JP2002342239A - Electronic mail system and electronic mail communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic mail system by which a transmission side can confirm the presence or absence of the erroneous distribution of an electronic mail, and can prevent the leakage of message contents, even if these is a wrong distribution is detected. SOLUTION: A mail transmission side terminal enciphers and transmits an electronic mail, and requests the registration of the electronic mal including decoding information to an encipherment management server. At receiving of the enciphered mail, a mail reception side terminal transmits information that the decoding information registered in the encipherment management sever is acquired, decoded, and already read to the encipherment managing server. The mail transmission side terminal accesses the encipherment managing server and confirms whether or not the information that the mail is decoded and already read by the mail reception side terminal is registered. Thus, it is possible for the mail transmission side to confirm the presence or absence of the erroneous distribution of the mail, and to prevent the leakage of the message contents, even if any erroneous distribution is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic mail system and an electronic mail communication method for transmitting and receiving electronic mail between a plurality of information terminals via a server, and the electronic mail can be encrypted. .

[0002]

2. Description of the Related Art Recently, with the spread of the Internet, electronic mail has come to be widely used. Such an e-mail system utilizes the storage processing function of a server without directly communicating between information terminals (for example, a so-called personal computer or a mobile phone with an e-mail function). In addition, a distributed e-mail system composed of a plurality of servers transfers a message sent from a sender between servers, and the transferred message is finally delivered to a server to which a receiver's information terminal belongs and temporarily stored. Is done. Then, the recipient can arbitrarily access the information terminal to retrieve the message addressed to the recipient.

In general, messages successively transferred between servers via a communication line in a network system include control information such as a destination address, a destination, a subject and information to be transmitted by a user corresponding to a text. The transmission / transmission / delivery of the message is processed based on the control information. Particularly, when sending a highly confidential message, as a means to prevent information leakage, for example, the sender encrypts the contents of the e-mail and sends it, and the receiver encrypts the contents using a secret decryption key. Techniques for decrypting encrypted emails are also known.

As a technique related to the encryption of electronic mail, a public key encryption method is known as a method for preventing an increase in the number of private keys managed when a large number of communication partners are to be encrypted. In public key cryptography, when a user creates a pair of secret key and public key, it is configured so that the private key cannot be derived from the public key. You don't have to. For example, when a certain user A performs an encrypted communication with the user B, the user A encrypts the message using the public key of the user B, and the user B that has received the encrypted e-mail stores the message. This is a method of decrypting the message using the secret key being used.

Further, as a technique relating to the encryption of electronic mail, for example, Japanese Patent Application Laid-Open No. 6-224898 (encrypted electronic mail apparatus) is known. In order to eliminate the problem that the encrypted e-mail arrives at the other party and the encrypted e-mail can be decrypted with the wrong person's private key,
The e-mail sender is prevented from sending an encrypted e-mail to an unintended recipient.

[0006]

By the way, in the conventional e-mail system, when there is an erroneous input of the destination information of the e-mail, the mail is simply delivered to the destination of the erroneous input. Therefore, for example, if there is an erroneous input of destination information or the like, the mail may be erroneously distributed and transmitted to an unintended party at all. In that case, in order to confirm that the e-mail has arrived at the other party, it was necessary to check the other party by telephone or the like. That is,
It was extremely troublesome to check whether or not there was an incorrect delivery of the mail by calling the other party over the telephone. In addition, in the case of a highly confidential message, encrypting and transmitting the message is one of the effective methods. Even if the message is encrypted and transmitted, there is a risk that the message will be incorrectly distributed. In such a case, if the wrong delivery party has a private key, the wrong delivery party can decrypt the contents of the e-mail by obtaining the public key, which causes another problem that the secret is leaked.

Further, the electronic mail system disclosed in Japanese Patent Laid-Open No. 6-224898 does not return to the sender that the encrypted electronic mail has been successfully decrypted. However, there has been a problem that it has not been possible to reliably confirm that the so-called decryption has succeeded. In addition, for example, a method of putting information (for example, an encryption key) for managing e-mail into a specific Web server on the Internet to manage e-mail can be considered. In this case, if the security of the Web server is broken, There is a risk that the contents of all the information to be managed may be seen, and the means of preventing damage in such a case are extremely limited and cannot be said to be perfect.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electronic mail system capable of confirming whether or not an electronic mail has been erroneously delivered and preventing the leakage of message contents even if the erroneous delivery has occurred.

[0009]

To achieve the above object, an electronic mail system according to the first aspect of the present invention comprises a server having a mail delivery function arranged via a communication network, and a plurality of servers connectable to the server. Information terminal,
An e-mail is transmitted and received between a plurality of information terminals via the server, and the e-mail is provided with an encryption management server in an email system capable of being encrypted. Access permission means for identifying a terminal and registering information for permitting access;
Information for managing the e-mail in message units or packet units, decryption information for decrypting the encrypted mail, and registration means for registering a sender address and a receiver address; and When the e-mail sender terminal encrypts the e-mail and sends it to the information terminal at the sender address, the e-mail sender terminal accesses the encryption management server together with the destination address including the decryption information for decrypting the encrypted e-mail. Comprising a registration requesting means for requesting registration, the e-mail receiving terminal of the information terminals, when receiving an encrypted e-mail,
A read notifying means for acquiring and decrypting the decryption information registered in the encryption management server in response to the electronic mail, and transmitting a read message to the encryption management server when decryption is performed; Among the terminals, the e-mail sending terminal
The cryptographic management server is accessed so that it is possible to confirm whether or not the mail receiving terminal has decrypted and read the mail and registered it in the cryptographic management server.

[0010] In the encryption management server according to the second aspect of the present invention, a communication network that enables transmission and reception of electronic mail between a plurality of information terminals via the server is formed, and the electronic mail can be encrypted. Providing an encryption management server connected to the communication network, wherein the encryption management server identifies the information terminal and registers information for permitting access; Information managed by
Decryption information for decrypting the encrypted mail, first registration means for registering the sender address and the receiver address, and the information terminal permitted to access the mail sender,
A second registration unit for permitting access and registering the decryption information and the sender address when the encrypted mail is transmitted together with the sender address including decryption information for decrypting the email; The information terminal permitted to access, when there is an access request, a decryption information transmitting means for transmitting the decryption information to the terminal, a read transmission means for transmitting the read information to the information terminal, It is characterized by having.

According to a third aspect of the present invention, there is provided an electronic mail communication method for transmitting and receiving mail between a plurality of information terminals via a communication network via a server. When encrypting the e-mail and transmitting the encrypted e-mail to the information terminal at the sender's address, the side terminal accesses a predetermined encryption management server together with the transmission destination address including the decryption information for decrypting the encrypted e-mail. Requesting registration, the e-mail receiving terminal among the information terminals, when receiving the encrypted e-mail, the decryption information registered in the encryption management server corresponding to the e-mail Acquisition and decryption, and when decrypted, send a message to the cryptographic management server that the information has been read, and the e-mail transmitting terminal among the information terminals is transmitted to the cryptographic management server. Access to mail recipient terminal that it has read to decode the e-mail is characterized in that so as to confirm whether or not it is registered in the encryption management server.

According to a fourth aspect of the present invention, a communication network is formed which enables transmission and reception of an electronic mail between a plurality of information terminals via a server, the electronic mail can be encrypted, and the communication can be performed. When a cryptographic management server connected to a network is provided, as the processing of the cryptographic management server, a process of identifying the information terminal and registering information for permitting access, and managing the e-mail in units of messages or packets. Information, decryption information for decrypting the encrypted mail, processing for registering the sender address and receiver address, and decrypting the encrypted mail from the information terminal permitted to access the mail sender. Is transmitted together with the sender address including the decryption information for the access, permit access and register the decryption information and the sender address. Processing, when there is an access request from the information terminal permitted to access the mail receiving side, sending the decoded information to the terminal, and sending read information to the information terminal. A recording medium storing a program for realizing an electronic mail communication method.

[0013] According to a fifth aspect of the present invention, a communication network is formed which enables transmission and reception of electronic mail between a plurality of information terminals via a server, and the electronic mail can be encrypted. An encryption management server connected to the network is provided, and when the electronic mail is managed by the encryption management server, as a process of the electronic mail transmission terminal among the information terminals, the electronic mail is encrypted and the transmission address is determined. When transmitting to an information terminal, a process of requesting registration by accessing a cryptographic management server together with a destination address including decryption information for decrypting an encrypted e-mail, and accessing the cryptographic management server A process in which the mail receiving terminal decrypts the mail and confirms that the message has been read is registered in the encryption management server. A recording medium characterized by storing a program for implementing the method.

According to a sixth aspect of the present invention, there is provided a communication network which enables transmission and reception of an electronic mail between a plurality of information terminals via a server, wherein the electronic mail can be encrypted. When an encryption management server connected to the network is provided, and when the encryption management server manages the e-mail, when receiving an encrypted e-mail as a process of the e-mail receiving terminal among the information terminals A process of acquiring and decrypting the decryption information registered in the encryption management server corresponding to the electronic mail, and a process of transmitting to the encryption management server that the mail has been read when decrypting the decryption information. And a program for realizing an electronic mail communication method including the following.

[0015]

According to the present invention, among the information terminals, the e-mail transmitting terminal transmits the decryption information for decrypting the encrypted e-mail when encrypting the e-mail and transmitting it to the information terminal of the transmitting address. While accessing the encryption management server together with the destination address and requesting registration, the e-mail receiving terminal among the information terminals, when receiving the encrypted e-mail, performs encryption management corresponding to the e-mail. The server acquires the decryption information registered in the server, decrypts the decrypted information, and transmits the read information to the encryption management server when decrypted.
Also, among the information terminals, the e-mail transmitting terminal accesses the encryption management server and checks whether or not the mail receiving terminal has decrypted the mail and has read it, and is registered in the encryption management server. Therefore, by accessing the cryptographic management server, it is possible to confirm whether or not the recipient of the e-mail has opened the message. Even if the e-mail is incorrectly distributed, the message cannot be decrypted at the incorrectly distributed destination. The contents cannot be decoded.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. A. Configuration of Embodiment A-1. FIG. 1 is a diagram showing a configuration of an electronic mail system to which the present invention is applied. In FIG. 1, 1 is a network,
The network 1 is a network such as the Internet (corresponding to a communication network). Here, the network 1 is not limited to the Internet, for example, a network formed by a dedicated line or an in-house LAN
The present invention can be applied to any network that can be used in a system capable of distributing e-mail. Network 1
, A transmission-side e-mail server 2, a reception-side e-mail server 3, and a cipher management server 4 are constantly connected to each other, and are arranged so as to be accessible to the network 1. Sending e-mail server 2 and receiving e-mail server 3
Is equivalent to a server having a mail distribution function, and has a function of performing e-mail distribution processing.

The sending-side e-mail server 2 and the receiving-side e-mail server 3 send or receive an e-mail to a destination via a plurality of computers on the network 1 (for example, the Internet) or the network 1. Or to perform processing as a mail server. In this case, for example, if the sent mail is addressed to the own organization (domain), the e-mail is sent to the destination, and if the sent mail is addressed to another organization, the e-mail is forwarded to the route of the destination. Such an electronic mail distribution process is a basic component of the electronic mail system. The sending-side e-mail server 2 and the receiving-side e-mail server 3 have not only a function of sending or receiving but also a function of both sending and receiving for mail distribution.

The encryption management server 4 is an electronic mail system in which the electronic mail servers 2 and 3 are arranged on the network 1 and can be encrypted. Information terminals (sending terminal 5 and receiving terminal 6 described later)
Access permission means for identifying information and registering information that permits access, information for managing e-mail in units of mail,
This is to realize a function as registration means for registering decryption information for decrypting the encrypted mail and the sender address and the receiver address, and is an important configuration of the present invention connected to the network 1. .

The sending terminal 5 is a sending e-mail terminal, has a function of encrypting an e-mail when sending an e-mail, and transmits decryption information for decrypting the encrypted e-mail to an encryption management server. A function of logging in to the cryptographic management server 4 with user ID information, registering the message management number with the addresses of both the transmitting and receiving sides, and acquiring and storing the message management number from the cryptographic management server 4;
The receiving terminal has a function of confirming whether or not the encrypted electronic mail has been decrypted and has been read is registered in the encryption management server 4, and is arranged so as to be connectable to the network 1.

On the other hand, the receiving terminal 6 is an e-mail terminal on the receiving side.
Has the function of acquiring and decrypting the decryption information corresponding to the received e-mail registered in the server, and transmitting the read information to the encryption management server 4 when decrypted, and arranged in a state where it can be connected to the network 1. Have been. The transmitting terminal 5
The receiving terminal 6 corresponds to an information terminal, and can realize both functions of transmitting and receiving. The receiving terminal 6 is always connected to the transmitting electronic mail server 2 and / or the receiving electronic mail server 3. Alternatively, the connection may be temporarily made via a business entity such as a provider.

The recording medium 7 is a recording medium on which a program created for the purpose of realizing the function of the encryption management server 4 is recorded. The recording medium 8 and the recording medium 9 are the transmission terminal 5 of the electronic mail, respectively. And a recording medium that records a program created for the purpose of realizing the function of the receiving terminal 6.

In the recording medium 7, as the processing of the encryption management server 4, processing for identifying an information terminal and registering information for which access is permitted, and managing e-mails in message units or packet units (may be in mail units). Processing for registering information, decryption information for decrypting encrypted mail, sender address and receiver address, and decrypting encrypted mail from an information terminal permitted to access the mail sender. If the message is transmitted together with the sender address including the decryption information, the access is permitted and the decryption information and the sender address are registered. A process for sending an e-mail communication method including a process of sending decrypted information to the terminal and a process of sending read information to the information terminal. Gram is stored.

The recording medium 8 is used for decrypting the encrypted e-mail when the e-mail is encrypted and transmitted to the information terminal at the transmission address as a process of the e-mail transmission terminal among the information terminals. Requesting registration by accessing the encryption management server together with the destination address, including the decryption information of the mail, and accessing the encryption management server and informing the encryption management server that the mail receiving terminal has decrypted the mail and read it. A program for realizing an e-mail communication method including a process of confirming whether or not the electronic mail is registered is stored.

In the recording medium 9, when an encrypted electronic mail is received as a process of the electronic mail receiving terminal among the information terminals, the encrypted electronic mail is registered in the encryption management server in correspondence with the electronic mail. A program for realizing an email communication method including a process of acquiring and decrypting the decryption information and a process of transmitting to the encryption management server that the email has been read when decrypting the decryption information is stored. ing. Recording media 7, 8 and 9 are usually CD-ROM
It is manufactured in a convenient environment. Of course, the recording medium may be a floppy (registered trademark) disk or MO (magneto-optical disk) other than the CD-ROM. Note that the recording media 7, 8, and 9 need not be each alone, and may be recorded as two or one. Furthermore, there is a method of installing a program on a target device by using the above-described recording medium.
A method of installing a program on the device via the network 1 without using the recording medium (for example, network distribution) may be used.

Although FIG. 1 shows the cryptographic management server 4 in an independent device configuration, the function of the cryptographic management server 4 is added to the e-mail server so that the cryptographic management server 4 does not need to be an independent device configuration. Good. Also, the encryption management server 4
It is needless to say that a special program may not be used to achieve the above function, but may be constituted by a file sharing function or the like which is a function of the operating system of the computer. Arrows 10 to 14 show the flow of information when an e-mail is sent from the transmitting terminal 5 to the receiving terminal 6.

A-2. Registration Information of Encryption Management Server FIG. 2 is a diagram showing email management information registered in the encryption management server 4 of the above-described email system. FIG.
In the electronic mail management information, information 21 including a user ID, a password, and a mail address for each user is included.
And information including an encryption key necessary for decrypting the encrypted e-mail in a message unit or a packet unit, an unread / decryption flag which is information when decrypted at the receiving terminal, mail addresses for both transmission and reception, and a management number thereof. 22. The unread / decoded flag is, for example,
It is not essential if the purpose of providing the unread / decryption flag can be achieved by another method, such as deleting the corresponding message information when the encrypted electronic mail received by the receiving terminal is decrypted. Further, as information to be registered in the encryption management server 4, for example, an item such as date and time when the information is registered may be added.

B. Description of Operation FIGS. 3 and 4 are flowcharts illustrating the operation of the electronic mail system to which the present invention is applied. Note that FIG.
Although the e-mail transmitting terminal 5 of FIG. 4 and the e-mail transmitting terminal 5 of FIG. 4 are the same terminal, the transmitting terminal 5 of FIG. 4 is shown as a terminal at the time of unread confirmation after message transmission. In addition, as a conceptual diagram of the network, the network 1, the sending e-mail server 2, the receiving e-mail server 3, the encryption management server 4, the transmitting terminal 5, the receiving terminal 6
It is expressed and shown.

First, the transmitting terminal 5 in FIG.
In 1 (message editing process), a message to be transmitted by e-mail is created or edited, and the message created in step S2 is encrypted (message encryption process). For example, if "ABCDE" is encrypted by a rule of shifting three characters, "DEFGH" is obtained, and the sentence / number is converted into another expression according to a certain rule. Of course, another encryption method may be used. At this time, an encryption key, which is decryption information for decrypting the message, is also generated. Then, step S
At 3, the user logs in to the encryption management server 4. With login,
For example, a permission to access the encryption management server 4 is requested using the user ID and the password, and when the permission is granted, the user can log in. If the user ID and the password are not registered in the encryption management server 4 in advance, the login operation fails. As a result, unauthorized access to the encryption management server 4 from a person who does not have the authority to use the electronic mail system of the present invention can be prevented.

If the log-in to the encryption management server 4 by the transmission side terminal 5 succeeds, the process proceeds to the registration process of step S4, and the encryption key generated in step S2 and the information of the transmission side mail address and the reception side mail address are encrypted and managed. Request to register with server 4. Step S5
In the message No. generated when registering the information
Is acquired from the encryption management server 4 and stored in the transmitting terminal (message No. acquisition and storage). The message number is a unique number for each message, and is automatically generated by the encryption management server 4. Message No. in cooperation with user ID
May be generated. Thereafter, in the mail transmission in step S6, the message N is added to the encrypted message.
The packet is sent to the transmission-side e-mail server 2 via the network 1 with "o" added.

In receiving the mail in step S7, the receiving terminal 6 accesses the receiving electronic mail server 3 via the network 1 and acquires a corresponding message.
Thereafter, in the login in step S8, the encryption management server 4
Is accessed using the user ID and the password. At that time, as described above, if the user ID and the password are not registered in the encryption management server 4 in advance, the login operation fails, and a person who does not have authority to use the e-mail system of the present invention is Unauthorized access to the encryption management server 4 can be prevented.

The receiving terminal 6 is connected to the encryption management server 4
When the above-mentioned login is successful, the corresponding mail address is obtained from the encryption management server 4 in the mail address acquisition in step S9, and the mail address is used as a search key in the confirmation of the number of mails in step S10.
Count the number of messages to be received from the information registered in. At this time, if the counted number is larger than the number of encrypted messages obtained from the e-mail server 3, it is possible to predict that there is a possibility that the message has been incorrectly distributed (step S11), and if necessary, resend the message to the sender. Make a request (step S12).

Next, in the encryption key acquisition in step S13, the encryption key corresponding to the message No is acquired from the encryption management server 4, and the message is decrypted in the decryption processing in step S14. Confirm whether decryption is possible (Step S1)
5) If decoding is not possible, it is determined that decoding has failed (step S16), and a retransmission request is sent to the transmission source (step S17).
multiply. If the decryption is successful, step S18
In (successful decryption), the unread / decryption flag of the encryption management server is changed, and the contents of the message decrypted in step S19 (message decryption) are viewed.

In step S20, the transmitting terminal 5 in FIG. 4 uses the user ID and the password in the encryption management server 4 in order to confirm whether or not the transmission destination has decrypted the transmitted encrypted e-mail message. In step S21, the user checks the unread / decryption flag corresponding to the message from the information registered in the encryption management server 4. If the content is unread, the destination message is unread (step S21). It is determined as S22). On the other hand, in the confirmation work in step 21, if the content has been read, it can be determined that the transmitted encrypted e-mail message has been decrypted by the destination, and in step S23 (message No deletion), the message is registered in the encryption management server 4. The corresponding line is deleted for the information.

As described above, the transmission-side e-mail server 2, the reception-side e-mail server 3, and the encryption management server 4 are constantly connected to the network 1 that can be used under a system capable of distributing e-mail. The electronic mail transmitting terminal 5 among the information terminals in an environment where the electronic mail is placed in a state where the electronic mail can be accessed when the encrypted electronic mail is transmitted to the information terminal of the transmitting address. Accessing the encryption management server 3 together with the transmission destination address including the decryption information for decryption and requesting registration, while the e-mail receiving terminal 6 of the information terminals receives the encrypted e-mail. Then, the decryption information registered in the encryption management server corresponding to the e-mail is acquired and decrypted, and when decrypted, the fact that it has been read is transmitted to the encryption management server 3. It is made to trust. The e-mail transmitting terminal 5 among the information terminals accesses the encryption management server 3 and determines whether the mail reception terminal 6 has decrypted and read the mail and registered in the encryption management server 3. Confirm. By performing the above processing, by accessing the encryption management server 3, it is possible to confirm whether or not the recipient of the e-mail has opened the message. Since the message cannot be decrypted and its contents cannot be decrypted, leakage of the mail contents is prevented.

As a modification of the present invention, the message acquisition process of step S5 in FIG. 3 is a method of acquiring the message No. generated by the encryption management server 4, but is not limited to this. A method may be used in which the message number is generated by the transmitting terminal 5 and registered in the encryption management server 4. However, when the message No. is generated by the transmitting terminal 5, it must not be the same as the message No. generated by the other transmitting terminals. May be.

[0036]

According to the first, second and third aspects of the present invention,
An encryption management server equipped with a means for registering e-mail management information is provided, and the e-mail sending terminal registers e-mail management information including means for encrypting e-mail messages and e-mail management information in the encryption management server. Means for checking the information sent to the cryptographic management server when the e-mail receiving terminal succeeds in decrypting the received e-mail. Thus, it is possible to confirm whether or not the e-mail has arrived at the correct destination and successfully decrypt the message. Therefore, it is possible to confirm whether or not the recipient of the e-mail has opened the message.

Further, when an encrypted e-mail message is transmitted by an access permitting unit for registering information permitting access to the encryption management server, the destination of the message is an encryption code for decrypting the message. In order to obtain the key, it is necessary to log in to the encryption management server using the user ID and password of the e-mail destination, so even if there is an incorrect distribution of e-mail,
Since the message cannot be decrypted at the wrong delivery destination and the content cannot be decrypted, there is an effect that information leakage can be prevented.

According to the fourth aspect of the present invention, the function of the encryption management server is realized in order to add the function of the encryption management server to a new dedicated encryption management server device or an existing electronic mail server device. To install a program for the purpose in the device. At this time, if the program is stored in a recording medium readable by the device, there is an advantage that the work can be performed quickly.

According to the fifth and sixth aspects of the present invention, the functions of the e-mail terminal are realized in order to add the functions of the e-mail transmitting terminal and the receiving terminal to a device such as a new information terminal. To install a program for performing the operation on the device. At that time, if the program is stored in a recording medium readable by the device, there is an advantage that the work can be performed quickly.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an electronic mail system of the present invention.

FIG. 2 is a diagram showing electronic mail management information of an encryption management server.

FIG. 3 is a flowchart illustrating the operation of the electronic mail system of the present invention.

FIG. 4 is a flowchart illustrating the operation of the electronic mail system of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Network (communication network), 2 ... E-mail server of transmission side (server, e-mail distribution means, e-mail transmission means), 3 ... E-mail server of reception side (server, e-mail distribution means, E-mail receiving means), 4
... Encryption management server (access permission means, first registration means, second registration means, decryption information transmission means, read transmission means), 5 ... transmission side terminal (information terminal), 6 ... Receiving terminal (information terminal), 7 to 9 ... recording medium

Claims (6)

[Claims] 1. A server having a mail distribution function is arranged via a communication network, and there are a plurality of information terminals connectable to the server, and electronic mail is transmitted and received between the plurality of information terminals via the server. Done, said email
In an electronic mail system capable of being encrypted, a cryptographic management server is provided, wherein the cryptographic management server identifies the information terminal and registers access-permitted information; Registration information for registering information managed on a unit or packet basis, decryption information for decrypting encrypted mail, and a sender address and a receiver address; and an e-mail sender terminal among the information terminals. When encrypting an e-mail and sending it to the information terminal at the sender's address, access the encryption management server together with the destination address, including the decryption information for decrypting the encrypted e-mail, and request registration. An e-mail receiving terminal among the information terminals receives an encrypted e-mail. In the case, there is provided read notification means for acquiring and decrypting the decryption information registered in the cryptographic management server in response to the email, and transmitting to the cryptographic management server that the decrypted information has been read when decrypted. The e-mail transmitting terminal among the information terminals can access the encryption management server to check whether the mail reception terminal has decrypted the mail and read it is registered in the encryption management server. An e-mail system, comprising: 2. A communication network which enables transmission and reception of an electronic mail between a plurality of information terminals via a server, wherein the electronic mail can be encrypted, and a cipher connected to the communication network is provided. A management server, the encryption management server includes: an access permission unit that identifies the information terminal and registers information for permitting access; information that manages the e-mail in a message unit or a packet unit; First information for registering the decryption information for decrypting the sender address and the recipient address
Registration means, and when the mail is sent together with the sender address including the decryption information for decrypting the encrypted mail from the information terminal permitted to access the mail sender, the access is permitted. Second registration means for registering decryption information and a sender address, and decryption information transmitting means for transmitting the decryption information to the terminal when an access request is made from the information terminal permitted to access the mail receiving side. A cipher management server, comprising: a read transmitting unit that transmits read information to the information terminal. 3. An e-mail communication method for transmitting and receiving e-mail between a plurality of information terminals via a communication network via a server, wherein the e-mail transmitting terminal among the information terminals encrypts and transmits the e-mail. When transmitting to the information terminal of the side address, access to a predetermined encryption management server together with the destination address including the decryption information for decrypting the encrypted e-mail and request registration, When receiving the encrypted e-mail, the e-mail receiving terminal acquires and decrypts the decryption information registered in the encryption management server corresponding to the e-mail, and decrypts the decrypted information when decrypted. The reading terminal transmits a message to the cryptographic management server, and among the information terminals, the e-mail transmitting terminal accesses the cryptographic management server and the mail receiving terminal decrypts the mail. E-mail communication method that was read is characterized in that so as to confirm whether or not it is registered in the encryption management server Te. 4. A communication network is formed to enable transmission / reception of e-mail between a plurality of information terminals via a server, wherein the e-mail can be encrypted, and a cipher connected to the communication network is provided. When a management server is provided, as the processing of the encryption management server, the information terminal is identified, information for permitting access is registered, and information for managing the electronic mail in a message unit or a packet unit is encrypted. Process for registering the decryption information for decrypting the email, the sender address and the recipient address, and the decryption information for decrypting the encrypted email from the information terminal permitted to access the email sender. If the message is sent along with the sender address, the process of permitting access and registering the decryption information and the sender address is performed. An e-mail communication method comprising: a process of transmitting the decrypted information to the terminal when there is an access request from the information terminal permitted to access the side; and a process of transmitting read information to the information terminal. A recording medium storing a program for realizing the recording medium. 5. A communication network which enables transmission and reception of an electronic mail between a plurality of information terminals via a server, wherein the electronic mail can be encrypted, and a cipher connected to the communication network is provided. When a management server is provided, and the management of the e-mail is performed by the encryption management server, when the e-mail transmitting terminal among the information terminals is used, the e-mail is encrypted and transmitted to the information terminal having the transmitting address. A process of requesting registration by accessing a cryptographic management server together with a destination address including decryption information for decrypting the encrypted e-mail; and Decrypting the message and confirming whether or not the message has been read is registered in the cryptographic management server. A recording medium characterized by storing the above program. 6. A communication network which enables transmission and reception of an electronic mail between a plurality of information terminals via a server, wherein the electronic mail can be encrypted, and a cipher connected to the communication network is provided. A management server is provided, and when the encryption management server manages the e-mail, when the encrypted e-mail is received as a process of the e-mail receiving terminal among the information terminals, the e-mail is sent to the e-mail. An e-mail including a process of obtaining and decrypting the decryption information registered in the cryptographic management server and a process of transmitting to the cryptographic management server that the mail has been read when decrypting the decryption information. A recording medium storing a program for realizing a communication method.