BTCrack

  Bluetooth PIN and LINK-KEY Cracker - Bluetooth Cracker reconstructs the PIN and LINKEY with data sniffed during a pairing exchange. The calculated PIN can be used to authenticate against a device in Pairing Mode (usualy with a hardcoded PIN), the LINKEY however can be used for to get complete access to the Master and the Slave without any Interaction from the user of these devices. Furthermore the resulting Link-key can be used to decrypt the Datastreams between these devices.

You need access to a Bluetooth Sniffer Device and Software (FTE, others) in order to capture the exchanges, there have been rumors these Sniffers can be created from a standard USB Dongle.
This is a Proof of Concept tool from n.runs AG and is released under the License set forward in the LICENSE text file