JP6337472B2 - Fraudulent email detection device - Google Patents

Description

  The present invention relates to an unauthorized mail detection program, a detection method thereof, and a detection device thereof.

  In recent years, targeted attacks targeting specific companies and personal computers have increased rapidly, and in particular, targeted attacks by illegal e-mails (hereinafter referred to as targeted attack emails) against companies and government agencies. It is increasing rapidly. Targeted attack e-mail is a virus e-mail sent to specific companies or organizations for the purpose of stealing confidential information. Personal information is leaked by opening an attachment with a malicious code. Unauthorized acts such as

  In conventional anti-virus software, malicious program verification information about problematic programs is registered as a signature, and infection is prevented by detecting matching information. However, such anti-virus software does not work for attack emails that use programs without signatures. Furthermore, with anti-virus software, the attached files and text are skillfully created and it is difficult to understand at first glance that they are suspicious. In addition, there is a limit for each user to strictly check the consistency of e-mail header, attached file, body text, sender address, and the like.

  There is a transmission domain authentication as a conventional countermeasure technique. This is a technology that realizes the validity of the outgoing mail server and the trail of the outgoing route on a server basis. Specifically, the domain of the e-mail address is checked, whether or not the e-mail is transmitted from a legitimate server, and the sender's address is proved to be legitimate.

  There are two main types of sender domain authentication: authentication by IP address and authentication by electronic signature. The former is SPF (Sender Policy Framework) and Sender ID, and the relationship (SPF record) between the domain of the email server and the IP address of the sender is disclosed to the DNS (Domain Name System) server. Confirm that the sender's address is legitimate by inquiring and verifying the DNS server. Details of this technique are disclosed in Non-Patent Document 1, for example.

  The latter is DKIM (Domain Keys Identified Mail), which publishes the public key information of the e-mail server to the DNS server, adds an electronic signature with the private key, sends the e-mail, and inquires the DNS server for the public key information when receiving it. By verifying the electronic signature, it is confirmed that the sender's address is authentic. For example, it is disclosed in Non-Patent Document 2.

  On the other hand, as a technique for taking measures on a client basis without using a server, the sending terminal encrypts the header information and body information of the email with secret information that the attacker cannot know, generates verification information, It has been proposed that a reception terminal regenerates similar verification information added to the header of an electronic mail to be transmitted, and compares the verification information with the verification information added to the header of the received electronic mail. For example, it is patent document 2. FIG.

International Publication No. 2005/067199 Japanese Patent Application No. 2012-108092 (Japanese Patent Laid-Open No. 2013-235463)

Sender Policy Framework Project Overview, Internet <http: // www. openspf. org /> DKIM. org, Internet <http: // www. dkim. org />

  However, in the case of targeted attack mail, the sender address is also spoofed, and it is spoofed as if it was sent using a legitimate server. Therefore, the identity cannot be ensured by checking the source address by the conventional method. In addition, it is necessary to install a DNS server for detecting the targeted attack mail, which increases the operation cost.

  Further, in the example where the client base is realized, if the secret information used for generating and verifying the identification information is leaked to the attacker, the targeted attack mail cannot be determined. Therefore, there is a problem that the security against leakage of confidential information is low.

  In one aspect, an object of the present invention is to provide a fraudulent mail detection program, a detection method thereof, and a detection apparatus thereof capable of more safely detecting fraudulent mail such as targeted attack mail on a client basis.

In one embodiment, the updated secret key information and the secret key version information of the updated secret key information are added to the updated old secret key information and the old secret key version information of the old secret key information. Update procedure of private key information to be saved,
A generated secret key information generation procedure for generating generated secret key information from a plurality of secret key information in a predetermined combination and secret information in the organization that is kept secret outside the organization;
A verification information generation procedure for generating verification information from the generated secret key information and the information included in the outgoing mail;
A feature information generation procedure for generating feature information of the secret key version information from the secret key version information of the plurality of secret key information in the predetermined combination and the secret information in the organization;
A combination verification information addition procedure for adding combination verification information, which is a combination of the verification information and feature information of the secret key version information corresponding to the verification information, to the outgoing mail;
A generated secret key information regeneration procedure for regenerating generated secret key information from a plurality of secret key information in the predetermined combination and the in-organization secret information;
A verification information regeneration procedure for regenerating verification information from the generated secret key information and the information included in the received mail;
A feature information regeneration procedure for regenerating the feature information of the secret key version information from the secret key version information of the plurality of secret key information in the predetermined combination and the secret information in the organization;
Verify whether the combination verification information obtained by combining the regenerated verification information and the feature information of the secret key version information corresponding to the verification information matches the combination verification information added to the received mail. A malicious mail detection program that causes a computer to execute a verification procedure.

  Even if some private key information is leaked, it is possible to detect fraudulent mail safely.

It is a figure which shows the whole structure of the electronic mail terminal etc. in this Embodiment. It is a block diagram of the mail checker management terminal 2 which an administrator uses. 3 is a configuration diagram of a common information generation device 22 and a secret information generation device 23 in the mail checker management terminal 2. FIG. It is a block diagram of the electronic mail transmission terminal which a sender uses. It is a block diagram of a combination verification information generation apparatus. It is a block diagram of the electronic mail receiving terminal which a receiver uses. It is a block diagram of a verification apparatus. It is a flowchart figure of the pre-processing by a mail checker terminal device. It is a figure which shows the example of an e-mail information item, and the example of a secret key information generation pattern. It is a flowchart figure of the pre-processing by an email transmission terminal and a receiving terminal. It is a figure which shows the storage state of the secret information in a transmission / reception terminal. It is a figure which shows the storage state of the secret information in a transmission / reception terminal. It is a figure which shows the storage state of the secret information in a transmission / reception terminal. 10 is a flowchart of a combination verification information generation process in the combination verification information generation device 32. It is a flowchart figure of the verification process of the combination verification information in the verification apparatus 62. FIG. It is a figure which shows the production | generation process of the combination verification information in this embodiment. It is a figure which shows the detail of the production | generation process of the combination verification information in 1st Embodiment. It is a flowchart figure of the production | generation process of combination verification information. It is a figure explaining the verification process of an electronic mail receiving terminal. It is a figure which shows the detail of the verification process in a verification means. It is a flowchart figure of a verification process. It is a figure which shows the detail of the production | generation process of the combination verification information in this Embodiment. It is a flowchart figure of the production | generation process of combination verification information. It is a figure which shows the detail of the verification process of the combination verification information in 2nd Embodiment. It is a flowchart figure of a verification process. It is a figure which shows the detail of the production | generation process of the combination verification information in 3rd Embodiment. It is a figure which shows the detail of the verification process of the combination verification information in 3rd Embodiment. It is a schematic flowchart figure of the production | generation process of the combination verification information by the mail checker of an electronic mail transmission terminal. It is a schematic flowchart figure of the verification process by the mail checker of an electronic mail receiving terminal. It is a figure which shows schematic structure of a mail checker management terminal, an electronic mail transmission terminal, and a receiving terminal.

[Outline of this embodiment]
FIG. 1 is a diagram showing an overall configuration of an electronic mail terminal or the like in the present embodiment. The overall configuration includes an e-mail transmission terminal 3, a transmission mail server 4, a reception mail server 5, and an e-mail reception terminal 6 that can be communicably connected via a network 1 such as the Internet or an intranet. Furthermore, it has the mail checker management terminal 2 which an administrator operates.

  FIG. 30 is a diagram illustrating a schematic configuration of a mail checker management terminal, an electronic mail transmission terminal, and a reception terminal. Each terminal has a CPU, a RAM, an input / output device I / O, communication devices 24, 34, 65, and a storage medium for storing a program, such as an HDD. The program storage media 24, 34, and 65 store a mailer that is a mail program, a mail checker program, a general OS, and the like.

  First, in a preparation stage for introducing an illegal mail checker, a mail checker program for detecting illegal mail is installed in the electronic mail sending terminal 2 and the electronic mail receiving terminal 6. In addition, the administrator sends in-house secret information (first secret information), which is secret information unique to the organization that is not disclosed outside the organization, such as a company or government office, to the sender and receiver who are members in the organization in advance. Notice. Furthermore, the administrator distributes the secret key information (second secret information) and the secret key version information to the sender and the receiver who are members in the organization regularly or irregularly. In this distribution, each version of the private key information and its private key version information is encrypted with, for example, the internal secret information and sent to each e-mail terminal by attaching it to an e-mail or the like. The received e-mail terminal stores it in the terminal. This secret key version information is used for determining whether the secret key information matches between the transmitting and receiving terminals. The administrator manages the version of the secret key information. Preferably, each e-mail terminal receives the new version of the secret key information and the secret key version information, and updates the old secret key information with the latest secret key information and secret key version information up to a predetermined number. Add to the information and private key version information and save. The upper limit can be arbitrarily set by the administrator. In the following description, the case where the upper limit number is 3 will be described as an example.

  Next, the process at the e-mail transmission terminal will be outlined.

  FIG. 28 is a schematic flowchart of combination verification information generation processing by the mail checker of the electronic mail transmitting terminal. The mail checker in the e-mail transmission terminal 3 has a single or a plurality of generated secrets based on a plurality of secret key information selected from a plurality of stored secret key information by a predetermined combination and in-organization secret information. Key information is generated (S5013_a). A secret key information generation pattern defining a predetermined combination is notified and stored from the mail checker management terminal 2 to each of the electronic mail terminals 3 and 6 at the preparation stage. The secret key information generation pattern defines a single or a plurality of combinations for a plurality of stored secret key information. Thereby, the mail checker generates single or plural pieces of generated secret key information.

  As described above, the mail checker management terminal 2 encrypts the latest secret key information and secret key version information updated regularly or irregularly with the in-organization secret information and transmits the encrypted information to the electronic mail terminal. Thereby, all the electronic mail terminals hold the same plurality of secret key information and version information thereof. However, in the case of a large organization, it may be assumed that all e-mail terminals have not received and stored all updated secret key information and its version information. As a result, the versions of the plurality of stored secret key information may be different between the e-mail transmission terminal and the reception terminal. Therefore, the secret key information generation pattern has a combination pattern of a plurality of secret key information, such as a pattern using all secret key information and a pattern using a part of a plurality of secret key information. The administrator determines which secret key information generation pattern is selected based on the individual circumstances of each organization.

  Further, the mail checker generates single or plural verification information from the generated secret key information and the transmitted mail information (for example, header, text, attached file, etc.) (S5013_b). The mail checker generates a single verification information when only a single generated secret key information is generated, and generates a plurality of verification information correspondingly when a plurality of generated secret key information is generated. . The mail checker management terminal 2 sends in advance an e-mail information item that defines which information of the outgoing mail is generated with the generated secret key information to the e-mail terminal for storage.

  Further, the mail checker generates feature information of single or plural secret key version information from secret key version information of a plurality of secret key information in a predetermined combination and in-organization secret information (S5013_c). The mail checker generates feature information of a single secret key version information when there is a single predetermined combination defined in the secret key generation pattern, and if there are multiple combinations, Generate feature information. The secret key version information of the plurality of secret key information is preferably the secret key version information of the latest secret key information of the latest version among the plurality of secret key information. The feature information of the secret key version information may be information that can identify the version of the secret key information. The feature information of the secret key version information is used to extract the version of verification information common between transmission and reception.

  Furthermore, the mail checker generates single or multiple combination verification information by combining single or multiple verification information and feature information of single or multiple private key version information corresponding to the verification information, respectively. Append to sent mail (S5013_d). Then, the e-mail transmission terminal 3 transmits a transmission mail to which the combination verification information is added.

  Next, the process at the e-mail receiving terminal will be outlined.

  FIG. 29 is a schematic flowchart of the verification process by the mail checker of the electronic mail receiving terminal. The e-mail receiving terminal 6 receives an e-mail. After reception, the mail checker in the e-mail receiving terminal 6 is configured as a single or a plurality of secret key information selected from a plurality of stored secret key information by a predetermined combination and in-organization secret information. A plurality of generated secret key information is regenerated (S6015_a).

  Further, the mail checker regenerates single or plural verification information from the generated secret key information and the information of the transmitted mail (for example, header, text, attached file, etc.) (S6015_b).

  Further, the mail checker regenerates the feature information of the single or plural secret key version information from the secret key version information of the plurality of secret key information in a predetermined combination and the secret information in the organization (S6015_c). .

  Further, the mail checker regenerates single or multiple combination verification information by combining single or multiple verification information and feature information of single or multiple private key version information corresponding to the verification information, respectively. (S6015_d). The above steps S6015_a to S6015_d are the same as steps S5013_a to S5013_d in FIG.

  Finally, the mail checker of the e-mail receiving terminal simply combines the regenerated single or plural verification information and the characteristic information of the single or plural secret key version information corresponding to the verification information. It is verified whether one or a plurality of combination verification information matches one or a plurality of combination verification information added to the received mail (S6017_a). If there is a single combination verification information, it is verified whether the regenerated single combination verification information matches the single combination verification information added to the received mail. If there are a plurality of pieces of combination verification information, the comparison target is changed to verify whether any of the comparison targets match.

  If there is no matching combination verification information, the mail checker notifies the recipient of an illegal mail (S6017_b).

  As described above, verification information is generated by combining a plurality of secret key information that is updated regularly or irregularly, so even if one secret key information leaks to a malicious third party, this embodiment This mail checker can detect illegal mail. In addition, even if the versions of multiple private key information stored between e-mail terminals are different, if multiple private key information that is partially duplicated is stored, the mail checker detects illegal mail. Can do.

[First Embodiment]
Hereinafter, the first embodiment will be described. First, the configuration and operation of the mail checker in the first embodiment will be described. Further, generation of combination verification information by the mail checker of the electronic mail sending terminal 3 in the first embodiment, and the electronic mail receiving terminal 6 The verification process by the mail checker will be described in detail.

  The overall configuration of the electronic mail terminal and the like in the present embodiment is as described with reference to FIG.

  Next, FIG. 2 is a configuration diagram of the mail checker management terminal 2 used by the administrator. The mail checker management terminal 2 includes management software 21 used for introducing the mail checker, generation of combination verification information by the mail checker, and common information generation device 22 for generating common information used at the time of verification. A secret information generating device 23 that performs generation and a communication device 24 that performs communication with the network 1 are included.

  FIG. 3 is a configuration diagram of the common information generation device 22 and the secret information generation device 23 in the mail checker management terminal 2. As shown in the upper part of FIG. 3, the common information generation device 22 includes a request reception unit 221 and a common information generation unit 222.

  The request receiving unit 221 receives a request for a common information generation request, and returns the generated common information C. The request receiving unit 221 includes an input / output unit 2211. The common information generation unit 222 generates common information in response to the common information generation request. Common information here is an e-mail information item that defines e-mail information (combination of header, body, attached file, etc.) used when the sender's mail checker generates verification information, and multiple secrets. It is a secret key information generation pattern that defines a combination of key information. The common information generation unit 222 includes a common information generation unit 2221.

  As shown in the lower part of FIG. 3, the secret information generating device 23 includes a request receiving unit 231 and a secret information generating unit 232.

  The request reception unit 231 receives a request for a secret information generation request and returns the generated secret information S. The request receiving unit 231 includes an input / output unit 2311. The secret information generation unit 232 generates secret information. The secret information here refers to in-organization secret information, secret key information, and secret key version information. The secret information generation unit 232 has a secret information generation unit 2321.

  FIG. 4 is a configuration diagram of an electronic mail transmission terminal used by the sender. The e-mail transmission terminal 3 generates e-mail software 31 for sending an e-mail and sending instructions from the sender, and generates “verification information” as information for confirming whether or not there is a possibility of a target e-mail. A combination verification information generation device 32 that performs the communication, and a communication device 34 that transmits an electronic mail to the transmission mail server 4. The e-mail software 31 corresponds to, for example, a mailer such as Microsoft Outlook or Mozilla Thunderbird.

  FIG. 5 is a configuration diagram of the combination verification information generation apparatus. The combination verification information generation device 32 includes a request reception unit 321, a common information management unit 322, a secret information management unit 323, and a combination verification information generation unit 324.

  The request receiving means 321 receives a request for a request for generating combination verification information, and returns the generated combination verification information. The request reception unit 321 has an input / output unit 3211. The common information management unit 322 manages the common information of the e-mail information item and the secret key information generation pattern. The common information management unit 322 includes an e-mail information item storage unit 3221 and a secret key information generation pattern storage unit 3222 that store e-mail information items that define items such as an e-mail header, text, and attached file. The secret information management unit 323 handles secret information used when generating combination verification information. The secret information management means 323 includes an intra-organization secret information storage unit 3231 and a secret key information storage unit 3232 that stores secret key information and version information thereof. The combination verification information generation unit 324 generates combination verification information and adds it to the transmitted mail. The combination verification information generation unit 324 includes a feature amount information generation unit 3241, a combination verification information generation unit 3242, and a header information addition unit 3243.

  FIG. 6 is a configuration diagram of an e-mail receiving terminal used by the recipient. The e-mail receiving terminal 6 includes an e-mail software 61 in which a recipient issues an e-mail receiving instruction, a verification device 62 for verifying verification information, a mail checker 63 that mediates between the e-mail software 61 and the received mail server 5, A display device 64 that clearly indicates the verification result to the recipient, and a communication device 65 that receives an email from the received mail server 5 are provided. The e-mail software 61 corresponds to, for example, a mailer such as Microsoft Outlook or Mozilla Thunderbird, similarly to the e-mail transmission terminal 3.

  FIG. 7 is a configuration diagram of the verification apparatus. The verification device 62 includes a request reception unit 621, a common information management unit 622, a secret information management unit 623, and a verification unit 624.

  The request reception unit 621 receives a request for verification of combination verification information and returns a verification result. The request receiving unit 621 has an input / output unit 6211. The shared information management unit 622 manages shared information used when verifying combination verification information. The shared information management unit 622 includes an e-mail information item storage unit 6221 and a secret key information generation pattern storage unit 6222.

  The secret information management means 623 manages secret information used when verifying combination verification information. The secret information management unit 623 includes an intra-organization secret information storage unit 6231 and a secret key information storage unit 6232. The verification unit 624 generates combination verification information and feature amount information from the combination of the electronic data information item and the secret key information, and verifies the combination verification information. The verification unit 624 includes a combination verification information generation unit 6241 and a verification unit 6242.

  The process flow of the system according to the present embodiment will be described with reference to flowcharts and data flowcharts.

  Before describing the specific processing flow, the premise in the present embodiment will be described in advance. As shown in FIG. 1, three operators, an administrator, a sender, and a receiver, participate in the system according to the present embodiment.

  The administrator is a user of the mail checker management terminal 2 and uses the mail checker management terminal 2 to transmit common information and secret information to the sender and the receiver. The sender is a user of the e-mail sending terminal 3 and uses the e-mail sending terminal 3 to create and send an e-mail addressed to the recipient. The recipient is a user of the e-mail receiving terminal 6 and uses the e-mail receiving terminal 6 to receive the e-mail from the sender and verify the e-mail.

[Pre-processing of mail checker management terminal]
First, the administrator generates common information and secret information in advance in the mail checker management terminal 2 and transmits the common information and secret information to the e-mail terminals 3 and 6 of the sender and the receiver.

  FIG. 8 is a flowchart of pre-processing by the mail checker terminal device. The left side of FIG. 8 is a flowchart of common information generation processing by the common information generation device 22. The common information is a secret key information generation pattern that defines a combination of an e-mail information item such as which header item of the e-mail is to be added, a body text, and an attached file, and a plurality of secret information.

  This e-mail information item and secret key information generation pattern must be determined in advance as common information in the sender terminal and the receiving terminal. The e-mail information item is information indicating which e-mail information item is to be verified, and the administrator generates and determines a plurality of e-mail information items. Also, the e-mail information items may be determined individually for each e-mail according to the importance of the mail contents, or all e-mails may be generated with the same e-mail information item. The selection of the e-mail information item may be performed by the administrator when selecting all at once, or by the sender when selecting individually by mail. When the information is generated individually for each mail, information specifying the electronic mail information item is added to the header of the outgoing mail and notified to the mail checker of the receiving terminal.

  FIG. 9 is a diagram illustrating an example of an e-mail information item and an example of a secret key information generation pattern. The upper part of FIG. 9 shows a list of candidate examples of e-mail information items generated according to the importance of the mail content. The higher the importance of mail (pattern A is the most important), the greater the number of email information items. This increases the security of the verification information.

  The administrator sends the list from the mail checker management terminal 2 to all terminals in advance and stores it. The administrator selects the e-mail information items from the candidate list in advance for all mails, and notifies the pattern names pattern A to pattern D, which are IDs of the selected e-mail information items, to all terminals. Alternatively, the sender determines the importance of the mail content, selects an e-mail information item from the candidate list, adds the pattern name of the selected e-mail information item to the outgoing mail, and notifies the receiving terminal. In a state where the electronic mail information item is selected by either, the mail checker generates combination verification information from the information of the electronic mail information item and the generated secret key information.

  Pattern A to pattern D, which are the IDs of the selected electronic mail information items, are added to the header of the outgoing mail and transmitted to the receiving side. As described above, the sending terminal and the receiving terminal share and store a list of candidates for the e-mail information item in the upper part of FIG. 9, and which e-mail information is used with the ID of the selected e-mail information item To see if verification information is generated. Alternatively, the mail checker management terminal 2 may transmit the IDs of the e-mail information items determined in advance to all the terminals so that they are not added to the e-mail header.

  In the present embodiment, the description will be made on the assumption that an e-mail information item of importance C is selected. In the case of importance C, it is a combination of From, To, Subject, Date in the header of the email, the body of the email (Body), and the attached file (File).

  The lower part of FIG. 9 is a list of secret key information generation pattern candidates. The secret key information generation pattern defines how one or a plurality of secret key information is generated by using a plurality of secret key information whose version numbers are managed. The mail checker generates one or more combination verification information after determining which secret key information generation pattern is used to generate the generated secret key information with reference to this list.

  The secret key information generation pattern candidate list is also notified to all terminals from the mail checker terminal device and stored in the same manner as the e-mail information item candidate list. Then, the administrator selects one of the secret key generation patterns in advance in consideration of the status of the organization and notifies the previous terminal of the ID (pattern 1 to pattern 3). Thereby, all the terminals can know whether or not to combine the secret key information with the secret key information generation pattern.

  In this embodiment, three generation patterns of “basic”, “extended 1”, and “extended 2” are prepared as classification names of secret key information generation patterns. The three secret key information generation patterns are as follows, for example. In the following cases, a plurality of secret key information is maintained in time series, that is, a combination of successive versions.

  (1) In the basic form, one generation secret key information is generated by combining the secret information in the organization and secret key information of all generations. For example, as shown in FIG. 11 to be described later, when both the transmitting terminal and the receiving terminal store three secret key information of generations (versions) 1, 2, and 3, the mail checker All the secret key information and the in-organization secret information are combined to generate one generated secret key information.

  (2) In the extended type 1, in addition to the in-house secret information, the secret key information of each generation is assumed to be the latest, and a combination of the assumed latest secret key information and one or more old secret key information is combined. Generate private key information for. For example, as shown in FIG. 12, which will be described later, the transmitting terminal stores three secret key information of generations 1, 2, and 3, whereas the receiving terminal stores two secret key information of generations 1, 2. In this case, the transmitting terminal generates the first generated secret key information with the three secret key information of the generations 1, 2, and 3 and the secret information in the organization, and sets the next generation 2 of the latest generation 3 as the latest. Assuming that the second generation secret key information is generated from the two secret key information of the generations 2 and 1 and the in-organization secret information. Then, the receiving terminal generates second generated secret key information with the two secret key information of generations 2 and 1 and the in-organization secret information. As a result, the second generated secret key information matches between the transmitting terminal and the receiving terminal. The same applies when the relationship between the transmitting terminal and the receiving terminal is reversed.

  (3) Extended type 2 generates generated secret key information by combining secret key information not including the oldest secret key information in addition to the combination of extended type 1. For example, as shown in FIG. 13 to be described later, when the transmitting terminal stores the secret key information of generations 1, 2, and 3, and the receiving terminal stores the secret key information of generations 2, 3, and 4, the transmitting terminal , Generation 3, 2 and 1 secret key information, generation 2 and 1 secret key information, and generation 3 and 2 secret key information. On the other hand, the receiving terminal generates generated secret key information by using the secret key information of generations 4, 3 and 2, the secret key information of generations 3 and 2, and the secret key information of generations 4 and 3, respectively. Therefore, the transmission terminal and the reception terminal match with the generated secret key information based on the generation 3 and 2 secret key information.

  According to the extensions 1 and 2, the combination of the plurality of secret key information is a continuous version of the plurality of secret key information stored in the electronic mail terminal device, or all or one of the plurality of secret key information stored. A combination having a part of secret key information.

  Further, according to the extension 1, the combination of the plurality of secret key information is continuous with the first version of the secret key information and the first version among the plurality of secret key information stored in the electronic mail terminal device. A first combination private key information with an old version private key information, a second version private key information older than the first version, and an old version private key information consecutive to the second version. And at least second combination secret key information.

  Further, according to the extension type 2, the combination of the plurality of secret key information includes the third version of the secret key information among the plurality of secret key information stored in the electronic mail terminal device in addition to the combination of the extension type 1. And the third version thereof, the third combination secret key information of the new version of the secret key information, the fourth version of the secret key information newer than the third version, and the fourth version of the secret key information. And at least fourth combination secret information with new version secret key information.

  Pattern 1 to pattern 3, which are IDs of the selected secret key information generation pattern, are added to the header of the outgoing mail and transmitted to the receiving side. As described above, the transmitting terminal and the receiving terminal share a list of secret key information generation pattern candidates in the lower part of FIG. 9 and use which combination of secret key information with the selected secret key information generation pattern ID. Know whether generated private key information is generated. Alternatively, the mail checker management terminal 2 may transmit the ID of the secret key information generation pattern determined in advance to all the terminals so that it is not added to the header of the email.

  As described above, by generating a plurality of secret key information by combining various secret key information, the version of the plurality of secret key information stored between the transmitting terminal and the receiving terminal is Even if the latest version is lacking or is different between the sending and receiving terminals, the secret key information between the sending terminal and the receiving terminal matches. Therefore, even if the management of the secret key information is not the same for all terminals, it is possible to check for illegal mail, and the generation management of the secret key information can be flexibly performed.

  Returning again to the flowchart on the left side of FIG.

  The administrator uses the mail checker management terminal 2 to activate the mail checker management software 21 of FIG. 2, opens the management menu, and operates the common information generation function. The mail checker management software 21 issues a common information generation request to the common information generation device 22. 3 receives the common information generation request from the mail checker management software 21 via the input / output unit 2211 of the request receiving unit 221. The request reception unit 221 issues a common information generation request to the common information generation unit 222 (S1001).

  The common information generation unit 222 receives the common information generation request (S1002). In response to this, the common information generating means 222 generates an electronic data information item (S1003) and a secret key information generation pattern (S1004). Both generations are performed by the common information generation means 222 in response to an input selected from the candidate list shown in FIG. When the generation of the electronic data information item and the secret key generation pattern is completed, the common information generation unit 222 transmits the electronic data information item and the secret key generation pattern as common information to the request reception unit 221 (S1005). The request receiving unit 221 receives the common information (S1006).

  The flowchart on the right side of FIG. 8 is a flowchart of secret information generation processing in the secret information generation device 23. The secret information is in-organization secret information, secret key information, and secret key version information. This secret information needs to be held in advance as secret information between the sender terminal and the receiving terminal.

  Intra-organizational confidential information is information that only users within the organization can know, is not disclosed outside the organization, and is handled with strict management so that each user does not leak outside . It is a kind of PIN code. This in-house confidential information is generated by the administrator.

  The secret key information is key information for generating combination verification information, and is information that is handled after being strictly managed so as not to be leaked to an attacker. This secret key information is generated by the administrator and updated periodically. Even if the secret key information may leak to the outside, the secret key information is updated irregularly.

  The secret key version information is information linked to the secret key information and is managed together with the secret key information. This secret key version information is also generated by the administrator. The secret key version information may be any information that can identify the version, but a time stamp is desirable as shown in FIGS. This is because it is possible to prompt the administrator to periodically update the secret key information based on the secret key version information.

  Returning to the flowchart on the left side of FIG. 8, the administrator uses the mail checker management terminal 2 to start the mail checker management software 21, opens the management menu, and operates the secret information generation function. The mail checker management software 21 issues a secret information generation request to the secret information generation device 23. The secret information generation device 23 in FIG. 3 receives a secret information generation request from the mail checker management software 21 via the input / output unit 2311 of the request reception unit 231. The request accepting unit 231 issues a secret information generation request to the secret information generating unit 232 (S2001). The secret information generation means 232 receives the secret information generation request (S2002). In response, the secret information generation means 232 generates in-organization secret information (S2003), secret key information (S2004), and secret key version information (S2005). When the generation of the secret information in the organization, the secret key information, and the secret key version information is completed, the secret information generating unit 232 sends the secret information, the secret key information, and the secret key version information to the request receiving unit 231 as the secret information. (S2006). The request receiving unit 231 receives secret information (S2007).

[Pre-processing of e-mail sending terminal and received mail sending terminal]
FIG. 10 is a flowchart of pre-processing by the e-mail transmission terminal and the reception terminal. The left side of FIG. 10 is a flowchart of common information storage processing in the combination verification information generation device 32 of the transmission terminal and the verification device 62 of the reception terminal. First, pre-processing of the e-mail transmission terminal will be described.

  The electronic mail transmission terminal 3 receives the common information from the administrator's mail checker management terminal 2 via the mail checker 32. This common information may be provided by being embedded in the mail checker installer, or may be stored in the mail checker later via the mail checker. In the present embodiment, the latter method will be described.

  The sender opens an optional function of the mail checker 33 and operates the shared information storage function. The mail checker 33 issues a common information storage request to the combination verification information generation device 32 in response to input of common information (transmission mail information item and secret key information generation pattern). The combination verification information generation device 32 receives the common information storage request from the mail checker 33 via the input / output unit 3211 of the request reception unit 321. At this time, the input common information is received. The request reception unit 321 issues a common information storage request to the common information management unit 322 (S3001). The common information storage unit 322 receives the common information storage request (S3002). Subsequently, the common information storage unit 322 stores the electronic mail information item and the secret key information generation pattern (S3003, S3004). When the storage of the common information is completed, the common information storage unit 322 transmits a completion notification to the request reception unit 321 (S3005). The request receiving unit 321 receives a completion notification (S3006).

  The mail checker of the electronic mail receiving terminal also executes common information storage processing similar to the operation of the transmitting terminal by the request receiving means 621 and common information management means 622 of the receiving terminal.

  The right side of FIG. 10 is a flowchart of the secret information storage process in the combination verification information generation device 32 of the transmission terminal and the verification device 62 of the reception terminal. First, secret information storage processing at the transmitting terminal will be described.

  The e-mail transmission terminal 3 receives secret information from the administrator's mail checker management terminal 2 and receives it via the mail checker 32. If this secret information is included in the mail checker installer, it cannot be dealt with if the installer leaks, so it is desirable to receive it via the mail checker and store it in the mail checker after the mail checker is installed. In addition, since confidential information within the organization is extremely important information, the administrator does not receive it via the email checker. What is the email checker such as e-mail or notification to the sender / receiver (user) in the organization? Desirably, it is provided by other means. In this embodiment, it is assumed that the confidential information in the organization has passed to all email users in the organization. The secret key information and the secret key version information are encrypted with the confidential information in the organization, and the mail checker is To provide through.

  The sender opens the option function of the mail checker 33 in FIG. 4 and operates the secret information storage function. The mail checker 33 inputs secret information (intra-organization secret information, secret key information, secret key version information) to the combination verification information generating device 32 and issues a request for storing secret information. The combination verification information generation apparatus 32 receives the confidential information storage request from the mail checker 33 together with the confidential information via the input / output unit 3211 of the request receiving unit 321 in FIG. The request receiving unit 321 issues a secret information storage request to the secret information managing unit 323 (S4001). The secret information storage unit 323 receives the secret information storage request (S4002).

  The secret information storage unit 323 continues to store the organization secret information, secret key information, and secret key version information (S4003, S4004, S4005). At this time, the secret key information and the secret key version information are stored by decrypting the secret information in the organization. When the storage of the secret information is completed, the secret information storage unit 323 transmits a completion notification to the request reception unit 321 (S4006). The request receiving unit 321 receives a completion notification (S4007).

  The confidential information storage process of the receiving terminal is the same as the confidential information storage process of the transmitting terminal.

  11, FIG. 12, and FIG. 13 are diagrams showing the storage state of the secret information at the transmission / reception terminal. In this example, when the secret key information is updated, the latest secret key information and the old secret key information are stored up to a maximum of three generations of secret key information. The maximum number of generations may be selected in advance by the administrator, for example.

  FIG. 11 shows an example of the first embodiment. In the first embodiment, the transmission / reception terminals 3 and 6 both store and manage the intra-organizational secret information SC1 and the secret key information SC2 of the generations 1 to 3. In this example, the three generations of continuous secret key information stored in the transmission / reception terminal is exactly the same. In each generation's secret key information, secret key version information SC2_V is stored as generation (version) information. The secret key version information is information that can specify the generation (version) of the secret key. In this example, the secret key version information is date information updated by the administrator.

  FIG. 12 shows an example of the second embodiment. In the second embodiment, the transmitting terminal 3 stores and manages the three generations of secret key information SC2 of generations 1 to 3, while the receiving terminal 6 stores only the secret keys of the two generations of generations 1 and 2. Information SC2 is stored and managed. The receiving terminal 6 has not updated the latest generation (third generation) private key information.

  FIG. 13 shows an example of the third embodiment. In the third embodiment, the transmission / reception terminals 3 and 6 both store and manage the third generation secret key information. However, the transmitting terminal 3 stores secret key information of generations 1 to 3, and the receiving terminal 6 stores secret key information of generations 2 to 4. The receiving terminal 6 is preceded by one generation of update, and a deviation of one generation from the transmitting terminal occurs.

[Processing by e-mail sending terminal]
In the first to third embodiments to be described later, the description will be made on the assumption that secret information in the transmission / reception terminal is stored in the three states of FIGS. 11 to 13.

  First, the combination verification information generation process in the combination verification information generation apparatus 32 in the first embodiment will be described.

  FIG. 14 is a flowchart of a combination verification information generation process in the combination verification information generation apparatus 32. First, the sender uses the e-mail transmission terminal 3 of FIG. 4 to activate the e-mail software 31 and create a transmission e-mail. After creating the electronic mail, the electronic mail software 31 inputs a transmission mail including the header information and the text information to the combination verification information generation device 32 and issues a request for generating the combination verification information.

  The combination verification information generating device 32 in FIG. 5 receives a request for generating combination verification information from the electronic mail software 31 via the input / output unit 3211 of the request receiving unit 321. The request reception unit 321 issues a combination verification information generation request to the combination verification information generation unit 324 (S5001). At this time, the request receiving unit 321 transmits a transmission mail including the header information and the text information received from the electronic mail software 31.

  The combination verification information generation unit 324 receives the combination verification information generation request (S5002), and transmits a secret information acquisition request to the secret information management unit 323 (S5003). The secret information management means 323 receives the secret information acquisition request (S5004). Subsequently, the secret information management unit 323 acquires secret information (intra-organization secret information, secret key information, secret key version information) from the storage units 3231 and 3232 (S5005), and transmits it to the combination verification information generation unit 324 ( S5006).

  The combination verification information generation unit 324 receives the secret information (S5007), and then transmits an acquisition request for the common information (e-mail information item and secret key information generation pattern) to the common information management unit 322 ( S5008). The common information management unit 322 receives the common information acquisition request (S5009), and acquires the e-mail information item from the e-mail information item management unit 3221 and the secret key information generation pattern from the secret key information generation pattern storage unit 3222. (S5010). The common information management unit 322 transmits the common information to the combination verification information generation unit 324 (S5011).

  After acquiring the common information (S5012), the combination verification information generating unit 324 generates combination verification information using the common information (S5013). In the generation of combination verification information, generated secret key information is generated from a plurality of secret key information, verification information is generated from e-mail information and generated secret key information, and the secret key of the organization secret information and the plurality of secret key information is generated. Feature information of the secret key version information is generated from the version information, and combination verification information is generated from the verification information and the feature information of the secret key version information. This combination verification information generation process will be described in detail later.

  The feature amount information generation unit 3241 of the combination verification information generation unit 324 generates the feature information of the secret key version information, and the combination verification information generation unit 3242 generates the generation secret key information and the verification information. The combination verification information is generated.

  Then, the header information adding unit 3243 of the combination verification information generating unit 324 adds the combination verification information, the e-mail information item, and the secret key information generation pattern to the outgoing mail as new header items (S5014). Further, the combination verification information generation unit 324 transmits the transmission mail with the combination verification information header to the request reception unit 321 (S5015), the request reception 321 receives (S5016), and the e-mail software 31 uses the transmission device 34. Then, a transmission mail with a combination verification information header is transmitted.

  The header information adding unit 3243 adds an e-mail information item and a secret key information generation pattern to all terminals in advance, and adds them as a header item of outgoing mail when combination verification information is generated accordingly. You don't have to. However, when combining verification information is generated by selecting an e-mail information item and a secret key information generation pattern only for that reason because it is a particularly important outgoing mail, etc. 3243 adds the combination verification information, the ID of the electronic mail information item, and the ID of the secret key information generation pattern to the outgoing mail as new header items.

  In this embodiment, the e-mail information item is not described in the header as it is, but an ID “pattern C” is added. This addition prevents generation of verification information spoofed by an attacker. In this case, a list of e-mail information item candidates similar to that in the upper part of FIG. 9 is also managed in the verification device 62 of the receiving terminal and needs to be shared with the transmitting terminal.

  In FIG. 16, an X-BoundTargetHead: header is generated as new header information of an e-mail information item, and “pattern C” as an e-mail information item is added. Further, as new header information of the secret key information generation pattern, an X-BoundKeys: header is generated, and “pattern 1” serving as a secret key information generation pattern is added. Further, as new header information of the combination verification information, an X-BoundMAC1: header is generated, and “48adf3e294b2: 82f93d0b9248” serving as the combination verification information is added.

[Combination verification information generation process]
FIG. 16 is a diagram illustrating a combination verification information generation process according to this embodiment. The combination verification information generation unit 324 acquires common information and secret information from each of the storage units 3221, 3222, 3231, 3232 (S5005, S5010), and uses them to specify the e-mail information item (pattern C). Generated from a combination of a plurality of secret key information for five items: From: header, To: header, Subject: header, Date: header, Body: body information and attached file (File) Verification information VR1 is generated based on the generated secret key information (S5013). In FIG. 16, “48adf3e294b2” is generated as the verification information VR1.

  The verification information VR1 corresponds to, for example, hash information generated using a one-way hash function for five e-mail information items and generated secret key information. However, it may be generated using a generation method other than the one-way hash function. This verification information generation algorithm needs to be shared with the verification unit 6242 of the verification device 62 of the receiving terminal 6 in order to ensure consistency during verification.

  Further, the combination verification information generating means 324 acquires the latest version information of the secret key information of the plurality of secret key information, and generates the feature information SC4 of the latest secret key information version information (S5013). In FIG. 16, “82f93d0b9248” is output as the feature information SC4.

  The feature information of the secret key version information is not necessarily feature information, and may be an identifier (ID or tag) of the secret key information. As shown in FIG. 11, it is assumed that time information, random numbers, etc. at the time of update are used as the secret key version information, and such information may be adopted as raw data. The information and the latest secret key version information may be converted into hash information using a one-way hash function as feature information. In this embodiment, it is generated as feature information of secret key version information.

  Further, the combination verification information generation means 324 combines the feature information of the secret key version information with the verification information to generate combination verification information VR1 (S5013). There are several methods for this combination, and the feature information SC4 may be combined either after or before the generated verification information VR1 (“82f93d0b9248”). In the present embodiment, an example of combining backward is shown. In the example of FIG. 16, the combination verification information VR2 is “82f93d0b9248 48adf3e294b2”. The format definition (combination method) of the combination verification information needs to be shared with the verification unit 6242 of the verification device 62.

  The header information adding unit 3243 adds the e-mail information item (pattern C), the secret key information generation pattern (pattern 1), and the combination verification information VR2 to the outgoing mail as header items (S5014).

  FIG. 17 is a diagram illustrating details of the generation process of the combination verification information according to the first embodiment. FIG. 18 is a flowchart of the combination verification information generation process. In the first embodiment, as the secret key information generation pattern, one generated secret key information combining “intra-organization secret information and secret key information of all generations” which is “basic” in the list of FIG. "Generate" is selected.

  The combination verification information generation unit 3242 in the combination verification information generation unit receives the internal secret information SC1 (“E43FD804A32F90E4BA3”) from the internal secret information storage unit 3231 and the first to third generations from the private key information storage unit 3232. All the secret key information SC2 is obtained (S5007), and the in-organization secret information SC1 and all the secret key information SC2 are connected to generate the generated secret key information SC3 (S5013_1). As shown in FIG. 17, in-house secret information, secret key information 1, secret key information 2, and secret key information 3 are sequentially connected in time series to generate generated secret key information SC3.

  The combination verification information generation unit 3242 continues to generate the generated secret key information SC3 and the From: header, To: header, Subject: header, Date: header, Body: body information, and attached file (File) of the transmission mail information item. Verification information VR1 is generated from the five items (S5013_2). This generation algorithm may be, for example, simply concatenation, but preferably, using the one-way hash function, based on the generated secret key information SC3, the hash information of the information of the outgoing mail information item is generated and the verification information VR1. Alternatively, using the one-way hash function, hash information of a combination (concatenated) of the information of the outgoing mail information item and the generated secret key information SC3 is generated and used as the verification information VR1. Alternatively, the transmission mail information may be encrypted with the generated secret key information. This generation algorithm needs to be determined in advance between the transmitting terminal and the receiving terminal.

  Next, the feature quantity information generation unit 3241 in the combination verification information generation unit updates the latest secret key version information SC2_V (three generation keys in the example of FIG. 17) from the secret key information storage unit 3232. "2013/02/08 11:36:12") is acquired, and feature information SC4 of the latest secret key version information is generated from the intra-organization secret information SC1 and the latest secret key version information SC2_V (S5013_3). This generation algorithm may be, for example, simply concatenation, but preferably, using a one-way hash function, the hash information of the combination information of the in-organization secret information SC1 and the latest secret key version information SC_V is converted into the latest secret key. This is feature information SC4 of the version information.

  Finally, the combination verification information generation unit 3242 in the combination verification information generation unit combines the verification information VR1 and the feature information SC4 of the latest secret key version information, and generates the combination verification information VR2 (S5013_4). This generation algorithm may be, for example, a process of connecting the verification information VR1 and the feature information SC4 of the latest secret key version information.

[Processing by e-mail receiving terminal]
Next, verification processing of combination verification information in the verification device 62 of the electronic mail receiving terminal 6 will be described. FIG. 15 is a flowchart of the combination verification information verification process in the verification device 62. FIG. 19 is a diagram for explaining the verification process of the electronic mail receiving terminal.

  The recipient uses the electronic mail receiving terminal 6. The receiver activates the e-mail software 61 and performs e-mail reception processing. At this time, the receiving terminal receives the mail with combination verification information via the received mail server 5 and the mail checker 63.

  After receiving the e-mail reception request, the e-mail software 61 inputs the e-mail with combination verification information to the verification device 62 and issues a verification request for the combination verification information. The verification device 62 receives a request for verification of combination verification information from the electronic mail software 61 via the input / output unit 6211 of the request receiving unit 621.

  As shown in FIG. 15, the request receiving unit 621 issues a verification request to the verification unit 624 (S6001). At this time, the mail with combination verification information received from the electronic mail software 61 is transmitted. The verification means 624 receives the verification request (S6002), and analyzes the header information and text information of the mail with combination verification information (S6003). Subsequently, an e-mail information item is acquired from the header information (S6004). Specifically, as shown in FIG. 19, the X-Inbound Target Head: header corresponding to the e-mail information item is referred to confirm which item is the verification information generation target. “Pattern C” is designated as the e-mail information item. Also, the generation pattern is confirmed with reference to the X-BoundKeys: header corresponding to the secret key information generation pattern. “Pattern 1” is designated as the secret key information generation pattern.

  The verification unit 624 transmits an e-mail information item serving as common information and a request for acquiring the content of the common information generation pattern to the common information management unit 622 (S6005). At this time, the information of the electronic mail information item “pattern C” and the secret key information generation pattern “pattern 1” acquired in S6004 is transmitted together. The common information management unit 622 receives the common information acquisition request (S6006). The common information management unit 622 acquires the content of the e-mail information item corresponding to “pattern C” from the target header item storage unit 6221 (S6007). In this embodiment, five items corresponding to “pattern C” are acquired: From: header, To: header, Subject: header, Date: header, Body: body information, and attached file (File). Further, the content of the secret key information generation pattern corresponding to “pattern 1” is acquired from the secret key information generation pattern storage unit 6222 (S6007).

  When the acquisition of the contents of the e-mail information item and the secret key information generation pattern is completed, the common information management unit 622 transmits the common information to the verification unit 624 (S6008). At this time, the contents of the target header item and secret key information generation pattern acquired in S6007 are transmitted. The verification unit 624 receives the common information (S6009).

  Next, the verification unit 624 transmits a secret information acquisition request to the secret information management unit 623 (S6010). The secret information management means 623 receives the secret information acquisition request (S6011). The secret information management means 623 obtains in-organization secret information, secret key information, and secret key version information, which are secret information (S6012), and transmits it to the verification means 624 (S6013). The verification unit 624 receives the secret information (S6014).

  Further, the verification unit 624 regenerates the combination verification information by the same method as the generation of verification information at the transmitting terminal shown in FIGS. 17 and 18 (S6015). Then, the verification means 624 acquires the received mail combination verification information from the received mail header (S6016), compares the regenerated combination verification information with the received mail combination verification information (S6017), and requests a verification result. It transmits to the reception means 621 (S6018).

  The verification unit transmits the verification result to the request reception unit 621 (S6018 in FIG. 15). Upon receiving the verification result (S6019), the request receiving unit 621 transmits the verification result to the electronic mail software 61, and the verification result is notified to the receiver via the output device 64.

  FIG. 20 is a diagram showing details of the verification processing in the verification means. FIG. 21 is a flowchart of the verification process. The verification means 624 uses the same method as the generation of verification information at the transmitting terminal shown in FIGS. 17 and 18, and the feature information of the latest secret key version information from the in-organization secret information SC1 and the latest secret key version information SC2_V. SC4 is regenerated (S6015_1). In FIG. 20, “82f93d0b9248” is output as the feature information SC4 of the latest secret key version information.

  The verification unit 624 acquires the X-BoundMAC1: header of the mail information with combination verification information, and acquires an item in which the feature information of the latest secret key version information is described (S6016 in FIG. 15). Then, the verification unit 624 compares the feature information of the received mail with the regenerated feature information SC4 and confirms whether they match (S6017_1). If they do not match, the receiver is notified of the verification failure or the latest secret key version mismatch (S6017_3).

  If they match, the verification means uses the information in the e-mail information item to regenerate the generated secret key information (S6015_2) and reproduce the verification information in the same manner as the verification information generation at the sending terminal. (S6015_3) is performed. Specifically, as shown in FIG. 19, through the verification means 624, the header information From: header, To: header, Subject: header, Date: header, Body: body information (File: including attached file) The verification information for the five items is regenerated. In FIG. 20, “48adf3e294b2” is regenerated as the verification information VR1.

  Next, the verification means acquires the X-BoundMAC1: header of the mail information with combination verification information, acquires the item in which the verification information is described (S6016 in FIG. 15), and compares it with the regenerated verification information VR1. It is confirmed whether or not they match (S6017_2). If they do not match, the receiver is notified of the verification failure or verification information mismatch (S6017_3).

  As described above, in the first embodiment, as shown in FIG. 11, both the e-mail transmission terminal 3 and the reception terminal 6 hold the first to third generation secret key information. In the case where “basic” pattern 1 is selected as the secret key information generation pattern, generation of combination verification information at the transmission terminal and verification processing by combination verification information at the reception terminal have been described. In the first embodiment, it is assumed that generation management of secret keys in an organization is relatively well performed. Then, the transmitting terminal generates generated secret key information from a plurality of continuous secret key information, generates verification information from the e-mail information using the generated secret key information, and updates the latest of the plurality of continuous secret key information. The feature information of the secret key version information is generated, the combination verification information is generated by combining them, and added to the header of the outgoing mail. Then, the receiving terminal generates combination verification information in the same manner as the transmitting terminal, and compares it with the combination verification information of the received mail to verify whether it is an illegal mail. Therefore, even if some of the secret key information that is updated one after another is leaked to a malicious third party, all of the continuous secret key information that is the source of the generated secret key information must be leaked together with the version information. For example, it is possible to verify illegal mail.

[Second Embodiment]
The basic processing flow of the generation and verification method of the combination verification information in the second embodiment is the same as that in FIGS. 14, 15, 16, and 19 of the first embodiment. In the second embodiment, as shown in FIG. 12, the e-mail transmission terminal 3 holds the first to third generation secret key information, and the receiving terminal holds only the first and second generation secret key information. In this case, it is assumed that “extended 1” pattern 2 is selected as the secret key information generation pattern of FIG.

  FIG. 22 is a diagram showing details of the generation processing of combination verification information in the present embodiment. FIG. 23 is a flowchart of the combination verification information generation process. As shown in FIG. 20, the mail checker of the transmission terminal 3 generates first to third combination verification information, adds it to the mail header, and transmits it. Since the transmission terminal 3 stores the first to third generation secret key information and the generation pattern of the secret key information is “extended”, the first of the continuous secret key information for generating the generated secret key information is the first. Is the first to third generation secret key information, the second combination is the first and second generation secret key information, and the third combination is the first generation secret key information. However, since the third combination has only a single secret key information, the security is not as high as the first and second combinations.

  In the first combination verification information VR2_1 in FIG. 22, the verification information VR1_1 is generated using the intra-organizational secret information managed by the transmission terminal 3, all the secret key information of generations 1 to 3, and e-mail information. , The feature information SC4_1 is generated using the latest generation 3 secret key version information among the three adopted secret key information, and the verification information VR2_1 is generated by concatenating the feature information SC4_1. This is added to the X-BoundMAC1: header. In FIG. 22, “48adf3e294b2: 82f93d0b9248” is added.

  In the second combination verification information VR2_2, the verification information VR1_2 is generated by using the in-organization secret information, the generation 1-2 secret key information, and the e-mail information managed by the transmission terminal 3, and the two adopted The feature information SC4_2 is generated using the latest generation 2 secret key version information in the secret key information, and is combined to generate the combination verification information VR2_2. This is added to the X-InboundMAC2: header. In FIG. 22, “29430b2ad8cd: 18293fbc6a72” is added.

  In the third combination verification information VR2_3, verification information VR1_3 is generated using the in-organization secret information, the generation 1 secret key information, and the e-mail information managed by the transmission terminal 3, and the generation 1 secret key version is generated. Feature information SC4_3 is generated using the information, and these are combined to generate combination verification information. This is added to the X-InboundMAC3: header. In FIG. 22, “98dbc2adf782: b290da618223” is added.

  Also, X-BoundKeys: header: “pattern 2” is added as new header information of the secret key information generation pattern.

  According to the flowchart of FIG. 23, the combination verification information generation unit 324 sets N = 1 as an initial value, and updates the latest secret key information (generation 3) among all the stored secret key information. It is assumed that the secret key information and the latest secret key version information are used (S5013_0). Then, similarly to FIG. 18, processing S5013_1 to S5013_4 is executed to generate first (N = 1) combination verification information. If N does not reach the maximum value 3, N = N + 1 and the next new secret key information (generation 2) is assumed to be the latest secret key information and the latest secret key version information (S5013_6). S5013_1 to S5013_4 are executed to generate second (N = 2) combination verification information. The above processing is repeated until N reaches the maximum value.

  FIG. 24 is a diagram illustrating details of the combination verification information verification processing according to the second embodiment. FIG. 25 is a flowchart of the verification process. Since the receiving terminal stores the secret key information of generations 1 and 2, the combination verification information based on the secret key information of generations 1 and 2 is generated when the secret key information generation pattern is “extension 1”. When the transmitting terminal generates the above-described third combination verification information, the receiving terminal may also generate combination verification information based on the generation 1 secret key information. However, the credibility of verification in this case is not so high.

  First, the verification means 624 uses the in-organization secret information SC1 managed by the receiving terminal and the secret key version information SC2_V of the latest generation 2 secret key information SC2 among the generation 2 and 1 secret key information. , The feature information SC4_2 of the latest secret key version information is regenerated (S6015_1). In FIG. 24, “18293fbc6a72” is output.

  Further, the verification means 624 uses the feature information SC4_2 of the latest regenerated secret key version information: “18293fbc6a72” to search the header in the combination verification information-added mail information and search for a matching combination verification information header. . X-BoundMAC2: Feature information of the secret key version information in the header: “18293fbc6a72” is referenced to confirm that they match (S6017_1).

  Subsequently, the verification unit 624 regenerates the verification information VR1_2 using the in-organization secret information SC1 and the generations 1 and 2 of the secret key information SC2 (S6015_2, S6015_3). In FIG. 24, “29430b2ad8cd” is output. Then, the verification unit refers to the verification information: “29430b2ad8cd” in the X-BoundMAC2: header, and confirms that it matches the regenerated verification information.

  As shown in FIG. 25, if the feature information does not match, the verification means 624 assumes that the next generation of secret key information is the latest secret key information, and the feature of the latest secret key version information as described above. Information is generated and it is confirmed whether or not it matches the feature information of the mail with combination verification information. This process is repeated until N reaches a maximum value of 3.

  In the second embodiment, as shown in FIG. 12, even if the transmitting terminal stores private key information of generations 1 to 3 and the receiving terminal stores private key information of generations 1 and 2, the secret terminal information is stored. By selecting the key information generation pattern as the extension 1 and generating the feature information of the verification information and the latest secret key version information, it is possible to verify whether or not it is an unauthorized mail. In the above example, the combination of the second verification information based on the generation 1 and 2 secret key information generated by the transmitting terminal and the feature quantity of the latest secret key version is the generation 1 and 2 secret key information generated by the receiving terminal. It matches the combination of the verification information by and the feature quantity of the latest secret key version. The second embodiment can also be applied to the case where the transmitting terminal holds generations 1 and 2 and the receiving terminal holds generations 1, 2 and 3.

[Third Embodiment]
The basic processing flow of the generation and verification method of the combination verification information in the third embodiment is also the same as that in FIGS. 14, 15, 16, and 19 of the first embodiment. In the third embodiment, as shown in FIG. 13, the e-mail transmission terminal 3 holds generations 1 to 3 private key information, and the reception terminal holds generations 2 to 4 private key information. , It is assumed that “extended 2” pattern 3 is selected as the secret key information generation pattern of FIG. That is, three consecutive generations are shifted between the transmitting terminal and the receiving terminal.

  FIG. 26 is a diagram illustrating details of the generation process of the combination verification information according to the third embodiment. The flowchart of the verification information generation process is the same as that in FIG. In the third embodiment, in addition to the first to third combination verification information VR2_1 to VR2_3 shown in FIG. 22 of the second embodiment, fourth combination verification information VR2_4 shown in FIG. 26 is generated. . The first to third combination verification information generation methods are the same as those in the second embodiment.

  In the fourth combination verification information VR2_4, fourth verification information VR1_4 is generated from the in-organization secret information, the generation 2 and generation 3 secret key information, and the e-mail information managed by the transmission terminal. The feature information SC4_4 of the latest secret key version is generated using the latest generation 3 secret key version information of the adopted secret key information, and combined with the fourth verification information to generate combination verification information VR2_4. Then, the fourth combination verification information VR2_4 is added to the X-BoundMAC4: header. In FIG. 26, “3193bc1adc12: 82f93d0b9248” is added. Also, X-BoundKeys: header: “pattern 3” is added as new header information of the secret key information generation pattern. As shown in FIG. 26, the first to fourth combination verification information is added to the mail header and transmitted.

  FIG. 27 is a diagram illustrating details of the combination verification information verification processing according to the third embodiment. The flowchart of the verification process is the same as that in FIG. First, the receiving terminal verification means 624 reproduces the feature information of the latest secret key version information using the in-organization secret information SC1 and the latest generation 4 secret key version information SC2_V managed by the receiving terminal. To do.

  The verification unit 624 searches for the header in the mail information with combination verification information using the feature information of the reproduced latest secret key version information, and searches for the combination verification information header having matching feature information. Since the generation terminal 4 private key information is not stored in the transmission terminal 3, generation 4 feature information is not found.

  As a result, the verification unit 624 regenerates the feature information of the generation 3 private key version information by using the internal secret information and the second generation 3 private key version information (S6015_1). In FIG. 27, “82f93d0b9248” is output.

  The verification means 624 searches the header in the mail information with combination verification information using the feature information of the latest reproduced secret key version information, and the feature information of the secret key version information in the X-BoundMAC1, 4: header: It is confirmed that “82f93d0b9248” matches.

  Subsequently, the verification unit 624 regenerates verification information using the intra-organizational secret information and the generation 2 and 3 secret key information (S6015_3). In FIG. 27, “3193bc1adc12” is output. Then, the verification means confirms that the verification information: “3193bc1adc12” of the X-BoundMAC4: header matches the verification information based on the regenerated generation 2 and 3 secret key information.

  In the third embodiment, as shown in FIG. 13, the e-mail transmission terminal 3 holds generations 1 to 3 secret key information, and the reception terminal holds generations 2 to 4 secret key information. Three consecutive generations are shifted between the transmitting terminal and the receiving terminal. However, since “extended 2” pattern 3 is selected as the secret key information generation pattern in FIG. 9, the verification information generated from the generation 2 and 3 secret key information at the transmitting terminal and the feature quantity of the latest secret key version The combination of the information matches the combination of the verification information generated from the generation 2 and 3 secret key information at the receiving terminal and the feature information of the latest secret key version. In other words, by selecting “Extended 2” of the secret key information generation pattern, the number of types of verification information has increased, so that even if the generation of the secret key information is different between the sending terminal and the receiving terminal, the verification of unauthorized mail It can be performed. The third embodiment can be similarly applied to the case where the transmitting terminal holds generation 2 to 4 private key information and the receiving terminal holds generation 1 to 3 private key information.

When the secret key information generation pattern of “extended 2” selected in the third embodiment is applied when the maximum number of secret key information is 5, a plurality of continuous secret key information of the following 10 combinations are obtained. Use to generate verification information.
(1) Generations 1, 2, 3, 4, 5
(2) Generations 1, 2, 3, 4
(3) Generation 1, 2, 3
(4) Generations 1 and 2
(5) Generation 2, 3, 4, 5
(6) Generation 2, 3, 4
(7) Generations 2 and 3
(8) Generation 3, 4, 5
(9) Generations 3 and 4
(10) Generations 4 and 5
Therefore, if the maximum number of secret key information is increased, the number of verification information to be generated on the transmission side and the reception side increases, so it is desirable to select an optimal number.

  The generation process of the combination verification information according to the first to third embodiments can be generalized as shown in FIG. Furthermore, the verification process can be generalized as shown in FIG. The description of FIGS. 28 and 29 is as described above.

  As described above, according to the first to third embodiments, verification information is generated using a plurality of pieces of secret key information, and verification of whether or not the mail is illegal is performed using the verification information. Even when key information is leaked, verification can be performed appropriately.

  Furthermore, according to the second and third embodiments, even when the versions of the secret key information stored on the transmission side and the reception side are different or are different, the transmission / reception terminal has a plurality of combinations. Since a plurality of pieces of verification information are generated using a plurality of continuous secret key information, the verification information can be properly verified by matching any of the pieces of verification information.

  In addition, by generating feature quantity information of the latest secret key version information of a plurality of consecutive secret key information, in the verification process, first, a match is detected in the feature quantity information, and then the matching secret key version is changed. It is only necessary to regenerate the corresponding verification information and determine whether or not they further match. Therefore, the verification information regeneration step can be shortened.

  Therefore, it becomes possible to detect targeted mail on a client basis. In addition, the detection probability of targeted emails can be expected to improve compared to conventional methods.

  The above embodiment is summarized as follows.

(Appendix 1)
Updating the private key information to be stored by adding the updated private key information and the private key version information of the updated private key information to the updated old private key information and the old private key version information of the old private key information Procedure,
A generated secret key information generation procedure for generating generated secret key information from a plurality of secret key information in a predetermined combination and secret information in the organization that is kept secret outside the organization;
A verification information generation procedure for generating verification information from the generated secret key information and the information included in the outgoing mail;
A feature information generation procedure for generating feature information of the secret key version information from the secret key version information of the plurality of secret key information in the predetermined combination and the secret information in the organization;
A combination verification information addition procedure for adding combination verification information, which is a combination of the verification information and feature information of the secret key version information corresponding to the verification information, to the outgoing mail;
A generated secret key information regeneration procedure for regenerating single or a plurality of generated secret key information from a plurality of secret key information in the predetermined combination and the in-organization secret information;
A verification information regeneration procedure for regenerating verification information from the generated secret key information and the information included in the received mail;
A feature information regeneration procedure for regenerating the feature information of the secret key version information from the secret key version information of the plurality of secret key information in the predetermined combination and the secret information in the organization;
Verify whether the combination verification information obtained by combining the regenerated verification information and the feature information of the secret key version information corresponding to the verification information matches the combination verification information added to the received mail. A malicious mail detection program that causes a computer to execute the verification procedure.

(Appendix 2)
In Appendix 1,
In the updating procedure, the updated secret key information and secret key version information are stored together with the old secret key information and old secret key version information up to a predetermined maximum number. An illegal mail detection program that discards old old secret key information and old secret key version information.

(Appendix 3)
In Appendix 1 or 2,
The illegal mail detection program, wherein the plurality of secret key information in the predetermined combination includes all secret key information stored in the electronic mail terminal device.

(Appendix 4)
In Appendix 1 or 2,
The plurality of secret key information in the predetermined combination is a continuous version of the plurality of secret key information stored by the electronic mail terminal device, and is all or part of the plurality of secret key information stored. Unauthorized mail detection program with private key information.

(Appendix 5)
In Appendix 4,
The all or a part of the secret key information includes a first version of the secret key information and a secret key of an older version consecutive to the first version among a plurality of secret key information stored in the electronic mail terminal device. First combination secret key information with information, second combination secret key information older than the first version, and second combination secret with the second version secret key information that is older than the second version An unauthorized mail detection program having key information.

(Appendix 6)
In Appendix 4 or 5,
The whole or a part of the secret key information includes a third version of the secret key information stored in the electronic mail terminal device and a new version of the secret key successively to the third version. Information, third combination secret key information, a fourth version secret key information newer than the third version, and a fourth combination secret consisting of a new version secret key information consecutive to the fourth version An illegal mail detection program having information.

(Appendix 7)
In Appendix 1 or 2,
The verification information generated and regenerated in the verification information generation procedure and the verification information regeneration procedure is generated based on the generated secret key information using a one-way hash function. A fraudulent email detection program that is hash information of the information it has.

(Appendix 8)
In Appendix 1 or 2,
The verification information generated and regenerated in the verification information generation procedure and the verification information regeneration procedure is generated using a one-way hash function, and the information included in the generated secret key information and the transmitted and received mails An illegal email detection program that is hash information of the combination of

(Appendix 9)
In any one of Supplementary Notes 1, 2, 7, and 8,
The information contained in the transmitted and received mails is any combination information of header information, body text, and attached file of the transmitted mail, and the combination information is determined in advance between the electronic mail terminal devices. program.

(Appendix 10)
In Appendix 1 or 2,
In the feature information generation procedure and the feature information regeneration procedure, the secret key version information of the plurality of secret key information in the predetermined combination is the latest secret of the newest secret key information among the plurality of secret key information. An illegal email detection program that is key version information.

(Appendix 11)
In Appendix 1 or 2,
Feature information of the secret key version information generated and regenerated in the feature information generation procedure and the feature information regeneration procedure is generated using a one-way hash function, and the secret key version information and the A fraudulent email detection program that is hash information of the combination of private key information in the organization.

(Appendix 12)
In Appendix 1 or 2,
In the combination verification information addition procedure and the verification procedure, the combination verification information is generated by concatenating the verification information and feature information of secret key version information corresponding to the verification information.

(Appendix 13)
A fraudulent mail detection method for detecting fraudulent mail received by an electronic mail terminal device, comprising:
Updating the private key information to be stored by adding the updated private key information and the private key version information of the updated private key information to the updated old private key information and the old private key version information of the old private key information Process,
A generated secret key information generating step for generating generated secret key information from a plurality of secret key information in a predetermined combination and secret information in the organization that is kept secret outside the organization;
A verification information generating step for generating verification information from the generated secret key information and the information included in the outgoing mail;
A feature information generating step for generating feature information of the secret key version information from the secret key version information of the plurality of secret key information in the predetermined combination and the secret information in the organization;
A combination verification information adding step of adding combination verification information to the outgoing mail, which is a combination of the verification information and the feature information of the secret key version information corresponding to the verification information;
A generated secret key information regeneration step for regenerating generated secret key information from a plurality of secret key information in the predetermined combination and the in-organization secret information;
A verification information regeneration step for regenerating verification information from the generated secret key information and the information included in the received mail;
A feature information regeneration step of regenerating the feature information of the secret key version information from the secret key version information of the plurality of secret key information in the predetermined combination and the secret information in the organization;
Verify whether the combination verification information obtained by combining the regenerated verification information and the feature information of the secret key version information corresponding to the verification information matches the combination verification information added to the received mail. A method for detecting fraudulent emails, comprising:

(Appendix 14)
A fraudulent mail detection device for detecting fraudulent mail received by an electronic mail terminal device,
Updating the private key information to be stored by adding the updated private key information and the private key version information of the updated private key information to the updated old private key information and the old private key version information of the old private key information Means,
When sending an email,
Generated secret key information generation processing for generating generated secret key information from a plurality of secret key information in a predetermined combination and secret information in the organization that is kept secret outside the organization;
Verification information generation processing for generating verification information from the generated secret key information and the information included in the outgoing mail;
A feature information generation process for generating feature information of the secret key version information from the secret key version information of the plurality of secret key information in the predetermined combination and the secret information in the organization;
A combination verification information generating means for executing combination verification information addition processing for adding the combination verification information to the outgoing mail by combining the verification information and the feature information of the secret key version information corresponding to the verification information; ,
When receiving an email,
A generated secret key information regeneration process for regenerating generated secret key information from a plurality of secret key information in the predetermined combination and the in-organization secret information;
Verification information regeneration processing for regenerating verification information from the generated secret key information and the information included in the received mail;
A feature information regeneration process for regenerating the feature information of the secret key version information from the secret key version information of the plurality of secret key information in the predetermined combination and the secret information in the organization;
Verify whether the combination verification information obtained by combining the regenerated verification information and the feature information of the secret key version information corresponding to the verification information matches the combination verification information added to the received mail. A fraudulent mail detection device having verification means for performing verification processing for executing the verification processing.

1: Network 2: Mail checker terminal device 3: Email sending terminal 6: Email receiving terminal

Claims (1)

A fraudulent mail detection device for detecting fraudulent mail received by an electronic mail terminal device,
Updating the private key information to be stored by adding the updated private key information and the private key version information of the updated private key information to the updated old private key information and the old private key version information of the old private key information Means,
When sending an email,
Generated secret key information generation processing for generating generated secret key information from a plurality of secret key information in a predetermined combination and secret information in the organization that is kept secret outside the organization;
Verification information generation processing for generating verification information from the generated secret key information and the information included in the outgoing mail;
A feature information generation process for generating feature information of the secret key version information from the secret key version information of the plurality of secret key information in the predetermined combination and the secret information in the organization;
A combination verification information generating means for executing combination verification information addition processing for adding the combination verification information to the outgoing mail by combining the verification information and the feature information of the secret key version information corresponding to the verification information; ,
When receiving an email,
A generated secret key information regeneration process for regenerating generated secret key information from a plurality of secret key information in the predetermined combination and the in-organization secret information;
Verification information regeneration processing for regenerating verification information from the generated secret key information and the information included in the received mail;
A feature information regeneration process for regenerating the feature information of the secret key version information from the secret key version information of the plurality of secret key information in the predetermined combination and the secret information in the organization;
Verifies whether the combination verification information obtained by combining the regenerated verification information and the feature information of the private key version information corresponding to the verification information matches the combination verification information added to the received mail. A fraudulent email detection device having verification means for executing verification processing.

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