Pattern is the key

ringzer0ctf

Task: 56-byte ciphertext (escaped hex) encrypted with repeating-key XOR; recover the plaintext. Solution: detect period-8 key via repeated block + per-column Index of Coincidence, crib-drag the 'FLAG' word at an 8-aligned non-zero offset to recover the 8-byte leet key '1337...', verify by re-encryption; decoded plaintext is ASCII art framing the real token.