer equipment. This is a result of taking each measurement error into consideration. In general, if this range is narrowed, it is proof that the time between the start of access by the client terminal and its acceptance at the server is close in time, but it is the responsibility of the client terminal and server such as communication line congestion. Authentication is rejected due to external reasons that cannot be attributed, and the possibility of hindering smooth operation increases. How to determine this predetermined range quantitatively must be determined according to the specific operational status. On the other hand, if this error deviates from the above-mentioned reasonable range, that is, the current communication time on the client terminal side that requested the authentication and the current communication time on the server side that received the request separated from each other beyond a predetermined range. In such a case, it may be assumed that there is a reasonable reason to suspect that data transmitted from the client terminal to the server on the network has been compromised or modified by a third party, and a countermeasure may be taken. The second requirement is a perfect match of the previous communication time. Here, the concept of error does not exist because the last communication time of the server is the one that was transmitted as the current communication time in the last successful communication with the client terminal, that is, the authentication that was successfully completed. As the last communication time used in the next authentication in the process was synchronized with the agreement of both the server and the client, and since the server was not obtained independently, no error could occur, so it became a perfect match Yes.

(Feature of the invention of claim 9)
A data communication program according to the invention described in claim 9 (hereinafter referred to as “program of claim 9”) is a data communication program for causing a computer to function as a server for transmitting data received by a client terminal via a network. It is. Specifically, the computer stores the reception means for receiving the encrypted data transmitted from the client terminal and the current identification code transmitted from the client terminal as the previous identification code at a predetermined timing for each communication. The storage unit and the decryption unit that decrypts the encrypted data received by the reception unit using the previous identification code related to the client terminal extracted from the storage unit as a decryption key, and the client The decryption step of receiving the encrypted data transmitted from the terminal and decrypting the previous communication time related to the client terminal extracted from the storage means using the decryption key, and the current communication time transmitted from the client terminal, A storage step for storing in the storage means as the previous communication time at a predetermined timing for the communication degree. And up, to the execution.

  According to the program of the ninth aspect, it is possible to cause a computer to function as the means and to function as a server that executes the steps.

(Features of the invention of claim 10)
A data communication program according to the invention of claim 10 (hereinafter referred to as "program of claim 10" as appropriate) is a data communication for causing a computer to function as a client terminal that receives data transmitted by a server via a network. A storage means for storing the previous identification code transmitted to the server in the immediately previous communication for each communication, and the previous identification code using the previous identification code extracted from the storage means as an encryption key. The encryption means for encrypting at least including the current identification code different from the previous identification code and the transmission means for transmitting the encrypted data encrypted by the encryption means to the server, Using the previous communication time with the server retrieved from the storage means as the encryption key, the current communication time and the previous communication time A transmission step of encrypting at least the transmission time and transmitting the encrypted encrypted data to the server; and the server receives the encrypted data transmitted from the client terminal and is retrieved from the storage means. A decrypting step for decrypting the previous communication time related to the client terminal as a decryption key, and storing the current communication time transmitted from the client terminal in the storage means as the previous communication time at a predetermined timing for communication degree Steps are executed.

  According to the program of claim 10, it is possible to cause a computer to function as the means and to function as a client terminal that executes the steps.

  According to the present invention, it becomes possible to shift the transmission / reception timing between the encrypted data and the encryption key used in the client terminal-server, and the content of the encryption key is changed / updated for each communication, In other words, a one-time password-like function is exhibited, which makes it difficult to decrypt the transmitted / received data on the network, resulting in an effect of effectively preventing spoofing by a third party.

1 is a schematic diagram of a communication system. It is a block diagram which shows the structure of a server. It is a block diagram which shows the structure of a client terminal. It is a flowchart which shows an authentication procedure. It is a flowchart which shows the acquisition procedure of the last communication time. It is a flowchart which shows the determination procedure. It is a flowchart which shows the authentication procedure using a password. It is a figure which shows the state which uses a some client terminal.

  Hereinafter, embodiments of the present invention will be described. FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention.

(Outline of communication system)
The communication system 1 includes a server 10 and at least one client terminal 20 that are connected to each other via the Internet 50 that is a communication line (network).

  The server 10 provides a service to a predetermined client terminal 20 via the Internet 50, and each function described below is provided to a computer having a function that does not provide the service according to the present embodiment to other computers. It can be realized by executing a program (data communication program) for realizing. Services include online banking, membership-based net games, and the like, for example, 24 hours 365 days non-stop. This program may be installed in a computer from a portable recording medium 15 as shown in FIG. 1, or may be downloaded from a server on a network.

  The client terminal 20 can be realized by causing a computer having a right to receive a service from the server 10 to execute a program (data communication program) for realizing each function described below. It may be installed in a computer from a portable recording medium 25 as shown in FIG. 1 or may be downloaded from a server on a network. The client terminal 20 operates by being powered on by the user only when it wants to receive a service. The client terminal 20 shown in FIG. 1 is not limited to a so-called personal computer, but via a network such as a PDA (Personal Digital Assistant) with communication function, a game machine with communication function, a mobile phone, a tablet terminal, a smartphone, or a mobile terminal. The concept is a terminal having a function of receiving a service from a server.

  The NTP server 30 is a computer that distributes highly accurate date and time information such as an atomic clock to devices on the Internet 50 using the Network Time Protocol. The server 10, the client terminal 20, and the NTP server 30 are connected to the Internet 50, which is a communication line. In FIG. 1, only one client terminal 20 and NTP server 30 are depicted, but a plurality of client terminals 20 and NTP servers 30 may exist.

(Server configuration)
FIG. 2 is a block diagram illustrating a configuration of the server 10. A CPU (Central Processing Unit) 100 is a central processing unit, executes a program (data communication program), and performs calculation, determination, and an instruction command to another block. The CPU 100 functions as an encryption / decryption device (encryption / decryption unit) 101, a determination device (determination unit) 103, and a service permission device (service permission unit) 105. The communication device 150 functions as a transmission / reception unit. A RAM 110 (Random Access Memory) is used as a work area when the CPU 100 executes a program. The RAM 110 is a temporary storage memory.

  The storage device 120 is a non-volatile storage unit that stores a program and various data and has a function that does not erase the data even when the power is turned off. As the storage device 120, a magnetic storage device such as a hard disk, an optical storage device such as a CD or a DVD, a semiconductor storage device such as a flash memory, and a combination thereof are used. The storage device 120 of this embodiment stores basic software (OS), application programs, and various data. In addition to these, a client DB 121 is placed in the storage device 120. In the client DB 121, a client account table 121a and an authentication history table 121b (FIG. 5) are placed.

  The operation device 130 is a man-machine input device used when inputting data when an operator operates the server 10. A keyboard, mouse and touch panel are used. The display device 140 is a man-machine output device used when an operator receives information from the server 10, and for example, a CRT display, a liquid crystal display (display means), a printer, or the like is used.

  The communication device 150 is used when the server 10 communicates with other devices. The communication device 150 of the present embodiment is a wired LAN device or a wireless LAN device capable of performing IP (Internet Protocol) communication in order to perform communication via the Internet 50, for example.

  The real-time clock 160 (the same applies to a real-time clock 260 described later) is a calendar clock that holds date and time information. The real-time clock 160 is backed up by a battery and retains date and time information as long as the battery is not exhausted even when the server 10 is turned off. Since the real-time clock 160 may cause an error of several seconds to several tens of seconds per day unless the date and time are adjusted by any means, it is preferable that the real-time clock 160 is configured to be able to correct this. The server 10 of this embodiment operates non-stop 24 hours a day, 365 days a year, and the CPU 100 periodically inquires date and time information to the NTP server 30 via the Internet 50 by a program and adjusts the date and time of the real-time clock 160. ing. Therefore, the date / time information is “corrected” date / time information. The bus 190 performs data transmission between the connected blocks.

(Configuration of client terminal)
FIG. 3 is a block diagram showing a configuration of the client terminal 20. Since the configuration of the client terminal 20 is basically the same as that of the server 10 described above, when only the number is different with the same member name, the member of the client terminal 20 and the member of the server 10 have the same configuration. The description thereof will be omitted. In the following description, different points will be described.

  The client terminal 20 includes a CPU 200, a RAM 210, a storage device 220, an operation device 230, a display device 240, a communication device 250, a real time clock 260 (clock 260), and a bus 290. The CPU 200 executes various basic functions and also functions as an encryption unit that encrypts data related to the corrected communication time with respect to the server 10. The communication device 250 functions as a transmission unit that transmits its own client identification ID to the server and a transmission unit that transmits data to be authenticated to the server. The bus 290 performs data transmission between the connected blocks.

(Communication method by communication system)
Hereinafter, a communication method using the communication system 1 will be described with reference to the drawings. The element used by the server 10 in the communication system 1 to identify the client (client terminal 20) that is the service receiver requires at least the current communication time and the previous communication time yyy. In this embodiment, in addition to these two communication time items, authentication data of four items (hereinafter referred to as “identification four items” as appropriate) including a client identification ID (hereinafter abbreviated as “identification ID”) and a password are included. As an element. Among the four items, the identification ID and password can be negotiated in some way when the service provider (server operator) and the service receiver (user or client) conclude a service provision contract (or thereafter). And At this time, the service provider distributes the identification IDaaa to the service professor and the service receiver declares the password bbb corresponding to the provided identification IDaaa to the service provider. Instead of this declaration, a method may be adopted in which a service provider distributes a password predetermined for each identification ID to the service recipient. In any case, it is assumed that the identification IDaaa and the password bbb are determined in advance as a premise for providing and enjoying the service.

(Start client terminal authentication)
Please refer to FIG. The client accesses a predetermined site from the client terminal 20 connected to the network (Internet 50) in an attempt to use a paid or free service (here, assuming a paid membership network game). At that time, the client inputs the identification ID aaa and the password bbb from the operation device 230 (S2010). This starts client authentication (S2020). In the client terminal 20 instructed to start authentication, preparation for that is performed as follows.

(Preparation for authentication on the client terminal)
In the client terminal 20 that has received the instruction, the CPU 200 of the client terminal 20 acquires the previous communication time yyy and the current communication time (including the year / month / day and the previous communication time yyy) zzz from the storage device 220 (S2030, S2040). In the present embodiment, the previous communication time yyy refers to the communication time immediately before (one time before) with the server 10, and the current communication time zzz also refers to the current communication time. Although these communication times will be described in detail later, these communication times are the times at which attempts to authenticate are started, and are generally obtained from the clock 260. In the flow of FIG. 4, acquisition of the previous communication time yyy is preceded, but acquisition of the current communication time zzz may be preceded, or both may be simultaneous. Details of how the setting is made for the “previous communication time” will be described later, but for the time being, the previous communication time yyy is already stored in the storage device 220 of the client terminal 20. Assuming that the service is provided “normally” at the time of the previous communication, the minimum requirement is two points that the same “previous communication time yyy” is also stored in the storage device 120 of the server 10. It becomes.

  Here, the current time is obtained by accessing the NTP server in FIG. 4, but if there is a premise described in the description of the server configuration, refer to the real-time clock in the client terminal. It is also possible to replace it.

  Usually, transmission / reception of authentication data consisting of four identification items between the client terminal 20 and the server 10 is encrypted by SSL or the like at the level of the communication protocol. In order to improve the performance, the encryption is performed independently of the existing encryption provided at the communication protocol level. As a result, even if the existing cipher such as SSL is broken, only the client identification IDaaa in the four identification items is exposed to the cryptanalyst. Fail-safe authentication is enabled for the three items of the password bbb, the previous communication time yyy, and the current communication time zzz.

  In general, the public key cryptosystem has the advantage that the user does not need to be conscious of encryption and does not place a burden on the user. However, the cipher strength is inferior to the common key system and the processing time is reduced. It has been pointed out that the burden is heavy. On the other hand, despite the above advantages (compared to public key cryptography), common key cryptography is equivalent to or better than data delivery. It is well known that the problem is standing up.

(Adopting common key cryptography without key delivery)
In other words, a common key cryptosystem that does not involve key delivery is relatively excellent. Therefore, in the present embodiment, among the four identification items necessary for the client terminal 20 to access the server 10 for authentication, data relating to the three items of the password bbb, the previous communication time yyy, and the current communication time zzz Using the communication time yyy, encryption is performed using a common key encryption method, and encrypted data relating to the three items of the password bbb, the previous communication time yyy, and the current communication time zzz is generated (S2050). This is possible if the same (synchronized) previous communication time yyy is shared between the client terminal 20 side and the server 10 side, as described in the above-mentioned authentication preparation at the client terminal. . This sharing should be confirmed by reading the description below.

  As a possible criticism of using the last communication time yyy as an encryption key (single), for example, there may be room for it to be deciphered by a technique such as a search for all cases because it is well known (that is, If you know the format of the time, for example, if you try to identify the previous time based on the probability that the previous communication would have been done during this month, 60 seconds × 60 minutes × 24 hours × 30 days = 2,592,000 It may be said that if you try 3 million cases at most, the code will be broken. However, the key to using the previous communication time yyy as the encryption key here is that it is not necessary to deliver the key at the same timing as the delivery of the encrypted data, and the complexity of the key can be treated as another problem. . That is, by rephrasing “if the key includes the previous communication time”, the problem of delivery and the complexity of the key are solved. For example, by combining the password and the previous communication time, the complexity of the key is stronger than the password, and the key cannot be decrypted unless the time passed last time is known (that is, the encryption key Both problems can be solved in the sense that it changes by having the previous time inside). In the following description, the description that the previous communication time is used as the encryption key is continued, but it should be noted that the above meaning is included.

(Transmission of encrypted data by client terminal)
The client terminal 20 transmits the data of the identification IDaaa and the encrypted data (password bbb, data related to the current communication time zzz and the previous communication time yyy) to the authentication site of the server 10 (S2060).

(Receiving encrypted data by server)
The identification IDaaa and the encrypted data transmitted by the client terminal 10 are received by the server 20 (S2070).

(Get current communication time)
Although it is not necessary to limit to this, for example, the server 10 acquires the current communication time zzz on the server 10 side at the timing when the access for authentication is detected from the client terminal 20 (S2080). A method for acquiring the current communication time ◎ will be described later. The current communication time zzz means the time when the server 10 receives the authentication data transmitted from the client terminal 20.

  Here, the current time is supposed to be obtained by accessing the NTP server in FIG. 4, but if the premise described above can be applied to the server, refer to the real-time clock inside the server, It is also possible to replace it.

(Decryption of encrypted data)
The CPU 100 of the server 10 searches the client DB 121 (see FIG. 5) using the received identification IDaaa of the client terminal 20 as a key, and extracts the corresponding password bbb and the previous communication time yyy (S2090). Using the previous communication time yyy taken out from the stored server 10 as a (decryption) key, the received encrypted data (password bbb, current communication time zzz, previous communication time yyy) is decrypted by a predetermined common key encryption method and decrypted. The password bbb, the current communication time zzz, and the previous communication time yyy obtained by the above are stored in the RAM 110 (S2100).

(Retrieval and acquisition of client information from the server-side DB)
The operation of S2090 shown in FIG. 4 will be described more specifically with reference to FIG. 5 once away from FIG. Here, it is assumed that the received identification ID is “BCD345” (S3030). The CPU 100 searches using the identification ID “BCD345” as a key, retrieves the corresponding password “GROTHENDICK” from the client account table 121a of the client DB 121, and the corresponding previous communication time “2012/12/2 2:44:18”. Are obtained from the authentication history table 121b (S3040, S3050). This password obtained by the search is defined as a search password, and this previous communication time is defined as a previous search communication time.

(Data comparison: password)
Here, returning to FIG. 4, the description will be continued. After completing the decryption / storage in S2100, the CPU 100 determines whether or not the client terminal 20 can be authenticated by comparing the decrypted identification ID and password (S2110). This authentication procedure will be described with reference to FIG. The CPU 100 first compares the passwords. If the search password matches the password bbb, the CPU 100 determines that the authentication is “permitted” and proceeds to S4020. If the search password does not match, the CPU 100 determines that the authentication is “no” and proceeds to S4050 (S4010). In S4050, an unauthenticated message is transmitted to the client terminal 20 and displayed on the display device 240 (FIG. 3) to prompt the operator to redo the authentication procedure.

(Data comparison: current communication time)
Next, the CPU 100 that has proceeded to S4020 compares the current communication time of the client terminal 20 whose validity has been confirmed with the current communication time of the server 10, and the current communication time zzz and the current communication time zzz are within a predetermined allowable range. If it is included, the process proceeds to S4030 as “Go”, and if it is not included, the process proceeds to S4050 as “No”. That is, the difference between the time T when the client terminal 20 starts authentication and the time T ′ when the server 10 receives the authentication data from the client terminal 20 is the time Δt that is appropriately specified by the service provider (server operator). If the requirement (T−T ′ <Δt) within the predetermined range of (> 0) is satisfied, “Yes” is determined, and otherwise “No” is determined. The comparison of the current communication time is based on the case where the client authentication data is intercepted and modified by a malicious third party on the Internet 50 and transmitted to the server 10. It is assumed that this third party intervention appears as a time difference between T and T ′ (T ≦ T ′ in the normal case) and a deviation from the average time required for normal data transmission / reception. Note that T = T ′ is not excluded here when the minimum unit of time is, for example, seconds, and authentication processing is performed in an ideal communication environment including the computer such as the server 10 and the client terminal 20. This is because the error between T and T ′ falls within one second, and as a result, there is a possibility that T = T ′ as a digital display.

  Therefore, Δt is generally determined by the service provider by comprehensively considering the traffic situation of the network line, the distribution situation of the client terminal group (for example, domestic or worldwide only) and the type of service to be provided. Can be set arbitrarily. In some cases, each characteristic may be set so that Δt is individually determined for each client terminal. Note that if Δt is too strict (that is, if Δt is too small), even though the client is a legitimate client, authentication will frequently fail due to network traffic conditions, leading to a loss of client convenience. Must. The Δt once set does not need to be rigid, and does not prevent it from being changed regularly or irregularly according to changes in the situation. Needless to say, the inequality T−T ′ <Δt can be appropriately replaced with T−T ′ ≦ or the absolute value | T−T ′ | <Δt as long as it matches the purpose of the current communication time comparison. When <is replaced with ≦, the requirement to be satisfied by Δt is 0 ≦ Δt.

  Returning to FIG. 6, the description will be continued. When the current communication time is “possible”, the CPU 100 further compares the previous communication time of the client terminal 20 with the previous communication time of the server 20, and if the previous search communication time matches the previous communication time yyy, “ "Yes" is determined, and a predetermined service is provided to the client terminal 20 (S4040). On the other hand, if they do not match, “NO” is determined and the process proceeds to S4060. In S4060, the CPU 100 transmits a message indicating that authentication is impossible to the client terminal 20 and issues a report to the service provider. The notification is made to notify the user of the client terminal 20 that there is a possibility that impersonation has been performed and that the countermeasure should be taken promptly if impersonation has been performed.

(Evaluation of legitimacy check and judgment of user eligibility)
As shown in FIG. 4, the determination as to whether authentication is possible is performed in the order of S2110 → S2120 → S2130. On the other hand, although illustration in FIG. 4 is omitted, when “No” occurs in any of the above steps, the subsequent steps are not necessary and an authentication failure message is transmitted to the client terminal 20. The authentication process on the server 10 side ends. When all the checks of S2110, S2120, and S2130 are cleared, the process proceeds to the next (previous communication time update process). Here, when “No” occurs, it is necessary for the server 10 to perform the evaluation (eligibility of the user) and processing corresponding thereto. In this regard, the points to be generally considered will be described in the following paragraphs in accordance with FIG.

  In other words, when it is determined as “No” in S2110 (FIG. 4), since the password input mistake may be a legitimate user, an appropriate error message is transmitted to the client terminal 20 side, and an authentication retry is prompted (S4050). . However, if the same error is repeated frequently, authentication retries exceeding the predetermined number of times are not permitted (for example, 3 times is the maximum number of times and access is denied after the 4th time). You may consider giving a separate response as a caution user. For this purpose, it is preferable that not only authentication but also a history when authentication is impossible can be recorded in the authentication history table 121b in the server 10 shown in FIG.

  When it is determined as “No” in S2120, this is an event that can also occur for a regular user due to a delay caused by an accident such as an unexpected increase in circuit traffic. In relation to the setting of [Delta] t shown in FIG. 5, the service provider (server 10 operator) is involved in the policy and management policy. Common sense is that A. mentioned above. As in the case of, it is possible to send an error message and a message prompting the authentication retry within a certain limit, and when exceeding the limit, treat as a user who needs attention.

  In the case of “NO” in S2130, it is preferable to clearly consider that an improper or system failure such as “spoofing” has occurred. That is, if the previous communication time does not match that of the server 10 and that of the client terminal 20, authentication (and therefore service use) of the client terminal 20 will no longer be possible, and this situation can be resolved. Is notified that the service provider needs to investigate and respond (such as resetting the previous communication time on the client terminal 20 side) (S4060). On the server 10 side, it is possible to collect and accumulate as much detailed and extensive authentication history information as possible regardless of whether authentication is possible or not. For this reason, it is preferable to design the authentication history table 121b in consideration of an effective method.

(Previous communication time update process)
Returning to FIG. 4, the description will be continued. If the authentication is successful, the server 10 transmits a message indicating that authentication is possible to the client terminal 20 (S2140). Upon receiving this message, the client terminal 20 replaces the current communication time used in the current authentication with the previous communication time (S2160, S2170). This is used as the previous communication time in the next authentication. The client terminal 20 storing the replaced previous communication time transmits a message to that effect to the server 10 (S2180, S2190). Upon receiving this message, the server 10 side stores (updates) the previous communication time yyy of the client terminal 10 at the current communication time zzz transmitted from the client terminal 20 in the current authentication (S2220, S2230). However, here, “update” means that if it is assumed that information is stored in the server 10 in the form of the authentication history table 121b (FIG. 5), a new record is created (inserted) as the current history (old record). Does not overwrite). The current communication time zzz transmitted from the client terminal 10 is set in the previous communication time field at that time. When the processes so far are normally performed, the previous communication time yyy on the client terminal 20 side and the previous communication time yyy on the server 10 side are the same. Thereafter, the server 10 ends the authentication work and permits the provision of the service requested from the client terminal (S2240). When there is a service provision request from the client terminal 20 (S2250), the server 10 provides a service to the requested client terminal 20 (S2260).

(If the last communication time update / synchronization failed)
After the authentication (S2110, S2120, S2130) on the server 10 side is successful and before the provision of the service is permitted (S2240), the server 10 and the client terminal 20 are disconnected due to communication interruption / disconnection. The following two points are assumed as a case where synchronization (sharing) of the previous communication time fails between the two. One is a case in which the authentication on the server 10 side succeeds, but the success message does not reach the client terminal 10 side for some reason (failure of S2140). The other one is the previous communication from the client terminal 20 This is a case where the time saving message has not reached the server 10 (failure of S2190). For each of these, the recovery processing that must be performed by the server 10 and the client terminal 20 is as follows.

  In the case of the first case, since an authenticable message is not sent from the server 10 (S2140), the client terminal 20 cannot store (update) the previous communication time in S2180 and send the message in S2190. Judge. On the other hand, even if the server 10 transmits a message (S2140), it cannot obtain a response (S2190) from the client terminal 20, and therefore cannot store (update) (S2230) the previous communication time. . As a result, neither authentication data (particularly the previous communication time) is updated (synchronized) in the client terminal 20 and the server 10. Therefore, the server 10 can be set to cancel the current authentication and continue the authentication work after waiting for the client terminal 20 to start the authentication work again, for example.

  In the case of the second case, the client terminal 20 updates the previous communication time (S2180) and simply sends a message to the server 10 (S2190) (although the server 10 does not receive this), the authentication operation is performed. Do nothing. On the server 10 side, when the message of S2190 is not received, the following two points can be considered as the cause. That is, for some reason, the communication is interrupted. As a result, the first is that the message of S2140 transmitted by the server 10 itself has not reached the client terminal 20, and the second is that of S2190 transmitted from the client terminal 20. It is speculated that the message will not arrive.

  In the first case, as in the former of the two cases, the previous communication time update (S2170) on the client terminal 20 side is regarded as attempted, and the server 10 itself also refrains from updating the previous communication time (S2230). Should. However, in the second case, the update of the previous communication time (S2170) by the client terminal 20 has ended, but in order for the server 10 to synchronize with this, the server 10 needs to perform the operation of S2230. However, since the server 10 in this case does not know the update state of the client terminal 20, the previous communication time cannot be updated (S2230). Therefore, in the second case, the normal process cannot be solved, and for example, it is necessary to handle and deal with an abnormal system such as knowing whether the client terminal 20 has updated the previous communication time by some method.

(The last communication time in the first authentication)
4 is normally executed, the authentication of the client terminal 20 by the server 10 is completed, and a predetermined service is provided from the server 10 to the client terminal 20 (S2260). When the client terminal 20 wants to provide the service again after the service session ends, the steps described above may be repeated. However, in the above description, it is assumed that the previous communication time at the time of authentication is shared between the server 10 and the client terminal 20 side. Therefore, in the case of the first communication between the two, that is, in the case of authentication (initial authentication) in the state where the previous communication time does not exist, there remains a problem of how to set the previous communication time that does not exist. Yes. This is described below.

(Countermeasure 1 for initial authentication)
The simplest method is to treat the identification ID and password in the same way. That is, as described above, the identification ID and password are negotiated between the service provider and the user (client) before the authentication process. In accordance with this, when the service provider distributes the identification ID to the client, the first previous communication time is also distributed and set in the client terminal 20, or when the client declares the password to the service provider. Another example is a method of reporting the initial previous communication time at the same time. By adopting such a method, the previous communication time used only at the time of the first authentication can be shared (synchronized) between the server 10 and the client terminal 20, so the second time even in the first authentication. It is possible to execute the authentication work in the same steps as the authentication.

(Countermeasure 2 for initial authentication)
On the other hand, the countermeasure 1 described above is also the opposite of the countermeasure. In this case, the previous communication time is not delivered. In this case, both the server 10 and the client terminal 20 are set so as to recognize that the initial authentication is based on the absence of the previous communication time, and using this, a special initial process is set for the initial authentication.

  The outline is shown in FIG. The main point is to replace the role of the previous communication time, which is lacking in the initial authentication process, with a password. The difference between the two is the following two points. First, steps S2030 and S2130 (both steps surrounded by a broken line) relating to the previous communication time existing in FIG. 4 are not shown in FIG. 7, and the second is the previous time used as a common key in FIG. Instead of the communication time, a password is used in FIG. Except for the above two points, all the drawings are the same. FIG. 7 was created using FIG. 4 as a template. The same description as FIG. 2 is attached | subjected to FIG. 7 about the part which is common in both figures, and the different description was described about the different part. Hereinafter, the initial authentication process will be described with an emphasis on the difference from the process of FIG. 7 (second and subsequent authentication processes).

  In FIG. 7, the previous communication time is not extracted (S5030) because the previous communication time does not exist (cannot be performed). Next, the client terminal 20 generates encrypted data by encrypting the password and the current communication time using the password as a common key (S5050). There is no previous communication time. Then, this encrypted data is transmitted to the server 10 (S5060), but naturally there is no previous communication time in this. Receiving this, the server 10 recognizes that there is no previous communication time data related to the identification ID, for example, by searching the authentication history table 121b (FIG. 5) and not having a hit record. In this case, the server 10 performs decryption by switching the decryption key to the password instead of the previous communication time (S5100). In the authentication check, the comparison of the previous communication time (S5130) is not performed (cannot be performed). Thereafter, the same steps as those shown in FIG. 4 may be executed. The current communication time synchronized between the server 10 and the client terminal 20 by this initial authentication becomes the previous communication time of the second authentication process.

  The above is the basic form of the implementation content proposed by the present invention including the initial authentication. Next, we will describe an application form that adapts this basic form to trends in the ICT environment.

(Applicable to terminal-independent service provision)
With the rapid spread of mobile terminals that are linked to the development of a communication infrastructure aimed at the ubiquitous society, a client terminal used by a client is not limited to one. The same client is required to connect to a network "anytime and anywhere" using a client terminal (for example, a tablet terminal or a smartphone) other than the above and receive a service using the same identification ID and the same password. In view of such a situation, according to the previously proposed communication system, the previous communication time in the client terminal 20 is the previous communication time stored in its own internal storage area (except for the initial authentication). The client did not need to be aware of it directly and could not. That is, in the previously proposed communication system, the identification of the client is the identification of the client terminal 20 itself, and does not necessarily identify the individual client. However, a client can receive a service from a client terminal (for example, a smartphone) carried on the go using the same identification ID or password assigned to a client terminal (for example, a personal computer) used in the workplace, for example. On the contrary, it is preferable that it can be used on a client terminal (for example, a personal computer) when returning to work. This is also within the range of the present invention. This point will be described in detail in the following section.

(Providing services to multiple client terminals)
In order to realize this, in the present embodiment, the client terminal 20 is provided with the following two functions. The functions are (1) a time extraction function for extracting the previous communication time to the outside, and (2) a time input function for inputting the previous communication time from the outside. By providing these functions, if the example described in the previous section is re-displayed, in addition to the user identification ID and password, the previous communication time taken out by the client from the work computer can be input to the smartphone used on the go. Thus, the same service (for example, mail delivery service) as that received at the workplace can be received through the same authentication as the authentication of the personal computer. In other words, the previous communication time can be made portable. For example, the time extraction function allows the client to recognize the previous communication time with the server providing the target service by, for example, displaying it on the display screen of the client terminal, etc. It refers to the function to make. Although it is not impossible to retrieve the previous communication time by email transmission (including communication time input), in order to minimize the risk of encountering impersonation, the confidential information inside the client terminal is put on the network in plain text form. Exposing should be avoided as much as possible. The time input function refers to a function for inputting the previous communication time recognized by the client to a client terminal for receiving a service using, for example, a keyboard or a mouse and storing the same in the storage device.

  This will be described in more detail with reference to FIG. Here, a client terminal (personal computer 200A) that is always used as a main machine and a client terminal (personal computer 200B) that are installed in a different place and are sometimes used are assumed. When using the personal computer 200A, the client X performs authentication by simply inputting the identification ID and password when attempting to use a certain service. Note that. The personal computer 200B has the same hardware and software functions as the personal computer 200A except that it does not store the previous communication time.

  Here, the client X that needs to use the service from the personal computer 200B takes out the previous communication time from the personal computer 200A using the time retrieval function (displays it on the display screen), and visually grasps this. (FIG. 8 (1) (2)). The client X makes a note of the taken out previous communication time on, for example, paper, and operates the personal computer 200B.

  More specifically, the client inputs and stores the previous communication time taken from the client terminal 200B into the personal computer 200B using the time input function (here, from the keyboard) (FIG. 8 (3)). As a result, the client X can use the service on the personal computer 200B using the identification ID and password used in the personal computer 200A (the conventional basic authentication can be used). If the authentication succeeds even once in the personal computer 200B, the previous communication time related to the authentication is automatically updated in the personal computer 200B, so that the previous communication time in the personal computer 200A is no longer valid authentication target. Cannot be. Therefore, service provision is not permitted even if it is obtained from the personal computer 200A as it is. Here, when the client X wants to use the service again with the personal computer 200A, the same operation as the “pushing” operation from the personal computer 200A to the personal computer 200B may be performed from the personal computer 200B to the personal computer 200A. As described above, the client X can authenticate and receive services from any client terminal having the hardware and software functions according to the present invention. Note that the time extraction function and the time input function described above form the basis of client authentication, and thus those that can use this function need to be limited to authorized users. For this reason, this function must be restricted to those that can correctly input a password (identification ID and password).

(Add-on effect on existing authentication system)
Currently, a method of using an identification ID and a password (only) in authentication is generally and widely adopted. However, there are the following two problems pointed out regarding this method. First, as a system design problem of the service provider, at least, first, the type of encryption of data passing over the line is limited (public key cryptography, etc.) As mentioned in the background section above, in order to enhance information security, passwords are frequently changed and their contents cannot be easily guessed by others, generally long and complicated. It's recommended that you set it, but there are times when clients can't keep up.

  Considering the client's position that things that cannot be inferred by others are more or less difficult for the client to understand, and that multiple passwords must be managed, there is a good point about the latter. There is clearly a situation that cannot be solved by shouting alone. With respect to these problems, the present communication time and the previous communication time in the authentication method proposed by the present invention can be added to and added to an authentication element used in an existing authentication system to achieve a considerable effect. In addition, when the client terminal is fixed to one unit, the modification of the existing authentication system does not give the client a load corresponding to the change in operation and usability, and the reverse side of the conventional use, It has the advantage that security is automatically strengthened inside the system.

(Effects specific to this embodiment)
It is possible to adopt a strong encryption method as the authentication system designer desires, and to take strong preventive measures against leakage of authentication information. In particular, the problem of key delivery, which is an important issue of the common key cryptosystem, is cleared by using the previous communication time that is changed in each authentication and shared in the previous authentication as a common key. That is, the key is already transferred one time before the data encrypted with the key is transferred. This also ensures the strength of information concealment in that an encryption key is used that changes with each authentication, compared to a fixed one such as a password.

  In the unlikely event that "spoofing" occurs, the fact is discovered in the form of the inability to use regular users. In addition to “spoofing” by a malicious third party, even if the client himself deliberately “rents” the identification ID and password to a third party, the valuable resources of the service provider are one user per service. Protection is possible by principle.

  Compared to an authentication system using an identification ID and a password that is generally used at present, the present communication time and the previous communication time proposed by the present invention can be made stronger by adding authentication conditions. In addition, if necessary, the client can reinforce the communication system (communication method) without being aware of it at all (without changing the usability of the client). Since the use of mobile terminals is becoming mainstream, service provision is not fixed to one terminal, and a request to enjoy services across terminals becomes inevitable (becoming). In addition, the trend is to avoid the important data stored on the terminal more and more, the data is centrally managed by the server, etc., and it is expected that the terminal will be positioned as a device that only accesses it. . Therefore, the role of user authentication is expected to become increasingly important. These can also be dealt with by the method of adding the previous communication time to the identification ID and password as a client-portable (movable with the client) authentication element as an application example of the present invention.

DESCRIPTION OF SYMBOLS 1 Communication system 10 Server 15 Recording medium 20 Client terminal 25 Recording medium 30 NTP server 50 Internet (communication line, network)
100, 200 CPU
101 Encryption Device 103 Determination Device 105 Service Permission Device 110, 210 RAM
120, 220 Storage device 121a Client account table 121b Authentication history table 130, 230 Operation device 140, 240 Display device 150, 250 Communication device 160, 260 Real time clock

Claims (10)

In a data communication system including a server that transmits data and a client terminal that receives data transmitted by the server via a network,
The client terminal
Storage means for storing the previous identification code transmitted in the previous communication to the server for each communication;
Encryption means for encrypting at least including the current identification code different from the previous identification code and the previous identification code, using the previous identification code extracted from the storage means as an encryption key;
Transmission means for transmitting the encrypted data encrypted by the encryption means to the server,
The server
Receiving means for receiving encrypted data transmitted from the client terminal;
Storage means for storing the current identification code transmitted from the client terminal as a previous identification code at a predetermined timing for each communication;
And a decryption unit that decrypts the encrypted data received by the reception unit using the previous identification code associated with the client terminal extracted from the storage unit as a decryption key. system. The current identification code is a current communication time indicating a current communication time between the client terminal and the server,
The data communication system according to claim 1, wherein the previous identification code is a previous communication time indicating a communication time communicated immediately before the current communication time between the client terminal and the server. In a data communication system including a server that transmits data and a client terminal that receives data transmitted by the server via a network,
The client terminal
Storage means for storing the previous communication time with the server for each communication;
Encryption means for encrypting at least the current communication time and the previous communication time with the previous communication time taken out from the storage means as an encryption key;
Transmission means for transmitting the encrypted data encrypted by the encryption means to the server,
The server
Receiving means for receiving encrypted data transmitted from the client terminal;
Storage means for storing the current communication time transmitted from the client terminal as a previous communication time at a predetermined timing for each communication;
And decrypting means for decrypting the encrypted data received by the receiving means using the previous communication time before the update relating to the client terminal extracted from the storage means as a decryption key. Data communication system. The server further includes:
Determining whether authentication is possible by comparing the current communication time and the previous communication time decrypted by the decryption means with the current communication time and the previous communication time relating to the client terminal extracted from the storage means With means,
The determination means is configured to determine that authentication is possible only when both current communication times are within a predetermined range and both previous communication times are completely matched. The data communication system according to claim 3. Storage means for updating and storing the previous communication time with the server for each communication;
Encryption means for encrypting at least the current communication time and the previous communication time with the previous communication time taken out from the storage means as an encryption key;
A client terminal for a data communication system, comprising: a transmission unit configured to transmit the encrypted data encrypted by the encryption unit to the server. Receiving means for receiving the encrypted data transmitted from the client terminal;
Storage means for storing the current communication time transmitted from the client terminal as the previous communication time at a predetermined timing for the communication degree;
A data communication device comprising: decryption means for decrypting the encrypted data received by the reception means using the previous communication time of the client terminal extracted from the storage means as a decryption key. Server for the system. In a data communication method of a data communication system including a server that transmits data and a client terminal that receives data transmitted by the server via a network,
The client terminal encrypts at least the current communication time and the previous communication time with the previous communication time with the server extracted from the storage means as an encryption key, and transmits the encrypted data to the server. A sending step to send;
A decryption step in which the server receives the encrypted data transmitted from the client terminal, and decrypts the previous communication time related to the client terminal extracted from the storage unit as a decryption key;
And a storage step of storing the current communication time transmitted from the client terminal as a previous communication time in a storage unit at a predetermined timing for communication degree. The server further comprises:
The decrypted current communication time and previous communication time are compared with the current communication time and the previous communication time of the client terminal taken out from the storage means, and both the current communication times are within a predetermined range. 8. The data communication method according to claim 7, wherein a determination step of determining that the comparison result is coincident is performed on the assumption that the two previous communication times coincide completely. A data communication program for causing a computer to function as a server that transmits data received by a client terminal via a network, the computer comprising:
Receiving means for receiving encrypted data transmitted from the client terminal;
Storage means for storing the current identification code transmitted from the client terminal as a previous identification code at a predetermined timing for each communication;
The encrypted data received by the receiving means is made to function as a decrypting means for decrypting the previous identification code relating to the client terminal extracted from the storage means with a decryption key,
A decryption step of receiving the encrypted data transmitted from the client terminal and decrypting the previous communication time related to the client terminal extracted from the storage unit as a decryption key;
A storage step of storing the current communication time transmitted from the client terminal in a storage unit as a previous communication time at a predetermined timing for the communication degree. A data communication program for causing a computer to function as a client terminal that receives data transmitted by a server via a network, the computer comprising:
Storage means for storing the previous identification code transmitted in the previous communication to the server for each communication;
Encryption means for encrypting at least including the current identification code different from the previous identification code and the previous identification code, using the previous identification code extracted from the storage means as an encryption key;
Function as transmission means for transmitting the encrypted data encrypted by the encryption means to the server,
A transmission step of encrypting at least the current communication time and the previous communication time with the previous communication time with the server extracted from the storage means as an encryption key and transmitting the encrypted encrypted data to the server When,
A decryption step in which the server receives the encrypted data transmitted from the client terminal, and decrypts the previous communication time related to the client terminal extracted from the storage unit as a decryption key;
A storage step of storing the current communication time transmitted from the client terminal in a storage unit as a previous communication time at a predetermined timing for the communication degree.