Verify - PicoCTF

Difficulty	Easy
Category	Forensics
Event	picocTF 2024

Hi everyone.

This is my first post in this blog. In this blog we solve the CTF Verify of PicoCTF.

So, by the tags we know that we will use forencis and grep. When we start it will give us a command to connect via SSH.

Verify

The page gives us the following command to connect via SSH ssh -p 61677 ctf-player@rhea.picoctf.net.

Just to remember, the option -p in ssh it serves to specify the port.

After execurting the command type the password provided by the website.

SSH Connection

Once inside the server run ls to list the files in the directory. We see that there is a file called checksum.txt, we open it with cat checksum.txt.

Command ls and cat

It look like a sha256 checksum. Now we entrer in the files directory with cd files, we see that have several files, we need to find the file with the same sha256 that is inside checksum.txt

List of files

To know this we can use the following command:

 sha256sum files/*

However this shows us the checksum of all the files, we need to find the one that matches the known checksum.

Checksum

For this we can use grep. So, the command would look like this:

 sha256sum files/* | grep checksum

Command grep

Now with the decrypt.sh file, we decrypt and get the flag.

Flag