JP2006287682A - E-mail distribution control method, system and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate only mail transmitted by malicious users without imposing a burden on a user without erroneously eliminating necessary mail at a server side. <P>SOLUTION: When controlling the distribution of e-mail transferred through a data network, an encryption key and a description key to be a pair of asymmetrical key encryption methods are generated, and e-mail including encryption information encrypted by using the encryption key is transmitted from a first mail server to a second mail server. The second mail server uses the decryption key to decrypt the encryption information of the received e-mail, authenticates the first mail server designated by the e-mail in accordance with a decryption result, and controls the distribution of the e-mail to a destination mail client designated by the e-mail in accordance with an authentication result. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to so-called junk mail filtering. The present invention also relates to delivery control of electronic mail (hereinafter simply referred to as mail), and relates to authentication of a mail transmission server by a mail reception server.

  With the spread of mail, mail that is not desired by recipients, so-called spam mail, is increasing. In order to cope with this, a technique for efficiently eliminating junk mail is required.

  In the prior art, there is a technique that eliminates junk mail by registering in advance a condition such as mail accepted by the user in a sorting system (see, for example, Patent Document 1). In addition, there is a database in which spam mail that has already been received is databased, it is determined whether or not it is spam mail according to the similarity to the received mail, and the spam mail is automatically deleted (see, for example, Patent Document 2).

JP-A-4-154340 JP 2003-348161 A

  According to the technique described in Patent Document 1, it is necessary for general users to consider rules for eliminating spam mail by themselves. However, since general users do not have detailed technical knowledge about mail delivery, it is difficult to set appropriate rules.

  According to the technique described in Patent Document 2, such a problem does not occur. However, if the header is tricked or the keyword is changed, the same filter cannot cope with it. Accordingly, it is necessary to continuously add / change filters. Further, if filtering is performed in the server filter, there is a possibility that even a mail necessary for the user may be deleted.

  The present invention has been made in view of such a situation, and the problem to be solved by the present invention is only a mail transmitted by a malicious user without erroneously removing a necessary mail on the server side. Is to provide a technique that can be eliminated without burdening the user.

  Moreover, the other subject of this invention is providing the technique which can confirm the mail server of a transmission source.

  In order to solve the above-described problems, the present invention provides the following techniques.

  That is, the present invention relates to a method for controlling delivery of an electronic mail transferred via a data network, wherein a key pair generating step of generating an encryption key and a decryption key which are a key pair of an asymmetric key encryption method using a computer A mail sending stage for sending an e-mail containing encrypted information encrypted by the first mail server using an encryption key from the first mail server to the second mail server, and the second mail server, A decryption step of decrypting the encrypted information of the received electronic mail using the decryption key, and an authentication step in which the second mail server authenticates the first mail server designated for the electronic mail according to the decryption result And a second mail server including a delivery control stage for controlling delivery of the e-mail to the destination mail client designated in the e-mail according to the authentication result. Door to provide an electronic mail delivery control method according to claim.

  The encryption information is information obtained by encrypting a part or all of the header of the email in the mail transmission stage, and the authentication stage includes part or all of the header obtained by decrypting the encryption information in the decryption stage, and The consistency may be determined based on the header of the electronic mail received by the second mail server, and authentication may be performed according to the determination result.

  For example, the encryption information may be encrypted information including at least one of a mail ID, a sender name, and a transmission time as a part of the header.

  The delivery control step may control delivery of the email depending on whether or not encryption information is included in the email received from the first mail server in addition to the authentication result.

  Either one of the decryption key and the encryption key may be distributed to a predetermined server via a key distribution server on the network.

  The encryption key may be registered in the mail transmission server, and the decryption key may be distributed via the key distribution server.

  In addition, according to the present invention, in a computer program for causing a computer to execute processing for transmitting an electronic mail to the other mail server, a part or all of a header of the mail to be transmitted is transferred to one of the key pairs of the asymmetric key cryptosystem. A process for generating encrypted information encrypted using the encryption key, a process for adding the encrypted information to the header, and a process for transmitting the e-mail with the encrypted information to the server specified in the header. A mail transmission server program characterized by causing a computer to execute the above.

  Further, the present invention provides a computer program for causing a computer to execute processing for receiving an e-mail from the other mail server, in a predetermined authentication field of a header of the received mail, one of the key pairs of the asymmetric key cryptosystem. A process for determining whether or not encryption information encrypted using an encryption key is stored, a process for specifying the mail server of the transmission source based on the header when the encryption information is stored, and a specification Processing for retrieving a decryption key associated with the mail server in advance, processing for decrypting encryption information using the decryption key when the retrieval of the decryption key is successful, a decryption result, and a predetermined field of the header And a computer that executes a process of authenticating the server that sent the mail. To provide a gram.

  According to the present invention, in a computer program that operates in cooperation with a mail server via a data network, one first key that is one of the asymmetric key encryption key pairs is associated with one mail transmission server. And a process of transmitting the other first registered key to a mail receiving server related to receiving an e-mail addressed to a mail address that sends a mail via the registered mail transmitting server. And a key distribution server program characterized by causing a computer to execute.

  Also provided is a computer comprising a computer-readable recording medium storing the above-described computer program and operating according to the computer program.

  The present invention also relates to a system for controlling delivery of an electronic mail transferred via a data network, using a computer that generates an encryption key and a decryption key that are a key pair of an asymmetric key encryption method, and an encryption key. A first mail server that generates and transmits an electronic mail including encrypted encryption information, receives the electronic mail from the first mail server, decrypts the encrypted information of the electronic mail using a decryption key, and decrypts the result. A second mail server that authenticates the first mail server specified for the e-mail according to the e-mail and controls delivery of the e-mail to the destination mail client specified for the e-mail according to the authentication result; An electronic mail delivery control system is provided.

  According to the present invention, a spam mail can be filtered without setting complicated filtering rules by a user who does not have knowledge. Because the mail receiving server performs different processing for mail depending on whether or not the source server is unguaranteed, the user only has to select whether or not to sort mail sent from an untrusted server This is because spam mail can be filtered.

  In addition, the filtering of the present invention uses only the information of the sender mail server used by the user who sent it without using keywords and the like, and the filtering target keyword was included in the email sent from a trusted party Undesirable operations such as accidental deletion on the server side are eliminated.

  A mail delivery control method according to an embodiment of the present invention will be described with reference to FIG.

  First, the administrator of the transmission server uses a computer to generate an encryption key and a decryption key that are public key (asymmetric key encryption) key pairs, registers the encryption key in the transmission server as a secret key, and sets the decryption key. Publish. The administrator of the receiving server who trusts the transmitting server registers the decryption key in the receiving server as a public key. Release may be limited to some people. For example, it may be disclosed only between administrators who trust each other.

  When transmitting mail, the transmission server acquires a predetermined field of the header of the electronic mail to be transmitted. Here, it is assumed that a mail ID field, a sender name field, and a transmission time field are acquired (procedure 1). The transmission server encrypts a part of the acquired header using an encryption key registered in advance. The partial header encrypted here is called encryption information. Further, the transmission server adds encryption information to a predetermined field of the header (procedure 2). This field is called an authentication field. In this way, the transmission server transmits the mail storing the encryption information in the authentication field to the reception server.

  The receiving server that has received the mail checks for the presence of an authentication field. If there is no authentication field, it is processed as unauthenticated mail. If there is an authentication field, the receiving server identifies the sending server from the mail header. If the identified transmission server is trusted by the reception server administrator, the decryption key of the transmission server is registered in advance as described above, so that the decryption of the encryption information is attempted using this (procedure 3). . The value obtained by decrypting the encryption information in this way is compared with the values obtained from the header's mail ID field, sender name field, and transmission time field (procedure 4) to confirm consistency. By storing encrypted information copied from the header of an untrusted sending server even if there is an authentication field, or from the header of a legitimately sent mail from a trusted sending server in the authentication field, the sending server can be spoofed. The attempted mail can be detected by this determination. If they match, it is processed as an email sent from a trusted sending server. If they do not match, they are processed as unauthenticated mail or mail spoofing the sending server.

  Here, the encryption key is a secret key and the decryption key is a public key, but conversely, the encryption key may be a public key and the decryption key may be an encryption key. In that case, the encryption key is made public among the administrators who trust each other, the transmission server generates the authentication information using the encryption key selected according to the reception server, and the reception server uses the decryption key of itself to generate the authentication information. It will be decrypted.

  With reference to FIG. 2, the junk mail elimination system 100 in this invention which is one Example of this invention is demonstrated. The spam mail rejection system 100 is connected to each other via a mail transmission server 1, a mail reception server 2, an authentication information management server 3, and a network 4 such as the Internet. Users 5 and 6, that is, mail clients are connected to the mail transmission server 1 and the mail reception server 2, respectively.

  As shown in FIG. 3, it is assumed that the mail transmission server 1 and the mail reception server 7 perform transmission / reception of mail using the same mail address used by the user 5. The administrator of the mail transmission server 1 generates a key pair of an asymmetric key encryption method, an encryption key A and a decryption key A in advance using a computer, and registers the encryption key A in the mail transmission server 1 while managing authentication information. The server 3 is requested to register the decryption key A. The computer that generates the key pair may be the mail transmission server 1. When the request is approved, the authentication information management server 3 registers the decryption key A in the decryption key database 321 and gives the access key to the decryption key database 321 to the reception key database 223. As a result, the reception key database 223 can obtain other decryption keys B to Z that are already registered, and at the same time, the decryption key registered in the future decryption key database 321 can be obtained.

  Referring to FIG. 4, the mail transmission server 1 includes a mail input unit 13, an encryption key attachment unit 12, and a mail transmission unit 11. First, the mail input unit 13 receives mail as input from the user 5 (step S1). Next, the encryption key attachment unit 12 acquires from the mail ID field, the sender name field, and the transmission time field of the header of the mail received from the user 5 (step S2), and the acquired value is registered in its own encryption. Encryption information is generated by encryption using the key (step S3) and stored in the authentication field of the header (step S4). Then, the mail having the encryption information stored in the authentication field is transmitted from the mail transmitting unit 11 to the mail receiving server 2 as the transmission destination via the network 4 (step S5).

  The mail receiving server 2 will be described with reference to FIGS. The mail receiving server 2 includes a mail receiving unit 21, an encryption information collating unit 22, and a mail sorting unit 23. The cipher information verification unit 22 includes an information separation unit 221, an information analysis unit 222, a reception key database 223, and a header information comparison unit 224. The administrator of the mail receiving server 2 registers in advance in the authentication information management server 3 a decryption key that forms a key pair with the encryption key registered in the mail transmitting server 1 ′ (not shown) used by the same user as the mail receiving server 2. It is assumed that the reception key database 223 registers the decryption key of another mail transmission server guaranteed by the authentication information management server 3.

  The mail receiving server 2 receives mail via the mail receiving unit 21 (step T1). The received mail is checked by the encryption information matching unit 22 to see if it is from a guaranteed server. The information separation unit 221 first checks whether there is an authentication field in the header of the received mail (step T2), and if not, the mail distribution unit 23 is processed so that it is processed as a mail not guaranteed by the authentication information management server 3. In response to this, the mail distribution unit 23 performs a predetermined process for the unguaranteed mail on the mail (step T3). The processing here is, for example, adding a predetermined character string to the subject (eg, adding a character string of “Unguaranteed:” at the beginning of the subject), discarding the mail, discarding the mail to the sender or source server Notifications and emails.

  When there is an authentication field, the information separation unit 221 extracts encryption information from the header (step T4). The information analysis unit 222 identifies the transmission source server from the header (step T5), and inquires of the reception key database 223 whether or not the decryption key of the identified server has been registered (step T6). If it is not registered, the mail distribution unit 23 is notified so as to process it as a mail not guaranteed by the authentication information management server 3 as in step T2, and the mail distribution unit 23 performs a predetermined process (step T3). ). If registered, the information analysis unit 222 decrypts the encrypted information using the decryption key (step T8).

  Subsequently, the header information comparison unit 224 compares the decoding result of step T8 with the header information and confirms whether they match (steps T9 and T10). If not matched, the process proceeds to step T3. If matched, a predetermined process is performed as a mail transmitted from a guaranteed server (step T11). This process is, for example, to deliver the mail in response to a request from the mail client as in the conventional mail receiving server.

  The authentication information management server 3 will be described with reference to FIG. First, a mail server administrator who wants to receive a guarantee registers a connection application and a decryption key in the connection management unit 31. When the connection application is accepted, the right to connect to the key distribution unit 32 is given. The mail server that has obtained this right can connect to the key distribution unit 32 and obtain the decryption keys of all currently guaranteed mail servers. When a new mail server guaranteed by the authentication information management server 3 is newly added, the key distribution unit 32 distributes the newly guaranteed mail server decryption key to the mail server that has already been guaranteed. The key distribution unit 32 includes a decryption key database (not shown) that stores the correspondence between the decryption key and the guaranteed mail server.

  Next, a process in which the authentication information management server 3 cancels the guarantee of the server once guaranteed will be described. This process is used when, for example, a server having a user who sends a junk mail is confirmed among the guaranteed servers, and the guarantee is canceled. First, a mail server whose guarantee is to be canceled is notified to the key distribution unit 32 via the connection management unit 31. Next, the key distribution unit 32 deletes the decryption key of the mail server from the decryption key database, and instructs all guaranteed mail servers to delete the decryption key of the mail server. Then, the mail receiving server 2 that has received the deletion instruction deletes the decryption key from the reception key database 223. In this way, the guarantee of the server that once received the guarantee is canceled.

  As a neutral third-party organization, an organization such as an SSL certificate authority will be established, and this third-party organization will operate an authentication information management server. The third-party organization examines the mail server for which a guarantee is required, exchanges a pledge and a contract with the administrator of the mail server, and guarantees the mail server. As the contents of the contract, it is conceivable to describe compensation for allowing a user to send a spam mail. When the administrator of the mail server makes a contract with the user, it incorporates in the contract that no spam mail is issued. Indirectly, a mail server guarantee system contract is established with the user, and a pseudo network is created only for the user who does not send spam mail.

  On this basis, the administrator of the mail server who receives the guarantee switches the server software. Thereby, even if an e-mail transmitted from a non-guaranteed mail server reaches the guaranteed mail server, it can be automatically sorted by the mail server.

  The present invention has been described above based on the embodiments. However, the present invention is not limited to this, and it is needless to say that modifications and improvements can be made within the ordinary knowledge of those skilled in the art. .

  For example, in the above-described first embodiment, the mail transmission server 1 encrypts using its own encryption key, and the mail reception server 2 identifies the mail transmission server 1 based on the header of the received mail and assigns a corresponding decryption key. As a result, the authentication information management server 3 disclosed the decryption key. That is, the decryption key is disclosed and the encryption key is kept secret. On the other hand, the encryption key may be disclosed and the decryption key may be kept secret.

  That is, referring to FIG. 2, the authentication information management server 3 registers and discloses the encryption key, and the mail transmission server 1 selects a corresponding one of the encryption keys disclosed according to the mail receiving server 2 as the destination. Then, the mail receiving server 2 performs decryption using its own decryption key. In this case, the encryption information attachment unit 12 includes a table in which the correspondence relationship between the plurality of mail reception servers 2 and the encryption keys of the respective mail reception servers 2 is received and received from the authentication information management server 3, while the information analysis unit Since 222 always uses the same decryption key, the decryption key database 223 becomes unnecessary.

It is a figure for demonstrating the mail delivery control method which is one embodiment of this invention. 1 is a block diagram for explaining a junk mail elimination system 100 as an embodiment of the present invention, focusing on mail transmission / reception. FIG. FIG. 2 is a block diagram for explaining the arrangement relation between the encryption key and the decryption key with respect to the spam mail rejection system 100 according to the embodiment of the present invention. 5 is a flowchart for explaining processing in which the mail transmission server 1 transmits mail to the mail reception server 2 in response to an input from a user 5. 3 is a block diagram of the mail receiving server 2. FIG. 4 is a flowchart for explaining the operation of the mail receiving server 2. 3 is a block diagram of an authentication information management server 3. FIG.

Explanation of symbols

1 Mail sending server 2, 7 Mail receiving server 3 Authentication information management server 4 Internet 5, 6 User (mail client)
DESCRIPTION OF SYMBOLS 11 Mail transmission part 12 Encryption information attachment part 13 Mail input part 21 Mail reception part 22 Encryption information collation part 23 Mail distribution part 31 Key distribution part 32 Connection management part 221 Information separation part 222 Information analysis part 223 Reception key database 224 Header information comparison 321 Decryption key database

Claims (19)

In a method for controlling delivery of emails transferred over a data network,
A key pair generation stage for generating, using a computer, an encryption key and a decryption key which are key pairs of an asymmetric key encryption method;
A mail transmission step of transmitting an electronic mail including encryption information encrypted by the first mail server using the encryption key from the first mail server to the second mail server;
A decryption step in which the second mail server decrypts the encrypted information of the received email using the decryption key;
An authentication stage in which the second mail server authenticates the first mail server designated in the electronic mail according to the decryption result;
An e-mail delivery control method, wherein the second mail server includes a delivery control step of controlling delivery of the e-mail to a destination e-mail client designated in the e-mail according to the authentication result; . The e-mail delivery control method according to claim 1,
The encryption information is information obtained by encrypting a part or all of the header of the email in the email transmission stage,
The authentication step determines consistency based on a part or all of the header obtained by decrypting the encryption information in the decryption step and the header of the email received by the second mail server. And an e-mail delivery control method, wherein authentication is performed according to the determination result.   3. The electronic mail delivery control method according to claim 2, wherein the encrypted information is encrypted information including at least one of a mail ID, a sender name, and a transmission time as a part of the header. E-mail delivery control method.   2. The electronic mail delivery control method according to claim 1, wherein the delivery control step depends on whether or not the encryption information is included in an electronic mail received from the first mail server in addition to the authentication result. Then, the electronic mail delivery control method characterized by controlling the electronic mail delivery.   2. The electronic mail delivery control method according to claim 1, wherein either one of the decryption key and the encryption key is delivered to a predetermined server via the key delivery server on the network. Delivery control method.   6. The electronic mail delivery control method according to claim 5, wherein the encryption key is registered in a mail transmission server, and the decryption key is delivered via the key delivery server. In a computer program for causing a computer to execute processing for transmitting an e-mail to the other mail server,
A process of generating encryption information obtained by encrypting a part or all of a header of an email to be transmitted using an encryption key that is one of the key pairs of an asymmetric key encryption method;
Processing to add the cryptographic information to the header;
A mail transmission server program for causing a computer to execute a process of transmitting an electronic mail to which the encryption information is added to a server specified in the header.   8. The mail transmission server program according to claim 7, wherein the encryption information is encrypted information including at least one of a mail ID, a sender name, and a transmission time as a part of the header. Mail transmission server program. In a computer program for causing a computer to execute processing for receiving an electronic mail from the other mail server,
A process for determining whether or not encryption information encrypted using an encryption key that is one of the key pairs of the asymmetric key encryption method is stored in a predetermined authentication field of the header of the received mail;
When the encryption information is stored, a process for identifying a mail server of a transmission source based on the header;
A process of searching for a decryption key associated in advance with the specified mail server;
When the retrieval of the decryption key is successful, a process of decrypting the encryption information using the decryption key;
A mail receiving server program for causing a computer to execute a process of comparing the decryption result with a predetermined field of the header and authenticating a server that is a source of the mail.   10. The mail receiving server program according to claim 9, further causing a computer to execute processing for controlling delivery of the e-mail according to a result of the authentication processing.   In the mail receiving server program according to claim 9, according to a result of determining whether or not encryption information encrypted using the encryption key is stored in the authentication field of a received mail header, A mail receiving server program for causing a computer to further execute processing for controlling delivery of electronic mail.   10. The mail receiving server program according to claim 9, wherein a decryption key and a decryption key associated with the decryption key are registered from a key distribution server that registers a decryption key that is one of the key pairs of the asymmetric key encryption method in association with the other mail server. A mail receiving server program for causing a computer to further execute a process of receiving, via a network, information specifying a designated mail server. In a computer program that operates in cooperation with a mail server via a data network,
A process of registering one first key which is one of the key pairs of the asymmetric key encryption method in association with one mail transmission server;
A process of transmitting the registered first key to the mail receiving server related to the reception of the e-mail addressed to the mail address that sends the mail through the registered mail sending server is executed on the computer. A key distribution server program characterized in that   A computer comprising a computer-readable recording medium on which the computer program according to any one of claims 7 to 13 is recorded and operating according to the computer program. In a system that controls the distribution of emails transferred over a data network,
A computer that generates an encryption key and a decryption key that form a key pair of an asymmetric key encryption method;
A first mail server that generates and transmits an electronic mail containing encrypted information encrypted using the encryption key;
The first mail server that receives the electronic mail from the first mail server, decrypts the encryption information of the electronic mail using the decryption key, and is designated in the electronic mail according to the decryption result And a second mail server that controls the delivery of the e-mail to the destination mail client specified in the e-mail according to the authentication result. The electronic mail delivery control system according to claim 15,
The encryption information is information obtained by encrypting a part or all of the header of the email in the email transmission stage,
The authentication step determines consistency based on a part or all of the header obtained by decrypting the encryption information in the decryption step and the header of the email received by the second mail server. And an e-mail delivery control system, wherein authentication is performed according to the determination result.   The electronic mail delivery control system according to claim 16, wherein the encrypted information is encrypted information including at least one of a mail ID, a sender name, and a transmission time as a part of the header. E-mail delivery control system.   16. The electronic mail delivery control system according to claim 15, wherein the second mail server determines whether or not the encryption information is included in an electronic mail received from the first mail server in addition to the authentication result. And an electronic mail delivery control system for controlling the delivery of the electronic mail according to the above. The electronic mail distribution control system according to claim 15, further comprising a key distribution server that distributes the decryption key to the second mail server.

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