crackle cracks BLE Encryption (AKA Bluetooth Smart).

crackle exploits a flaw in the BLE pairing process that allows an attacker to
guess or very quickly brute force the TK (Temporary Key). With the TK and
other data collected from the pairing process, the STK (Short Term Key) and
later the LTK (Long Term Key) can be collected.

With the STK and LTK, all communications between the master and the slave
can be decrypted.