s2s messaging | TG:HACK 2020| Misc Write-up

s2s messaging is a challenge of Misc category from TG:HACK 2020.

TG:HACK

The challenge description displays the following:

Description page

There is a pcap file which has been provided to us and a hint too . Let’s open the hint and read it.

Hint

The hint given to us is MQTT. MQTT is a machine-to-machine (M2M)/”Internet of Things” connectivity protocol. It was designed as an extremely lightweight publish/subscribe messaging transport.

Let us open up the pcap file given to us and analyze it.

pcap file

Now going by the hint “MQTT” given to us let us filter out the packets using the filter “mqtt”.The displayed packets are:

Filtered packets

We can see from these packets that there is a communication going on and messages are being sent.Let us check one one of the packets publishing the messages.Let us analyze the TCP stream to see what data is being transmitted.The message is being sent in encrypted form.Let us copy the message into a text file and analyze the encryption being used.

Tcp stream showing the data

Encrypted message

The encoding seems to be base 64. Let us decode the content by simply uploading the file.

Upload the file to decode

Interesting the decoded file seems to be an image!

When it is opened the image displays the text in flag format.

This is the flag of the challenge.

TG20{THIS IS A SHIP 2 SHIP MESSAGE: Prepare your disk space for boarding}