• URL: https://play.picoctf.org/practice/challenge/62
• Title: 13
• Tags: Easy, Cryptography, picoCTF 2019
• Author: Alex Fulton/Daniel Tunitis
• Started: 20 July 2025
• Solved: 20 July 2025
• Description: Cryptography can be easy, do you know what ROT13 is? cvpbPGS{abg_gbb_onq_bs_n_ceboyrz}

The encrypted flag is in the description. In fact, this is a similar problem to Mod 26. I just use my swiss-army knife for CTF which is CyberChef again.

picoCTF{not_too_bad_of_a_problem}

…

• URL: https://play.picoctf.org/practice/challenge/144
• Title: Mod 26
• Tags: Cryptography, Easy, picoCTF 2021
• Author: PANDU
• Started: 20 July 2025
• Solved: 20 July 2025
• Description: Cryptography can be easy, do you know what ROT13 is? values.txt

values.txt contains this text

cvpbPGS{arkg_gvzr_V'yy_gel_2_ebhaqf_bs_ebg13_45559noq}

As stated by definition, I was expected to decrypt the flag using ROT13. ROT13 is a way to decrypt and encrypt an alphabetic text by shifting its order cyclically by 13. A becomes N, B becomes M, et cetera. Below is the table

…