What type of encryption does iOS 8 use for Bluetooth?

I know that iOS 8 encrypts Bluetooth connections:

http://ift.tt/1zRc9bJ http://ift.tt/1ztRsFh

What I don't know is what kind of encryption it uses. For Airplay, for example, the PDF above says that iOS uses "AES-128 in CTR mode."

What type of encryption does iOS 8 use for Bluetooth?