Patent ID: 7380135

Claim:
A method of transmitting contents, which are to be received at a reception side where a portion of contents is previewed while the contents are not accessible for playing other than for a preview purpose, comprising the steps of: encrypting the contents by a first encryption key; generating information indicative of an elapsed time of the contents that indicates a relationship between positions on a time axis of the contents representing an amount of time that passes as the contents are played and a time count that accrues as a preview time when the contents are previewed; encrypting the first encryption key and the information indicative of an elapsed time of the contents by a second encryption key, thereby generating first encrypted information; encrypting the second encryption key and content-usage control information by a third encryption key, thereby generating second encrypted information, said content-usage control information indicating usage of the contents on the reception side; and transmitting the encrypted contents, the first encrypted information, and the second encrypted information to the reception side, wherein the information indicative of the elapsed time of the contents is arranged such that the time count indicates a first time length accrued as the preview time for passage of a predetermined time length on the time axis of the contents at a first portion of the contents, and indicates a second time length accrued as the preview time for passage of the predetermined time length on the time axis of the contents at a second portion of the contents, the first time length being different from the second time length wherein said first time length increases while said second time length decreases.