JP2004078559A - Encryption mail communication method and encryption mail system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow anyone to execute encryption mail communication without anxiety. <P>SOLUTION: An encryption mail service device 300 transmits an encryption program to a transmitting terminal 100, and transmits an encryption key/decoding key generation program and a decoding program to a receiving terminal 200. The transmitting terminal 100 installs the encryption program. The receiving terminal 200 registers the encryption key in an encryption mail service device 300, and installs the decoding program and a decoding key. The transmitting terminal 100 receives the encryption key of the receiving terminal 200 at the destination from the encryption mail service device 300, and transmits an encryption mail where a plain text is encrypted with the encryption program to a mail server device 40A. The receiving terminal 200 reads the mail to its own destination from a mail server device 40B, and decodes the mail with the decoding program and the decoding key. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an encrypted mail communication method and an encrypted mail system, and more particularly, to an encrypted mail capable of performing encrypted mail communication without an individual user being aware of an encryption program, an encryption key, a decryption program, and a decryption key. The present invention relates to a communication method and an encrypted mail system.
[0002]
[Prior art]
For example, a PGP (Pretty Good Privacy) system and an S / MIME (Secure / Multipurpose Internet Mail Extensions) system are known as encryption technologies for enhancing the security of electronic mail exchanged on the Internet.
In the PGP system, a transmission source sends a ciphertext obtained by encrypting a plaintext with a public key of the destination to the destination. At the destination, the ciphertext is decrypted with its own secret key.
In the S / MIME system, a transmission source sends a ciphertext obtained by encrypting a plaintext with a public key authenticated by a specific certificate authority to a destination. At the destination, the ciphertext is decrypted with its own secret key.
[0003]
[Problems to be solved by the invention]
With the conventional encrypted mail communication method, it is necessary for each user to be aware of and manage the encryption program, encryption key, decryption program, and decryption key, so that anyone cannot easily perform encrypted mail communication. There was a point.
Therefore, an object of the present invention is to enable an individual user to perform encrypted mail communication without being aware of an encryption program, an encryption key, a decryption program, and a decryption key. The present invention provides an encrypted mail communication method and an encrypted mail system capable of performing the above.
[0004]
[Means for Solving the Problems]
In a first aspect, the present invention provides a method for connecting a transmitting terminal, an encrypted mail service device, a mail server device, and a receiving terminal via a network, wherein the encrypted mail service device sends an encrypted program to the transmitting terminal, An encryption key / decryption key generation program for generating an encryption key used at the source and a decryption key used at the destination and a decryption program are sent to the reception terminal, and the transmission terminal incorporates the encryption program in its own terminal The receiving terminal sends the encryption key generated by executing the encryption key generation program to the encryption mail service device, and outputs the decryption program and the decryption key generated by executing the decryption key generation program. Built in its own terminal, the encrypted mail service device receives the encryption key and The transmitting terminal executes a mail program and requests the encryption mail service device for an encryption key of the destination receiving terminal, and the encrypted mail service device To the transmitting terminal, the transmitting terminal encrypts the plaintext with the encryption program and the encryption key of the destination receiving terminal to generate an encrypted mail, and sends the encrypted mail to the mail server device. Sending, the receiving terminal executes a mail program, accesses the mail server device, reads out the mail addressed to itself, and decrypts the encrypted mail with the decryption program and the decryption key if it is an encrypted mail. Provide a method.
In the encrypted mail communication method according to the first aspect, the transmitting terminal simply encrypts the plaintext using the encryption program and the destination encryption key sent from the encrypted mail service device, and sends the encrypted plaintext to the mail server device. In addition, there is no need to manage encryption programs and encryption keys with consideration, and there is no need to consider the receiving terminal. On the other hand, the receiving terminal only decrypts the encrypted mail read from the mail server device using the decryption program sent from the encrypted mail service device and the decryption key generated by the decryption key generation program. There is no need to be aware of the decryption key and to manage the transmission terminal. Therefore, anyone can easily perform encrypted mail communication.
Further, since the encryption program and the decryption program operate integrally with the mail program, the user does not need to be conscious of the encryption program and the decryption program at all.
Note that the encryption key is sent only to the sending terminal that sends the mail, so the encryption key may be the decryption key. However, the security is improved when the encryption key is divided by the decryption key. Further, the mail server device accessed by the transmitting terminal and the mail server device accessed by the receiving terminal may be the same or different.
[0005]
In a second aspect, the present invention provides a transmitting terminal, a first mail server device having a built-in first encrypted mail service device and accessible by the transmitting terminal, a receiving terminal, and a second encrypted mail service. A second mail server device having a built-in device and accessible by the receiving terminal is connected via a network, the first encrypted mail service device sends an encrypted program to the transmitting terminal, and the transmitting terminal The second encryption mail service device has the encryption program incorporated in its own terminal, and the second encryption mail service device has an encryption key / decryption key generation program and a decryption program for generating an encryption key used at a transmission source and a decryption key used at a destination. To the receiving terminal, and the receiving terminal transmits the encryption key generated by executing the encryption key generation program to the second encrypted mail service. And the decryption key generated by executing the decryption program and the decryption key generation program in its own terminal, the second encrypted mail service device receives the encrypted key, The registration is performed in association with the mail address of the reception terminal, and the transmission terminal executes a mail program, requests the first mail server device for an encryption key of the destination reception terminal, and transmits the first mail. The server device transfers the request to the second mail server device, and the second encrypted mail service device sends an encryption key of the destination receiving terminal to the first mail server device, 1 mail server device sends the encryption key of the destination receiving terminal to the transmitting terminal, and the transmitting terminal encrypts the plaintext with the encryption program and the destination receiving terminal. The encrypted mail is generated by the encryption method, and the encrypted mail is sent to the first mail server device. The receiving terminal executes a mail program to access the second mail server device, and receives the mail addressed to itself. And decrypting the encrypted mail with the decryption program and the decryption key.
In the encrypted mail communication method according to the second aspect, since the encrypted mail service device is incorporated in the mail server device, the destination encryption key is registered in the second encrypted mail service device that cannot be directly accessed from the transmission terminal. Even in this case, the encryption key of the destination can be transferred to the first mail server device and can be transferred to the transmission terminal. Accordingly, for example, an administrator can provide an encrypted mail service by combining a number of different mail server devices.
[0006]
In a third aspect, the present invention provides the encrypted mail communication method according to the above configuration, wherein the transmitting terminal transmits the unencrypted plaintext mail if the destination terminal does not acquire the destination encryption key from the encrypted mail service device. There is provided an encrypted mail communication method characterized by sending the encrypted mail to a mail server device.
In the encrypted mail communication method according to the third aspect, the plaintext mail without encryption is sent to the destination where the encryption key could not be obtained from the encrypted mail service device, that is, the receiving terminal not subscribed to the encrypted mail service. Can include normal email functionality.
[0007]
According to a fourth aspect of the present invention, in the encrypted mail communication method having the above configuration, a public key that is not easily estimated from a decryption key secretly managed by the receiving terminal is employed as the encryption key. Provide an encrypted mail communication method.
In the encrypted mail communication method according to the fourth aspect, since a public key that is not easily estimated from the decryption key is employed as the encryption key, security can be improved.
[0008]
In a fifth aspect, the present invention provides a transmitting terminal, an encrypted mail service device, a mail server device, a receiving terminal, and a network connecting the transmitting terminal, the encrypted mail service device, the mail server device, and the receiving terminal. An encrypted mail system comprising: an encrypted mail service device that transmits an encrypted program to the transmitting terminal, and generates an encrypted key used at a transmission source and a decryption key used at a destination. A key generation program and a decryption program are sent to the receiving terminal, the transmitting terminal incorporates the encryption program in its own terminal, and the receiving terminal executes the encryption key generation program to generate an encryption key. Executing the decryption program and the decryption key generation program while sending the decryption key to the encrypted mail service device. The generated decryption key is embedded in its own terminal, the encrypted mail service device receives the encrypted key, registers it in association with the mail address of the receiving terminal, and the transmitting terminal executes a mail program. Executing, requesting the encryption key of the destination receiving terminal to the encrypted mail service device, the encrypted mail service device sends the encryption key of the destination receiving terminal to the transmitting terminal, and the transmitting terminal The plaintext is encrypted with the encryption program and the encryption key of the destination receiving terminal to generate an encrypted mail, and the encrypted mail is sent to the mail server device. The receiving terminal executes a mail program and executes the mail server. An encryption device for accessing a device, reading out the mail addressed to itself, and decrypting the encrypted mail with the decryption program and the decryption key. To provide a system.
In the encrypted mail system according to the fifth aspect, the encrypted mail communication method according to the first aspect can be suitably implemented.
[0009]
In a sixth aspect, the present invention provides a transmitting terminal, a first mail server device having a built-in first encrypted mail service device and accessible by the transmitting terminal, a receiving terminal, and a second encrypted mail service. A second mail server device having a built-in device and accessible by the receiving terminal; and a network connecting the transmitting terminal, the first mail server device, the receiving terminal, and the second mail server device. The first encrypted mail service device sends an encrypted program to the transmitting terminal, and the transmitting terminal incorporates the encrypted program in its own terminal; 2 is an encryption key / decryption key generation program for generating an encryption key used at a transmission source and a decryption key used at a destination, and a decryption program To the receiving terminal, the receiving terminal sends the encryption key generated by executing the encryption key generation program to the second encrypted mail service device, and transmits the decryption program and the decryption key generation program The decryption key generated and executed is built in its own terminal, and the second encrypted mail service device receives the encrypted key, registers the encrypted key in association with the mail address of the receiving terminal, and transmits the encrypted key. The terminal executes a mail program, requests the encryption key of the destination receiving terminal from the first mail server device, and the first mail server device sends the request to the second mail server device. Forwards, the second encrypted mail service device sends the encryption key of the destination receiving terminal to the first mail server device, and the first mail server device Sending the encryption key of the destination receiving terminal to the transmitting terminal, the transmitting terminal encrypts plaintext with the encryption program and the encryption key of the destination receiving terminal to generate an encrypted mail, and generates the encrypted mail. To the first mail server device, the receiving terminal executes a mail program to access the second mail server device, reads the mail addressed to itself, and if the mail is an encrypted mail, the decryption program and the decryption Provided is an encrypted mail system characterized by decrypting with a key.
In the encrypted mail system according to the sixth aspect, the encrypted mail communication method according to the second aspect can be suitably implemented.
[0010]
In a seventh aspect, the present invention provides the encrypted mail system having the above-described configuration, wherein the transmitting terminal transmits the unencrypted plaintext mail to the mail when the transmission terminal has not obtained the destination encryption key from the encrypted mail service device. Provided is an encrypted mail system that is sent to a server device.
In the encrypted mail system according to the seventh aspect, the encrypted mail communication method according to the third aspect can be suitably implemented.
[0011]
According to an eighth aspect, the present invention provides the cipher mail system having the above-mentioned configuration, wherein the public key which is not easily estimated from the decryption key secretly managed by the receiving terminal is adopted as the encryption key. Provide a mail system.
In the encrypted mail system according to the eighth aspect, the encrypted mail communication method according to the fourth aspect can be suitably implemented.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. Note that the present invention is not limited to this.
[0013]
FIG. 1 is a block diagram showing an encrypted mail system 1000 according to the first embodiment of the present invention.
This encrypted mail system 1000 subscribes to a network 1 such as the Internet, a LAN (Local Area Network), and a WAN (Wide Area Network), a encrypted mail service device 300 that provides a encrypted mail service, and a encrypted mail service. The transmitting terminal 100, the first mail server device 40A accessible by the transmitting terminal 100, the receiving terminal 200 subscribed to the encrypted mail service, and the second mail server device 40B accessible by the receiving terminal 200 It is provided with.
Further, a general terminal 150 not subscribed to the encrypted mail service is also connected to the network 1.
[0014]
The first mail server device 40A includes an SMTP (Simple Mail Transfer Protocol) server 41A, a POP3 (Post Office Protocol version 3) server 42B, and a mail box 43A capable of storing electronic mail.
The second mail server device 40B includes an SMTP server 41B, a POP3 server 42B, and a mailbox 43B that can store electronic mail.
[0015]
FIG. 2 is a configuration diagram showing the encrypted mail service device 300.
The encrypted mail service device 300 includes a communication unit 301, a web page storage unit 302, a program execution unit for encrypted mail service 303, an encrypted program storage unit 304, a public key / private key generation program storage unit 305, and a decryption unit. It includes a program storage unit 306, a user management database 307, and a data storage unit 308.
[0016]
FIG. 3 is an explanatory diagram showing an example of the contents of the user management database 307.
In the “mail address” column, the mail address of the subscriber of the encrypted mail service is registered.
The “public key” column stores an encryption key necessary for the transmission terminal 100 of the transmission source destined for the mail address in the left column to encrypt an e-mail. Note that the “public key” does not need to be widely disclosed to the entire subscriber because the transmitting terminal 100 of the transmission source receives the “public key” from the encrypted mail service device 300 as described later with reference to FIG.
[0017]
FIG. 4 is a configuration diagram showing the transmitting terminal 100.
The transmitting terminal 100 includes a communication unit 101, a web browser 102, a mail program 103, a program execution unit 104, a data storage unit 105, and a display unit 106.
The receiving terminal 200 and the general terminal 150 have basically the same configuration as the transmitting terminal 100.
Although the transmitting terminal 100 and the receiving terminal 200 are distinguished for convenience of description, the same terminal is actually the transmitting terminal 100 or the receiving terminal 200.
[0018]
FIG. 5 is a flowchart showing a procedure when the general terminal 150 subscribes to the encrypted mail service and becomes the transmitting terminal 100 or the receiving terminal 200.
In step C1, the general terminal 150 activates the web browser 102, and transmits a request for browsing the web page for the encrypted mail service to the encrypted mail service apparatus 300 via the network 1.
[0019]
In step S1, the encrypted mail service device 300 receives a browsing request. In step S2, the encrypted mail service device 300 transmits the encrypted mail service web page to the general terminal 150.
[0020]
In step C2, the general terminal 150 receives the encrypted mail service web page and displays it on the display unit 106. FIG. 6 illustrates a display screen of the web page for the encrypted mail service.
In step C3, the operator of the general terminal 150 inputs his / her mail address in the input form of the web page for the encrypted mail service.
In step C4, the operator of the general terminal 150 transmits the mail address to the encrypted mail service device 300 by clicking the determination button of the encrypted mail service web page.
[0021]
In step S3, the encrypted mail service device 300 receives the mail address.
In step S4, the encrypted mail service device 300 decrypts the encrypted program stored in the encrypted program storage unit 304, the public key / private key generation program stored in the public key / private key generation program storage unit 305, and decrypts it. The decryption program stored in the program storage unit 306 is transmitted to the general terminal 150. For example, when the operator of the general terminal 150 performs an operation of clicking the install button on the screen of the installation web page shown in FIG. 7 displayed on the display unit 106 of the general terminal 150, each program is transmitted. I do. Note that it is preferable to use SSL (Secure Socket Layer) or the like from the viewpoint of security.
[0022]
In step C5, the general terminal 150 receives the encryption program, the public key / private key generation program, and the decryption program.
In step C6, the general terminal 150 causes the program execution unit 104 to execute the public key / private key generation program to generate a public key and a secret key. Note that the public key and the secret key may be generated based on, for example, a random number, or may be generated based on a mail address or an IP (Internet Protocol) address of the general terminal 150.
In Step C7, the public key generated in Step C6 is transmitted to the encrypted mail service device 300.
[0023]
In step S5, the encrypted mail service device 300 receives the public key.
In step S6, the encrypted mail service device 300 registers the mail address of the general terminal 150 and the public key in the user management database 307 (see FIG. 3) in association with each other.
[0024]
In step C8, as shown in FIG. 8, the general terminal 150 installs the encryption program 107, the decryption program 108, and the secret key K. Thereby, the general terminal 150 can function as the transmitting terminal 100 or the receiving terminal 200.
[0025]
The processes in steps C5 to C8 are automatically performed, for example, when the installation button is clicked on the installation web page (see FIG. 7) displayed on the general terminal 150.
However, the encrypted mail service device 300 transmits an e-mail attached with an encryption program, a public key / private key generation program, and an execution format installation program of a decryption program to the general terminal 150 via the first mail server device 40A. You may. In this case, since each program can be transferred to the general terminal 150 using a protocol (for example, SMTP and POP3) different from a communication protocol of the web page (for example, HTTP; HyperText Transport Protocol), there is an advantage that security can be further improved.
[0026]
FIG. 9 is a flowchart showing a procedure for sending an e-mail from transmitting terminal 100. The flow on the left is a flow of processing by the mail program 103. The flow on the right side is a flow of processing by the encryption program 107.
[0027]
In step T1, the operator of the transmitting terminal 100 activates the mail program 103 and inputs plain text. The destination may be either the receiving terminal 200 or the general terminal 150.
In step T2, the operator of the transmitting terminal 100 selects, for example, [Tool] → [Encrypted transmission] on the mail program screen as shown in FIG. As a result, an encryption request for the encryption process is sent to the encryption program 107.
[0028]
In step A1, the encryption program 107 requests the public key of the destination receiving terminal 200 or general terminal 150 from the encrypted mail service device 300.
In step A2, if the public key of the destination is successfully obtained from the encrypted mail service device 300, the process proceeds to step A4. If the public key of the destination is not successfully obtained, the process proceeds to step A3. In other words, if the destination mail address is already registered in the user management database 307 of the encrypted mail service device 300, the public key is sent and the acquisition succeeds, but the registration is not registered in the user management database 307 (or the trial period). ), The public key is not sent and the acquisition fails.
In step A3, the encryption program 107 sends an encryption failure notification to the mail program 103. Then, the processing by the encryption program 107 ends.
[0029]
In step A4, the encryption program 107 sends a plaintext request requesting a plaintext notification to the mail program 103.
[0030]
In step T3, the mail program 103 determines the content of the message from the encryption program 107. If it is an encryption failure notification, the process proceeds to step T4. If it is a plaintext request, the process proceeds to step T5.
In step T4, the mail program 103 sends the plaintext mail in which the plaintext input in step T1 is not encrypted to the first mail server device 40A using the SMTP protocol. Then, the processing by the mail program 103 ends.
It is assumed that the first mail server device 40A is set as the transmission mail server in the mail program of the transmission terminal 100.
[0031]
In step T5, the mail program 103 notifies the encryption program 107 of the plain text input in step T1.
[0032]
In step A5, the encryption program 107 encrypts the plaintext received from the mail program 103 with the destination public key, and converts it into a ciphertext.
In step A6, the encryption program 107 notifies the mail program 103 of the cipher text.
[0033]
In step T6, the mail program 103 sends the encrypted mail of the cipher text received from the encryption program 107 to the first mail server device 40A using the SMTP protocol.
[0034]
FIG. 11 is a flowchart showing a procedure for receiving an e-mail by the receiving terminal 200.
In step R1, the operator of the receiving terminal 200 activates the mail program 103 and requests the second mail server device 40B to retrieve the mail addressed to the mail program 103 using the POP3 protocol.
In the mail program 103 of the sending terminal 200, the second mail server device 40B is set as a receiving mail server, and the plain text mail or the encrypted mail from the encrypted mail service device 300 is stored in the mailbox 43B of the receiving mail server. Has arrived.
In Step R2, the mail to itself is received from the second mail server device 40B.
[0035]
In step R3, a plaintext or a ciphertext is displayed. That is, when a plaintext mail (see step T4 in FIG. 9) is received, plaintext is displayed, and when an encrypted mail (see step T6 in FIG. 9) is received, a ciphertext is displayed.
[0036]
In step R4, the operator of the receiving terminal 200 reads the displayed mail if it is plain text and ends the mail program 103, and if the displayed mail is cipher text, proceeds to step R5.
[0037]
In step R5, the operator of the receiving terminal 200 selects, for example, [Tool] → [Decryption] on the mail program screen as shown in FIG. As a result, the ciphertext is converted into plaintext using the decryption program 108 and the secret key K, and the plaintext is displayed as shown in FIG. The operator of the receiving terminal 200 reads the displayed plain text and ends the mail program.
[0038]
When the plaintext is sent to the general terminal 150, the plaintext is delivered from the transmission mail server of the transmission terminal 100 to the reception mail server of the general terminal 150.
[0039]
According to the above cipher mail system 1000, the cipher mail service device 300 centrally manages the encryption program 107, the public key / decryption key generation program, and the decryption program 108. There is no need to manage it. Therefore, anyone can easily perform encrypted mail communication. In addition, since mail can be transmitted and received to and from the general terminal 150 that does not subscribe to the encrypted mail service, the usability is improved. Further, since the encrypted mail service can be received only by the mail address, leakage and diffusion of the user information (name, address, telephone number, etc.) can be prevented.
[0040]
-2nd Embodiment-
FIG. 14 is a block diagram showing an encrypted mail system 2000 according to the second embodiment of the present invention.
The encrypted mail system 2000 includes a network 1, a transmitting terminal 100 subscribed to an encrypted mail service, a first mail server device 400A accessible by the transmitting terminal 100, and a receiving terminal subscribed to the encrypted mail service. 200, and a second mail server device 400B accessible to the receiving terminal 200.
Further, a general terminal 150 not subscribed to the encrypted mail service is also connected to the network 1.
[0041]
The first mail server device 400A includes an SMTP server 41A, a POP3 server 42B, a mailbox 43A that can accommodate electronic mail, and an encrypted mail service device 300A that provides an encrypted mail service.
The second mail server device 400B includes an SMTP server 41B, a POP3 server 42B, a mailbox 43B that can accommodate electronic mail, and an encrypted mail service device 300B that provides an encrypted mail service.
[0042]
In the encrypted mail system 2000, the encrypted mail service device 300A transmits a web page to the general terminal 150 when the general terminal 150 subscribes to the cryptographic mail service and becomes the transmission terminal 100, or transmits an encryption program and a public key / private key. A process of transmitting the key generation program and the decryption program is performed (see FIG. 5).
Further, when the general terminal 150 subscribes to the cryptographic mail service and becomes the receiving terminal 200, the encrypted mail service device 300B transmits a web page to the general terminal 150, and transmits an encryption program and a public key / private key generation program. A process for transmitting the decryption program is performed.
[0043]
Next, the operation of the encrypted mail system 2000 will be described.
(1) When the transmitting terminal 100 executes the mail program and requests the public key of the destination receiving terminal 200 from the first mail server device 400A, the first mail server device 400A transmits the request to the second mail server 400A. Transfer to server device 400B.
(2) The encrypted mail service device 300B of the second mail server device 400B sends the public key of the destination receiving terminal 200 to the first mail server device 400A.
[0044]
(3) The first mail server device 400A sends the public key of the destination receiving terminal 200 to the transmitting terminal 100.
(4) The transmitting terminal 100 encrypts the plaintext with the encryption program and the public key of the destination receiving terminal 200 to generate an encrypted mail, and sends it to the first mail server device 400A. The first mail server device 400A transfers the encrypted mail to the second mail server device 400B.
[0045]
(5) The receiving terminal executes the mail program, accesses the second mail server device 400B, and reads the mail addressed to itself from the mailbox 43B. If it is an encrypted email, it decrypts it using a decryption program and its own secret key, and displays plain text.
(6) The operator of the receiving terminal 200 reads the displayed plain text and ends the mail program.
[0046]
According to the above-described encrypted mail system 2000, for example, even if the service provider of the mail server device 400A accessible to the transmitting terminal 100 and the service provider of the mail server device 400B accessible to the receiving terminal 200 are different, the public key is not changed. The service can be delivered to the transmission terminal 100, and the service area of the encrypted mail can be easily widened (however, it is necessary to unify the encryption and decryption methods and communication protocols among the respective traders).
[0047]
-Other embodiments-
(1) It is preferable that the encrypted mail service device 300 periodically sends the encryption program to the transmission terminal 100 and updates the encryption program periodically. This increases security.
(2) The cryptographic mail service device 300 sends a public key / private key generation program and a decryption program to the receiving terminal 200 periodically or when transmitting the cryptographic mail to the receiving terminal 200, and transmits the public key, the secret key, and the decryption. Preferably, the program is updated regularly. This increases security.
(3) At step T2 in FIG. 5, the encryption request may be sent automatically without dividing the transmission instruction into [(plaintext) transmission] and [encrypted transmission]. In this case, the operator of the transmitting terminal 100 only needs to perform the operation of transmitting the plaintext, and the usability is improved.
(4) At step R4 in FIG. 11, it may be automatically determined whether the data is a plaintext or a ciphertext. For example, if identification information of plain text mail or encrypted mail is entered in a mail header (for example, Message-ID), automatic determination can be made from the contents of the mail header. In this case, the operator of the receiving terminal 200 only needs to perform the operation of receiving the mail, and the usability is improved.
(5) An encryption program, a public key / private key generation program, and a decryption program may be provided on a CD-ROM or the like, and a key for enabling them may be transmitted via the network 1. Also in this case, it is substantially equivalent to “sending the encryption program to the transmission terminal”, “sending the public key / private key generation program to the reception terminal”, and “sending the decryption program to the reception terminal”.
(6) A mail with an attached file may be sent. In this case, an e-mail with an attached file or its coded file is equivalent to "plaintext e-mail", and an e-mail with an attached file or its encoded file is equivalent to "encrypted e-mail". I do. Incidentally, as a method of converting a binary attached file into a text file, for example, uuencode, MIME (Base64), and BinHex are known.
[0048]
【The invention's effect】
According to the encrypted mail communication method and the encrypted mail system of the present invention, the following effects can be obtained.
(1) Since the encrypted mail service device centrally manages the encryption program, the encryption / decryption key generation program, and the decryption program, there is no need to consciously manage these programs at the transmission terminal or the reception terminal. In addition, since the encryption program, the decryption program, and the decryption key are installed in the own terminal, it is possible to transmit and receive the encrypted mail according to the operation procedure that the user is accustomed to. Therefore, anyone can easily perform encrypted mail communication.
(2) By incorporating a cryptographic mail service device in a mail server device, for example, it is possible to exchange cryptographic mail between subscribers who subscribe to a cryptographic mail service provided by different companies.
(3) If the transmitting terminal cannot obtain the destination encryption key from the encrypted mail service device, the plaintext mail without encryption is transmitted, so that the mail can be transmitted to the non-subscriber of the encrypted mail service.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an encrypted mail system according to a first embodiment.
FIG. 2 is a configuration diagram showing an encrypted mail service device.
FIG. 3 is an explanatory diagram showing an example of the contents of a user management database.
FIG. 4 is a configuration diagram illustrating a transmission terminal.
FIG. 5 is a flowchart showing a procedure when a general terminal subscribes to an encrypted mail service and becomes a transmitting terminal or a receiving terminal.
FIG. 6 is an exemplary view showing a display screen of a web page for an encrypted mail service.
FIG. 7 is an exemplary view showing a display screen of a web page for installation.
FIG. 8 is an exemplary diagram showing a general terminal after an encryption program, a decryption program, and a secret key are installed.
FIG. 9 is a flowchart showing a procedure for sending an electronic mail from a transmitting terminal.
FIG. 10 is an explanatory diagram showing a state where “encrypted transmission” is selected on the mail program screen.
FIG. 11 is a flowchart showing a procedure for receiving an e-mail at the receiving terminal.
FIG. 12 is an explanatory diagram showing a state in which “cipher text decryption” is selected on the mail program screen.
FIG. 13 is an explanatory diagram showing a state in which decrypted plain text is displayed on the mail program screen.
FIG. 14 is a block diagram illustrating an encrypted mail system according to a second embodiment.
[Explanation of symbols]
1 Network
40A, 40B mail server device
100 sending terminal
101, 301 communication unit
102 Web Browser
103 mail program
104 Program execution unit
105,308 Data storage unit
106 Display
107 encryption program
108 Decryption program
150 general terminal
200 receiving terminal
300, 300A, 300B encrypted mail service device
302 Web page storage
303 Encrypted mail service program execution unit
304 Encrypted program storage unit
305 Public key / private key generation program storage
306 Decryption program storage
307 User management database
400A, 400B mail server device
1000, 2000 encrypted mail system
K secret key

Claims (8)

Connect the sending terminal, the encrypted mail service device, the mail server device and the receiving terminal via a network,
The encryption mail service device sends an encryption program to the transmission terminal, and generates an encryption key / decryption key generation program and a decryption program for generating an encryption key used at a transmission source and a decryption key used at a destination. To
The transmitting terminal incorporates the encryption program in its own terminal,
The receiving terminal sends the encryption key generated by executing the encryption key generation program to the encryption mail service device, and transmits the decryption program and the decryption key generated by executing the decryption key generation program to its own. Built in the terminal, the encrypted mail service device receives the encryption key, and registers it in association with the mail address of the receiving terminal,
The sending terminal executes a mail program, requests an encryption key of a destination receiving terminal from the encrypted mail service device,
The encrypted mail service device sends an encryption key of the destination receiving terminal to the transmitting terminal,
The transmitting terminal encrypts a plaintext with the encryption program and an encryption key of the destination receiving terminal to generate an encrypted mail, and sends the encrypted mail to the mail server device.
The encrypted mail communication method, wherein the receiving terminal executes a mail program to access the mail server device, reads mail addressed to itself, and decrypts the encrypted mail with the decryption program and the decryption key. A transmitting terminal, a first mail server device containing the first encrypted mail service device and accessible by the transmitting terminal, a receiving terminal, and a second mail server device containing the second encrypted mail service device and accessed by the receiving terminal; Connect to a possible second mail server device via a network,
The first encrypted mail service device sends an encrypted program to the transmitting terminal,
The transmitting terminal incorporates the encryption program in its own terminal,
The second encrypted mail service device sends an encryption key / decryption key generation program and a decryption program for generating an encryption key used at a transmission source and a decryption key used at a destination to the reception terminal,
The receiving terminal sends the encryption key generated by executing the encryption key generation program to the second encrypted mail service device, and also executes the decryption program and the decryption key generated by executing the decryption key generation program. In your own device,
The second encrypted mail service device receives the encrypted key, and registers the encrypted key in association with the mail address of the receiving terminal;
The transmitting terminal executes a mail program, requests the encryption key of the destination receiving terminal from the first mail server device,
The first mail server device transfers the request to the second mail server device,
The second encrypted mail service device sends an encryption key of the destination receiving terminal to the first mail server device,
The first mail server device sends an encryption key of the destination receiving terminal to the transmitting terminal,
The transmitting terminal encrypts a plaintext with the encryption program and an encryption key of the destination receiving terminal to generate an encrypted mail, and sends the encrypted mail to the first mail server device;
The receiving terminal executes a mail program to access the second mail server device, reads out mail addressed to itself, and decrypts the encrypted mail with the decryption program and the decryption key. Communication method. 3. The encrypted mail communication method according to claim 1, wherein the transmitting terminal transmits the unencrypted plaintext mail to the mail server device when the destination encryption key is not obtained from the encrypted mail service device. 4. An encrypted mail communication method characterized by being sent to: 4. The method according to claim 1, wherein a public key that is not easily estimated from a decryption key secretly managed by the receiving terminal is used as the encryption key. Encryption mail communication method. An encrypted mail system comprising a transmitting terminal, an encrypted mail service device, a mail server device, a receiving terminal, and a network connecting the transmitting terminal, the encrypted mail service device, the mail server device, and the receiving terminal. ,
The encryption mail service device sends an encryption program to the transmission terminal, and generates an encryption key / decryption key generation program and a decryption program for generating an encryption key used at a transmission source and a decryption key used at a destination. To
The transmitting terminal incorporates the encryption program in its own terminal,
The receiving terminal sends the encryption key generated by executing the encryption key generation program to the encryption mail service device, and transmits the decryption program and the decryption key generated by executing the decryption key generation program to its own. Built in the terminal, the encrypted mail service device receives the encryption key, and registers it in association with the mail address of the receiving terminal,
The sending terminal executes a mail program, requests an encryption key of a destination receiving terminal from the encrypted mail service device,
The encrypted mail service device sends an encryption key of the destination receiving terminal to the transmitting terminal,
The transmitting terminal encrypts a plaintext with the encryption program and an encryption key of the destination receiving terminal to generate an encrypted mail, and sends the encrypted mail to the mail server device.
The cipher mail system wherein the receiving terminal executes a mail program to access the mail server device, reads mail addressed to itself, and decrypts the encrypted mail with the decryption program and the decryption key. A transmitting terminal, a first mail server device containing the first encrypted mail service device and accessible by the transmitting terminal, a receiving terminal, and a second mail server device containing the second encrypted mail service device and accessed by the receiving terminal; An encrypted mail system comprising a possible second mail server device, and a network connecting the transmitting terminal, the first mail server device, the receiving terminal, and the second mail server device,
The first encrypted mail service device sends an encrypted program to the transmitting terminal,
The transmitting terminal incorporates the encryption program in its own terminal,
The second encrypted mail service device sends an encryption key / decryption key generation program and a decryption program for generating an encryption key used at a transmission source and a decryption key used at a destination to the reception terminal,
The receiving terminal sends the encryption key generated by executing the encryption key generation program to the second encrypted mail service device, and also executes the decryption program and the decryption key generated by executing the decryption key generation program. In your own device,
The second encrypted mail service device receives the encrypted key, and registers the encrypted key in association with the mail address of the receiving terminal;
The transmitting terminal executes a mail program, requests the encryption key of the destination receiving terminal from the first mail server device,
The first mail server device transfers the request to the second mail server device,
The second encrypted mail service device sends an encryption key of the destination receiving terminal to the first mail server device,
The first mail server device sends an encryption key of the destination receiving terminal to the transmitting terminal,
The transmitting terminal encrypts a plaintext with the encryption program and an encryption key of the destination receiving terminal to generate an encrypted mail, and sends the encrypted mail to the first mail server device;
The receiving terminal executes a mail program to access the second mail server device, reads out mail addressed to itself, and decrypts the encrypted mail with the decryption program and the decryption key. system. 7. The encrypted mail system according to claim 5, wherein the transmitting terminal sends the unencrypted plaintext mail to the mail server device when the destination encryption key is not obtained from the encrypted mail service device. An encrypted mail system characterized by sending. 8. The encryption mail system according to claim 5, wherein a public key that is not easily estimated from a decryption key secretly managed by the receiving terminal is adopted as the encryption key. Mail system.

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