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{{ SECURITY Network packet Forensic }} 

Chapter 17 : Wireless Packet Analysis

With [Aircrack-ng] tool, you can try to de-crypt the messages of WEP from PCAP.

Depends on the release version of aircrack-ng tool, you may need to change the execusion file name like below :

From WiKipedia, you can check the simple method how to encrypt the message.

• In Open System authentication, the WLAN client need not provide its credentials to the Access Point during authentication. Any client can authenticate with the Access Point and then attempt to associate. In effect, no authentication occurs. Subsequently WEP keys can be used for encrypting data frames. At this point, the client must have the correct keys.

• In Shared Key authentication, the WEP key is used for authentication in a four-step challenge-response handshake:

1. The client sends an authentication request to the Access Point.
2. The Access Point replies with a clear-text challenge.
3. The client encrypts the challenge-text using the configured WEP key and sends it back in another authentication request.
4. The Access Point decrypts the response. If this matches the challenge text, the Access Point sends back a positive reply.

• After the authentication and association, the pre-shared WEP key is also used for encrypting the data frames using RC4.
  

• At first glance, it might seem as though Shared Key authentication is more secure than Open System authentication, since the latter offers no real authentication. However, it is quite the reverse. It is possible to derive the keystream used for the handshake by capturing the challenge frames in Shared Key authentication.

{{ SECURITY Network packet Forensic }} 

Chapter 17 : Wireless Packet Analysis

WLAN standard

• https://en.wikipedia.org/wiki/Template:802.11_network_standards

For the encryption, 802.11 is widely using WEP(Wired Equivalency Protocol). This protocol will encrypt each MAC frames with 40bit WEP key and random 24 bits Initialization Vector(IV) as RC4 Stream encryption method. But it should share the KEY ID and IV with plain text between AP and the devices which can be the threaten for the security.

{+WPA/WPA2-}

To make a connection, a device will send 'Probe Request' with AP's SSID information. If the AP can accept the request, it will reply 'Probe Response'. This procedure can be use for Service denial attack with massive 'Probe Request' trials.

Following is an example of simple WiFi connection.

1) Probe Request > Probe Response

2) Authentication

3) Association Request > Association Response

4) Key negotiation

5) Transfer data

As the packet has been encrypted, there is no message available to check from [Conversation] window.

If you know the key of the encryption, Wireshark will support the decryption. 

Now, you can see the decrypted messages from [Conversation] window 

References :

http://www.tcpdump.org/

www.iana.org/assignments/port-numbers

{{ SECURITY Network packet Forensic }} 

Chapter 13-1 : Shell code packet analysis

From following example, there is some suspicious data to run [calc.exe].

After converting it hex format, there are many 0x90 in-front of the data. This could be NOP(No Operation) code to use buffer overflow attach. To know what those codes mean, it should be converted to assembly code. The last 4 bytes will indicate the CRLF (Carriage Return) to change the line for HTTP. Let us make some assumption it will be a shell code.

Wireshark provides a good way to display the data for C array type as following.

After copy the content to a text file, change it to a binary file. And try to check whether it's real binary code or not.

References :

http://codinguy.net/2013/06/03/insertion-encoderdecoder-shellcode/

http://gnuwin32.sourceforge.net/packages/hex2bin.htm

{{ SECURITY Network packet Forensic }} 

Chapter 9-2 : Port scan and Packet analysis

For TCP scan, 3-way handshaking will be used to check the opened ports.

Fro UDP scan, if some ports are opened then there will be no response. So in this case, you can checked 'ICMP unreachable' message for the closed ports.

In [Conversation] menu, select [UDP] tab.

There is no TCP like session establishment procedure. But there is ICMP protocol which is belong to layer 3.

And using filter, you can checked the open UDP ports.

   [ip.src==192.168.0.112 && ip.dst==192.168.0.15&&udp&not icmp]

{{ SECURITY Network packet Forensic }} 

Chapter 9-1 : Port scan and Packet analysis

For TCP scan, 3-way handshaking will be used to check the opened ports.

Fro UDP scan, if some ports are opened then there will be no response. So in this case, you can checked 'ICMP unreachable' message for the closed ports.

From [Conversation] menu, you can estimate the port scan tries with following patterns. If you use [Follow Stream] button, there will be no information.

To check more detail for each conversion, apply filter for that conversations.

The first conversation has [RST] response from [192.168.0.15] with port [1] for the [SYN] request of [192.168.0.112]. That means the requested port[1] is closed.

But, the port 25 has some information with [220 Welcome trinitysoft] string.

Unlike the 1st conversation for port [1], this has TCP 3 way Handshaking. And right after that, there is session close procedure. From this procedure, you can notice that the port [25] has been opened.

Please also note that the data has been sent with [PSH,ACK] flag. And then there is [ACK] response from the peer.

To check the opened ports only, try TCP flag filtering. Set value [1] for [==] relation for [tcp.flags.syn] field name.

Then you can add more condition in Filter input box.

For failed port open, you can modify the filter as [tcp.flags.reset == 1 && tcp.flags.ack == 1].