JP2007266674A - Method of transferring file - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily realize file transfer of high level of security. <P>SOLUTION: A personal computer 1 at the side of a sender A selects cipher key information from the transmission and reception message and the transmission and reception history information of an electronic mail to a saved receiver B, generates a cipher key based on the cipher key information, performs the encryption processing of a common key cipher system to the file to be transferred, attaches an encryption file to the electronic mail, records the extraction condition information of the cipher key information used for generating the cipher key in the electronic mail, and transmits the electronic mail. A personal computer 2 at the side of the receiver B who receives the electronic mail extracts the cipher key information from the transmission and reception message and the transmission and reception history information of the electronic mail to the saved sender A, based on the extraction condition information of the cipher key information recorded in the electronic mail to which the received encryption file is attached, generates a decipher key based on the cipher key information, and performs the decoding processing of the common key cipher system to the encryption file attached to the electronic mail by using the decipher key. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a file transfer method in which an electronic file (hereinafter referred to as a file) is attached to an electronic mail and transmitted.

  Conventionally, when a file is attached to an e-mail and transmitted, in order to ensure the security of file transfer, a method of applying an encryption process to the file and attaching it to the e-mail after being encrypted is employed.

  Here, as a file encryption method, a common key using the same key as an encryption key (hereinafter referred to as “encryption key”) and a decryption key (hereinafter referred to as “decryption key”). There are two types, encryption methods and public key encryption methods that use different keys for encryption keys and decryption keys. Each encryption method has the following advantages and disadvantages.

Advantages and disadvantages of the common key cryptosystem: The same key is used for encryption and decryption, and the encryption and decryption algorithms are symmetric, so that high-speed processing is possible.
Cons: It is necessary to send the encryption key to the recipient using some method in advance. (Examples of sending the encryption key include a method of sending the encryption key by an e-mail different from the e-mail attached to the encrypted file, and a method of contacting by a medium different from the e-mail such as a telephone.) First, if the encryption key leaks to a third party at the time of sending, there is a high risk that all subsequent ciphers will be decrypted. In addition, sending is required every time the encryption key is changed.

Advantages and disadvantages of public key cryptography: If one key is disclosed, anyone can use that key (public key). In the case of the public key cryptosystem, since the encryption key and the decryption key are separate, there is no risk of leaking the key to a third party because it is not necessary to send the key.
Disadvantages: High-speed processing is difficult because the encryption and decryption algorithms are asymmetric, and the algorithm itself has many mathematically difficult processes.

In addition, the e-mail transmission method disclosed in Patent Document 1 aims at automatic encryption at the time of e-mail transmission and automatic encryption at the time of e-mail reception. Also, the encryption message communication method disclosed in Patent Document 2 is characterized in that an encryption message is attached to a transmission e-mail addressed to a mobile device from a management apparatus, and thereafter, the encryption message is transmitted from the mobile device to a store terminal. . In addition, the Internet facsimile communication method disclosed in Patent Document 3 uses e-mail to transmit unique information stored individually in both the sending device and the receiving device before sending encrypted facsimile image data. The facsimile image data is encrypted with the encryption key generated based on the unique information that is notified to each other.
JP 2005-285111 A JP 2004-266716 A JP 2002-300410 A

  In the conventional file transfer method by sending an e-mail with an encrypted file attached, there is a problem in security at the time of sending the encryption key when using the common key encryption method, and encryption / decryption processing is used when using the public key encryption method. There was a problem with processing speed.

  The e-mail transmission method described in Patent Document 1 is based on the premise that the encryption key is sent in advance by some method, and does not mention improvement in security at the time of sending the encryption key. The problem has not been solved.

  The encryption message communication method described in Patent Document 2 is the same as that of Patent Document 1 except that the encryption key is transmitted directly from the management device to the store terminal without going through the mobile device. It does not mention improvement of security at the time of key sending, and does not solve the problem of the conventional method.

  The Internet facsimile communication method described in Patent Document 3 has improved security as compared with the direct transmission of the encryption key. However, since the unique information is used, the same information is transmitted each time, and multiple transmissions are performed. There is a risk that security will be lowered later.

  An object of the present invention is to provide a file transmission / reception method, a terminal, and a program that easily realize high-security file transfer.

  The e-mail transmission method of the present invention is a random encryption key based on e-mail transmission / reception messages and transmission / reception history information (e.g., information in a mail header) exchanged with a receiver at a sender terminal. A step of selecting information, a step of generating an encryption key from the selected encryption key information, a step of performing encryption processing of a common key cryptosystem on a file to be transferred using the generated encryption key, and e-mail And attaching the encrypted file to the e-mail and describing the extraction condition information of the encryption key information used to generate the encryption key.

  The e-mail receiving method of the present invention has been exchanged with the sender of the e-mail previously at the receiver's terminal based on the extraction condition information of the encryption key information described in the received e-mail. A step of extracting encryption key information from the transmitted / received message and transmission / reception history information of the received email, a step of generating a decryption key based on the extracted encryption key information, and the received email using the generated decryption key And performing a decryption process of a common key encryption method on the encrypted file attached to.

  By executing the above steps, high-speed encryption / decryption processing is realized by taking advantage of the common key encryption method, and the security at the time of sending the encryption key is improved by compensating for the disadvantages of the common key encryption method. be able to.

  Before sending the encrypted file, the encryption key information is selected from the transmission / reception message and the transmission / reception history information of the e-mail that has already been exchanged between the sender and the receiver, and the encryption key is generated based on that information. Even if information is leaked to a third party when sending key information, it is very difficult to determine the actual encryption key, so sending the encryption key information to the recipient can be done easily and with a high degree of security. Furthermore, the encryption key can be changed frequently. Also, since the encryption key for each recipient is selected from the email transmission / reception message and the transmission / reception history information for each recipient, encryption key management (selection / generation and notification of encryption key) for each recipient is easily performed. be able to.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, it is assumed that a personal computer 1 of a sender A and a personal computer 2 of a receiver B are connected to a network 3. As shown in FIG. 2, the personal computers 1 and 2 include a computer main unit 11, a display unit 12, and an input unit 13, and the computer main unit 11 includes a processor 14, a primary memory 15, and a secondary memory 16.

  The processor 14 of the personal computer 1 on the sender A side uses the transmission / reception message and transmission / reception history information (such as information in the mail header) of the electronic mail (FIG. 3 (1)) previously exchanged with the receiver B. Processing to randomly select encryption key information, processing to generate an encryption key based on the selected encryption key information, and encryption of the common key encryption method using the encryption key generated for the file to be transferred The process and the encrypted file attached to the e-mail are attached, and the extraction condition information of the encryption key information used to generate the encryption key is described in the e-mail (FIG. 3 (2)) and received. Processing to send an e-mail to the person B. The processor 14 of the personal computer 2 on the receiver B side previously exchanged with the sender A based on the extraction condition information of the encryption key information described in the received e-mail attached to the encrypted file. Processing for extracting encryption key information from the transmitted / received message and transmission / reception history information of the received email, processing for generating a decryption key based on the extracted encryption key information, and email received using the generated decryption key And decrypting the common key cryptosystem on the encrypted file attached.

  Next, the operation of the present embodiment will be described with reference to the sequence diagram of FIG.

  First, electronic mail is frequently exchanged between the personal computer 1 on the sender A side and the personal computer 2 on the receiver B side, and the exchanged electronic mail is stored in the secondary memory 16 of both personal computers. Transmission / reception messages and transmission / reception history information (such as information in the mail header) are stored.

  Next, when an event occurs in which an electronic file is transferred from the sender A side to the receiver B side, the processor 14 of the personal computer 1 on the sender A side receives the receiver stored in the secondary memory 16. The encryption key information is randomly selected from the transmission / reception message and transmission / reception history information of the electronic mail with B (step 101), and an encryption key is generated based on the selected encryption key information (step 102) and transferred. The encryption key of the common key cryptosystem is applied with the encryption key generated in the file (step 103), the encrypted file is attached to the e-mail, and the encryption key information used to generate the encryption key The extraction condition information is described in the e-mail, and the e-mail is transmitted to the personal computer 2 of the recipient B (step 104).

  On the other hand, the processor 14 of the personal computer 2 on the receiver B side who received the electronic mail attached with the encrypted file from the transmission side A extracts the extraction condition of the encryption key information described in the received electronic mail attached with the encrypted file. Based on the information, the encryption key information is extracted from the transmission / reception message and the transmission / reception history information of the e-mail with the sender A stored in the secondary memory 16 (step 105). A decryption key is originally generated (step 106), and the decryption process of the common key encryption method is performed on the encrypted file attached to the received electronic mail using the generated decryption key (step 107).

  The file transfer method of the present invention records a program for realizing the function on a computer-readable recording medium, and causes the computer to read and execute the program recorded on the recording medium. May be. The computer-readable recording medium refers to a recording medium such as a flexible disk, a magneto-optical disk, a CD-ROM, or a storage device such as a hard disk device built in a computer system. Further, the computer-readable recording medium is a medium that dynamically holds the program for a short time (transmission medium or transmission wave) as in the case of transmitting the program via the Internet, and in the computer serving as a server in that case Such as a volatile memory that holds a program for a certain period of time.

  The present invention can be suitably used as a file transfer method with improved security by using electronic mail. That is, it is possible to perform file transfer with high security between clients without using an FTP server or a Web server.

It is a figure which shows a mode that two personal computers are connected to the network. It is a figure which shows the structure of the personal computer in FIG. It is a figure which shows the structure of an email. It is a sequence diagram which shows the operation | movement accompanying electronic mail transmission / reception between the personal computers of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Personal computer 3 Network 11 Computer main body part 12 Display part 13 Input part 14 Processor 15 Temporary memory 16 Secondary memory 101-107 step

Claims (6)

In the method of sending e-mail on the terminal,
Randomly selecting encryption key information from email sent / received messages and send / receive history information previously exchanged with the recipient;
Generating an encryption key from the selected encryption key information;
Applying the encryption process of the common key cryptosystem to the file to be transferred using the generated encryption key;
An e-mail transmission method comprising: attaching the encrypted file to an e-mail and describing extraction condition information of the encryption key information used to generate the encryption key in the e-mail. In the method of receiving e-mail at the terminal,
Based on the extraction condition information of the encryption key information described in the received email, the encryption key information is extracted from the email transmission / reception message and the transmission / reception history information previously exchanged with the sender of the email. And steps to
Generating a decryption key based on the extracted encryption key information;
And a step of performing a decryption process of a common key cryptosystem on an encrypted file attached to the received electronic mail using the generated decryption key. On the terminal,
Means for randomly selecting the encryption key information from the sent / received message and the sent / received history information of the email exchanged with the recipient;
Means for generating an encryption key from the selected encryption key information;
Means for performing encryption processing of a common key cryptosystem on a file to be transferred using the generated encryption key;
And a means for attaching the encrypted file to an e-mail and describing extraction condition information of the encryption key information used to generate the encryption key in the e-mail. On the terminal,
Based on the extraction condition information of the encryption key information described in the received email, the encryption key information is extracted from the email transmission / reception message and the transmission / reception history information previously exchanged with the sender of the email. Means to
Means for generating a decryption key based on the extracted encryption key information;
A terminal that uses the generated decryption key to subject the encrypted file attached to the received e-mail to decryption processing using a common key cryptosystem. Randomly select encryption key information from email sent / received messages and send / receive history information previously exchanged with recipients,
Generating an encryption key from the selected encryption key information;
Using the generated encryption key, a procedure for applying a common key encryption method to the file to be transferred;
A program for causing a computer to execute the procedure of attaching the encrypted file to an e-mail and describing extraction condition information of the encryption key information used to generate the encryption key in the e-mail. Based on the extraction condition information of the encryption key information described in the received email, the encryption key information is extracted from the email transmission / reception message and the transmission / reception history information previously exchanged with the sender of the email. And the steps to
A procedure for generating a decryption key based on the extracted encryption key information,
A program for causing a computer to execute a procedure of performing a decryption process of a common key cryptosystem on an encrypted file attached to a received electronic mail using the generated decryption key.

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