JP2001345832A - Mail system, mail guard device and operation terminal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exclude enciphered mail through an illegal route in enciphered mail communications by means of a virtual private network(VPN). SOLUTION: A mail repeating path is provided with one or more mail guards MG for repeating mail data. A mail transmitting source T1 edits, generates and transmits a mail message containing a mail header, a content cipher part provided from the mail text and route guarantee control information having a transfer destination signature part/mail guard name which is to become its own repeating party. Each of mail guards MG1, MG2 and son edits, generates and sends out a mail message containing the mail header, the content cipher part and the route guarantee control information, after verifying safety/ transmitter to the inputted mail message. A main transmitting destination T2 receives the mail message, after verifying safety and the transmitter of the mail message sent via the mail guards MG.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a public key infrastructure (PKI: P
Secure mail system with functions such as data concealment (encryption), sender authentication (digital signature), and data integrity assurance (hashing) using ublic Key Infrastructure), especially its encryption The present invention relates to a secure mail system, a mail guard device, and an operation terminal for controlling the flow of mail data on a network based on the contents of the mail data including the data contents obtained.

[0002]

2. Description of the Related Art A function of controlling the flow of communication data according to the contents of user data (in a data communication network, etc., it generally means that data communication is controlled by use conditions, network conditions, etc.). In many cases, this means transfer control of the data in accordance with the security policy). In the case of text data, a method is generally used in which data flow control is performed by collating with a character string registered in advance. It is a target. This is applied to flow control of general mail data without encryption. Further, when it is not possible to mechanically check image data, audio data, and the like, a human system has intervened to perform data flow control.

On the other hand, as a method of encrypting communication data, for example, Internet Protocol IP (Internet Protocol) is used.
col), etc. to perform encryption with a network layer such as
c, SSL (Secure Socket L) which performs encryption with a transport layer such as TCP (Transport Control Protocol).
ayer. A virtual communication network VPN (Virtual Private Network, which is a cryptographic communication protocol that has a function of encrypting data to be transferred and authenticating the other party), etc. A technology that can use a public line as if it were a dedicated line. In general, a method of performing secure communication by using a security function such as security is provided. However, the above-described virtual communication path technology is an encryption method implemented by a protocol layer, and is a protocol of an application layer, which is a higher-level protocol of the above-described protocols, such as SMTP (Send Mail Transform).
fer Protocol. Controls e-mail transfer between mail systems. ), The data encrypted at the protocol level in the mail server or the like that controls the transfer of mail is decrypted on the mail server, so the confidentiality is limited. That is, if each system administrator or the like managing an unspecified number of mail servers existing on the communication path has malicious intent, the mail data can be easily eavesdropped. So, in the mail system,
The mail data itself is encrypted at the highest level of the application layer, and a method is adopted in which any device on the network cannot read the mail by anyone other than an authorized user. At present, PEM (Privacy E) is an email system that supports text data.
Enhanced Mail), PGP (Pretty Good Privacy), and multimedia data MIME format (Multipurpose
Internet Mail Extensions. S / MIME (Secure MIME) that supports multi-media data such as characters, images, voices, and videos other than ASC11, which is the US standard character code for information exchange, that can be handled by Internet e-mail. And other secure mail systems have become widespread. In these technologies, the above-described data concealment, authentication of a sender by a digital signature, a function of ensuring data integrity, and the like are realized.

[0004] However, since the above-mentioned technology encrypts the mail data at the highest level of the application, it has a sufficient security function between the end-to-end sending and receiving the mail data, but has a sufficient security function between the networks. Data flow control cannot be performed based on the mail data contents. Therefore, the encrypted mail data is decrypted on the mail server, and the security policy (from the viewpoint of how much security is maintained.
A mail guard MG (Mail Gard) is used as a technique for performing data flow control in accordance with equipment costs (including software) and safety). This device mainly uses IP address, TCP (Transport Control Pro
Tocol) Port No. and the like are used together with a device called a firewall FW (FW: Firewall) having a function of performing flow control, and realize flow control of each network layer and the entire application layer.

[0005]

A mail system is a DNS (Domain Name Service) which is an Internet telephone directory.
Use e) to control mail transfer according to the priority value of the transfer destination mail server. Therefore, the communication route of mail
It cannot be specified and follows a plurality of communication paths. Therefore, there is a possibility that a malicious user may always be present in the mail transfer path, and the destination user receives his / her own data at the mail server on the way using a mobile terminal, etc. It is also possible to check the data. This problem will be described below.

FIG. 2 shows T which is a user terminal in each of the security domain D1 and the security domain D2.
1 shows a case where mail data is transmitted from one user U1 to a user U2 of a terminal T2. Here, each security domain is a set of networks having the same security policy. For data passing through the boundary, data transmission from the inside to the outside and data reception from the outside to the inside, In order to perform the flow control described above, a mail guard device (hereinafter referred to as mail guard) MG is installed. In general, the mail guard MG installed at each domain boundary has no relation to the security policy with the mail guard MG installed in another domain, and the data passing according to the security policy of its own domain is Implement control according to the security policy of the own domain. In terminal T1, terminal T2
If you send email data to
Since the data transmission policy to the outside of the domain D1 has been matched, the mail guard MG1 existing at the boundary of the security domain D1 permits the passage of data. Assuming that the transmission destination user U2 can receive this data on a mail server existing on a route halfway with the mail guard MG2 of the security domain D2, this performs flow control of the mail guard MG existing in the security domain D2. This means that the user U2 has received the mail addressed to himself, which means that the check by the security policy of the security domain D2 is not performed.

On the other hand, when a user of the security domain D1 illegally takes out data existing in the security domain D1 and transmits the data from another domain to a user of the user U2 of the security domain D2 (an illegal route shown in FIG. 2). Consider a). Also in this case, if there is no problem with the policy of the mail guard MG of the security domain, the mail data is transmitted to the terminal T2, and the user U2 can read the mail data. These examples show that mail communication that violates the security policy of a plurality of security domains as a whole in the mail system separated by the mail guard MG can be performed.
Therefore, in any mail communication between security domains, it is necessary to guarantee that mail data is transmitted and received via the flow control of the mail guard MG existing in each security domain. In order to realize this, it is necessary to control the flow of mail data based on the contents of mail data in each mail guard MG while constructing a virtual communication path (VPN) for mail data between end-to-end. No.

A known example is disclosed in Japanese Patent Application Laid-Open No. 11-33115.
No. 2 and JP-A-7-250059. JP-A-11-
No. 3,315,152 is a method of encrypting a destination address itself of a mail header portion specified by a mail protocol such as SMTP, and cannot use an existing protocol. The problem of this known example is that a commercially available mailer or the like cannot be used and cannot be adopted as a mail system used on the Internet. JP-A-7-2500
No. 59 is a method of using a common key and guaranteeing a route using nodes having the same key. There is a problem of key distribution to be used because a common key system is used (conversely, a public key system as in the present invention is not used).

[0009] An object of the present invention is that mail data transmitted via a route other than a legitimate communication path to a destination user (ie, mail data that does not pass through a legitimate flow control) is not transmitted to the destination user, or And a mail system, a mail guard device, and an operation terminal for ensuring that reading is not possible.

Further, as described above, there is a limit in performance in mechanically controlling all the contents of user data by all the mail guards MG, and multimedia data such as images and sounds need to be confirmed by a human system. It is even more difficult to realize the above flow control. Therefore, a further object of the present invention is to provide a mail system, a mail system, and a mail system capable of eliminating the duplication of these processes, optimizing flow control in a virtual communication channel of mail data, and minimizing operation work. A guard device and an operation terminal are provided.

[0011]

SUMMARY OF THE INVENTION The present invention relates to a mail system in which encrypted mail is transmitted and received between a mail source and a destination user via a virtual communication path. One or more e-mail guard devices are provided, and at the e-mail sender, the e-mail header, the content encryption part obtained from the e-mail text, the destination signature part, and the name of the e-mail guard apparatus to be relayed by itself A mail message including a token part having a token signature, a content signature part, and a path assurance control information part is edited, generated, and transmitted.
After verifying the sender, the mail header, the content encryption part obtained from the mail body, the transfer destination signature part, the token part with the name of the mail card device to be relayed by itself,
A mail message including a path assurance control information having a content signature section is edited, generated and transmitted. At a mail transmission destination, the security of the mail message transmitted through the mail guard device and the sender A mail system that receives a mail message after verifying the above is disclosed.

Further, according to the present invention, the mail transmission source and the mail guard device determine the mail guard device to be their own relay partner based on a route assurance control table indicating the correspondence between the mail sender and the mail guard device of the relay partner. A mail system according to claim 1 is disclosed.

Further, in the present invention, the mail source uses the mail transmission path assurance control table, the mail guard device uses the mail guard path assurance control table, and the mail transmission path assurance control table uses the mail transmission path assurance control table. From the viewpoint of the sender, if there is a route through the mail guard device, in addition to the instruction of the correspondence between the mail sender and the mail guard device of the relay partner, an instruction to that effect if there is a route where the mail does not pass through the device. In the case of a route instruction not via the mail guard device, the mail sender sends out the mail data without generating the above-mentioned route guarantee control information. If there is a route through the mail guard device from the viewpoint of the mail guard device as the self, the instruction of the correspondence relationship between itself and the mail guard device of the relay partner is If there is a route connected to the user terminal without passing through the mail guard device, it is assumed that the user terminal has an instruction to that effect, and the mail guard device that has received the message sends the mail message to this user terminal. A mail system is disclosed in which when it is confirmed that the token portion for the user is created and transmitted to the user terminal.

Further, according to the present invention, the route assurance control table
Disclose a mail system that is assumed to be created statically.

Further, according to the present invention, a plurality of mail guard devices existing on a certain mail communication route overlap and process the flow control contents of mail data executed by another mail guard device existing on the communication route. In order to avoid this, the flow control of mail data performed by another mail guard device is checked by checking the policy data of the other mail guard device, so that the mail data can be transmitted between end-to-end of the mail data. A mail system that avoids duplicate flow control processing is disclosed.

Further, according to the present invention, the mail guard path assurance control table is provided in a search directory server connected to a mail system network, and the mail card device reads and uses this table. Disclosed mail system.

Further, the present invention relates to a mail system for performing encrypted mail communication between a mail source and a destination by a virtual communication path, wherein the mail is interposed between the mail source and the destination. In a mail guard device that relays data, a mail gateway unit that performs mail verification and flow control on a sent mail message,
Relay path determining means for determining another mail guard device of the relay destination to be the other party based on the destination user address; a token part, a content signature part, and a content based on the received mail message and the determined mail guard device name of the determined relay destination Means for generating path assurance control information having an encryption section, means for editing and generating a mail message including a mail header, a transfer destination signature section, and the generated path assurance control information, and means for controlling transfer of the mail message Are disclosed.

Further, the present invention relates to a mail system for performing encrypted mail communication between a mail source and a destination by a virtual communication path via a mail guard device. Means for determining the mail guard device of the relay destination from the user address of the transmission destination, and a token part, a content signature part, and a content encryption part based on the outgoing mail data and the determined mail guard device name of the relay destination. A mail comprising: means for generating path assurance control information; means for editing and generating a mail message including a mail header, a transfer destination signature unit, and the generated path assurance control information; and means for controlling transfer of the mail message. An operation terminal in a system is disclosed.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In this embodiment, a public key management base is assumed, and a public key and a secret key used for authentication of secure mail and the like are stored in an authentication server (CA: Certification Authority) which is a component of PKI. ), And each user terminal, mail guard MG, etc. 509, LD
Using a directory service such as an AP (Light Weight Directory Access Protocol), a directory server (DS:
Directory Server. From a server that provides a search function)
X. An environment where a public key can be obtained by receiving a certificate such as 509 is assumed. In addition, a master key such as a common key or a secret key used for encryption
It is assumed that there is a key management platform that can distribute and update the key management information, and detailed description will not be given in the following embodiments.

FIG. 1 shows a network configuration and network components described in an embodiment of the present invention. Security domain D1 (1) having the same security policy
0), D2 (11) and D3 (12) are connected by an external network (20). Mail guard The mail guard MG1 (40) is assigned to the security domain D1 (1
0) and the outside thereof, and similarly, the mail guard MG2 (41) and the mail guard MG3 (42) also have the security domain D2 (1).
1), installed at the boundary point between D3 (12) and the outside. Each secure domain D1 (10), D2 (11) and D3 (12) includes a plurality of mail servers (MS: Mail S).
erver) (51 to 60) and a terminal T (Terminal) (70 to 73) on which a mail agent (Agent) is mounted. The external network includes a directory server (DS) (30) for providing information such as PKI.
The mail guard MG, the terminal T, and the like obtain public key information, route assurance control information, and the like from the directory server DS (30), and implement security mail communication, a route assurance control function, and the like.

In the mail server MS (51-60) in each security domain, the smtpd of the mail server
(Mail transfer protocol) The server function performs mail path control and mail data transfer processing. An unspecified number of mail servers MS exist in the external network (20).
The mail data transferred by the smtpd server function of S reaches the mail guard MG installed at the entrance of the security domain to which the destination user belongs via the plurality of mail servers MS. The mail server has
It is not necessary to provide the functions shown in the embodiments of the present invention, and there is no problem even if the Internet is considered.

The mail terminal T generates data for constructing a virtual communication path between the mail sender and the mail receiver based on the mail data transmitted from the general-purpose mailer and the mail address of the destination user. A mail agent function for converting mail data received from a mailer into a mail format necessary for forming a virtual communication path is provided. The receiving mail agent function includes the following functions. -E-mail encryption / signature function: Encrypts the e-mail data received from the mailer and creates a message digest of the e-mail body (MD: Message Digest, for example, a digest obtained by using a digest function on the e-mail body). And a function to generate a digital signature using the sender's private key. Relay route control function: A function of determining the mail guard MG of the relay destination of the user from the domain of the user mail address of the transmission destination. For example, in the terminal T1, the mail guard MG1 which is the exit is determined. -Route assurance control information generation function: a certificate of the mail server MG including the public key of the relay destination mail server MG is obtained from the directory server DS, a common key obtained by encrypting the mail text, and the mail address of the user of the mail transmission destination And the like with the public key of the above-mentioned relay destination mail guard MG and generate it as route assurance control information (token).
-E-mail message editing function: Encrypted data, digital signature data,
A function that generates a digital signature for the hash value of the entire token and edits the mail format accordingly. The mail guard MG relays the mail, verifies the integrity of the transferred mail and verifies the sender, performs flow control according to the security policy, and determines the relay mail guard MG of the transmission destination user. Provide a mail gateway function. The mail gateway function is composed of the following functions.・ Email verification function: In addition to verifying the entire integrity of the transferred mail and the authentication of the mail agent, decrypting the encrypted data part,
A function to authenticate a sending user of received data or a mail guard MG. Flow control function: a function of determining whether or not the mail data can pass based on the data content of the decrypted mail body in accordance with the flow control policy held for each mail guard MG. In the case of a policy violation, a message notifying the message discarding is transmitted to the transmission source user.

Further, the mail guard MG also has a relay route control function, a route assurance control information generation function, and a mail message editing function in the same manner as the agent function. A token of the mail guard MG is generated, and the mail format is edited by replacing the token portion of the received mail format with the generated new token. Further, the mail guard MG decodes the received and relayed mail message, transmits the data to a proxy function (a proxy is a proxy) that performs flow control according to a security policy, and in the case of data that can be transferred, Mail guard M of relay destination
A transfer control function for generating a token for G and replacing the token of the received mail format is provided.

Next, an outline of the flow of mail data in the route assurance control system used in the present invention will be described. FIG.
In the configuration of FIG. 1, the security domain D1 (1
Using the terminal T1 (70) installed in the user u), the user u
serX is the user use of each of the terminals T2 (71) and T3 (72) of the security domain D2 (11).
rA and userB and security domain D3 (1
The case where a mail is broadcast to the user userC of the terminal T4 (73) of 2) is shown. In the following, after userX uses a mailer to send an email, the destination user
The flow of mail data and the outline of processing until the mail is received by A will be described with reference to FIG.

When userX creates a mail using the mailer and presses the send button (S100), the mail data is received by a mail agent (Agent) existing in the terminal (S200). At this time, the mailer sends mail data to the agent using SMTP. Therefore, from the mailer point of view, the agent is smtp
Operate as d server. The agent first sends the destination users userA, userB, and use
With reference to the agent path assurance control table (FIG. 4) of the directory server DS using the rC domain name as a key, it is determined whether or not the path assurance control function is required (S30).
0). In the embodiment, userA, userB, user
C are both users who use terminals existing in different security domains, and mail is sent to the mail guard MG1.
(40), the MI to which the route assurance control information for the mail guard MG1 (40) is added.
The mail data in the ME format is edited (S400), and the mail is transferred according to the transfer control function of the mail server (S500). The above is the outline of the operation of the mailer and the agent operating in the terminal.

Next, the mail data to which the route assurance control information transmitted by the agent is added arrives at the mail guard MG1 (40) after passing through an arbitrary number of mail servers. The mail guard MG1 (4
In 0), verification of various signatures of the received mail data and flow control based on the flow control policy are performed, and it is determined whether the data can be transferred. If the signature can be verified and there is no violation of the security policy of the mail guard MG1 (40), the mail guard MG2 (41), which is the relay mail guard MG obtained from the mail guard MG path assurance control table (FIG. 5), The mail data in the MIME format to which the path guarantee control information for the mail guard MG3 (42) is added is edited (S600), and a transfer of the mail data is requested to the smtpd server (S700). In this example, the mail addressed to userA and userB from FIG.
Since the mails addressed to the mail guard MG2 (41) and userC are directed to the mail guard MG3 (42), the mail guard MG2 (41) and the mail guard MG3 (42)
Is converted to the MIME format to which the path guarantee control information is added.

The mail addressed to userA and userB is
The mail transfer control in the external network eventually results in the mail guard MG2 (41), which is the boundary point of the external domain of the security domain D2 (11).
To reach. In the mail guard MG2 (41), as in the case of the mail guard MG1 (40), after verifying the signature of the received mail, the transfer destination is set to "user" according to the path assurance table (FIG. 5) of the directory server DS (30). 』
, The route assurance control information for the destination user in the route assurance control information is created, and the received mail is replaced with the mail guard MG control information.
The same processing as in the mail guard MG1 (40) is performed, and Sm
Requests transmission of mail to the tpd server function. The mail is passed through an arbitrary mail server and finally received by the agent of the terminal T2 (71) of userA (S800). Since this mail is also a mail addressed to user3, similarly, the mail guard MG3 (42)
To reach. The agent of the terminal T2 (71) verifies the signature of the mail guard MG2 (41) in the same manner as the mail guard MG1 (40) when the user A clicks the mailer's reception button at the terminal T2 (71). , U
The common key DEK (Dat
The e-mail is decrypted using the e-encrypted key and the mail data is converted into a normal mail format (S900), and then the mailer receives the mail from the agent using a mail reception protocol such as POP3 (S900).
1000). The unspecified number of smtpd servers existing in the network between the agent of the sender terminal, each mail guard MG, and the agent of the receiver terminal are based on a mail transfer algorithm using DNS which is an Internet telephone directory. It transfers each mail and is realized by the existing technology, and the description is omitted.

Next, in order to perform the route assurance control which is the central part of the present invention, the route assurance control function implemented in the agent and the mail guard MG adds an operation to the mail data and thereby constructs a virtual communication path. Will be described.
First, the details of the format of the mail data in this embodiment including the route assurance control information added to the mail data will be described, and then the details of the processing of creating and changing the mail data in each agent and the mail guard MG will be described.

FIG. 6 shows a MIME format mail format with path guarantee control information used in this embodiment. This mail format is a mail header (MH: Mail Header) 80a and a mail body in the normal mail format.
A content signature unit 80d, a token unit 80c, and a transfer source signature unit 80b are added in addition to a content encryption unit 80e that encrypts (hereinafter referred to as content) 81. The three types of information 80b and 80 added to this normal mail
c and 80d are collectively referred to as route assurance control information. The mail message sent from the mailer to the agent is
Usually, it is composed of a message header (MH) and content. Here, the content includes data of a mail body created by a mailer and data of an attached file. The content is subjected to an encryption process using a common key DEK used for encryption generated by the sender. This is shown by the shaded portion at the bottom of the mail format on the left side of FIG. The content encryption unit 80e. By encrypting the content, the content itself is concealed and secure mail is realized.

Next, the content signature unit 80d will be described. This part is performed by encrypting the cache value obtained by the hash algorithm with the secret key of the mail transmitting agent or the mail guard MG transmitting the mail to the plaintext content 81 to obtain the digital value of the transmission source or the transmission source. It is obtained by signing. Based on the signature of the transfer source and the path guarantee control table (FIGS. 4 and 5), the mail transfer path in the present invention is specified, and the path guarantee is realized. That is, it is possible to prevent unauthorized mail transmission or transfer by discarding mail from a computer other than the computer specified in the path assurance control table as being illegal transmission or transfer and discarding the mail. . The data used for the authentication of the transmission source or the transfer source is the above-described content signature unit 80d. The token portion 80c is a portion obtained by encrypting the common key DEK used in encrypting the above-described content and the recipient's mail address using the mail guard MG of the transfer destination or the public key of the mail recipient. , A token recipient ID and a signer ID. Note that the token section 80c is composed of a plurality of parts, and the mail guard MG and the agent that have received the mail data use the token part of their token receiver ID from the plurality of token parts. By using the token unit 80c, the mail guard MG or the agent that has received the mail decrypts the token unit using the secret key and extracts the common key DEK used when encrypting the mail body. Next, by using the decrypted common key DEK, it is possible to decrypt the content encryption unit which is the encrypted content. When it is necessary to perform flow control on the contents of the mail body due to the security policy, the mail guard MG passes the decrypted content to various flow applications that perform flow control, and implements flow control based on the content of the content. It is possible to do. As described above, the token unit 80c can provide a mechanism for only the mail guard MG or the agent specified in the path assurance control table to decrypt the received mail, whereby the encrypted secure mail communication path can be provided. On the way, we provide the basis to realize the flow control based on the mail contents. Further, the token part 80c and the content signature part 80
d and the hash value of the entire content encryption unit 80e are obtained, and a digital signature of the sender or the transferor is obtained. This is the transfer source signature unit 80b. This allows
It is possible to verify the integrity of the entire mail data including unencrypted token data, unencrypted data such as the content type defined in the MIME format indicating the content and the content of each data in the encryption unit. It becomes possible. In FIG. 6, 82 is tokens 1 to n, 83
Is the token information person ID, signer ID, DEC (Data Enp.
liction Key), user address list, etc.

As described above, in each agent and the mail guard MG, route guarantee control information is added to the received mail data, and the mail data is transferred, so that other than the mail guard MG for relaying the mail and the agent receiving the mail. It is guaranteed that the received mail cannot be verified and decrypted. As a result, Mailguard M
The mail data transferred via a route other than the normal G route cannot reach the receiving user or cannot be decrypted, so that the mail content cannot be read. Next, the details of the processing of the agent and the mail guard MG, which are divided into the agent processing at the terminal transmitting the mail, that is, the agent processing on the mail start side, the mail transfer processing on the mail guard MG, and the agent processing on the reception side, will be described.

FIG. 7 shows a process in which the transmitting agent converts a mail received from the mailer into a mail format with path assurance control information. FIG.
Shows the processing flow. First, the mail data received from the mailer is separated into a mail header (MH) 80a and content (S410). Next, a message digest of the content is created (S420), and the message digest is signed using the secret key of userX, and a content signature unit 80d is created (S430). The content is encrypted using the execution key DEK, which is a common key, for the separated content, and the content encryption unit 80e is created in accordance with the MIME format (S440). Next, the certificate of the mail guard MG1 (40) is obtained using the directory service (S
450), the common key DEK and the mail address of the mail receiver are encrypted using the public key of the mail guard MG1 (40), and the receiver's identifier (token reception ID)
And the signer ID, and the token unit 80c is created (S460). Here, regarding the mail address included in the token part 80c, the mail guard MG2 (41)
The token part for us is the destination of mail data us
erA, userB, and the mail guard MG3 (4
The token part for 2) is the mail address of userC. Further, in order to enable the integrity of the entire path assurance control information and the source of the path assurance control data to be identified, the transfer source signature is executed for the entire content encryption unit 80e, content signature unit 80d, and token unit 80c.
A transfer source signature unit is created (S470). Finally, the mail header 80a, the transfer source signature unit 80b, and the token unit 80
c, content signature unit 80d and content encryption unit 8
0e is edited into a mail format with path assurance control information in accordance with the MIME format (S480).

FIG. 8 shows that the mail guard MG1 (40)
The mail 90 with the path assurance control information transferred from the agent is received, and the mail guard MG2 as the transfer destination is received.
The process for changing to the mail format 92 with the route guarantee control information for (41) is shown. FIG.
Shows the processing flow. First, the mail data in MIME format with the path assurance control information created by the agent is decomposed into a mail header 90a, a transfer source signature unit 90b, a token unit 90c, a content signature unit 90d, and a content encryption unit 90e (S610). Next, the source signature part is decrypted using the public key of the source agent,
The integrity of the received mail is verified by comparing it with the hash of the token part, the content signature part, and the hash of the entire content encryption part (S620). Next, Mail Guard MG1
Decrypts the token part using the secret key of
Is taken out (S630). Using this common key DEK,
Each content portion of the content encryption unit is decrypted, and the mail content is extracted (S640). Furthermore, the integrity of the content is verified by comparing the hash value of the decrypted content with the hash value of the content obtained by decrypting the content signature part with the public key of the transfer source agent (S650). When performing flow control based on the contents of the content, the decrypted content is passed to the flow control application, and the result is used to determine whether or not the mail can be flowed (S660).

When the mail can be transferred, a content signature part and a transfer source signature part are created using the secret key of the mail guard MG1 (40), like the agent (S).
670). Further, a token part is created using the public key of the mail guard MG2 that is the transfer destination (S680). Finally, a mail header is added to the created transfer source signature section, token section, content signature section, and content encryption section, and edited in the MIME format to create the format 92 (S690).

FIG. 9 shows a process in which the agent of the terminal T2 (72) of the user A receives the transferred mail 93 with the route guarantee control information and changes the mail format to the mail format to be transmitted to the mailer. FIG. 13 shows the processing flow. The mail data in MIME format with the path assurance control information created by the agent
It is decomposed into a transfer source signature part, a token part, a content signature part, and a content encryption part (S910). Next, by decrypting the transfer source signature unit using the public key of the transfer source mail guard MG1 (40), and comparing it with the hash of the token unit, the content signature unit, and the entire content encryption unit,
The integrity of the received mail is verified (S920). Next, the token part is decrypted using the secret key of the agent, and the common key DEK is extracted (S930). This common key DEK
Is used to decrypt each content part of the content encryption unit and extract the content (S940). Furthermore, the integrity of the content is verified by comparing the hash value of the decrypted content with the hash value of the content obtained by decrypting the content signature part with the public key of the relay source mail guard MG1 (40) (S950). The processing so far is basically the same as the operation of the mail guard MG.

Next, the decrypted content and the mail header are assembled, and the mail is passed to the mailer (S960).
Next, an outline of the configuration of a route assurance control table (FIGS. 4 and 5) used by the mail guard MG and the sending agent for performing the route assurance control to specify the mail guard MG or the receiving agent of the transfer destination and this table are shown. A method for determining a relay destination mail guard MG or an agent using the method will be described.

FIG. 4 is a table referred to by the route assurance control function having the agent attribute. This table is referred to when the agent provided in the terminal transmits mail data. Agent attribute is Mailguard M
Along with the G attribute, it is data set statically (for example, at the time of installation, at the time of product delivery, or at the time of start) in the agent and the mail guard MG configuring this embodiment. "Unnecessary" in the table indicates mail communication within the same security domain, and indicates that the route assurance control is unnecessary. In this case, the agent transmits the mail to the smtpd server without processing the mail data received from the mailer, that is, without editing the mail data into the MIME format to which the path guarantee control information is added. If there is a mail guard MG name in the table, route assurance control information for the mail guard MG is created. Specifically, by encrypting the token portion with the public key of the mail guard MG, it is assured that only the mail guard MG can decrypt the token portion.

FIG. 5 shows a table referred to by the route assurance control function having the mail guard MG attribute. "-" Indicates that no data is set because the mail guard MG does not exist in the transfer source domain. If the name of the mail guard MG is described, like the agent,
A token part for the mail guard MG is created. In addition, if it is described as a user, there is no mail guard MG of the transfer destination, and the received mail data is created in the token part for the user of the mail address of the transmission destination, and sm
Transfer to tpd server.

In the embodiment shown in FIG. 3, the agent of the terminal T1 (70) has a domain belonging to userX of MG-dm.
n-1. co. jp, and the domain to which the destination user belongs is userA and userB, respectively, Mg-d
mn-2a. co. jp, Mg-dmn-2b. c
o. jp, it can be seen from the path assurance control table (FIG. 4) that the mail guard MG of the transfer destination is the mail guard MG1. In addition, mail guard MG2 (41)
Domain is Mg-dmn-g2. co. jp, and the domain to which the receiving user belongs is userA, us
erB is Mg-dmn-2a. co. j
p, Mg-dmn-2b. co. jp,
The transfer destinations are T1 (71) and T1 which are the terminals of userA and userB, respectively, from the route assurance control table (FIG. 5).
2 (72).

FIG. 14 shows functional blocks of the mail guard MG described in this embodiment. Regarding the agent, when it functions as a sending agent and when it functions as a receiving agent, it is almost the same as the function of the MG, respectively.
A detailed function of the present embodiment will be described. Mail communication function (1
00) has a function of a mail transfer control protocol having a function of an ordinary Smtpd server. When a mail is transferred from another mail server MS or the like, a received mail serial number is assigned to the received mail, and the received mail box (Box) is received.
The mail is stored in (200).

Next, the data analysis function unit (110) is activated using the received mail serial number as a key. The data analysis function unit fetches the mail into the local area using the received mail serial number as a key, performs format conversion such as Base64, and then decomposes the mail data with path guarantee control information in MIME format into each content. Then, the transfer source signature unit and the content signature unit are verified. When the authentication of the transfer source and the integrity of the received mail can be verified by the verification processing, the received mail serial number is notified to the decryption function unit (120). The decryption function unit (120) extracts the received mail from the received mailbox (200) and stores it in the local area. Next, the common key DEK used for content encryption is extracted from the data obtained by decrypting the token part using the secret key of the mail guard MG, and the encrypted content part is decrypted using the DEK. It stores itself (mail headquarters and attached file) in the content table (220) together with the serial number of the received mail, and sequentially activates various flow control function units (130) registered in the flow control entry table (210).

The various flow control function units (130) read the security policy relating to the flow control of the mail guard MG from the security policy file (230), and the type of the content registered in the content table (220) and its content Based on the contents of the content, it is determined whether or not the mail can be transferred, and the transfer function is notified to the decryption function unit (120). If the decryption function unit (120) determines that the content is untransferable, the decryption function unit (120) notifies the mail communication function unit (100) to delete the entire mail with the mail serial number in the reception mailbox (200). The communication function unit (100) transmits the received mail box (20)
0), the received mail is deleted, and a notification that the mail cannot be transferred is transmitted to the mail sender. If all the registered flow control function units (130) determine that the mail can be transferred, the decryption function unit (120)
Starts the encryption function unit (140) using the reception serial number of the mail as a key. Using the LDAP from the directory server DS, the encryption function unit (140) determines the mail guard MG or the like of the relay destination and obtains the public key of the MG or the agent of the transfer destination.

Next, a token portion is created using the transfer destination public key, and a transfer source signature portion and a content signature portion are generated using its own private key. Conversion table (240)
Then, the data configuration function unit (150) is started using the received mail serial number as a key. The data configuration function unit (150) uses the received mail serial number as a key
The received mail and the converted content are read from the received mailbox (200) and the content conversion table (240).

Next, a MIME format extended content type is provided, and the content is assembled into the extended MIME format of this embodiment.
After the conversion of the data format such as ase64, the converted mail is stored in the transfer mailbox (250). The mail assembled here is shown in FIG. Finally,
The mail transfer function unit (100) transfers the transfer mail from the transfer mailbox (250) using a route control function based on DNS which is an Internet telephone directory.

In order to prevent a plurality of MGs present on a certain mail communication path from performing duplicate processing of mail data flow control contents executed by another MG existing on the communication path, another MG is required. By checking the flow control contents of the mail data performed by the MG of the other MG by checking the policy data of other MGs, the end-to-to
It is possible to avoid the duplication of the mail data flow control processing between the ends, minimize the processing time of each MG, and further minimize the arrival time of the mail data between the end and the end. This is based on the premise that the route guarantee control tables for the operation terminal and the mail guard are used. And in the end-to-end communication path,
As shown in FIG. 16, the communication path between the MGs is included and defined as “MG as an end point of the communication path between the MGs”.
Take a viewpoint of whether or not this MG. The mail guard having the path guarantee control mechanism has control functions such as a flow control function (see FIG. 14). This function performs flow control using the security policy information (230). By passing this information between MGs,
It is possible to avoid performing flow control based on the same security policy within a single path implemented by the present invention. As a result, the security policy is centrally managed using technology such as a policy server, and the necessary security policy information is distributed to each mail guard MG, thereby eliminating redundant processing of flow control within a single path. I do.

As described above, according to the embodiment of the present invention, in a secure mail system in which the body of a mail is encrypted between end-to-end, concealment of communication data, authentication of a transmission source, and integrity of communication data By incorporating various flow control functions based on the contents of the mail data on a virtual communication path that guarantees security attributes such as the above, the flow control based on the mail contents is performed in the same way as a normal mail system that is sent and received in equal parts The mechanism which enables it is provided. By using such a method,
Even in the secure mail system that will spread rapidly in the future, it will be possible to perform communication audits, as well as ordinary mail systems without encryption, as well as information leakage via networks, sender impersonation, A great effect can be expected in preventing unauthorized reception or the like during the relaying of. As a result, data communication using the mail system can be performed even for the most important data such as national secret and corporate secret.

[0047]

According to the present invention, in an encrypted mail system realized between end users, transmission and reception of encrypted mail on a path other than a communication path other than a prescribed communication path are impossible. In addition, the present invention provides a base that enables various security policies, including the contents of encrypted mail data, to be incorporated along the regular communication path.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a network configuration according to the present invention.

FIG. 2 is a conceptual diagram of an entire system.

FIG. 3 is a detailed configuration example diagram of the present invention.

FIG. 4 is a diagram showing an example of a path guarantee control table (for agent) according to the present invention.

FIG. 5 is a diagram showing an example of a path guarantee control table (for MG) of the present invention.

FIG. 6 is a mail format diagram with route assurance control information created by the present invention.

FIG. 7 is an explanatory diagram of a mail format editing method with route assurance control information of a mail transmission agent.

FIG. 8 is an explanatory diagram of a mail format editing method with route assurance control information of MG.

FIG. 9 is an explanatory diagram of a mail format editing method with route assurance control information of a mail receiving agent.

FIG. 10 shows the entire processing flow.

FIG. 11 is a flowchart of a transmission agent process.

FIG. 12 is a flowchart of an MG transfer process.

FIG. 13 is a reception agent processing flowchart.

FIG. 14 is a block diagram of a route assurance control function.

FIG. 15 is a mail format with path guarantee control information.
(MIME format).

FIG. 16 is an explanatory diagram of avoiding redundant processing in flow control.

[Explanation of symbols]

 Reference Signs List 10 security domain D1 11 security domain D2 12 security domain D3 20 external network 30 directory server 40 mail guard 1 41 mail guard 2 43 mail guard 3 51-60 mail server 70 terminal 1 71 terminal 2 72 terminal 3 73 terminal 4 100 mail communication Function unit 110 Data analysis function unit 120 Decryption function unit 130 Flow control function unit 140 Encryption function unit 150 Data configuration function unit 200 Receive mailbox 210 Flow control entry table 220 Content table 230 Security policy DB 240 Content conversion table 250 Transfer mailbox

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H04L 9/10 H04L 9/00 675B 9/32 11/26 12/22

Claims (8)

[Claims] In a mail system in which an encrypted mail is transmitted and received between a mail source and a destination user via a virtual communication path, mail data is relayed in a mail relay path.
One or more e-mail guard devices are provided, and the e-mail sender has an e-mail header, a content encryption part obtained from the e-mail body, a signature part of the transfer destination, and a name of the e-mail guard apparatus to be relayed by itself. A mail message including a token part, a content signature part, and a path assurance control information part shall be edited, generated and transmitted. In each mail guard device, security and sender Path verification control that has a mail header, a content encryption part obtained from the body of the mail, a transfer destination signature part, a token part with the name of the mail card device to be relayed by itself, and a content signature part Edit and generate a mail message containing the information and send it. At the mail destination, the mail message is sent via the mail guard device. Mail system was assumed to receive mail message safety of e-mail messages and after performing the verification of the sender was. 2. The mail transmission source and the mail guard device,
2. The mail system according to claim 1, wherein the mail guard device serving as the relay partner is determined based on a path assurance control table indicating the correspondence between the mail guard device and the relay partner mail guard device. 3. An e-mail transmission source uses an e-mail transmission path assurance control table, an e-mail guard device uses an e-mail guard path assurance control table, and the e-mail transmission path assurance control table is transmitted from the e-mail transmission source. If there is a route via the mail guard device, in addition to the instruction of the correspondence between the mail sender and the mail guard device of the relay partner, if there is a route where the mail does not pass through the device, there is an instruction to that effect. If the route is not routed through the mail guard device, the mail sender sends out the mail data without generating the route guarantee control information. From the viewpoint of the mail guard device, if there is a route through the mail guard device, in addition to the instruction of the correspondence between itself and the mail guard device of the relay partner, the mail If the path to the user terminal connected not through the over de device, the mail guard device shall have an indication of the effect of the user terminal, receiving the message,
3. The mail system according to claim 2, wherein when it is confirmed that the transmission destination of the mail message is this user terminal, a token portion for the user is created and transmitted to the user terminal. 4. The mail system according to claim 2, wherein said route assurance control table is created statically. 5. The mail guard path assurance control table is provided in a search directory server connected to a mail system network, and the mail card device reads out this table and uses it. Item 3. The mail system. 6. A plurality of mail guard devices existing on a certain mail communication route avoid duplicate processing of mail data flow control contents executed by another mail guard device existing on the communication route. Therefore, by checking the flow control of mail data performed by another mail guard device and the policy data of the other mail guard device, the flow control process of mail data between end-to-end of mail data is performed. 2. The mail system according to claim 1, wherein duplicate processing of the mail is avoided. 7. A mail system for performing encrypted mail communication between a mail source and a destination via a virtual communication path, wherein mail data is relayed between the mail source and the destination. A mail gateway means for verifying a mail message sent and controlling the flow of the mail message, and a relay path for determining another mail guard device to be a partner of the self from the destination user address. Determining means; generating means for generating path assurance control information having a token part, a content signature part, and a content encryption part based on the received mail message and the name of the mail guard device at the determined relay destination; a mail header and a transfer destination signature part Means for editing and generating a mail message including the above and the generation path assurance control information, and controlling transfer of the mail message E-mail gate device comprising: a stage, a. 8. A mail system for performing encrypted mail communication between a mail source and a destination by a virtual communication path via a mail guard device, wherein an operation terminal serving as a mail source includes a destination Means for determining a mail guard device of its own relay destination from the user address of the user, and path assurance control having a token part, a content signature part and a content encryption part based on the transmitted mail data and the determined mail guard device name of the relay destination Operation in a mail system comprising: means for generating information; means for editing and generating a mail message including a mail header, a transfer destination signature unit, and the above-mentioned generated path assurance control information; and means for controlling transfer of the mail message. Terminal.