WO2016200007A1

WO2016200007A1 - Secure chat method using distributed key exchange protocol and self-defense security technology

Info

Publication number: WO2016200007A1
Application number: PCT/KR2016/000887
Authority: WO
Inventors: 윤석구
Original assignee: 주식회사 엔오디비즈웨어
Priority date: 2015-06-12
Filing date: 2016-01-27
Publication date: 2016-12-15
Also published as: KR101596479B1

Abstract

According to one embodiment of the present invention, a secure chat method using a distributed key exchange protocol of a first chat application, which is installed and executed in a first communication terminal, enables the first chat application to generate a private key by using a private key management module installed in the first chat application without sharing an encoding key with a chat server, and to directly share the generated private key with a second chat application, which is installed and executed in a second communication terminal by using a key exchange protocol, thereby allowing a secure chat to be performed with the second chat application through the chat server.

Description

Secure Chatting Method Using Distributed Key Exchange Protocol and Self-Defense Security Technology

An embodiment according to the concept of the present invention relates to a secure chat method, and in particular, a chat application installed and executed in a user's communication terminal may use a distributed key exchange protocol with a chat application of a chat counterpart without sharing an encryption key with a chat server. The present invention relates to a secure chat method that can improve security by directly sharing an encryption key and preventing a chat message from being captured and leaked using a self-defense security technology.

Recently, there are cases where messages sent and received privately by users using the online chat application are leaked out due to hacking or capture. If the messages relate to a person's privacy or a company's trade secrets, leakage of the messages can cause economic or mental harm.

Since conventional chat applications each share an encryption key with a chat server, the chat server decrypts an encrypted message received from a specific chat application, extracts the message, and encrypts the extracted message with the chat application of the conversation partner. Re-encrypt with key and send to chat partner's application. Therefore, there is a possibility that a message is leaked from the chat server. In addition, since the chat server performs encryption and decryption on all messages, it may cause a load on the chat server.

The technical problem to be achieved by the present invention is to share the encryption key directly by using a distributed key exchange protocol with the chat application of the chat partner, without sharing the encryption key with the chat server in order to improve the security of messages sent and received for chat In addition, the present invention provides a secure chat method that can improve security by preventing a displayed message from being captured using self-defense security technology.

The first chat application installed in the first communication terminal according to an embodiment of the present invention and the second chat application installed and executed in the second communication terminal through the chat server, without sharing the encryption key with the chat server; In a secure chat method using a distributed key exchange protocol of the first chat application capable of secure chat, the first chat application generates a secret key using a secret key management module embedded in the first chat application. And directly sharing the generated secret key with a second chat application installed and executed in the second communication terminal using a key exchange protocol, and from the user of the first communication terminal to the second communication terminal. When the first message to be sent to the first message is input, the first chat application uses the secret key to send the first message. And encrypting the message, the first chat application, via the chat server, the encrypted first message and transmitting to the second chat application.

The secure chat method may include: receiving, by the first chat application, the encrypted second message when a second message encrypted by the second chat application is transmitted to the first communication terminal through the chat server. And decrypting, by the first chat application, the encrypted second message using the secret key.

The secure chat method may include: displaying, by the first chat application, a decrypted second message through a display included in the first communication terminal, and wherein the first chat application is embedded in the first chat application. Preventing the second message displayed using the capture prevention module from being captured.

According to an embodiment of the present disclosure, preventing the second message from being captured may cause the first chat application to disable a screen capture function of the first communication terminal.

According to another embodiment of the present disclosure, the preventing of the second message from being captured may force the first chat application to terminate the screen capture application executed in the first communication terminal.

According to another embodiment of the present disclosure, preventing the second message from being captured may include: at least one of a folder and a clipboard in which the screen capture data of the first communication terminal is stored, by the first chat application. Monitoring and deleting, by the first chat application, data stored in at least one of the folder and the clipboard while the second message is displayed.

According to another embodiment of the present disclosure, the preventing of the second message from being captured may be performed by the first chat application, in order to prevent the displayed second message from being captured by an external electronic device. Display on the display.

The secure chat method may include: when the first chat application detects a capture attempt for the second message, transmitting a notification message for notifying the capture attempt to the second communication terminal through the chat server. It includes more.

According to another embodiment of the present invention, a first chat application installed and executed in a first communication terminal directly shares a secret key with a second chat application installed and executed in a second communication terminal, and uses the shared secret key. Secure chat method using a self-defense security technology of the first chat application that can perform a secure chat with the second chat application, the first chat application, via a chat server that can communicate with the first communication terminal Receiving an encrypted first message sent from the second chat application, the first chat application decrypts the received first encrypted message using the secret key, and decrypted the first message Displaying a message on a display of the first communication terminal, wherein the first chat application comprises: Preventing the displayed first message from being captured using a capture protection module embedded in a first chat application.

The capture prevention module may be configured to deactivate a screen capture function of the first communication terminal, forcibly terminate a capture program executed in the first communication terminal, prevent screen capture of an external device using an image disturbance pattern, and screen through a clipboard monitoring. The captured first message is prevented from being captured using at least one of capture data deletion.

A computer-readable storage medium according to an embodiment of the present invention stores an application for performing the secure chat method.

Since the chat application performing the secure chat method according to the embodiment of the present invention has a built-in capture prevention module to which the self-defense security technology is applied, the displayed message is prevented from being leaked by the capture, thereby improving security.

In addition, since a secret key (or encryption key) is directly shared between communication terminals executing a chat application through a distributed key exchange protocol, messages transmitted and received between the communication terminals are not encrypted and decrypted by a chat server, thereby enabling the chat. It can reduce the processing load on the server. In addition, since only the encrypted messages exist in the chat server, even if the chat server is hacked, the risk of leaking the contents of the messages is reduced.

1 is a schematic block diagram of a secure chat system for performing a secure chat method according to an embodiment of the present invention.

FIG. 2 is a schematic block diagram illustrating an embodiment of a first communication terminal and a chat application shown in FIG. 1.

3 to 5 are data flow charts for explaining a secure chat method according to embodiments of the present invention.

A module in the present specification may mean hardware capable of performing functions and operations according to each name described in the present specification, or computer program code capable of performing specific functions and operations. It may mean, or may mean, an electronic recording medium, for example, a processor, on which computer program code is capable of performing specific functions and operations.

In other words, a module may mean a functional and / or structural combination of hardware for performing the technical idea of the present invention and / or software for driving the hardware.

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

1, a secure chat system 10 for performing a secure chat method according to an embodiment of the present invention may include a first communication terminal 100-1, a second communication terminal 100-2, and a chat server ( 200).

Each of the first communication terminal 100-1 and the second communication terminal 100-2 performs a chat application (an application program or an app; C_APP) that can perform a secure chat method according to an embodiment of the present invention. Can be stored.

Each of the first communication terminal 100-1 and the second communication terminal 100-2 may be implemented as a PC, a notebook PC, or a mobile computing device. The mobile computing device may be a smart phone, a tablet PC, a mobile phone, a personal digital assistant, a mobile internet device (MID), an enterprise digital assistant (EDA), or a PND ( It may be implemented as a personal navigation device or a portable navigation device, an Internet of things (IoT) device, an internet of everything (IoE) device, or a wearable device.

Although the secure chat system 10 is illustrated as including only the first communication terminal 100-1 and the second communication terminal 100-2 in the present specification, the number of communication terminals may vary according to embodiments. . That is, the user of the first communication terminal 100-1 may select a plurality of chat counterparts, and may transmit a message to each of the selected chat counterparts in parallel.

The chat server 200 may provide a secure chat service according to the secure chat method according to an embodiment of the present invention. The chat server 200 manages the user connecting to the chat server 200 using the chat application C_APP, and transmits a message transmitted from the first communication terminal 100-1 to the second communication terminal 100-2. ) Or a message transmitted from the second communication terminal 100-2 to the first communication terminal 100-1.

According to an embodiment, the chat server 200 may include a database DB or access the database DB. The database DB may store user information (eg, ID, name, phone number, etc.) for a user who uses the secure chat service, and store a chat counterpart list for the user to select a chat counterpart. The chat counterpart list may be set by the user, but is not limited thereto and may be automatically set by the chat server 200.

The secure chat system 10 may further include an application download server 300. The application download server 300 may store a chat application C_APP that performs a secure chat method according to an embodiment of the present invention, and may communicate with a plurality of communication terminals through a wired and / or wireless network. The application download server 300 may provide a download service for a user of the first communication terminal 100-1 and / or the second communication terminal 100-2 to download the chat application C_APP according to the present invention. Can be.

For example, the application download server 300 may be a server in an app store market selling various applications or a personal server or an enterprise server for distributing the applications, but is not limited thereto.

In FIG. 2, only the structure and operation of the first communication terminal 100-1 are illustrated, but the structures and operations of the first communication terminal 100-1 and the second communication terminal 100-2 may be substantially the same. Similarly, the above structure and operation of the first communication terminal 100-1 can be applied to the second communication terminal 100-2.

1 and 2, the first communication terminal 100-1 may include a processor 110, a memory 120, an input interface 130, a display 140, and a communication module 150. have.

The processor 110 may control the operation of at least one of the

components

120, 130, 140, and 150 included in the first communication terminal 100-1. According to an embodiment, the processor 110 may be implemented as an application processor (AP) and a mobile AP, but is not limited thereto. The processor 110 may execute a chat application C_APP stored in the memory 120.

The memory 120 may store instructions and / or a plurality of applications required for the operation of the processor 110. In particular, the memory 120 may store a chat application C_APP according to an embodiment of the present invention.

According to an embodiment, the memory 120 may operate as an operating memory of the processor 110 and may be implemented as a dynamic random access memory (DRAM) or a static RAM (SRAM). According to another embodiment, the memory 120 may be implemented as a flash-based memory. The flash-based memory may be a multimedia card (MMC), an embedded MMC (eMMC), universal flash storage (UFS), or a solid state drive (SSD). It can be implemented as.

Memory 120 may be understood in a collective sense including one or more memories. For example, the memory 120 may include a clipboard in which the screen capture image is temporarily stored.

The chat application C_APP stored in the memory 120 and executed by the processor 110 may include a connection management module 162, a secret key management module 164, a message management module 166, and an encryption / decryption module 168. The message viewer 170 and the capture prevention module 172 may be embedded (or included).

The connection management module 162 may manage a connection between the first communication terminal 100-1 and the chat server 200. When the user of the first communication terminal 100-1 executes the chat application C_APP to use the secure chat service, the connection management module 162 connects to the chat server 200 (or logs in). Information may be transmitted to the chat server 200. The user information may be an ID and / or a password, but is not limited thereto. The user information may be information for identifying the first communication terminal 100-1 or the user. For example, when the first communication terminal 100-1 is a PC, the user information may include an IP (internet protocol) address of the first communication terminal 100-1, and the first communication terminal 100-1. If the smartphone is the user information may include the telephone number of the first communication terminal (100-1). The user information may be input through the input interface 130 or may be stored in advance in the access management module 162.

According to an embodiment of the present disclosure, when the chat application C_APP is terminated, the connection management module 162 may perform a logout operation for terminating the connection with the chat server 200.

The secret key management module 164 may include a second secret key (or an encryption key) for encrypting a message exchanged with a chat application (C_APP) installed in the communication terminal of the chat counterpart, for example, the second communication terminal 100-2. And directly share with the communication terminal 100-2.

The secret key management module 164 may directly share the secret key with the second communication terminal 100-2 using a distributed key exchange protocol (or distributed key exchange protocol). The secret key management module 164 may use a known key exchange protocol (or known key exchange algorithm), such as a diffie-hellman key exchange algorithm. Sharing the secret key directly means that the first communication terminal 100-1 and the second communication terminal 100-2 directly exchange signals and / or data for sharing the secret key. That is, when sharing the secret key, the first communication terminal 100-1 and the second communication terminal 100-2 transmit the signal and / or the data for sharing the secret key to the chat server 200. Do not send. Therefore, since the chat server 200 may not have any information about the secret key, the messages transmitted to the chat server 200 cannot be decrypted by the chat server 200.

When the user inputs a first message to be transmitted to the chat counterpart via the input interface 130, the message management module 166 receives the input first message and encrypts / decrypts the received first message. Module 168 can be used to encrypt. The encryption / decryption module 168 may encrypt the first message using the secret key generated by the secret key management module 164. The message management module 166 may transmit the encrypted first message to the second communication terminal 100-2 through the communication module 150.

According to an embodiment, when a second message is received from the second communication terminal 100-2 to the first communication terminal 100-1 through the communication module 150, the message management module 166 may transmit the second message. Can be decrypted using the encryption / decryption module 168. The encryption / decryption module 168 may decrypt the second message using the secret key.

The message viewer 170 may display the decrypted second message through the display 140 included in the first communication terminal 100-1. According to an embodiment, the message viewer 170 may also display the first message input by the user of the first communication terminal 100-1 together.

The capture protection module 172 may perform various operations to prevent the displayed second message and / or the first message from being captured in order to prevent the displayed second message and / or the first message from leaking to the outside. Can be done. That is, the capture prevention module 172 may perform a self-defense security operation on the chat application C_APP.

The capture prevention module 172 may disable the screen capture function of the first communication terminal 100-1 to prevent the displayed second message and / or the first message from being captured. For example, the capture prevention module 172 may disable the operation of the screen capture key of the first communication terminal 100-1 through a system application programming interface (API).

According to an embodiment, the capture prevention module 172 may monitor a location (eg, a photo folder or a screenshot folder) in which the screen captured image is stored. The capture prevention module 172 may activate the chat application C_APP while the chat between the first communication terminal 100-1 and the second communication terminal 100-2 is in progress or the display 140 is displayed on the display 140. 2 If a file and / or data is generated at the location while the message and / or the first message is displayed, the generated file and / or data is displayed on the displayed second message and / or the screen for the first message. The generated file and / or data may be deleted by recognizing that the image is a captured image.

According to an embodiment, the capture prevention module 172 may forcibly terminate the operation of the capture application executed in the first communication terminal 100-1. The capture prevention module 172 may include a database for detecting the capture application, and detect the capture application using the database.

According to another embodiment, the capture prevention module 172 may monitor the clipboard of the first communication terminal 100-1. The capture prevention module 172 activates the chat application C_APP so that a chat between the first communication terminal 100-1 and the second communication terminal 100-2 is in progress or on the display 140. While the message and / or the first message are being displayed, if the clipboard is filled with data, the data is recognized as being a screen capture image for the displayed second message and / or the first message. You can delete it.

According to another embodiment of the present disclosure, the capture prevention module 172 may capture the display 140 through an external electronic device to prevent the displayed second message and / or the first message from leaking. Although it is difficult to see, when the image is taken by the external electronic device, an image disturbance pattern may be displayed on the display 140 to cause an image interference so that the displayed second message and / or the first message does not leak.

In the present specification, various examples of the operation of the capture prevention module 172 are described as described above, but the embodiment of the capture prevention module 172 may be varied in a range predictable by those skilled in the art. Can be modified. The capture prevention module 172 may perform a capture prevention operation using at least one of the above embodiments.

The capture prevention module 172 may detect a screen capture attempt of the first communication terminal 100-1 and inform the user of the second communication terminal 100-2 of the screen capture attempt. According to an embodiment, the capture prevention module 172 may detect a screen capture attempt from an external electronic device. For example, when the input interface 130 included in the first communication terminal 100-1 is a microphone, the capture prevention module 172 may detect the screen capture attempt by recognizing a camera photographing sound using the microphone. have.

The capture prevention module 172 may generate a notification message when detecting the screen capture attempt, and transmit the generated notification message to the second communication terminal 100-2 through the communication module 150. The notification message may be directly transmitted from the first communication terminal 100-1 to the second communication terminal 100-2 or transmitted to the second communication terminal 100-2 through the chat server 200.

The input interface 130 may transmit a first message input by the user to the user input interworking module 116 or transmit user information to the connection management module 162. According to an embodiment, the input interface 130 may be implemented as a keyboard, a mouse, a microphone, and / or a touch panel, but is not limited thereto.

When the encrypted second message received from the chat server 200 is decrypted by the encryption / decryption module 168, the display 140 may display the decrypted second message under the control of the message viewer 170. have. According to an embodiment, the display 140 may display the first message input through the input interface 130.

For example, the display 140 may be a thin film transistor-liquid crystal display (TFT-LCD), a light emitting diode (LED) display, an organic LED (OLED) display, an active-matrix OLED (AMOLED) display, or a flexible display. It can be implemented as.

When the chat application C_APP is executed, the communication module 150 may transmit user information transmitted from the connection management module 162 to the chat server 200. In addition, when the message management module 166 encrypts the first message using the encryption / decryption module 168, the communication module 150 may transmit the encrypted first message to the chat server 200. According to an embodiment, the communication module 150 may transmit the notification message generated by the capture prevention module 172 to the chat server 200 or the second communication terminal 100-2.

The communication module 150 may receive an encrypted second message transmitted from the chat server 200 and transmit the encrypted second message to the message management module 166.

The communication module 150 may be implemented in a wired communication method and / or a wireless communication method. The radio communication method may include a method such as ^TM LTE (long term evolution), W-CDMA (wideband code division multiple access (W -CDMA)), WiFi (Wi-Fi).

3 to 5 are data flow charts illustrating a secure chat method according to embodiments of the present invention.

1 to 3, when the chat application C_APP stored (or installed) in the first communication terminal 100-1 is executed, the connection management module 162 included in the chat application C_APP is a user. The information may be connected (or logged in) to the chat server 200 using the information (S100).

The chat server 200 loads the chat counterpart list U_LIST from the database DB accessed by the chat server 200 (S110), and loads the loaded chat counterpart list U_LIST in the first communication terminal 100-1. (S120). For example, the chat server 200 may load the chat counterpart list U_LIST set in the user of the first communication terminal 100-1 using the user information, but is not limited thereto.

When at least one chat counterpart included in the chat counterpart list U_LIST is selected by the user of the first communication terminal 100-1 (S130), the secret key management module 164 embedded in the chat application C_APP is selected. The secret key may be generated using the secret key, and the generated secret key may be directly shared with the chat application C_APP installed in the second communication terminal 100-2 using the distributed key exchange protocol (S150).

1 to 4, when the first message MSG1 to be transmitted from the user of the first communication terminal 100-1 to the second communication terminal 100-2 is input through the input interface 130 (S200). ), The message management module 166 included in the chat application C_APP may encrypt the first message MSG1 using the encryption / decryption module 168 (S210). The encryption / decryption module 168 may generate the encrypted first message E_MSG1 by encrypting the first message MSG1 using the secret key generated by the secret key management module 164.

The message management module 166 transmits the encrypted first message E_MSG1 to the chat server 200 through the communication module 150 (S220), and the chat server 200 transmits the first communication terminal 100-1. The encrypted first message E_MSG1 transmitted from the second communication terminal 100-2 may be transmitted to the second communication terminal 100-2 (S230). According to an embodiment, the chat server 200 may store the encrypted first message E_MSG1 in the database DB.

The message management module 166 of the chat application C_APP executed in the second communication terminal 100-2 encrypts / decrypts the encrypted first message E_MSG1 transmitted from the chat server 200. Can be decoded using (S240). The encryption / decryption module 168 may generate the first message MSG1 by decrypting the encrypted first message E_MSG1 using the secret key shared with the first communication terminal 100-1.

The message viewer 170 of the chat application C_APP executed in the second communication terminal 100-2 may display the decrypted first message MSG1 on the display (S250). The capture prevention module 172 may prevent the displayed first message MSG1 from being captured using the self-defense security technology (S260). The capture prevention module 172 may disable the screen capture function of the second communication terminal 100-2, forcibly terminate the screen capture application executed in the second communication terminal 100-2, or perform a second communication. The clipboard (or picture folder, screenshot folder, etc.) where the clipboard and / or image of the terminal 100-2 is generated is monitored to display the clipboard and / or the location while the first message MSG1 is displayed. At least one of an operation of displaying an image disturbance pattern may be used to delete stored data or to prevent the displayed first message MSG1 from being captured by an external electronic device.

1 to 5, when a second message MSG2 to be transmitted from the user of the second communication terminal 100-2 to the first communication terminal 100-1 is input through the input interface 130 (S300). ), The message management module 166 included in the chat application C_APP may encrypt the second message MSG2 using the encryption / decryption module 168 (S310). The encryption / decryption module 168 may generate the encrypted second message E_MSG2 by encrypting the second message MSG2 using the secret key shared with the first communication terminal 100-1.

The message management module 166 transmits the encrypted second message E_MSG2 to the chat server 200 through the communication module 150 (S320), and the chat server 200 transmits the second communication terminal 100-2. The encrypted second message E_MSG2 transmitted from the second communication terminal 100-1 may be transmitted to the first communication terminal 100-1 (S330). According to an embodiment, the chat server 200 may store the encrypted second message E_MSG2 in the database DB.

The message management module 166 of the chat application C_APP executed in the first communication terminal 100-1 encrypts / decrypts the encrypted second message E_MSG2 transmitted from the chat server 200. Can be decoded using (S340). The encryption / decryption module 168 may decrypt the second message E_MSG2 encrypted using the secret key to generate a second message MSG2.

The message viewer 170 of the chat application C_APP executed in the first communication terminal 100-1 may display the decrypted second message MSG2 on the display 140 (S350). According to an embodiment, the message viewer 170 may also display the previously generated first message MSG1.

The capture prevention module 172 may prevent the displayed second message MSG2 from being captured using the self-defense security technology (S360). According to an embodiment, the capture prevention module 172 may detect a capture attempt of the displayed second message MSG2 and generate a notification message for notifying the second communication terminal 100-2 of the detection result. The generated notification message may be transmitted to the second communication terminal 100-2 through the chat server 200 or directly to the second communication terminal 100-2 (S370).

That is, the first message MSG1 and / or the second message MSG2 transmitted and received between the first communication terminal 100-1 and the second communication terminal 100-2 are encrypted and decrypted by the chat server 200. Since not, the processing load of the chat server 200 can be reduced. In addition, since only the encrypted first message E_MSG1 and the encrypted second message E_MSG2 exist in the chat server 200, even when the chat server 200 is hacked, the first message MSG1 and the second message ( The risk of leakage of the contents of MSG2) can be reduced.

In addition, the chat application (C_APP) according to an embodiment of the present invention has a built-in capture protection module 172, the built-in capture protection module 172 prevents the displayed messages MSG1 and / or MSG2 is captured. To improve security.

The present invention can be used in a secure chat method using a distributed key exchange protocol and a secure chat method using a self-defense security technology.

Claims

The first chat application installed and executed in the first communication terminal may perform secure chat with the second chat application installed and executed in the second communication terminal through the chat server without sharing an encryption key with the chat server. In the secure chat method using a distributed key exchange protocol of the first chat application,

Wherein the first chat application generates a secret key using a secret key management module embedded in the first chat application, and the generated secret key is installed and executed in the second communication terminal using a key exchange protocol. Sharing directly with a second chat application;

Encrypting the first message by using the secret key when the first message to be transmitted from the user of the first communication terminal to the second communication terminal is input; And

Sending, by the first chat application, the encrypted first message to the chat server for transmission to the second chat application.
The method of claim 1,

Receiving, by the first chat application, the encrypted second message if a second message encrypted by the second chat application is transmitted to the first communication terminal through the chat server; And

Decrypting, by the first chat application, the encrypted second message using the secret key.
The method of claim 2,

Displaying, by the first chatting application, the decrypted second message through a display included in the first communication terminal; And

Preventing the first chat application from capturing the displayed second message by using a capture prevention module embedded in the first chat application.
The method of claim 3, wherein the preventing of the second message from being captured includes:

And a first chat application using a distributed key exchange protocol for disabling a screen capture function of the first communication terminal.
The method of claim 3, wherein the preventing of the second message from being captured includes:

And the first chat application forcibly terminates the screen capture application executed in the first communication terminal.
The method of claim 3, wherein the preventing of the second message from being captured includes:

Monitoring, by the first chat application, at least one of a folder and a clipboard in which screen capture data of the first communication terminal is stored; And

And deleting, by the first chat application, data stored in at least one of the folder and the clipboard while the second message is displayed.
The method of claim 3, wherein the preventing of the second message from being captured includes:

Secure chat method using a distributed key exchange protocol to display a video disturbance pattern on the display to prevent the first chat application from capturing the displayed second message by an external electronic device.
The method of claim 3,

If the first chat application detects a capture attempt for the second message, transmitting the notification message for notifying the capture attempt to the chat server for transmitting to the second communication terminal; Secure chat method using key exchange protocol.
The first chat application installed and executed on the first communication terminal directly shares a secret key with the second chat application installed and executed on the second communication terminal, and uses the shared secret key to secure the second chat application with the second chat application. In the secure chat method using a self-defense security technology of the first chat application capable of chatting,

Receiving, by the first chat application, an encrypted first message sent from the second chat application via a chat server capable of communicating with the first communication terminal;

Decrypting, by the first chat application, the received first encrypted message using the secret key and displaying the decrypted first message on a display of the first communication terminal; And

Preventing the first chat application from capturing the displayed first message by using a capture prevention module embedded in the first chat application.
The method of claim 9, wherein the capture prevention module,

At least one of deactivating a screen capture function of the first communication terminal, forcibly terminating a capture program executed in the first communication terminal, preventing screen capture of an external device using an image disturbance pattern, and deleting screen capture data through clipboard monitoring Secure chat method using a self-defense security technology to prevent the first message displayed by using the capture.
The method of claim 9,

If the first chat application detects a capture attempt for the first message, sending a notification message for notifying the capture attempt to the chat server to send the second chat application to the chat server; Secure chat method using defensive security technology.
A computer-readable storage medium storing an application for performing the secure chat method according to any one of claims 1 to 11.