Trading system and recording medium

1. A trading system comprising a first computer apparatus that a seller of contents consisting of sounds or images uses and a second computer apparatus that a purchaser of the contents uses, wherein

the first computer apparatus comprises a first processor which

generates a private contents key randomly selected from integers using a cryptographically-secure random number;

encrypts the contents using the private contents key; and

generates a public contents key by applying a hash function to the private contents key,

and the second computer apparatus comprises a second processor which

acquires the public contents key and an encrypted contents; and

publishes a first transaction which executes a process of delivering crypto assets on a condition of publication to a distributed ledger of the private contents key to which the public contents key is generated by applying the hash function, the first transaction including the public contents key,

wherein

the first processor further receives the crypto assets by publishing to the distributed ledger a second transaction for receiving the crypto assets, when the first transaction is published to the distributed ledger, the second transaction including the private contents key, and

the second processor further acquires the private contents key, when the second transaction is published, to decode the encrypted contents using the private contents key.

2. A trading system comprising a first computer apparatus that a seller of contents consisting of sounds or images uses and a second computer apparatus that a purchaser of the contents uses, wherein

the first computer apparatus comprises a first processor which generates a private contents key randomly selected from integers using a cryptographically-secure random number;

encrypts the contents using the private contents key; and

generates a public contents key by scalar multiplication of a base point on a group for which a discrete logarithm problem is intractable, by the private contents key,

and the second computer apparatus comprises a second processor which

acquires the encrypted contents;

generates a temporary key selected from integers; and

transmits to the first computer apparatus the generated temporary key,

wherein

the first processor further receives the temporary key from the second computer apparatus,

the second processor publishes a first transaction which executes a process of delivering crypto assets on a condition of publication of argument information that enables derivation of the private contents key that is a sum of or a difference between the temporary key and the private contents key,

the first processor calculates the argument information using the generated private contents key and the received temporary key,

the first processor further receives the crypto assets by publishing to a distributed ledger a second transaction for receiving the crypto assets, when the first transaction is published to the distributed ledger, the second transaction including the argument information, and

the second processor further acquires the argument information, when the second transaction is published to the distributed ledger, calculates the private contents key using the acquired argument information and the generated temporary key, and decodes the encrypted contents using the calculated private contents key.

3. A trading system comprising a first computer apparatus that a seller of contents consisting of sounds or images uses and a second computer apparatus that a purchaser of the contents uses, wherein

the first computer apparatus comprises a first processor which

separates the contents to which frequency separation is performed into high frequency components and low frequency components;

encrypts the high frequency components using a private contents key randomly selected from integers using a cryptographically-secure random number,

and the second computer apparatus comprises a second processor which

acquires the low frequency components and the encrypted high frequency components;

decompress the low frequency components to enable the decompressed low frequency components to be confirmed, and;

when the decompressed low frequency is confirmed to be low frequency components of the contents, publishes a first transaction which executes a process of delivering crypto assets on a condition that the private contents key is published to a distributed ledger,

wherein

the first processor further receives the crypto assets by publishing to the distributed ledger a second transaction for receiving the crypto assets, when the first transaction is published to the distributed ledger, the second transaction including the private contents key, and

the second processor further acquires the private contents key, when the second transaction is published, and to decode the encrypted high frequency components using the private contents key so as to decompress the whole contents.

4. A trading method executed by a trading system comprising a first computer apparatus comprising a first processor that a seller of contents consisting of sounds or images uses and a second computer apparatus comprising a second processor that a purchaser of the contents uses, the method comprising:

generating, by the first processor, a private contents key randomly selected from integers using a cryptographically-secure random number;

encrypting, by the first processor, the contents using the private contents key;

generating, by the first processor, a public contents key by applying a hash function to the private contents key;

acquiring, by the second processor, the public contents key and an encrypted contents; and

publishing, by the second processor, a first transaction which executes a process of delivering crypto assets on a condition of publication to a distributed ledger of the private contents key to which the public contents key is generated by applying the hash function, the first transaction including the public contents key;

the method further comprising:

further receiving, by the first processor, the crypto assets by publishing to the distributed ledger a second transaction for receiving the crypto assets, when the first transaction is published to the distributed ledger, the second transaction including the private contents key, and

further acquiring, by the second processor, the private contents key, when the second transaction is published, to decode the encrypted contents using the private contents key.

5. A trading method executed by a trading system comprising a first computer apparatus comprising a first processor that a seller of contents consisting of sounds or images uses and a second computer apparatus comprising a second processor that a purchaser of the contents uses, the method comprising:

generating, by the first processor, a private contents key randomly selected from integers using a cryptographically-secure random number;

encrypting, by the first processor, the contents using the private contents key; and

generating, by the first processor, a public contents key by scalar multiplication of a base point on a group for which a discrete logarithm problem is intractable, by the private contents key;

acquiring, by the second processor, the encrypted contents;

generating, by the second processor, a temporary key selected from integers; and

transmitting, by the second processor, to the first computer apparatus the generated temporary key,

the method further comprising:

further receiving, by the first processor, the temporary key from the second computer apparatus;

publishing, by the second processor, a first transaction which executes a process of delivering crypto assets on a condition of publication of argument information that enables derivation of the private contents key that is a sum of or a difference between the temporary key and the private contents key;

calculating, by the first processor, the argument information using the generated private contents key and the received temporary key;

further receiving, by the first processor, the crypto assets by publishing to a distributed ledger a second transaction for receiving the crypto assets, when the first transaction is published to the distributed ledger, the second transaction including the argument information; and

further, by the second processor, acquiring the argument information, when the second transaction is published to the distributed ledger, calculating the private contents key using the acquired argument information and the generated temporary key, and decoding the encrypted contents using the calculated private contents key.

6. A trading method executed by a trading system comprising a first computer apparatus comprising a first processor that a seller of contents consisting of sounds or images uses and a second computer apparatus comprising a second processor that a purchaser of the contents uses,

the method comprising:

separating, by the first processor, the contents to which frequency separation is performed into high frequency components and low frequency components; and

encrypting, by the first processor, the high frequency components using a private contents key randomly selected from integers using a cryptographically-secure random number;

acquiring, by the second processor, the low frequency components and the encrypted high frequency components;

decompressing, by the second processor, the low frequency components to enable the decompressed low frequency components to be confirmed; and

when the decompressed low frequency is confirmed to be low frequency components of the contents, publishing, by the second processor, a first transaction which executes a process of delivering crypto assets on a condition that the private contents key is published to a distributed ledger,

the method comprising:

further receiving, by the first processor, the crypto assets by publishing to the distributed ledger a second transaction for receiving the crypto assets, when the first transaction is published to the distributed ledger, the second transaction including the private contents key, and

further acquiring, by the second processor, the private contents key, when the second transaction is published, and to decode the encrypted high frequency components using the private contents key so as to decompress the whole contents.