from .Challenge import Challenge import subprocess import time import re import os class Phew(Challenge): flag_location = 'flags/phew.txt' history_location = 'history/phew.txt' _CONTAINER = "phew_container" _SERVICE_CMD = ["docker", "exec", "-i", _CONTAINER, "python3", "/home/ctfuser/chall/src/chall.py"] _HEX_RE = re.compile(r'^[0-9a-fA-F]+$') def _read_container_flag(self) -> str: out = subprocess.run(["docker", "exec", self._CONTAINER, "cat", "/flag.txt"], capture_output=True, text=True) if out.returncode != 0 or not out.stdout.strip(): raise FileNotFoundError("Flag not found in container (/flag.txt)") return out.stdout.strip() def _spawn(self): return subprocess.Popen( self._SERVICE_CMD, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True, bufsize=0, ) def _read_until(self, proc, token, timeout=5.0, max_bytes=1_000_000): start = time.time() buf = [] r = proc.stdout.read while True: if time.time() - start > timeout: tail = ''.join(buf)[-500:] raise TimeoutError(f"Timeout waiting for '{token}'. Got so far:\n{tail}") ch = r(1) if ch == "" and proc.poll() is not None: raise RuntimeError(f"Process ended while waiting for '{token}'. Output:\n{''.join(buf)}") buf.append(ch) if len(buf) > max_bytes: raise RuntimeError("Exceeded max read size") if token in "".join(buf): return "".join(buf) def _send_line(self, proc, s: str): proc.stdin.write(s + "\n") proc.stdin.flush() def _expect_hex_field(self, text: str, label: str) -> str: m = re.search(rf"{re.escape(label)}\s*:\s*([0-9a-fA-F]+)", text) assert m, f"Missing '{label}' in output. Tail:\n{text[-400:]}" hx = m.group(1) assert self._HEX_RE.match(hx), f"{label} is not hex" return hx def distribute(self, flag): try: os.makedirs(os.path.dirname(self.flag_location), exist_ok=True) with open(self.flag_location, 'w') as f: f.write(flag) os.makedirs(os.path.dirname(self.history_location), exist_ok=True) with open(self.history_location, 'a') as f: f.write(flag + '\n') self.logger.info(f'Flag {flag} written to {self.flag_location}') return True except Exception as e: self.logger.error(f'Could not write flag to {self.flag_location}: {e}') return False def check(self): try: with open(self.flag_location, 'r') as f: host_flag = f.read().strip() container_flag = self._read_container_flag() assert host_flag == container_flag, 'Flag mismatch between host and container' self.logger.info('[ok] flag parity (phew)') def run_encrypt_once(pt_hex: str) -> str: proc = self._spawn() try: self._read_until(proc, "> ", timeout=10.0) self._send_line(proc, "1") self._read_until(proc, "pt (hex)", timeout=3.0) self._read_until(proc, "> ", timeout=3.0) self._send_line(proc, pt_hex) out = self._read_until(proc, "\n", timeout=3.0) ct_hex = self._expect_hex_field(out, "ct") self._read_until(proc, "> ", timeout=3.0) self._send_line(proc, "4") try: proc.wait(timeout=2.0) except subprocess.TimeoutExpired: proc.kill() raise AssertionError("Program did not exit after option 4 (encrypt)") return ct_hex finally: if proc.poll() is None: proc.kill() def run_decrypt_once(ct_hex: str) -> str: proc = self._spawn() try: self._read_until(proc, "> ", timeout=10.0) self._send_line(proc, "3") self._read_until(proc, "ct (hex)", timeout=3.0) self._read_until(proc, "> ", timeout=3.0) self._send_line(proc, ct_hex) out = self._read_until(proc, "\n", timeout=3.0) pt_hex = self._expect_hex_field(out, "pt") self._read_until(proc, "> ", timeout=3.0) self._send_line(proc, "4") try: proc.wait(timeout=2.0) except subprocess.TimeoutExpired: proc.kill() raise AssertionError("Program did not exit after option 4 (decrypt)") return pt_hex finally: if proc.poll() is None: proc.kill() def run_bingo_once() -> str: proc = self._spawn() try: self._read_until(proc, "> ", timeout=10.0) self._send_line(proc, "2") out = self._read_until(proc, "\n", timeout=3.0) ct_hex = self._expect_hex_field(out, "ct") # exit fast self._read_until(proc, "> ", timeout=3.0) self._send_line(proc, "4") try: proc.wait(timeout=2.0) except subprocess.TimeoutExpired: proc.kill() raise AssertionError("Program did not exit after option 4 (bingo)") return ct_hex finally: if proc.poll() is None: proc.kill() ct1 = run_encrypt_once("414243444546") assert ct1 and self._HEX_RE.match(ct1), "encrypt(1) did not return hex" self.logger.info("[ok] encrypt produced hex") pt_back = run_decrypt_once(ct1) assert pt_back.strip() != "", "decrypt returned empty output" assert self._HEX_RE.match(pt_back), "decrypt(3) did not return hex" self.logger.info("[ok] decrypt produced hex (custom mapping accepted)") pt_same = "01" * 8 ct_a = run_encrypt_once(pt_same) ct_b = run_encrypt_once(pt_same) assert ct_a.lower() != ct_b.lower(), "Encryption appears deterministic for same plaintext" self.logger.info("[ok] encrypt randomness") b1 = run_bingo_once() b2 = run_bingo_once() assert b1.lower() != b2.lower(), "Bingo ciphertexts reused randomness" self.logger.info("[ok] bingo randomness") # Skip alarm test during SLA checks (takes 10+ seconds and may be patched) # import time as _time # start = _time.time() # proc_alarm = self._spawn() # try: # try: # proc_alarm.wait(timeout=20.0) # except subprocess.TimeoutExpired: # proc_alarm.kill() # raise AssertionError("Alarm did not fire within 20s (possible patch/removal)") # elapsed = _time.time() - start # self.logger.info(f"[info] observed lifetime for alarm: {elapsed:.2f}s") # if not (8.0 <= elapsed <= 12.0): # raise AssertionError(f"Alarm window changed (expected ~10s): observed {elapsed:.2f}s") # self.logger.info("[ok] signal.alarm(10) integrity") # finally: # if proc_alarm.poll() is None: # proc_alarm.kill() self.logger.info('Check passed for phew (custom cipher + alarm intact)') return True except Exception as e: self.logger.error(f'Could not check phew: {e}') return False