JP6417813B2 - E-mail relay device, e-mail system and program - Google Patents

Description

  The present invention relates to an electronic mail relay device, an electronic mail system, and a program.

  In Patent Document 1, the transmission side relay device encrypts the texts of all electronic mails transmitted from the transmission side terminal and then transmits them via the Internet, and the reception side relay device decrypts the received texts of all the electronic mails. Then, a technique for transmitting to the receiving terminal has been proposed.

JP 2003-198626 A

  An object of the present invention is to reduce information leakage due to unauthorized access to a mail server, as compared to a case where unencrypted electronic mail is held in a mail server on an external network.

  The program according to the present invention includes: an encryption unit that encrypts an email; a decryption unit that decrypts an email encrypted by the encryption unit; and a mail server that temporarily holds an email addressed to a client. When an e-mail that is not encrypted by the encryption unit is acquired, the e-mail is encrypted by the encryption unit and then sent to the mail server. An encryption control means for controlling the electronic mail to be replaced with the encrypted electronic mail, and receiving the electronic mail from the mail server in response to an electronic mail receiving request from the client; Relay that performs relay control of e-mail to be transmitted to the client after being decrypted by the means Your means, to function as.

The encryption control means temporarily stores an unencrypted e-mail acquired from the mail server in a temporary storage means, and the relay control means stores the e-mail requested to be received by the client in the temporary storage. If stored in the means, the stored electronic mail is read from the temporary storage means and transmitted to the client.

  An e-mail relay device according to the present invention includes an encryption unit that encrypts an e-mail, a decryption unit that decrypts the e-mail encrypted by the encryption unit, and a mail server that temporarily holds an e-mail addressed to a client When an e-mail that is not encrypted by the encryption unit is acquired from the encryption unit, the e-mail is encrypted by the encryption unit, and then transmitted to the mail server. When the electronic mail is received from the mail server in response to an email reception request from the client, the encryption control means for controlling the electronic mail to be replaced with the encrypted email, the email Relay control for performing relay control of e-mail to be transmitted to the client after the decryption means decrypts And having a means.

  An electronic mail system according to the present invention includes: a mail server that temporarily holds an electronic mail addressed to a client; and an electronic mail relay device that relays an electronic mail transmitted from the mail server to the client. The relay device includes: an encryption unit that encrypts an email; a decryption unit that decrypts the email encrypted by the encryption unit; and an email that is not encrypted by the encryption unit from the mail server. Once acquired, the electronic mail is sent to the mail server in response to an electronic mail reception request from the client, and an encryption control means for controlling the electronic mail to be transmitted to the mail server after being encrypted by the encryption means. So that the e-mail is decrypted by the decryption means and then sent to the client. Relay control means for performing relay control of the child mail, and the mail server holds the unencrypted e-mail held by the encrypted e-mail transmitted from the e-mail relay apparatus. It is characterized by replacing with e-mail.

  According to the first aspect of the present invention, information leakage due to unauthorized access to the mail server is reduced as compared with the case where the unencrypted electronic mail is held in the mail server on the external network. be able to.

  According to the second aspect of the present invention, an unencrypted e-mail can be transmitted to the client without decrypting the e-mail.

  According to the invention described in claim 3, information leakage due to unauthorized access to the mail server is reduced as compared with the case where the unencrypted electronic mail is held in the mail server on the external network. be able to.

  According to the invention described in claim 4, information leakage due to unauthorized access to the mail server is reduced as compared with the case where the unencrypted e-mail is held in the mail server on the external network. be able to.

It is the figure which showed the whole structure in Embodiment 1 of the electronic mail system which concerns on this invention, and the block structure of a gateway. 2 is a hardware configuration diagram of a gateway according to Embodiment 1. FIG. 3 is a flowchart showing encryption processing in the first embodiment. FIG. 3 is a sequence diagram showing encryption processing in the first embodiment. 3 is a flowchart showing relay processing in the first embodiment. FIG. 3 is a sequence diagram illustrating relay processing in the first embodiment. It is the figure which showed the whole structure in Embodiment 2 of the electronic mail system which concerns on this invention, and the block structure of a gateway. 10 is a flowchart showing encryption processing in the second embodiment. 10 is a diagram illustrating a data configuration example of a UID correspondence table in Embodiment 2. FIG. 10 is a flowchart showing relay processing in the second embodiment. 6 is a diagram illustrating a data configuration example of UIDL in Embodiment 2. FIG.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a diagram showing an overall configuration of an electronic mail system and a block configuration of a gateway according to the present embodiment. FIG. 1 shows an external mail server 2 installed on the Internet 3 and an in-house gateway 10 and client 1 connected to a LAN (local area network) 4. The mail server 2 is a server computer that holds and manages electronic mail addressed to the client 1. The client 1 is realized by an information processing apparatus such as a PC, and receives an electronic mail held by the mail server 2 via the gateway 10. The gateway 10 corresponds to an electronic mail relay device according to the present invention, and relays electronic mail transmitted from the mail server 2 to the client 1.

  Note that although a plurality of clients 1 are normally connected to the LAN 4, only one client 1 is shown for convenience because it is not used in the description in the present embodiment.

  FIG. 2 is a hardware configuration diagram of a computer built in the gateway 10 according to the present embodiment. In this embodiment, the computer built in the gateway 10 may be realized by a general-purpose hardware configuration that has existed in the past. That is, as shown in FIG. 2, the computer has a CPU 31, ROM 32, RAM 33, hard disk drive (HDD) 34, network interface 35 provided as a communication means with the Internet 3, and LAN interface provided as a communication means with the LAN 4. 36 is connected to an internal bus 37.

  Returning to FIG. 1, in this embodiment, the gateway 10 includes a first communication processing unit 11, a second communication processing unit 12, an encryption unit 13, an encryption control unit 14, a decryption unit 15, a relay control unit 16, and user information. A storage unit 17 and a common key storage unit 18 are included. Note that components not used in the description of the present embodiment are omitted from the drawings.

  The first communication processing unit 11 is realized by the network interface 35 and performs data communication with the mail server 2 via the Internet 3. The second communication processing unit 12 is realized by the LAN interface 36 and performs data communication with the client 1 via the LAN 4. The encryption unit 13 is provided as an encryption unit and encrypts an electronic mail. The encryption control unit 14 is provided as an encryption control unit. When an email that is not encrypted by the encryption unit 13 is acquired from the mail server 2, the encryption unit 13 encrypts the email and then encrypts the email. By transmitting to the mail server 2, control is performed so that the unencrypted electronic mail held in the mail server 2 is replaced with the encrypted electronic mail. The decryption unit 15 is provided as a decryption unit, and decrypts the electronic mail encrypted by the encryption unit 13.

  The relay control unit 16 is provided as a relay control unit. When an email is received from the mail server 2 in response to an email reception request from the client 1, the email is encrypted by the encryption unit 13, After the decrypting unit 15 decrypts the electronic mail, the electronic mail relay control is performed so that the electronic mail is transmitted to the client 1 that has issued the electronic mail reception request. The user information storage unit 17 stores, as user information, a set of a mail account name and password of a user who uses e-mail. The mail account name and password are registered in advance by the user, or acquired from the data at the time of the first POP (Post Office Protocol) reception request from the client 1. The common key storage unit 18 stores a common key used for encryption by the encryption unit 13 and decryption by the decryption unit 15.

  Each component 11-16 in the gateway 10 is implement | achieved by cooperation operation | movement of the computer which forms the gateway 10, and the program which operate | moves by CPU31 mounted in the computer. The storage units 17 and 18 are realized by the HDD 34 mounted on the gateway 10. Or you may implement | achieve with RAM33.

  Further, the program used in this embodiment can be provided not only by communication means but also by storing it in a computer-readable recording medium such as a CD-ROM or USB memory. The program provided from the communication means or the recording medium is installed in the computer, and various processes are realized by the CPU 31 of the computer sequentially executing the program.

  Next, the operation in this embodiment will be described. In the present embodiment, the gateway 10 encrypts the electronic mail held and managed in the mail server 2, and the electronic mail is received when the client 1 receives the electronic mail held by the mail server 2. It can be roughly divided into relay processing relayed by the gateway 10. First, an encryption process performed under the control of the encryption control unit 14 will be described with reference to the flowchart shown in FIG. FIG. 4 shows a sequence shown at the protocol level corresponding to the encryption process. The encryption processing in the present embodiment may be performed periodically for each user whose user information is registered in the user information storage unit 17 or may be operated according to the frequency of reception requests from the client 1. You may make it implement automatically. In the present embodiment, it is only necessary to perform the same processing for all users, and therefore, the following description will be made as processing for one user who uses the client 1. In addition, there are cases where a plurality of e-mails are held in the mail server 2 for one user, but it is only necessary to perform the same processing for each e-mail. This will be described as processing.

  The gateway 10 first confirms the presence or absence of the user's e-mail on the mail server 2 after authenticating to the mail server 2 using the mail account name and password registered in advance in the user information storage unit 17. In this embodiment, the POP protocol is used as an example, but other mail protocols such as IMAP (Internet Message Access Protocol) may be used.

  When there is no e-mail addressed to the user to be received in the mail server 2 (N in step 101), the encryption process ends. If there is an e-mail in the mail server 2 (Y in step 101), the encryption control unit 14 acquires the header information of the e-mail, and whether or not it has already been encrypted by the encryption unit 13 based on that information Judging. If it has been encrypted (N in step 102), the processing for the e-mail is terminated. On the other hand, if it is not encrypted (Y in step 102), the encryption control unit 14 acquires the unencrypted e-mail from the mail server 2 (step 103). When the e-mail is acquired, the encryption unit 13 uses the common key stored in the common key storage unit 18 for the e-mail (the entire e-mail including header information and attached files as well as the message body). Encryption is performed (step 104).

  The encryption control unit 14 newly adds header information to the encrypted e-mail (e-mail data), adds information indicating encryption to the header information, and transmits it to the mail server 2 (step 105). ). In step 102, it is determined by referring to the information indicating that encryption has been set here. It should be noted that SMTP (Simple Mail Transfer Protocol) authentication information may be input in advance by the user, or may be prompted to input when the same authentication information as that of the POP fails.

  When the encrypted e-mail is transmitted, the mail server 2 uses the e-mail transmitted from the gateway 10, that is, the encrypted e-mail, as the non-encrypted e-mail held. replace.

  In the present embodiment, as described above, the mail server 2 holds the electronic mail in an encrypted state. Further, by replacing the unencrypted e-mail with the encrypted e-mail, an increase in storage capacity can be suppressed as much as possible. Furthermore, information leakage due to unauthorized access can be prevented by holding the email in an encrypted state. Strictly speaking, there is a time lag between when the mail server 2 receives an email addressed to the client 1 (an unencrypted email address) and when the email server 2 is replaced with the encrypted email generated by the encryption process described above. However, the chance of information leakage is reduced as compared with the case where the mail server 2 keeps the e-mail in an unencrypted state until the client 1 receives the e-mail from the mail server 2. Will be.

  Next, the relay process performed under the control of the relay control unit 16 will be described using the flowchart shown in FIG. A sequence shown at the protocol level corresponding to the relay processing is shown in FIG. The relay processing in the present embodiment is performed in response to receiving an e-mail reception request from the client 1.

  That is, when an e-mail reception request from the client 1 is acquired (step 121), the gateway 10 authenticates the mail server 2 using the user's mail account name and password, and sets the mail server 2 as a reception target. Check for the presence of an email addressed to the user. This process may be the same as the encryption process. If there is no e-mail addressed to the user in the mail server 2 (N in step 122), the relay process ends. When there is an email in the mail server 2 (Y in Step 122), the relay control unit 16 receives an email addressed to the user from the mail server 2 (Step 123).

  Subsequently, the relay control unit 16 determines whether the electronic mail is encrypted by referring to the header information of the received electronic mail. If the email is encrypted (Y in step 124), the decryption unit 15 decrypts the email (entire message including header information) using the common key stored in the common key storage unit 18. (Step 125). If it is not encrypted (N in step 124), it is not necessary to decrypt it. Note that the e-mail received by the mail server 2 after the above-described encryption process and before the encryption process is executed in the next cycle corresponds to the unencrypted e-mail here.

  By the way, since the header information is added to the encrypted email in Step 105, the header information added in Step 105 is deleted from the decrypted email so that the client 1 is aware of the presence or absence of encryption. It may not be allowed to.

  Then, the relay control unit 16 transmits the unencrypted electronic mail to the client 1 from which the reception request is issued (step 126). In the present embodiment, at the time of receiving a reception request, regardless of whether or not the email is encrypted, all the emails addressed to the user held in the mail server 2 are transmitted to the client 1. However, only the encrypted electronic mail may be transmitted to the client 1.

  The gateway 10 in this embodiment relays the electronic mail held in the mail server 2 to the client 1 as described above. In this embodiment, since the e-mail is encrypted and held in the mail server 2 installed outside the company, it is not necessary to acquire and hold the e-mail in advance in the company connected to the LAN 4. In other words, it is not necessary to install a storage device or the like for holding e-mail at an in-house cost.

Embodiment 2. FIG.
In contrast to the first embodiment, this embodiment is characterized in that the cache is effectively used. FIG. 7 is a configuration diagram corresponding to FIG. 1 in the first embodiment. Note that the same components as those in Embodiment 1 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. The gateway 10 in the present embodiment has a configuration in which a cache data storage unit 19, a UID (Unique ID) information storage unit 20, and a UIDL (Unique ID Listing) storage unit 21 are added to the configuration shown in the first embodiment. ing. Information stored in each of the storage units 19 to 21 will be described together with an explanation of the operation. The storage units 19 to 21 are realized by the HDD 34 mounted on the gateway 10. Or you may implement | achieve with RAM33.

  Next, the operation in this embodiment will be described. In the present embodiment, encryption processing and relay processing are executed in the same manner as in the first embodiment. The present embodiment may be basically the same as the first embodiment except for the process of effectively using cache data. First, the encryption process performed under the control of the encryption control unit 14 will be described with reference to the flowchart shown in FIG. Note that the same processing is given the same step number, and description thereof is omitted as appropriate.

  When the encryption control unit 14 obtains an unencrypted e-mail from the mail server 2 by performing the same processing as in the first embodiment (steps 101 to 103), the obtained unencrypted e-mail Are stored in the cache data storage unit 19 as cache data (step 201). At this time, the encryption control unit 14 uses “UID” information indicating that the e-mail is stored in the cache data storage unit 19 as a UID (UID before encryption) for uniquely identifying the acquired e-mail. Are registered in the UID information storage unit 20 as UID information (step 202). FIG. 9 shows a UID correspondence table for registering UID information in a table format. The UID information includes the UID of the email before encryption (UID before encryption), the UID of the email after encryption (UID after encryption), which is acquired and associated in the subsequent processing, and the email Is generated in association with information (cache data) indicating whether or not is stored as cache data in the cache data storage unit 19. When the cache area of the cache data storage unit 19 is tight and it is necessary to delete old cache data in order to hold new cache data, the cache data is not held in the UID correspondence table together with deletion of old cache data. In other words, “not present” is set instead of “present”.

  Subsequently, after encrypting, the encryption control unit 14 transmits the e-mail to the mail server 2 to replace the unencrypted e-mail (steps 104 and 105). When the encrypted electronic mail is registered, the mail server 2 transmits the encrypted UID of the electronic mail to the gateway 10. When receiving the UID of the electronic mail transmitted from the mail server 2, the encryption control unit 14 additionally registers the encrypted UID information in the UID information of the electronic mail (step 203). Thereby, each UID before and after encryption for one electronic mail is associated.

  Next, the relay process performed under the control of the relay control unit 16 will be described using the flowchart shown in FIG.

  In response to an e-mail reception request from the client 1 (step 121), the relay control unit 16 confirms the presence or absence of an e-mail to be received in the mail server 2 after authentication. Although the description is omitted in the first embodiment, at this time, the relay control unit 16 registers a list (UIDL) acquired from the mail server 2 by the UIDL command in the UIDL storage unit 21. A data configuration example of UIDL registered in the acquired UIDL storage unit 21 is shown in FIG. The UIDL is set by associating the encrypted UID with the message number for identifying the e-mail. The gateway 10 transmits the acquired UIDL to the client 1.

  As a result of checking whether or not there is an e-mail, if an e-mail exists in the mail server 2 (Y in step 122), the relay control unit 16 uses the cache data storage unit 19 to store the e-mail received from the client 1 as cache data. Check whether it is saved in. The cache data storage unit 19 stores an unencrypted e-mail. Here, if not stored (N in Step 221), the relay control unit 16 receives an email addressed to the user from the mail server 2 as in the first embodiment (Step 123). If the received e-mail is encrypted, the e-mail is decrypted (Y, 125 in step 124), and the e-mail not encrypted by the decryption is transmitted to the client 1 from which the reception request is issued (step). 126).

  On the other hand, when an unencrypted e-mail is stored in the cache data storage unit 19 (Y in step 221), the relay control unit 16 sends the e-mail registered in the cache data storage unit 19 to the client. 1 (step 222). However, in this case, since the e-mail that is originally acquired from the mail server 2 is not acquired, the corresponding e-mail remains in the mail server 2 as it is. Therefore, the relay control unit 16 deletes the email held in the mail server 2 (step 223).

  By the way, in the description of the above processing procedure, the gateway 10 confirms the presence / absence of an electronic mail after performing authentication in response to a reception request from the client 1 (steps 121 and 122). However, strictly speaking, the processing is performed in the following procedure.

  That is, the client 1 performs authentication by issuing a reception request, identifies the email to be received with reference to the UIDL sent thereafter, and notifies the gateway 10 of it. That is, the client 1 designates an e-mail to be received after issuing a reception request in step 121 and before performing step 122. The same applies to the first embodiment.

  As described above, the client 1 specifies the e-mail to be received based on the UID set in the UIDL. In the present embodiment, the UID transmitted from the client 1 to the gateway 10 is the encrypted UID. is there. Therefore, the relay control unit 16 refers to the UID correspondence table, converts the transmitted encrypted UID into a pre-encrypted UID, and stores the corresponding e-mail (encrypted) in the cache data storage unit 19. No email) will be registered. As described above, when the corresponding e-mail is stored in the cache data storage unit 19 (Y in step 221), the relay control unit 16 sends the e-mail registered in the cache data storage unit 19 to the client. 1 (step 222).

  As described above, when the corresponding electronic mail is transmitted to the client 1, the relay control unit 16 deletes the UID information of the electronic mail from the UID correspondence table (step 224).

  DESCRIPTION OF SYMBOLS 1 Client, 2 Mail server, 3 Internet, 4 LAN, 10 Gateway, 11 1st communication processing part, 12 2nd communication processing part, 13 Encryption part, 14 Encryption control part, 15 Decryption part, 16 Relay control part, 17 User information storage unit, 18 Common key storage unit, 19 Cache data storage unit, 20 UID information storage unit, 21 UIDL storage unit, 31 CPU, 32 ROM, 33 RAM, 34 Hard disk drive (HDD), 35 Network interface, 36 LAN interface, 37 Internal bus.

Claims (4)

Computer
An encryption means for encrypting email,
Decryption means for decrypting the electronic mail encrypted by the encryption means;
When an e-mail not encrypted by the encryption means is acquired from a mail server that temporarily holds an e-mail addressed to a client, the e-mail is encrypted by the encryption means and then sent to the mail server And an encryption control means for controlling to replace the unencrypted email stored in the mail server with the encrypted email,
Relay control means for performing relay control of the e-mail so that when the e-mail is received from the mail server in response to the e-mail reception request from the client, the e-mail is decrypted by the decryption means and then sent to the client ,
Program to function as. The encryption control means temporarily stores an unencrypted e-mail acquired from the mail server in a temporary storage means,
The relay control unit, when an email requested to be received by the client is stored in the temporary storage unit, reads the stored email from the temporary storage unit and transmits the email to the client. The program according to claim 1. An encryption means for encrypting the email;
Decryption means for decrypting the email encrypted by the encryption means;
When an e-mail not encrypted by the encryption means is acquired from a mail server that temporarily holds an e-mail addressed to a client, the e-mail is encrypted by the encryption means and then sent to the mail server And an encryption control means for controlling to replace the unencrypted email stored in the mail server with the encrypted email,
Relay control means for performing relay control of the e-mail so that when the e-mail is received from the mail server in response to the e-mail reception request from the client, the e-mail is decrypted by the decryption means and then sent to the client When,
An electronic mail relay device comprising: A mail server that temporarily holds email addressed to the client;
An e-mail relay device that relays an e-mail transmitted from the mail server to the client;
Have
The e-mail relay device
An encryption means for encrypting the email;
Decryption means for decrypting the email encrypted by the encryption means;
An encryption control means for controlling the e-mail to be transmitted to the mail server after the e-mail is encrypted by the encryption means upon obtaining the e-mail not encrypted by the encryption means from the mail server;
Relay control means for performing relay control of the e-mail so that when the e-mail is received from the mail server in response to the e-mail reception request from the client, the e-mail is decrypted by the decryption means and then sent to the client When,
Have
The mail server replaces the unencrypted electronic mail held by the encrypted electronic mail transmitted from the electronic mail relay device,
An e-mail system characterized by that.

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