JP2008262282A - Encryption/decryption device and electronic mail system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for safely transmitting a password for decrypting a file to a reception side when attaching an encrypted file to electronic mail. <P>SOLUTION: A transmission side prepares a password table and the index of the password table by using an arbitrarily determined hint character string, and determines a password for encrypting an attachment file, and encrypts and transmits the attachment file with a hint character string. The reception side prepares the same password table as that of the transmission side and the index of the password table by using the hint character string, and determines the password for decrypting the attachment file, and decodes the attachment file. Supposing that even when any electronic mail leaks on the transmission path of electronic mail, it is not possible to prepare any password table or index only with the hint character string, and any password for decoding the attachment file is not acquired. Therefore, it is possible to safely transmit the password to the reception side. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an encryption / decryption device and an electronic mail system, and more particularly to a mechanism capable of more safely executing transmission / reception of an encrypted file attached to an electronic mail.

  In recent years, with the advance of communication technology, it has become easy to send and receive e-mails with large files attached, and this is done on a daily basis. However, there is a possibility that a person who does not want to receive the e-mail, such as e-mail being intercepted by a third party or the sender making a mistake in the destination, obtains the e-mail.

  For this reason, an operation in which an attached file is encrypted and then attached to an electronic mail is becoming widespread. In relation to this, for example, Patent Document 1 discloses a method of automatically encrypting and compressing an attached file with a password stored in advance when the file is attached to an e-mail. .

JP-A-2005-285111

  In preparation for the case where an attached file of an e-mail leaks, it is becoming popular to encrypt the file and attach it to the e-mail. In practice, however, the recipient often does not know the password for decryption. In order to compensate for this, a “hint for guessing a password” is added to the body of an email. For example, a statement such as “The password for decrypting the attached file is the fax number on the business card of XX” is added. For this reason, when a third party intercepts this mail, there is a possibility that the encrypted attachment is decrypted by analogy with the password. This makes it meaningless to encrypt.

  The present invention has been made in view of such circumstances, and provides a mechanism capable of encrypting / decrypting an attached file more securely and further transmitting / receiving an email attached with the encrypted file more safely. Is.

  In order to solve the above problem, in the present invention, when data is encrypted, the input character string is not used as a password as it is, but a predetermined operation is performed on the input character string to obtain another character string. Is used as a password for encryption / decryption.

  That is, the encryption / decryption device according to the present invention creates a character string different from the character string based on an arbitrary character string as a password, and executes the encryption process using this password.

  In addition, the encryption / decryption device creates a password table including a plurality of passwords using one arbitrary character string, and further creates an index based on the arbitrary character string. Then, the password used for the encryption process is selected from the plurality of passwords included in the password table by the index.

  In addition, a specific individual may be identified by biometric authentication, and a password may be created only when the identified individual is confirmed to be a valid user.

  The e-mail system according to the present invention creates a character string different from the character string based on an arbitrary character string as a password, executes an encryption process using the password, and creates a cipher created by the encryption process. The encrypted file, the mail text, and an arbitrary character string used for creating the password are combined and transmitted as one electronic mail. Note that an arbitrary character string used for creating a password is included in a predetermined part of the mail text.

  Also, in this e-mail system, when an e-mail attached with an encrypted file is received, the encrypted file, an arbitrary character string, and the mail body are separated, and a password is created using the arbitrary character string. The encrypted file is decrypted using the password, and the decrypted file is presented.

  Further features of the present invention will become apparent from the best mode for carrying out the present invention and the accompanying drawings.

  According to the present invention, an attached file can be encrypted and decrypted more safely, and an electronic mail to which the encrypted file is attached can be transmitted and received safely.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be noted that this embodiment is merely an example for realizing the present invention and does not limit the present invention. In each drawing, the same reference numerals are assigned to common components.

<Configuration of e-mail system>
FIG. 1 is a diagram showing a schematic configuration of an electronic mail system 100 according to an embodiment of the present invention. By this electronic mail system, a password transmission method described later is realized.

  The electronic mail system 100 is connected to other electronic mail systems via a network, and functions as both a mail transmission side and a reception side. Then, as shown in FIG. 1, the electronic mail system 100 includes a biometric information input unit 101, a character input unit 102, a file input unit 103, a biometric information comparison unit 104, a password creation unit 105, a file encryption Unit 106, biometric information storage unit 107 for personal identification, e-mail output unit 108, e-mail input unit 109, file decryption unit 110, file output unit 111, character string output unit 112, and message output unit 113. The e-mail system 100 is realized by, for example, a computer. In this case, each unit in FIG. 1 is realized by a processing control unit such as a CPU (not shown) and a computer program corresponding to a flowchart described later. .

  The biometric information input unit 101 inputs biometric information such as a finger and a face, extracts its characteristics, and creates biometric information for personal identification. The personal identification biometric information storage unit 107 stores personal identification biometric information for a person who is permitted to use the electronic mail system 100.

  The biometric information comparison unit 104 compares the biometric information stored in the biometric information storage unit 107 for personal identification with the biometric information for personal identification created by the biometric information input unit 101, and uses the electronic mail system 100. Determine if you are good. If the biometric information comparison unit 104 determines that the person should not be used, the biometric information comparison unit 104 instructs the password creation unit 105 to prohibit the operation. Furthermore, the biometric information comparison unit 104 instructs the message output unit 113 to display a message that the system cannot be used because the biometric information of the input person of the information is not registered, and the biometric information input unit The process waits until (new) biometric information is input to 101 again. On the other hand, when it is determined that the person can use the system, the biometric information comparison unit 104 instructs the password creation unit 105 to permit password creation.

  The character string input unit 102 is a means for a user to input a mail text or a hint character string (“hint for obtaining a password” that can only be understood by a valid recipient), for example, a keyboard, This is realized by a pointing device such as a mouse. Then, the input hint character string is supplied to the password creation unit 105. The mail text is supplied to the e-mail output unit 108.

  The password creation unit 105 creates a password table and an index based on the input hint character string by a method shown in FIGS. 3 and 4 described later. Then, one password is selected from the password table by the index, and this is provided to the file encryption unit 106.

  A file to be attached to an e-mail is input to the file input unit 103 by the user, and the file is provided to the file encryption unit 106. The file encryption unit 106 encrypts the content of the file input to the file input unit 103 using the password created by the password creation unit 105 and determined to be used for encryption, and sends it to the e-mail output unit 108. Output. Note that any encryption processing may be used, and the present invention does not limit the processing content.

  The e-mail output unit 108 collects the mail text and hint character string input from the character string input unit 502 and the content of the encrypted file from the file encryption unit 106 as an e-mail, and sends the e-mail to the network. . The encrypted file is attached to the e-mail. The hint character string is embedded in a predetermined place of the mail text and a place decided in advance by both the sender and receiver, for example, Signature, Subject, tag, and the like.

  The e-mail input unit 109 receives an e-mail transmitted via the network, extracts the e-mail body from the content, and supplies it to the character string output unit 112. Also, the e-mail input unit 109 extracts the encrypted attachment from the e-mail and provides it to the file decryption unit 110, and further extracts the hint character string embedded in the mail body and provides it to the password creation unit 105. .

  The file decryption unit 110 decrypts the encrypted attached file provided from the e-mail input unit with the password created by the password creation unit 105, and outputs the content to the file output unit 111. The file output unit 111 writes the contents of the attached file decrypted by the file decrypting unit 110 into a file.

  The character string output unit 112 displays the mail text extracted by the e-mail input unit 109 on the screen. Further, the message output unit 113 displays a message from the biometric information comparison unit 104 or the like (for example, “You cannot use this system”) on the screen.

<Details of email transmission processing>
FIG. 2 is a diagram for explaining the outline of the process from encrypting the attached file to sending the mail.

  The input hint character string 201 is an arbitrary character string (one piece) that becomes raw data for creating the password table, and is described or embedded in the mail body as described above. It is communicated to the recipient as part of the email. The hint character string 201 is an arbitrary character string and can be determined as appropriate by the user. However, the present invention is not limited to this form, and a character string linked to the biometric information when the user's biometric information is input as described above may be used as a hint character string. For example, a hint character string table including a plurality of hint character string candidates is provided, and one of the hint character string tables is selected corresponding to the biological information, or a part of the digitized biological information Can be extracted as a hint character string.

  In the password table creation process 205, the password table 206 is created based on the hint character string 201. Details of the process 205 will be described later with reference to FIG.

  In the index creation process 204, an index 210 for the password table 206 is created based on the hint character string 201. Details of the process 204 will be described later with reference to FIG. Since there is basically one password used for encryption, one password is selected by the index 210 from the password table 206. However, if more secure file encryption is desired, a plurality of passwords may be selected from the password table 206 using the index 210. For example, in the password table 206, an algorithm may be used that selects a password that is three passwords above and three passwords below that specified by the index 210. Which password is extracted from the password table can be freely determined by an algorithm.

  In the encryption process 207, the file 202 attached to the e-mail is encrypted using the password obtained from the password table 206 and the index 210, and an encrypted file 208 is generated.

  In the mail transmission process 209, the mail body 203, the encrypted file 208, and the hint character string 201 are integrated, and a process of sending out to the network as an e-mail is executed. As described above, the hint character string 201 is arranged at a predetermined location of the e-mail. Note that the user may manually add the hint character string 201 to the mail body 203.

<Password table creation process>
FIG. 3 is a diagram for explaining in detail the process for creating a password table from an arbitrary hint character string (the process 205 in FIG. 2). The password table is generated by applying a predetermined regular logical operation to the hint character string. In this example, the character string “ABC” will be described as a hint character string. In FIG. 3, symbol 307 is a symbol indicating “exclusive OR”.

  In FIG. 3, the character “A” 301 and the character “B” 302 are subjected to an exclusive OR 307 to obtain a binary value 00000011 indicated by a numerical value 304. Further, an exclusive OR of the numerical value 304 and the character “C” 303 is taken, and a binary numerical value 01000000 shown by the numerical value 305 is obtained. Note that the operation for taking the exclusive OR is merely an example, and a normal OR may be applied, but it is effective as a process for making the password more random.

  Next, the numerical value 305 is set as the initial value of the numerical value generation processing 306. Here, the numerical value generation processing is to sequentially generate values determined for the set initial value. The numerical value generation method may be arbitrary. For example, when the initial value is subtracted 1 and the value is returned each time the numerical value generation process is called, when the initial value is 100, a numerical value such as 99, 98, 97, 96, 95, etc. is returned. It will be.

  Then, in order to create passwords to be stored in the password table 308, m numbers are extracted from the process 306, and the remainder obtained by dividing each number by 26 is obtained. Get the characters in the range of A ”to“ Z ”to make one password. This process is repeated (n + 1) times to create (n + 1) passwords. The hexadecimal value 41 is a value representing the character “A” in hexadecimal.

  The password table 308 is created every time a hint character string is input. The password table 308 includes a plurality of passwords, but depending on the algorithm, only one password may be generated and used for encryption. One reason for having a plurality of passwords in the password table 308 is that it is effective for confusion without being able to immediately recognize which password was used by an unauthorized person and using which password.

<Index creation process>
FIG. 4 is a diagram for explaining details of processing for creating an index for selecting a password to be used for encryption from a password table from an arbitrary hint character string. In this example, the character string “ABC” will be described as a hint character string. In FIG. 4, symbol 406 is a symbol indicating addition of two numerical values.

  First, the character “A” 401 and the character “B” 402 are added to obtain a binary value 10000011 shown by a numerical value 404. Next, the numerical value 404 and the character “C” 403 are added to obtain a binary numerical value 11000110 indicated by the numerical value 405.

  As described above, the number of items in the password table 308 is (n + 1). Therefore, the index of the password table 308 uses a remainder obtained by dividing the numerical value 405 by (n + 1). In this way, any password in the password table 308 is always designated by the index.

<Details of email reception processing>
FIG. 5 is a diagram for explaining an outline of processing for receiving an electronic mail and decrypting an attached file.

  The received electronic mail is separated into a mail body 503, an encrypted file 507, and a hint character string 502 by a mail reception process 501. As described above, the hint character string 502 may be written in the mail body or may be manually extracted from the mail body by the user.

  In the password table creation process 505, a password table 506 is created based on the input hint character string 502. This password table 506 is the same as the password table 206 in FIG. Since the method for creating the password table is the same as the process shown in FIG. 3, the description thereof is omitted here.

  In the index creation process 504, an index 510 for the password table 506 is created based on the hint character string 502. Since the index creation method is the same as the process shown in FIG. 4, the description thereof is omitted here.

  In the decryption processing 508, the encrypted file 507 extracted from the electronic mail is decrypted, and a file 509 is obtained. In the decryption, the password obtained from the password table 506 and the index 510 is used.

  In FIG. 2 to FIG. 5, a password table composed of a plurality of passwords is created, and an index for retrieving this is created and one password is taken out. You may create a password table consisting of passwords. That is, as described above, instead of creating a password table, one password may be created from the hint character string, and encryption / decryption processing may be performed using the password. Further, as described above, a plurality of passwords may be selected from the password table using an index, and encryption / decryption processing may be performed using the plurality of passwords. In this case, it is expected that a more secure electronic mail system can be realized.

<Operation of email system>
The operation of the e-mail system to which the password transmission method configured as described above is applied will be described below with reference to the flowcharts of FIGS. In the flowcharts of FIGS. 6 and 7, unless otherwise specified, the processing subject is a control processing unit such as a CPU not shown in FIG.

(1) FIG. 6 is a flowchart for explaining an operation when an e-mail is transmitted in the e-mail system to which the password transmission method according to the present invention is applied.

  In FIG. 6, when an electronic mail is transmitted, it is checked whether an attached file is designated (step S601). If the attached file is not specified, the encryption process is not required, so the mail text is input by the user (step S611) and sent as an e-mail (step S612).

  On the other hand, if it is determined in step S601 that the attached file is designated, it is confirmed whether or not personal identification biometric information is input (step S602). Step S602 is repeated until personal identification biometric information is input. When it is determined that the biometric information for personal identification is input, the registered biometric information for personal identification is compared with the biometric information for personal identification input in step S602 (step S603), and the use of the electronic mail system 100 is confirmed. It is determined whether or not the person is permitted (step S604).

  If it is determined in step S604 that use of the e-mail system 100 is not permitted, a message to that effect is displayed on the screen and the process ends (step S613).

  If it is determined in step S604 that the use of the electronic mail system is permitted, the hint character string input by the user is accepted (step S605). It is confirmed whether or not a hint character string has been input (step S606), and if not input, the process returns to step S605.

  If it is determined in step S606 that a hint character string has been input, a password table and an index are created in step S607. The creation method is as described with reference to FIGS.

  In step S608, one password is extracted from the password table and index created in step S607, and the attached file is encrypted.

  Further, the input of the mail text created by the user is accepted (step S609), and the mail text and the hint character string and the encrypted attached file are integrated as an electronic mail and transmitted to the other party according to the instruction of the sender (step S609). S610).

(2) FIG. 7 is a flowchart for explaining an operation when receiving an e-mail in the e-mail system to which the password transmission method according to the present invention is applied.
First, in step S701, an e-mail is received. The received electronic mail is checked in step S702 to see if a file is attached.

  If it is determined in step S702 that no file is attached, step S710 is executed, and the content of the mail text is displayed on the screen.

  If it is determined in step S702 that the file is attached, it is determined whether or not personal identification biometric information is input (step S703). The process of step S703 is repeated until biometric information for personal identification is input.

  In step S704, the input personal identification biometric information is compared with the registered personal identification biometric information. In step S705, it is determined whether or not the user is permitted based on the comparison result of the biometric information for personal identification.

  If it is determined in step S705 that the user is not permitted, a message indicating that decryption cannot be performed is output (displayed) on the screen in step S711, and then the mail text is displayed on the screen in step S710. Ends.

  On the other hand, if it is determined in step S705 that the user is permitted, a hint character string is extracted in step S706, and a password table and an index are created in step S707. These creation methods are as described with reference to FIGS.

  In step S708, one password is extracted from the password table and index created in step S707, and the file attached with this password is decrypted.

  In step S709, the contents of the attached file decrypted in step S708 are output as a file. Then, the mail text is displayed on the screen (step S710), and the process ends.

<Summary>
As described above, in the embodiment of the present invention, when data is encrypted, an input character string is not used as a password as it is, but a predetermined calculation (with respect to an input character string (hint character string)) ( A regular logical operation) is performed to generate another character string (password), which is used for encryption / decryption. In this way, since the input character string is not used for encryption, even if an unauthorized user obtains the input character string, it is difficult to decrypt the encrypted data, and the data should be handled more safely. Will be able to.

  In the present embodiment, creation of a password table including a plurality of passwords is created using a hint character string. Further, an index is created based on the hint character string. This index acts as a password table pointer, and a password to be used for encryption processing is selected from a plurality of passwords included in the password table. Since the password creation algorithm is different from that of the index, it is very difficult to know both the password and the index creation algorithm even if an unauthorized person obtains a hint string. Further, since one or a plurality (not all) of passwords are selected from the algorithm table, any password used as an unauthorized person can be recognized but may be confused. Therefore, data can be handled more safely.

  Furthermore, a specific individual is identified by biometric authentication, and a password can be created only when it is confirmed that the identified individual is a valid user. As a result, security can be further enhanced by another method in addition to the encryption method.

  In the present embodiment, the e-mail system combines the encrypted file created by the above-described encryption process, the mail body, and the hint character string used for password creation and transmits it as one e-mail. The hint character string is included in a predetermined part of the mail text. This eliminates the need to negotiate a password with a legitimate recipient. Even if an unauthorized person (third party) intercepts an e-mail, the attached file cannot be decrypted only with the hint character string.

  Note that the present invention can also be realized by software program codes that implement the functions of the embodiments. In this case, a storage medium in which the program code is recorded is provided to the system or apparatus, and the computer (or CPU or MPU) of the system or apparatus reads the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code itself and the storage medium storing the program code constitute the present invention. As a storage medium for supplying such program code, for example, floppy (registered trademark) disk, CD-ROM, DVD-ROM, hard disk, optical disk, magneto-optical disk, CD-R, magnetic tape, non-volatile A memory card, ROM, or the like is used.

  Also, based on the instruction of the program code, an OS (operating system) running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing. May be. Further, after the program code read from the storage medium is written in the memory on the computer, the computer CPU or the like performs part or all of the actual processing based on the instruction of the program code. Thus, the functions of the above-described embodiments may be realized.

  Further, the program code of the software that realizes the functions of the embodiment is distributed via a network, so that it is stored in a storage means such as a hard disk or memory of a system or apparatus or a storage medium such as a CD-RW or CD-R. It may also be achieved by the computer (or CPU or MPU) of the system or apparatus reading and executing the program code stored in the storage means or the storage medium.

It is a schematic block diagram of the electronic mail system to which the password transmission method is applied. It is explanatory drawing of the method of producing the password for encrypting an attached file. It is explanatory drawing of the example which produces a password table from arbitrary character strings. It is explanatory drawing of the example which produces the index of a password table from arbitrary character strings. It is explanatory drawing of the method of producing the password for decoding an attached file. It is a flowchart for demonstrating the operation | movement in the case of transmitting an email in the email system to which the password transmission method is applied. It is a flowchart for demonstrating operation | movement when receiving an email in the email system to which the password transmission method is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Biometric information input part, 102 ... Character string input part, 103 ... File input part, 104 ... Biometric information comparison part, 105 ... Password preparation part, 106 ... File encryption part, 107 ... Biometric information storage part for personal identification, 108 DESCRIPTION OF SYMBOLS ... E-mail output part, 109 ... E-mail input part, 110 ... File decoding part, 111 ... File output part, 112 ... Character string output part, 113 ... Message output part

Claims (9)

An encryption device for encrypting data,
A password creating unit that creates a password by creating a character string different from the arbitrary character string based on the arbitrary character string;
An encryption processing unit that executes an encryption process using the password;
An encryption device comprising: Furthermore, an index creation unit that creates an index based on the arbitrary character string is provided,
The password creation unit creates a password table including a plurality of passwords based on the arbitrary character string, and further uses the index to determine a password to be used for the encryption process from a plurality of passwords included in the password table. The encryption apparatus according to claim 1, wherein the encryption apparatus is selected.   Furthermore, a specific individual is identified by biometric authentication, and a biometric information identifying unit that enables creation of a password by the password creating unit only when it is confirmed that the identified individual is a valid user is provided. The encryption device according to claim 1, wherein: A decryption device for decrypting data encrypted using a password,
Based on the same character string as the arbitrary character string for generating the password used for the encryption processing, a password creating unit that creates a password different from the arbitrary character string,
A decryption processing unit for performing decryption processing using the password;
A decoding device comprising: Furthermore, an index creation unit that creates an index based on the arbitrary character string is provided,
The password creation unit creates a password table including a plurality of passwords based on the arbitrary character string, and further uses the index to determine a password to be used for the decryption process from a plurality of passwords included in the password table. The decoding device according to claim 4, wherein the decoding device is selected.   Furthermore, a specific individual is identified by biometric authentication, and a biometric information identifying unit that enables creation of a password by the password creating unit only when it is confirmed that the identified individual is a valid user is provided. 6. The decoding device according to claim 4 or 5, wherein: An email system for sending and receiving emails with attached files,
The encryption device according to any one of claims 1 to 3,
A mail transmission / reception unit configured to combine the encrypted file created by encrypting the file by the encryption device, the mail body, and the arbitrary character string, and transmit as one electronic mail;
An e-mail system comprising:   The electronic mail system according to claim 7, wherein the mail transmission / reception unit includes the arbitrary character string in a predetermined portion of the mail text. Furthermore, it comprises the decoding device according to any one of claims 4 to 6,
The mail transmission / reception unit receives an email in which an encrypted file is attached and the arbitrary character string is combined with a mail body, and separates the encrypted file, the arbitrary character string, and the mail body,
The e-mail system according to claim 7 or 8, wherein the decryption device decrypts the encrypted file using the password and presents the decrypted file.

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