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