hyunsikjeong

from typing import Any, Union
from pwn import *

exe = ELF("./main")

context.binary = exe

# curve25519 is from https://gist.github.com/nickovs/cc3c22d15f239a2640c185035c06f8a3
from curve25519 import *
from curve25519 import _fix_secret, _unpack_number, _point_add, _point_double, _pack_number, _raw_curve25519, P

hyunsikjeong

from tqdm import tqdm

p = 0x00000001748a30b311afb13858f1dccf
q = 0x0000000120c02771bb5f8edae9364f45
N = p * q

# enc = 0x012a0a1ed3553e95527dedcf481b59d0fcad2c0ab5c3e8ac23
# enc = 0x017e72989e281ebe960631cd5d913e1b5d88ca5f50ca27904a
enc = int(sys.argv[1], 16)

hyunsikjeong

from Crypto.Cipher import AES
from Crypto.Util.number import *
from pwn import *
import sys

F.<x> = GF(2^128, name='x', modulus=x^128+x^7+x^2+x+1)

def bytes_to_element(b):
    v = bytes_to_long(b)
    e = 0

hyunsikjeong

#!/usr/bin/env python3

from z3 import *
import random
import string


def print_board(board):
    height, width = len(board), len(board[0])

hyunsikjeong

oflo

There are several anit-reversing logic, so I just patched with \x90 (nop instruction) to avoid them. After this process, it was able to figure out the logic of the program.

1. Use /bin/cat to something to get a string
2. XOR the prologue of a function by the first 5 bytes of the given input.
3. XOR the given input and the string from 1., then check the result is right.

The part 2. is easy to patch, because the first 5 bytes of the given input is always n1ctf.

hyunsikjeong

val = 0xB77C7C
ans = []

while val > 0:
    print(val)
    val >>= 2
    val -= 1
    ans.append(val % 4)

ans = ans[::-1]

hyunsikjeong

from Crypto.Util.number import *
from pwn import *

r = remote("crypto.kosenctf.com", 13003)

r.recvuntil("your query: ")
r.sendline('b')

l = r.recvuntil('\n')
c = [int(x) for x in l.split('[')[1].split(']')[0].split(",")]

hyunsikjeong

from Crypto.Util.number import *
from binascii import unhexlify, hexlify
import gmpy2

from pwn import *

def get_cube():
    sock = remote('crypto.kosenctf.com', 13001)
    n = int(sock.recvuntil('\n')[3:-1].decode())

hyunsikjeong

{
    "name": "XTerm-like",

    "cursorColor": "#ebebeb",
    "selectionBackground": "#ffffff",

    "background" : "#000000",
    "foreground" : "#ebebeb",

    "black" : "#000000",

hyunsikjeong

Keybase proof

I hereby claim:

• I am jhs7jhs on github.
• I am rbtree (https://keybase.io/rbtree) on keybase.
• I have a public key whose fingerprint is 3A77 4E51 675A E05C 40A8 AC1F A3C7 8ADB E4F0 C0DC

To claim this, I am signing this object: