JP2007281925A - Cipher communication system, storage device for cipher communication, and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cipher communication system for transmitting a file to a specific party while keeping security utilizing the Internet or the like, and a portable storage device dedicated to the system. <P>SOLUTION: A storage device 3 for cipher communication that each user carries with him, stores a private key of the user himself, an electronic certificate, a cipher communication program and a recipient information table. When the storage device 3 for cipher communication is brought into communicable status with a computer 1, the cipher communication program is read onto a memory of the computer 1, and the cipher communication program makes the computer 1 function as a transmission terminal for adding an electronic certificate of a transmission destination to a file encrypted by a public key of the transmission destination and sending the file to a file storage server 2 of transmission destination designation, and on the other hand, makes the computer function as a reception terminal for accessing the file storage server to extract a file destined to the computer itself from stored files based on information of the electronic certificate, and decrypting the file using its own private key. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an encryption communication system, an encryption communication storage device, and a computer program for transmitting a file to a specific partner while maintaining safety while using a communication network such as the Internet that anyone can use.

In recent years, the use of the Internet has been remarkable, but the Internet has also been used for sending and receiving files and the like with a specific partner. However, since anyone can easily access the Internet, information flowing on the Internet is exposed to dangers such as eavesdropping and tampering. In order to protect information from such danger, VPN (Virtual Private Network) has been attracting attention.
VPN creates a virtual state in a communication network that is open to the public as if it is a dedicated path between parties, and provides a mechanism that allows secure communication between the parties.
There are many documents regarding this VPN, and those cited in Patent Documents 1 and 2 are one of them.

  In addition, as represented by electronic commerce, there is an increasing number of cases where personal (including corporations such as companies) information must be sent on the Internet. PKI (Public Key Infrastructure) based on a public key scheme provides a basic framework for ensuring the safety of such electronic commerce.

JP 2000-59357 A JP 2006-25097 A

Currently implemented VPNs are broadly classified into IP-VPN and SSL-VPN.
In order to construct an IP-VPN, it is necessary to connect a router at a user base to a large number of router networks connected to each other, and to notify the route information of the user base to a router constituting the router network. A large amount of capital investment is required, and a certain amount of knowledge about the network is required on the user side. Also, inside the virtual private path, the file is protected by encryption, but the file is in plain text between the source computer and the entrance to the private path and between the exit of the private path and the destination computer. It is in the state of.
On the other hand, in SSL-VPN, inconveniences such as the need for dedicated equipment, knowledge on the user side, and weak file protection in some sections are the same as for IP-VPN. .

Taking the inventions disclosed in Patent Documents 1 and 2 as examples, there are the following problems.
That is, in the invention disclosed in Patent Document 1, the server distributes the common key to both the sender and the receiver. For this reason, not only is it troublesome and expensive to operate and manage the server, but it is not preferable from the standpoint of file protection that the parties other than the parties (servers) are in a position to know the common key.
In the invention disclosed in Patent Document 2, the file remains plain in a partial section on the path connecting the sender to the receiver.

In view of the above-mentioned problems, the present invention eliminates the need for a new infrastructure for VPN, eliminates the need for an administrator on the user side, and allows safe and inexpensive file transmission between the sender and the receiver. It is an object of the present invention to provide a mechanism for ensuring the above and a portable device used for this mechanism.
Another object of the present invention is to realize the above mechanism based on public key-based PKI in view of the increase in the number of individuals who are issued digital certificates from certificate authorities (an element of PKI).

  In order to achieve the above object, a cryptographic communication system according to claim 1 includes a cryptographic communication storage device possessed by each user, a computer having an input / output interface with the cryptographic communication storage device, and An encryption communication system comprising a file storage server connected via a communication network, wherein the storage device for encryption communication includes a user's own private key and electronic certificate, a recipient information table, and a file stored in the computer. An encryption communication program for sending and receiving is stored, and the recipient information table includes an electronic certificate of the other party to whom the user intends to send a file and file storage server information for designating a file storage server. When the encryption communication storage device becomes communicable with the computer, The encrypted communication program is read on the memory, and when the recipient is identified, the encrypted communication program retrieves the recipient's electronic certificate and file storage server information from the recipient information table; A function for encrypting a file body to be transmitted to the recipient with a common key; a function for encrypting the common key with a public key of the recipient; and the encrypted common to the encrypted file body While the sender side computer realizes a function of creating an encrypted file by adding a key and the electronic certificate of the recipient, and a function of transmitting the encrypted file to a designated file storage server A function for automatically accessing the file storage server, and taking out the encrypted file addressed to itself from the encrypted files stored in the file storage server And a function of decrypting the encrypted common key in the encrypted file with its own secret key and decrypting the file body with the common key, on the receiver side computer, To do.

A “user” is a person who uses the system of the present invention to send and receive files, and each user has his / her own encryption communication storage device.
The “encrypted communication storage device” is a portable storage medium in which data and a program necessary for file transmission / reception of the present invention are built. The storage medium may be a USB memory, an IC card, a CD, or the like, and is not particularly limited. Further, it may be a non-contact type storage medium on the computer side. However, it is necessary to have a PKI area.
The “input / output interface” is an interface for establishing communication between the computer and the encryption communication storage device. For example, if the storage medium is a USB memory, a USB port corresponds to the interface.
The “communication network” includes the Internet of the following embodiment, but includes an intranet, an extranet, and the like.

The “electronic certificate” is a certificate issued by a certificate authority that proves that the owner's public key is valid. The certificate authority is not limited to an institution that performs authentication, but may be a private certificate authority established by a company or the like for internal members. This electronic certificate is stored in a predetermined location managed by mail software installed in most computers.
A “private key” is paired with an electronic certificate that has been proved to be the owner's legitimate public key, and the one that is encrypted with the public key can be decrypted unless it is based on the paired private key. Can not be converted.
The “file body” refers to a file that stores contents that the user wants to send to the other party. In the present invention, the encrypted common key and the recipient's electronic certificate are added to the encrypted file body, and the encrypted file is transmitted to the other party as an “encrypted file”.

  Thus, the file can be safely delivered from the sender to the receiver while using an open communication network such as the Internet. To achieve this, both the sender and the receiver can (1) use a computer that has a storage device for encrypted communication and connect to a communication network, and (2) have been issued an electronic certificate. There is no need to introduce a new device dedicated to this system. Therefore, the cost can be reduced to a much lower cost than that of the existing VPN. In addition, since most of the processing of this system is performed almost automatically when a program stored in the storage device for encrypted communication is read into the computer, the user requires advanced knowledge about communication and computers. Not. That is, secure file transmission / reception can be performed easily and inexpensively.

  In addition, since the file body is encrypted by the common key method, the processing time can be greatly reduced as compared with the case of encrypting by the public key method. The file main body targeted by the system of the present invention can include, for example, a set of design documents for a large-scale construction, a CAD drawing with many parts, etc. Therefore, the length of the required time is important. Furthermore, since this common key is encrypted with the recipient's public key, only the recipient who has the paired secret key can extract the common key and is more secure. Moreover, since a series of decryption processing is automatically performed by the program, the receiver does not need to know what the common key is.

As described below, the system of the present invention is fundamentally different from the conventional VPN.
In the conventional VPN, since communication networks such as the Internet are used by an unspecified number of people, files passing through them are considered to be at risk of eavesdropping, tampering, and file loss. In order to protect it, an attempt is made to provide a virtual dedicated path in a dangerous communication network. Therefore, a special mechanism or device is required at the entrance and exit of this exclusive path.
On the other hand, in the present invention, since the use of the Internet or the like is considered to inevitably involve danger, even if an attempt is made to eavesdrop on or tamper with a file in the middle of transmission, there is no actual harm to the parties. That's why it's good. I don't want to protect it by creating a private road. In the present invention, the file is kept encrypted immediately after leaving the sender's hand until immediately before reaching the receiver's hand. Even if the encrypted file is wiretapped or tampered with, no real harm will occur. In addition, even if a file is lost for some reason on the communication path, there is no concern that meaningful information will be leaked, and the party only has to send the same file again.

  According to a second aspect of the present invention, in the cryptographic communication system according to the first aspect, the recipient information table includes a name of a sender of the electronic mail based on an electronic mail transmitted with an electronic certificate. An electronic certificate, an e-mail address, etc. are registered as recipient information.

  Thereby, the other party who has transmitted the electronic mail with the electronic certificate can be registered in the receiver information table as a receiver.

  The invention according to claim 3 is the encryption communication system according to claim 1 or 2, wherein the file body transmitted to the receiver is encrypted after being compressed. .

As a result, even for a large-scale file, both the time required for encryption and the transmission time to the file storage server can be shortened.
The “file body” is not limited to one file, but also includes an arbitrary number of two or more files, or a file having a hierarchical structure including one or more folders.

  According to a fourth aspect of the present invention, in the cryptographic communication system according to any one of the first to third aspects, the common key for encrypting the file body is generated by generating a random number each time transmission is performed. Features.

Thereby, since the common key used for encryption is different each time transmission is performed, it is safer.
The disadvantage of the common key method is that key distribution is difficult, but this drawback is solved by being encrypted with the recipient's public key.

  According to a fifth aspect of the present invention, in the cryptographic communication system according to any one of the first to fourth aspects, the computer on the sender side receives the reception when the transmission of the file to the file storage server is completed. The e-mail address of the recipient of the file is acquired from the recipient information table, and an e-mail notifying the file transmission is sent to the recipient.

  As a result, the receiver can know that the file has been transmitted. At that time, if the storage device for encryption communication is made communicable with the computer, the file can be received. Although it is easy to forget to connect the storage device for encryption communication with a computer, since there are many people who check e-mails relatively infrequently, it is possible to avoid losing the file as much as possible.

  According to a sixth aspect of the present invention, in the cryptographic communication system according to the first aspect, the recipient-side computer adds an electronic certificate added from among the encrypted files stored in the file storage server. The issuer information is compared with information identifying the recipient who is the recipient, and when the two match, it is determined that the file is addressed to the recipient.

  “Issued person information” of an electronic certificate is information belonging to an item called a subject, and includes a user name (Common Name), an e-mail address, and the like. “Information identifying the self” includes, for example, a combination of a user name and an e-mail address.

  As a result, it is possible to quickly find the one addressed to itself from a large number of files in the file storage server. Since the electronic certificate in the plaintext state is searched as a clue, the file body may remain encrypted. Since the decryption process is not required for the search in the file storage server, the recipient's private key does not have to be taken out from the recipient's computer to the outside (communication network and file storage server). Since the electronic certificate is scheduled to be disclosed to others, it is not a problem in the present invention to use it in plain text.

The invention according to claim 7 is the encryption communication system according to claim 6, wherein the recipient computer uses the public key used for encrypting the encrypted file addressed to itself taken out from the file storage server. It is characterized by automatically searching for a corresponding private key.

  As a result, even if the receiver has a plurality of electronic certificates, that is, even when the receiver has a plurality of pairs of public and private keys, the encryption communication program is not required to be operated by the receiver. Automatically selects and decrypts an appropriate private key.

  The invention according to claim 8 is the encryption communication system according to any one of claims 1 to 7, wherein the encryption communication program loaded into the memory of the computer in a communicable state is in a communication cut-off state. The feature is that it has a function of erasing its own loaded program immediately.

The “communication cut-off state” refers to a state in which the USB memory type encryption communication storage device is disconnected from the USB port of the computer.
As a result, the program in the encryption communication storage device can be executed only when the encryption communication storage device and the computer are in a communicable state, and thus safety is maintained.

  In order to achieve the above object, the encryption communication storage device used in the encryption communication system and the stored computer program are also the present invention.

Existing equipment can be used as it is. Just prepare a program with the necessary program and data (recipient information and electronic certificate stored in the PKI area) in a storage medium such as a USB memory. Safe file transmission and reception can be easily realized at low cost.
Since the file is protected by encryption in a state where the party is not in the hands of the party, there is no real harm caused by eavesdropping or falsification when passing through the Internet or the like. This means that a virtual dedicated path is provided between the file sender and the file receiver, that is, VPN is realized.

An embodiment of the cryptographic communication system of the present invention will be described with reference to FIGS.
In the system configuration example shown in FIG. 1, two computers 1A and 1B and one file storage server 2 are connected via a communication network N such as the Internet. Storage devices 3A and 3B for encryption communication are connected to the computers 1A and 1B.
The file storage server 2 may be anything as long as it has a means 2a for storing a file in response to a request from another computer. However, the transmission protocol is preferably FTP (File Transfer Protocol). This is because FTP is a protocol used in many application software.
FIG. 1 illustrates a minimum configuration, and two or more computers 1 and one or more arbitrary file storage servers 2 can be connected.

In the following description, it is assumed that user A transmits a file to user B and user B receives a file from user A. Therefore, it is assumed that the computer 1A used by the user A performs transmission processing, and the computer 1B used by the user B performs reception processing. However, it goes without saying that the computer 1 in a state capable of communicating with the encryption communication storage device 3 performs both transmission and reception processes.
Each user has his / her own encryption communication storage device 3 and must use it, but the computer need not be limited. When the user needs to use this system, the user can use a computer at hand, and there is no restriction due to the IP address or installation location of the computer to be used.

Next, the configuration of the computer 1 and the encryption communication storage device 3 will be described with reference to the block diagram of FIG.
The encryption communication storage device 3 stores an I / F unit 4 for establishing a communication path with the computer 1, its own private key 5 and electronic certificate 6, an encryption communication program 7, and a recipient information table 8. Yes. In addition, drivers not shown are also stored.
The private key 5 is necessary for decrypting the encrypted file when the owner of the encryption communication storage device 3 receives the file. In the electronic certificate 6, the certificate authority proves that the public key paired with the private key 5 is a valid public key of the owner of the encryption communication storage device 3. The combination of the private key 5 and the electronic certificate 6 is not limited to one and may be a plurality. This is because there are people who have issued multiple electronic certificates by themselves.
The encryption communication program 7 is a program that covers most of the functions required for users of this system to send and receive files. Details of the function of this program will be described later.
The receiver information table 8 stores information on the person (transmission destination) who wants to transmit the file by the owner of the encryption communication storage device 3, and the format will be described later.

The computer 1 includes an I / F unit 9 that establishes communication with the encryption communication storage device 3, a storage unit 10, a processing unit 11, and an I / F unit 12. In addition, it is necessary to provide input means and screen display means for various settings and confirmation.
The storage means 10 stores various programs, various files, and the like. In addition to application software such as mail software, Web page browsing software, word processing software, spreadsheet software, and CAD software, the various programs include drivers for the encryption communication program 7 and the encryption communication storage device 3. Furthermore, files created by various application software are also stored. The storage means 10 is realized by an external auxiliary storage medium such as a RAM, a ROM, or a hard disk according to the type of program or file to be stored.

If the encryption communication storage device 3 is a USB memory type, the USB memory connector corresponds to the I / F unit 4 and the USB port corresponds to the I / F unit 9. When the I / F unit 4 and the I / F unit 9 are connected, the computer 1 can communicate with the encryption communication storage device 3, and the encryption communication program 7 is transferred to the computer 1 side and stored in the storage unit 10. The On the other hand, when the connection between the I / F unit 4 and the I / F unit 9 is released and communication between the computer 1 and the encryption communication storage device 3 is interrupted, the encryption communication program 7 identifies itself from the storage means 10. to erase. That is, the encryption communication program 7 can be executed only when the encryption communication storage device 3 is connected to the computer 1.
However, even if the program is stored in the encryption communication storage device 3, the drivers may be stored in the hard disk of the computer 1 or the like. This is because when the encryption communication storage device 3 is inserted into the USB port, the computer 1 can automatically read the encryption communication program 7 and the like immediately.

  The processing means 11 is realized mainly by a CPU (not shown), reads an appropriate instruction code of the encryption communication program 7 on the memory and executes encryption communication processing, executes various application software, and input / output means ( (Not shown). In the following description, unless otherwise specified, the function realized by the processing means 11 is based on the execution of the encryption communication program 7.

  The I / F unit 12 is a communication interface that sends a file to a communication network N such as the Internet or receives a file sent via the communication network N.

Next, the operation of the system of this embodiment will be described.
Execution of file transmission / reception by this system is based on the premise that a driver (including necessary middleware) of the encryption communication storage device 3 is installed in the computer 1. When the encryption communication storage device 3 is inserted into the USB port, the OS of the computer 1 confirms the presence or absence of a driver. If not, the driver is read from the encryption communication storage device 3 and installed on the computer 1 side. Once the driver is installed, thereafter, when the encryption communication storage device 3 is inserted into the USB port, the encryption communication program 7 is transferred to the computer 1 and becomes executable.

  In order to notify the user that encryption communication can be executed, for example, an icon is displayed on a screen (not shown) of the computer 1. For example, the user selects a process to be executed in the present system by an operation of selecting a menu item from a pop-up menu following an operation of clicking an icon. Since these operations are also used in many application software, details are omitted.

Before describing file transmission, registration of a recipient in the recipient information table 8 will be described.
The format of the recipient information table 8 is, for example, as shown in FIG. One record corresponds to one recipient. However, some users may have a plurality of electronic certificates, and in this case, a plurality of records correspond.
Editing of the recipient information table 8 such as registration (deletion and update is similar) of the recipient is executed by the encryption communication program 7 based on the contents input by the user via the input means (not shown).

  In the format example of FIG. 3, items excluding information on the file storage server are registered based on information obtained from an electronic mail with an electronic certificate sent from the other party to which the file is to be transmitted. It is premised that electronic mail should be exchanged with the other party who sends and receives files using this system.

The specific registration method differs depending on the mail software used by the user.
For example, if Outlook (registered trademark) Express is used, a list of persons having digital certificates is automatically read onto the memory. A person to be registered from this list is specified through an input means such as a mouse and registered in the recipient information table 8.
If you are using other mail software, refer to the electronic certificate of the user you are registering from the electronic certificate storage location managed by that mail software, and manually extract the data extracted from the electronic certificate. To the receiver information table 8. Here, the electronic certificate itself is also registered in the recipient information table 8. As described above, since the electronic certificate is also stored in the encryption communication storage device 3, even when a different computer is used at a business trip destination or the like, if the encryption communication storage device 3 is connected. , File transmission is possible.

  As described above, the recipient information registration process differs in implementation level depending on the mail software. However, the data for registering as a recipient is still data extracted from the electronic certificate sent with the electronic mail. Therefore, if a mail with an electronic signature has been received even once, the other party can be registered in the receiver information table 8 as a receiver. However, if you have not received it, you must contact the other party and ask them to send you an email with an electronic signature or ask them to send you an electronic certificate file (.cer).

  Information regarding the file storage server designated by the transmission destination is also registered in the recipient information table 8. Since it is necessary to set the host name or IP address of the file storage server, folder designation, port designation, etc. for FTP transfer, these pieces of information are also registered in the recipient information table 8.

Hereinafter, a procedure for transmitting a file from the user A to the user B will be described with reference to FIG. In this transmission process, it is assumed that the computer 1A of the user A is connected to a communication network N such as the Internet.
As in the case of registration in the table 8, the following procedure is realized by the processing means 11 executing the encryption communication program 7 unless otherwise specified.

When the user A selects the file body to be sent to the user B, the processing unit 11 of the computer 1A takes out the selected file from the storage unit 10 and compresses it (step S1). If there are a plurality of selected file bodies, they are compressed together.
Next, the user A is selected as the recipient of the file (step S2). The contents of the recipient information table 8 may be read from the encryption communication storage device 3, displayed on the screen of the computer 1A, and selected via the input means. In this example, it is assumed that user B is selected as the recipient.

The processing unit 11 extracts the electronic certificate of the user B from the recipient information table 8 and performs revocation verification confirmation (step S3). Specifically, whether or not the expiration date has passed, and if it is within the expiration date, a CRL (Certificate Revocation List) is obtained, and whether or not the information of the electronic certificate is posted is verified.
If it is determined to be valid in step S3, the processing means 11 generates a common key by generating a random number, encrypts the file body compressed with this common key (step S4), and then receives information 8 The user B's electronic certificate is taken out from the server, and the previous common key is encrypted with the public key included in the certificate (step S5).
As shown in FIG. 5, the encrypted compressed file D1, the encrypted common key D2, and the electronic certificate D3 of the user B are combined into one encrypted file and given a file name (step S6). Here, the recipient's electronic certificate is included in the encrypted file because it is necessary when the recipient searches for the file addressed to himself / herself from the storage location 2 a of the file storage server 2. This will be described later.

  When the encrypted file is created, the processing unit 11 extracts the information of the file storage server designated by the user B from the recipient information table 8, and the file storage server via the I / F unit 12 and the communication network N. 2 (step S7). After the transmission is completed, the processing means 11 automatically transmits to the user B who is the recipient an email indicating that the transmission has been made to the file storage server 2 (step S8). A fixed sentence is prepared for the body of this e-mail. Needless to say, the user A may edit the standard sentence as appropriate and transmit it.

  If it is determined in step S3 that the electronic certificate has expired, a warning message is displayed on the screen (step S9). For example, “This public key certificate has expired and cannot be revoked. The private key may have been passed to a third party and could be read by a third party. ”And prompts the sender to determine whether or not to continue the transmission process (step S10). If the continuation of the transmission process is selected (YES in step S10), the processes after step S4 are performed.

On the other hand, if it is determined that the electronic certificate has expired, the user information is urged to be deleted from the recipient information table 8 (step S11), and the transmission process is terminated. A certificate is revoked when a storage medium storing a private key is stolen or lost, and the private key corresponding to the public key cannot be used. Therefore, if a file encrypted using a public key that has been revoked is transmitted, there is a risk that a malicious party may eavesdrop on or tamper with the contents during communication. Therefore, unlike the case where the expiration date has expired, it has been determined that transmission is always disabled in the case of expiration.
In the case of expiration or expiration, it is necessary to take action such as having user B send a new electronic certificate.
The above is the outline of the processing on the sender side.

Next, the reception process on the file receiver side (user B in this example) will be described with reference to FIG. In this reception process, it is assumed that the computer 1B of the user B is connected to a communication network N such as the Internet.
User B has his / her encryption communication storage device 3B communicable with the computer 1B, and has been set to allow automatic access to the file storage server 2 (YES in step S101). The processing unit 11 of the computer 1B automatically accesses the file storage server 2 every predetermined time (step S102).

If communication is not possible (NO in step S101), the encryption communication storage device 3B is connected to the computer 1B when reception is necessary, and the file storage server 2 is accessed by manual operation such as clicking an icon (step). S103). Even if communication is possible, if the automatic access permission is not set (NO in step S101), the file storage server 2 is accessed manually when reception is necessary (step S103). Here, the time when the reception is necessary is a case where a mail notifying the file transmission from the user A is received.
Note that, regardless of whether automatic access is possible, the user B can access the file storage server 2 by manual operation at any time.
Here, the time interval for automatically accessing the file storage server 2 may be a default value set by the program or a value specified by the user. Further, the user may make a setting not to perform automatic access.

  The processing unit 11 searches for a file stored in the file storage unit 2a of the file storage server 2, and if there is no file ("None" in step S104), the processing unit 11 may once be in a communication cut-off state or can communicate. You may wait for a transmission notification mail in the state or wait for the processing means 11 to automatically search every predetermined time. If the stored file is found (“Yes” in step S104), it is checked whether it is an encrypted file addressed to itself (step S105). The information extracted from the user name field and the mail address field from the electronic certificate storage area D3 of the encrypted file is compared with the name and mail address of the user B. If they match, the encrypted file addressed to the user B It can be judged that. In addition, although the information used for collation can also be considered, it may be any information as long as it can be uniquely identified as being addressed to itself.

  If the file taken out in step S104 is a file addressed to user B (Yes in step S105), the encrypted file is taken into the storage means 10 of the computer 1B (step S106). The processing means 11 takes out the secret key 5 of the user B from the encryption communication storage device 3B (step S107), and decrypts the common key from the common key area D2 of the encrypted file using the secret key 5 (step S107). S108). The file body compressed using the common key is decrypted from the area D1 of the encrypted file body (step S109).

By the way, when the user B has a plurality of electronic certificates, the processing means 11 must automatically find a suitable private key in step S107. In this case, the following processing examples can be considered. The processing means 11 compares the electronic certificate extracted from the area D3 of the encrypted file with its own electronic certificate 6 possessed by the user B, and the public key proved by the matching electronic certificate 6 is encrypted. Since it is the public key used, the secret key 5 paired with it can be discriminated.

Thus, the decryption of the file body addressed to itself is performed after the encrypted file is taken into the storage means 10 of the own computer 1B. That is, since the file body is encrypted until it is received from the file storage server 2 via the communication network N to the computer 1B, the security is maintained. This advantage will be apparent when compared with a case where the file found in the file storage server 2 is decrypted inside the file storage server 2 and then taken into the computer 1B.
The above is the outline of the processing on the receiver side.

In the above embodiment, the case where the transmission destination is one was described. However, when the same file is transmitted to two or more transmission destinations, encrypted files encrypted with the public keys of the respective transmission destinations are created for the number of persons. Then, it can be sent to a file storage server designated by each destination.

The above embodiment has been described on the assumption that the encrypted file to be transmitted is connected to the communication network N. However, there are also users who only create an encrypted file in advance in order to connect to the communication network N later. The processing flow in this case will be described with reference to FIG. In addition, the same code | symbol (S1, S2, etc.) is used for the step of the same content as FIG.

The processing means 11 of the computer 1A compresses the selected file body (step S1), and confirms whether or not there is a connection with the communication network N when the recipient of the file is selected (step S2). If connected (YES in step S201), the processing from step S3 onward in FIG. 4 is performed.
If not connected to the communication network N (NO in step S201), a warning message is displayed on the screen or the like (step S202). For example, “This computer is not connected to a communications network, so the public key certificate cannot be revoked. The private key may have been passed to a third party and read by the third party. This is a warning of “Would you like to create an encrypted file yet?” And prompts the user to determine whether or not to continue creating the encrypted file (step S203).

When the continuation of the process is selected (YES in step S203), the processes after step S4 are performed. Steps S4 to S6 are the same as those in FIG. The processing means 11 stores the created encrypted file in the designated location (step S204) and ends the process. The storage location of the encrypted file may be the hard disk of the computer 1A that the user A is currently working on or an auxiliary storage medium such as MO. Further, if there is an empty space in the encryption communication storage device 3A, it may be stored there.

As a system that realizes secure file transmission / reception via a communication network such as the Internet at low cost and simply, it can be introduced not only at companies and organizations but also at an individual level.

1 is a system configuration diagram of a cryptographic communication system according to an embodiment of the present invention. It is a block diagram of a computer and a storage device for encryption communication. It is a figure which shows the example of a format of a recipient information table. It is a flowchart which shows the transmission process of the encryption file by the sender side computer. It is a figure explaining the encryption file transmitted to a receiver. It is a flowchart which shows the acquisition process of the encryption file by the receiver side computer. It is a flowchart which shows the production | generation process of the encryption file by a sender side computer.

Explanation of symbols

1, 1A, 1B Computer 2 File storage server 3, 3A, 3B Storage device for encrypted communication 5 Private key 6 Electronic certificate 7 Encrypted communication program 8 Recipient information table N Communication network

Claims (10)

An encryption communication system comprising a storage device for encryption communication possessed by each user, a computer having an input / output interface with the storage device for encryption communication, and a file storage server to which these computers are connected via a communication network. And
The encryption communication storage device includes the user's own private key and electronic certificate,
A recipient information table;
Storing an encryption communication program for causing the computer to send and receive files;
The recipient information table includes an electronic certificate of the other party to whom the user intends to send a file, and file storage server information for specifying a file storage server,
When the encryption communication storage device becomes communicable with the computer,
The encrypted communication program is read on the computer memory,
The encryption communication program is:
When a recipient is specified, a function of retrieving the recipient's electronic certificate and file storage server information from the recipient information table;
A function of encrypting a file body to be transmitted to the recipient with a common key;
A function of encrypting the common key with the public key of the recipient;
A function of creating an encrypted file by adding the encrypted common key and the electronic certificate of the recipient to the encrypted file body;
While realizing the function of transmitting the encrypted file to a designated file storage server on the computer on the sender side,
A function of automatically accessing the file storage server;
A function to retrieve an encrypted file addressed to itself from among the encrypted files stored in the file storage server;
An encryption communication system characterized in that a computer on a receiver side realizes a function of decrypting an encrypted common key in the encrypted file with its own secret key and decrypting the file body with the common key . In the recipient information table, based on an email sent with an electronic certificate, the name, electronic certificate, email address, etc. of the sender of the email are registered as recipient information. The cryptographic communication system according to claim 1. 3. The encryption communication system according to claim 1, wherein the file main body transmitted to the recipient is encrypted after being compressed. The encryption communication system according to claim 1, wherein the common key for encrypting the file body is generated by generating a random number each time transmission is performed. When the computer on the sender side completes the transmission of the file to the file storage server, the sender's computer obtains the email address of the recipient of the file from the recipient information table, and sends the email to notify the file transmission. The encryption communication system according to claim 1, wherein the encryption communication system transmits the message to a receiver. The recipient computer refers to the attached electronic certificate from among the encrypted files stored in the file storage server, and identifies the issuer information and the recipient's self The cryptographic communication system according to claim 1, wherein when the two coincide with each other, the file is determined to be a file addressed to itself. The computer on the receiver side automatically searches for a secret key corresponding to the public key used for encrypting the encrypted file addressed to itself taken out from the file storage server. Cryptographic communication system. 8. The encryption communication program loaded in the memory of the computer in a communicable state has a function of deleting its own loaded program as soon as the communication is cut off. The encryption communication system of any one. With an input / output interface with a computer,
The user's private key and electronic certificate,
A recipient information table;
An encryption communication program that allows a computer to send and receive files via a communication network,
The recipient information table includes an electronic certificate of the other party to whom the user intends to send a file, and file storage server information for specifying a file storage server,
When communication with the computer is enabled via the input / output interface,
The encrypted communication program is read out on a memory of the computer,
The encryption communication program is:
When a recipient is specified, a function of retrieving the recipient's electronic certificate and file storage server information from the recipient information table;
A function of encrypting a file body to be transmitted to the recipient with a common key;
A function of encrypting the common key with the recipient's public key;
A function of creating an encrypted file by adding the encrypted common key and the electronic certificate of the recipient to the encrypted file body;
While realizing the function of transmitting the encrypted file to a designated file storage server on the computer on the sender side,
A function of automatically accessing the file storage server;
A function to retrieve an encrypted file addressed to itself from among the encrypted files stored in the file storage server;
A function for decrypting an encrypted common key in the encrypted file with its own secret key and causing a computer on the receiver side to realize a function of decrypting the file body with the common key Storage device. A computer program stored in the storage device for encrypted communication according to claim 9 for causing a computer to transmit and receive an encrypted file via a communication network.

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