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FairPlay is a digital rights management (DRM) technology created by Apple Inc., based on technology created by the company Veridisc. FairPlay is built into the QuickTime multimedia software and used by the iPhone, iPod, iPad, Apple TV, iTunes, iTunes Store and the App Store. Formerly, all songs in the iTunes Store were encoded with FairPlay. Apple later started offering a selection of songs, that after an additional 30 cents per song is charged, could be downloaded FairPlay-free.〔(【引用サイトリンク】accessdate=June 22, 2011 )〕 Apple no longer sells individual songs or albums with FairPlay encryption from the iTunes store. However, apps downloaded from the iTunes store and Apple Music subscription songs saved for offline listening are still encrypted with FairPlay.〔(【引用サイトリンク】url=http://theiphonewiki.com/wiki/Copy_Protection_Overview )〕 FairPlay digitally encrypts AAC audio files and prevents users from playing these files on unauthorized computers. The majority of FairPlay-encrypted content is purchased through the iTunes Store, using the iTunes software. The iTunes software relies on Apple's QuickTime multimedia software for decoding and playback of the encrypted files. Every media player capable of using QuickTime is capable of playing back FairPlay-encrypted files, including RealPlayer, JRiver Media Center, Media Player Classic and Songbird. ==How it works== FairPlay-protected files are regular MP4 container files with an encrypted AAC audio stream. The audio stream is encrypted using the AES algorithm in combination with MD5 hashes. The master key required to decrypt the encrypted audio stream is also stored in encrypted form in the MP4 container file. The key required to decrypt the master key is called the "user key". Each time a new customer uses iTunes to buy a track, a new random user key is generated and used to encrypt the master key. The random user key is stored, together with the account information, on Apple’s servers, and also sent to iTunes. iTunes stores these keys in its own encrypted key repository. Using this key repository, iTunes is able to retrieve the user key required to decrypt the master key. Using the master key, iTunes is able to decrypt the AAC audio stream and play it. When a user authorizes a new computer, iTunes sends a unique machine identifier to Apple’s servers. In return, it receives all the user keys that are stored with the account information. This ensures that Apple is able to limit the number of computers that are authorized and makes sure that each authorized computer has all the user keys that are needed to play the tracks they bought. When a user deauthorizes a computer, iTunes will instruct Apple’s servers to remove the unique machine identifier from their database, and at the same time it will remove all the user keys from the deauthorized computer's encrypted key repository. The iPod also has its own encrypted key repository. Every time a FairPlay-protected track is copied onto the iPod, iTunes will copy the user key from its own key repository to the key repository on the iPod. This makes sure that the iPod has everything it needs to play the encrypted AAC audio stream. FairPlay does not affect the ability of the file itself to be copied. It only manages the decryption of the audio content. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「FairPlay」の詳細全文を読む スポンサード リンク
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