Data transmission system and data transmission method

A data transmission method comprising the steps of:

• transmitting in advance, to a terminal, one key to decrypt encrypted data obtained by encrypting data;
• generating a plurality of encrypted data by encrypting data with a plurality of keys;
• transmitting the generated encrypted data to the terminal;
• and
• decrypting the encrypted data by the terminal with the key transmitted in advance.

A data transmission server comprising:

• key storage means for storing a plurality of keys to encrypt data;
• encryption means for generating a plurality of encrypted data by encrypting data with the plurality of keys stored in said key storage means, concatenating the generated encrypted data, adding, to a start of concatenated encrypted data, a header containing encrypted-data start information serving as information representing a start position of each encrypted data, and generating concatenated encrypted data;
• key transmission means for transmitting in advance one key to decrypt one of the encrypted data generated by said encryption means;
• and
• encrypted-data transmission means for transmitting the concatenated encrypted data generated by said encryption means.

A data reception terminal comprising:

• data reception means for receiving concatenated encrypted data obtained by concatenating a plurality of encrypted data prepared by encrypting data, and adding, to a start of concatenated encrypted data, a header containing encrypted-data start information serving as information representing a start position of each encrypted data;
• key reception means for receiving one key transmitted in advance, the key being used to decrypt one of the encrypted data;
• and
• decryption means for decrypting, on the basis of the encrypted-data start information contained in the received concatenated encrypted data, encrypted data corresponding to the received key out of the encrypted data which are concatenated as the concatenated encrypted data.