JP3803522B2 - E-mail server system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electronic mail server system, and more particularly, to an electronic mail server system that realizes a mailing list that transmits a mail to a plurality of recipients only by the sender sending one mail.
[0002]
[Prior art]
With the development of the local area network such as an intranet laid inside a company or university, or a global network configured by connecting local area networks with routers, such as the Internet, various information can be obtained via computers. Digitized and transmitted / received. One of services via a network by a server connected to the network is transmission / reception of electronic mail. An e-mail is assigned to each user in advance, and is basically sent by the sender of the e-mail specifying the address of the recipient. As a general rule, the sender and the receiver are one-to-one. Transmit and receive.
[0003]
When sending multiple emails with the same contents, you can send them by specifying multiple destinations. May occur. Therefore, if an email address is registered in advance in the list and one of the registered members sends an email to a specific address, an email with the same content as the sent content is sent to another member. Mailing lists to be sent to have been put into practical use.
[0004]
Since e-mail is basically created in text format (meaning that it is not binary format), the transmitted content may be viewed, deleted, altered, etc. by a third party. There is a security problem that information is leaked. The same applies to the mailing list. For this reason, in recent years, various techniques for encrypting the contents of information between users as well as electronic mail have been developed. Encryption techniques can be broadly classified into two types: one that uses the same key for encryption and one for decryption, and another that uses different keys. When information is exchanged between remote users without the contents being known by a third party, it is suitable to use two keys for decryption different from the key for encryption. In recent years, public key cryptosystems in which one key is disclosed and the other key is secret are often used.
[0005]
There are mainly two methods for the existing encrypted mailing list processing for transmitting an electronic mail encrypted end-to-end from the sender to the receiver using the mailing list described above. One method is to create a public key encryption key pair for a mailing list. In this method, when the mail sender to the mailing list encrypts the mail using the public key for the mailing list and sends it, the mail is re-encrypted using the public key for each mailing list recipient and then forwarded. ing.
[0006]
The other way is not to create a public key encryption key pair for the mailing list. In this method, a mail sender to the mailing list is encrypted from the beginning with each recipient's public key and sent.
In this method, when there are a large number of recipients of the mailing list, it takes time to specify all the recipients of the mailing list for the sender to the mailing list. Therefore, it is common to use the method of creating the public key encryption key pair described above. is there.
[0007]
[Problems to be solved by the invention]
By the way, even when creating a public key encryption key pair, there are the following problems when there are a plurality of encrypted mail protocols premised on the use of public key encryption.
First, assuming that each mailing list recipient has a mail tool that supports the common encryption mail protocol for each mailing list, mailing list senders and recipients who are subscribed to multiple mailing lists must match the mailing list. Therefore, it may be necessary to use different encryption mail protocols. If a mail tool that you are familiar with supports only a single encrypted mail protocol, you must use another mail tool if you want to use another mailing list.
[0008]
The second point is that if the mailing list server supports multiple encryption mail protocols and the sender and receiver can freely select the encryption mail protocol, the public key for the mailing list is encrypted. This means that a mailing list server must be prepared in a format acceptable to each mail protocol. If there are n (n is a natural number) types of encrypted mail protocols, and an attempt is made to operate m (m is a natural number) mailing lists on a mailing list server, the mailing list key is set on the mailing list server. It is necessary to manage a maximum of n × m pairs. Further, even if the same encrypted mail protocol is used, if there are k types of encryption algorithms (k is a natural number), a maximum of n × m × k key pairs are required.
[0009]
At present, most of the mail tools only support a single encrypted mail protocol before the two points described above become a problem. The larger the mailing list, the more the encrypted mail protocol for all mailing list recipients. It is difficult to unify Therefore, there is a problem that it is difficult to encrypt an existing mailing list that is particularly large.
[0010]
The present invention has been made in view of the above circumstances, and is based on the premise that safety is achieved by transmitting and receiving an e-mail in an encrypted state between a sender and a receiver. An email server that can send and receive emails encrypted with different encryption methods and algorithms without unifying email encryption protocols and without having to prepare public keys for multiple encryption methods and algorithms The purpose is to provide a system.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a transmission unit that encrypts and transmits an e-mail, an encryption method storage unit that stores an encryption method used for each recipient, and a method for each recipient. a public key storage means for storing a public key, performs decoding of the transmitted e-mail from the previous SL transmitting means, stored in the public key storage means the stored encryption method to the encrypting method storage means Server means for encrypting and sending an e-mail for each recipient using the public key, and when the sending means sends the e-mail, the server means sends the public key of the server means to the sending means. The notification and transmission means encrypts the electronic mail using the public key of the server means .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an electronic mail server system according to an embodiment of the present invention will be described in detail. In this embodiment, the members of the ML are related to the encryption processing of the email message in all the delivery paths from the sender to the receiver of the mailing list (hereinafter, the mailing list is abbreviated as ML in the present specification and drawings). An e-mail server system that can perform encryption processing according to the encryption protocol for each recipient without being aware of the ML sender even when using mail tools corresponding to different encryption protocols will be described. In other words, in the present embodiment, since the content of the email is transmitted from the sender in an encrypted state and the receiver receives the content in an encrypted state, the delivery path between the sender and the email server Even if the delivery path between the e-mail server and the recipient is delivered by any delivery path, the communication contents are not viewed, deleted, altered, etc. by a third party, and information can be exchanged safely. It is assumed that.
[0013]
FIG. 1 is a block diagram showing a schematic configuration of an electronic mail server system according to an embodiment of the present invention. In the present embodiment, the contents of electronic mail are transmitted and received using TLS (Transport Layer Security) or SSL (Secure Sockets Layer) protocol. Referring to FIG. 1, an e-mail server system according to an embodiment of the present embodiment includes a TLS (SSL) -compatible e-mail transmission tool 10 used by an ML sender and an e-mail encryption process transmitted to the ML. Each of the ML recipients that performs the multi-protocol-compliant encryption ML server 20, the ML database D1 in which the ML recipient list F1 is recorded, the public key database D2 in which the public keys of the ML recipients are stored, and PGP (Pretty Good Privacy) compatible mail tools 30a and 30b, and S / MIME (Multi-purpose Internet Mail Extension) compatible mail tools 30c, which are mail tools to be used. The PGP compatible mail tools 30a and 30b and the S / MIME compatible mail tool 30c are described as examples of mail tools used by each ML recipient. The network configuration between the TLS (SSL) compatible mail transmission tool 10 and the multi-protocol compatible encryption ML server 20 is arbitrary.
[0014]
The TLS (SSL) -compatible mail transmission tool 10 holds an ML server name for each ML and has a TLS (SSL) client function. FIG. 2 is a block diagram showing an outline of the internal configuration of the multi-protocol-compatible encryption ML server 20. As shown in FIG. 2, the multi-protocol compatible encryption ML server 20 includes a TLS (SSL) server unit 21, an ML recipient search unit 22, a PGP processing unit 23, an S / MIME processing unit 24, a mail And a transmission processing unit 25.
[0015]
The TLS (SSL) server unit 21 receives an e-mail transmitted to the ML by TLS (SSL). The ML receiver search unit 22 searches the ML database D1 to acquire a list of ML receivers. The PGP processing unit 23 obtains the ML recipient's public key using the public key database D2, and encrypts the e-mail addressed to the ML recipient using the PGP. The S / MIME processing unit 24 obtains the public key of the ML recipient using the public key database D2, and encrypts the e-mail addressed to the ML recipient using S / MIME. The mail transmission processing unit 25 receives the processing results of the PGP processing unit 23 and the S / MIME processing unit 24 and transmits an e-mail.
[0016]
Referring to FIG. 1, the ML database D1 holds a recipient list F1 in which a recipient and a cryptographic protocol used by the recipient are paired for each ML. In addition, in FIG. 1, although the case where the receiver number uniquely assigned to each receiver is associated with the encryption protocol is described as an example, the present invention is not limited to this. For example, the e-mail address of the recipient may be associated with the encryption protocol. The ML database D1 may be on the same system as the multi-protocol-compatible encryption ML server 20 or on another system.
[0017]
Also, the public key database D2 in FIG. 1 holds public key data corresponding to the receiver and the encryption protocol used by the receiver. The public key database D1 may be on the same system as the multi-protocol compatible encryption ML server 20 or on another system.
[0018]
Next, the operation of the electronic mail server system according to the embodiment of the present invention having the above configuration will be described. FIG. 3 is a flowchart showing processing when a user transmits an e-mail addressed to ML in the e-mail server system according to the embodiment of the present invention. In FIG. 3, an ML sender inputs the contents of an e-mail from a terminal device such as a personal computer, for example, and inputs an ML address so as to be transmitted to the ML (step S10). Next, the TLS (SSL) compatible mail transmission tool 10 in FIG. 1 communicates with the ML server using the TLS (SSL) client function, and transmits mail (step S12). At this time, since the TLS (SSL) -compatible mail transmission tool 10 transmits the contents of the e-mail using the TLS (SSL) client function, the contents of the e-mail are encrypted in a broad sense and compatible with the multi-protocol. It is transmitted to the encrypted ML server 20. Through the above processing, the content of the electronic mail is encrypted and transmitted to the multi-protocol-compatible encrypted ML server 20.
[0019]
Next, the operation of the multi-protocol compatible ML server 20 that has received the e-mail will be described. FIG. 4 is a flowchart showing processing when the multi-protocol-compliant encrypted ML server 20 receives an e-mail. When receiving the access from the TLS (SSL) compatible mail transmission tool 10, the multi-protocol compatible encrypted ML server 20 receives an e-mail from the TLS (SSL) server unit 21 (see FIG. 2) (step S20). The mail addressed is received (step S22). Here, the TLS (SSL) server unit 21 and the TLS (SSL) compatible mail transmission tool 10 are in a client-server relationship, and the content of the encrypted electronic mail transmitted from the TLS (SSL) compatible mail transmission tool 10 Is received by the TLS (SSL) server unit 21, the content of the e-mail is decrypted.
[0020]
Next, the ML database D1 is accessed to search the recipient list F1, identify the ML recipient to which the transmitted e-mail is sent, and obtain the encryption protocol list used by the recipient (step) S24). Then, the following processing is performed for each ML receiver. First, it is determined whether or not the ML receiver uses S / MIME as an encryption protocol (step S26). If the determination result is “YES”, the S / MIME processing unit 24 (see FIG. 2) obtains the ML recipient's public key from the public key database D2, and sends an encrypted mail in a format corresponding to S / MIME. Create (step S28).
[0021]
On the other hand, if the determination result in step S26 is “NO”, it is determined whether or not the ML receiver uses PGP as the encryption protocol (step S30). If the determination result is “YES”, the PGP processing unit 23 obtains the ML recipient's public key from the public key database D1, and creates an encrypted mail in a format corresponding to the PGP (step S32). Finally, the mail transmission processing unit 25 transmits the encrypted processing result, that is, the processing result in step S28 or the processing result in step S32 to the ML member (step S34). At this time, the e-mail to be sent is encrypted with an encryption method suitable for the mail tool used by the recipient of the e-mail, so the encryption method of the mail tool used for each recipient Even if they are different, there is no problem.
In the process shown in FIG. 4, only the case where the mail tool used by the recipient is S / MIME or PGP is shown, but in the case of another encryption method, the process of step S30 is performed. A determination process and an encryption process when the determination result is “NO” are added.
[0022]
According to the embodiment of the present invention described above, since the multi-protocol compatible encryption ML server 20 supports a plurality of encryption protocols, the encryption protocol used between ML receivers is unified in each ML. Nonetheless, even if the network between the sender and the ML server is not secure, the encrypted mail can be received in a state where the sender's mail is encrypted from the time of transmission, so that it is possible to exchange information safely. .
In addition, since only the public key for TLS (SSL) needs to be prepared, it is not necessary to prepare the public key for the ML server for each of the plurality of encryption protocols on the multi-protocol compatible encryption ML server 20 side. Moreover, even when a plurality of encrypted ML operations are performed by the same multi-protocol-compatible encrypted ML server 20, the public key for the multi-protocol-compatible encrypted ML server 20 can be made one.
In addition, it is not necessary to change the encryption protocol to be used depending on the subscribed ML, and it is only necessary to register the encryption protocol that is normally used at the time of ML subscription. Therefore, the ML receiver can easily join multiple encrypted MLs. be able to.
In addition, since the multi-protocol compatible encryption ML server 20 absorbs the difference in environment between ML receivers, even if the ML sender does not have a mail tool corresponding to the encryption mail protocol, TLS (SSL) The encrypted ML can be transmitted using a general tool such as a compatible WWW (World Wide Web) browser.
In addition, since the multi-protocol-compatible encryption ML server 20 absorbs the difference in algorithm, even if all the ML recipients use the same encryption mail protocol but the encryption algorithm used is different, If the protocol-compliant encryption ML server 20 supports a plurality of encryption algorithms, the encryption ML can be exchanged.
[0023]
【The invention's effect】
As described above, according to the present invention, since the server means supports a plurality of encryption methods, the encryption for each recipient can be performed without unifying the encryption protocol used between the senders and receivers of the email. This method has an effect that an electronic mail can be encrypted and transmitted by this method. In addition, even if the network between the sender and the server means is not secure, since the email is encrypted from the time of sending the sender's mail, the safety can be ensured. In addition, it is possible to send and receive e-mails encrypted with different encryption methods and encryption algorithms without preparing a public key for each of a plurality of encryption methods and encryption algorithms.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of an electronic mail server system according to an embodiment of the present invention.
FIG. 2 is a block diagram showing an outline of an internal configuration of a multi-protocol-compliant encryption ML server 20;
FIG. 3 is a flowchart showing processing when a user transmits an e-mail addressed to ML in the e-mail server system according to the embodiment of the present invention;
FIG. 4 is a flowchart showing processing when the multi-protocol-compatible encrypted ML server 20 receives an e-mail.
[Explanation of symbols]
10 TLS (SSL) compatible email transmission tool (transmission means)
20 Multi-protocol encryption ML server (server means)
21 TLS (SSL) server part (decryption means)
22 ML recipient search unit (search means)
23 PGP processing part (encryption means)
24 S / MIME processing part (encryption means)
25 Mail transmission processing part (e-mail transmission means)
D1 ML database (encryption method storage means)
D2 public key database (public key storage means)
F1 recipient list

Claims (2)

A transmission means for encrypting an e-mail addressed to the mailing list and sending it together with the mailing list destination ;
An encryption method storage means for storing the recipient and the encryption method used by the recipient for each mailing list ;
Public key storage means for storing a public key for each recipient;
E-mail sent from the sending means is decrypted without having a public key for each mailing list, encryption method, and encryption algorithm, and the recipient is specified from the mailing list stored in the encryption method storage means and, for each of the recipient, the email electrodeposition using the public key stored in the public key storage means the stored encryption method for encrypting method storage means; and a server means for encrypting and transmitting When the transmission means transmits an email, the server means notifies the transmission means of the public key of the server means, and the transmission means encrypts the email using the public key of the server means. An e-mail server system that generates a common key for encryption and encrypts e-mail. The server means, decryption means for decrypting the email without having a public key for each mailing list, encryption method, and encryption algorithm;
Searching the encryption method storage means from a mailing list destination , specifying the recipient, and obtaining the encryption method for each recipient;
Encryption means for searching the public key for each recipient stored in the public key storage means for each encryption method and encrypting the content of the e-mail;
The e-mail server system according to claim 1, further comprising an e-mail transmission unit that transmits the e-mail encrypted by the encryption unit to the recipient.

Images