I’ve released JustePort, a tool which lets you stream MPEG4 Apple Lossless files to your AirPort Express.

The stream is encrypted with AES and the AES key is encrypted with RSA.

AirPort Express RSA Public Key, Modulus:
59dE8qLieItsH1WgjrcFRKj6eUWqi+bGLOX1HL3U3GhC/j0Qg90u3sG/1CUtwC
5vOYvfDmFI6oSFXi5ELabWJmT2dKHzBJKa3k9ok+8t9ucRqMd6DZHJ2YCCLlDR
KSKv6kDqnw4UwPdpOMXziC/AMj3Z/lUVX1G7WSHCAWKf1zNS1eLvqr+boEjXuB
OitnZ/bDzPHrTOZz0Dew0uowxf/+sG+NCK3eQJVxqcaJ/vEHKIVd2M+5qL71yJ
Q+87X6oV3eaYvt3zWZYD6z5vYTcrtij2VZ9Zmni/UAaHqn9JdsBWLUEpVviYnh
imNVvYFZeCXg/IdTQ+x4IRdiXNv5hEew==
Exponent: AQAB

MD5(JustePort-0.1.tar.gz) = fe13e96751958c6e9d57cce0caa7b17b

Update: JustePort is not Windows-only. Thanks to mono it runs under GNU/Linux, MacOS X and Windows.

Update: List of all iTunes RSA Public keys.