Terminal device, computer program, communication system, and communication method

1 . A terminal device that performs communication with an external device through a broker based on a publish-subscribe message model, the terminal device comprising: a processor; and a memory including a program that, when executed by the processor, causes the processor to perform functions, the functions including: acquiring external data; encrypting at least a part of the external data to generate cipher message data including ciphertext; generating topic designation data of plaintext, the topic designation data including pattern identification data; and distributing an encrypted publish message including the topic designation data of the plaintext and the cipher message data to the broker, the pattern identification data identifying an arrangement pattern of the ciphertext in the encrypted publish message, wherein the cipher message data is a data string including the ciphertext in which at least one of a plurality of types of the external data is encrypted.

2 . The terminal device according to claim 1 ,

wherein the external data includes first external data and second external data,

wherein the processor is capable of generating the cipher message data including the plaintext and the ciphertext by keeping the first external data in plaintext and encrypting the second external data, and

wherein the processor is further capable of generating the cipher message data by encrypting the first external data and the second external data by a method in which at least one of an encryption rule or an encryption key is different from each other.

3 . The terminal device according to claim 1 , wherein the functions further include:

determining whether an encryption condition is satisfied,

wherein, when the processor determines that the encryption condition is satisfied, the processor generates the cipher message data and distributes the encrypted publish message to the broker, and

wherein, when the processor determines that the encryption condition is not satisfied, the processor distributes a non-encrypted publish message including the topic designation data of the plaintext and message data of the plaintext to the broker.

4 . The terminal device according to claim 3 , wherein the

pattern identification data identifies the arrangement pattern of the ciphertext in each of the encrypted publish message and the non-encrypted publish message and is included in the topic designation data.

5 . The terminal device according to claim 1 , wherein the functions further include:

generating encryption rule data including at least one of a decryption rule for decrypting the cipher message data or an encryption key,

wherein the processor distributes the encrypted publish message including the topic designation data and the encryption rule data to the broker.

6 . The terminal device according to claim 5 ,

wherein the encryption rule data includes the decryption rule, the encryption key, and a delimiter which is a delimiter separating the decryption rule and the encryption key and is a plurality of character strings.

7 . The terminal device according to claim 6 , wherein the functions further include:

determining whether an encryption change condition is satisfied,

wherein, when the processor determines that the encryption change condition is satisfied, the processor generates new encryption rule data, which is obtained by changing at least one of the decryption rule, the encryption key, or the delimiter.

8 . The terminal device according to claim 7 ,

wherein the processor determines whether each of a first encryption change condition and a second encryption change condition, which is more frequently satisfied than the first encryption change condition, is satisfied,

wherein, when the processor determines that the first encryption change condition is satisfied, the processor generates new first encryption rule data obtained by changing at least one of the decryption rule or the encryption key, and

wherein, when the processor determines that the second encryption change condition is satisfied, the processor generates new second encryption rule data, which is obtained by changing the delimiter.

9 . The terminal device according to claim 1 , wherein the ciphertext includes confidential external data and the plaintext includes public data.

10 . The terminal device according to claim 9 , wherein

the confidential external data includes personal data,

the personal data includes at least one of a body temperature, a pulse, or location data of a person, and

the public data includes weather data.

11 . A non-transitory computer readable medium containing a computer program that causes a computer, provided in a terminal device that performs communication with an external device through a broker based on a publish-subscribe message model, to execute functions, the functions comprising:

acquiring external data;

encrypting at least a part of the external data to generate cipher message data including ciphertext;

generating topic designation data of plaintext, the topic designation data including pattern identification data;

generating an encrypted publish message including the topic designation data of the plaintext and the cipher message data, the pattern identification data identifying an arrangement pattern of the ciphertext in the encrypted publish message; and

distributing the encrypted publish message to the broker,

wherein the cipher message data is a data string including the ciphertext in which at least one of a plurality of types of the external data is encrypted.

12 . A communication system that performs communication based on a publish-subscribe message model between a plurality of terminal devices through a broker, the communication system comprising:

the plurality of terminal devices; and

the broker,

wherein at least a first one of the plurality of terminal devices:

acquires external data;

encrypts at least a part of the external data to generate cipher message data including ciphertext;

generating topic designation data of plaintext, the topic designation data including pattern identification data; and

distributes an encrypted publish message including the topic designation data of the plaintext and the cipher message data to the broker, the pattern identification data identifying an arrangement pattern of the ciphertext in the encrypted publish message,

wherein at least a second one of the plurality of terminal devices, which is different from the first one of the plurality of terminal devices:

subscribes to the encrypted publish message from the broker; and

decrypts the cipher message data included in the encrypted publish message, and

wherein the cipher message data is a data string including the ciphertext in which at least one of a plurality of types of the external data is encrypted.

13 . A communication method for performing communication based on a publish-subscribe message model between a plurality of terminal devices through a broker, the communication method comprising:

by at least a first one of the plurality of terminal devices, which conducts a publishing process:

acquiring external data;

encrypting at least a part of the external data to generate cipher message data including ciphertext;

generating topic designation data of plaintext, the topic designation data including pattern identification data;

generating an encrypted publish message including the topic designation data of the plaintext and the cipher message data, the pattern identification data identifying an arrangement pattern of the ciphertext in the encrypted publish message; and

distributing the encrypted publish message generated by the data generation process to the broker; and

by at least a second one of the plurality of terminal devices, which is different from the first one of the plurality of terminal devices and which conducts a subscribe process:

subscribing to the encrypted publish message from the broker; and

decrypting the cipher message data included in the encrypted publish message,

wherein the cipher message data is a data string including the ciphertext in which at least one of a plurality of types of the external data is encrypted.