Instruction:
Can you tell what is the following Python 3 function doing
def begin_send(self, x):
        with self.tx_mutex:
            if self.tx_state != ISOTP_IDLE:
                raise Scapy_Exception("Socket is already sending, retry later")

            self.tx_done.clear()
            self.tx_exception = None
            self.tx_state = ISOTP_SENDING

            length = len(x)
            if length > ISOTP_MAX_DLEN_2015:
                raise Scapy_Exception("Too much data for ISOTP message")

            if len(self.ea_hdr) + length <= 7:
                # send a single frame
                data = self.ea_hdr
                data += struct.pack("B", length)
                data += x
                self.tx_state = ISOTP_IDLE
                self.can_send(data)
                self.tx_done.set()
                for cb in self.tx_callbacks:
                    cb()
                return

            # send the first frame
            data = self.ea_hdr
            if length > ISOTP_MAX_DLEN:
                data += struct.pack(">HI", 0x1000, length)
            else:
                data += struct.pack(">H", 0x1000 | length)
            load = x[0:8 - len(data)]
            data += load
            self.can_send(data)

            self.tx_buf = x
            self.tx_sn = 1
            self.tx_bs = 0
            self.tx_idx = len(load)

            self.tx_state = ISOTP_WAIT_FIRST_FC
            self.tx_timer.set_timeout(self.fc_timeout, self._tx_timer_handler)

Response: Starts sending an ISOTP message. This method does not block.


Instruction:
How would you explain what the following Python 3 function does
def send(self, p):
        with self.send_mutex:
            self.begin_send(p)

            # Wait until the tx callback is called
            self.tx_done.wait()
            if self.tx_exception is not None:
                raise Scapy_Exception(self.tx_exception)
            return

Response: Send an ISOTP frame and block until the message is sent or an error occurs.


Instruction:
Explain what the following Python 3 code does
def recv(self, timeout=None):

        try:
            return self.rx_queue.get(timeout is None or timeout > 0, timeout)
        except queue.Empty:
            return None

Response:
Receive an ISOTP frame blocking if none is available in the buffer
        for at most timeout seconds.


Instruction:
Can you generate the documentation for the following Python 3 function
def should_add_ClientCertificate(self):
        hs_msg = [type(m) for m in self.cur_session.handshake_messages_parsed]
        if TLSCertificateRequest not in hs_msg:
            return
        certs = []
        if self.mycert:
            certs = [self.mycert]
        self.add_msg(TLSCertificate(certs=certs))
        raise self.ADDED_CLIENTCERTIFICATE()

Response: Check if we should add a client certificate.


Instruction:
Explain what the following Python 3 code does
def should_add_ClientVerify(self):
        hs_msg = [type(m) for m in self.cur_session.handshake_messages_parsed]
        if (TLSCertificateRequest not in hs_msg or
            self.mycert is None or
                self.mykey is None):
            return
        self.add_msg(TLSCertificateVerify())
        raise self.ADDED_CERTIFICATEVERIFY()

Response: This method is used to add a CertificateVerify message to the current session.


Instruction:
Can you tell what is the following Python 3 function doing
def add_ClientData(self):
        if not self.data_to_send:
            data = six.moves.input().replace('\\r', '\r').replace('\\n', '\n').encode()  # noqa: E501
        else:
            data = self.data_to_send.pop()
        if data == b"quit":
            return
        if self.linebreak:
            data += b"\n"
        self.add_record()
        self.add_msg(TLSApplicationData(data=data))
        raise self.ADDED_CLIENTDATA()

Response: Add client data to the message buffer.


Instruction:
Here you have a function in Python 3, explain what it does
def dispatch_hook(cls, _pkt=None, *args, **kargs):

        cls = conf.raw_layer
        if _pkt is not None:
            ptype = orb(_pkt[0])
            return globals().get(_param_set_cls.get(ptype), conf.raw_layer)

        return cls

Response: Dispatches the class to get the right parameter set class.


Instruction:
Given the following Python 3 function, write the documentation
def source_addr_mode2(pkt):
    if pkt.sac == 0x0:
        if pkt.sam == 0x0:
            return 16
        elif pkt.sam == 0x1:
            return 8
        elif pkt.sam == 0x2:
            return 2
        elif pkt.sam == 0x3:
            return 0
    else:
        if pkt.sam == 0x0:
            return 0
        elif pkt.sam == 0x1:
            return 8
        elif pkt.sam == 0x2:
            return 2
        elif pkt.sam == 0x3:
            return 0

Response: source_addr_mode2 - Returns the amount of bits that are used by the source address.


Instruction:
Make a summary of the following Python 3 code
def sixlowpan_fragment(packet, datagram_tag=1):
    if not packet.haslayer(IPv6):
        raise Exception("SixLoWPAN only fragments IPv6 packets !")

    str_packet = raw(packet[IPv6])

    if len(str_packet) <= MAX_SIZE:
        return [packet]

    def chunks(l, n):
        return [l[i:i + n] for i in range(0, len(l), n)]

    new_packet = chunks(str_packet, MAX_SIZE)

    new_packet[0] = LoWPANFragmentationFirst(datagramTag=datagram_tag, datagramSize=len(str_packet)) / new_packet[0]  # noqa: E501
    i = 1
    while i < len(new_packet):
        new_packet[i] = LoWPANFragmentationSubsequent(datagramTag=datagram_tag, datagramSize=len(str_packet), datagramOffset=MAX_SIZE // 8 * i) / new_packet[i]  # noqa: E501
        i += 1

    return new_packet

Response: Split a packet into different links to transmit as 6lowpan packets.


Instruction:
Implement a function in Python 3 to
add an internal value to a string

Response:
def addfield(self, pkt, s, val):
        """Add an internal value  to a string"""
        tmp_len = self.length_of(pkt)
        if tmp_len == 0:
            return s
        internal = self.i2m(pkt, val)[-tmp_len:]
        return s + struct.pack("!%ds" % tmp_len, internal)


Instruction:
Write a Python 3 function that can
add an internal value to a string

Response:
def addfield(self, pkt, s, val):
        """Add an internal value to a string"""
        if self.length_of(pkt) == 8:
            return s + struct.pack(self.fmt[0] + "B", val)
        if self.length_of(pkt) == 16:
            return s + struct.pack(self.fmt[0] + "H", val)
        if self.length_of(pkt) == 32:
            return s + struct.pack(self.fmt[0] + "2H", val)  # TODO: fix!
        if self.length_of(pkt) == 48:
            return s + struct.pack(self.fmt[0] + "3H", val)  # TODO: fix!
        elif self.length_of(pkt) == 64:
            return s + struct.pack(self.fmt[0] + "Q", val)
        elif self.length_of(pkt) == 128:
            # TODO: FIX THE PACKING!!
            return s + struct.pack(self.fmt[0] + "16s", raw(val))
        else:
            return s


Instruction:
Can you tell what is the following Python 3 function doing
def post_dissect(self, data):

        # uncompress payload
        packet = IPv6()
        packet.version = IPHC_DEFAULT_VERSION
        packet.tc, packet.fl = self._getTrafficClassAndFlowLabel()
        if not self.nh:
            packet.nh = self._nhField
        # HLIM: Hop Limit
        if self.hlim == 0:
            packet.hlim = self._hopLimit
        elif self.hlim == 0x1:
            packet.hlim = 1
        elif self.hlim == 0x2:
            packet.hlim = 64
        else:
            packet.hlim = 255
        # TODO: Payload length can be inferred from lower layers from either the  # noqa: E501
        # 6LoWPAN Fragmentation header or the IEEE802.15.4 header

        packet.src = self.decompressSourceAddr(packet)
        packet.dst = self.decompressDestinyAddr(packet)

        if self.nh == 1:
            # The Next Header field is compressed and the next header is
            # encoded using LOWPAN_NHC

            packet.nh = 0x11  # UDP
            udp = UDP()
            if self.header_compression and \
               self.header_compression & 0x4 == 0x0:
                udp.chksum = self.udpChecksum

            s, d = nhc_port(self)
            if s == 16:
                udp.sport = self.udpSourcePort
            elif s == 8:
                udp.sport = 0xF000 + s
            elif s == 4:
                udp.sport = 0xF0B0 + s
            if d == 16:
                udp.dport = self.udpDestinyPort
            elif d == 8:
                udp.dport = 0xF000 + d
            elif d == 4:
                udp.dport = 0xF0B0 + d

            packet.payload = udp / data
            data = raw(packet)
        # else self.nh == 0 not necessary
        elif self._nhField & 0xE0 == 0xE0:  # IPv6 Extension Header Decompression  # noqa: E501
            warning('Unimplemented: IPv6 Extension Header decompression')  # noqa: E501
            packet.payload = conf.raw_layer(data)
            data = raw(packet)
        else:
            packet.payload = conf.raw_layer(data)
            data = raw(packet)

        return Packet.post_dissect(self, data)

Response: This function is called by IPHC to dissect the IPv6 packet. It is called after the packet is decompressed and the payload needs to be decompressed and depending on the arguments.


Instruction:
How would you code a function in Python 3 to
page 6 draft feb 2011

Response:
def _getTrafficClassAndFlowLabel(self):
        """Page 6, draft feb 2011 """
        if self.tf == 0x0:
            return (self.tc_ecn << 6) + self.tc_dscp, self.flowlabel
        elif self.tf == 0x1:
            return (self.tc_ecn << 6), self.flowlabel
        elif self.tf == 0x2:
            return (self.tc_ecn << 6) + self.tc_dscp, 0
        else:
            return 0, 0


Instruction:
Create a Python 3 function for
depending on the payload content, the frame type we should interpretate

Response:
def dispatch_hook(cls, _pkt=b"", *args, **kargs):
        """Depending on the payload content, the frame type we should interpretate"""  # noqa: E501
        if _pkt and len(_pkt) >= 1:
            if orb(_pkt[0]) == 0x41:
                return LoWPANUncompressedIPv6
            if orb(_pkt[0]) == 0x42:
                return LoWPAN_HC1
            if orb(_pkt[0]) >> 3 == 0x18:
                return LoWPANFragmentationFirst
            elif orb(_pkt[0]) >> 3 == 0x1C:
                return LoWPANFragmentationSubsequent
            elif orb(_pkt[0]) >> 6 == 0x02:
                return LoWPANMesh
            elif orb(_pkt[0]) >> 6 == 0x01:
                return LoWPAN_IPHC
        return cls


Instruction:
Make a summary of the following Python 3 code
def get_issuer_str(self):
        name_str = ""
        attrsDict = self.get_issuer()
        for attrType, attrSymbol in _attrName_mapping:
            if attrType in attrsDict:
                name_str += "/" + attrSymbol + "="
                name_str += attrsDict[attrType]
        for attrType in sorted(attrsDict):
            if attrType not in _attrName_specials:
                name_str += "/" + attrType + "="
                name_str += attrsDict[attrType]
        return name_str

Response: Returns a one - line string containing every type and value of the user s issuer.


Instruction:
Can you generate a brief explanation for the following Python 3 code
def on_packet_received(self, pkt):
        if not pkt:
            return
        if self.store:
            self.lst.append(pkt)
        if self.prn:
            result = self.prn(pkt)
            if result is not None:
                print(result)

Response: Called by the filter handler when a packet is received.


Instruction:
Can you write a function in Python 3 where it
binds 2 layers for dissection.

Response:
def bind_bottom_up(lower, upper, __fval=None, **fval):
    """Bind 2 layers for dissection.
    The upper layer will be chosen for dissection on top of the lower layer, if
    ALL the passed arguments are validated. If multiple calls are made with the same  # noqa: E501
    layers, the last one will be used as default.

    ex:
        >>> bind_bottom_up(Ether, SNAP, type=0x1234)
        >>> Ether(b'\xff\xff\xff\xff\xff\xff\xd0P\x99V\xdd\xf9\x124\x00\x00\x00\x00\x00')  # noqa: E501
        <Ether  dst=ff:ff:ff:ff:ff:ff src=d0:50:99:56:dd:f9 type=0x1234 |<SNAP  OUI=0x0 code=0x0 |>>  # noqa: E501
    """
    if __fval is not None:
        fval.update(__fval)
    lower.payload_guess = lower.payload_guess[:]
    lower.payload_guess.append((fval, upper))


Instruction:
Given the following Python 3 function, write the documentation
def bind_top_down(lower, upper, __fval=None, **fval):
    if __fval is not None:
        fval.update(__fval)
    upper._overload_fields = upper._overload_fields.copy()
    upper._overload_fields[lower] = fval

Response: Bind 2 layers for building.


Instruction:
Given the following Python 3 function, write the documentation
def bind_layers(lower, upper, __fval=None, **fval):
    if __fval is not None:
        fval.update(__fval)
    bind_top_down(lower, upper, **fval)
    bind_bottom_up(lower, upper, **fval)

Response: Bind 2 layers on some specific fields values. It makes the packet being built when the arguments are present.


Instruction:
Here you have a function in Python 3, explain what it does
def split_layers(lower, upper, __fval=None, **fval):
    if __fval is not None:
        fval.update(__fval)
    split_bottom_up(lower, upper, **fval)
    split_top_down(lower, upper, **fval)

Response: Split 2 layers previously bound.


Instruction:
Write a Python 3 script for
functioning used to explore the Scapy layers and protocols.

Response:
def explore(layer=None):
    """Function used to discover the Scapy layers and protocols.
    It helps to see which packets exists in contrib or layer files.

    params:
     - layer: If specified, the function will explore the layer. If not,
              the GUI mode will be activated, to browse the available layers

    examples:
      >>> explore()  # Launches the GUI
      >>> explore("dns")  # Explore scapy.layers.dns
      >>> explore("http2")  # Explore scapy.contrib.http2
      >>> explore(scapy.layers.bluetooth4LE)

    Note: to search a packet by name, use ls("name") rather than explore.
    """
    if layer is None:  # GUI MODE
        if not conf.interactive:
            raise Scapy_Exception("explore() GUI-mode cannot be run in "
                                  "interactive mode. Please provide a "
                                  "'layer' parameter !")
        # 0 - Imports
        try:
            import prompt_toolkit
        except ImportError:
            raise ImportError("prompt_toolkit is not installed ! "
                              "You may install IPython, which contains it, via"
                              " `pip install ipython`")
        if not _version_checker(prompt_toolkit, (2, 0)):
            raise ImportError("prompt_toolkit >= 2.0.0 is required !")
        # Only available with prompt_toolkit > 2.0, not released on PyPi yet
        from prompt_toolkit.shortcuts.dialogs import radiolist_dialog, \
            button_dialog
        from prompt_toolkit.formatted_text import HTML
        # 1 - Ask for layer or contrib
        action = button_dialog(
            title="Scapy v%s" % conf.version,
            text=HTML(
                six.text_type(
                    '<style bg="white" fg="red">Chose the type of packets'
                    ' you want to explore:</style>'
                )
            ),
            buttons=[
                (six.text_type("Layers"), "layers"),
                (six.text_type("Contribs"), "contribs"),
                (six.text_type("Cancel"), "cancel")
            ])
        # 2 - Retrieve list of Packets
        if action == "layers":
            # Get all loaded layers
            _radio_values = conf.layers.layers()
            # Restrict to layers-only (not contribs) + packet.py and asn1*.py
            _radio_values = [x for x in _radio_values if ("layers" in x[0] or
                                                          "packet" in x[0] or
                                                          "asn1" in x[0])]
        elif action == "contribs":
            # Get all existing contribs
            from scapy.main import list_contrib
            _radio_values = list_contrib(ret=True)
            _radio_values = [(x['name'], x['description'])
                             for x in _radio_values]
            # Remove very specific modules
            _radio_values = [x for x in _radio_values if not ("can" in x[0])]
        else:
            # Escape/Cancel was pressed
            return
        # Python 2 compat
        if six.PY2:
            _radio_values = [(six.text_type(x), six.text_type(y))
                             for x, y in _radio_values]
        # 3 - Ask for the layer/contrib module to explore
        result = radiolist_dialog(
            values=_radio_values,
            title="Scapy v%s" % conf.version,
            text=HTML(
                six.text_type(
                    '<style bg="white" fg="red">Please select a layer among'
                    ' the following, to see all packets contained in'
                    ' it:</style>'
                )
            ))
        if result is None:
            return  # User pressed "Cancel"
        # 4 - (Contrib only): load contrib
        if action == "contribs":
            from scapy.main import load_contrib
            load_contrib(result)
            result = "scapy.contrib." + result
    else:  # NON-GUI MODE
        # We handle layer as a short layer name, full layer name
        # or the module itself
        if isinstance(layer, types.ModuleType):
            layer = layer.__name__
        if isinstance(layer, str):
            if layer.startswith("scapy.layers."):
                result = layer
            else:
                if layer.startswith("scapy.contrib."):
                    layer = layer.replace("scapy.contrib.", "")
                from scapy.main import load_contrib
                load_contrib(layer)
                result_layer, result_contrib = (("scapy.layers.%s" % layer),
                                                ("scapy.contrib.%s" % layer))
                if result_layer in conf.layers.ldict:
                    result = result_layer
                elif result_contrib in conf.layers.ldict:
                    result = result_contrib
                else:
                    raise Scapy_Exception("Unknown scapy module '%s'" % layer)
        else:
            warning("Wrong usage ! Check out help(explore)")
            return

    # COMMON PART
    # Get the list of all Packets contained in that module
    try:
        all_layers = conf.layers.ldict[result]
    except KeyError:
        raise Scapy_Exception("Unknown scapy module '%s'" % layer)
    # Print
    print(conf.color_theme.layer_name("Packets contained in %s:" % result))
    rtlst = [(lay.__name__ or "", lay._name or "") for lay in all_layers]
    print(pretty_list(rtlst, [("Class", "Name")], borders=True))


Instruction:
Can you implement a function in Python 3 that
lists available layers or infos on a given Packet or name.

Response:
def ls(obj=None, case_sensitive=False, verbose=False):
    """List  available layers, or infos on a given layer class or name.
    params:
     - obj: Packet / packet name to use
     - case_sensitive: if obj is a string, is it case sensitive?
     - verbose
    """
    is_string = isinstance(obj, six.string_types)

    if obj is None or is_string:
        tip = False
        if obj is None:
            tip = True
            all_layers = sorted(conf.layers, key=lambda x: x.__name__)
        else:
            pattern = re.compile(obj, 0 if case_sensitive else re.I)
            # We first order by accuracy, then length
            if case_sensitive:
                sorter = lambda x: (x.__name__.index(obj), len(x.__name__))
            else:
                obj = obj.lower()
                sorter = lambda x: (x.__name__.lower().index(obj),
                                    len(x.__name__))
            all_layers = sorted((layer for layer in conf.layers
                                 if (isinstance(layer.__name__, str) and
                                     pattern.search(layer.__name__)) or
                                 (isinstance(layer.name, str) and
                                     pattern.search(layer.name))),
                                key=sorter)
        for layer in all_layers:
            print("%-10s : %s" % (layer.__name__, layer._name))
        if tip and conf.interactive:
            print("\nTIP: You may use explore() to navigate through all "
                  "layers using a clear GUI")
    else:
        is_pkt = isinstance(obj, Packet)
        if issubtype(obj, Packet) or is_pkt:
            for f in obj.fields_desc:
                cur_fld = f
                attrs = []
                long_attrs = []
                while isinstance(cur_fld, (Emph, ConditionalField)):
                    if isinstance(cur_fld, ConditionalField):
                        attrs.append(cur_fld.__class__.__name__[:4])
                    cur_fld = cur_fld.fld
                if verbose and isinstance(cur_fld, EnumField) \
                   and hasattr(cur_fld, "i2s"):
                    if len(cur_fld.i2s) < 50:
                        long_attrs.extend(
                            "%s: %d" % (strval, numval)
                            for numval, strval in
                            sorted(six.iteritems(cur_fld.i2s))
                        )
                elif isinstance(cur_fld, MultiEnumField):
                    fld_depend = cur_fld.depends_on(obj.__class__
                                                    if is_pkt else obj)
                    attrs.append("Depends on %s" % fld_depend.name)
                    if verbose:
                        cur_i2s = cur_fld.i2s_multi.get(
                            cur_fld.depends_on(obj if is_pkt else obj()), {}
                        )
                        if len(cur_i2s) < 50:
                            long_attrs.extend(
                                "%s: %d" % (strval, numval)
                                for numval, strval in
                                sorted(six.iteritems(cur_i2s))
                            )
                elif verbose and isinstance(cur_fld, FlagsField):
                    names = cur_fld.names
                    long_attrs.append(", ".join(names))
                class_name = "%s (%s)" % (
                    cur_fld.__class__.__name__,
                    ", ".join(attrs)) if attrs else cur_fld.__class__.__name__
                if isinstance(cur_fld, BitField):
                    class_name += " (%d bit%s)" % (cur_fld.size,
                                                   "s" if cur_fld.size > 1
                                                   else "")
                print("%-10s : %-35s =" % (f.name, class_name), end=' ')
                if is_pkt:
                    print("%-15r" % (getattr(obj, f.name),), end=' ')
                print("(%r)" % (f.default,))
                for attr in long_attrs:
                    print("%-15s%s" % ("", attr))
            if is_pkt and not isinstance(obj.payload, NoPayload):
                print("--")
                ls(obj.payload)

        else:
            print("Not a packet class or name. Type 'ls()' to list packet classes.")


Instruction:
Explain what the following Python 3 code does
def fuzz(p, _inplace=0):
    if not _inplace:
        p = p.copy()
    q = p
    while not isinstance(q, NoPayload):
        for f in q.fields_desc:
            if isinstance(f, PacketListField):
                for r in getattr(q, f.name):
                    print("fuzzing", repr(r))
                    fuzz(r, _inplace=1)
            elif f.default is not None:
                if not isinstance(f, ConditionalField) or f._evalcond(q):
                    rnd = f.randval()
                    if rnd is not None:
                        q.default_fields[f.name] = rnd
        q = q.payload
    return p

Response: Transform a layer into a fuzzy layer by replacing some default values by random objects


Instruction:
How would you code a function in Python 3 to
initialize each field of the fields_desc dict.

Response:
def init_fields(self):
        """
        Initialize each fields of the fields_desc dict
        """

        if self.class_dont_cache.get(self.__class__, False):
            self.do_init_fields(self.fields_desc)
        else:
            self.do_init_cached_fields()


Instruction:
Here you have a function in Python 3, explain what it does
def do_init_fields(self, flist):
        for f in flist:
            self.default_fields[f.name] = copy.deepcopy(f.default)
            self.fieldtype[f.name] = f
            if f.holds_packets:
                self.packetfields.append(f)

Response: Initialize each field of the fields_desc dict


Instruction:
Can you tell what is the following Python 3 function doing
def do_init_cached_fields(self):

        cls_name = self.__class__

        # Build the fields information
        if Packet.class_default_fields.get(cls_name, None) is None:
            self.prepare_cached_fields(self.fields_desc)

        # Use fields information from cache
        if not Packet.class_default_fields.get(cls_name, None) is None:
            self.default_fields = Packet.class_default_fields[cls_name]
            self.fieldtype = Packet.class_fieldtype[cls_name]
            self.packetfields = Packet.class_packetfields[cls_name]

            # Deepcopy default references
            for fname in Packet.class_default_fields_ref[cls_name]:
                value = copy.deepcopy(self.default_fields[fname])
                setattr(self, fname, value)

Response:
Initialize each fields of the fields_desc dict or use the cached
            fields information


Instruction:
How would you explain what the following Python 3 function does
def prepare_cached_fields(self, flist):

        cls_name = self.__class__

        # Fields cache initialization
        if flist:
            Packet.class_default_fields[cls_name] = dict()
            Packet.class_default_fields_ref[cls_name] = list()
            Packet.class_fieldtype[cls_name] = dict()
            Packet.class_packetfields[cls_name] = list()

        # Fields initialization
        for f in flist:
            if isinstance(f, MultipleTypeField):
                del Packet.class_default_fields[cls_name]
                del Packet.class_default_fields_ref[cls_name]
                del Packet.class_fieldtype[cls_name]
                del Packet.class_packetfields[cls_name]
                self.class_dont_cache[cls_name] = True
                self.do_init_fields(self.fields_desc)
                break

            tmp_copy = copy.deepcopy(f.default)
            Packet.class_default_fields[cls_name][f.name] = tmp_copy
            Packet.class_fieldtype[cls_name][f.name] = f
            if f.holds_packets:
                Packet.class_packetfields[cls_name].append(f)

            # Remember references
            if isinstance(f.default, (list, dict, set, RandField, Packet)):
                Packet.class_default_fields_ref[cls_name].append(f.name)

Response: Prepare the cached fields of the fields_desc object.


Instruction:
Write a Python 3 function that can
call when a dissection is complete.

Response:
def dissection_done(self, pkt):
        """DEV: will be called after a dissection is completed"""
        self.post_dissection(pkt)
        self.payload.dissection_done(pkt)


Instruction:
How would you code a function in Python 3 to
return a deep copy of the instance.

Response:
def copy(self):
        """Returns a deep copy of the instance."""
        clone = self.__class__()
        clone.fields = self.copy_fields_dict(self.fields)
        clone.default_fields = self.copy_fields_dict(self.default_fields)
        clone.overloaded_fields = self.overloaded_fields.copy()
        clone.underlayer = self.underlayer
        clone.explicit = self.explicit
        clone.raw_packet_cache = self.raw_packet_cache
        clone.raw_packet_cache_fields = self.copy_fields_dict(
            self.raw_packet_cache_fields
        )
        clone.wirelen = self.wirelen
        clone.post_transforms = self.post_transforms[:]
        clone.payload = self.payload.copy()
        clone.payload.add_underlayer(clone)
        clone.time = self.time
        return clone


Instruction:
Can you generate the documentation for the following Python 3 function
def _superdir(self):
        attrs = set()
        cls = self.__class__
        if hasattr(cls, '__all_slots__'):
            attrs.update(cls.__all_slots__)
        for bcls in cls.__mro__:
            if hasattr(bcls, '__dict__'):
                attrs.update(bcls.__dict__)
        return attrs

Response: Return a list of slots and methods including those from subclasses.


Instruction:
Create a Python 3 function for
clearing the raw packet cache for the field and all its subfields

Response:
def clear_cache(self):
        """Clear the raw packet cache for the field and all its subfields"""
        self.raw_packet_cache = None
        for _, fval in six.iteritems(self.fields):
            if isinstance(fval, Packet):
                fval.clear_cache()
        self.payload.clear_cache()


Instruction:
Here you have a function in Python 3, explain what it does
def self_build(self, field_pos_list=None):
        if self.raw_packet_cache is not None:
            for fname, fval in six.iteritems(self.raw_packet_cache_fields):
                if self.getfieldval(fname) != fval:
                    self.raw_packet_cache = None
                    self.raw_packet_cache_fields = None
                    self.wirelen = None
                    break
            if self.raw_packet_cache is not None:
                return self.raw_packet_cache
        p = b""
        for f in self.fields_desc:
            val = self.getfieldval(f.name)
            if isinstance(val, RawVal):
                sval = raw(val)
                p += sval
                if field_pos_list is not None:
                    field_pos_list.append((f.name, sval.encode("string_escape"), len(p), len(sval)))  # noqa: E501
            else:
                p = f.addfield(self, p, val)
        return p

Response: Create the default layer regarding fields_desc dict


Instruction:
Can you generate the documentation for the following Python 3 function
def do_build(self):
        if not self.explicit:
            self = next(iter(self))
        pkt = self.self_build()
        for t in self.post_transforms:
            pkt = t(pkt)
        pay = self.do_build_payload()
        if self.raw_packet_cache is None:
            return self.post_build(pkt, pay)
        else:
            return pkt + pay

Response: Create the default version of the layer and return the payload


Instruction:
Can you create a Python 3 function that
creates the current layer and return the string with the payload

Response:
def build(self):
        """
        Create the current layer

        :return: string of the packet with the payload
        """
        p = self.do_build()
        p += self.build_padding()
        p = self.build_done(p)
        return p


Instruction:
Can you tell what is the following Python 3 function doing
def do_dissect_payload(self, s):
        if s:
            cls = self.guess_payload_class(s)
            try:
                p = cls(s, _internal=1, _underlayer=self)
            except KeyboardInterrupt:
                raise
            except Exception:
                if conf.debug_dissector:
                    if issubtype(cls, Packet):
                        log_runtime.error("%s dissector failed" % cls.__name__)
                    else:
                        log_runtime.error("%s.guess_payload_class() returned [%s]" % (self.__class__.__name__, repr(cls)))  # noqa: E501
                    if cls is not None:
                        raise
                p = conf.raw_layer(s, _internal=1, _underlayer=self)
            self.add_payload(p)

Response: Perform the dissection of the payload of the layer.


Instruction:
Implement a Python 3 function for
guessing the next payload class from the layer bonds.

Response:
def guess_payload_class(self, payload):
        """
        DEV: Guesses the next payload class from layer bonds.
        Can be overloaded to use a different mechanism.

        :param str payload: the layer's payload
        :return: the payload class
        """
        for t in self.aliastypes:
            for fval, cls in t.payload_guess:
                if all(hasattr(self, k) and v == self.getfieldval(k)
                       for k, v in six.iteritems(fval)):
                    return cls
        return self.default_payload_class(payload)


Instruction:
Create a Python 3 function to
remove fields values that are the same as default values.

Response:
def hide_defaults(self):
        """Removes fields' values that are the same as default values."""
        # use list(): self.fields is modified in the loop
        for k, v in list(six.iteritems(self.fields)):
            v = self.fields[k]
            if k in self.default_fields:
                if self.default_fields[k] == v:
                    del self.fields[k]
        self.payload.hide_defaults()


Instruction:
Here you have a function in Python 3, explain what it does
def layers(self):
        layers = []
        lyr = self
        while lyr:
            layers.append(lyr.__class__)
            lyr = lyr.payload.getlayer(0, _subclass=True)
        return layers

Response: returns a list of layer classes including subclasses in this packet


Instruction:
Make a summary of the following Python 3 code
def getlayer(self, cls, nb=1, _track=None, _subclass=None, **flt):
        if _subclass is None:
            _subclass = self.match_subclass or None
        if _subclass:
            match = lambda cls1, cls2: issubclass(cls1, cls2)
        else:
            match = lambda cls1, cls2: cls1 == cls2
        if isinstance(cls, int):
            nb = cls + 1
            cls = None
        if isinstance(cls, str) and "." in cls:
            ccls, fld = cls.split(".", 1)
        else:
            ccls, fld = cls, None
        if cls is None or match(self.__class__, cls) \
           or ccls in [self.__class__.__name__, self._name]:
            if all(self.getfieldval(fldname) == fldvalue
                   for fldname, fldvalue in six.iteritems(flt)):
                if nb == 1:
                    if fld is None:
                        return self
                    else:
                        return self.getfieldval(fld)
                else:
                    nb -= 1
        for f in self.packetfields:
            fvalue_gen = self.getfieldval(f.name)
            if fvalue_gen is None:
                continue
            if not f.islist:
                fvalue_gen = SetGen(fvalue_gen, _iterpacket=0)
            for fvalue in fvalue_gen:
                if isinstance(fvalue, Packet):
                    track = []
                    ret = fvalue.getlayer(cls, nb=nb, _track=track,
                                          _subclass=_subclass, **flt)
                    if ret is not None:
                        return ret
                    nb = track[0]
        return self.payload.getlayer(cls, nb=nb, _track=_track,
                                     _subclass=_subclass, **flt)

Response:
Return the nb^th layer that is an instance of cls matching flt
values.


Instruction:
Can you tell what is the following Python 3 function doing
def show(self, dump=False, indent=3, lvl="", label_lvl=""):
        return self._show_or_dump(dump, indent, lvl, label_lvl)

Response: Print the value of the key - value layer.


Instruction:
How would you explain what the following Python 3 function does
def show2(self, dump=False, indent=3, lvl="", label_lvl=""):
        return self.__class__(raw(self)).show(dump, indent, lvl, label_lvl)

Response: Print the packet as a hierarchical view of the packet.


Instruction:
Can you generate a brief explanation for the following Python 3 code
def sprintf(self, fmt, relax=1):

        escape = {"%": "%",
                  "(": "{",
                  ")": "}"}

        # Evaluate conditions
        while "{" in fmt:
            i = fmt.rindex("{")
            j = fmt[i + 1:].index("}")
            cond = fmt[i + 1:i + j + 1]
            k = cond.find(":")
            if k < 0:
                raise Scapy_Exception("Bad condition in format string: [%s] (read sprintf doc!)" % cond)  # noqa: E501
            cond, format_ = cond[:k], cond[k + 1:]
            res = False
            if cond[0] == "!":
                res = True
                cond = cond[1:]
            if self.haslayer(cond):
                res = not res
            if not res:
                format_ = ""
            fmt = fmt[:i] + format_ + fmt[i + j + 2:]

        # Evaluate directives
        s = ""
        while "%" in fmt:
            i = fmt.index("%")
            s += fmt[:i]
            fmt = fmt[i + 1:]
            if fmt and fmt[0] in escape:
                s += escape[fmt[0]]
                fmt = fmt[1:]
                continue
            try:
                i = fmt.index("%")
                sfclsfld = fmt[:i]
                fclsfld = sfclsfld.split(",")
                if len(fclsfld) == 1:
                    f = "s"
                    clsfld = fclsfld[0]
                elif len(fclsfld) == 2:
                    f, clsfld = fclsfld
                else:
                    raise Scapy_Exception
                if "." in clsfld:
                    cls, fld = clsfld.split(".")
                else:
                    cls = self.__class__.__name__
                    fld = clsfld
                num = 1
                if ":" in cls:
                    cls, num = cls.split(":")
                    num = int(num)
                fmt = fmt[i + 1:]
            except Exception:
                raise Scapy_Exception("Bad format string [%%%s%s]" % (fmt[:25], fmt[25:] and "..."))  # noqa: E501
            else:
                if fld == "time":
                    val = time.strftime("%H:%M:%S.%%06i", time.localtime(self.time)) % int((self.time - int(self.time)) * 1000000)  # noqa: E501
                elif cls == self.__class__.__name__ and hasattr(self, fld):
                    if num > 1:
                        val = self.payload.sprintf("%%%s,%s:%s.%s%%" % (f, cls, num - 1, fld), relax)  # noqa: E501
                        f = "s"
                    elif f[-1] == "r":  # Raw field value
                        val = getattr(self, fld)
                        f = f[:-1]
                        if not f:
                            f = "s"
                    else:
                        val = getattr(self, fld)
                        if fld in self.fieldtype:
                            val = self.fieldtype[fld].i2repr(self, val)
                else:
                    val = self.payload.sprintf("%%%s%%" % sfclsfld, relax)
                    f = "s"
                s += ("%" + f) % val

        s += fmt
        return s

Response: Return a string that can be used as a sprintf statement in a log file.


Instruction:
Implement a function in Python 3 to
return a string representing the command you have to type to obtain the same packet

Response:
def command(self):
        """
        Returns a string representing the command you have to type to
        obtain the same packet
        """
        f = []
        for fn, fv in six.iteritems(self.fields):
            fld = self.get_field(fn)
            if isinstance(fv, (list, dict, set)) and len(fv) == 0:
                continue
            if isinstance(fv, Packet):
                fv = fv.command()
            elif fld.islist and fld.holds_packets and isinstance(fv, list):
                fv = "[%s]" % ",".join(map(Packet.command, fv))
            elif isinstance(fld, FlagsField):
                fv = int(fv)
            else:
                fv = repr(fv)
            f.append("%s=%s" % (fn, fv))
        c = "%s(%s)" % (self.__class__.__name__, ", ".join(f))
        pc = self.payload.command()
        if pc:
            c += "/" + pc
        return c


Instruction:
Can you implement a function in Python 3 that
initializes the TLS session.

Response:
def INIT_TLS_SESSION(self):
        """
        XXX We should offer the right key according to the client's suites. For
        now server_rsa_key is only used for RSAkx, but we should try to replace
        every server_key with both server_rsa_key and server_ecdsa_key.
        """
        self.cur_session = tlsSession(connection_end="server")
        self.cur_session.server_certs = [self.mycert]
        self.cur_session.server_key = self.mykey
        if isinstance(self.mykey, PrivKeyRSA):
            self.cur_session.server_rsa_key = self.mykey
        # elif isinstance(self.mykey, PrivKeyECDSA):
        #    self.cur_session.server_ecdsa_key = self.mykey
        raise self.WAITING_CLIENTFLIGHT1()


Instruction:
How would you explain what the following Python 3 function does
def should_check_ciphersuites(self):
        if isinstance(self.mykey, PrivKeyRSA):
            kx = "RSA"
        elif isinstance(self.mykey, PrivKeyECDSA):
            kx = "ECDSA"
        if get_usable_ciphersuites(self.cur_pkt.ciphers, kx):
            return
        raise self.NO_USABLE_CIPHERSUITE()

Response: Check if cipher suites are usable.


Instruction:
Given the following Python 3 function, write the documentation
def should_add_ServerHello(self):
        if isinstance(self.mykey, PrivKeyRSA):
            kx = "RSA"
        elif isinstance(self.mykey, PrivKeyECDSA):
            kx = "ECDSA"
        usable_suites = get_usable_ciphersuites(self.cur_pkt.ciphers, kx)
        c = usable_suites[0]
        if self.preferred_ciphersuite in usable_suites:
            c = self.preferred_ciphersuite
        self.add_msg(TLSServerHello(cipher=c))
        raise self.ADDED_SERVERHELLO()

Response: Add a server hello message to the message queue.


Instruction:
Write a Python 3 function for
parsing the arguments for the KrackAP object.

Response:
def parse_args(self, ap_mac, ssid, passphrase,
                   channel=None,
                   # KRACK attack options
                   double_3handshake=True,
                   encrypt_3handshake=True,
                   wait_3handshake=0,
                   double_gtk_refresh=True,
                   arp_target_ip=None,
                   arp_source_ip=None,
                   wait_gtk=10,
                   **kwargs):
        """
        Mandatory arguments:
        @iface: interface to use (must be in monitor mode)
        @ap_mac: AP's MAC
        @ssid: AP's SSID
        @passphrase: AP's Passphrase (min 8 char.)

        Optional arguments:
        @channel: used by the interface. Default 6, autodetected on windows

        Krack attacks options:

         - Msg 3/4 handshake replay:
        double_3handshake: double the 3/4 handshake message
        encrypt_3handshake: encrypt the second 3/4 handshake message
        wait_3handshake: time to wait (in sec.) before sending the second 3/4
         - double GTK rekeying:
        double_gtk_refresh: double the 1/2 GTK rekeying message
        wait_gtk: time to wait (in sec.) before sending the GTK rekeying
        arp_target_ip: Client IP to use in ARP req. (to detect attack success)
                       If None, use a DHCP server
        arp_source_ip: Server IP to use in ARP req. (to detect attack success)
                       If None, use the DHCP server gateway address
        """
        super(KrackAP, self).parse_args(**kwargs)

        # Main AP options
        self.mac = ap_mac
        self.ssid = ssid
        self.passphrase = passphrase
        if channel is None:
            if WINDOWS:
                try:
                    channel = kwargs.get("iface", conf.iface).channel()
                except (Scapy_Exception, AttributeError):
                    channel = 6
            else:
                channel = 6
        self.channel = channel

        # Internal structures
        self.last_iv = None
        self.client = None
        self.seq_num = count()
        self.replay_counter = count()
        self.time_handshake_end = None
        self.dhcp_server = DHCPOverWPA(send_func=self.send_ether_over_wpa,
                                       pool=Net("192.168.42.128/25"),
                                       network="192.168.42.0/24",
                                       gw="192.168.42.1")
        self.arp_sent = []
        self.arp_to_send = 0
        self.arp_retry = 0

        # Bit 0: 3way handshake sent
        # Bit 1: GTK rekeying sent
        # Bit 2: ARP response obtained
        self.krack_state = 0

        # Krack options
        self.double_3handshake = double_3handshake
        self.encrypt_3handshake = encrypt_3handshake
        self.wait_3handshake = wait_3handshake
        self.double_gtk_refresh = double_gtk_refresh
        self.arp_target_ip = arp_target_ip
        if arp_source_ip is None:
            # Use the DHCP server Gateway address
            arp_source_ip = self.dhcp_server.gw
        self.arp_source_ip = arp_source_ip
        self.wait_gtk = wait_gtk

        # May take several seconds
        self.install_PMK()


Instruction:
Can you generate the documentation for the following Python 3 function
def install_PMK(self):
        self.pmk = PBKDF2HMAC(
            algorithm=hashes.SHA1(),
            length=32,
            salt=self.ssid.encode(),
            iterations=4096,
            backend=default_backend(),
        ).derive(self.passphrase.encode())

Response: Compute and install the PMK


Instruction:
Write a Python 3 script to
use the client nonce to compute and install the unicast keys for the current client.

Response:
def install_unicast_keys(self, client_nonce):
        """Use the client nonce @client_nonce to compute and install
        PTK, KCK, KEK, TK, MIC (AP -> STA), MIC (STA -> AP)
        """
        pmk = self.pmk
        anonce = self.anonce
        snonce = client_nonce
        amac = mac2str(self.mac)
        smac = mac2str(self.client)

        # Compute PTK
        self.ptk = customPRF512(pmk, amac, smac, anonce, snonce)

        # Extract derivated keys
        self.kck = self.ptk[:16]
        self.kek = self.ptk[16:32]
        self.tk = self.ptk[32:48]
        self.mic_ap_to_sta = self.ptk[48:56]
        self.mic_sta_to_ap = self.ptk[56:64]

        # Reset IV
        self.client_iv = count()


Instruction:
Can you generate a brief explanation for the following Python 3 code
def install_GTK(self):

        # Compute GTK
        self.gtk_full = self.gen_nonce(32)
        self.gtk = self.gtk_full[:16]

        # Extract derivated keys
        self.mic_ap_to_group = self.gtk_full[16:24]

        # Reset IV
        self.group_iv = count()

Response:
Compute a new GTK and install it alongs
        MIC


Instruction:
Given the following Python 3 function, write the documentation
def build_ap_info_pkt(self, layer_cls, dest):
        return RadioTap() \
            / Dot11(addr1=dest, addr2=self.mac, addr3=self.mac) \
            / layer_cls(timestamp=0, beacon_interval=100,
                        cap='ESS+privacy') \
            / Dot11Elt(ID="SSID", info=self.ssid) \
            / Dot11EltRates(rates=[130, 132, 139, 150, 12, 18, 24, 36]) \
            / Dot11Elt(ID="DSset", info=chb(self.channel)) \
            / Dot11EltRSN(group_cipher_suite=RSNCipherSuite(cipher=0x2),
                          pairwise_cipher_suites=[RSNCipherSuite(cipher=0x2)],
                          akm_suites=[AKMSuite(suite=0x2)])

Response: Build a packet with info describing the current AP.


Instruction:
Can you implement a function in Python 3 that
builds the Key Data Encapsulation for GTK.

Response:
def build_GTK_KDE(self):
        """Build the Key Data Encapsulation for GTK
        KeyID: 0
        Ref: 802.11i p81
        """
        return b''.join([
            b'\xdd',  # Type KDE
            chb(len(self.gtk_full) + 6),
            b'\x00\x0f\xac',  # OUI
            b'\x01',  # GTK KDE
            b'\x00\x00',  # KeyID - Tx - Reserved x2
            self.gtk_full,
        ])


Instruction:
Can you generate the documentation for the following Python 3 function
def send_wpa_enc(self, data, iv, seqnum, dest, mic_key,
                     key_idx=0, additionnal_flag=["from-DS"],
                     encrypt_key=None):
        """Send an encrypted packet with content @data, using IV @iv,
        sequence number @seqnum, MIC key @mic_key
        """

        if encrypt_key is None:
            encrypt_key = self.tk

        rep = RadioTap()
        rep /= Dot11(
            addr1=dest,
            addr2=self.mac,
            addr3=self.mac,
            FCfield="+".join(['protected'] + additionnal_flag),
            SC=(next(self.seq_num) << 4),
            subtype=0,
            type="Data",
        )

        # Assume packet is send by our AP -> use self.mac as source

        # Encapsule in TKIP with MIC Michael and ICV
        data_to_enc = build_MIC_ICV(raw(data), mic_key, self.mac, dest)

        # Header TKIP + payload
        rep /= Raw(build_TKIP_payload(data_to_enc, iv, self.mac, encrypt_key))

        self.send(rep)
        return rep

Response: Send an encrypted packet with content data using IV seqnum MIC key mic_key and key_idx.


Instruction:
Can you create a Python 3 function that
sends an Ethernet packet over the WPA channel.

Response:
def send_ether_over_wpa(self, pkt, **kwargs):
        """Send an Ethernet packet using the WPA channel
        Extra arguments will be ignored, and are just left for compatibility
        """

        payload = LLC() / SNAP() / pkt[Ether].payload
        dest = pkt.dst
        if dest == "ff:ff:ff:ff:ff:ff":
            self.send_wpa_to_group(payload, dest)
        else:
            assert dest == self.client
            self.send_wpa_to_client(payload)


Instruction:
How would you implement a function in Python 3 that
raises state on the next packet.

Response:
def raise_on_packet(self, pkt_cls, state, get_next_msg=True):
        """
        If the next message to be processed has type 'pkt_cls', raise 'state'.
        If there is no message waiting to be processed, we try to get one with
        the default 'get_next_msg' parameters.
        """
        # Maybe we already parsed the expected packet, maybe not.
        if get_next_msg:
            self.get_next_msg()
        if (not self.buffer_in or
                not isinstance(self.buffer_in[0], pkt_cls)):
            return
        self.cur_pkt = self.buffer_in[0]
        self.buffer_in = self.buffer_in[1:]
        raise state()


Instruction:
Can you tell what is the following Python 3 function doing
def add_record(self, is_sslv2=None, is_tls13=None):
        if is_sslv2 is None and is_tls13 is None:
            v = (self.cur_session.tls_version or
                 self.cur_session.advertised_tls_version)
            if v in [0x0200, 0x0002]:
                is_sslv2 = True
            elif v >= 0x0304:
                is_tls13 = True
        if is_sslv2:
            self.buffer_out.append(SSLv2(tls_session=self.cur_session))
        elif is_tls13:
            self.buffer_out.append(TLS13(tls_session=self.cur_session))
        else:
            self.buffer_out.append(TLS(tls_session=self.cur_session))

Response: Add a new TLS or SSLv2 or TLS 1. 3 record to the packets buffered out.


Instruction:
Implement a Python 3 function for
adding a TLS message to the message buffer.

Response:
def add_msg(self, pkt):
        """
        Add a TLS message (e.g. TLSClientHello or TLSApplicationData)
        inside the latest record to be sent through the socket.
        We believe a good automaton should not use the first test.
        """
        if not self.buffer_out:
            self.add_record()
        r = self.buffer_out[-1]
        if isinstance(r, TLS13):
            self.buffer_out[-1].inner.msg.append(pkt)
        else:
            self.buffer_out[-1].msg.append(pkt)


Instruction:
How would you explain what the following Python 3 function does
def flush_records(self):
        s = b"".join(p.raw_stateful() for p in self.buffer_out)
        self.socket.send(s)
        self.buffer_out = []

Response: Send all buffered records and update the session accordingly.


Instruction:
Can you generate the documentation for the following Python 3 function
def util_srcpanid_present(pkt):
    '''A source PAN ID is included if and only if both src addr mode != 0 and PAN ID Compression in FCF == 0'''  # noqa: E501
    if (pkt.underlayer.getfieldval("fcf_srcaddrmode") != 0) and (pkt.underlayer.getfieldval("fcf_panidcompress") == 0):  # noqa: E501
        return True
    else:
        return False

Response: A source PAN ID is included if and only if both src addr mode and PAN ID Compression in FCF == 0


Instruction:
Write a Python 3 script for
converting internal value to a nice representation

Response:
def i2repr(self, pkt, x):
        """Convert internal value to a nice representation"""
        if len(hex(self.i2m(pkt, x))) < 7:  # short address
            return hex(self.i2m(pkt, x))
        else:  # long address
            x = "%016x" % self.i2m(pkt, x)
            return ":".join(["%s%s" % (x[i], x[i + 1]) for i in range(0, len(x), 2)])


Instruction:
How would you code a function in Python 3 to
add an internal value to a string

Response:
def addfield(self, pkt, s, val):
        """Add an internal value to a string"""
        if self.adjust(pkt, self.length_of) == 2:
            return s + struct.pack(self.fmt[0] + "H", val)
        elif self.adjust(pkt, self.length_of) == 8:
            return s + struct.pack(self.fmt[0] + "Q", val)
        else:
            return s


Instruction:
Write a Python 3 function that can
provide the implementation of P_hash function defined in section 5 of RFC 4346 (and section 5 of RFC 5246). Two parameters have been added (hm and req_len): - secret : the key to be used. If RFC 4868 is to be believed, the length must match hm.key_len. Actually, python hmac takes care of formatting every key. - seed : the seed to be used. - req_len : the length of data to be generated by iterating the specific HMAC function (hm). This prevents multiple calls to the function. - hm : the hmac function class to use for iteration (either Hmac_MD5 or Hmac_SHA1 in TLS <= 1.1 or Hmac_SHA256 or Hmac_SHA384 in TLS 1.2)

Response:
def _tls_P_hash(secret, seed, req_len, hm):
    """
    Provides the implementation of P_hash function defined in
    section 5 of RFC 4346 (and section 5 of RFC 5246). Two
    parameters have been added (hm and req_len):

    - secret : the key to be used. If RFC 4868 is to be believed,
               the length must match hm.key_len. Actually,
               python hmac takes care of formatting every key.
    - seed : the seed to be used.
    - req_len : the length of data to be generated by iterating
               the specific HMAC function (hm). This prevents
               multiple calls to the function.
    - hm : the hmac function class to use for iteration (either
           Hmac_MD5 or Hmac_SHA1 in TLS <= 1.1 or
           Hmac_SHA256 or Hmac_SHA384 in TLS 1.2)
    """
    hash_len = hm.hash_alg.hash_len
    n = (req_len + hash_len - 1) // hash_len
    seed = bytes_encode(seed)

    res = b""
    a = hm(secret).digest(seed)  # A(1)

    while n > 0:
        res += hm(secret).digest(a + seed)
        a = hm(secret).digest(a)
        n -= 1

    return res[:req_len]


Instruction:
How would you explain what the following Python 3 function does
def _ssl_PRF(secret, seed, req_len):
    if req_len > 416:
        warning("_ssl_PRF() is not expected to provide more than 416 bytes")
        return ""

    d = [b"A", b"B", b"C", b"D", b"E", b"F", b"G", b"H", b"I", b"J", b"K", b"L",  # noqa: E501
         b"M", b"N", b"O", b"P", b"Q", b"R", b"S", b"T", b"U", b"V", b"W", b"X",  # noqa: E501
         b"Y", b"Z"]
    res = b""
    hash_sha1 = _tls_hash_algs["SHA"]()
    hash_md5 = _tls_hash_algs["MD5"]()
    rounds = (req_len + hash_md5.hash_len - 1) // hash_md5.hash_len

    for i in range(rounds):
        label = d[i] * (i + 1)
        tmp = hash_sha1.digest(label + secret + seed)
        res += hash_md5.digest(secret + tmp)

    return res[:req_len]

Response: Returns the SSLv3 PRF function for the given secret and seed.


Instruction:
Explain what the following Python 3 code does
def _tls_PRF(secret, label, seed, req_len):
    tmp_len = (len(secret) + 1) // 2
    S1 = secret[:tmp_len]
    S2 = secret[-tmp_len:]

    a1 = _tls_P_MD5(S1, label + seed, req_len)
    a2 = _tls_P_SHA1(S2, label + seed, req_len)

    return strxor(a1, a2)

Response: Returns the PRF function for the given secret label and seed.


Instruction:
Implement a Python 3 function for
returning the implementation of TLS 1. 2 PRF function as

Response:
def _tls12_SHA256PRF(secret, label, seed, req_len):
    """
    Provides the implementation of TLS 1.2 PRF function as
    defined in section 5 of RFC 5246:

    PRF(secret, label, seed) = P_SHA256(secret, label + seed)

    Parameters are:

    - secret: the secret used by the HMAC in the 2 expansion
              functions (S1 and S2 are the halves of this secret).
    - label: specific label as defined in various sections of the RFC
             depending on the use of the generated PRF keystream
    - seed: the seed used by the expansion functions.
    - req_len: amount of keystream to be generated
    """
    return _tls_P_SHA256(secret, label + seed, req_len)


Instruction:
Can you write a function in Python 3 where it
computes the master secret from the pre_master_secret client_random and server_random.

Response:
def compute_master_secret(self, pre_master_secret,
                              client_random, server_random):
        """
        Return the 48-byte master_secret, computed from pre_master_secret,
        client_random and server_random. See RFC 5246, section 6.3.
        """
        seed = client_random + server_random
        if self.tls_version < 0x0300:
            return None
        elif self.tls_version == 0x0300:
            return self.prf(pre_master_secret, seed, 48)
        else:
            return self.prf(pre_master_secret, b"master secret", seed, 48)


Instruction:
Can you implement a function in Python 3 that
derives a key_block from a master_secret.

Response:
def derive_key_block(self, master_secret, server_random,
                         client_random, req_len):
        """
        Perform the derivation of master_secret into a key_block of req_len
        requested length. See RFC 5246, section 6.3.
        """
        seed = server_random + client_random
        if self.tls_version <= 0x0300:
            return self.prf(master_secret, seed, req_len)
        else:
            return self.prf(master_secret, b"key expansion", seed, req_len)


Instruction:
How would you explain what the following Python 3 function does
def compute_verify_data(self, con_end, read_or_write,
                            handshake_msg, master_secret):
        """
        Return verify_data based on handshake messages, connection end,
        master secret, and read_or_write position. See RFC 5246, section 7.4.9.

        Every TLS 1.2 cipher suite has a verify_data of length 12. Note also:
        "This PRF with the SHA-256 hash function is used for all cipher
         suites defined in this document and in TLS documents published
         prior to this document when TLS 1.2 is negotiated."
        Cipher suites using SHA-384 were defined later on.
        """
        if self.tls_version < 0x0300:
            return None
        elif self.tls_version == 0x0300:

            if read_or_write == "write":
                d = {"client": b"CLNT", "server": b"SRVR"}
            else:
                d = {"client": b"SRVR", "server": b"CLNT"}
            label = d[con_end]

            sslv3_md5_pad1 = b"\x36" * 48
            sslv3_md5_pad2 = b"\x5c" * 48
            sslv3_sha1_pad1 = b"\x36" * 40
            sslv3_sha1_pad2 = b"\x5c" * 40

            md5 = _tls_hash_algs["MD5"]()
            sha1 = _tls_hash_algs["SHA"]()

            md5_hash = md5.digest(master_secret + sslv3_md5_pad2 +
                                  md5.digest(handshake_msg + label +
                                             master_secret + sslv3_md5_pad1))
            sha1_hash = sha1.digest(master_secret + sslv3_sha1_pad2 +
                                    sha1.digest(handshake_msg + label +
                                                master_secret + sslv3_sha1_pad1))  # noqa: E501
            verify_data = md5_hash + sha1_hash

        else:

            if read_or_write == "write":
                d = {"client": "client", "server": "server"}
            else:
                d = {"client": "server", "server": "client"}
            label = ("%s finished" % d[con_end]).encode()

            if self.tls_version <= 0x0302:
                s1 = _tls_hash_algs["MD5"]().digest(handshake_msg)
                s2 = _tls_hash_algs["SHA"]().digest(handshake_msg)
                verify_data = self.prf(master_secret, label, s1 + s2, 12)
            else:
                if self.hash_name in ["MD5", "SHA"]:
                    h = _tls_hash_algs["SHA256"]()
                else:
                    h = _tls_hash_algs[self.hash_name]()
                s = h.digest(handshake_msg)
                verify_data = self.prf(master_secret, label, s, 12)

        return verify_data

Response: Compute verify_data based on handshake messages master_secret and read_or_write.


Instruction:
Can you generate a brief explanation for the following Python 3 code
def postprocess_key_for_export(self, key, client_random, server_random,
                                   con_end, read_or_write, req_len):
        """
        Postprocess cipher key for EXPORT ciphersuite, i.e. weakens it.
        An export key generation example is given in section 6.3.1 of RFC 2246.
        See also page 86 of EKR's book.
        """
        s = con_end + read_or_write
        s = (s == "clientwrite" or s == "serverread")

        if self.tls_version < 0x0300:
            return None
        elif self.tls_version == 0x0300:
            if s:
                tbh = key + client_random + server_random
            else:
                tbh = key + server_random + client_random
            export_key = _tls_hash_algs["MD5"]().digest(tbh)[:req_len]
        else:
            if s:
                tag = b"client write key"
            else:
                tag = b"server write key"
            export_key = self.prf(key,
                                  tag,
                                  client_random + server_random,
                                  req_len)
        return export_key

Response: Postprocess cipher key for EXPORT cipher suite.


Instruction:
How would you implement a function in Python 3 that
generates an export IV for the specified ciphersuite.

Response:
def generate_iv_for_export(self, client_random, server_random,
                               con_end, read_or_write, req_len):
        """
        Generate IV for EXPORT ciphersuite, i.e. weakens it.
        An export IV generation example is given in section 6.3.1 of RFC 2246.
        See also page 86 of EKR's book.
        """
        s = con_end + read_or_write
        s = (s == "clientwrite" or s == "serverread")

        if self.tls_version < 0x0300:
            return None
        elif self.tls_version == 0x0300:
            if s:
                tbh = client_random + server_random
            else:
                tbh = server_random + client_random
            iv = _tls_hash_algs["MD5"]().digest(tbh)[:req_len]
        else:
            iv_block = self.prf("",
                                b"IV block",
                                client_random + server_random,
                                2 * req_len)
            if s:
                iv = iv_block[:req_len]
            else:
                iv = iv_block[req_len:]
        return iv


Instruction:
Explain what the following Python 3 code does
def load_protocols(filename, _integer_base=10):
    spaces = re.compile(b"[ \t]+|\n")
    dct = DADict(_name=filename)
    try:
        with open(filename, "rb") as fdesc:
            for line in fdesc:
                try:
                    shrp = line.find(b"#")
                    if shrp >= 0:
                        line = line[:shrp]
                    line = line.strip()
                    if not line:
                        continue
                    lt = tuple(re.split(spaces, line))
                    if len(lt) < 2 or not lt[0]:
                        continue
                    dct[lt[0]] = int(lt[1], _integer_base)
                except Exception as e:
                    log_loading.info(
                        "Couldn't parse file [%s]: line [%r] (%s)",
                        filename,
                        line,
                        e,
                    )
    except IOError:
        log_loading.info("Can't open %s file", filename)
    return dct

Response: Parse / etc / protocols and return values as a dictionary.


Instruction:
How would you explain what the following Python 3 function does
def load_manuf(filename):
    manufdb = ManufDA(_name=filename)
    with open(filename, "rb") as fdesc:
        for line in fdesc:
            try:
                line = line.strip()
                if not line or line.startswith(b"#"):
                    continue
                parts = line.split(None, 2)
                oui, shrt = parts[:2]
                lng = parts[2].lstrip(b"#").strip() if len(parts) > 2 else ""
                lng = lng or shrt
                manufdb[oui] = plain_str(shrt), plain_str(lng)
            except Exception:
                log_loading.warning("Couldn't parse one line from [%s] [%r]",
                                    filename, line, exc_info=True)
    return manufdb

Response: Load the manuf file from Wireshark.


Instruction:
Implement a Python 3 function for
finding the OUI name matching to a MAC

Response:
def lookup(self, mac):
        """Find OUI name matching to a MAC"""
        oui = ":".join(mac.split(":")[:3]).upper()
        return self[oui]


Instruction:
Write a Python 3 script for
returning a dict of all MACs registered to a OUI.

Response:
def reverse_lookup(self, name, case_sensitive=False):
        """Find all MACs registered to a OUI
        params:
         - name: the OUI name
         - case_sensitive: default to False
        returns: a dict of mac:tuples (Name, Extended Name)
        """
        if case_sensitive:
            filtr = lambda x, l: any(x == z for z in l)
        else:
            name = name.lower()
            filtr = lambda x, l: any(x == z.lower() for z in l)
        return {k: v for k, v in six.iteritems(self.__dict__)
                if filtr(name, v)}


Instruction:
Explain what the following Python 3 code does
def answers(self, other):
        if not hasattr(other, "ctr"):
            return 0
        if self.ctr != other.ctr:
            return 0
        if not hasattr(other, "cmd"):
            return 0

        new_pl_cls = self.get_dto_cls(other.cmd)
        if self.payload_cls != new_pl_cls and \
                self.payload_cls == DEFAULT_DTO:
            data = bytes(self.load)
            self.remove_payload()
            self.add_payload(new_pl_cls(data))
            self.payload_cls = new_pl_cls
        return 1

Response: This function is used to determine the class of the payload of another DTO packet.


Instruction:
Write a Python 3 function that can
read the version from git describe.

Response:
def _version_from_git_describe():
    """
    Read the version from ``git describe``. It returns the latest tag with an
    optional suffix if the current directory is not exactly on the tag.

    Example::

        $ git describe --always
        v2.3.2-346-g164a52c075c8

    The tag prefix (``v``) and the git commit sha1 (``-g164a52c075c8``) are
    removed if present.

    If the current directory is not exactly on the tag, a ``.devN`` suffix is
    appended where N is the number of commits made after the last tag.

    Example::

        >>> _version_from_git_describe()
        '2.3.2.dev346'
    """
    if not os.path.isdir(os.path.join(os.path.dirname(_SCAPY_PKG_DIR), '.git')):  # noqa: E501
        raise ValueError('not in scapy git repo')

    process = subprocess.Popen(['git', 'describe', '--always'],
                               cwd=_SCAPY_PKG_DIR,
                               stdout=subprocess.PIPE, stderr=subprocess.PIPE)

    out, err = process.communicate()

    if process.returncode == 0:
        tag = out.decode().strip()
        match = re.match('^v?(.+?)-(\\d+)-g[a-f0-9]+$', tag)
        if match:
            # remove the 'v' prefix and add a '.devN' suffix
            return '%s.dev%s' % (match.group(1), match.group(2))
        else:
            # just remove the 'v' prefix
            return re.sub('^v', '', tag)
    else:
        raise subprocess.CalledProcessError(process.returncode, err)


Instruction:
Implement a Python 3 function for
returning a string representation of the object.

Response:
def _show_or_dump(self, dump=False, indent=3,
                      lvl="", label_lvl="", first_call=True):
        """ Reproduced from packet.py """
        ct = AnsiColorTheme() if dump else conf.color_theme
        s = "%s%s %s %s \n" % (label_lvl, ct.punct("###["),
                               ct.layer_name(self.name), ct.punct("]###"))
        for f in self.fields_desc[:-1]:
            ncol = ct.field_name
            vcol = ct.field_value
            fvalue = self.getfieldval(f.name)
            begn = "%s  %-10s%s " % (label_lvl + lvl, ncol(f.name),
                                     ct.punct("="),)
            reprval = f.i2repr(self, fvalue)
            if isinstance(reprval, str):
                reprval = reprval.replace("\n", "\n" + " " * (len(label_lvl) +
                                                              len(lvl) +
                                                              len(f.name) +
                                                              4))
            s += "%s%s\n" % (begn, vcol(reprval))
        f = self.fields_desc[-1]
        ncol = ct.field_name
        vcol = ct.field_value
        fvalue = self.getfieldval(f.name)
        begn = "%s  %-10s%s " % (label_lvl + lvl, ncol(f.name), ct.punct("="),)
        reprval = f.i2repr(self, fvalue)
        if isinstance(reprval, str):
            reprval = reprval.replace("\n", "\n" + " " * (len(label_lvl) +
                                                          len(lvl) +
                                                          len(f.name) +
                                                          4))
        s += "%s%s\n" % (begn, vcol(reprval))
        if self.payload:
            s += self.payload._show_or_dump(dump=dump, indent=indent,
                                            lvl=lvl + (" " * indent * self.show_indent),  # noqa: E501
                                            label_lvl=label_lvl, first_call=False)  # noqa: E501

        if first_call and not dump:
            print(s)
        else:
            return s


Instruction:
Can you tell what is the following Python 3 function doing
def getfield(self, pkt, s):
        ext = pkt.get_field(self.length_of)
        tmp_len = ext.length_from(pkt)
        if tmp_len is None or tmp_len <= 0:
            v = pkt.tls_session.tls_version
            if v is None or v < 0x0304:
                return s, None
        return super(_ExtensionsLenField, self).getfield(pkt, s)

Response: Return the length of the record from the extension field.


Instruction:
How would you code a function in Python 3 to
add a field to the internal buffer.

Response:
def addfield(self, pkt, s, i):
        """
        There is a hack with the _ExtensionsField.i2len. It works only because
        we expect _ExtensionsField.i2m to return a string of the same size (if
        not of the same value) upon successive calls (e.g. through i2len here,
        then i2m when directly building the _ExtensionsField).

        XXX A proper way to do this would be to keep the extensions built from
        the i2len call here, instead of rebuilding them later on.
        """
        if i is None:
            if self.length_of is not None:
                fld, fval = pkt.getfield_and_val(self.length_of)

                tmp = pkt.tls_session.frozen
                pkt.tls_session.frozen = True
                f = fld.i2len(pkt, fval)
                pkt.tls_session.frozen = tmp

                i = self.adjust(pkt, f)
                if i == 0:  # for correct build if no ext and not explicitly 0
                    return s
        return s + struct.pack(self.fmt, i)


Instruction:
Can you generate the documentation for the following Python 3 function
def _GenNetflowRecordV9(cls, lengths_list):
    _fields_desc = []
    for j, k in lengths_list:
        _f_data = NetflowV9TemplateFieldDecoders.get(k, None)
        _f_type, _f_args = (
            _f_data if isinstance(_f_data, tuple) else (_f_data, [])
        )
        _f_kwargs = {}
        if _f_type:
            if issubclass(_f_type, _AdjustableNetflowField):
                _f_kwargs["length"] = j
            _fields_desc.append(
                _f_type(
                    NetflowV910TemplateFieldTypes.get(k, "unknown_data"),
                    0, *_f_args, **_f_kwargs
                )
            )
        else:
            _fields_desc.append(
                _CustomStrFixedLenField(
                    NetflowV910TemplateFieldTypes.get(k, "unknown_data"),
                    b"", length=j
                )
            )

    # This will act exactly like a NetflowRecordV9, but has custom fields
    class NetflowRecordV9I(cls):
        fields_desc = _fields_desc
        match_subclass = True
    NetflowRecordV9I.name = cls.name
    NetflowRecordV9I.__name__ = cls.__name__
    return NetflowRecordV9I

Response: Internal function used to generate the Records from the given class and the given list of lengths.


Instruction:
Write a Python 3 function that can
use internally to process a single packet during defragmenting.

Response:
def _netflowv9_defragment_packet(pkt, definitions, definitions_opts, ignored):
    """Used internally to process a single packet during defragmenting"""
    # Dataflowset definitions
    if NetflowFlowsetV9 in pkt:
        current = pkt
        while NetflowFlowsetV9 in current:
            current = current[NetflowFlowsetV9]
            for ntv9 in current.templates:
                llist = []
                for tmpl in ntv9.template_fields:
                    llist.append((tmpl.fieldLength, tmpl.fieldType))
                if llist:
                    tot_len = sum(x[0] for x in llist)
                    cls = _GenNetflowRecordV9(NetflowRecordV9, llist)
                    definitions[ntv9.templateID] = (tot_len, cls)
            current = current.payload
    # Options definitions
    if NetflowOptionsFlowsetV9 in pkt:
        current = pkt
        while NetflowOptionsFlowsetV9 in current:
            current = current[NetflowOptionsFlowsetV9]
            # Load scopes
            llist = []
            for scope in current.scopes:
                llist.append((
                    scope.scopeFieldlength,
                    scope.scopeFieldType
                ))
            scope_tot_len = sum(x[0] for x in llist)
            scope_cls = _GenNetflowRecordV9(
                NetflowOptionsRecordScopeV9,
                llist
            )
            # Load options
            llist = []
            for opt in current.options:
                llist.append((
                    opt.optionFieldlength,
                    opt.optionFieldType
                ))
            option_tot_len = sum(x[0] for x in llist)
            option_cls = _GenNetflowRecordV9(
                NetflowOptionsRecordOptionV9,
                llist
            )
            # Storage
            definitions_opts[current.templateID] = (
                scope_tot_len, scope_cls,
                option_tot_len, option_cls
            )
            current = current.payload
    # Dissect flowsets
    if NetflowDataflowsetV9 in pkt:
        datafl = pkt[NetflowDataflowsetV9]
        tid = datafl.templateID
        if tid not in definitions and tid not in definitions_opts:
            ignored.add(tid)
            return
        # All data is stored in one record, awaiting to be split
        # If fieldValue is available, the record has not been
        # defragmented: pop it
        try:
            data = datafl.records[0].fieldValue
            datafl.records.pop(0)
        except (IndexError, AttributeError):
            return
        res = []
        # Flowset record
        # Now, according to the flow/option data,
        # let's re-dissect NetflowDataflowsetV9
        if tid in definitions:
            tot_len, cls = definitions[tid]
            while len(data) >= tot_len:
                res.append(cls(data[:tot_len]))
                data = data[tot_len:]
            # Inject dissected data
            datafl.records = res
            datafl.do_dissect_payload(data)
        # Options
        elif tid in definitions_opts:
            (scope_len, scope_cls,
                option_len, option_cls) = definitions_opts[tid]
            # Dissect scopes
            if scope_len:
                res.append(scope_cls(data[:scope_len]))
            if option_len:
                res.append(
                    option_cls(data[scope_len:scope_len + option_len])
                )
            if len(data) > scope_len + option_len:
                res.append(
                    conf.padding_layer(data[scope_len + option_len:])
                )
            # Inject dissected data
            datafl.records = res
            datafl.name = "Netflow DataFlowSet V9/10 - OPTIONS"


Instruction:
Create a Python 3 function to
process all NetflowV9 and NetflowOptionsFlowsetV9 packets to match IDs of the Headers of the DataFlowsets with the Headers of the DataFlowsets .

Response:
def netflowv9_defragment(plist, verb=1):
    """Process all NetflowV9/10 Packets to match IDs of the DataFlowsets
    with the Headers

    params:
     - plist: the list of mixed NetflowV9/10 packets.
     - verb: verbose print (0/1)
    """
    if not isinstance(plist, (PacketList, list)):
        plist = [plist]
    # We need the whole packet to be dissected to access field def in
    # NetflowFlowsetV9 or NetflowOptionsFlowsetV9/10
    definitions = {}
    definitions_opts = {}
    ignored = set()
    # Iterate through initial list
    for pkt in plist:
        _netflowv9_defragment_packet(pkt,
                                     definitions,
                                     definitions_opts,
                                     ignored)
    if conf.verb >= 1 and ignored:
        warning("Ignored templateIDs (missing): %s" % list(ignored))
    return plist


Instruction:
Write a Python 3 function for
converting a DER octet string to PEM format.

Response:
def der2pem(der_string, obj="UNKNOWN"):
    """Convert DER octet string to PEM format (with optional header)"""
    # Encode a byte string in PEM format. Header advertizes <obj> type.
    pem_string = ("-----BEGIN %s-----\n" % obj).encode()
    base64_string = base64.b64encode(der_string)
    chunks = [base64_string[i:i + 64] for i in range(0, len(base64_string), 64)]  # noqa: E501
    pem_string += b'\n'.join(chunks)
    pem_string += ("\n-----END %s-----\n" % obj).encode()
    return pem_string


Instruction:
How would you implement a function in Python 3 that
converts PEM string to DER format

Response:
def pem2der(pem_string):
    """Convert PEM string to DER format"""
    # Encode all lines between the first '-----\n' and the 2nd-to-last '-----'.
    pem_string = pem_string.replace(b"\r", b"")
    first_idx = pem_string.find(b"-----\n") + 6
    if pem_string.find(b"-----BEGIN", first_idx) != -1:
        raise Exception("pem2der() expects only one PEM-encoded object")
    last_idx = pem_string.rfind(b"-----", 0, pem_string.rfind(b"-----"))
    base64_string = pem_string[first_idx:last_idx]
    base64_string.replace(b"\n", b"")
    der_string = base64.b64decode(base64_string)
    return der_string


Instruction:
Can you generate the documentation for the following Python 3 function
def split_pem(s):
    pem_strings = []
    while s != b"":
        start_idx = s.find(b"-----BEGIN")
        if start_idx == -1:
            break
        end_idx = s.find(b"-----END")
        end_idx = s.find(b"\n", end_idx) + 1
        pem_strings.append(s[start_idx:end_idx])
        s = s[end_idx:]
    return pem_strings

Response: Split PEM objects. Useful to process concatenated certificates.


Instruction:
Write a Python 3 function for
creating a CAfile from the list of anchor_list and write the result to filename.

Response:
def _create_ca_file(anchor_list, filename):
    """
    Concatenate all the certificates (PEM format for the export) in
    'anchor_list' and write the result to file 'filename'. On success
    'filename' is returned, None otherwise.

    If you are used to OpenSSL tools, this function builds a CAfile
    that can be used for certificate and CRL check.
    """
    try:
        with open(filename, "w") as f:
            for a in anchor_list:
                s = a.output(fmt="PEM")
                f.write(s)
    except IOError:
        return None
    return filename


Instruction:
How would you explain what the following Python 3 function does
def verifyCert(self, cert):
        tbsCert = cert.tbsCertificate
        sigAlg = tbsCert.signature
        h = hash_by_oid[sigAlg.algorithm.val]
        sigVal = raw(cert.signatureValue)
        return self.verify(raw(tbsCert), sigVal, h=h, t='pkcs')

Response: Verifies either a Cert or X509_Cert.


Instruction:
Make a summary of the following Python 3 code
def signTBSCert(self, tbsCert, h="sha256"):
        sigAlg = tbsCert.signature
        h = h or hash_by_oid[sigAlg.algorithm.val]
        sigVal = self.sign(raw(tbsCert), h=h, t='pkcs')
        c = X509_Cert()
        c.tbsCertificate = tbsCert
        c.signatureAlgorithm = sigAlg
        c.signatureValue = _Raw_ASN1_BIT_STRING(sigVal, readable=True)
        return c

Response: Signs a TBSCert and returns a X509_Cert object with the signature field set to the signatureValue of the TBSCert.


Instruction:
Implement a function in Python 3 to
return True if the certificate is self - signed.

Response:
def isSelfSigned(self):
        """
        Return True if the certificate is self-signed:
          - issuer and subject are the same
          - the signature of the certificate is valid.
        """
        if self.issuer_hash == self.subject_hash:
            return self.isIssuerCert(self)
        return False


Instruction:
Can you tell what is the following Python 3 function doing
def isRevoked(self, crl_list):
        for c in crl_list:
            if (self.authorityKeyID is not None and
                c.authorityKeyID is not None and
                    self.authorityKeyID == c.authorityKeyID):
                return self.serial in (x[0] for x in c.revoked_cert_serials)
            elif self.issuer == c.issuer:
                return self.serial in (x[0] for x in c.revoked_cert_serials)
        return False

Response: This function returns True if the certificate is marked as revoked by one of the trusted CRLs in crl_list.


Instruction:
Write a Python 3 function for
exporting certificate in fmt format to file filename

Response:
def export(self, filename, fmt="DER"):
        """
        Export certificate in 'fmt' format (DER or PEM) to file 'filename'
        """
        f = open(filename, "wb")
        if fmt == "DER":
            f.write(self.der)
        elif fmt == "PEM":
            f.write(self.pem)
        f.close()


Instruction:
Write a Python 3 function for
verifying the chain for this certificate.

Response:
def verifyChain(self, anchors, untrusted=None):
        """
        Perform verification of certificate chains for that certificate.
        A list of anchors is required. The certificates in the optional
        untrusted list may be used as additional elements to the final chain.
        On par with chain instantiation, only one chain constructed with the
        untrusted candidates will be retained. Eventually, dates are checked.
        """
        untrusted = untrusted or []
        for a in anchors:
            chain = Chain(self + untrusted, a)
            if len(chain) == 1:             # anchor only
                continue
            # check that the chain does not exclusively rely on untrusted
            if any(c in chain[1:] for c in self):
                for c in chain:
                    if c.remainingDays() < 0:
                        break
                if c is chain[-1]:      # we got to the end of the chain
                    return chain
        return None


Instruction:
Implement a Python 3 function for
verifying the certificates in the cafile and return a list of anchors and untrusted certificates.

Response:
def verifyChainFromCAFile(self, cafile, untrusted_file=None):
        """
        Does the same job as .verifyChain() but using the list of anchors
        from the cafile. As for .verifyChain(), a list of untrusted
        certificates can be passed (as a file, this time).
        """
        try:
            f = open(cafile, "rb")
            ca_certs = f.read()
            f.close()
        except Exception:
            raise Exception("Could not read from cafile")

        anchors = [Cert(c) for c in split_pem(ca_certs)]

        untrusted = None
        if untrusted_file:
            try:
                f = open(untrusted_file, "rb")
                untrusted_certs = f.read()
                f.close()
            except Exception:
                raise Exception("Could not read from untrusted_file")
            untrusted = [Cert(c) for c in split_pem(untrusted_certs)]

        return self.verifyChain(anchors, untrusted)


Instruction:
Can you generate a brief explanation for the following Python 3 code
def verifyChainFromCAPath(self, capath, untrusted_file=None):
        try:
            anchors = []
            for cafile in os.listdir(capath):
                anchors.append(Cert(open(os.path.join(capath, cafile), "rb").read()))  # noqa: E501
        except Exception:
            raise Exception("capath provided is not a valid cert path")

        untrusted = None
        if untrusted_file:
            try:
                f = open(untrusted_file, "rb")
                untrusted_certs = f.read()
                f.close()
            except Exception:
                raise Exception("Could not read from untrusted_file")
            untrusted = [Cert(c) for c in split_pem(untrusted_certs)]

        return self.verifyChain(anchors, untrusted)

Response: Verify the chain of certificates in a directory.


Instruction:
How would you explain what the following Python 3 function does
def answers(self, other):
        if other.__class__ == self.__class__:
            return (other.service + 0x40) == self.service or \
                   (self.service == 0x7f and
                    self.request_service_id == other.service)
        return False

Response: Returns True if self is an answer from other.


Instruction:
Given the following Python 3 function, write the documentation
def _sndrcv_snd(pks, timeout, inter, verbose, tobesent, hsent, timessent, stopevent):  # noqa: E501
    try:
        i = 0
        rec_time = timessent is not None
        if verbose:
            print("Begin emission:")
        for p in tobesent:
            # Populate the dictionary of _sndrcv_rcv
            # _sndrcv_rcv won't miss the answer of a packet that has not been sent  # noqa: E501
            hsent.setdefault(p.hashret(), []).append(p)
            if stopevent.is_set():
                break
            # Send packet
            pks.send(p)
            if rec_time:
                timessent[i] = p.sent_time
            i += 1
            time.sleep(inter)
        if verbose:
            print("Finished sending %i packets." % i)
    except SystemExit:
        pass
    except KeyboardInterrupt:
        pass
    except Exception:
        log_runtime.exception("--- Error sending packets")
    if timeout is not None:
        def _timeout(stopevent):
            stopevent.wait(timeout)
            stopevent.set()
        thread = threading.Thread(
            target=_timeout, args=(stopevent,)
        )
        thread.setDaemon(True)
        thread.start()

Response: Function used in the sending thread of sndrcv


Instruction:
Given the following Python 3 function, write the documentation
def _sndrcv_rcv(pks, hsent, stopevent, nbrecv, notans, verbose, chainCC,
                multi, _storage_policy=None):
    """Function used to receive packets and check their hashret"""
    if not _storage_policy:
        _storage_policy = lambda x, y: (x, y)
    ans = []

    def _get_pkt():
        # SuperSocket.select() returns, according to each socket type,
        # the selected sockets + the function to recv() the packets (or None)
        # (when sockets aren't selectable, should be nonblock_recv)
        selected, read_func = pks.select([pks])
        read_func = read_func or pks.__class__.recv
        if selected:
            return read_func(selected[0])

    try:
        while True:
            r = _get_pkt()
            if stopevent.is_set():
                break
            if r is None:
                continue
            ok = False
            h = r.hashret()
            if h in hsent:
                hlst = hsent[h]
                for i, sentpkt in enumerate(hlst):
                    if r.answers(sentpkt):
                        ans.append(_storage_policy(sentpkt, r))
                        if verbose > 1:
                            os.write(1, b"*")
                        ok = True
                        if not multi:
                            del hlst[i]
                            notans -= 1
                        else:
                            if not hasattr(sentpkt, '_answered'):
                                notans -= 1
                            sentpkt._answered = 1
                        break
            if notans == 0 and not multi:
                del r
                break
            if not ok:
                if verbose > 1:
                    os.write(1, b".")
                nbrecv += 1
                if conf.debug_match:
                    debug.recv.append(r)
            del r
    except KeyboardInterrupt:
        if chainCC:
            raise
    finally:
        stopevent.set()
    return (hsent, ans, nbrecv, notans)

Response: Function used to receive packets and check their hashret


Instruction:
How would you explain what the following Python 3 function does
def send(x, inter=0, loop=0, count=None,
         verbose=None, realtime=None,
         return_packets=False, socket=None, *args, **kargs):
    """Send packets at layer 3
send(packets, [inter=0], [loop=0], [count=None], [verbose=conf.verb], [realtime=None], [return_packets=False],  # noqa: E501
     [socket=None]) -> None"""
    need_closing = socket is None
    socket = socket or conf.L3socket(*args, **kargs)
    results = __gen_send(socket, x, inter=inter, loop=loop,
                         count=count, verbose=verbose,
                         realtime=realtime, return_packets=return_packets)
    if need_closing:
        socket.close()
    return results

Response: Send a packet at layer 3.


Instruction:
Implement a Python 3 function for
sending packets at layer 2.

Response:
def sendp(x, inter=0, loop=0, iface=None, iface_hint=None, count=None,
          verbose=None, realtime=None,
          return_packets=False, socket=None, *args, **kargs):
    """Send packets at layer 2
sendp(packets, [inter=0], [loop=0], [iface=None], [iface_hint=None], [count=None], [verbose=conf.verb],  # noqa: E501
      [realtime=None], [return_packets=False], [socket=None]) -> None"""
    if iface is None and iface_hint is not None and socket is None:
        iface = conf.route.route(iface_hint)[0]
    need_closing = socket is None
    socket = socket or conf.L2socket(iface=iface, *args, **kargs)
    results = __gen_send(socket, x, inter=inter, loop=loop,
                         count=count, verbose=verbose,
                         realtime=realtime, return_packets=return_packets)
    if need_closing:
        socket.close()
    return results


Instruction:
Write a Python 3 function that can
send packets at layer 2 using tcpreplay for performance

Response:
def sendpfast(x, pps=None, mbps=None, realtime=None, loop=0, file_cache=False, iface=None, replay_args=None,  # noqa: E501
              parse_results=False):
    """Send packets at layer 2 using tcpreplay for performance
    pps:  packets per second
    mpbs: MBits per second
    realtime: use packet's timestamp, bending time with real-time value
    loop: number of times to process the packet list
    file_cache: cache packets in RAM instead of reading from disk at each iteration  # noqa: E501
    iface: output interface
    replay_args: List of additional tcpreplay args (List[str])
    parse_results: Return a dictionary of information outputted by tcpreplay (default=False)  # noqa: E501
    :returns stdout, stderr, command used"""
    if iface is None:
        iface = conf.iface
    argv = [conf.prog.tcpreplay, "--intf1=%s" % iface]
    if pps is not None:
        argv.append("--pps=%i" % pps)
    elif mbps is not None:
        argv.append("--mbps=%f" % mbps)
    elif realtime is not None:
        argv.append("--multiplier=%f" % realtime)
    else:
        argv.append("--topspeed")

    if loop:
        argv.append("--loop=%i" % loop)
    if file_cache:
        argv.append("--preload-pcap")

    # Check for any additional args we didn't cover.
    if replay_args is not None:
        argv.extend(replay_args)

    f = get_temp_file()
    argv.append(f)
    wrpcap(f, x)
    results = None
    with ContextManagerSubprocess("sendpfast()", conf.prog.tcpreplay):
        try:
            cmd = subprocess.Popen(argv, stdout=subprocess.PIPE,
                                   stderr=subprocess.PIPE)
        except KeyboardInterrupt:
            log_interactive.info("Interrupted by user")
        except Exception:
            os.unlink(f)
            raise
        else:
            stdout, stderr = cmd.communicate()
            if stderr:
                log_runtime.warning(stderr.decode())
            if parse_results:
                results = _parse_tcpreplay_result(stdout, stderr, argv)
            elif conf.verb > 2:
                log_runtime.info(stdout.decode())
    os.unlink(f)
    return results


Instruction:
Implement a function in Python 3 to
parse the output of tcpreplay and modify the results_dict to populate the output information.

Response:
def _parse_tcpreplay_result(stdout, stderr, argv):
    """
    Parse the output of tcpreplay and modify the results_dict to populate output information.  # noqa: E501
    Tested with tcpreplay v3.4.4
    Tested with tcpreplay v4.1.2
    :param stdout: stdout of tcpreplay subprocess call
    :param stderr: stderr of tcpreplay subprocess call
    :param argv: the command used in the subprocess call
    :return: dictionary containing the results
    """
    try:
        results = {}
        stdout = plain_str(stdout).lower()
        stderr = plain_str(stderr).strip().split("\n")
        elements = {
            "actual": (int, int, float),
            "rated": (float, float, float),
            "flows": (int, float, int, int),
            "attempted": (int,),
            "successful": (int,),
            "failed": (int,),
            "truncated": (int,),
            "retried packets (eno": (int,),
            "retried packets (eag": (int,),
        }
        multi = {
            "actual": ("packets", "bytes", "time"),
            "rated": ("bps", "mbps", "pps"),
            "flows": ("flows", "fps", "flow_packets", "non_flow"),
            "retried packets (eno": ("retried_enobufs",),
            "retried packets (eag": ("retried_eagain",),
        }
        float_reg = r"([0-9]*\.[0-9]+|[0-9]+)"
        int_reg = r"([0-9]+)"
        any_reg = r"[^0-9]*"
        r_types = {int: int_reg, float: float_reg}
        for line in stdout.split("\n"):
            line = line.strip()
            for elt, _types in elements.items():
                if line.startswith(elt):
                    regex = any_reg.join([r_types[x] for x in _types])
                    matches = re.search(regex, line)
                    for i, typ in enumerate(_types):
                        name = multi.get(elt, [elt])[i]
                        results[name] = typ(matches.group(i + 1))
        results["command"] = " ".join(argv)
        results["warnings"] = stderr[:-1]
        return results
    except Exception as parse_exception:
        if not conf.interactive:
            raise
        log_runtime.error("Error parsing output: " + str(parse_exception))
        return {}


Instruction:
Here you have a function in Python 3, explain what it does
def sr(x, promisc=None, filter=None, iface=None, nofilter=0, *args, **kargs):
    s = conf.L3socket(promisc=promisc, filter=filter,
                      iface=iface, nofilter=nofilter)
    result = sndrcv(s, x, *args, **kargs)
    s.close()
    return result

Response: Send and receive packets at layer 3


Instruction:
Write a Python 3 function that can
send packets at layer 3 and return only the first answer

Response:
def sr1(x, promisc=None, filter=None, iface=None, nofilter=0, *args, **kargs):
    """Send packets at layer 3 and return only the first answer"""
    s = conf.L3socket(promisc=promisc, filter=filter,
                      nofilter=nofilter, iface=iface)
    ans, _ = sndrcv(s, x, *args, **kargs)
    s.close()
    if len(ans) > 0:
        return ans[0][1]
    else:
        return None


Instruction:
How would you explain what the following Python 3 function does
def srp(x, promisc=None, iface=None, iface_hint=None, filter=None,
        nofilter=0, type=ETH_P_ALL, *args, **kargs):
    """Send and receive packets at layer 2"""
    if iface is None and iface_hint is not None:
        iface = conf.route.route(iface_hint)[0]
    s = conf.L2socket(promisc=promisc, iface=iface,
                      filter=filter, nofilter=nofilter, type=type)
    result = sndrcv(s, x, *args, **kargs)
    s.close()
    return result

Response: Send and receive packets at layer 2


Instruction:
Write a Python 3 function that can
send and receive packets at layer 2 and return only the first answer

Response:
def srp1(*args, **kargs):
    """Send and receive packets at layer 2 and return only the first answer"""
    ans, _ = srp(*args, **kargs)
    if len(ans) > 0:
        return ans[0][1]
    else:
        return None