JP2006174519A - Method and apparatus for security - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and surely protect contents of conversations in an electronic conference room. <P>SOLUTION: The present invention may be used together with a chat system or the like. A command interpretation unit 3 specifies a channel name CHi, time Ti and private key Si under participation in a predetermined timing, notifies a common key generation unit 5 of them and instructs the generation of a common key CSi. The common key generation unit 5 generates the common key from CHi, Ti and Si and stores it in a common key storage unit 6. The common key generation unit 5 associates generated common keys with timing information indicating their generation timings and stores them. An encryption/decryption unit 8 encrypts inputted conversation data using a latest common key and sends them out to a communication device together with the timing information of the common key. Conversation data are received from another user terminal via the communication device and decrypts them using the common key. The common key to be used for decryption is acquired from the common key storage unit 6 based according to timing information transmitted together with the conversation data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a technology for improving the security of conversation in an electronic conference room. More particularly, the present invention relates to a technology for improving the security of communication contents when a plurality of users communicate by sharing the same electronic conference room, such as a chat system and an e-mail mailing list.
Here, the chat system is a system in which a plurality of user terminals can talk simultaneously while sharing the same space, that is, a channel. A mailing list is a system in which the same content can be distributed to a plurality of users by sending an e-mail to an address of a list in which a plurality of users are registered.

  In recent years, with the spread of personal computer communication and the Internet, communication between a plurality of users on a network has become active. Among them, not only asynchronous communication such as conventional electronic bulletin boards and mailing lists, but also the use of chat systems capable of real-time communication, that is, conversation, is increasing. In such a communication system, a plurality of users share the same virtual space, and this virtual space, that is, a channel is set as a conference room, and browsing and speaking are limited to users entering the conference room. Is common.

  Electronic conference rooms that are logically held on a communication server include the mailing list and chat system channel. These limit the sending and receiving of conversation texts only among multiple users entering the electronic conference room, and want to keep conversations made in the electronic conference room confidential to users outside the conference room. . In the case of one-to-one communication such as e-mail, encrypted communication using a public key cryptosystem can be performed. However, in an electronic conference room where multiple users participate, in order to encrypt / decrypt conversations exchanged by public key cryptography, it is necessary to encrypt each person with a separate public key and distribute the data. There is. Therefore, a large burden is placed on the server that distributes data to each user terminal.

  In order to avoid a burden on the server, it is necessary to share an encryption key (common key) between clients by some means. If an arbitrary server manages this shared key and distributes it to clients, the shared key must be encrypted and distributed, which complicates processing. However, in a method in which a fixed secret key is simply built in the user terminal and used as a shared key, the key may be easily deciphered.

  In an electronic conference room system in which a plurality of users share an electronic conference room at the same time and perform communication, it is possible to save the trouble of distributing an encryption key on a communication path and make it difficult to decrypt the key. The object is to efficiently and safely perform encryption / decryption of data transmitted and received between users.

In order to solve the above-described problem, the present invention 1 provides a security method executed by a user terminal connected to a communication system in which a plurality of user terminals share the same electronic conference room and perform communication. This method includes the following steps.
-A time interval for generating a secret key is set in advance, and whenever the set time interval elapses, time information at that time is acquired from the user terminal, and a secret key is generated based on the acquired time information. Secret key generation step,
A secret key storage step of storing time information and the secret key generated in the secret key generation step based on the time information in association with each other;
When a change in the electronic conference room is detected, one of the secret keys stored in the secret key storage step is specified based on the time when the change is detected, and based on the specified secret key A public key generation step for generating a public key
A public key storage step for storing the public key generated in the public key generation step and the public key identification information for specifying the public key in association with each other;
When the conversation data is transmitted, the conversation data is encrypted by using the latest public key stored in the public key storage step and the public key identification information, and the encrypted conversation. An encryption processing step of transmitting the public key identification information together with data;
When the public key identification information is received together with the conversation data, one of the public keys stored in the public key storage step is specified based on the received public key identification information, and received with the specified public key A decryption processing step for decrypting the conversation data.

  In this method, the change in the electronic conference room is a change in the password for joining the electronic conference room, a change in the user sharing the electronic conference room, an instruction to change the common key, a statement in the user terminal, a file This is the case when a transfer instruction or the like occurs. Taking the case where the present invention is applied to a chat system as an example, when a command “JOIN” or “PART” for changing a user participating in a channel is acquired from a chat client, a public key is generated. For example, by generating a public key at the timing when the user withdraws from the channel and encrypting the conversation data using this public key, the withdrawn user cannot illegally eavesdrop on the conversation contents.

The present invention 2 provides a security device mounted on a user terminal connected to a communication system in which a plurality of user terminals share the same electronic conference room and perform communication. This apparatus has the following configuration requirements.
-A time interval for generating a secret key is set in advance, and whenever the set time interval elapses, time information at that time is acquired from the user terminal, and a secret key is generated based on the acquired time information. Secret key generator,
A secret key storage unit that stores time information and a secret key generated by the secret key generation unit based on the time information in association with each other;
When a change in the electronic conference room is detected, one of the secret keys stored in the secret key storage unit is specified based on the time when the change is detected, and based on the specified secret key A public key generation unit for generating a public key
A public key storage unit that stores the public key generated by the public key generation unit and public key identification information for specifying the public key in association with each other;
When transmitting conversation data, out of the public keys stored in the public key storage unit, the latest stored public key and public key identification information are read from the public key storage unit to encrypt the conversation data An encryption processing unit for transmitting the public key identification information together with the encrypted conversation data,
When the public key identification information is received together with the conversation data, one of the public keys stored in the public key storage unit is specified based on the received public key identification information, and is received with the specified public key A decoding processing unit for decoding the conversation data.

The same effects as those of the first aspect of the present invention are achieved.
The present invention 3 provides a computer-readable recording medium in which a security program executed by a user terminal connected to a communication system in which a plurality of user terminals share the same electronic conference room and perform communication is recorded. To do. The security program recorded on this recording medium executes the following steps.
-A time interval for generating a secret key is set in advance, and whenever the set time interval elapses, time information at that time is acquired from the user terminal, and a secret key is generated based on the acquired time information. Secret key generation step,
A secret key storage step of storing time information and the secret key generated in the secret key generation step based on the time information in association with each other;
When a change in the electronic conference room is detected, one of the secret keys stored in the secret key storage step is specified based on the time when the change is detected, and based on the specified secret key A public key generation step for generating a public key
A public key storage step for storing the public key generated in the public key generation step and the public key identification information for specifying the public key in association with each other;
When the conversation data is transmitted, the conversation data is encrypted by using the latest public key stored in the public key storage step and the public key identification information, and the encrypted conversation. An encryption processing step of transmitting the public key identification information together with data;
When the public key identification information is received together with the conversation data, one of the public keys stored in the public key storage step is specified based on the received public key identification information, and received with the specified public key A decryption processing step for decrypting the conversation data.

The same effects as those of the first aspect of the present invention are achieved.
In addition to the first to third aspects of the present invention, as another aspect of the present invention, a security method used in a communication system in which a plurality of user terminals share the same electronic conference room and perform communication is also conceivable. The method can include the following steps.
A: Each user terminal has a common key based on the name of the electronic conference room that identifies the electronic conference room that is communicating with each other at a timing common to each user terminal, the time when the timing occurs, and the secret key. Generated on the terminal,
B: The generated common key and the timing information indicating the timing at which the common key is generated are associated with each other and accumulated in each user terminal,
C: Sending the communication content encrypted using any of the generated common keys to the communication system together with the timing information of the common key used for encryption,
D: Obtain encrypted communication content and timing information transmitted from another user terminal from the communication system, identify one of the common keys based on the timing information, and decrypt the communication content To do.

The common timing is, for example, 0 minute per hour at an hour interval when the date changes. This is because each user terminal participating in the electronic conference room generates a common key at a common timing. The electronic conference room name is identification information for specifying the electronic conference room, and is, for example, a channel name in the case of a chat system and an address in the case of a mailing list.
A common key is generated at a common timing in each user terminal, and the generation timing and the common key are stored in correspondence with each other. When the communication content is encrypted, the generation timing of the common key used for encryption is transmitted together with the encrypted data. The receiving side knows which common key should be used for decryption from the generation timing of the common key. Even when there is a time difference between the user terminals, the common keys used for encryption and decryption can be matched.

  Another aspect of the present invention is a security device used in a communication device in which a plurality of user terminals share the same electronic conference room and perform communication, and includes a storage unit, an instruction unit, a generation unit, A security device including an encryption unit and a decryption unit can be provided. The storage means stores at least one secret key. The instructing means specifies the name of the electronic conference room shared by the communication device, the time, and the secret key at a timing common to the plurality of user terminals, and instructs generation of a common key. The generation unit generates a common key based on the specified electronic conference room name, time, and secret key, and stores the generated common key and timing information indicating the common timing in association with each other in the storage unit.

  The encryption means acquires communication contents to be transmitted from the communication device, encrypts the communication contents using the latest common key, and includes the timing information of the used common key and the encrypted communication contents. A communication message is sent to the communication device. The decrypting means acquires the communication message transmitted from the other user terminal from the communication device, extracts the timing information from the acquired communication message, and extracts a common key from the storage means based on the timing information. And the encrypted communication content is decrypted.

  The instruction means specifies the participating electronic conference room name CHi, time Ti, and secret key Si at a predetermined timing, notifies the generation means to instruct generation of the common key CSi. The generation unit generates a common key based on the electronic conference room name CHi, the time Ti, and the secret key Si, and stores the common key in the storage unit. Further, the generating means stores each common key generated according to a change that occurs one after another and timing information indicating generation timing in association with each other.

  The encryption means encrypts the conversation content input at the user terminal using the latest common key, and sends a communication message including the common key timing information and the encrypted conversation data via the communication device. To do. The decrypting means receives a communication message from another user terminal via the communication device, and decrypts the conversation data with the common key. The common key used for decryption is acquired from the storage means based on the timing information included in the communication message.

  For example, consider a case where a common key is generated at 0 minutes every hour. The conversation data uttered at 11:59 on the user terminal A is encrypted with the common key CS11a generated on the user terminal A at 11:00. The decrypting means describes the encrypted conversation data and the timing information indicating the generation time of the common key used for encryption in the communication message, and sends them to the communication device. In the user terminal B that receives this communication message, if the time is already 12:01, the latest common key in the user terminal B is the common key CS12b generated at 12:00. However, the decryption means of the user terminal B knows from the timing information included in the communication message that the common key used for encryption was generated at 11:00. Therefore, the decryption means obtains the previous common key CS11b from the storage means and decrypts the conversation data. By generating a common key at a common timing in each user terminal, it becomes unnecessary to distribute the encryption key on the communication path. Moreover, it is difficult to decrypt the common key by updating the shared key with time. By storing the generation timing of the common key together with the common key, it is possible to prevent the common key from being shifted due to the time difference between the user terminals.

In the security device according to another aspect, the instructing unit detects the change in the electronic meeting room and sets the common timing, specifies the electronic meeting room name, the time when the change occurred, and the secret key, and generates the information. A means may be notified to instruct generation of a common key.
Changes in the electronic conference room include changes in passwords for participation in the electronic conference room, changes in users sharing the electronic conference room, instructions for changing the common key, statements on the user terminal, instructions for transferring files, etc. Say when happens.

In the security device according to another aspect, the storage unit stores a plurality of secret keys in association with time, and the instruction unit stores any one of the secret keys based on the time at which the common timing occurs. May be specified.
For example, when the instruction means instructs generation of the common key CSi (i = 00 to 23) at 0 minutes per hour, 24 secret keys Sj (j = 00 to 23) are prepared for each hour. The instructing means uses the secret key Sj (i = j) for generating the common key CSi. When a change in the electronic conference room occurs at, for example, 13:46, the instruction unit acquires the secret key Sj (j = 13) from the storage unit.

In the security device according to another aspect, the storage unit may store a secret key generation unit instead of the secret key.
Specifically, the secret key generating means is a secret key generating program. Avoiding the incorporation of the secret key itself, making it difficult for the secret key to be deciphered and thus making the common key difficult to decipher.
In the security device according to another aspect, the time at which the common timing occurs may be used as the timing information indicating the common timing.

Usually, since a clock is built in the user terminal, the time when the common timing occurs is obtained from the internal clock, and the time is stored in association with the common key. Even when there is a time difference between internal clocks between user terminals, it becomes easy to associate mutual common keys.
In the security device according to another aspect, the encryption unit may receive an instruction for encryption by a user and encrypt the communication content based on the instruction.

For example, the encryption unit displays a command button for designating on / off of encryption on the screen, and performs encryption according to the command button. The user can perform encryption and decryption according to the communication partner and conversation contents.
In the security device according to another aspect, the encryption unit may send the communication message further including a flag for identifying that the communication content is encrypted to the communication device. Furthermore, the decoding means can perform decoding according to a flag of a communication message acquired from the communication device. The encrypted communication content can be automatically decrypted and displayed.

  In the security device according to another aspect, the encryption unit may send the communication message further including a flag for identifying that the communication content is encrypted to the communication device. Furthermore, the decryption means can output a mark visually indicating whether or not the communication content is encrypted according to the flag of the communication message transmitted from the other user terminal.

The decrypting means displays a key mark or the like at the beginning of the channel name or conversation character string to indicate whether or not the received communication content is encrypted. The user can visually determine whether or not it is encrypted.
In the security device according to another aspect, the instruction unit acquires a password for joining the electronic conference room from the communication device, and further notifies the password in addition to the electronic conference room name, time, and secret key. The generation unit may generate a common key based on the notified electronic conference room name, time, secret key, and password.

For example, in a chat system, a password for entering a channel may be set. By using this password as one of the variables of the common key, it is possible to make the decryption of the common key more difficult.
In the security device according to another aspect, the common timing may be a timing at which a date is changed in the user terminal.

The instructing means obtains the time every minute from the clock in the user terminal, and instructs the generation of the common key when the time reaches 00:00. Even if there is no change in the electronic conference room and no action is taken by the user, the common key can be automatically updated.
In the security device according to another aspect, the common timing may be a timing that occurs every predetermined time interval.

For example, a common key is automatically generated at predetermined time intervals such as every hour. It has the same effect as the security device of another aspect described above.
In the security device according to another aspect, the common timing may be a timing at which a change occurs in a configuration of user terminals that share the electronic conference room.
Taking the chat system as an example, the instruction means instructs generation of a common key when a command “JOIN” or “PART” for changing a user participating in the channel is acquired from the chat client. For example, by updating the common key at the time of withdrawal, the withdrawn user cannot illegally eavesdrop on the conversation contents.

In the security device according to another aspect, when a password is set in the electronic conference room, the common timing may be a timing when the password set in the electronic conference room is changed.
Taking the chat system as an example, when the command means “MODE #CH + k” for changing the password is obtained from the chat client, the instruction means instructs generation of a common key. By changing the common key in response to the password being changed, it is possible to make it more difficult for a third party to eavesdrop.

In the security device according to another aspect, the common timing may be a timing at which a change of a common key is instructed.
Taking the chat system as an example, a command that can be used only by the chat server administrator to change the common key is prepared. When the command is acquired from the chat client, the command means instructs to generate a common key. The common key can be changed at any timing desired by the administrator, and the security of the conversation content can be further enhanced.

In the security device according to another aspect, the generation unit receives a setting of the maximum number of common keys stored in the storage unit, and after storing the common keys up to the maximum number, deletes the oldest common key and newly creates a new one. The generated common key can be stored.
By making it possible to set the maximum number of stored common keys, the resources of the user terminal can be used effectively.

Another aspect of the present invention is a computer-readable recording medium on which a security program is recorded, which is used in a communication apparatus in which a plurality of user terminals share the same electronic conference room and perform communication. A computer-readable recording medium on which a security program for executing the E stage is recorded is provided.
A; accumulating at least one secret key;
B: Specifying the name and time of the electronic conference room shared by the communication device at a timing common to the plurality of user terminals, the secret key, and instructing the generation of a common key;
C; generating a common key based on the specified electronic conference room name, time and secret key, and storing the generated common key in association with timing information indicating the common timing in the storage unit;
D: Obtaining communication contents to be transmitted from the communication device, encrypting the communication contents using the latest common key, and including a communication message including the timing information of the used common key and the encrypted communication contents Sending to the communication device;
E; acquiring the communication message from the communication device, extracting the timing information from the acquired communication message, specifying a common key from the storage unit based on the timing information, and decrypting the encrypted communication content Stage.

Another aspect of the present invention provides a security system comprising a plurality of user terminals that communicate by sharing the same electronic conference room, and a server that distributes the communication to the user terminals. The user terminal of this security system includes storage means, instruction means, generation means, encryption means, and decryption means.
The storage means stores at least one secret key. The instructing means specifies the name of the electronic conference room shared by the communication device, the time, and the secret key at a timing common to the plurality of user terminals, and instructs generation of a common key. The generation unit generates a common key based on the specified electronic conference room name, time, and secret key, and stores the generated common key and timing information indicating the common timing in association with each other in the storage unit.

  The encryption means acquires communication contents to be transmitted from the communication device, encrypts the communication contents using the latest common key, and includes the timing information of the used common key and the encrypted communication contents. A communication message is sent to the communication device. The decrypting means acquires the communication message transmitted from the other user terminal from the communication device, extracts the timing information from the acquired communication message, and extracts a common key from the storage means based on the timing information. And the encrypted communication content is decrypted.

  It has the same effect as the security device of another aspect described above.

  If the present invention is used, a common key that changes with time in each user terminal is generated at a common timing in each terminal, so there is no need to distribute the key, and the possibility of decryption can be reduced. By notifying the generation timing of the common key together with the encrypted communication content, it is possible to decrypt with the common key used for encryption even if there is a time difference between the terminals.

Hereinafter, the security system of the present invention will be specifically described with reference to an embodiment.
<First embodiment>
As an example, a case where the conversation content in the chat system is encrypted / decrypted will be described as an example. The chat system is configured by connecting a chat server and a user terminal capable of operating a chat client via a communication network for transmitting and receiving data. Examples of the communication network include computer networks such as a LAN (Local Area Network) and the Internet. The server of the chat system manages channel users and managers and channels, and distributes conversation contents to each user terminal. In the example in the chat system, a channel name is used as the identifier of the electronic conference room. For example, in the case of an e-mail mailing list, a mailing list address, for example, a character string “foo@bar.com” is used.

FIG. 1 is an overall configuration diagram of a security system according to the first embodiment. As shown in FIG. 1, the security system is configured by providing a security device to each user terminal that configures the chat system.
[Security device]
FIG. 2 shows a functional configuration diagram of the security device provided in each user terminal. 2 includes a secret key storage unit 1, a secret key holding unit 2, a command interpretation unit 3, a time acquisition unit 4, a common key generation unit 5, a shared key storage unit 6, and an encryption / decryption unit 7. Have.

  The secret key storage unit 1 stores a plurality of secret keys Si in a memory inside the user terminal. FIG. 3 shows a conceptual diagram of the secret key table. The plurality of secret keys Si are preferably registered in the secret key table in association with, for example, time, and the secret key is preferably changed according to time. FIG. 3 shows an example in which a secret key for each hour is prepared in advance and the secret key is changed at 0 minutes every hour. For example, at the time from 00:00 to 00:59, the private key S0 with the index number “0” is valid. Further, a plurality of secret key generation programs may be stored in the secret key table in association with the index, and the secret key may be generated each time by specifying the index.

  The secret key holding unit 2 obtains an index using the time data Ti passed from the command interpretation unit 3 or the time acquisition unit 4, extracts the secret key Si from the secret key storage unit 1, and extracts the command interpretation unit 3 or the time acquisition unit 4. To pass. Taking FIG. 3 as an example, when time data Ti from 10: 0 to 10:59 is specified as an index, the secret key holding unit 2 searches the secret key table using the index number “10” as a key, and The secret key S10 to be acquired is acquired. As will be described later, when the common key is generated using the secret key Si, the index number is obtained from the time when the common key is generated, and the secret key to be used is acquired.

  The command interpreter 3 detects the occurrence of various triggers in the chat client, notifies the channel name CHi, the time data Ti and the secret key Si in which the trigger has occurred, and instructs the common key generator 5 to generate a common key. To do. When the password Pi is set for the channel CHi, the command interpretation unit 3 sends the password Pi together to the common key generation unit 5 and instructs generation of the common key. Specifically, the command interpretation unit 3 acquires the channel name from the chat client when some change relating to the channel, that is, a trigger occurs. If the password Pi is set for the channel, the password is also acquired. Further, the command interpretation unit 3 acquires the time data Ti when the trigger is generated from the time acquisition unit, passes the acquired time data Ti to the secret key holding unit 2, and acquires the secret key Si from the secret key holding unit 2. Below, the specific example of the trigger which the command interpretation part 3 detects from a chat client is given.

  (1) When the command interpreter 3 acquires message data from the chat client informing the change of the members participating in the channel or the change of the channel password, for example, the command interpreter 3 generates the common key in the common key generator 5. Instruct. FIG. 4 shows a conceptual structural diagram of message data D1 that the command interpreter 3 acquires from the chat client. As shown in FIG. 4, the message data D1 includes a header portion including a transmission source identifier and a transmission destination identifier, and a data portion. The source identifier is the IP address of the sender or server. The destination identifier is a channel name, an IP address of a specific user, or the like. In the data portion, data indicating a change in the channel is described.

For example, when the channel member changes, the data portion of the message data D1 includes commands “JOIN” and “PART” indicating the member change and the IP address of the user terminal that has changed. Has been. The command interpretation unit 3 issues an instruction to the common key generation unit 5 according to the command.
For example, when the password P1 of the channel name # CH1 changes to “newP1”, the command interpreter acquires message data D2 shown in FIG. 5 from the chat client. In the data part of the message data D2, a command indicating a password change, for example, “MODE # CH1 + k” and a new password “newP1” are described. The command interpretation unit 3 interprets the command and instructs the common key generation unit 5 to generate a common key.

  (2) When the command interpretation unit 3 acquires message data D3 instructing generation of a common key from the chat client, the command interpretation unit 3 instructs the common key generation unit 5 to generate a common key. FIG. 6 shows a conceptual structural diagram of the message data D3. The message data D3 is sent out by the channel manager, and after being confirmed by the server as to whether or not the message is from the manager, it is distributed from the server to each chat client. In this case, a command for instructing the generation of the common key is described in the data portion of the message data D3. For example, in accordance with the command “MODE #CHi + c”, the command interpretation unit 3 instructs the common key generation unit 5 to generate a common key. However, this command needs to be newly provided separately.

  (3) When the conversation data to be transmitted is acquired from the chat client, the command interpretation unit 3 instructs the common key generation unit 5 to generate a common key and encrypts / decrypts if the encryption is instructed. The conversation data is sent to the unit 7. The encryption instruction will be described later. If the encryption is not instructed, the command interpretation unit 3 does not give an instruction to the common key generation unit 5, but simply sends the conversation data to the encryption / decryption unit 7 to request creation of a communication message. .

  The time acquisition unit 4 acquires time data Ti at a predetermined timing, and acquires the secret key Si based on the acquired time data Ti. Further, the channel name CHi and the password Pi of the channel that are participating from the chat client are acquired and transmitted to the common key generation unit 5 together with the time data Ti and the secret key Si to instruct generation of the common key. First, the time acquisition unit 4 acquires time data Ti at a predetermined timing. Specifically, as a means for acquiring the time data Ti, a time data acquisition program routine that uses the internal clock of the user terminal may be used. Usually, this time data acquisition program routine is provided by an operating system operating on the information terminal. As the time data Ti, it is preferable to use GMT (total seconds since January 1, 1970) output by the time data acquisition program routine. The predetermined timing for acquiring the time data may be, for example, the time when the time data is acquired at an interval of 1 minute and the time becomes 0:00 am of the day, or the time of 0 minutes per hour. The time acquisition unit 4 sends the acquired time data Ti to the secret key holding unit 2 and acquires the secret key Si corresponding to the time data Ti.

  The common key generation unit 5 generates a common key CSi based on the acquired channel name CHi, secret key Si, time data Ti, and password Pi, if any, according to instructions from the command interpretation unit 3 and the time acquisition unit 4. . A common one-way function F may be used to generate the common key. Therefore, the common key CSi is obtained by CSi = F (secret key Si, channel name CHi, time data Ti). Specifically, MD5 (see Message Digest Algorithm: RFC1321) is used as a one-way function, and the output 128-bit hash value is set as a common key CSi.

  Further, the common key generation unit 5 stores the generated common key CSi in the common key storage unit 6 in association with the timing at which the common key is generated. FIG. 7 shows a conceptual diagram of a common key table stored in each common key storage unit 6 of the user terminals A and B. In FIG. 7, the version indicates the timing when the common key is generated. In the present embodiment, a common key is generated according to an instruction from the time acquisition unit 4 at 0 minutes every hour, and when the command interpretation unit 3 detects any trigger, a common key is generated according to the instruction of the command interpretation unit 3. The common key whose time is indicated as a version indicates that it is generated at that time in each user terminal. Further, the common key indicated by “ver1”, “ver2”, etc. indicates that it was generated by some kind of trigger. The common keys having the same version are generated at the same timing. The reason that the versions and the common keys are different in the user terminals A and B is that the internal clock between the terminals is shifted. By storing the version in association with the common key in each user terminal, it is possible to decrypt with the common key of the same version as the common key used for encryption.

Further, the common key generation unit 5 accepts the setting by the user of the maximum number of common keys Max stored in the common key table. The generated common key is added to the common key table until the maximum number Max is reached. In the common key table, when the maximum number of common keys is accumulated, the old common key is deleted one by one, and the latest common key is always accumulated.
The encryption / decryption unit 7 acquires the conversation data to be transmitted from the command interpretation unit 3, encrypts the conversation data using the latest stored shared key CSi, adds destination information, and message data D4. Create FIG. 8 shows a conceptual diagram of the message data D4. The message data D4 includes an encryption flag in addition to the header part and the data part. The encryption flag is a bit field indicating whether the conversation data is encrypted, and is 0: encryption off, 1: encryption on. In the data portion, the encrypted conversation data is described when the encryption flag is 1, and the unencrypted conversation data is described when the encryption flag is 0. The header portion of the message data D4 includes version information in addition to the transmission source identifier and the transmission destination identifier. One of the versions of the common key table is described in the version information, and the generation timing of the common key used for encryption is shown. By including the version of the common key used for encryption in the message data, it is possible to decrypt with the same version of the common key. The created message data D4 is sent to the chat client and transmitted to other user terminals via the server.

  The encryption / decryption unit 7 receives an instruction from the user as to whether or not to encrypt the conversation content. FIG. 9 shows an example of a screen on which an instruction button for instructing on / off of encryption is displayed. When instructing the encryption of the conversation character, clicking the instruction button with the mouse changes the color of the instruction button, and the encryption on mode is set. When the encryption / decryption unit 7 acquires conversation data in the encryption-on mode, the encryption flag of the communication message is set to 1, and the encrypted conversation data is written in the data part. When the mouse is clicked again, the color of the instruction button is restored to the encryption off mode.

  On the other hand, the encryption / decryption unit 7 obtains message data D4 created in another user terminal from the chat client and decrypts it. First, when the message data D4 is acquired, the encryption / decryption unit 7 refers to the encryption flag, and when the flag is 1, extracts the version information of the header part. The shared key CSi is extracted from the shared key storage unit 6 based on the extracted version, the conversation data part is extracted and decrypted with the shared key CSi. For example, it is assumed that message data encrypted with the common key of the version “ver1” is transmitted from the user terminal A when the common keys of the user terminals A and B are in the state shown in FIG. The user terminal B that has received the message data obtains a common key corresponding to the version information “ver1” of the message data from the common key table, and decrypts the conversation data. The decrypted conversation data is sent to the chat client and displayed on the screen. For the encryption / decryption, a program routine using a general encryption / decryption algorithm can be used. The common key CSi used for decryption refers to the version information in the message data D4, and uses the common key CSi extracted from the common key table using the version information as an index.

  Further, the encryption / decryption unit 7 can display whether or not the displayed conversation data is encrypted. FIG. 10 shows a screen example of the user terminal. In the screen example of FIG. 10, when the transmitted conversation data is encrypted, an icon indicating encryption is displayed next to the channel name. FIG. 11 shows another screen example of the user terminal. In the screen example of FIG. 11, when transmitted conversation data is encrypted, an icon indicating encryption is displayed at the head of the conversation sentence.

[Process flow]
(1) Common Key Generation Processing Next, common key generation processing using the security device will be described. FIG. 12 is a flowchart showing a common key generation process based on an instruction from the command interpretation unit 3. FIG. 13 is a flowchart showing a common key generation process according to an instruction from the time acquisition unit 4. The processes shown in FIGS. 12 and 13 are performed independently.

First, FIG. 12 will be described. For ease of explanation, a case where a change in channel members, a password change, and a common key change occur as triggers is shown as an example. The process of FIG. 12 is started when any trigger occurs.
In step S1, the command interpretation unit 3 determines whether or not the channel member has changed. Specifically, when the command interpretation unit 3 acquires message data D1 including the user participation command “JOIN” or the leaving command “PART” from the chat client, the command interpretation unit 3 determines that a change has occurred in the user and performs step S4 described later. Migrate to If it is any other command, the process proceeds to step S2.

  In step S2, the command interpretation unit 3 determines whether or not the password of the participating channel has changed. Specifically, when the command interpreter 3 obtains from the chat client message data D2 in which the password change command “MODE #channel name + k” and the new password are included in the data portion, it is assumed that the password has been changed. Determination is made and the process proceeds to step S4. In other cases, the process proceeds to step S3.

In step S3, the command interpretation unit 3 determines whether or not an instruction for changing the common key is given. Specifically, when the command interpreter 3 obtains from the chat client message data D3 including a command for changing the common key in the data part, the command interpreter 3 determines that a new common key is to be generated, and proceeds to step S4. Transition. In other cases, the process ends.
If the command interpretation unit 3 determines that any of the triggers has occurred, the command interpretation unit 3 proceeds to the process of step S4. In step S4, the command interpretation unit 3 acquires the channel name and password Pi where the trigger has occurred from the chat client. Now, let the channel name be CHi.

In step S5, the command interpretation unit 3 acquires the time when the trigger occurred from the time acquisition unit, and sets the acquired time as time data Ti.
In step S <b> 6, the command interpretation unit 3 passes the acquired time data Ti to the secret key holding unit 2. The secret key holding unit 2 obtains the index number from the time data Ti, searches the secret key table to acquire the secret key Si, and sends it to the command interpreting unit 3.

In step S7, the command interpretation unit 3 sends the channel name #CHi, password Pi, time data Ti, and secret key Si to the common key generation unit 5 and instructs generation of the common key.
In step S8, the common key generation unit 5 generates a common key CSi using a one-way function, and stores it in the common key table in association with the version.
Next, a case where a common key is generated by an instruction from the time acquisition unit 4 will be described with reference to FIG. For ease of explanation, a case where a common key is generated at 0 minutes per hour is taken as an example, but the processing is the same at other time intervals.

In steps S11 to S12, the time acquisition unit 4 acquires time data from the time data acquisition program routine, for example, every minute.
In step S13, it is determined whether or not the acquired time data is 0 minutes per hour. If it is 0 minutes, the process proceeds to step S14. If it is not 0 minutes, steps S11 to S12 are repeated.
In step S14, the time acquisition unit 4 sets the acquired latest time data as time data Ti.

In step S15, the acquired time data Ti is sent to the secret key acquisition unit, and the secret key Si is acquired via the secret key acquisition unit.
In step S16, the time acquisition unit 4 acquires the channel name CHi currently participating and the password Pi of the channel from the chat client.
In step S17, the acquired time data Ti, channel name CHi, password Pi, and secret key Si are notified to the common key generation unit 5 to instruct generation of the common key. Then, it returns to step S11 again and repeats the said process.

(2) Encryption / Decryption Processing Next, the flow of processing for encrypting / decrypting a conversation in the chat system using the security device will be described. FIG. 14 is a flowchart showing the flow of encryption processing performed by the security device. FIG. 15 is a flowchart showing a flow of decryption processing performed by the security device. First, the encryption process of FIG. 14 will be described. The process is started when the encryption / decryption unit 7 acquires the conversation data input in the chat client.

In step S21, the encryption / decryption unit 7 determines whether or not the encryption is on, and if it is on, the process proceeds to step S22. If it is off, there is no need to encrypt the conversation data, so the process proceeds to step S25 described later.
In step S <b> 22, the encryption / decryption unit 7 acquires the time data Ti when the conversation is made from the time acquisition unit 4.

In step S23, the encryption / decryption unit 7 acquires the latest common key CSi from the common key table. The encryption / decryption unit 7 also acquires information indicating the latest version of the common key CSi, that is, information indicating the timing at which the common key is generated, from the common key table.
In step S24, the encryption / decryption unit 7 encrypts the conversation data using the acquired common key CSi.

  In step S25, the encryption / decryption unit 7 creates message data D4 including a header part, an encryption flag, and a data part. If it is determined in step S21 that the encryption mode is on, the encryption / decryption unit 7 sets the encryption flag to 1, and creates message data D4 describing the encrypted conversation data in the data part. If it is determined in step S21 that the mode is the encryption off mode, the encryption / decryption unit 7 sets the encryption flag to 0, and creates message data D4 in which the unencrypted conversation data is described in the data unit.

In step S26, the message data D4 created in step S25 is sent to the chat client. The sent message data D4 is distributed to other user terminals by the server, and is decrypted as necessary.
Next, the decoding process in FIG. 15 will be described. The encryption / decryption unit 7 acquires the message data D4 created at another user terminal from the chat client, and the process is started.

In step S31, the encryption / decryption unit 7 determines whether the encryption flag of the received message data is 0 or 1. If it is 1, the process proceeds to step S32. If it is 0, there is no need to decode the conversation data, and the process proceeds to step S36 described later.
In step S32, the encryption / decryption unit 7 extracts the version information included in the header part of the message data, that is, information indicating the timing at which the common key is generated, from the message data D4.

In step S33, the encryption / decryption unit 7 acquires the corresponding common key CSi from the common key table using the extracted version information as an index.
In step S34, the encryption / decryption unit 7 extracts the encrypted conversation data from the message data D4 and decrypts it using the acquired common key CSi.
In step S35, the encryption / decryption unit 7 displays an icon indicating encryption at the top of the display screen area where the conversation text is displayed.

In step S36, since the encryption / decryption unit 7 determines that the encryption flag is 0 in step S31, the conversation data included in the data part of the message data D4 is extracted as it is.
In step S37, the encryption / decryption unit 7 sends the decrypted conversation data or the extracted conversation data to the chat client, displays it on the display screen, and ends the process.

<Second Embodiment>
When a one-to-one conversation is performed in the chat system, an identifier for the electronic conference room can be created using the identifier of the user who is talking. For example, when the identifier of the user A is the character string “foo”, the identifier of the user B is the character string “bar”, and the user terminal A starts a conversation with the user terminal B, the electronic conference room Let the identifier be the string "foobar".

  Further, when a file is transmitted from the user terminal A to the user terminal B, it is conceivable to generate the common key CS as follows. First, message data D5 including predetermined data in the data portion is transmitted from user terminal A to user terminal B. The data portion of the message data D5 includes at least a command indicating that a file is transferred, a file name, and a file size. Both user terminals treat the header part and data part of the message data D5 as character strings and regard them as identifiers for the electronic conference room. Then, the same common key CS is generated at both user terminals to perform encrypted communication.

  If the present invention is used, a common key that changes with time in each user terminal is generated at a common timing in each terminal, so there is no need to distribute the key, and the possibility of decryption can be reduced. By notifying the generation timing of the common key together with the encrypted communication content, it is possible to decrypt with the common key used for encryption even if there is a time difference between the terminals.

1 is an overall configuration diagram of a security system according to a first embodiment. The function block diagram of the security apparatus which concerns on the example of 1st Embodiment. Explanatory drawing which shows the concept of a secret key table. An example of message data indicating changes in members. An example of message data indicating a password change. An example of the message data which instruct | indicates change of a common key. Explanatory drawing which shows the concept of a common key table. An example of message data including conversation data. Explanatory drawing which shows the example of a screen on which the instruction button of encryption was displayed. An example of a screen indicating that it is encrypted. Another example of a screen indicating that it is encrypted. The flowchart which shows the flow of a common key generation process by the instruction | indication of a command interpretation part. The flowchart which shows the flow of the common key generation process by the instruction | indication of a time acquisition part. The flowchart which shows the flow of an encryption process. The flowchart which shows the flow of a decoding process.

Claims (3)

A security method executed by a user terminal connected to a communication system in which a plurality of user terminals share the same electronic conference room and perform communication,
A time interval for generating a secret key is set in advance, and whenever the set time interval elapses, time information at that time is acquired from the user terminal, and a secret key is generated based on the acquired time information. A secret key generation step;
A secret key storage step of storing time information and the secret key generated in the secret key generation step based on the time information in association with each other;
When a change in the electronic conference room is detected, one of the secret keys stored in the secret key storage step is specified based on the time when the change is detected, and based on the specified secret key A public key generation step for generating a public key;
A public key storage step of storing the public key generated in the public key generation step and public key identification information for specifying the public key in association with each other;
When transmitting conversation data, among the public keys stored in the public key storage step, the conversation data is encrypted using the latest stored public key and public key identification information, and the encrypted conversation data And an encryption processing step for transmitting the public key identification information together with,
When the public key identification information is received together with the conversation data, one of the public keys stored in the public key storage step is identified based on the received public key identification information, and the public key is received with the identified public key A decryption processing step for decrypting the conversation data;
Including security methods. A security device mounted on a user terminal connected to a communication system in which a plurality of user terminals share the same electronic conference room and perform communication,
A time interval for generating a secret key is set in advance, and whenever the set time interval elapses, time information at that time is acquired from the user terminal, and a secret key is generated based on the acquired time information. A secret key generation unit;
A secret key storage unit that stores time information and a secret key generated by the secret key generation unit based on the time information in association with each other;
When a change in the electronic conference room is detected, one of the secret keys stored in the secret key storage unit is specified based on the time when the change is detected, and based on the specified secret key A public key generation unit for generating a public key;
A public key storage unit that stores the public key generated by the public key generation unit and public key identification information for specifying the public key in association with each other;
When transmitting the conversation data, out of the public keys stored in the public key storage unit, the latest stored public key and public key identification information are read from the public key storage unit and the conversation data is encrypted. An encryption processing unit for transmitting the public key identification information together with the encrypted conversation data;
When the public key identification information is received together with the conversation data, one of the public keys stored in the public key storage unit is identified based on the received public key identification information, and the public key is received with the identified public key A decryption processing unit for decrypting conversation data;
A security device comprising: A computer-readable recording medium that records a security program executed by a user terminal connected to a communication system in which a plurality of user terminals share the same electronic conference room and perform communication,
A time interval for generating a secret key is set in advance, and whenever the set time interval elapses, time information at that time is acquired from the user terminal, and a secret key is generated based on the acquired time information. A secret key generation step;
A secret key storage step of storing time information and the secret key generated in the secret key generation step based on the time information in association with each other;
When a change in the electronic conference room is detected, one of the secret keys stored in the secret key storage step is specified based on the time when the change is detected, and based on the specified secret key A public key generation step for generating a public key;
A public key storage step of storing the public key generated in the public key generation step and public key identification information for specifying the public key in association with each other;
When transmitting conversation data, among the public keys stored in the public key storage step, the conversation data is encrypted using the latest stored public key and public key identification information, and the encrypted conversation data And an encryption processing step for transmitting the public key identification information together with,
When the public key identification information is received together with the conversation data, one of the public keys stored in the public key storage step is identified based on the received public key identification information, and the public key is received with the identified public key A decryption processing step for decrypting the conversation data;
A computer-readable recording medium on which a security program for executing the program is recorded.

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