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" # <-- set to your container name _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: """ Extracts 'ct : ' or 'pt : ' (label = 'ct' or 'pt') The service prints with spaces around the colon: 'ct : ' """ 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)') proc = self._spawn() def menu(): self._read_until(proc, "> ", timeout=5.0) menu() self._send_line(proc, "1") self._read_until(proc, "pt (hex)", timeout=3.0) self._read_until(proc, "> ", timeout=3.0) pt_hex = "414243444546" # "ABCDEF" self._send_line(proc, pt_hex) out = self._read_until(proc, "\n", timeout=3.0) ct_hex = self._expect_hex_field(out, "ct") self.logger.info("[ok] encrypt(1) produced hex CT") menu() 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_dec = self._read_until(proc, "\n", timeout=3.0) pt_back_hex = self._expect_hex_field(out_dec, "pt") # Normalize leading zeros for comparison def norm(h): return (h.lstrip("0") or "0").lower() assert norm(pt_back_hex) == norm(pt_hex), f"decrypt(encrypt(pt)) mismatch: {pt_back_hex} != {pt_hex}" self.logger.info("[ok] decrypt(3) round-trip") menu() self._send_line(proc, "1") self._read_until(proc, "pt (hex)", timeout=3.0) self._read_until(proc, "> ", timeout=3.0) same_pt = "01" * 8 self._send_line(proc, same_pt) out_a = self._read_until(proc, "\n", timeout=3.0) ct_a = self._expect_hex_field(out_a, "ct") menu() 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, same_pt) out_b = self._read_until(proc, "\n", timeout=3.0) ct_b = self._expect_hex_field(out_b, "ct") assert ct_a.lower() != ct_b.lower(), "Encryption appears deterministic for same plaintext" self.logger.info("[ok] encrypt(1) randomness") menu() self._send_line(proc, "2") out2a = self._read_until(proc, "\n", timeout=3.0) bingo1 = self._expect_hex_field(out2a, "ct") menu() self._send_line(proc, "2") out2b = self._read_until(proc, "\n", timeout=3.0) bingo2 = self._expect_hex_field(out2b, "ct") assert bingo1.lower() != bingo2.lower(), "Bingo ciphertexts reused randomness" self.logger.info("[ok] bingo(2) randomness") menu() self._send_line(proc, "1") self._read_until(proc, "pt (hex)", timeout=3.0) self._read_until(proc, "> ", timeout=3.0) pt_hex2 = "deadbeef" self._send_line(proc, pt_hex2) out_enc2 = self._read_until(proc, "\n", timeout=3.0) ct2 = self._expect_hex_field(out_enc2, "ct") menu() 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, ct2) out_dec2 = self._read_until(proc, "\n", timeout=3.0) pt2_back = self._expect_hex_field(out_dec2, "pt") assert norm(pt2_back) == norm(pt_hex2), f"decrypt(encrypt(pt2)) mismatch: {pt2_back} != {pt_hex2}" self.logger.info("[ok] decrypt(3) round-trip (case 2)") menu() 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") self.logger.info("[ok] service exit on 4") self.logger.info('Check passed for phew') return True except Exception as e: self.logger.error(f'Could not check phew: {e}') return False