Garbage In, Flag Out

broncoctf2026

Task: two ciphertexts (random-lowercase garbage + flag) encrypted with the SAME random key, where the flag's key is the per-byte bit-reversal of the garbage key. Solution: a two-time-pad style attack — recover each key byte from the known-lowercase garbage plaintext, bit-reverse it, XOR with the flag ciphertext, and narrow candidates with a second garbage block whose derived-key high nibble is deterministic.