Remote Audio Output Protocol (RAOP) is an

Internet streaming Streaming media is multimedia that is delivered and consumed in a continuous manner from a source, with little or no intermediate storage in network elements. ''Streaming'' refers to the delivery method of content, rather than the content it ...

protocol based on

RTSP The Real Time Streaming Protocol (RTSP) is an application-level network protocol designed for multiplexing and packetizing multimedia transport streams (such as interactive media, video and audio) over a suitable transport protocol. RTSP is us ...

/ RTP authored by

Apple Inc. Apple Inc. is an American multinational technology company headquartered in Cupertino, California, United States. Apple is the largest technology company by revenue (totaling in 2021) and, as of June 2022, is the world's biggest company b ...

It powers the

AirPlay Airplay is how frequently a song is being played through broadcasting on radio stations. A song which is being played several times every day (spins) would have a significant amount of airplay. Music which became very popular on jukeboxes, in n ...

technology built into

AirPort Express The AirPort Express is a Wi-Fi base station product from Apple Inc., part of the AirPort product line. While more compact and in some ways simpler than another Apple Wi-Fi base station, the AirPort Extreme, the Express offers audio output cap ...

wireless ( 802.11b/g/n) access point as well as the

Apple TV An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...

. The major difference from RTSP is an initial

asymmetric key Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic alg ...

verification made by

iTunes iTunes () is a software program that acts as a media player, media library, mobile device management utility, and the client app for the iTunes Store. Developed by Apple Inc., it is used to purchase, play, download, and organize digital mul ...

to verify it is communicating with an AirPort Express or an

(as opposed to a simulation), and vice versa. The data channel is also encrypted by AES, with a random key protected by the asymmetric key mentioned above. The RSA public key stored in iTunes was extracted by

Jon Lech Johansen Jon Lech Johansen (born November 18, 1983 in Harstad, Norway), also known as DVD Jon, is a Norwegian programmer who has worked on reverse engineering data formats. He wrote the DeCSS software, which decodes the Content Scramble System used for ...

, enabling third-party software to stream music to an Airport Express. The RSA private key stored in the

was extracted by James Laird, enabling simulation of an Airport Express. The Shairport-sync application which emulates Airport Express hardware is available.

References

{{Reflist

External links

Technical note to describe the Remote Audio Access Protocol (RAOP) as used in Apple iTunes to stream music to the Airport Express (ApEx)

RAOP-play
an open source implementation of the protocol Data transmission Network protocols