'Parse server challenge'

def parse_ntlm_chal(self, msg2, ack):

    global challenge_acks
    Signature = msg2[0:8]
    try:
        msg_type = struct.unpack('<I', msg2[8:12])[0]
    except Exception:
        return
    assert (msg_type == 2)
    ServerChallenge = msg2[24:32].encode('hex')
    if (len(challenge_acks) > 50):
        challenge_acks.popitem(last=False)
    challenge_acks[ack] = ServerChallenge
