JP2007150976A - Data transmission and reception system, and data transmitting and receiving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data transmission and reception system enabling transmission-side and reception-side persons in charge to dynamically update an encryption key without synchronization. <P>SOLUTION: A transmitter 100 after adding a session key as data for authentication to plaintext data ciphers the data by using the session key. Further, the transmitter 100 processes the session key according to a specified rule without synchronizing itself with a receiver 200. The receiver 200, on the other hand, deciphers the ciphered data from the transmitter 100 by using a session key, extracts the session key added as the data for authentication, and checks the validity of the data based upon whether the extracted session key matches the generated session key. When they do not match each other, the session key is processed according to a specified rule and deciphering and authentication are performed again. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a data transmission / reception system and a data transmission / reception method capable of appropriately updating a common key used for encrypting and decrypting communication data on the transmission side without synchronizing with the reception side.

  In recent years, with the spread of the Internet and the like, the opportunity to transmit and receive various data via a general-purpose network accessible by an unspecified number of people has increased dramatically. Security protection when data is transmitted and received via a general-purpose network such as the Internet is mainly based on data encryption. For this reason, various methods for handling encryption keys used for data encryption and decryption have been proposed. (For example, refer to Patent Documents 1-3).

By using various methods such as Patent Documents 1 to 3 and dynamically updating the encryption key while synchronizing on the transmission side and the reception side, the damage when the encryption key is leaked is minimized. It becomes possible to suppress to.
Japanese Patent Laid-Open No. 11-55241 JP 2003-134106 A Japanese Laid-Open Patent Publication No. 5-292078

  By the way, the encryption key is generally updated on both the transmission side and the reception side in synchronization. However, if mobility is taken into consideration, transmission can be performed without synchronization with the reception side. It is desirable that the update can be performed at any timing on the side, and that the reception side can follow the update without synchronizing with the transmission side.

  The present invention has been made in consideration of such circumstances, and a data transmission / reception system capable of dynamically updating an encryption key without synchronization between a transmitting side and a receiving side, and An object is to provide a data transmission / reception method.

  In order to achieve the above-described object, a data transmission / reception system according to the present invention is a data transmission / reception system in which a data transmission apparatus and a data reception apparatus transmit / receive data after encrypting data, and the data transmission apparatuses confirm each other. Authentication means for executing authentication processing with the data receiving device, encryption means for encrypting data using a session key generated by the authentication processing of the authentication means as a common key, and plaintext to be transmitted The data reception in which the encryption means is encrypted with the entire data obtained by adding the session key as verification data to the data as transmission data, and the authentication processing is performed on the obtained encrypted data by the authentication means A data transmission means for transmitting to the apparatus, and the encryption key and the data transmission means for the common key and the verification. Processing means for processing the value of the session key used as the data for use based on a predetermined rule, and the data receiving device performs an authentication process for confirming each other with the data transmitting device. Using as a common key the authentication means to be executed in the data, the data receiving means for receiving the encrypted data from the data transmitting apparatus subjected to the authentication processing by the authentication means, and the session key generated by the authentication processing of the authentication means The decryption means for decrypting the encrypted data, and the session key added as verification data to the plaintext data to be received is extracted from the entire reception data decrypted by the decryption means, and the value of the extracted session key And a value of the generated session key to determine whether the plaintext data to be received is correct or not When the first determination means determines that the value is incorrect, the generated session key value is processed based on a predetermined rule, and the encrypted data using the processed session key as a common key is processed. The decryption means is re-executed, the session key added as verification data is re-extracted from the entire received data obtained thereby, and the value of the re-extracted session key and the processed session And second determination means for comparing the key value with each other to determine whether the plaintext data to be received is correct or not.

  The data transmission / reception method of the present invention is a data transmission / reception method of a data transmission / reception system in which a data transmission device and a data reception device encrypt data and transmit / receive the data. An authentication step for executing authentication processing with the data receiving device, an encryption step for encrypting data using a session key generated by the authentication processing of the authentication step as a common key, and plaintext data to be transmitted The data receiving apparatus in which the encryption step is encrypted using the entire data with the session key added as verification data as transmission data, and the encrypted data obtained thereby is subjected to authentication processing by the authentication step A data transmission step for transmitting to the encryption step, the encryption step and the data transmission step. A processing step for processing the value of the session key used as a common key and verification data according to a predetermined rule, and the data receiving device performs an authentication process for confirming each other. An authentication step executed with the transmitting device, a data receiving step for receiving encrypted data from the data transmitting device subjected to the authentication process in the authentication step, and a session key generated by the authentication process in the authentication step. A decryption step for decrypting the encrypted data using the common key, and extracting the session key added as verification data to the plaintext data to be received from the entire reception data decrypted by the decryption step. Comparing the generated session key value with the generated session key value, A first determination step for determining whether the plaintext data to be trusted is correct and if the first determination step determines that the data is not correct, the generated session key value is processed based on a predetermined rule; The decryption step re-executes decryption of the encrypted data using the processed session key as a common key, and re-extracts the session key added as verification data from the entire received data obtained thereby. A second determination step of comparing the value of the re-extracted session key with the value of the processed session key to determine whether the plaintext data to be received is correct or not. To do.

  According to the present invention, it is possible to provide a data transmission / reception system and a data transmission / reception method capable of dynamically updating an encryption key without synchronizing between a transmission side and a reception side party.

  Embodiments of the present invention will be described below with reference to the drawings.

  Here, an example is shown in which the data transmission / reception system of the present invention is applied for data transmission / reception via a general-purpose data bus in an information processing apparatus. First, the configuration of an information processing apparatus according to an embodiment of the present invention will be described with reference to FIG. 1 and FIG. This information processing apparatus is realized as, for example, a notebook personal computer 1.

  FIG. 1 is a perspective view of the notebook personal computer 1 with the display unit opened. The computer 1 includes a computer main body 2 and a display unit 3. In the display unit 3, a display device composed of a TFT-LCD (Thin Film Transistor Liquid Crystal Display) 4 is incorporated, and the display screen of the LCD 4 is positioned substantially at the center of the display unit 3.

  The display unit 3 is attached to the computer main body 2 so as to be rotatable between an open position and a closed position. The computer main body 2 has a thin box-shaped casing. The upper surface of the computer main body 2 has a keyboard 5, a power button 6 for powering on / off the computer 1, an input operation panel 7, a touch pad 8, and a speaker 9A. , 9B, etc. are arranged.

  The input operation panel 7 is an input device for inputting an event corresponding to the pressed button, and includes a plurality of buttons for starting a plurality of functions. These button groups also include a TV start button 7A and a DVD / CD start button 7B. The TV activation button 7A is a button for activating a TV function for reproducing and recording TV broadcast program data, and when pressed by the user, a TV application program for executing the TV function is activated. The

  In the computer 1, in addition to a general-purpose main operating system, a dedicated sub-operating system for processing AV (audio / video) data is installed. The TV application program is a program that operates on the sub-operating system.

  When the power button 6 is pressed by the user, the main operating system is activated. On the other hand, when the TV start button 7A is pressed by the user, the sub operating system is started instead of the main operating system, and the TV application program is automatically executed. The sub-operating system has only a minimum function for executing the AV function. For this reason, the time required for booting up the sub operating system is much shorter than the time required for booting up the main operating system. Therefore, the user can immediately watch / record TV by simply pressing the TV start button 7A.

  The computer 1 can receive and reproduce terrestrial digital TV broadcasts. An antenna terminal 10 for terrestrial digital TV broadcasting is provided on the right side of the computer main body 1.

  The DVD / CD start button 7B is a button for playing back video content recorded on a DVD or CD. When the DVD / CD activation button 7B is pressed by the user, a video reproduction application program for reproducing video content is activated. This video playback application program is also an application program that runs on the sub-operating system. When the DVD / CD start button 7B is pressed by the user, the sub operating system is started instead of the main operating system, and the video playback application program is automatically executed.

  Next, the system configuration of the computer 1 will be described with reference to FIG.

  As shown in FIG. 2, the computer 1 includes a CPU 11, a north bridge (NB) 12, a system memory 13, a south bridge (SB) 14, a graphics controller 15, a sound controller 16, a video enhancer 17, and a BIOS-ROM 18. , LAN controller 19, hard disk drive (HDD) 20, DVD drive (DVDD) 21, card controller 22, wireless LAN controller 23, IEEE 1394 controller 24, embedded controller (EC) 25, digital TV broadcast reception processing unit 26, and encryption A machine 27 is provided.

  The CPU 11 is a processor that controls the operation of the computer 1 and executes various application programs such as a main operating system / sub operating system and a TV application program loaded from the HDD 20 to the system memory 13. The CPU 11 also executes a system BIOS (Basic Input Output System) stored in the BIOS-ROM 18. The system BIOS is a program for hardware control.

  The NB 12 is a bridge device that connects the local bus of the CPU 11 and the SB 14. The NB 12 also includes a memory controller that controls access to the system memory 13. The NB 12 also has a function of executing communication with the graphics controller 15 via an AGP (Accelerated Graphics Port) bus, a PCI express standard serial bus, or the like.

  The graphics controller 15 is a display controller that controls the LCD 4 used as a display monitor of the computer 1. The video data generated by the graphics controller 15 is sent to the video enhancer 17 and is subjected to video processing (image quality adjustment processing) for improving the image quality of the video data. The video data whose image quality has been improved by the video enhancer 17 is sent to the LCD 4. Also, the video data with high image quality by the video enhancer 17 can be sent to an external TV monitor or HDMI monitor via a connector provided in the computer main body 1.

  The SB 14 controls each device on an LPC (Low Pin Count) bus and each device on a PCI (Peripheral Component Interconnect) bus. The SB 14 includes an IDE (Integrated Drive Electronics) controller for controlling the HDD 20 and the DVDD 21. Further, the SB 14 has a function of executing communication with the sound controller 16.

  The sound controller 16 is a sound source device, and outputs audio data to be reproduced to an external 5.1 channel speaker system connected via speakers 9A and 9B and a connector.

  The card controller 22 controls cards such as PC cards and SD (Secure Digital) cards. The wireless LAN controller 23 is a wireless communication device that performs wireless communication of, for example, the IEEE 802.11 standard. The IEEE 1394 controller 24 executes communication with an external device via an IEEE 1394 standard serial bus. The EC 25 is a one-chip microcomputer in which an embedded controller for power management and a keyboard controller for controlling the keyboard 5 and the touch pad 8 are integrated. The EC 25 has a function of powering on / off the computer 1 in accordance with the operation of the power button 6 by the user. Further, the EC 25 can also power on the computer 1 in accordance with the operation of the TV start button 7A and the DVD / CD start button 7B by the user.

  The digital TV broadcast reception processing unit 26 is a device that receives a digital broadcast program such as terrestrial digital TV broadcast, and is connected to the antenna terminal 10. The digital TV broadcast reception processing unit 26 includes a digital TV tuner 28 and an OFDM (Orthogonal Frequency Division Multiplexing) demodulator 29 as shown in the figure. The digital TV tuner 28 and the OFDM demodulator 29 function as a tuner module that receives broadcast program data of terrestrial digital TV broadcasting. In terrestrial digital TV broadcasting, MPEG2 is used as a compression encoding method for each broadcast program data (video, audio). Further, high definition HD (High Definition) is used as the video format.

  The digital TV broadcast reception processing unit 26 including the digital TV tuner 28 and the OFDM demodulator 29 receives a broadcast signal of a specific channel from the TV broadcast signals input from the antenna terminal 10 and receives the received TV broadcast. A transport stream (TS) is extracted from the signal. The transport stream is a stream in which broadcast content that has been compression-encoded is multiplexed. In terrestrial digital TV broadcasting, a plurality of programs are multiplexed for each channel (physical channel).

  The encryption device 27 decrypts the transport stream input from the digital TV broadcast reception processing unit 26, re-encrypts it using the encryption key shared with the TV application program, and transfers it to the system memory 13 via the PCI bus. To do. This re-encryption is performed in order to prevent the extracted broadcast program data from being reproduced even if the broadcast program data is illegally extracted via the PCI bus.

  That is, the computer 1 encrypts and transmits important data via a general-purpose interface such as a PCI bus. The computer 1 can update the encryption key used for the encryption at any timing on the transmission side without synchronization between the parties on the transmission side and the reception side, and on the reception side. This update can be followed, and this point will be described in detail below.

  In order to be able to update the encryption key at any timing on the transmission side and to follow the update on the reception side without synchronizing between the parties on the transmission side and the reception side, this computer 1 is based on the premise that the transmission side adds verification data for verifying the validity of the received data on the reception side to the transmission data. First, referring to FIG. 3, the encryption executed by the computer 1 is performed. The basic operation principle of data communication will be described.

  FIG. 3 is a functional block diagram for explaining the basic operation principle of encrypted data communication executed between the encryption device 27 and the TV application program via the PCI bus which is a general-purpose interface. The transmitter 100 in the figure corresponds to the encryption device 27, and the receiver 200 corresponds to the TV application program.

  The transmitter 100 and the receiver 200 have an authentication processing unit that performs an authentication process for establishing an encrypted data communication path. There is no particular restriction on the timing of performing this authentication process, and when the authentication process ends normally, a session key is generated in each authentication processing unit. For example, when the encryption method is AES (Advanced Encryption Standard) -128 bits, the session key generated by the authentication processing unit is 128 bits. In this case, the data block to be encrypted is CBC (Cipher Block Chaining) encrypted in 128-bit units.

  The plain text data in the figure is data to be actually transferred, and here it is assumed to be 128-bit data. And in this embodiment, when transmitting this plaintext data from the transmitter 100 to the receiver 200, the session key produced | generated between the parties by an authentication process is utilized also as verification data. In this example, it is assumed that the session key data is 128-bit data.

  In the transmitter 100, the session key generated by the session key generation unit 101 is added to the head of the plaintext data as verification data. Then, the entire 256-bit data composed of the session key and the plaintext data is transferred to the encryption unit 102, and as a result, the CBC encryption is performed with the 128-bit key of the session key as a 256-bit data block. Become. In this example, the session key is added to the head of the plaintext data. However, the present invention is not limited to this, and for example, the session key may be added to the end.

  The encrypted data (encrypted data) is decrypted by the decryption unit 202 using the session key generated by the session key generation 201 in the transfer destination receiver 200. In addition, the session key extraction unit 203 extracts the first 128 bits from the decrypted data as verification data, that is, a session key. The session key verification unit 204 compares the session key extracted as the verification data by the session key extraction unit 203 with the session key generated by the session key generation unit 201, and there is no problem in the verification result. In this case, it is determined that the plaintext data after decryption is normal data.

  Next, referring to FIG. 4, in this computer 1 that executes cryptographic data communication according to such an operation principle, the operation principle of encryption key update that is executed without synchronization between the parties on the transmission side and the reception side. Will be described.

  In the figure, (A) shows the state of encryption data communication between the transmitter 100 and the receiver 200 before the encryption key is updated, and (B) shows the transmitter 100 and the receiver after the encryption key is updated. The state of encryption data communication between 200 is shown.

  First, the transmitter 100 uses the value of the session key (K1) generated by the authentication process performed with the receiver 200 as it is (K1a), and adds to the plaintext data and encrypts the entire data. Execute. Similarly, the receiver 200 also uses the value of the session key (K2) generated by the authentication process executed with the transmitter 100 as it is (K2a) to execute the above-described decryption and verification of the entire data.

  Here, for example, assume that the transmitter 100 updates the encryption key without any synchronization with the receiver 200 for some reason. In this case, the transmitter 100 uses the value obtained by replacing (processing) the upper and lower bits of the session key generated by the authentication process performed with the receiver 200 (K1b), and the plaintext described above. Append to data and encrypt entire data.

  Even when the encryption key is updated, the receiver 200 (not knowing that the encryption key has been updated) first receives the session key value generated by the authentication process performed with the transmitter 100. Is used as it is (K2a), and the above-described decoding and verification of the entire data is executed. Then, the verification result naturally has a problem, but at this point, the receiver 200 of the computer 1 tentatively determines that the transmitter 100 has updated the encryption key.

  When this determination is made, similarly to the transmitter 100, the receiver 200 uses a value obtained by exchanging the upper and lower bits of the session key generated by the authentication process performed with the transmitter 100 (K2b). ) Re-decrypt and verify the entire data as described above. If there is no problem in the verification result, the receiver 200 determines that the plaintext data after decryption is normal data and determines that the encryption key has been updated. As a result, the value (K2b) obtained by exchanging the upper and lower bits of the session key generated by the authentication process executed with the transmitter 100 is continued in the subsequent decoding and verification of the entire data. Will be used.

  On the other hand, if the verification result also has a problem, the receiver 200 determines that the decrypted plaintext data is abnormal data and discards the determination that the encryption key has been updated (process the session key). Disable). As a result, the session key value (K2a) generated by the authentication process executed with the transmitter 100 is used as it is for the subsequent decryption and verification of the data.

  That is, the transmitter 100 can update the encryption key according to a predetermined rule (here, the upper bit and the lower bit are interchanged) at any timing without synchronizing with the receiver 200. The device 200 can follow the update of the encryption key without synchronizing with the transmitter 100.

  When the encryption key is further updated after updating the encryption key shown in FIG. 4B, the upper and lower bits of the value used at that time are replaced, so that the initial session key value Will return. Therefore, the update of the encryption key is synonymous with the application of two types of values alternately. However, instead of selectively using two given values in advance, the second value from one value is used. The difference is that the value is derived according to a predetermined rule, and one of them follows the exchange timing by self-judgment without any exchange.

  Various rules can be applied as the rules for updating the encryption key held by the transmitter 100 and the receiver 200 in addition to the above-described replacement of the upper bits and the lower bits. For example, the session key is divided into m (if m = 4, divided every 32 bits, if m = 8, divided every 16 bits), and the array of m data after this division is shuffled according to a predetermined procedure. You may do it. Alternatively, a cyclic slide in which the entire value used at that time is moved, for example, by m bits to the upper side and the value existing in the upper m bits is rearranged to the lower m bits may be used as a rule. Depending on the rule, it is possible to derive two or more values from one value.

  FIG. 5 is a flowchart showing an operation procedure of the transmitter 100 during encrypted data communication.

  The transmitter 100 first determines whether or not it is necessary to change the encryption key when data is encrypted and transmitted (step A1). If there is a need to change (YES in step A1), the transmitter 100 processes the session key based on a predetermined rule (step A2).

  The transmitter 100 adds the existing or processed session key to the plaintext data (step A3), encrypts the plaintext data with the session key added using the session key (step A4), and The encrypted data is transmitted to the receiver 200 (step A5).

  FIG. 6 is a flowchart showing an operation procedure of the receiver 200 during encrypted data communication.

  When receiving the encrypted data from the transmitter 100 (step B1), the receiver 200 decrypts the encrypted data using the existing session key (step B2), and uses the decrypted data as verification data. A session key is extracted (step B3).

  Next, the receiver 200 checks whether or not the extracted session key matches the existing session key (step B4). If they match (YES in step B4), the received plaintext data is converted into normal data. (Step B5).

  On the other hand, if they do not match (NO in step B4), the receiver 200 processes the session key based on a predetermined rule (step B6), and decrypts the encrypted data using the processed session key. Re-execute (step B7). The receiver 200 extracts a session key as verification data from the decrypted data (step B8), and checks whether the extracted session key matches an existing session key (step B9). . If they match (YES in step B9), the receiver 200 determines the processing of the session key (step B10), and processes the received plaintext data as normal data (step B5). If they do not match (NO in step B9), the receiver 200 invalidates the processing of the session key (step B11), and processes the received plaintext data as abnormal data (step B12).

  As described above, the computer 1 according to the present embodiment can dynamically update the encryption key without synchronizing between the parties on the transmission side and the reception side. As a result, even if you continue to use the same session key, multiple values as encryption keys are derived from this session key, so you can limit the observation data obtained from third parties, Improve security level.

  In the above example, the session key is used as the verification data. However, in addition to the session key, for example, the hash value of plain text data, intermediate data generated in the process of generating the session key, etc. May be used as Furthermore, it is also possible to use a value predetermined between the sender and the receiver as verification data.

  That is, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The perspective view in the state which opened the display unit of the notebook type personal computer which concerns on embodiment of this invention The figure which shows the system configuration | structure of the computer of the embodiment Functional block diagram for explaining the basic operation principle of encrypted data communication executed between the encryption device and the TV application program via the PCI bus which is a general-purpose interface in the computer of the embodiment The figure for demonstrating the operation principle of the encryption key update performed without synchronizing between the party of a transmission side and a receiving side in the computer of the embodiment The flowchart which shows the operation | movement procedure by the side of the transmitter of the computer of the embodiment The flowchart which shows the operation | movement procedure by the side of the receiver of the computer of the embodiment

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Computer, 2 ... Computer main body, 3 ... Display unit, 4 ... LCD, 5 ... Keyboard, 6 ... Power button, 7 ... Input operation panel, 8 ... Touchpad, 9A, B ... Speaker, 10 ... Terrestrial digital TV Broadcasting antenna terminal, 11 ... CPU, 12 ... North bridge (NB), 13 ... System memory, 14 ... South bridge (SB), 15 ... Graphics controller, 16 ... Sound controller, 17 ... Video enhancer, 18 ... BIOS-ROM , 19 LAN controller, 20 hard disk drive (HDD), 21 DVD drive (DVDD), 22 card controller, 23 wireless LAN controller, 24 IEEE 1394 controller, 25 embedded controller (EC), 26 digital TV broadcast reception 27: Encryption machine, 28 ... Digital TV tuner, 29 ... OFDM demodulator, 100 ... Transmitter, 101 ... Session key generation unit, 102 ... Encryption unit, 200 ... Receiver, 201 ... Session key generation unit 202. Decryptor 203. Session key extraction unit 204. Session key verification unit

Claims (10)

In a data transmission / reception system in which a data transmission device and a data reception device encrypt and transmit data,
The data transmission device includes:
Authentication means for executing authentication processing for mutual confirmation with the data receiving device;
An encryption means for encrypting data using a session key generated by an authentication process of the authentication means as a common key;
The entire data obtained by adding the session key as verification data to the plaintext data to be transmitted is sent to the encryption means as transmission data, and the obtained encrypted data is subjected to authentication processing by the authentication means. Data transmitting means for transmitting to the data receiving device;
Processing means for processing the value of the session key used as a common key and verification data by the encryption means and the data transmission means based on a predetermined rule;
Comprising
The data receiving device is:
Authentication means for executing an authentication process for confirming each other with the data transmission device;
Data receiving means for receiving encrypted data from the data transmitting apparatus subjected to authentication processing by the authenticating means;
Decryption means for decrypting the encrypted data using a session key generated by the authentication process of the authentication means as a common key;
The session key added as verification data to the plaintext data to be received is extracted from the entire reception data decrypted by the decryption means, the value of the extracted session key and the value of the generated session key A first determination means for determining whether the plaintext data to be received is correct or not,
When the first determination means determines that the value is not correct, the generated session key value is processed based on a predetermined rule, and the encrypted data is decrypted using the processed session key as a common key. And re-extracting the session key added as verification data from the entire received data obtained thereby, and the re-extracted session key value and the processed session key A second determination unit that determines whether the plaintext data to be received is correct or not by comparing
A data transmission / reception system comprising:   2. The data transmission / reception system according to claim 1, wherein the predetermined rule is to divide the n-bit data indicating the value of the session key into two and to replace the upper bit and the lower bit.   The predetermined rule is that n-bit data indicating the value of the session key is divided into m, and the arrangement order of the m (n / m) bit data is changed in a predetermined procedure. The data transmission / reception system according to claim 1.   2. The data transmission / reception system according to claim 1, wherein the predetermined rule is to cyclically shift n-bit data indicating the value of the session key by m bits in a predetermined direction.   The said 2nd determination means of the said data receiving apparatus invalidates the process performed with respect to the said session key, when it determines that the plaintext data of the said reception object is not correct. Data transmission / reception system. A data transmission / reception method for a data transmission / reception system in which a data transmission device and a data reception device transmit / receive data by encrypting data,
The data transmission device includes:
An authentication step of performing an authentication process for confirming each other with the data receiving device;
An encryption step of encrypting data using a session key generated by the authentication process of the authentication step as a common key;
The entire data obtained by adding the session key as verification data to the plaintext data to be transmitted is encrypted as transmission data in the encryption step, and the obtained encrypted data is subjected to authentication processing by the authentication step. A data transmission step for transmitting to the data receiving device;
A processing step of processing the value of the session key used as a common key and verification data by the encryption step and the data transmission step based on a predetermined rule;
Comprising
The data receiving device is:
An authentication step of performing an authentication process for confirming each other with the data transmission device;
A data receiving step for receiving encrypted data from the data transmitting apparatus that has undergone the authentication process in the authentication step;
A decryption step of decrypting the encrypted data using a session key generated by the authentication process of the authentication step as a common key;
The session key added as verification data to the plaintext data to be received is extracted from the entire reception data decrypted by the decryption step, and the extracted session key value and the generated session key value are And a first determination step for determining whether the plaintext data to be received is correct or not,
If the first determination step determines that the value is not correct, the generated session key value is processed based on a predetermined rule, and the encrypted data is decrypted using the processed session key as a common key. And re-extracting the session key added as verification data from the entire received data obtained thereby, and the value of the re-extracted session key and the processed session key A second determination step that determines whether the plaintext data to be received is correct or not by comparing
A data transmission / reception method comprising:   7. The data transmission / reception method according to claim 6, wherein the predetermined rule is to divide the n-bit data indicating the value of the session key into two and to replace the upper bit and the lower bit.   The predetermined rule is that n-bit data indicating the value of the session key is divided into m, and the arrangement order of the m (n / m) bit data is changed in a predetermined procedure. The data transmission / reception method according to claim 6.   7. The data transmission / reception method according to claim 6, wherein the predetermined rule is to cyclically shift n-bit data indicating the value of the session key by m bits in a predetermined direction.   The said 2nd determination step of the said data reception apparatus invalidates the process performed with respect to the said session key, when it determines with the plaintext data of the said reception object being incorrect. Data transmission / reception method.

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