- setup a web server that has ssl certificate configured.
- get the network traffic using wireshark.
- decode and analyze the network traffic using wireshark.
So first, what is SSL?
Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL), are cryptographic protocols designed to provide communication security over the Internet. They use X.509 certificates and hence asymmetric cryptography to authenticate the counterparty with whom they are communicating, and to exchange a symmetric key.
If you already have a web server with ssl certicate configured, you can skip step 1. This is the documentation which I used primarily. You may not succeed on the first attempt as it took me several attempts to get the ssl traffic decrypted. Words of advice, just do not give up.
1. setup a web server that has ssl certificate configured.
With this, you can either get the certificate from an authority or you can generate one. If you do not know how, you can google or you can request in the comment, maybe in the future, I will write a simple one. But here, I assume you have the certicate ready.
In the web server, with apache httpd being the most common, edit the configuration file. In the apache directory, edit the ssl.conf. Example.
<apache httpd directory>/sites-available/default-ssl.conf
change to according where you place the certificate and its private key. Enable this site and restart apache httpd and then you are set. I won't go into details for troubleshoothing problem if you encounter as this is not the main focus of this article and should leave as an exercise.
2. get the network traffic using wireshark.
Make sure wireshark that is currently installed has GnuTLS compiled. You can check using command below. The output must have GnuTLS and Gcrypt available.
$ wireshark --version | grep GnuTLS
with GnuTLS 2.12.23, with Gcrypt 1.5.3, with MIT Kerberos, with GeoIP, with
1.6.1, with libz 1.2.8, GnuTLS 2.12.23, Gcrypt 1.5.4, without AirPcap.
Then now launch wireshark using root. Ignore about the warnings or information you receive during launch wireshark as root. Note, you can also using dumpcap when you need to capture in the server, but I have not verify if this solution is working. $ sudo dumpcap -i wlan0 -f 'host 192.168.133.49 and tcp port 443' . Probably not because you need to configure the server private key and the client (browser) random key. That should leave as another exercise.
$ sudo wireshark
There are some fields black out for obvious reason, we want to protect the server and client. But it should be self descriptive when you complete the steps as mentioned here.
We will first configure section in ssl configuration so that wireshark will be able to decrypt the data traffic. As such, you will need the server private key, which you can get from step 1 above. To configure that, go to Edit then Preferences... see screenshot below.
A window from Wireshark: Preferences pop up. Now on the left menu, expand the Protocols in the tree and look for SSL. See screenshot below.
First, we will configure RSA keys list. Click on the Edit... button. Then another window pop up. Now add the server key. There are four out of five fields you need to fill in. See screenshot below for final output. Here I will explain the fields.
|IP address||The IP address of the SSL server in IPv4 or IPv6 format, or the following special values: any, anyipv4, anyipv6, 0.0.0.0. Put your server hostname or ip address if you know.|
|Port||The TCP port number, or the special value start_tls or 0. For web server, normally it run on port 443 and in this example, I gave port 443 because it is a remote server listening https traffic on port 443.|
|Protocol||A protocol name for the decrypted network data. Popular choices are http or data. If you enter an invalid protocol name an error message will show you the valid values. Because http data are encrypted using ssl, thus, we should put value http here.|
|Key File||path to the RSA private key. So locate where you put the server private key at your local workstation and then select the file here.|
|Password||only needed when the private key is in format PCKS#12 (typically a file with a .pfx or .p12 extension). In step 1, the server private key is in format PEM and thus, for this field, you can leave it empty. Saved by clicking OK. Click on Apply and then OK.|
The next field we are going to configure is the SSL debug file. This is a file written by this ssl module and I recommend you put a valid value here. You can tail this file later when the capture is started and you can inspect this file quickly (on the fly) when the decryption is happening. It is very good when your ssl decryption went wrong and this serve as a source of debug.
You should check the following fields.
- Reassemble SSL records spanning multiple TCP segments
- Reassemble SSL Application Data spanning multiple SSL records
Leave the field Message Authentication Code (MAC), ignore "mac failed and Pre-Shared-Key as is.
For the last field, (Pre)-Master-Secret log filename, fill in a value where in the next step, you will configure for the web browser environment. This is a file written by the client (web browser in our example) which is used by the client as a key to encrypt the data. Wireshark will read this file to decrypt the data.
That's it for the configuration, click on Apply button and OK button.
Now open another terminal and we will setup the environment so that client (browser) will dump the random key. Browser chromium will start to dump the keys to the file premaster.txt.
user@localhost:~$ export SSLKEYLOGFILE=/home/user/premaster.txt
Now tail the ssl debug file and this premaster file in another two terminal tabs and watch the progress.
Right now, we will capture the traffic. To do that, click on Capture from the menu then Options... See the screenshot below. Set the configuration correctly, I check wlan0 because this is a laptop where the https request will flow to and fro within this channel. Capture filter, put on the host and the IP address of the web server where you configure in step 1 above. In this example, my server ip address is 192.168.133.49, so host 192.168.133.49.
To start the capture, click on the Start button.
Now, trigger a https call to the server from the web browser (in this example, chromium) and watch wireshark capture and decrypt the https data! Check also the tabs in terminal when debug log and premaster.txt are rolling. Click on stop button when you are satisfy with the https request.
3. decode and analyze the network traffic using wireshark.
From step 2 above, you are now have a complete ssl dumped and it is decrypted! See screenshot below. You may have noticed that SSL data has another tab at the bottom know as Decrypted SSL data. In this screenshot, it is 9000bytes. Pretty awesome I must say.
Right click on the row of packet which has protocol TLSv1 and click on Follow SSL Stream. It will show the encrypted ssl traffic (https) which has been decrypted into a http traffic.
That's it folks. I hope you learn something and please visit on donation page to donate to us.