Patent ID: 7688860

Claim:
A data transmission apparatus for transmitting data protected by a copyright protection mechanism for inhibiting simultaneous existence of data at both of a source and a sink of the movement, to a first apparatus via a computer network, the data transmission apparatus comprising: a key exchange unit that exchanges an encryption key with a second apparatus, the encryption key being used for encrypting and decrypting the data; a first control unit that transmits information for performing the key exchange by the second apparatus; a second control unit that transmits a first packet having a header section configured to indicate that data contained in a data section of the first packet is encrypted and that a size of the data section is zero, to the first apparatus after the transmission of the information by the first control unit; and a third control unit that staffs to transmit a second packet having a header section and a data section containing encrypted data provided by encrypting the data to be transmitted, to the first apparatus after completion of the key exchange performed by the key exchange unit.