Presumably, you're looking for information about which frequencies are appropriate for unlicensed operation...
<<cut-n-paste from another thread>>
The link for unlicensed bands up to 1 GHz:
There are more unlicensed bands above 1 GHz of course...
<<end c-n-p>>
With respect to 'keys', I assume that Mr. Goat is going to provide a matching receiver. Aftermarket remote car starters are not really integrated into the car's computers - they just tap into the car's wiring (dozens of wires for the many safety features and interlocks).
Also, the ones that I've seen do not use 'challenges' because they are a one-way system (the keyfob is only a transmitter).
For security, they'll often use rolling codes (off-the-shelf chip sets).
It will be very easy to underestimate the complexity of this project. The safety features, interlocks, and various timers all lead to a much larger state-machine diagram than you might think. It will sneak up on you... (speaking from experience with house alarm systems).