Class BTLE

scapy/layers/bluetooth4LE.py:210–267

##########

class BTLE(Packet):
    name = "BT4LE"
    fields_desc = [
        XLEIntField("access_addr", 0x8E89BED6),
        X3BytesField("crc", None)
    ]

    @staticmethod
    def compute_crc(pdu, init=0x555555):
        def swapbits(a):
            v = 0
            if a & 0x80 != 0:
                v |= 0x01
            if a & 0x40 != 0:
                v |= 0x02
            if a & 0x20 != 0:
                v |= 0x04
            if a & 0x10 != 0:
                v |= 0x08
            if a & 0x08 != 0:
                v |= 0x10
            if a & 0x04 != 0:
                v |= 0x20
            if a & 0x02 != 0:
                v |= 0x40
            if a & 0x01 != 0:
                v |= 0x80
            return v

        state = swapbits(init & 0xff) + (swapbits((init >> 8) & 0xff) << 8) + (swapbits((init >> 16) & 0xff) << 16)  # noqa: E501
        lfsr_mask = 0x5a6000
        for i in (orb(x) for x in pdu):
            for j in range(8):
                next_bit = (state ^ i) & 1
                i >>= 1
                state >>= 1
                if next_bit:
                    state |= 1 << 23
                    state ^= lfsr_mask
        return struct.pack("<L", state)[:-1]

    def post_build(self, p, pay):
        # Switch payload and CRC
        crc = p[-3:]
        p = p[:-3] + pay
        p += crc if self.crc is not None else self.compute_crc(p[4:])
        return p

    def post_dissect(self, s):
        self.raw_packet_cache = None  # Reset packet to allow post_build
        return s

    def pre_dissect(self, s):
        # move crc
        return s[:4] + s[-3:] + s[4:-3]

    def hashret(self):
        return struct.pack("!L", self.access_addr)