PicoCTF Mod 26 Challenge Solved by Brute-Forcing All 26 Caesar Cipher Shifts

A beginner-level cryptography challenge on the picoGym platform tasked participants with decrypting a ciphertext secured using a Caesar cipher. The hint embedded in the challenge explicitly referenced adding 26 to each letter modulo the alphabet size, pointing directly to a Caesar cipher approach. Since the Caesar cipher has only 26 possible shift values, a short Python script could test every combination in under a second. Scanning all 26 outputs for the known flag prefix 'picoCTF{' immediately identified shift 4 as the correct key. The exercise highlights a fundamental weakness of classical ciphers: an extremely small key space makes brute-force attacks trivially fast and effective.