Shairport – someone reversed an AirPort Express

Low Latency Network Audio was a dream for the past years (see an article of 2005 and 2008) and with AirPlay it’s finally there.

I am using the Apple AirPlay technology for several years now… after it got implemented into iOS it’s just fantastic to have the option to have whatever sound source I want to playing loud and clear in any room I want to…

Okay it’s not quite as sophisticated as the sonos solution regarding the control of multiple music sources in multiple rooms but it get’s the job done in an apartment.

So back to the topic: Apple integrated the AirPlay technology into their wireless base station “AirPort Express”. Basically AirPlay is a piece of software which receives an encrypted audio stream over the network and outputs the stream to the SPDIF or audio jack.

Back in 2005 there already was an emulator of this protocol called “Fairport” but Apple decided to encrypt the AirPlay traffic. This led to the problem that the encryption key was unkown because it’s baked into the AirPort Express firmware. And this is where the good news start:

“My girlfriend moved house, and her Airport Express no longer made it with her wireless access point. I figured it’d be easy to find an ApEx emulator – there are several open source apps out there to play to them. However, I was disappointed to find that Apple used a public-key crypto scheme, and there’s a private key hiding inside the ApEx. So I took it apart (I still have scars from opening the glued case!), dumped the ROM, and reverse engineered the keys out of it.”

So to keep things short: Someone got an AirPort Express, dumped the firmware, extracted the AirPlay encryption keys and wrote an emulator of the AirPlay protocol which uses the key. Voilá!

ShairPort is available in source code on the site of the guy and obviously it’s unsure if Apple will react by changing the encryption key in the future. But for the time being it works as advertised:

I took one of my computers and followed the instructions to update perl, install Macports and then run ShairPort. So when ShairPort is run it looks not as appealing as expected:

Notably  it uses IPv6 to communicate between iTunes and ShairPort… Oh I almost forgot to show how it looks in iTunes:

On another side note: It works on Linux, Windows and Mac OS X 🙂

Source 1: Apple AirPlay
Source 2: Sonos
Source 3: Apple AirPort Express
Source 4: ShairPort

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