JP2009205430A - Electronic mail-relaying device and electronic mail-relaying method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic mail-relaying device which enables a mail client side to recognize a result of verification, when an encoded signature mail is not perfectly decoded and the signature is not verified, and also enables a mail client side to decode a signature mail and verify the signature. <P>SOLUTION: A mail gateway server 17, which relays electronic mails between a mail server 15 and a mail client 11, is provided with: a decoding part 23 which executes decoding processing to encoded signature mails received from the mail server 15; a report-generating part 26 which generates reports on the results of the decoding processing; and a transmission/distribution part 27 which regards the reports on the results of the decoding processing as the main bodies of mails and distributes the mails to the mail client 11, together with the original encoded signature mails as the attached files. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an e-mail relay apparatus and an e-mail relay method, and more particularly to an e-mail relay apparatus and an e-mail relay method that support encryption / signature mail.

  In recent years, transmission / reception of electronic mail has been widely performed via a network such as the Internet. Since e-mail passes through a plurality of computers (mail servers) before reaching the transmission destination, there is a risk of eavesdropping, tampering, and impersonation. In order to ensure the security of electronic mail in such an environment, message encryption and electronic signature addition are performed. That is, by encrypting the message, confidentiality of the message is ensured, and by adding an electronic signature, authentication and integrity of the message are ensured.

Here, in Patent Document 1 below, when an electronic mail is transferred from a mail server to a mail client, the encrypted mail is decrypted and the electronic signature is verified. An encrypted mail server is disclosed that adds a verification result as a comment to the body of an e-mail if it is an attached mail.
JP 2006-148658 A

  However, the decryption is not finally completed, for example, when decryption or signature verification fails or when an encrypted email is decrypted m (<n) times (n times). When a result report is added or attached to an e-mail, it is encrypted and signed by many mailers (for example, Becky !, Outlook Express (registered trademark), Outlook (registered trademark), etc.) installed in the mail client. There is a possibility that it is not determined to be email. Therefore, even if the mailer installed in the mail client has a function of performing decryption / signature verification, there has been a problem that the mail client cannot perform decryption / signature verification.

  The present invention has been made to solve the above problems, and when the encrypted / signature mail cannot be completely decrypted / signature verified, the result of the encryption / signature mail distribution destination is obtained. It is an object of the present invention to provide an e-mail relay apparatus and an e-mail relay method that can be recognized on the mail client side and that can be decrypted and verified on the mail client side.

  An e-mail relay apparatus according to the present invention is an e-mail relay apparatus that relays an e-mail between a mail server and a mail client, and performs a decryption unit that decrypts an encrypted / signed mail received from the mail server And a report generation means for generating a decryption result report of the decryption process by the decryption means, and a decryption result generated by the report generation means when the encrypted / signature mail is not completely decrypted as a result of the decryption process. And a distribution means for distributing the report as a mail body and distributing the original encrypted / signature mail as an attached file to a mail client.

  The electronic mail relay method according to the present invention is an electronic mail relay method for relaying electronic mail between a mail server and a mail client, and includes a decryption step for decrypting an encrypted / signature mail received from the mail server. And a report generation step for generating a decryption result report of the decryption process in the decryption step, and a decryption result generated in the report generation step when the decryption process is performed and the encrypted / signature mail is not completely decrypted. And a delivery step of delivering the original encrypted / signature mail as an attached file to a mail client.

  According to the e-mail relay apparatus or e-mail relay method of the present invention, when the encrypted / signature mail is not completely decrypted (for example, when decryption fails or encrypted mail is encrypted n times) Is decrypted m (<n) times), the decryption result report is the mail body, and the original encrypted / signed mail is attached as an attachment and delivered to the mail client. Therefore, the decryption result can be recognized on the mail client side by reading the mail text. Further, when the mailer installed in the mail client has a function of performing decryption / signature verification, the original encryption / signature mail decryption process can be performed by opening the attached file with the mailer. As a result, the decryption result at the relay time can be recognized on the mail client side, and decryption / signature verification can be performed on the mail client side.

  Preferably, when the encrypted / signature mail is encrypted a plurality of times, the distribution means attaches and distributes the electronic mail at the stage of successful decryption as the original encrypted / signature mail.

  In the distribution step, when the encrypted / signature mail is encrypted a plurality of times, it is preferable that the electronic mail at the stage of successful decryption is attached and distributed as the original encrypted / signature mail.

  In this case, since the attached encrypted / signature mail is decrypted halfway, it is possible to reduce the load of decryption processing on the mail client side.

  The electronic mail relay device according to the present invention includes a signature verification unit that performs signature verification of encryption / signature mail, a report generation unit generates a verification result report of a signature verification process by the signature verification unit, and a distribution unit includes: When signature verification fails, it is preferable to deliver the verification result report generated by the report generation means to the mail body and the original encrypted / signature mail as an attached file to the mail client.

  Further, the electronic mail relay method according to the present invention includes a signature verification step for performing signature verification of the encrypted / signature mail, and in the report generation step, generates a verification result report of the signature verification processing in the signature verification step, and a distribution step When the signature verification fails, it is preferable to distribute the verification result report generated in the report generation step as the mail body and distribute the original encrypted / signature mail as an attached file to the mail client.

  According to the e-mail relay apparatus or e-mail relay method of the present invention, when signature verification fails, the verification result report is set as the mail body, and the original encrypted / signed mail is attached as an attached file and distributed to the mail client. Is done. Therefore, the mail client side can recognize the signature verification result by reading the mail text. If the mailer installed in the mail client has a function for performing signature verification, the signature verification processing of the original encrypted / signed mail can be performed by opening the attached file with the mailer. As a result, the signature verification result at the time of relay can be recognized on the mail client side, and signature verification can be performed on the mail client side.

  When the signature of the encryption / signature mail is a clear signature, the distribution means preferably distributes the original encryption / signature mail as the mail body and the verification result report as an attached file to the mail client.

  In the distribution step, when the signature of the encrypted / signed mail is a clear signature, it is preferable to distribute the original encrypted / signed mail as the mail body and the verification result report as an attached file to the mail client.

  When the signature is a clear signature, the mail body is plain text, so there is no need to decrypt it on the mail client side. In this case, since the original encryption / signature mail is distributed as the mail body, the original encryption / signature mail can be displayed and confirmed as it is. Since the verification result report is distributed as an attached file, the signature verification result can be recognized by opening the attached file.

  According to the present invention, when the encrypted / signature mail is not completely decrypted, the decryption result report is set as the mail body, and the original encrypted / signed mail is delivered to the client as an attached file. If the encryption / signature mail cannot be completely decrypted / signature verified at that time, the result can be recognized by the client that is the delivery destination of the encryption / signature mail, and the client side Decryption / signature verification can be performed.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. First, the configuration of an e-mail system including an e-mail relay device (hereinafter referred to as “mail gateway server”) according to the embodiment and the overall configuration of the mail gateway server will be described with reference to FIGS. FIG. 1 is a diagram illustrating a configuration example of an electronic mail system including a mail gateway server. FIG. 2 is a block diagram showing the overall configuration of the mail gateway server.

  The e-mail system shown in FIG. 1 includes a plurality of e-mail clients 10 and 11 serving as transmission sources / destinations of e-mail (hereinafter simply referred to as “mail”), and network multifunction peripherals (MFPs) 12 and 13 Between the mail servers 14 and 15 that manage mail distribution between the mail source and the destination, the mail client 10 (11), the network multifunction device 12 (13), and the mail server 14 (15). A mail gateway server 16 (17) that forwards mail and ensures the security of the mail is provided. The mail client 10 and the mail client 11, the network multifunction device 12 and the network multifunction device 13, the mail server 14 and the mail server 15, and the mail gateway server 16 and the mail gateway server 17 have the same or similar configurations. Yes.

  Further, the arrows in FIG. 1 indicate the flow of mail when mail is transmitted from the mail client 10 and network multifunction device 12 to the mail client 11 and network multifunction device 13. Therefore, when sending mail from the mail client 11 and the network multifunction device 13 to the mail client 10 and the network multifunction device 12, the flow is reversed. The mail client 10 (11), the network multifunction device 12 (13), the mail gateway server 16 (17), and the mail server 14 (15) are connected by a LAN or the like. The mail server 14 and the mail server 15 are connected via the Internet.

The mail clients 10 and 11 generate mail, SMTP (Simple Mail Transfer)
This is a personal computer in which electronic mail software (hereinafter also referred to as “mailer”) that performs transmission of mail using Protocol) and reception of mail using POP3 (Post Office Protocol version 3) is implemented. The mailer installed in the mail clients 10 and 11 corresponds to S / MIME (Secure Multipurpose Internet Mail Extensions) and has an encryption / decryption function and a signature addition / signature verification function.

  The network multifunction peripherals 12 and 13 have an IFAX (Internet facsimile) function. The network multifunction peripherals 12 and 13 transmit the transmission document as TIFF / PDF format image data attached to a mail. Further, the network multifunction peripherals 12 and 13 receive mail from the mail gateway servers 16 and 17 every set time and automatically print out.

  The mail servers 14 and 15 are server computers that manage mail distribution between a mail transmission source and a transmission destination. For example, the mail servers 14 and 15 have a function of sorting and storing mail received from the mail sender according to the mail address in a mail box or transferring it to another mail server using SMTP. In addition, the mail servers 14 and 15 have a function of distributing mail stored in the mailbox in response to a request from the mail gateway servers 16 and 17.

  The mail gateway servers 16 and 17 support S / MIME, encrypt plain text mail received from the mail clients 10 and 11 and the network multifunction peripherals 12 and 13, and add an electronic signature to the mail server 14 and 15 is transmitted using SMTP. Further, the mail gateway servers 16 and 17 decrypt the encrypted / signature mail received from the mail servers 14 and 15 using the POP3, verify the signature, and store the mail text and the decryption / signature verification result in a mailbox for each user. Store temporarily. The mail gateway servers 16 and 17 distribute the stored mail text and decryption / signature verification results to the mail clients 10 and 11 and the network multifunction peripherals 12 and 13 in response to a request according to POP3.

  The mail gateway servers 16 and 17 are configured by a microprocessor that performs calculations, a ROM that stores programs for causing the microprocessor to execute each process, a RAM that temporarily stores various data such as calculation results, and the like. . The mail gateway servers 16 and 17 execute a program stored in the ROM, whereby a storage unit 21, an encryption unit 22, a decryption unit 23, a signature unit 24, a signature verification unit 25, and a report generation unit described below 26 and the function of the transmission / distribution unit 27 are realized.

  The storage unit 21 stores a pair of a mail address and a corresponding private key, and a pair of a mail address and a corresponding public key. The private key is used when an electronic signature of the mail sender is added to the mail and when the encrypted mail is decrypted. On the other hand, the public key is used when encrypting mail and verifying an electronic signature.

  The encryption unit 22 acquires the public key corresponding to the mail address of the mail destination from the storage unit 21 and encrypts the plain text mail transmitted from the mail clients 10 and 11 and the network multifunction peripherals 12 and 13 with the public key. Turn into.

  The decryption unit 23 acquires the secret key corresponding to the mail address of the mail destination from the storage unit 21 and decrypts the encrypted mail received from the mail servers 14 and 15 with the secret key. That is, the decoding unit 23 functions as a decoding unit described in the claims.

  The signature unit 24 acquires a secret key corresponding to the mail address of the mail sender from the storage unit 21 and obtains a message digest (hash value) of the mail. The signature unit 24 encrypts the obtained message digest with a secret key and generates an electronic signature of the mail sender. The generated electronic signature is added to the mail.

  The signature verification unit 25 acquires a public key corresponding to the mail address of the mail sender from the storage unit 21, and decrypts the electronic signature added to the mail with the public key. Also, the signature verification unit 25 generates a message digest from the mail body, and compares the decrypted electronic signature value (message digest) with the generated message digest to determine whether the mail has been tampered with. Validate. That is, the signature verification unit 25 functions as signature verification means described in the claims.

  The report generation unit 26 generates a decoding result report according to the decoding result by the decoding unit 23. When decoding is successful, for example, a decoding result report “decoding succeeded” is generated. When decoding fails, for example, a decoding result report “decoding failed” is generated. The report generation unit 26 generates a verification result report according to the signature verification result by the signature verification unit 25. If the signature verification is successful, for example, a verification result report “successful signature verification” is generated, and if the signature verification fails, a verification result report “successful signature verification” is generated. That is, the report generation unit 26 functions as a report generation unit described in the claims.

  The transmission / distribution unit 27 transmits the encrypted / signature mail generated by the encryption unit 22 and the signature unit 24 to the mail servers 14 and 15 using SMTP. Further, the transmission / distribution unit 27 sends the mail body, the decryption result report, and the verification result report generated by the decryption unit 23, the signature verification unit 25, and the report generation unit 26 to the mail clients 10 and 11, the network multifunction peripheral 12, 13 is delivered.

  More specifically, when the mail is completely decrypted (that is, when decryption is successful) and the signature verification is successful, the transmission / distribution unit 27 sets the decrypted mail as the mail body, and displays the decryption result report and the verification result report. It is distributed to the mail clients 10 and 11 and the network multifunction peripherals 12 and 13 as attached files. On the other hand, when the mail is not completely decrypted (for example, when decryption fails or when encrypted mail encrypted n times is decrypted m (<n) times) and / or signature verification fails In this case, the decryption result report and the verification result report are used as the mail body, and the original encryption / signature mail (up to the point where the decryption is successful when encrypted several times) is attached to the mail client 10, 11. Distribute to the network multifunction peripherals 12 and 13. However, even if the signature verification fails, the transmission / distribution unit 27 uses the original mail as the mail body and the verification result report as the attached file when the added signature is a clear signature. 10 and 11 and distributed to the network multifunction peripherals 12 and 13. That is, the transmission / distribution unit 27 functions as a distribution unit described in the claims.

  Next, referring to FIGS. 1 to 3 together, the operation of the mail gateway server 17 when mail is received via the mail server (SMTP server) 14 and the mail server (POP server) 15, and the mail gateway server The mail delivery method according to FIG. FIG. 3 is a flowchart showing a processing procedure of mail delivery processing by the mail gateway server 17.

  When a mail is received from the mail server 15 in step S100, whether or not the received mail is an encrypted / signature mail, that is, whether it is encrypted and an electronic signature is added in step S102. A determination is made as to whether or not. Here, if the received mail is not an encrypted / signature mail, that is, if it is a plain text mail and no electronic signature is added, in step S114, the received mail is the destination (receiving user). Stored in a mailbox. On the other hand, if the received mail is an encryption / signature mail, that is, if encryption and / or an electronic signature is added, the process proceeds to step S104.

  In step S104, the received mail is decrypted and signature verification is performed. More specifically, the received encrypted mail is decrypted with the secret key corresponding to the mail destination (mail address), the mail body and the encrypted message digest are acquired, and the decryption result report is acquired. . Further, the encrypted message digest is decrypted with the public key corresponding to the mail address of the mail sender, and the message digest is generated from the mail body by the same hash function as the sender. Then, signature verification is performed by comparing the decrypted sender message digest with the generated mail message digest to determine whether or not they match. Further, a verification result report corresponding to the determination result is acquired.

  In the subsequent step S106, it is determined whether or not the mail decrypted in step S104 is still an encrypted / signature mail, that is, whether or not it has been completely decrypted. If the mail is completely decrypted and the signature verification is successful, the process proceeds to step S108. On the other hand, when decryption is not complete (for example, when decryption fails or when encrypted mail encrypted n times is decrypted m (<n) times) and when signature verification fails In step S110, the process proceeds.

  In step S108, the decryption result report and the verification result report are attached to the decrypted plain text mail (mail body) as an attached file. In step S114, it is stored in the mailbox of the transmission destination (reception user).

  In step S110, it is determined whether or not the added signature is a clear signature. Here, when the signature is a clear signature, since the mail text is plain text, the process proceeds to step S108. On the other hand, if the signature is not a clear signature, the process proceeds to step S112. In addition, since the processing content in step S108 is as above-mentioned, description is abbreviate | omitted here.

  In step S112, the decryption result report and the verification result report are used as the mail body, and the original encrypted / signed mail (up to the point where the decryption is successful if encrypted several times) is used as the attached file. In step S114, the data is stored in a mailbox of a transmission destination (reception user). The mail client 11 periodically accesses the mail gateway server 17 using the POP 3 and receives mail stored in the mail box.

  According to this embodiment, when the encrypted / signature mail is not completely decrypted (for example, when decryption fails or when encrypted mail encrypted n times is decrypted m (<n) times ), The decryption result report is set as the mail body, and the original encrypted / signed mail is attached as an attached file and delivered to the mail client 11. Therefore, the decryption result can be recognized on the mail client 11 side by reading the mail text. Further, since the mailer installed in the mail client 11 has a function of performing decryption / signature verification, the original encryption / signature mail can be decrypted by opening the attached file with the mailer. As a result, the decryption result at the time of relay by the mail gateway server 17 can be recognized on the mail client 11 side, and decryption / signature verification can be performed again on the mail client 11 side.

  Further, according to the present embodiment, when the encrypted / signature mail is encrypted a plurality of times, up to the point where the decryption is successful is attached as an attached file and distributed. In this case, since the attached encrypted / signature mail is decrypted partway, it is possible to reduce the load of decryption processing on the mail client 11 side.

  According to this embodiment, when signature verification fails in the mail gateway server 17, the verification result report is set as the mail body, and the original encrypted / signed mail is attached as an attached file and distributed to the mail client 11. Therefore, the mail client 11 side can recognize the signature verification result by reading the mail text. Further, since the mailer installed in the mail client 11 has a function of performing signature verification, the signature verification processing of the original encrypted / signed mail can be performed by opening the attached file with the mailer. As a result, the signature verification result at the time of relay can be recognized on the mail client 11 side, and signature verification can be performed again on the mail client 11 side.

  Further, according to the present embodiment, even when signature verification fails, if the signature is a clear signature, the original encrypted / signature email is delivered as the email body, so the email client 11 side The encrypted / signed mail can be displayed and checked as it is. Since the verification result report is distributed as an attached file, the signature verification result can be recognized by opening the attached file.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made. For example, in the above-described embodiment, the S / MIME system is used as the encryption / signature mail. However, the present invention is not limited to this and, for example, the PGP system can be used.

  Moreover, in the said embodiment, although the mail gateway server 16 (17) and the mail server 14 (15) were comprised as another hardware, you may comprise by one hardware.

It is a figure which shows the structural example of the electronic mail system containing the electronic mail relay apparatus which concerns on embodiment. It is a block diagram which shows the whole structure of the electronic mail relay apparatus which concerns on embodiment. It is a flowchart which shows the process sequence of the email delivery process by the email relay apparatus which concerns on embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,11 Mail client 12,13 Network multifunction device 14,15 Mail server 16,17 Mail gateway server 21 Memory | storage part 22 Encryption part 23 Decoding part 24 Signature part 25 Signature verification part 26 Report generation part 27 Transmission / distribution part

Claims (8)

An email relay device that relays email between a mail server and a mail client,
Decryption means for decrypting encrypted / signature mail received from the mail server;
Report generation means for generating a decoding result report of decoding processing by the decoding means;
If the encrypted / signed mail is not completely decrypted as a result of the decryption process, the decrypted result report generated by the report generating means is used as the mail body, and the original encrypted / signed mail is attached. An e-mail relay apparatus comprising: a distribution unit that distributes to the mail client.   The distribution means, when the encrypted / signature mail is encrypted a plurality of times, attaches and distributes an electronic mail at a stage where the decryption is successful as the original encrypted / signature mail The electronic mail relay device according to claim 1. Comprising signature verification means for verifying the signature of the encrypted / signed mail,
The report generation unit generates a verification result report of the signature verification process by the signature verification unit,
When the signature verification fails, the distribution unit distributes the verification result report generated by the report generation unit as an email body and distributes the original encrypted / signature email as an attached file to the email client. The electronic mail relay device according to claim 1 or 2, characterized in that   When the signature of the encryption / signature email is a clear signature, the delivery means delivers the original encryption / signature email as an email body and delivers the verification result report as an attached file to the email client. 4. The electronic mail relay device according to claim 3, wherein An email relay method for relaying email between a mail server and a mail client,
A decryption step of decrypting the encrypted / signature mail received from the mail server;
A report generation step of generating a decoding result report of the decoding process in the decoding step;
If the encrypted / signed mail is not completely decrypted as a result of the decryption process, the decrypted result report generated in the report generating step is used as the mail body, and the original encrypted / signed mail is attached. A distribution step of distributing to the mail client as an electronic mail relay method.   In the distribution step, when the encrypted / signature mail is encrypted a plurality of times, an electronic mail at a stage where the decryption is successful is attached and distributed as the original encrypted / signature mail. The e-mail relay method according to claim 5. A signature verification step for verifying the signature of the encrypted / signature email;
In the report generation step, a verification result report of the signature verification process in the signature verification step is generated,
In the distribution step, when the signature verification fails, the verification result report generated in the report generation step is used as an email body, and the original encrypted / signature email is delivered as an attachment to the email client. The e-mail relay method according to claim 5 or 6, characterized in that: In the distribution step, when the signature of the encrypted / signed mail is a clear signature, the original encrypted / signed mail is used as a mail body, and the verification result report is distributed as an attached file to the mail client. The e-mail relay method according to claim 7, wherein the e-mail is relayed.

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