JP2014212474A - Secret key distribution method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent security degradation in performing communication.SOLUTION: A communication method uses a communication medium storing a secret key and a communication terminal to encrypt data stored in the communication terminal and transmit the encrypted data to an external communication terminal. The method includes the steps of: acquiring random number information previously used in the communication medium; encrypting the secret key stored in the communication medium by using the random number information previously used; generating next random number information to be used, in the communication medium; transmitting the encrypted secret key and the next random number information to be used to the communication terminal from the communication medium; acquiring random number information which is previously used and stored in the communication terminal; decrypting the encrypted secret key by using the acquired random information that is previously used to acquire the secret key, in the communication terminal; and storing the acquired next random information to be used, in the communication terminal.

Description

  The present invention relates to a method for distributing a secret key used for data encryption.

Conventionally, data is encrypted and transmitted / received (Patent Documents 1, 2, etc.).
Examples of the encryption method include a common key encryption method and a public key encryption method. The common key encryption method is a method in which encryption and decryption are performed with the same key, and DES (Data Encryption Standard) is known as a typical one. The public key scheme is a scheme for encrypting and decrypting data using two keys, a public key and a secret key, and RSA (Rivest Shamir Adleman) is known as a representative one.

The public key method uses two types of keys as a pair, uses a key opened to an unspecified person as a key for encryption, and uses a specific key as a key for decryption. This is a method that uses a secret key for a key that can only be used by people. In the RSA system, it is also possible to sign with a private key and verify the signature with a public key.
In the common key method, the common key must be distributed to the side that encrypts and transmits data and the side that receives and decrypts the data in a secure state. There is an advantage that the key does not need to be communicated to anyone, and the public key does not need to be considered for security and can be distributed to anyone.

When transmitting and receiving data encrypted between a plurality of terminals, for example, as shown in FIG. 2, a server storing the secret keys of the plurality of terminals is provided. It is known to obtain a secret key and encrypt / decrypt data.
However, this method has a problem of secret key leakage due to interception between the server and the terminal.

Also, a method is known in which a secret key is stored in a security device such as an IC card, and the terminal obtains the secret key from the IC card when the terminal tries to use the secret key. With this method, it is possible to prevent leakage of the secret key on the net.
However, even in this method, there is a possibility that the secret key may be leaked by intercepting communication between the terminal and the IC card.

JP 61-163746 A Japanese Patent Laid-Open No. 02-095042

  In view of the above circumstances, an object of the present invention is to provide a technique for suppressing a decrease in security that occurs when performing communication. That is, an object of the present invention is to provide a technique for reducing the risk of secret key leakage in data communication using an encryption technique using a secret key.

  The present invention is a communication method for encrypting data stored in a communication terminal using a communication medium storing a secret key and the communication terminal, and communicating with the external communication terminal. The communication method is stored in the communication medium. Generating the previously used random number information, encrypting the secret key stored in the communication medium using the previously used random number information, and generating the next random number information to be used on the communication medium A step, a step of transmitting a secret key encrypted in a communication medium and random number information to be used next time to the communication terminal, a step of acquiring previously used random number information stored in the communication terminal, and a communication terminal, Decrypting the encrypted private key using the previously used random number information to obtain the private key, and storing the obtained random number information to be used next time at the communication terminal. And delivery method of the private key and said Rukoto.

  In addition, there are a plurality of previously used random number information stored in the communication medium and a plurality of previously used random number information stored in the communication terminal, and the encryption of the secret key is performed using the plurality of random number information, The secret key is decrypted using a plurality of pieces of random number information.

  Further, the acquired secret key is stored in a volatile memory in the communication terminal.

  According to the present invention, it is possible to suppress a decrease in security that occurs when performing communication. That is, in data communication using an encryption technique using a secret key, it becomes possible to reduce the risk of leakage of the secret key.

Schematic which shows an example of a structure of the communication system used for this invention. Schematic which shows an example of a structure of the conventional communication system. The schematic block diagram which shows an example of a structure of the communication system used for this invention. The sequence diagram which shows an example of the communication method of this invention. The sequence diagram which shows an example of the communication method of this invention.

Hereinafter, the present invention will be described with reference to the drawings.
FIG. 3 is a schematic block diagram showing an example of the configuration of the communication system of the present invention. In FIG. 3, the communication terminal 10, the IC card 20, and the external communication terminal 30 are provided.
The communication terminal 10 is configured using an information processing device. The communication terminal 10 performs communication when the IC card 20 is brought closer. The communication terminal 10 communicates with the external communication terminal 30 through a line.
The IC card 20 includes a storage circuit inside. The IC card 20 receives a radio signal from the communication terminal 10 and transmits a radio signal including ID information to the communication terminal 10. Although an IC card is used as an example of the communication medium here, a memory having a security area in which a secret key can be stored, such as a memory mounted with an IC chip or a mobile phone, may be used.

Next, functional configurations of the communication terminal 10, the IC card 20, and the external communication terminal 30 will be described. First, the functional configuration of the communication terminal 10 will be described.
The communication terminal 10 includes a CPU (Central Processing Unit) connected via a bus, a memory, an auxiliary storage device, and the like, and executes an authentication program. By executing the authentication program, the communication terminal 10 functions as a device including an input unit, a control unit, an interface, a communication unit, a storage unit, an output unit, an encryption unit, a decryption unit, and the like. Note that all or a part of each function of the communication terminal 10 may be implemented by hardware such as ASIC (Application Specific Integrated Circuit), PLD (Programmable Logic Device), or FPGA (Field Programmable Gate Array). The authentication program may be recorded on a computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, or a storage device such as a hard disk built in the computer system. Further, the authentication program may be transmitted / received via a telecommunication line.

The input unit is configured using an existing input device such as a keyboard, a pointing device (mouse, tablet, etc.), a button, and a touch panel. The input unit is operated by the user when inputting a user instruction to the authentication terminal. The input unit may be an interface for connecting the input device to the communication terminal 10. In this case, the input unit inputs an input signal generated in response to a user input in the input device to the communication terminal 10.
The control unit controls the operation of the communication terminal 10.

  The interface transmits and receives radio signals to and from the IC card 20 in accordance with instructions from the control unit.

The operation unit performs operations such as encryption and decryption. In the encryption / decryption operation, the encrypted information is decrypted and the data is encrypted. For example, the encrypted information including the secret key transmitted from the IC card 20 is decrypted, or the encrypted information including the secret key transmitted from the IC card 20 is decrypted and transmitted from the transmission partner using the extracted secret key. The received data is decrypted, or information such as data to be transmitted to the external communication terminal is encrypted using the public key of the transmission partner obtained from the transmission partner.
Further, in the signature operation, the encryption information including the secret key transmitted from the IC card 20 is decrypted, or the encryption information including the secret key transmitted from the IC card 20 is decrypted and the secret key and the data extracted A signature is generated by calculating a hash value, or signature verification is performed using the public key of the transmission partner acquired from the transmission partner of the data transmitted from the transmission partner.

The storage unit is configured using a storage device such as a magnetic hard disk device or a semiconductor storage device. The storage unit stores random number information for decrypting the encrypted secret key, data to be transmitted to the external communication terminal, and the like.
The random number information can be stored in association with the ID number of the IC card. Further, it can be stored in association with the generated time. Furthermore, a plurality of random numbers received in the past can be stored.

  The memory unit stores the secret key obtained by decrypting the encrypted secret key received from the IC card 20 by the decryption unit. Since it is necessary to sufficiently consider the security of this secret key, not only is it discarded when the communication terminal 10 cannot recognize the IC card 20, but also the secret in the memory when communication with the external terminal 30 is completed. Discard the key.

  The output unit outputs operation instructions and error messages to the user via an output device (not shown) connected to the communication terminal 10. The output device may be configured using, for example, a device that outputs images and characters on a screen. For example, the output device can be configured using a CRT (Cathode Ray Tube), a liquid crystal display, an organic EL (Electro-Luminescent) display, or the like. In addition, the output device may be configured using a device that converts characters into speech and outputs the speech. In this case, the output device can be configured using a voice synthesizer and a voice output device (speaker).

The communication unit transmits and receives radio signals to and from an external communication terminal in accordance with instructions from the control unit.
Data can be transmitted to the external communication terminal by using transmission / reception of the radio signal. The data includes data encrypted by the communication terminal 10.

Next, the functional configuration of the IC card 20 will be described.
The IC card 20 includes a control unit, a communication unit, a ROM (Read Only Memory), a RAM (Random Access Memory), an authentication information storage unit, an encryption unit, and a random number generation unit. The functional units of the IC card 20 are connected to each other via a bus.

The control unit controls the operation of the IC card 20. The control unit instructs the random number generation unit to generate a random number when the encrypted information including the Nth secret key is transmitted. For example, the control unit generates a random number (hereinafter referred to as “next random number”) used for the encrypted information including the (N + 1) th secret key when transmitting the encrypted information including the Nth secret key. Instruct.
The interface transmits and receives radio signals to and from the communication terminal 10 in accordance with instructions from the control unit.
The ROM is a read-only memory and stores a program for operating the IC card 20.

The RAM is a read / write memory that stores various information. A program read from the ROM is expanded in the RAM. The RAM stores various data generated by executing the program. The RAM temporarily stores data transmitted from the communication terminal 10. The RAM stores a PIN counter. The PIN counter is a counter used for PIN verification.
The storage unit is configured by using a storage device such as a flash memory or a nonvolatile semiconductor memory such as an EEPROM (Electrically Erasable Programmable Read-Only Memory). The storage unit stores information related to the secret key and the like.
Note that random number information generated by a random number generation unit to be described later can also be stored. The random number information can be stored in association with the ID number of the communication terminal. Further, it can be stored in association with the generated time. Furthermore, a plurality of random numbers received in the past can be stored.

  The calculation unit performs calculation. Specifically, the calculation unit encrypts information such as a secret key stored in the storage unit using a random number generated by a random number generation unit described later. For example, encryption is performed using DES (Data Encryption Standard) to generate DES encryption information.

  The random number generation unit generates a random number in accordance with an instruction from the control unit. For example, the random number generation unit generates a next random number (authentication information) in accordance with an instruction from the control unit.

  The external communication terminal 30 includes a CPU, a memory, an auxiliary storage device, and the like, and executes an authentication program. By executing the authentication program, the communication terminal 10 functions as a device including an input unit, a control unit, a communication unit, a storage unit, an output unit, a calculation unit, an interface, a memory, and the like.

The storage unit can store a public key that is paired with the above-described secret key.
The communication unit receives data transmitted from the communication terminal 10. The arithmetic unit can decrypt the received encrypted data and verify the signature.

FIG. 4 is a sequence diagram showing an example of the communication method of the present invention. Here, data encryption communication will be described as an example.
First, when the user brings the IC card 20 close to the communication terminal 10 and authentication is established, transmission / reception of a secret key is started (step S101). If authentication is not established, error processing is performed.

A known method can be used for authentication of the communication terminal 10 and the IC card 20. For example, a method using a PIN or the like can be used, and mutual authentication using an encryption method using a common key such as DES can also be used. Further, a method may be used in which random number information used for encryption is updated every time and a random number to be used next time is shared in advance.
The communication terminal 10 and the IC card 20 can be linked in advance. In this way, the IC card 20 can store random number information used for a plurality of terminals and set random number information described later for each terminal.

  When the authentication is established, the transmission / reception of the Nth encrypted private key is started by requesting the private key from the communication terminal 10 (step S102). When communication is started, the control unit of the IC card 20 acquires a random number (previous random number) generated at the time of transmission / reception of the previous (N-1th) secret key and a secret key stored in the storage unit ( Steps S103 and 104). Then, the secret key is encrypted using the previously generated random number (step S105). Note that the encryption of the private key is not performed after the authentication with the current communication terminal is established, but after the random number is generated when the previous encrypted private key is transmitted and received, and stored in the storage unit. You can also.

  Next, the control unit of the IC card 20 instructs the random number generation unit to generate a random number. The random number generation unit generates a random number to be used for the next time (Nth time) in accordance with an instruction from the control unit (step S106). The control unit transmits the secret key encrypted through the interface and the generated random number to be used next time (next random number) to the communication terminal 10 (step S107).

The interface of the communication terminal 10 receives the encrypted secret key transmitted from the IC card 20 and the generated random number to be used next time (step S108).
The received random number is stored in the storage unit.

  Next, the control unit of the communication terminal 10 obtains the random number (previous random number) received when receiving the previous (N-1th) encrypted secret key from the storage unit (step S109). Then, the computerized unit of the communication terminal 10 decrypts the received encrypted secret key using the acquired previous random number, and acquires the secret key (step S110). The acquired secret key is preferably stored in a volatile memory such as a RAM of the memory unit. This is because if stored in the non-volatile memory, there is a risk that the secret key will be leaked when the communication terminal is illegally accessed such as hacking.

  By doing in this way, even if the encrypted secret key and random number transmitted / received between the communication terminal 10 and the IC card 20 in the N-th authentication are wiretapped, the encrypted secret is encrypted with this random number. Since the key cannot be decrypted, security problems such as “spoofing” can be eliminated.

On the other hand, the external communication terminal 30 acquires data (send data) to be sent to the communication terminal 10 (step S111). Then, a public key paired with the secret key is acquired (step S112). The public key can be obtained by a known method. For example, the public key can be obtained via a network from a terminal such as a server in which the public key is stored.
Then, the sent data is encrypted with the acquired public key (step S113). Next, the encrypted sending data is transmitted to the communication terminal 10 (step S114).

  The communication terminal 10 receives the encrypted sending data (step S115), and decrypts it using the secret key acquired in step 110 (step S116).

FIG. 5 is a sequence diagram showing another example of the communication method of the present invention. Here, verification of signature data will be described as an example.
Steps 101 to 110 are the same as in the example of FIG.

When the private key is obtained in step 110, signature data is obtained (step S111). The signature data may be acquired before acquiring the secret key.
A copy of the acquired signature data is created, and one is calculated using the secret key acquired in step 110. Both the calculated signature and the non-calculated signature are transmitted to the external communication terminal 30 (step S113).

On the other hand, the external communication terminal 30 acquires a public key paired with the secret key (step S114).
Then, the calculated signature data and the uncalculated signature data are received from the communication terminal 10 (step S115). The calculated signature data is calculated using the public key acquired in step 114, and the signature data that has not been calculated is verified by verification (steps S116 and S116).

When the secret key is encrypted using a random number in the IC card, it may be encrypted using a plurality of random numbers received in the past. These random numbers may be calculated and used. For example, a value obtained by adding random numbers transmitted / received one time before and twice before is used.
In addition, when a secret key encrypted using a random number is transmitted to the communication terminal, it can be transmitted together with the time information generated by the random number used. In this case, the communication terminal can collate the received random number generation time information with the stored generation time of the previously received random number information, and decrypt the encrypted secret key if they match. It is regarded as valid random number information, and the secret key can be decrypted using this random number.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

Claims (3)

A communication method for encrypting data stored in a communication terminal and communicating with an external communication terminal using a communication medium storing a secret key and a communication terminal,
Obtaining previously used random number information stored in a communication medium;
Encrypting the private key stored in the communication medium using random number information previously used;
Generating random number information to be used next time on the communication medium;
Transmitting a secret key encrypted with a communication medium and random number information to be used next time to the communication terminal;
Obtaining previously used random number information stored in the communication terminal;
Decrypting the encrypted secret key using the previously used random number information and acquiring the secret key at the communication terminal; and
In the communication terminal, storing the acquired random number information to be used next time;
A secret key delivery method characterized by comprising: There are a plurality of previously used random number information stored in the communication medium and a plurality of previously used random number information stored in the communication terminal,
Private key encryption is performed using multiple pieces of random number information,
2. The secret key delivery method according to claim 1, wherein the secret key is decrypted using a plurality of pieces of random number information.   3. The secret key delivery method according to claim 1, wherein the acquired secret key is stored in a volatile memory in the communication terminal.

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