CTF- Mod 26 (picoCTF)

CTF- Mod 26 (picoCTF)

We delve again into the world of cryptography.

This a simple problem worth 10pts.

This problem was taken from the picoCTF 2021 and the solution will be discussed below. So proceed with caution.

The problem provides what seems to be a ciphertext:


It also asks us if we know what ROT13 is.

Just doing a simple Google search (as the hint suggests), we find that ROT refers to Caesar cipher and 13 refers to how much each character needs to be shifted if the character (26 letters of the alphabet only) is assigned its equivalent number.

For example, let's just decrypt the character cvpb. The cvpb is equivalent to 3-22-16-2. If we add 13 to each of the equivalent numbers (resetting the count if the sum goes over 26) we get 16-9-3-15. The decrypted code is equivalent to pico.

Rather than solving each letter individually, let's just use an online tool called https://rot13.com/

We have decoded the following flag using the tool:


Until next time. Keep learning.

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