Challenge Description
Why "Mod 26"?
ROT13 shifts each letter by 13 positions in the alphabet. Since the English alphabet has 26 letters, this shift wraps around modularly (hence “Mod 26”). Mathematically, for a letter at position
x(0–25), ROT13 computes(x + 13) mod 26. Because 13 + 13 = 26 ≡ 0 (mod 26), ROT13 is self-inverse: encrypting and decrypting use the exact same operation.
For this challenge, we do not need to download any files. We can copy the encrypted string cvpbPGS{arkg_gvzr_V'yy_gel_2_ebhaqf_bs_ebg13_Ncualgvd} and head over to CyberChef.
The Flag
As the challenge description suggests, the string is encrypted using ROT13. So we use ROT13 to decrypt it.
Flag
picoCTF{next_time_I’ll_try_2_rounds_of_rot13_Aphnytiq}