KR100420735B1 - Mail transmitting/receiving system using watermarking and encoding technique, and method thereof - Google Patents

Abstract

Conventional e-mail has a high risk of easily exposing valuable information or personal information of an e-mail sender through hacking, document alteration, etc. As a countermeasure to solve this problem, the present invention provides a watermarking technique when transmitting important data by e-mail. And it provides a system and method for sending and receiving mail using the encryption technology to increase the level of security and to prevent the leakage of data.

Create and insert a watermark on the data to be transmitted, encrypt the data and transmit the data through a wired or wireless communication network by mail, decode the watermark with the watermark inserted in the mail receiver terminal, extract the watermark, This watermark is used as a means for controlling the use of the above-mentioned important data.

Description

Mail sending / receiving system using watermarking and encryption technology and method thereof {MAIL TRANSMITTING / RECEIVING SYSTEM USING WATERMARKING AND ENCODING TECHNIQUE, AND METHOD THEREOF}

The present invention relates to a system for transmitting and receiving mail for transmitting data, and more particularly, to a system for transmitting and receiving an important data by using a mail, and a method of transmitting and receiving a mail, using a watermarking technique and an encryption technique to increase security and to prevent data leakage. And to a method.

In recent years, with the spread of computers and the Internet, it has become common to send letters, postcards, etc. by electronic mail (hereinafter referred to as "e-mail") through wired and wireless communication networks. In addition, e-mail is not merely a means of communicating memos or greetings, but is becoming the most important communication medium leading the 21st century information and communication society such as business, finance, e-commerce, and information delivery. However, the existing conventional mail has a high risk of easily exposing the valuable information or the personal information of the mail sender through hacking, document alteration, peeping, etc., so that it appeared as a countermeasure against this.

Generally, secure mail refers to secure e-mails transmitted and received through a public key infrastructure (PKI) encryption system, unlike general e-mails that may cause information leakage due to hacking. In other words, most of the commercially available security mails are encrypted and transmitted by the encryption system, so that even if a third party illegally hacks or steals the mail, the encrypted mail can be decrypted. The contents of the e-mail sent are not known. In practice, by performing a process such as encrypting and decrypting mail data to be transmitted and received through a certificate issued from an accredited certification authority or a private certification authority, no one other than the designated recipient can read the encrypted data. In other words, by encrypting, no one but the sender can pretend to be able to steal, so that personal information protection and security of mail contents can be secured.

Meanwhile, as digital signatures are legally recognized in electronic commerce, an e-mail solution that has built a security device using a public key infrastructure technology among encryption-based mail systems has emerged.

A general description of the public key infrastructure is as follows. Recently, with the activation of electronic commerce, the necessity of securing the safety and reliability of electronic commerce has emerged. At present, due to the information protection problem of electronic commerce, many problems are exposed to the activation of electronic commerce, and many discussions have been made to solve this problem.

Against this background, it can be said that the establishment of the electronic certification system is the start of securing the stability and reliability of electronic commerce. Electronic certification system is related to the important certification of electronic business such as identity verification function of the parties in related electronic business such as electronic documents, electronic transactions in virtual space, information protection and integrity function of electronic business contents, and denial of electronic activity. It is a system that is verified and certified by a trusted certification body. The core of the electronic certification system is the safe operation of digital signature technology, which is a key technology to secure the stability and reliability of electronic commerce.

Digital signature technology uses a public key as a public key cryptographic algorithm. The secret key used in the public key cryptographic algorithm becomes a generation key for generating the digital signature, and the public key serves as a verification key for verifying the digital signature. Therefore, stable operation of digital signature technology means safe storage of signature key (secret key of public key cryptographic algorithm) and verification key (public key of public key cryptographic algorithm), and safe operation of verification key means safe management of public key. it means. Since the public key is public information, it is necessary to solve the public key authentication problem in order to solve the problem of forgery and forgery of the public key. What emerged for this is the public key infrastructure.

In other words, in order to secure the safety and reliability of electronic commerce, an electronic authentication system is required, which means the safe operation of electronic signature technology, and again the confidentiality and disclosure of the secret key of the public key cryptographic algorithm used for digital signatures. The integrity of the key must be guaranteed, and the solution to this is the public key infrastructure.

The public key infrastructure is a network of objects that establishes and provides policies, means, and tools that facilitate the use of certificates in various fields such as information system security, e-commerce, and secure communication.

The conventional encryption-based secure mail as described above has the following problems.

If the encrypted data attached while the mail is being transmitted by the e-mail hacking is leaked, the person who hacked can decrypt the encrypted data, and the decrypted data can be distributed without permission.

Accordingly, it is an object of the present invention to overcome the above problems of existing secure mails and to securely send and receive important information data by mail.

Another object of the present invention is to prevent unauthorized users from decrypting sensitive information received without permission, thereby preventing information leakage.

Further, another object of the present invention is to prevent unauthorized distribution of decrypted information even if information is leaked and decrypted by a third party during transmission.

In order to achieve the above object, the present invention provides a security management server for generating and inserting a predetermined watermark on the data to be transmitted, and encrypting the data into which the watermark is inserted; A mail server for inserting a predetermined watermark transmitted from the security management server and transmitting encrypted data through a wired or wireless communication network by mail; And a mail receiver terminal for receiving mail, decrypting the data in which the predetermined watermark is inserted and encrypted, and extracting a watermark, wherein the predetermined watermark contains information for controlling output and viewing of the data. It provides a mail transmission and reception system comprising.

In addition, the mail transmission and reception system, if necessary, is further connected to the security management server, and manages the encryption key required to perform encryption in the security management server, the decryption key required for decryption at the mail receiver terminal, and the user unique key; A key management server for storing, a mail service providing server capable of downloading a program for decrypting encrypted data having a predetermined watermark inserted therein, and downloading a program for reading the inserted data to the mail receiver terminal; A program providing server connected to the mail service providing server, and an advertisement server connected to the mail server in order to include the multimedia information for advertisement in the mail.

In addition, in order to achieve the above object, the present invention provides a mail transmitting and receiving system comprising a mail sending system for transmitting water with embedded watermarks and a mail receiver terminal for receiving the mail. A first step of inserting a predetermined watermark into data to be transmitted; A second step of encrypting data having a predetermined watermark embedded therein; A third step of transmitting the encrypted data by mail through a wired or wireless communication network; Receiving a mail at a mail receiver terminal and decrypting the encrypted data from the received mail; And a fifth step of extracting a watermark inserted in the decoded data to control output and viewing of the data.

1 is a block diagram showing a schematic configuration of a mail transmission system according to an embodiment of the present invention.

2 is a block diagram showing a detailed configuration of a key management server and a security management server of FIG.

3 is a flowchart illustrating a mail transmission method according to an embodiment of the present invention.

4 is a block diagram showing a schematic configuration of a mail reception / confirmation system according to an embodiment of the present invention;

5 is a flowchart illustrating a user unique key registration process according to an embodiment of the present invention.

6 is a flowchart illustrating a mail receiving / confirming method according to an embodiment of the present invention.

※ Description of the main parts of the drawings.

1: Mail sending system 100: Key management server

102: key transmission and reception management unit 104: key generation unit

106: key management unit

120: data generation unit 140: security management server

142: data management unit 144: watermark insertion unit

146: encryption unit 148: watermark generation and management unit

160: mail server 180: ad server

190: communication network 200: mail recipient terminal

500: mail receiving / confirmation system 520: mail service providing server

540: program providing server

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

1 is a block diagram showing a schematic configuration of a mail transmission system 1 according to an embodiment of the present invention. The system 1 includes a key management server 100 for generating and managing all keys related to mail encryption and decryption, a data generation unit 120 for generating various data to be transmitted, and a mail server 160 for mail transmission. And a security management server 140 that exchanges data with the key management server 100, the data generation unit 120, and the mail server 160 and performs security related processing. In addition, the mail transmission system 1 may include an advertisement server 180 that can provide various advertisement multimedia. Meanwhile, the mail transmitted in this manner is transmitted to each mail receiver terminal 200 through the wired or wireless communication network 190.

Hereinafter, the configuration of the mail transmission system 1 will be described in more detail.

The key management server 100 is, for example, when a licensed user downloads and installs a program, a unique key generation module is operated to generate a user unique key and information about an encryption key for encrypting digital information sent to the user. Store and manage it.

Looking at the user's unique key, in order to use the mail service, the mail receiver accesses the server 520 which provides the mail service proposed by the present invention through wired and wireless communication. Here, when a user registers through a series of registration processes, the program providing server 540 is interlocked with the mail service providing server 520 to provide a user program executed in the user terminal. When a user unique password is first set using the user program, a unique key generation module operates to generate a user unique key (to be described later with reference to FIG. 5). The unique key can be operated only in the terminal of the user who originally generated the unique key, for example, by generating a unique key using a unique system ID of the user terminal hardware. However, the user unique key is not necessarily limited thereto, and various methods are possible, and the user unique key may be generated using the user unique information itself (resident registration number, student number, credit card number, etc.).

The data generating unit 120 serves to generate various data to be transmitted. Such data may be important documents, various certificates, various bills, bills, receipts, and the like. That is, various service companies such as insurance companies, credit card companies, and telecommunication companies may issue and transmit information to a service subscriber by wire or wirelessly.

The security management server 140 performs security-related processing such as inserting a watermark and encrypting the data generated by the data generator 120. First, the security management server 140 loads the data to be transmitted from the data generation unit 120, inserts the generated watermark into the data, encrypts the data, and prepares the encrypted data, and the multimedia file generated by the advertisement server 180. The data with the watermark embedded therein is attached and transmitted through the mail server 160. The watermark may include, for example, unique information regarding data, information of a customer who will receive the data, information for controlling the data output and reading, and the like.

The mail server 160 performs a function of transmitting a mail to which a watermark is inserted and encrypted data is attached at the same time in association with the security management server 140.

Hereinafter, the linkage between the key management server 100 and the security management server 140 corresponding to the core components of FIG. 1 will be described. 2 is a block diagram illustrating a detailed configuration of a key management server 100 and a security management server 140 according to an embodiment of FIG. 1.

The key management server 100 includes a key transmission and reception management unit 102, a key generation unit 104, and a key management unit 106. The key generation unit 104 is responsible for generating an encryption key for encrypting the data requested by the security management server 140 in the encryption process and a decryption key requested by the mail receiver terminal 200 in the decryption process. The encrypted encryption key and decryption key are transmitted to the key management unit 106, stored, and managed.

In addition to the encryption key and the decryption key, the key manager 106 is also responsible for managing a user unique key transmitted through the mail service providing server 520. Therefore, the mail receiver terminal 200 is responsible for a function of checking whether or not the user unique key generated when the program is downloaded and installed in the key management unit 106 and the user unique key generated through the user password when receiving the mail. .

The key transmission and reception management unit 102 is connected to the key management unit 102 and the mail service providing server 520, respectively, and receives a user unique key generated in the mail receiver terminal 200 through the mail service providing server 520. The decryption key transmitted from the key management unit 105 is transmitted to the mail service providing server 520.

Meanwhile, the security management server 140 includes a watermark generation and management unit 148, a data management unit 142, a watermark insertion unit 144, and an encryption unit 146. The data manager 142 selects and manages the data generated by the data generator 120 and transmits the data to the watermark inserter 144, where the watermark is transmitted from the watermark generator and manager 148. Insert in Next, the encryption unit 146 encrypts the data with the watermark embedded therein using the encryption key transmitted from the key management unit 106 of the key management server 100. The data in which the encrypted watermark is inserted is transmitted to the mail server 160.

Hereinafter, a mail transmission method according to the present invention will be described with reference to FIGS. 1 to 3. 3 is a flowchart of a mail transmission according to an embodiment of the present invention.

First, the security management server 140 loads the data to be transmitted from the data generation unit 120 (S101). As described above, the data may be various specifications, a receipt, a certificate, and the like, and are not particularly limited, and may be any multimedia file such as audio and video. Preferably, it is an image file. Therefore, the following mainly describes the case of video data. Once the data file to be sent to the mail recipient is prepared, data analysis is performed on the image (S103). The image data for inserting the generated watermark needs to first adjust the image data to a constant level value in order to form a space in which the watermark can be inserted in the image data without degrading the image quality of the image. For this adjustment, the data management unit 142 performs the preprocessing, and generates a space in which the watermark can be inserted by adjusting the pixel value of the image data according to the preprocessing algorithm (S105). "Generate a space" means that the pixel value is adjusted in advance so that it is always a predetermined valid value even after the watermark is inserted.

The preprocessed image data is transmitted to the watermark inserting unit 144 while the data management unit 142 transmits the size information of the target data to which the watermark is to be inserted to the watermark inserting unit 144.

On the other hand, the watermark generation and management unit 148 generates a watermark to be inserted based on the content to be inserted as a watermark (S107). The watermark generation method is not limited to a particular method, and can be performed in various ways. Preferred methods can be largely divided into two types, a logo method and a key method. The logo method is a method of imaging the written text itself and inserting it into a multimedia file such as an image. The key method means not forming an image but inserting a bit string based on the generated text. In other words, the created text information is inserted into the multimedia data as a series of random sequences. Hereinafter, the key method will be described in consideration of the convenience and usefulness of the implementation of the present invention. However, the watermark generation method used in the present invention is not limited to a specific method and various methods are possible.

Subsequently, the generated watermark is inserted into the data by the watermark embedding unit 144 (S109).

When the above watermark embedding process is completed, the encryption unit 146 performs the encryption process (S111). In the encryption process, the key management server 100 requests an encryption key for encrypting the data file, and the key management server 100 transmits the encryption key to the security management server 140. Such an encryption key has bytes of a predetermined size, for example 128 bits. Encryption may be performed using various commercially available encryption algorithms, for example, a Twofish encryption algorithm or a Blowfish encryption algorithm.

When the encryption process is completed, the watermark is inserted and the encrypted data is transmitted to the mail server 160 (S113). At this time, the mail server 160 works with the advertisement server 180 to select an advertisement mail suitable for the corresponding recipient, and attaches the data file to the advertisement mail and transmits it to the recipient.

Hereinafter, a mail reception / confirmation system 500 and a mail reception / confirmation method according to an embodiment of the present invention will be described with reference to FIGS. 4, 5, and 6.

4 is a block diagram showing a schematic configuration of a mail receiving / confirmation system 500 according to an embodiment of the present invention. In the mail sent by the mail transmission system 1, as described above, the watermarked data is encrypted and attached to the advertisement mail. Therefore, in order to check the attached data by receiving such a mail, first, a user program executed at the mail receiver terminal must be downloaded and installed.

The mail reception / confirmation system 500 includes a mail server providing server 520 for providing a mail service such as mail reception, a program providing server 540 for downloading a user program connected thereto, and a watermark by installing the program. Mail receiver terminal 200 provided to check the inserted mail, and a wired or wireless communication network 190 is provided.

The mail service providing server 520 connects to the mail receiver terminal 200 through a wired or wireless communication network and performs user registration as necessary, and downloads a user program from the program providing server 520 to the mail receiver terminal 200. And transmits information such as an encryption key and a user's unique key provided from the mail receiver terminal 200 to the key management server 100 of the mail transmission system 1.

The program providing server 540 provides a user program according to the instructions of the mail service providing server 520. Therefore, when such a program is installed in the mail receiver terminal 200, the set user unique key is transmitted to the key management server 100 of the mail transmission system 1 connected with the mail service providing server. That is, when a user program is downloaded and installed, a user using the program sets a series of passwords, and the user program generates a user unique key by operating a unique key generation module in the user program. The generated user unique key is managed in the key management server 100 together with the encryption key generated for data encryption.

Hereinafter, a mail receiver terminal in which such a user program is installed will be described in more detail.

The mail receiver terminal 200 in which the user program is installed has a user password generation means, a user unique key generation means, data management means for managing received data, encrypted data decryption means, and decrypted data viewing means due to the installation of the program. It is provided.

The user password generating means is used for the user's input in the first authentication process for decrypting the encrypted mail in the mail receiving process. It is responsible for generating a password. This user password is used in the process of generating a user unique key through the unique key generation module, the user unique key generated through this process is transmitted to the key management server 100 through the mail service providing server 520, for example. . Preferably, the step of generating such a user unique key and the step of transmitting the user unique key proceed without being recognized by the user.

In addition, the user unique key generated through the set password is stored in the key management server 100, and is generated through the password entered primarily for decryption of the received data afterwards When the user's unique key is transmitted to the key management server 100, it is determined whether or not the stored key matches the transmitted key and determines whether to transmit the decryption key to the mail receiver terminal. This will be described later.

The user unique key generating means is responsible for generating a user unique key by the user unique key generating module at the time of setting a password or authenticating. The user unique key and the decryption key may not be transmitted and received through the mail service providing server 520, but may be transmitted and received to the key management server 100 through various wired or wireless communication networks. For example, the user unique key from the mail receiver terminal may be transmitted to the key management server 100 wirelessly.

The data management means can be embodied in a form that can be seen in a normal user program, and includes a series of processing steps such as storing or retrieving encrypted data.

The data decrypting means decrypts the encrypted data based on the decryption key transmitted by the key management server 100, and the data viewing means provides a viewer capable of reading the decrypted data. The watermark embedded in the data controls this browsing function.

Hereinafter, a unique key storing process and a mail receiving / confirming process of a mail receiver according to the present invention will be described with reference to FIGS. 5 and 6.

In FIG. 5, a mail receiver shows a flow of storing a user unique key in the key management server 100. Usually, the process in FIG. 5 is a process performed before the mail transmission system 1 transmits a mail to the mail receiver.

First, the user accesses the mail service providing server 520 (S301). Normally, the mail service providing server 520 exchanges data with a mail receiver through a home page, and after logging in, logs in to a mail service screen through a login screen output to a web browser (S303).

In the login phase, you apply for service through a series of sign-up processes. If the application is approved, the user downloads the program (S305). When the program is downloaded and installed, the subsequent series of processes are performed by the program installed in the mail receiver terminal. First, the mail user sets a series of passwords (S307). Thereafter, the user terminal generates a unique key by operating the unique key generation module inherent in the program through the password (S309).

Next, the generated unique key is transmitted to the key management server 100 (S311), and the transmitted unique key is managed by the key management server 100.

As described above, the steps of S307 to S311 are performed by the user program, and preferably, the steps S309 and S311 are carried out without the knowledge of the mail recipient.

6 is a flowchart illustrating a process of confirming data by receiving a mail from a user side. As described above, the mail receiver is connected to the mail service providing server 520 in a preliminary step for receiving mail and decrypting data, and downloads a user program through steps S303 to S311, and installs it in his terminal.

Therefore, the following series of processes are performed by the installed user program. First, when the mail to which the encrypted data is attached according to the present invention is received (S401), the user opens the attached file and simultaneously operates the program (S403), and a password input window appears. If the user inputs the password set in step S307 (S405), the user program again generates a user unique key using the input password (S407). Of course, if the password entered in step S405 does not match the password set in step S307, it is obvious that the process does not proceed to the next step.

The user unique key generated in step S407 is transmitted to the key management unit 106 of the key management server 100 (S409), the key management unit 106 is registered and stored and managed in step S309 and the received user unique key It is determined whether the unique key matches (S411). Thereafter, if the user unique key matches the unique key registered initially, the decryption key generated by the key generation unit 104 is transmitted to the user through the key transmission / reception management unit 102 (S413). In this case, the decryption key of the data is not transmitted. Therefore, only the former case, the mail receiver terminal 200 may decrypt the encrypted data using the decryption key (S415).

The mail recipient then retrieves the data using the user program. For example, a watermark may be used in the viewing process of such data. This will be described in detail below.

Further, in another embodiment of the present invention, the data with the watermark embedded and encrypted at the same time and the above-described user program can be sent together as a file in an e-mail. In this case, the user does not download and install the program, but instead attaches it to an e-mail, thereby improving user convenience.

In such an embodiment, when a mail is received and a program is installed, for example, a user's social security number or a password registered in advance may be used as a unique key for user authentication for decryption. If the pre-registration password is inputted, the input information is transmitted to the key management server 100, and the key management server 100 stores and manages the resident registration number of the mail recipient or the user's unique key information registered in advance. When the mail is received, the user unique key information transmitted to the key management server 100 is compared with the user unique key information previously stored and managed, and if they match, a decryption key for confirming the mail is transmitted to the mail receiver terminal.

In this embodiment, in comparison with the above-described embodiment, since a separate mail service providing server and a program providing server are not provided, user unique keys are not transmitted when the program is installed, but information for user authentication is registered in advance. There are differences such as points. After receiving the decryption key, the process of decrypting and reading the data with the watermark inserted and encrypted through the installed program is the same as the above-described embodiment.

The decoded data according to the present invention basically embeds a visible or invisible watermark. Thereafter, a watermark signal controls the output portion of the decoded data. It may be (S417). The watermark can be displayed visually by inserting a series of phrases, and the automatic printer function can be set to display the contents specified by the administrator so that the invisible watermark is extracted and only visible when printed to the printer. Based on the extracted watermark information. Limits such as the number of printouts can be set.

In this case, for example, when an invisible watermark, for example, a phrase such as "Do not copy" is inserted invisibly, the data is opened by extracting the watermark at the same time when the output command is transmitted. For example, after reconstructing the extracted watermark image on an image of a certificate (such as a certificate) and transmitting the reconstructed image to a printer, the phrase “Do not copy” may be visualized and output. Therefore, by authenticating the original of the printed matter and limiting the number of times of output using the watermark, important data can be safely transmitted and received, and safety can be ensured even when managing and including such data.

While the invention has been particularly shown and described with reference to the above embodiments, it has been used for the purpose of illustration and those of ordinary skill in the art, having the spirit and scope of the invention as defined in the appended claims. Various modifications can be made without departing.

According to the present invention, not only can securely transmit / receive various data files such as bills containing data or personal information requiring security, but also use a user program, even if a third party hacks mail in the middle. By generating a key and checking a user's unique key when decrypting a file, data leakage can be prevented.

In addition, there is an effect of preventing the leakage of information by preventing unauthorized users from decrypting important information received without permission.

Claims (22)

delete delete A security management server generating and inserting a predetermined watermark into the data to be transmitted, and encrypting the data into which the watermark is inserted; A mail server to which the predetermined watermark transmitted from the security management server is inserted and encrypted data through a wired or wireless communication network by mail; A key management server connected to the security management server to manage and store an encryption key for performing data encryption in the security management server, a decryption key for decrypting data in a mail receiver terminal, and a user unique key; And A mail receiver terminal for receiving the mail, decrypting the data in which the predetermined watermark is inserted and encrypted, and extracting a watermark; The key management server, A key generator for generating the encryption key and the decryption key; A key manager for managing the user unique key, the encryption key and the decryption key generated by the key generator; A key transmission / reception manager configured to transmit and receive the decryption key and the user unique key between the mail receiver terminal and the key manager; And the predetermined watermark includes information for controlling output and viewing of the data. The method of claim 3, wherein The security management server, A data manager for selecting and managing data to be transmitted; A watermark generation and management unit for generating and managing a predetermined watermark to be inserted into data selected by the data manager; A watermark embedding unit for embedding the predetermined watermark in the data; And And an encryption unit for encrypting the data into which the predetermined watermark is inserted. The method of claim 3, wherein A mail service providing server for downloading the program to decrypt the data in which the predetermined watermark is inserted and encrypted, and to download the program for reading the inserted data to the mail receiver terminal; And And a program providing server connected to the mail service providing server. The method of claim 5, wherein The program, A first step of generating a user password; A second step of generating a user unique key using the user password; And And a third step of transmitting the generated user unique key to the key management server, thereby storing the generated user unique key in the key management server. The method of claim 5, wherein The program, A first step of inputting and confirming a user password; A second step of generating a user unique key through the input password; A third step of transmitting the generated user unique key to a key management server; Receiving a decryption key from the key management server and decrypting the data using the decryption key; And And receiving the data received through a fifth step of reading the decrypted mail. The method of claim 6, The second step and the third step is performed so that the mail recipient is not recognized. The method according to claim 6 or 7, And the user unique key is generated using system information of a user terminal. The method according to any one of claims 3 to 8, And an advertisement server connected to the mail server in order to include the advertisement multimedia information in the mail. The method according to any one of claims 3 to 8, And a data generation unit for generating the data and transmitting the generated data to the security management server, wherein the data is a specification containing various certificates, receipts, or personal information as video images. The method according to any one of claims 3 to 8, And the watermark is generated and inserted in a key manner. The method according to any one of claims 3 to 8, The mail receiver terminal is a personal computer, a PDA, or a mobile phone, characterized in that the mobile phone. delete A data generator for generating data to be transmitted; A security management server generating and inserting a predetermined watermark into the data generated by the data generator and encrypting the data into which the watermark is inserted; An advertisement server connected to a mail server and generating multimedia information for advertisement; A mail server to which the predetermined watermark transmitted from the security management server is inserted and attached with encrypted data, and transmitted through a wired or wireless communication network together with the advertisement mail generated by the advertisement server; A key management server for managing and storing an encryption key required for performing encryption, a decryption key required for decryption at a mail receiver terminal, and a user unique key; A mail service providing server for downloading a program for decrypting and reading the encrypted data having the watermark inserted therein into the mail receiver terminal; And And a mail receiver terminal including a program for receiving the mail and decrypting and reading the data in which the predetermined watermark is inserted and encrypted, The watermark includes information for controlling the output and reading of the data, and generates a user unique key from the mail receiver terminal by a predetermined method, and transmits it to a key management server through the mail service providing server. Mail sending and receiving system. delete In a mail transmitting and receiving system comprising a mail transmitting system for transmitting data with a watermark inserted into a mail and a mail receiver terminal for receiving the mail, the method for transmitting and receiving the mail, the method comprising: Inserting a predetermined watermark into data to be transmitted; Encrypting data in which the predetermined watermark is embedded; A third step of transmitting the encrypted data by mail through a wired or wireless communication network; Receiving a mail at the mail receiver terminal and decrypting the encrypted data in the received mail; And A fifth step of extracting a watermark embedded in the decoded data to control output and reading of the data, Before the fourth step, further comprising the step of installing a program for checking the received mail in the mail receiver terminal, The program registers a user unique key in the mail transmission system. Generating a user password; Generating a user unique key using the user password; And transmitting the generated user unique key to the mail transmission system. The method of claim 17, The program checks the received mail, Entering a user password; Generating a user unique key through the input password; Transmitting the generated user unique key to the mail transmission system; Receiving a decryption key from the mail transmission system, and decrypting the data using the decryption key; And And reading the decoded data. The method of claim 17 or 18, The data is a video image, the mail transmission and reception method, characterized in that the statement containing various certificates, receipts, or personal information. The method of claim 17 or 18, And the watermark of the first step is generated and inserted in a key manner. The method of claim 17 or 18, The mail receiver terminal is a personal computer, PDA, or mobile phone, characterized in that the mobile phone. The method of claim 17 or 18, And the user unique key is generated using system information of a user terminal.