Recording media of many types, including semiconductor recording media, magnetic disks, optical disks, and magneto-optical disks, are used to record music content, video content, still picture content, and other types of digital data (referred to below as “content”).
In addition to small size and light weight, semiconductor recording media have seen rapid advances in storage capacity, speed, and price reduction in recent years, leading to widespread use in digital cameras, cell phones, portable music players, televisions, DVD recorders, and other products. Common examples of semiconductor recording media include SD Memory cards (R), memory sticks, and Compact Flash (R) media. Some semiconductor recording media, such as SD Memory cards, also have a copyright protection function and enable recording copyrighted content.
One method of storing content to semiconductor recording media using a copyright protection function is described next. Such semiconductor recording media have a protected memory area that can only be accessed after mutual authentication by the semiconductor recording medium and the reading device or writing device that is the host device, and an unprotected memory area that can be accessed without mutual authentication. Encrypted content is recorded in the unprotected memory area, and the key used to encrypt the content is stored in the protected memory area. See, for example, patent reference 1.
Content that is stored using the copyright protection function cannot be played back by an unauthenticated device that cannot be mutually authenticated. The content also cannot be used by simply copying the content stored in the unprotected memory area to a different card.
New applications for content using the copyright protection function of such semiconductor recording media continue to emerge. Users can rip content from music CDs purchased by the user, and can download content from the Internet. More specifically, using a personal computer connected to the Internet, users can purchase and download music, books, and other copyrighted content from on-line content providers, record the downloaded content to a semiconductor recording medium, and can listen to the music or read the book using the semiconductor recording medium and a compact semiconductor player.
In addition to using a personal computer connected to the Internet, users can also purchase content through electronic terminals (digital kiosks) installed in specific fixed locations such as convenience stores, other types of businesses, and even train stations. Because such applications are particularly convenient for the user and afford an expanded sales network for the providers, the type of content and the user environment continue to evolve.
Various recording standards based on the type of semiconductor recording medium and the type of content have been defined for recording copyrighted content to semiconductor recording media, and the recording device records the content according to the standard. This enables any device conforming to the standard to read and write content to the semiconductor recording medium.
Using a music application program by way of example, the content of a song is encrypted using an encryption key, and the key and the encrypted content are stored to the semiconductor recording medium.
Patent reference 2 teaches a semiconductor recording medium for storing a plurality of encryption keys in a predetermined order in a protected memory area that can only be accessed by mutual authentication of the semiconductor recording medium and the host device, and storing encrypted content and corresponding management information in an unprotected memory area. This semiconductor recording medium protects music content from unauthorized decryption (decoding) while still enabling changing the play-back sequence of individual tracks and deleting selected tracks, and thus affords great convenience.
[Patent reference 1] Japanese Patent 3389186
[Patent reference 2] Japanese Unexamined Patent Appl. Pub. 2001-249695