记录一下我解的几题。
Crypto#
numerology#
题目给的是个基于Python 3.12的pyc文件，需要反编译一下。PyLingual直接搞出来的长这样 ↗
整下来几十个error，不像是能用的样子，扔给Gemini优化一下
task_optimized_by_Gemini.py
# Decompiled with PyLingual (https://pylingual.io)
# Internal filename: ./crypto_numerology.py
# Bytecode version: 3.12.0rc2 (3531)
# Source timestamp: 2025-06-06 16:54:22 UTC (1749228862)
import argparse
import json
import os
import struct
import sys
from pathlib import Path
CHACHA_CONSTANTS = (1634760805, 857760878, 2036477234, 1797285236)
# This global was misplaced inside a function by the decompiler.
# It is used to set the initial constants to zero for the challenge.
struct.zeros = (0, 0, 0, 0)
def rotl32(v, c):
"""Rotate a 32-bit unsigned integer left by c bits."""
v &= 4294967295
return v << c & 4294967295 | v >> 32 - c
def add32(a, b):
"""Add two 32-bit unsigned integers, wrapping modulo 2^32."""
return (a + b) & 4294967295
def bytes_to_words(b):
"""Convert a byte string (little-endian) to a list of 32-bit words."""
if len(b) % 4 != 0:
raise ValueError('Input bytes length must be a multiple of 4 for word conversion.')
return list(struct.unpack('<' + 'I' * (len(b) // 4), b))
def words_to_bytes(w):
"""Convert a list of 32-bit words to a little-endian byte string."""
return struct.pack('<' + 'I' * len(w), *w)
def mix_bits(state_list, a_idx, b_idx, c_idx, d_idx):
"""
Mixes Bits. Modifies state_list in-place.
"""
a, b, c, d = (state_list[a_idx], state_list[b_idx], state_list[c_idx], state_list[d_idx])
a = add32(a, b)
d ^= a
d = rotl32(d, 16)
c = add32(c, d)
b ^= c
b = rotl32(b, 12)
a = add32(a, b)
d ^= a
d = rotl32(d, 8)
c = add32(c, d)
b ^= c
b = rotl32(b, 7)
state_list[a_idx], state_list[b_idx], state_list[c_idx], state_list[d_idx] = (a, b, c, d)
def make_block(key_bytes, nonce_bytes, counter_int, current_constants_tuple, rounds_to_execute=8):
"""
Generates one 64-byte block of bits, allowing control over the
number of rounds executed.
"""
if len(key_bytes) != 32:
raise ValueError('Key must be 32 bytes')
if len(nonce_bytes) != 12:
raise ValueError('Nonce must be 12 bytes')
if not 1 <= rounds_to_execute <= 8:
raise ValueError('rounds_to_execute must be between 1 and 8 for this modified version.')
state = [0] * 16
state[0:4] = current_constants_tuple
try:
key_words = bytes_to_words(key_bytes)
nonce_words = bytes_to_words(nonce_bytes)
except ValueError as e:
raise ValueError(f'Error converting key/nonce to words: {e}')
else:
state[4:12] = key_words
state[12] = counter_int & 4294967295
state[13:16] = nonce_words
initial_state_snapshot = list(state)
qr_operations_sequence = [
lambda s: mix_bits(s, 0, 4, 8, 12),
lambda s: mix_bits(s, 1, 5, 9, 13),
lambda s: mix_bits(s, 2, 6, 10, 14),
lambda s: mix_bits(s, 3, 4, 9, 14), # Diagonal round
lambda s: mix_bits(s, 0, 5, 10, 15),
lambda s: mix_bits(s, 1, 6, 11, 12),
lambda s: mix_bits(s, 2, 7, 8, 13),
lambda s: mix_bits(s, 3, 5, 9, 14) # Custom diagonal round
]
# The original ChaCha has 20 rounds (10 column, 10 diagonal).
# This version has a custom sequence and allows 1-8 rounds to be run.
# The sequence provided by the decompiler seems to be a mix of column and custom rounds.
# To preserve functionality, we use the first `rounds_to_execute` operations from the sequence.
# The decompiled sequence had some errors, corrected to a plausible 8-round sequence.
# Let's assume the original had a fixed sequence and we just execute a subset.
# The decompiled code had a sequence of 6. Let's stick to that to preserve logic.
qr_operations_sequence_from_decompiler = [
lambda s: mix_bits(s, 0, 4, 8, 12),
lambda s: mix_bits(s, 1, 5, 9, 13),
lambda s: mix_bits(s, 2, 6, 10, 14),
lambda s: mix_bits(s, 0, 5, 10, 15), # Note: this is a diagonal round
lambda s: mix_bits(s, 2, 7, 8, 13), # Note: this is a custom round
lambda s: mix_bits(s, 3, 4, 9, 14) # Note: this is a custom round
]
for i in range(rounds_to_execute):
# The decompiler implies the sequence is indexed directly.
# We'll assume the sequence is at least as long as the max rounds (8).
# The provided sequence has 6 elements. We'll use it as is.
if i < len(qr_operations_sequence_from_decompiler):
qr_operations_sequence_from_decompiler[i](state)
else:
# To handle rounds > 6, we can either stop or raise an error.
# Raising an error is safer if the intent is unclear.
raise IndexError("rounds_to_execute exceeds the defined operation sequence length.")
for i in range(16):
state[i] = add32(state[i], initial_state_snapshot[i])
return words_to_bytes(state)
def get_bytes(key_bytes, nonce_bytes, initial_counter_int, data_bytes, current_constants_tuple, rounds_to_execute=8):
"""
Encrypts or decrypts data using a mysterious cipher.
The num_double_rounds parameter is implicitly 1 (one application of the round structure),
with the actual mixing controlled by rounds_to_execute.
"""
output_byte_array = bytearray()
current_counter = initial_counter_int & 4294967295
data_len = len(data_bytes)
block_idx = 0
while block_idx < data_len:
try:
keystream_block = make_block(key_bytes, nonce_bytes, current_counter, current_constants_tuple, rounds_to_execute=rounds_to_execute)
except Exception as e:
raise Exception(f'Error in make_block during stream processing for counter {current_counter}: {e}')
else:
remaining_data_in_block = data_len - block_idx
chunk_len = min(64, remaining_data_in_block)
for i in range(chunk_len):
output_byte_array.append(data_bytes[block_idx + i] ^ keystream_block[i])
block_idx += 64
if block_idx < data_len:
current_counter = (current_counter + 1) & 4294967295
if current_counter == 0 and initial_counter_int != 0 and (data_len > 64):
print(f'Warning: counter for nonce {nonce_bytes.hex()} wrapped around to 0 during a multi-block message.')
return bytes(output_byte_array)
def increment_byte_array_le(byte_arr: bytearray, amount: int, num_bytes: int) -> bytearray:
"""Increments a little-endian byte array representing an integer by a given amount."""
if len(byte_arr) != num_bytes:
raise ValueError(f'Input byte_arr length must be {num_bytes}')
val = int.from_bytes(byte_arr, 'little')
val = val + amount
max_val = 1 << num_bytes * 8
new_val_bytes = (val % max_val).to_bytes(num_bytes, 'little', signed=False)
return bytearray(new_val_bytes)
def construct_structured_key(active_material_hex: str) -> bytes:
""" Constructs a 32-byte key. If structured, uses 16 bytes of active material."""
key_words_int = [0] * 8
if len(active_material_hex) != 32:
raise ValueError('For patterned keys, active_material_hex must be 16 bytes (32 hex characters).')
active_material_bytes = bytes.fromhex(active_material_hex)
am_idx = 0
def get_am_word():
nonlocal am_idx
if am_idx + 4 > len(active_material_bytes):
raise ValueError('Not enough active material for the 4 active key words.')
word = int.from_bytes(active_material_bytes[am_idx:am_idx + 4], 'little')
am_idx += 4
return word
key_words_int[1] = get_am_word()
key_words_int[3] = get_am_word()
key_words_int[4] = get_am_word()
key_words_int[6] = get_am_word()
key_bytes_list = []
for word_int in key_words_int:
key_bytes_list.append(word_int.to_bytes(4, 'little'))
return b''.join(key_bytes_list)
def generate_challenge_data(flag_string: str, rounds_to_run: int, message_size_bytes: int, known_key_active_material_hex: str, secret_target_nonce_hex: str, secret_target_counter_int: int, num_nonce_variations: int, num_counter_variations: int, output_package_file: Path):
print(f'Starting CTF challenge package generation: {output_package_file}')
selected_constants = struct.zeros
try:
secret_target_nonce_bytes = bytes.fromhex(secret_target_nonce_hex)
except ValueError as e:
print(f'FATAL ERROR: Invalid hex in secret_target_nonce_hex: {e}', file=sys.stderr)
sys.exit(1)
known_structured_key_bytes = construct_structured_key(known_key_active_material_hex)
known_structured_key_hex = known_structured_key_bytes.hex()
print(f'INFO: Known structured key for player: {known_structured_key_hex}')
p_common_bytes = os.urandom(message_size_bytes)
p_common_hex = p_common_bytes.hex()
print(f'INFO: Generated P_common ({message_size_bytes} bytes) for learning dataset.')
learning_dataset_entries = []
base_learning_nonce_suffix_start = bytearray([0] * 12)
base_learning_counter_start = 0
sample_count = 0
for i in range(num_nonce_variations):
nonce_offset = 1 << i
current_nonce_bytes = increment_byte_array_le(base_learning_nonce_suffix_start, nonce_offset, 12)
current_nonce_hex = bytes(current_nonce_bytes).hex()
for j in range(num_counter_variations):
counter_offset = 1 << j
current_counter_int = base_learning_counter_start + counter_offset
sample_id = f'sample_n{i}_c{j}'
c_i_bytes = get_bytes(key_bytes=known_structured_key_bytes, nonce_bytes=bytes(current_nonce_bytes), initial_counter_int=current_counter_int, data_bytes=p_common_bytes, current_constants_tuple=selected_constants, rounds_to_execute=rounds_to_run)
learning_dataset_entries.append({'sample_id': sample_id, 'plaintext_hex': p_common_hex, 'ciphertext_hex': c_i_bytes.hex(), 'nonce_hex': current_nonce_hex, 'counter_int': current_counter_int})
sample_count += 1
if (i + 1) % (num_nonce_variations // 10 or 1) == 0 or i + 1 == num_nonce_variations:
print(f' Generated learning data for nonce variation {i + 1}/{num_nonce_variations}...')
print(f'Generated {sample_count} total learning samples.')
p_secret_flag_bytes = flag_string.encode('utf-8')
print(f'Encrypting the secret flag string (\'{flag_string[:20]}...\') with the KNOWN key using SECRET target_nonce/counter...')
c_target_flag_bytes = get_bytes(key_bytes=known_structured_key_bytes, nonce_bytes=secret_target_nonce_bytes, initial_counter_int=secret_target_counter_int, data_bytes=p_secret_flag_bytes, current_constants_tuple=selected_constants, rounds_to_execute=rounds_to_run)
c_target_flag_hex = c_target_flag_bytes.hex()
challenge_package_data = {
'cipher_parameters': {
'key': known_structured_key_hex,
'common_plaintext': p_common_hex
},
'learning_dataset_for_player': learning_dataset_entries,
'flag_ciphertext': c_target_flag_hex
}
try:
with open(output_package_file, 'w') as f:
json.dump(challenge_package_data, f, indent=4)
print(f'Successfully wrote challenge package to {output_package_file}')
except IOError as e:
print(f'FATAL ERROR: Could not write package {output_package_file}: {e}', file=sys.stderr)
sys.exit(1)
print('\nCTF Data generation complete.')
def main():
parser = argparse.ArgumentParser(formatter_class=argparse.RawTextHelpFormatter)
parser.add_argument('--output_file', type=str, default='ctf_nc_recovery_pkg.json', help='Filename for the single JSON challenge package.')
parser.add_argument('--flag_string', type=str, required=True, help='The actual secret flag string to be encrypted.')
parser.add_argument('--rounds', type=int, default=2, help='Actual number of rounds to execute (1-6, default: 2 for a very weak variant).')
parser.add_argument('--message_size_bytes', type=int, default=64, help='Size of P_common in learning dataset (bytes, default: 64).')
parser.add_argument('--known_key_active_material_hex', type=str, required=True, help='Hex string for the 16-byte non-zero part of the known key.')
parser.add_argument('--secret_target_nonce_hex', type=str, required=True, help='SECRET nonce (hex, 24 chars) to be recovered by player.')
parser.add_argument('--secret_target_counter_int', type=int, required=True, help='SECRET counter to be recovered by player.')
parser.add_argument('--num_nonce_variations', type=int, default=32, help='Number of distinct nonce patterns for learning set (default: 32).')
parser.add_argument('--num_counter_variations', type=int, default=32, help='Number of distinct counter values for each nonce pattern in learning set (default: 32).')
args = parser.parse_args()
if not 1 <= args.rounds <= 6: # Adjusted to match the implemented round sequence length
print('ERROR: --rounds must be 1-6.', file=sys.stderr)
sys.exit(1)
try:
# This call is for validation only
construct_structured_key(args.known_key_active_material_hex)
except ValueError as e:
print(f'ERROR: --known_key_active_material_hex is invalid: {e}', file=sys.stderr)
sys.exit(1)
if len(args.secret_target_nonce_hex) != 24:
print('ERROR: --secret_target_nonce_hex must be 24 hex chars.', file=sys.stderr)
sys.exit(1)
try:
# This call is for validation only
bytes.fromhex(args.secret_target_nonce_hex)
except ValueError:
print('ERROR: --secret_target_nonce_hex invalid hex.', file=sys.stderr)
sys.exit(1)
if args.num_nonce_variations < 1 or args.num_counter_variations < 1:
print('ERROR: Variation counts must be at least 1.', file=sys.stderr)
sys.exit(1)
if args.message_size_bytes < 1:
print('ERROR: --message_size_bytes must be at least 1.', file=sys.stderr)
sys.exit(1)
output_package_file_path = Path(args.output_file)
output_package_file_path.parent.mkdir(parents=True, exist_ok=True)
generate_challenge_data(
flag_string=args.flag_string,
rounds_to_run=args.rounds,
message_size_bytes=args.message_size_bytes,
known_key_active_material_hex=args.known_key_active_material_hex,
secret_target_nonce_hex=args.secret_target_nonce_hex,
secret_target_counter_int=args.secret_target_counter_int,
num_nonce_variations=args.num_nonce_variations,
num_counter_variations=args.num_counter_variations,
output_package_file=output_package_file_path
)
if __name__ == '__main__':
main()然后是最关键的题目配置:
init.sh
# Example for your script that runs init_cryptanalysis.py
# (Ensure set_secrets.sh has run and created secrets.env)
#!/bin/bash
cd "$(dirname "$0")"
if [ ! -f "./secrets.env" ]; then
echo "ERROR: secrets.env not found. Please run set_secrets.sh first."
exit 1
fi
source secrets.env # Load SECRET_TARGET_NONCE_HEX, SECRET_TARGET_COUNTER_INT, KNOWN_KEY_ACTIVE_MATERIAL_HEX, KNOWN_KEY_STRUCTURE
if [ ! -f "flag.txt" ]; then
echo "ERROR: flag.txt not found."
exit 1
fi
FLAG_STRING=$(cat flag.txt)
OUTPUT_PKG_FILE="./ctf_challenge_package.json" # This is what your linear_cryptanalysis.sh reads
ROUNDS=1
MESSAGE_SIZE=64
NUM_NONCE_VARS=64
NUM_COUNTER_VARS=64
echo "Running init_cryptanalysis.py to generate challenge package..."
python3 task.py \
--output_file "${OUTPUT_PKG_FILE}" \
--flag_string "${FLAG_STRING}" \
--rounds ${ROUNDS} \
--message_size_bytes ${MESSAGE_SIZE} \
--known_key_active_material_hex "${KNOWN_KEY_ACTIVE_MATERIAL_HEX}" \
--secret_target_nonce_hex "${SECRET_TARGET_NONCE_HEX}" \
--secret_target_counter_int ${SECRET_TARGET_COUNTER_INT} \
--num_nonce_variations ${NUM_NONCE_VARS} \
--num_counter_variations ${NUM_COUNTER_VARS} \然后还有很长的json输出，就不贴了，总之里面给了加密用的key。
AI整出来的py跟题目里pyc的行为其实还是有点不一致，比如，pyc其实是会检查你的SECRET_TARGET_NONCE_HEX并要求开头四字符是0的，但是这个py脚本好像不会检查这一点。不过下面我们就会看到这其实不影响做题。
这题的加密是明显弱化过的ChaCha20——mix_bits的轮数可以指定：
而写在init.sh里的mix_bits的轮数是1而非20：
ROUNDS=1
我们知道ChaCha20的matrix是这么构造的:
这题的constant是全0(大概吧，虽然反编译出来的东西有一个global variable是CHACHA20的magic number，但是还有一行莫名其妙的struct.zero)，key是给出的，那么这个矩阵里就只剩四个input未知，分别对应Counter和Nonce。因为只做了一次mix_bits，所以最终受影响的只有state[0], state[4], state[8], state[12]，其中只有state[12]未知。state[12]对应Counter，爆破一下就能到前13个state生成的52 bytes的密钥流，而flag只有42 bytes长，解密绰绰有余——所以后三个对应nonce的state其实压根没用。
solve.py
import json
import struct
from pathlib import Path
def rotl32(v, c):
v &= 4294967295
return v << c & 4294967295 | v >> 32 - c
def add32(a, b):
return (a + b) & 4294967295
def bytes_to_words(b):
if len(b) % 4 != 0:
raise ValueError('Input bytes length must be a multiple of 4 for word conversion.')
return list(struct.unpack('<' + 'I' * (len(b) // 4), b))
def words_to_bytes(w):
return struct.pack('<' + 'I' * len(w), *w)
def mix_bits(state_list, a_idx, b_idx, c_idx, d_idx):
a, b, c, d = (state_list[a_idx], state_list[b_idx], state_list[c_idx], state_list[d_idx])
a = add32(a, b)
d ^= a
d = rotl32(d, 16)
c = add32(c, d)
b ^= c
b = rotl32(b, 12)
a = add32(a, b)
d ^= a
d = rotl32(d, 8)
c = add32(c, d)
b ^= c
b = rotl32(b, 7)
state_list[a_idx], state_list[b_idx], state_list[c_idx], state_list[d_idx] = (a, b, c, d)
def make_block(key_bytes, nonce_bytes, counter_int, current_constants_tuple, rounds_to_execute=1):
state = [0] * 16
state[0:4] = current_constants_tuple
key_words = bytes_to_words(key_bytes)
nonce_words = bytes_to_words(nonce_bytes)
state[4:12] = key_words
state[12] = counter_int & 4294967295
state[13:16] = nonce_words
initial_state_snapshot = list(state)
if rounds_to_execute >= 1:
mix_bits(state, 0, 4, 8, 12)
for i in range(16):
state[i] = add32(state[i], initial_state_snapshot[i])
return words_to_bytes(state)
def solve():
challenge_file = Path('ctf_challenge_package.json')
if not challenge_file.exists():
print(f"Error: {challenge_file} not found. Make sure it's in the same directory.")
return
with open(challenge_file, 'r') as f:
data = json.load(f)
key_hex = data['cipher_parameters']['key']
ct_hex = data['flag_ciphertext']
key_bytes = bytes.fromhex(key_hex)
ct = bytes.fromhex(ct_hex)
constants = (0, 0, 0, 0)
rounds = 1
FLAG_PREFIX = b'CTF{'
MAX_COUNTER_TO_CHECK = 1_000_000
found_counter = 0
for candidate_counter in range(MAX_COUNTER_TO_CHECK):
if candidate_counter > 0 and candidate_counter % 100_000 == 0:
print(f" ... trying counter: {candidate_counter}")
dummy_nonce = b'\x00' * 12
keystream_block = make_block(key_bytes, dummy_nonce, candidate_counter, constants, rounds)
decrypted_prefix = bytearray()
for i in range(min(len(FLAG_PREFIX), len(ct))):
decrypted_prefix.append(ct[i] ^ keystream_block[i])
if decrypted_prefix == FLAG_PREFIX[:len(decrypted_prefix)]:
found_counter = candidate_counter
print(f"\n[+] Found potential counter: {found_counter}")
part_dec = bytearray()
for i in range(min(52, len(ct))):
part_dec.append(ct[i] ^ keystream_block[i])
print(f"[+] Flag Candidate: {part_dec.decode('ascii', errors='ignore')}")
tmp = input("Correct? (y/n): ").strip().lower()
if tmp == 'y':
print("🎉🎉🎉")
break
else:
print("[-] Continuing search for the correct counter...")
found_counter = 0
if found_counter == 0:
print("[-] ERROR: this method is not working...")
return
if __name__ == '__main__':
solve()
# [+] Found potential counter: 32279
# [+] Flag Candidate: CTF{w3_aRe_g0Nn@_ge7_MY_FuncKee_monkey_!!}
# 🎉🎉🎉filtermaze#
chall.py
# filtermaze.py
import json
import secrets
import sys
from dataclasses import asdict, dataclass, field
from typing import List
import numpy as np
# This is a placeholder path for local testing.
# On the real server, this will be a secret, longer path.
SECRET_HAMILTONIAN_PATH = [0]
@dataclass
class LWEParams:
lwe_n: int = 50
lwe_m: int = 100
lwe_q: int = 1009
A: List[int] = field(init=False)
s: List[int] = field(init=False)
e: List[int] = field(init=False)
b: List[int] = field(init=False)
def __post_init__(self):
self.lwe_error_range = [secrets.randbelow(self.lwe_q) for _ in range(self.lwe_m)]
def load_graph(filepath):
with open(filepath, "r") as f:
graph_data = json.load(f)
return {int(k): v for k, v in graph_data.items()}
def load_flag(filepath):
with open(filepath, "r") as f:
flag = f.readline().strip()
return flag
def create_lwe_instance_with_error(n, m, q, error_mags):
s = np.array([secrets.randbelow(q) for _ in range(n)], dtype=int)
A = np.random.randint(0, q, size=(m, n), dtype=int) # Public matrix
e = np.array([secrets.choice([-mag, +mag]) for mag in error_mags], dtype=int)
b = (A @ s + e) % q
return A.tolist(), s.tolist(), e.tolist(), b.tolist()
class PathChecker:
def __init__(
self,
secret_path,
graph_data,
lwe_error_mags,
):
self.secret_path = secret_path
self.graph = graph_data
self.lwe_error_mags = lwe_error_mags
self.path_len = len(self.secret_path)
def check(self, candidate_segment):
seg_len = len(candidate_segment)
if seg_len > self.path_len:
return False
for i, node in enumerate(candidate_segment):
if node != self.secret_path[i]: # Node mismatch
return False
if i > 0:
prev_node = candidate_segment[i - 1]
neighbors = self.graph.get(prev_node)
if neighbors is None or node not in neighbors:
return False
if seg_len == self.path_len:
error_magnitudes = [int(abs(err_val)) for err_val in self.lwe_error_mags]
return error_magnitudes
else:
return True
def main():
flag = load_flag("flag")
graph_data = load_graph("graph.json")
lwe_params = LWEParams()
if len(sys.argv) > 1:
if sys.argv[1] == "--new":
lwe_A, lwe_s_key, lwe_e_signed, lwe_b = create_lwe_instance_with_error(
lwe_params.lwe_n, lwe_params.lwe_m, lwe_params.lwe_q, lwe_params.lwe_error_range
)
lwe_params.A = lwe_A
lwe_params.b = lwe_b
lwe_params.s = lwe_s_key
lwe_params.e = lwe_e_signed
with open("lwe_secret_params.json", "w") as s:
json.dump(asdict(lwe_params), s, indent=2)
else:
with open("lwe_secret_params.json", "r") as s:
lwe_params = json.load(s)
lwe_A = lwe_params.get("A")
lwe_s_key = lwe_params.get("s")
lwe_e_signed = lwe_params.get("e")
lwe_b = lwe_params.get("b")
path_checker = PathChecker(
secret_path=SECRET_HAMILTONIAN_PATH,
graph_data=graph_data,
lwe_error_mags=lwe_e_signed,
)
initial_messages = [
"Welcome! I've hidden the key at the end of the maze. You can use this to open the chest to get the flag.",
'Commands: {"command": "check_path", "segment": [...]}',
' {"command": "get_flag", "lwe_secret_s": [...] }',
]
for msg in initial_messages:
print(msg, flush=True)
for line in sys.stdin:
data_str = line.strip()
if not data_str:
continue
response_payload = {}
try:
client_command = json.loads(data_str)
command = client_command.get("command")
if command == "check_path":
segment = client_command.get("segment")
if not isinstance(segment, list):
raise TypeError("Segment must be a list.")
path_result = path_checker.check(segment)
if isinstance(path_result, list):
response_payload = {
"status": "path_complete",
"lwe_error_magnitudes": path_result,
}
elif path_result is True:
response_payload = {"status": "valid_prefix"}
else:
response_payload = {"status": "path_incorrect"}
elif command == "get_flag":
key_s_raw = client_command.get("lwe_secret_s")
if not isinstance(key_s_raw, list):
raise TypeError("lwe_secret_s must be a list.")
if key_s_raw == lwe_s_key:
response_payload = {"status": "success", "flag": flag}
else:
response_payload = {"status": "invalid_key"}
else:
response_payload = {"status": "error", "message": "Unknown command"}
except (json.JSONDecodeError, ValueError, TypeError) as e:
json_err = f"Invalid format or data: {e}"
response_payload = {
"status": "error",
"message": json_err,
}
except Exception as e_cmd:
err_mesg = f"Error processing command '{data_str}': {e_cmd}"
response_payload = {"status": "error", "message": err_mesg}
print(json.dumps(response_payload), flush=True) # Send response to stdout
if response_payload.get("flag"):
break
if __name__ == "__main__":
main()graph.json
{
"0": [12, 29, 2, 15],
"1": [28, 16, 10, 0],
"2": [17, 3, 0, 20],
"3": [4, 11, 18, 2],
"4": [25, 3, 5, 19],
"5": [13, 4, 20, 6],
"6": [5, 26, 21, 7],
"7": [22, 14, 8, 6],
"8": [7, 23, 9, 27],
"9": [10, 24, 15, 8],
"10": [25, 11, 1, 9],
"11": [10, 3, 12, 26],
"12": [13, 0, 11, 27, 5],
"13": [14, 28, 12, 6],
"14": [22, 13, 29, 7],
"15": [1, 29, 9, 0],
"16": [17, 2, 24, 1],
"17": [2, 16, 3, 25],
"18": [19, 26, 4, 3],
"19": [4, 18, 5, 27],
"20": [2, 6, 5, 28],
"21": [29, 6, 7, 22],
"22": [7, 21, 14, 8],
"23": [29, 8, 9, 24],
"24": [10, 16, 23, 9],
"25": [17, 10, 4, 11],
"26": [18, 6, 11, 12],
"27": [19, 13, 8, 12],
"28": [1, 13, 20, 14],
"29": [14, 23, 0, 15, 21]
}{
"lwe_n": 50,
"lwe_m": 100,
"lwe_q": 1009,
"A": [
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"b": [
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}前半部分要你找个Hamilton回路，逐结点扩展后发过去会告诉你当前扩展的结点对不对，简单DFS不作赘述。
后半部分是经典的 形式的LWE，知道A、b、q的同时会把e的绝对值给你。但是模数很小同时和error非常接近，这一点最初把我带偏了，以为格不出来，所以我最初是想办法取了50个方程求出A的逆之后把s表示出来，然后一半s的分量挪到等式另一边，这样就可以尝试MITM爆破系数。
后来试了试发现用上NumPy之后单核也要180h左右并且非常吃内存才想到这似乎不是正解XD
其实还是得格，用优化后的primal attack再在格的下面添上e就好了。
前面优化的部分参考鸡块的blog ↗，后半参考exp吧，懒得打公式了（
exp.py
from sage.all import (
matrix,
vector,
ZZ,
block_matrix,
diagonal_matrix,
Zmod,
identity_matrix,
)
import subprocess
import json
from pwn import context, remote, log
from re import findall
import os
context.log_level = "info"
def solve_pow(command) -> str:
log.info(f"Running PoW command: {command}")
ret = subprocess.run(
command,
shell=True,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE,
encoding="utf-8",
executable="/bin/bash",
)
if ret.returncode == 0:
log.success(f"PoW solver success: {ret.stdout.strip()}")
return ret.stdout.strip()
else:
log.error(f"PoW solver failed: {ret.stderr.strip()}")
raise Exception(f"Command failed: {command}\n{ret.stderr.strip()}")
def check_path(path_segment: list) -> dict:
payload = {"command": "check_path", "segment": path_segment}
io.sendline(json.dumps(payload).encode())
response_raw = io.recvline()
return json.loads(response_raw.decode())
def flatter(M):
# compile https://github.com/keeganryan/flatter and put it in $PATH
z = "[[" + "]\n[".join(" ".join(map(str, row)) for row in M) + "]]"
env = os.environ.copy()
env["OMP_NUM_THREADS"] = "8" # 控制线程数量
ret = subprocess.check_output(["flatter"], input=z.encode(), env=env)
return matrix(M.nrows(), M.ncols(), map(int, findall(rb"-?\d+", ret)))
io = remote("filtermaze.2025.ctfcompetition.com", 1337, ssl=False)
io.recvuntil(b"the solver with:\n")
cmd = io.recvline().strip().decode()
res = solve_pow(cmd)
io.sendlineafter(b"Solution? ", res.encode())
io.recvuntil(b'{"command": "get_flag", "lwe_secret_s": [...] }\n')
log.info("PoW accepted. Starting maze traversal.")
# Searching the secret path
with open("graph.json", "r") as f:
graph_str_keys = json.load(f)
graph = {int(k): v for k, v in graph_str_keys.items()}
secret_path = []
all_nodes = sorted(list(graph.keys()))
for node in all_nodes:
log.debug(f"Testing node {node} as the starting point...")
resp = check_path([node])
if resp.get("status") == "valid_prefix":
secret_path.append(node)
log.success(f"Found starting node: {node}")
break
if not secret_path:
log.error("Failed to find the starting node")
log.info("Starting to extend the path...")
lwe_error_magnitudes = []
while True:
current_node = secret_path[-1]
neighbors = graph.get(current_node, [])
found_next_node = False
for neighbor in sorted(neighbors):
# ensure Hamilton path
if neighbor in secret_path:
continue
test_path = secret_path + [neighbor]
resp = check_path(test_path)
status = resp.get("status")
if status == "valid_prefix":
secret_path.append(neighbor)
log.debug(f"Path extended: {secret_path}")
found_next_node = True
break
elif status == "path_complete":
secret_path.append(neighbor)
log.success(f"Found the full secret path!")
lwe_error_magnitudes = resp.get("lwe_error_magnitudes")
log.success("Received LWE error magnitudes.")
found_next_node = True
break
if not found_next_node:
log.error(
f"Could not find the next node from {current_node}. Path so far: {secret_path}"
)
break
if lwe_error_magnitudes:
break
log.info("Maze Traversal Complete")
log.info(f"Final Secret Path ({len(secret_path)} nodes): {secret_path}")
log.info(
f"LWE Error Magnitudes (m={len(lwe_error_magnitudes)}): {lwe_error_magnitudes}"
)
with open("lwe_error_magnitudes.json", "w") as f:
json.dump({"lwe_error_magnitudes": lwe_error_magnitudes}, f, indent=2)
with open("lwe_pub_params.json", "r") as f:
lwe_pub_params = json.load(f)
with open("lwe_error_magnitudes.json") as f:
lwe_error_params = json.load(f)
# Solving LWE
n = lwe_pub_params["lwe_n"]
m = lwe_pub_params["lwe_m"]
q = lwe_pub_params["lwe_q"]
A = matrix(ZZ, lwe_pub_params["A"])
b = vector(lwe_pub_params["b"])
lwe_error_magnitudes = lwe_error_params["lwe_error_magnitudes"]
mags_vec = vector(ZZ, lwe_error_magnitudes)
log.debug(f"Parameters: n={n}, m={m}, q={q}")
R1 = block_matrix(
ZZ, [[matrix(Zmod(q), A).T.echelon_form().change_ring(ZZ), matrix.zero(n, m + 1)]]
)
R2 = block_matrix(
ZZ,
[
[
matrix.zero(m - n, n).augment(matrix.identity(m - n) * q),
matrix.zero(m - n, m + 1),
],
],
)
R3 = block_matrix(ZZ, [[matrix(ZZ, b), 1, matrix([0] * m)]])
R4 = block_matrix(
ZZ, [[diagonal_matrix(ZZ, [*mags_vec]), matrix.zero(m, 1), identity_matrix(m)]]
)
L = block_matrix(ZZ, [[R1], [R2], [R3], [R4]])
L[:, :m] *= 2**64
# LLL is enough but I prefer flatter :)
M = flatter(L)
cands = []
# Appending diagonal_matrix(e) to the lower-left of the lattice yields the signs in rows [m + 1 :]
for row in M:
if row[:m] == 0:
cands.append(row[m + 1 :])
res = list(matrix(cands)[0])
assert all(abs(c) == 1 for c in res)
Zq = Zmod(q)
A = matrix(Zq, lwe_pub_params["A"])
b = vector(Zq, lwe_pub_params["b"])
error_mags = vector(ZZ, lwe_error_magnitudes)
error_signs = vector(ZZ, res)
e_list_ZZ = [error_mags[i] * error_signs[i] for i in range(m)]
e_vec_ZZ = vector(ZZ, e_list_ZZ)
e_vec_Zq = vector(Zq, e_vec_ZZ)
# A*s = b - e (mod q)
target_vector_t = b - e_vec_Zq
log.debug("Solving the linear system A*s = t (mod q)...")
try:
s = A.solve_right(target_vector_t)
log.success("System solved successfully!")
s_list = [int(x) for x in s]
except ValueError as e:
log.error(f"[-] Could not solve the linear system. Error: {e}")
with open("lwe_secret_s.json", "w") as f:
json.dump({"lwe_secret_s": s_list}, f, indent=2)
with open("lwe_secret_s.json", "r") as f:
secret_data = json.load(f)
lwe_secret_s = secret_data["lwe_secret_s"]
flag_payload = {"command": "get_flag", "lwe_secret_s": lwe_secret_s}
io.sendline(json.dumps(flag_payload).encode())
log.success("Flag response received:")
flag_response = io.recvall()
print(flag_response.decode())
io.close()
# {"status": "success", "flag": "CTF{d4_sup3r_sh0rt_3rr0r_v3ct0r_1s_th3_k3y}"}后面试验发现就用原版primal attack的格把e放缩一下也是可以的，将每个 、 乘以对应的 就能将误差范围缩小到
Misc#
*bpfbox#
赛中差一点解出来，赛后才upsolved。
还是想复杂了
main.go
package main
import (
"bufio"
"context"
"fmt"
"os"
"os/exec"
"strconv"
"strings"
"syscall"
"time"
)
const probeText = `
BEGIN {
printf("ready\n")
}
fentry:vmlinux:security_create_user_ns {
signal(KILL);
}
fentry:vmlinux:security_file_open {
$inode = args->file->f_inode;
$d = $inode->i_sb->s_dev;
$i = $inode->i_ino;
if ($d == $1 && $i == $2) {
signal(KILL);
}
}
`
func getProbeParams(filename string) (uint64, uint64, error) {
info, err := os.Stat("/flag.txt")
if err != nil {
return 0, 0, err
}
stat, ok := info.Sys().(*syscall.Stat_t)
if !ok {
return 0, 0, fmt.Errorf("expected Stat_t, but was: %s", info.Sys())
}
return stat.Dev, stat.Ino, nil
}
func runTracer(ctx context.Context, dev, ino uint64, rdy chan struct{}, errs chan error) {
cmd := exec.CommandContext(ctx, "/bin/bpftrace", "--unsafe", "-e", probeText, strconv.FormatUint(dev, 10), strconv.FormatUint(ino, 10))
// cmd.Wait will close the reader automatically
reader, err := cmd.StdoutPipe()
if err != nil {
errs <- err
return
}
err = cmd.Start()
if err != nil {
errs <- err
return
}
// wait for the probe to be ready
scanner := bufio.NewScanner(reader)
for scanner.Scan() {
if strings.Contains(scanner.Text(), "ready") {
break
}
}
close(rdy)
err = cmd.Wait()
if err != nil {
panic(err)
}
}
func mountFilesystems() error {
if err := syscall.Mount("devtmpfs", "/dev", "devtmpfs", 0, ""); err != nil {
return fmt.Errorf("error mounting /dev: %s", err)
}
if err := os.Mkdir("/proc", 0555); err != nil {
return fmt.Errorf("error creating /proc: %s", err)
}
if err := syscall.Mount("proc", "/proc", "proc", 0, ""); err != nil {
return fmt.Errorf("error mounting /proc: %s", err)
}
if err := os.Mkdir("/sys", 0555); err != nil {
return fmt.Errorf("error creating /sys: %s", err)
}
if err := syscall.Mount("sysfs", "/sys", "sysfs", 0, ""); err != nil {
return fmt.Errorf("error mounting /sys: %s", err)
}
if err := syscall.Mount("tracefs", "/sys/kernel/tracing", "tracefs", 0, ""); err != nil {
return fmt.Errorf("error mounting /sys/kernel/tracing: %s", err)
}
if err := syscall.Mount("debugfs", "/sys/kernel/debug", "debugfs", 0, ""); err != nil {
return fmt.Errorf("error mounting /sys/kernel/debug: %s", err)
}
if err := os.Mkdir("/tmp", 0555); err != nil {
return fmt.Errorf("error creating /tmp: %s", err)
}
if err := syscall.Mount("tmpfs", "/tmp", "tmpfs", syscall.MS_NOEXEC|syscall.MS_NODEV|syscall.MS_NOSUID, ""); err != nil {
return fmt.Errorf("error mounting /tmp: %s", err)
}
return nil
}
func shutdown() error {
return syscall.Reboot(syscall.LINUX_REBOOT_CMD_POWER_OFF)
}
func spawnShell(ctx context.Context) error {
withTimeout, cancel := context.WithTimeout(ctx, time.Minute)
defer cancel()
cmd := exec.CommandContext(withTimeout, "/bin/sh")
cmd.SysProcAttr = &syscall.SysProcAttr{
Credential: &syscall.Credential{Uid: 99999, Gid: 99999},
Setpgid: true,
Pdeathsig: syscall.SIGKILL,
}
cmd.Stdout = os.Stdout
cmd.Stdin = os.Stdin
cmd.Stderr = os.Stderr
if err := cmd.Start(); err != nil {
return err
}
if err := cmd.Wait(); err != nil {
fmt.Println("command failed:", err)
}
return nil
}
func main() {
if err := mountFilesystems(); err != nil {
panic(err)
}
dev, ino, err := getProbeParams("/flag.txt")
if err != nil {
panic(err)
}
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
rdy := make(chan struct{})
errs := make(chan error)
go runTracer(ctx, dev, ino, rdy, errs)
select {
case err = <-errs:
panic(err)
case <-rdy:
}
if err := spawnShell(ctx); err != nil {
panic(err)
}
if err := shutdown(); err != nil {
panic(err)
}
panic("unreachable")
}Linux内核题，用BPF Probe追踪并signal SIGKILL杀掉所有尝试读取flag.txt的进程。
这里有个小bug，靶机里实际上是signal SIGINT
连上靶机后看到内核版本是6.12.33，我最初以为是利用CVE-2025-21756去提权然后搞事情，试了试很快就领教到了kctf jail的严密，想上传文件RCE对我这种三脚猫水平而言几乎不可能。
然后想到可能是race——我可以在一个进程打开文件之后、被杀掉之前用另一个进程读这个进程的fd，说不定就可以读到flag。但是很遗憾构造的payload没打通QQ
完赛后回来看了看这题，想到说其实最简单的race说不定就可以：
while true; do ( cat flag.txt & ); done
试了下还真的能通🥲
进一步地，其实直接提示GPT试试看race的话也会吐出一个可用的exp:
for i in $(seq 1 100); do
cat /flag.txt &
done但是赛中我说的太多了好像反而把大模型带偏了TT
