The string looks – it ends with = padding and only contains the usual Base64 alphabet.
with open(sys.argv[1], 'rb') as f: raw = f.read().strip() result = decode_until_plaintext(raw) print(result.decode(errors='replace')) mypassword.foundever
Some CTF challenges hide data behind multiple transformations (Base64 → XOR → ROT, etc.). The string looks – it ends with =
Thus, the solution was to decode until the data stopped looking like Base64. mypassword.foundever