FairPlay: Meaning (information, definition, explanation, facts)

FairPlay is Apple Computer's name for its digital rights management (DRM) built in to the QuickTime multimedia technology and used by the iPod, iTunes and the iTunes Music Store. Every file sold by the iTunes Music Store is protected by FairPlay. It digitally encrypts AAC audio files and prevents users from playing these files on unauthorized computers.

While the iTunes jukebox remains the most popular method to buy and play FairPlay protected files, the actual decoding is performed by Apple's QuickTime. In fact every QuickTime based player is capable of using these files, including RealPlayer and Media Player Classic.

FairPlay is rumored to have been based on technology created by the company Veridisc. Neither Apple, nor Veridisc have confirmed this.

Restrictions

FairPlay is considered to be one of the most reasonable DRM implementations currently available, since it is relatively user friendly, and not as restrictive as some other systems. However there will always be critics of any form of DRM; many feel that any restrictions at all are too many.

FairPlay will allow protected track to be used in the following ways:

• The protected track may be copied to any number of iPod portable music players.
• The protected track may be played on up to five (originally three) authorized computers.
• The protected track may be copied to a standard CD audio track any number of times. (The resulting CD has no DRM and may be re-converted to MP3, but this will aggravate the sound artifacts of encoding, since the resulting sound file will have been encoded twice).
• A particular playlist within iTunes containing a protected track can only be copied to a CD up to seven times (originally ten times) before the playlist must be changed.

FairPlay is a fairly simple implementation of common DRM techniques. FairPlay protected files are regular MP4 container files with an encrypted AAC audio stream. The audio stream is encrypted using the Rijndael 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 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 send 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 you authorize 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 that that particular user bought.

When you deauthorize 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 its 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.

At this time, it looks like the restrictions mentioned above are hard-coded into QuickTime and the iTunes application, and not configurable in the protected files itself.

In July 2004, RealNetworks introduced their Harmony technology. The Harmony technology is built into RealPlayer and allows users of the RealPlayer Music Store to play their songs on the iPod. Before the introduction of Harmony this was not possible, because the RealPlayer Music Store uses a different scheme, called Helix DRM, to protect their content. While using RealPlayer to transfer a Helix DRM protected song onto the iPod, Harmony transparently converts it to a FairPlay compatible protected file.

After the lauch of the iTunes Music Store efforts were made by various people to circumvent the encryption of the FairPlay protected files.

Jon Johansen - also known for his DeCSS program - was the first to discover a way to circumvent the DRM protection. The open source application QTFairUse intercepted the decrypted output and wrote it to a raw AAC file. Most media players do not support such raw files and the files had to be processed with a tool like faad to create normal files. One of the few media players that is able to play raw AAC files is Foobar2000.

The second time around, Johansen reverse engineered the encryption technique used in FairPlay and created an algorithm to completely remove the encryption without re-encoding the encrypted AAC stream. This method is currently used by VLC media player in order to play FairPlay protected tracks.

A software package named PlayFair - created by an anonymous author - has also appeared. It can remove the encryption from files using the FairPlay DRM mechanism. The author of Playfair also used the methods discovered by Jon Johansen and used by VLC. Apple's legal department forced Playfair to be first removed from SourceForge.net and then when the Indian open source web site Sarovar.org hosted the project they too were sent a cease and desist by Apple's lawyers. However, Playfair's successor Hymn is alive and well. Hymn is an acronym for "hear your music anywhere".

Jon Johansen himself also released a tool to remove the encryption called DeDRMS. Later on he released FairKeys which uses Apple’s own servers to retrieve the keys needed by DeDRMS.

All these applications have two things in common. First of all, they use the user keys from either the Apple servers, the iTunes key repository or the iPod key repository, which ensures they can only decrypt files that are legally bought. You cannot use these applications to decrypt files somebody else bought. And secondly, they keep the meta data inside the MP4 container intact, so it is possible to track down the user who originally bought the file after the file is decrypted.