Mod 26
1 minute to read
We are given a ciphertext:
cvpbPGS{arkg_gvzr_V'yy_gel_2_ebhaqf_bs_ebg13_GYpXOHqX}
We see that the message has more or less the format of a picoCTF flag (picoCTF{...}), due to the fact that there are 4 lowercase and 3 uppercase letters before {, and ends with }. Moreover, there are several _.
It seems clear that the encryption is based on a substitution algorithm (Caesar cipher). The most common algorithm is ROT13. Using CyberChef, we can decrypt the message using ROT13 and read the flag:
