Probably Unbreakable

broncoctf2026

Task: a service XORs the flag with random key bytes drawn from a fixed 64-character alphabet and lets you request up to 20000 encryptions. Solution: for each flag position, intersect the candidate plaintext bytes (those where ciphertext XOR p lands in the alphabet) across all ciphertexts until exactly one survives — a restricted-alphabet XOR candidate-intersection attack, no PRNG state recovery needed.