JP5336315B2 - Password determining apparatus for e-mail encrypted file, e-mail server, and operation control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine a password of an encrypted file attached to electronic mail. <P>SOLUTION: Electronic mail including the same subject name as a subject name 42 of an electronic mail 40 to which an encrypted file is attached is found. A password candidate is extracted from a text of the found electronic mail. The extracted password candidate is used to decrypt the encrypted file. When succeeded in the decryption, the password candidate used for the successful decryption is determined to be the password. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a password determination device for an encrypted e-mail file, an e-mail server, and an operation control method thereof.

  When attaching an e-mail file, it may be encrypted using a password. When receiving an e-mail with an encrypted file attached, the recipient must enter a password, but the password entry is troublesome for the recipient, and in particular, it is inconvenient to enter characters like a mobile phone. The password entry is even more troublesome for a simple device. For this purpose, an e-mail header analysis (Patent Document 1), an e-mail header, personal information extracted from the text (Patent Document 2), and a password for a device without an input device such as a keyboard There exists what performs authentication (patent document 3).

  However, it is not possible to determine a password relatively easily in either case. In particular, the burden of entering a password is high on a mobile terminal such as a mobile phone.

JP 2002-236649 A JP-A-9-244969 Japanese Patent Laid-Open No. 11-187016

  An object of the present invention is to determine a password relatively easily. In particular, it aims to reduce the burden of password entry on a portable terminal such as a cellular phone.

  According to a first aspect of the present invention, there is provided an electronic mail encrypted file password determining apparatus for receiving an electronic mail and for controlling the storage device so as to store the received electronic mail, under the control of the storage control means. Of the e-mails stored in the storage device, encryption determination means for determining whether or not an attachment file of a predetermined e-mail is encrypted, and the attachment file of the predetermined e-mail is encrypted by the encryption determination means E-mail search means for finding an e-mail containing the same subject as the subject of the predetermined e-mail from the storage device as a password-containing candidate e-mail, The password that detects the password candidate from the body of the password-containing candidate email found by the search means. Candidate detection means, decryption means for decrypting the attached file using the password candidate detected by the password candidate detection means, and a password candidate that can decrypt the attached file by the decryption means is determined as the password of the attached file. A password determining means is provided.

  The first invention also provides an operation control method suitable for the password determination device for the encrypted file of the e-mail. That is, in this method, the storage control means receives the electronic mail, controls the storage device so as to store the received electronic mail, and the encryption judgment means controls the storage under the control of the storage control means. It is determined whether or not an attachment file of a predetermined e-mail is encrypted among e-mails stored in the apparatus, and an e-mail search unit encrypts the attachment file of the predetermined e-mail by the encryption determination unit. In response to the determination that the subject is the same, the email containing the same subject as the subject of the predetermined email is found as a password-containing candidate email from the storage device, and the password candidate detecting means A password candidate is detected from the body of the password-containing candidate e-mail found by the e-mail search means, and the password candidate is detected. Using the password candidates detected by the detecting means decodes the attachment, the password determination means, the password candidates can be decrypted with the attachment by said decoding means is for determining a password for the attachment.

  The first invention also provides a program for controlling the computer of the password determination device for the encrypted file of the e-mail. A recording medium storing such a program may be provided.

  According to the first invention, a password-containing candidate e-mail including the same subject as the subject of the predetermined e-mail attached with the encrypted file is found from the e-mail stored in the storage device. Password candidates are detected from the password-containing candidate e-mails, and the encrypted attached file is decrypted using the detected password candidates. If decryption is possible, the decrypted password candidate is determined as the password. When a file attached to a predetermined electronic mail is encrypted, the password is often described in another electronic mail having the same subject as the subject of the predetermined electronic mail. According to the first invention, the password can be determined from the other electronic mail. Conventionally, when an attached file of an e-mail is encrypted, an e-mail in which a password is described is received separately from an e-mail in which the attached file is encrypted, the e-mail is browsed, After that, the password input image must be displayed and the password must be input. However, according to the present invention, it is not necessary to view the e-mail in which the password is described or to display the password input image. The number of images to be displayed on (the number of transition images) can be small. The password determined as described above may be stored in a file or database in association with an e-mail.

  The e-mail search means, for example, finds an e-mail that matches the sender of the predetermined e-mail and has a transmission date and time within a predetermined time from the transmission date and time of the predetermined e-mail as a password-containing candidate e-mail It is.

  A display control means for controlling the display device to display a password input image when the password determination means cannot determine the password may be further provided.

  You may further provide the attachment file transmission means which transmits the said attachment file which could be decoded by the said decoding means to the transmission destination of an email.

  The electronic mail server according to the second invention is attached with a storage device storing the same electronic mail as the electronic mail stored in the client computer, and an encrypted file transmitted from the client computer. An identification data receiving means for receiving e-mail identification data for identifying a predetermined e-mail, and finding the predetermined e-mail identified by the e-mail identification data received by the identification data receiving means from the storage device A password-containing candidate e-mail that finds a password-containing candidate e-mail containing the same subject as the predetermined e-mail received from the storage device, and a password-containing candidate e-mail found by the e-mail search means Password to detect password candidates in the text Complementary detection means, decryption means for decrypting the encrypted file attached to the predetermined e-mail using the password candidate detected by the password candidate detection means, and a password for decrypting the encrypted file by the decryption means A password determination unit that determines a candidate as a password of the encrypted file; and a password that is determined by the password determination unit, and a password transmission unit that transmits the password to the client computer as the password of the encrypted file. To do.

  The second invention also provides an operation control method suitable for the electronic mail server. That is, in this method, the storage device stores the same electronic mail as the electronic mail stored in the client computer, and the identification data receiving means is attached with the encrypted file transmitted from the client computer. The e-mail identification data for identifying the predetermined e-mail is received, and the e-mail search means receives the predetermined e-mail identified by the e-mail identification data received by the identification data receiving means from the storage device. A password containing candidate e-mail containing the same subject as the subject of the predetermined e-mail found and found in the storage device, and the password candidate detection means finds the password found by the e-mail search means Detect password candidates from the body of the inclusion candidate email, The decrypting means decrypts the encrypted file attached to the predetermined e-mail using the password candidate detected by the password candidate detecting means, and the password determining means decrypts the encrypted file by the decrypting means. The password candidate thus made is determined as the password of the encrypted file, and the password transmission means transmits the e-mail identification data to the client computer using the password determined by the password determination means as the password of the encrypted file. To do.

  The second invention also provides a program for controlling the electronic mail server. A recording medium storing such a program may also be provided.

  According to the second invention, the e-mail identification data for identifying the predetermined e-mail attached with the encrypted file is transmitted from the client computer to the e-mail server. In the e-mail server, a password-containing candidate e-mail including the same subject as the subject of the predetermined e-mail identified by the e-mail identification data is found. Password candidates are detected from the password-containing candidate e-mails, and the encrypted attached file is decrypted using the detected password candidates. The password candidate that can be decrypted is determined as the password. The determined password is transmitted from the email server to the client computer along with the email identification data. In the client computer, the encrypted file is decrypted using the password transmitted from the electronic mail server. When a file attached to a predetermined electronic mail is encrypted, the password is often described in another electronic mail having a subject including the subject of the predetermined electronic mail. In the second invention as well, the password can be determined from the other e-mail.

  When a plurality of encrypted files are attached to the predetermined e-mail, the password determining means determines, for example, a password corresponding to each encrypted file of the plurality of encrypted files. And the password transmitting means transmits, for example, the password determined corresponding to each encrypted file of the plurality of encrypted files to the mobile phone in association with the identification data of each encrypted file. Is.

  For example, the password transmission unit may transmit the password determined by the password determination unit and the e-mail identification data to the client computer.

Provides an overview of the email system. It is a block diagram which shows the electric constitution of an electronic mail server. It is a flowchart which shows a password determination processing procedure. It is a flowchart which shows a password determination processing procedure. It is an example of an email. It is an example of the attached file of an electronic mail. It is an example of an email. It is an example of the attached file of an electronic mail. It is an example of an email. It is a flowchart which shows a password determination processing procedure. It is a flowchart which shows a password determination processing procedure. Shows an email with an encrypted file attached. The relationship among e-mail identification data, encrypted file identification data, and passwords is shown.

  FIG. 1 shows an embodiment of the present invention and shows an outline of an electronic mail system.

  The electronic mail system according to this embodiment includes an electronic mail transmission computer 1, an electronic mail server 10, and a mobile phone 2 that can communicate with each other via the Internet.

  An e-mail is transmitted from the e-mail transmission computer 1 and received and stored in the e-mail server 10. The electronic mail stored in the electronic mail server 10 is transmitted to the mobile phone 2 in response to a request from the mobile phone 2. In this embodiment, the e-mail transmission computer 1 transmits an e-mail for the sake of simplicity, but it goes without saying that the e-mail can be received as well as a general client computer. Nor. Further, if the electronic mail server 10 can be accessed, an electronic mail can be received using a general client computer other than the mobile phone 2.

  A CD-ROM (compact disk-read only memory) 18 in which an operation program of the e-mail server 10 is stored is loaded in the e-mail server 10, and the operation program stored in the CD-ROM 18 is Installed on the email server 10. Further, the memory card 3 storing the operation program of the mobile phone 2 is loaded into the mobile phone 2, and the operation program stored in the memory card 3 is installed in the mobile phone 2. However, even if the operation program is not stored in the CD-ROM 18 or the memory card 3, an operation program that is transmitted via a network may be installed.

  FIG. 2 is a block diagram showing an electrical configuration of the electronic mail server 10.

  The electronic mail server 10 is controlled by the CPU 11.

  The e-mail server 10 includes a communication circuit 12 for communicating with the e-mail sending computer 1 and the cellular phone 2 via the Internet, a display device 13, a hard disk drive 14 for accessing a hard disk (not shown), a memory 15, A CD-ROM drive 16 for accessing the CD-ROM 18 described above and an input device 17 such as a keyboard and a mouse are included. The received e-mail is recorded on the hard disk.

  Similarly to the electronic mail server 10, the cellular phone 2 is provided with a CPU, a display device, a communication circuit, a memory, a memory card interface, a keypad, an antenna, and the like (all not shown). Needless to say, the mobile phone 2 also has a function of making a call.

  FIGS. 3 and 4 are flowcharts showing the processing procedure of the e-mail server 10 (password determination device for encrypted file of e-mail).

  In this embodiment, when the attached file of an electronic mail is encrypted, it is considered that the password of the encrypted attached file is described in another electronic mail. A password described in another e-mail is extracted to determine the password.

  As described above, a large number of e-mails are recorded on the hard disk of the e-mail server 10. A predetermined e-mail is read out from these e-mails (step 21 in FIG. 3). It is confirmed whether or not there is an attached file in the read electronic mail (YES in step 22 in FIG. 3). If there is an attached file, it is confirmed whether the attached file is encrypted (step 23 in FIG. 3). Whether the attached file is encrypted can be determined from the header information described in the header of the attached file. Even if the attached file is encrypted, the header information can be read.

  If the attached file is encrypted (YES in step 23 in FIG. 3), the subject, sender and date / time of the predetermined e-mail read from the hard disk are read (step 24 in FIG. 3).

  FIG. 5 shows the contents of a predetermined electronic mail that is read from the hard disk and attached with an encrypted file.

  The sender 41 of this e-mail 40 is “XX Trading”, and the subject 42 is “Estimate”. A text 43 is described in the e-mail 40. In this text 43, an attached file name (estimate.zip) 44 indicating that the electronic mail 40 has an attached file is described. The text 43 describes that the password of the attached file is described in another electronic mail. Further, the transmission date and time of this e-mail is “10:00 am on August 15, 2001”.

  When such a predetermined e-mail 40 is read from the hard disk, the subject of the e-mail is “estimate”, the sender is “XX Trading”, and the transmission date is “August 2001” It will be 10:00 am on the 15th ".

  FIG. 6 shows the contents of the attached file of the electronic mail 40 shown in FIG.

  The file name of the attached file 50 is “estimate.zip” 51, and the file having the file name “estimate.xls” 52 and the file having the file name “dealing terms.doc” 53 are attached files. Included in 50. It is assumed that a file having the file name “Estimate.xls” 52 is encrypted. Of course, it is needless to say that the file having the file name “trade terms.doc” 53 may be encrypted.

  Returning to FIG. 3, an e-mail having the same subject as the subject “estimate” of the predetermined e-mail 40 to which the encrypted file is attached is found from the hard disk (step 25 in FIG. 3). The e-mail thus found will be referred to as a password-containing candidate e-mail. If a password-containing candidate e-mail is found (YES in step 26 in FIG. 4), password candidates are extracted from the text of the password-containing candidate e-mail (step 29 in FIG. 4). If there are multiple password candidates, all of the multiple passwords are extracted.

  FIG. 7 is an example of a password-containing candidate e-mail.

  The sender 61 of the password-containing candidate email 60 is “XX Trading”, and the subject 62 is “Re: Estimate”. The password 64 “xxxxxxxx” is described in the body 63 of the password-containing candidate e-mail 60.

  When extracting password candidates from the body 63 of the password-containing candidate e-mail 60, the character string “password” is extracted from the body 63. The character string of the ASCII (American Standard Code for Information Interchange) code following the extracted “password” character string is a password candidate. In the case of the text 63 of the password-containing candidate e-mail 60, the ASCII code following the password character string is “xxxxxxxx”, so this character string “xxxxxxxx” is a password candidate. ASCII code that follows the character string that the password is considered to follow, such as "pass", "authentication code", "cancellation code", "pasword", "passwd", "pass" Is also a password candidate.

  Returning to FIG. 4, when a password candidate is found from the body 63 of the password-containing candidate email 60 (YES in step 30 in FIG. 4), an encrypted attachment (file name “estimate.xls”) is found. Decryption processing is actually performed using the password candidates (step 31 in FIG. 4). If the encrypted attached file can be decrypted (YES in step 32 in FIG. 4), the password candidate used for the decryption process is determined as the password of the encrypted attached file (step 33 in FIG. 4).

  If a password-containing candidate email containing the same subject as the subject of the predetermined email attached with the encrypted file is not found (NO in step 25 in FIG. 3 and step 26 in FIG. 4), the predetermined electronic An e-mail whose transmission date matches the sender and whose transmission date and time is within a predetermined time from the transmission date and time of the predetermined e-mail is found as a password-containing candidate e-mail from the hard disk (step 27 in FIG. 4). The senders match and the transmission date / time is set as a password-containing candidate e-mail within a predetermined time (for example, within 30 minutes but may be about 1 day) from the transmission date / time of the predetermined e-mail (step in FIG. 4). 28 is YES).

  The above-described processing may be performed periodically, or may be a background job so as to be performed in response to reception of an electronic mail. When executed as a background job, the identification data of the email and the password will be stored in association with each other under security measures so that they cannot be viewed by a third party.

  In addition, in the above processing, when a password-containing candidate email including the same subject as the subject of the predetermined email is found, no processing for finding a password-containing candidate email of the same sender or the like is performed. Even when a password-containing candidate e-mail including the same subject as the e-mail subject is found, a process for finding a password-containing candidate e-mail from the same sender or the like may be performed.

  FIG. 9 shows an example of a password-containing candidate e-mail in which the sender matches and the transmission date / time is within a predetermined time from the transmission date / time of the predetermined e-mail.

  The sender 81 of the password-containing candidate e-mail 80 is “xx trading”, and the subject 82 is “password matter”. In the body 83, a password 84 is described. Further, the transmission date of the password-containing candidate e-mail 80 is “10:10 am on August 15, 2001”.

  The subject 41 of the predetermined e-mail 40 (see Fig. 5) to which the encrypted file is attached is "estimate", and the subject 82 of the password-containing candidate e-mail 80 is "password matter", including the password The subject 82 of the candidate e-mail 80 does not include the subject 41 of the predetermined e-mail 40, but the transmission date and time of the password-containing candidate e-mail 80 is “10:10 am on August 15, 2001” The transmission date and time of the predetermined e-mail 40 is within a predetermined time from “10:00 am on August 15, 2001”. The password candidate “xxxxxxxx” is extracted from the text 43 of the password-containing candidate e-mail 80 as described above (step 29 in FIG. 4). When a password candidate is found (step 30 in FIG. 4), the actually encrypted attached file is decrypted using the found password candidate (step 31 in FIG. 4), and the password candidate that can be decrypted when the attached file is decrypted. Is determined as a password (step 33 in FIG. 4).

  When the password is determined, the encrypted file is decrypted with the determined password. The decrypted file is transmitted from the electronic mail server 10 to the mobile phone 2. The cellular phone 2 can browse the contents of the encrypted file without entering a password. For example, when “Estimate.zip” 44 shown in FIG. 5 is clicked, the image shown in FIG. 6 is displayed, and when “Transaction conditions.Doc” 53 in FIG. 6 is clicked, it is shown in FIG. The content of the encrypted file shown in FIG. 7 is displayed without displaying the password input image. As described above, when the mobile phone user designates the encrypted file after the encrypted file is decrypted with the password and requests the browsing of the content of the encrypted file, the password input image is displayed on the mobile phone. The content of the decrypted file is displayed without displaying. Since the encrypted file can be decrypted without requiring the user to input a password, there is no need to display a password input image on the mobile phone 2.

  In the embodiment described above, the password is determined in the e-mail server 10, but the password may be determined in the mobile phone 2 instead of the e-mail server 10. In that case, since the predetermined e-mail to which the encrypted file is attached is stored in the memory of the mobile phone 2, the process for determining the password as described above is performed by the mobile phone (e-mail encryption). The encrypted file is decrypted by using the password obtained by being executed in the password determination apparatus 2 of the encrypted file.

  If the password cannot be determined, a password input image may be displayed on the display screen of the mobile phone 2. If the password cannot be determined, the password input image can be used to input the password and decrypt the encrypted file.

  FIG. 10 and FIG. 11 show another embodiment and are flowcharts showing processing procedures of the mobile phone 2 and the electronic mail server 10.

  In this embodiment, the same e-mail (including attached files) as all e-mails (including attached files) stored in the mobile phone 2 is also stored in the e-mail server 10.

  When an electronic mail to be browsed is selected on the mobile phone 2 (step 91 in FIG. 10), whether there is an attached file in the selected electronic mail (step 92 in FIG. 10), whether the attached file is encrypted ( Step 93) in FIG. 10 is confirmed. If the selected email has an attached file (YES in step 92 in FIG. 10) and the attached file is encrypted (YES in step 93 in FIG. 10), the encrypted file is attached. Identification data for identifying a predetermined electronic mail is transmitted from the mobile phone 2 to the electronic mail server 10 (step 94 in FIG. 10). As described above, X-UIDL data and message ID recorded in the header of the e-mail can be used as data for identifying the predetermined e-mail.

  When the identification data transmitted from the mobile phone 2 is received by the e-mail server 10 (step 101 in FIG. 10), the same as the predetermined e-mail identified by the received identification data and the subject of the predetermined e-mail A password-containing candidate e-mail including the subject is found from the hard disk (step 102 in FIG. 10). When a password-containing candidate e-mail is found (YES in step 103 in FIG. 10), as described above, password candidates are extracted from the text of the found password-containing candidate e-mail (step 104 in FIG. 10).

  If a password candidate is found (YES in step 105 in FIG. 10), the encrypted attached file is decrypted using the found password candidate (step 106 in FIG. 11). If it can be decrypted (YES in step 107 in FIG. 11), the decrypted password candidate is determined as a password (step 108 in FIG. 11). The determined password is transmitted from the electronic mail server 10 to the mobile phone 2 together with the electronic mail identification data (step 109 in FIG. 11). In the above-described embodiment, the e-mail identification data and the password are transmitted from the e-mail server 10 to the mobile phone 2, but from the e-mail server 10 in a series of flows according to the request from the mobile phone 2. When the mobile phone 2 and the e-mail server 10 communicate synchronously so that the password is transmitted to the mobile phone 2, the mobile phone 2 is attached to which e-mail the password is attached even if there is no e-mail identification data. Recognize existing encrypted files. Therefore, only the password may be transmitted from the e-mail server 10 to the mobile phone 2 without transmitting the e-mail identification data from the e-mail server 10 to the mobile phone 2. The electronic mail server 10 stores a large number of electronic mails, and the above-described processing is performed on each electronic mail to which an encrypted file is attached.

  When the password and the email identification data transmitted from the email server 10 are received by the mobile phone 2 (step 95 in FIG. 10), a predetermined email identified by the email identification data is found from the memory. . The encrypted file attached to the found predetermined e-mail is decrypted using the received password. After the encrypted file is decrypted with the password, if the user of the mobile phone specifies the encrypted file and requests to view the contents of the encrypted file, the password input image is displayed on the mobile phone. The contents of the decrypted file are displayed without any problem.

  FIG. 12 shows a modified example, and shows a state in which a plurality of encrypted files (encrypted files) 111 to 113 are attached to a predetermined electronic mail 110.

  The identification data for identifying the predetermined electronic mail 110 is “ID1234”. In each of the encrypted files 111 to 113, MIME-ID is described in the header. This Multipurpose Internet Mail Extension (MIME) -ID is unique to the file, and can be identified by the MIME-ID. The MIME-ID of the first encrypted file 111 is “AAA”, the MIME-ID of the second encrypted file 112 is “BBB”, and the MIME-ID of the third encrypted file 113 is “CCC”. Is.

  As shown in FIG. 12, when there are a plurality of encrypted files 111 to 113 attached to a predetermined e-mail 110, the password determined as described above is associated with each encrypted file 111 to 113. There must be.

  FIG. 13 shows the correspondence between data for identifying a predetermined electronic mail, MIME-ID (encrypted file identification data), and password.

  The predetermined email 110 identified by the email identification data “ID 1234” is attached with three encrypted attachment files, and the identification data of these three attachment files is “AAA”, “BBB”, “CCC”. The password of the encrypted file 111 specified by the identification data “AAA” is “PA123”, the password of the encrypted file 112 specified by the identification data “BBB” is “PA456”, and the identification data “CCC” The password of the encrypted file 113 specified by “PA789” is “PA789”. Needless to say, these passwords are determined by the above-described processing.

  When a plurality of encrypted files 111 to 113 are attached to a predetermined e-mail 110, e-mail identification data, encrypted file identification data, and password are carried from the e-mail server 10 as shown in FIG. Sent to phone 2. When the e-mail identification data, the encrypted file identification data, and the password are received by the mobile phone 2, even when a plurality of encrypted files are attached to the predetermined e-mail 110, it can be decrypted using the corresponding password. I understand.

  The data for identifying the encrypted file is not the MIME-ID, but simply the order of the encrypted file.

2 Cellular phone (E-mail encrypted file password determination device, client computer)
10 E-mail server (E-mail encrypted file password determination device)
40, 60, 80, 110 Email
111, 112, 113 encrypted files

Claims (11)

Storage control means for receiving an e-mail and controlling a storage device to store the received e-mail;
Encryption determination means for determining whether an attached file of a predetermined e-mail is encrypted among e-mails stored in the storage device under the control of the storage control means;
In response to the fact that the attachment of the predetermined email is determined to be encrypted by the encryption determination means, an email containing the same subject as the subject of the predetermined email is selected as a password containing candidate. E-mail search means to find out from the storage device as e-mail,
Password candidate detection means for detecting a password candidate from the body of the password-containing candidate e-mail found by the e-mail search means;
Decrypting means for decrypting the attached file using the password candidate detected by the password candidate detecting means; and password determining means for determining the password candidate that has been able to decrypt the attached file by the decrypting means as the password of the attached file;
E-mail encrypted file password determination device comprising: The above e-mail search means
The sender of the predetermined e-mail matches, and an e-mail having a transmission date and time within a predetermined time from the transmission date and time of the predetermined e-mail is found as a password-containing candidate e-mail.
The apparatus for determining a password for an encrypted e-mail file according to claim 1. Display control means for controlling the display device to display a password input image in response to the fact that the password could not be determined in the password determination means;
The apparatus for determining a password for an encrypted file of electronic mail according to claim 1 or 2, further comprising:   The encrypted file for electronic mail according to any one of claims 1 to 3, further comprising attached file transmission means for transmitting the attached file decrypted by the decryption means to an electronic mail transmission destination. Password determination device. A storage device that stores the same email as that stored on the client computer,
Identification data receiving means for receiving e-mail identification data for identifying a predetermined e-mail attached with an encrypted file, transmitted from the client computer;
A password containing the same subject as the subject of the found predetermined e-mail found in the storage device when the predetermined e-mail identified by the e-mail identification data received by the identification data receiving means is found E-mail search means for finding candidate e-mails from the storage device,
Password candidate detection means for detecting password candidates from the body of the password-containing candidate e-mail found by the e-mail search means;
Decryption means for decrypting the encrypted file attached to the predetermined e-mail using the password candidate detected by the password candidate detection means;
Password determining means for determining a password candidate that can decrypt the encrypted file by the decrypting means as a password for the encrypted file, and the client computer using the password determined by the password determining means as the password for the encrypted file Password sending means to send to
E-mail server with A plurality of encrypted files are attached to the predetermined e-mail,
The password determination means is
A password is determined corresponding to each encrypted file of the plurality of encrypted files.
The password transmission means is
A password determined corresponding to each encrypted file of the plurality of encrypted files is transmitted to the mobile phone in association with identification data of each encrypted file;
The e-mail server according to claim 5. The password transmitting means is for transmitting the password determined by the password determining means and the e-mail identification data to the client computer;
The e-mail server according to claim 5 or 6. The storage control means receives the e-mail and controls the storage device to store the received e-mail;
An encryption determination unit for determining whether an attachment file of a predetermined e-mail is encrypted among e-mails stored in the storage device under the control of the storage control unit;
When the e-mail search means determines that the attachment file of the predetermined e-mail is encrypted by the encryption determination means, the same subject as that of the predetermined e-mail is included. Find the e-mail from the storage device as a password containing candidate e-mail,
The password candidate detection means detects the password candidate from the text of the password-containing candidate e-mail found by the e-mail search means,
Decrypting the attached file using the password candidate detected by the password candidate detecting means;
The password determining means determines the password candidate that was able to decrypt the attached file by the decrypting means as the password of the attached file;
An operation control method for a password determination device for an encrypted e-mail file. The storage device stores the same email as the email stored on the client computer;
An identification data receiving means for receiving e-mail identification data for identifying a predetermined e-mail attached with an encrypted file, transmitted from the client computer;
The e-mail search means finds the predetermined e-mail identified by the e-mail identification data received by the identification data receiving means from the storage device, and the same subject as the found e-mail is found. Find the password-containing candidate emails included in the storage device,
The password candidate detection means detects a password candidate from the text of the password-containing candidate e-mail found by the e-mail search means,
A decrypting unit decrypts the encrypted file attached to the predetermined e-mail using the password candidate detected by the password candidate detecting unit;
The password determining means determines a password candidate that has been able to decrypt the encrypted file by the decrypting means as a password of the encrypted file;
A password transmission means transmits the password determined by the password determination means to the client computer as a password of the encrypted file;
An operation control method for an e-mail server. A computer readable program for controlling a device for determining a password for an encrypted e-mail file,
Receive e-mail, control the storage device to store the received e-mail,
Of the emails stored in the storage device, it is determined whether the attached file of a predetermined email is encrypted,
In response to determining that the attached file of the predetermined e-mail is encrypted, the storage device includes an e-mail including the same subject as the subject of the predetermined e-mail as a password-containing candidate e-mail To find out from
The password candidate is detected from the body of the password-containing candidate e-mail found, and the attached file is decrypted using the detected password candidate.
A program for controlling a password determination device for an encrypted e-mail file so that a password candidate that can decrypt the attached file is determined as a password for the attached file. A computer readable program for controlling an email server,
Store the same email in the storage device as the email stored in the client computer,
Identifying a predetermined e-mail attached with an encrypted file sent from the client computer,
The predetermined e-mail identified by the received e-mail identification data is found from the storage device, and the password-containing candidate e-mail including the same subject as the found e-mail is stored. Let's find it in the device,
Detect password candidates from the body of the password-contained candidate email that was found,
The encrypted file attached to the predetermined email is decrypted using the detected password candidate,
The password candidate that was able to decrypt the encrypted file is determined as the password of the encrypted file,
A program for controlling the operation of the e-mail server so that when the determined password is transmitted to the client computer as the password of the encrypted file, the e-mail identification data is transmitted to the client computer.

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