peripherals.py

import bluepy.btle as btle
import random

from crypto import encrypt, decrypt

class UUIDS:
    FIRMWARE_VERSION   = btle.UUID("64ac0001-4a4b-4b58-9f37-94d3c52ffdf7")

    BATTERY_LEVEL      = btle.UUID(0x2a19)

    APP_CHALLENGE      = btle.UUID("64ac0002-4a4b-4b58-9f37-94d3c52ffdf7")
    DEVICE_CHALLENGE   = btle.UUID("64ac0003-4a4b-4b58-9f37-94d3c52ffdf7")
    DEVICE_RESPONSE    = btle.UUID("64ac0004-4a4b-4b58-9f37-94d3c52ffdf7")

    CONFIG             = btle.UUID("06ef0002-2e06-4b79-9e33-fce2c42805ec")
    PROBE1_TEMPERATURE = btle.UUID("06ef0002-2e06-4b79-9e33-fce2c42805ec")
    PROBE1_THRESHOLD   = btle.UUID("06ef0003-2e06-4b79-9e33-fce2c42805ec")
    PROBE2_TEMPERATURE = btle.UUID("06ef0004-2e06-4b79-9e33-fce2c42805ec")
    PROBE2_THRESHOLD   = btle.UUID("06ef0005-2e06-4b79-9e33-fce2c42805ec")
    PROBE3_TEMPERATURE = btle.UUID("06ef0006-2e06-4b79-9e33-fce2c42805ec")
    PROBE3_THRESHOLD   = btle.UUID("06ef0007-2e06-4b79-9e33-fce2c42805ec")
    PROBE4_TEMPERATURE = btle.UUID("06ef0008-2e06-4b79-9e33-fce2c42805ec")
    PROBE4_THRESHOLD   = btle.UUID("06ef0009-2e06-4b79-9e33-fce2c42805ec")


def find_peripheral():
    service = btle.Scanner()
    while True:
        scanresults = service.scan(2)
        for scanresult in scanresults:
            name = scanresult.getValueText(8)
            print "Found ", scanresult.addr, name

            if name == "iGrill_mini":
                return IGrillMiniPeripheral(scanresult.addr)


class IDevicePeripheral(btle.Peripheral):
    encryption_key = None

    def __init__(self, address):
        """
        Connects to the device given by address performing necessary authentication
        """
        btle.Peripheral.__init__(self, address)

        # iDevice devices require bonding. I don't think this will give us bonding
        # if no bonding exists, so please use bluetoothctl to create a bond first
        self.setSecurityLevel("medium")

        # enumerate all characteristics so we can look up handles from uuids
        self.characteristics = self.getCharacteristics()

        # authenticate with iDevices custom challenge/response protocol
        if not self.authenticate():
            raise RuntimeError("Unable to authenticate with device")

    def characteristic(self, uuid):
        """
        Returns the characteristic for a given uuid.
        """
        for c in self.characteristics:
            if c.uuid == uuid:
                return c

    def authenticate(self):
        """
        Performs iDevices challenge/response handshake. Returns if handshake succeeded

        """
        print "Authenticating..."
        # encryption key used by igrill mini
        key = "".join([chr((256 + x) % 256) for x in self.encryption_key])

        # send app challenge
        challenge = str(bytearray([(random.randint(0, 255)) for i in range(8)] + [0] * 8))
        self.characteristic(UUIDS.APP_CHALLENGE).write(challenge, True)

        # read device challenge
        encrypted_device_challenge = self.characteristic(UUIDS.DEVICE_CHALLENGE).read()
        print "encrypted device challenge:", str(encrypted_device_challenge).encode("hex")
        device_challenge = decrypt(key, encrypted_device_challenge)
        print "decrypted device challenge:", str(device_challenge).encode("hex")

        # verify device challenge
        if device_challenge[:8] != challenge[:8]:
            print "Invalid device challenge"
            return False

        # send device response
        device_response = chr(0) * 8 + device_challenge[8:]
        print "device response: ", str(device_response).encode("hex")
        encrypted_device_response = encrypt(key, device_response)
        self.characteristic(UUIDS.DEVICE_RESPONSE).write(encrypted_device_response, True)

        print("Authenticated")

        return True


class IGrillMiniPeripheral(IDevicePeripheral):
    """
    Specialization of iDevice peripheral for the iGrill Mini (sets the correct encryption key
    """

    # encryption key for the iGrill Mini
    encryption_key = [-19, 94, 48, -114, -117, -52, -111, 19, 48, 108, -44, 104, 84, 21, 62, -35]