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zer0pts CTF 2021 OT or NOT OT solver script
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| from ptrlib import Socket | |
| from sys import exit | |
| con = Socket('crypto.ctf.zer0pts.com', 10130) | |
| enc = con.recvlineafter('Encrypted flag: ') | |
| p = int(con.recvlineafter('p = ')) | |
| bitsize = int(con.recvlineafter('key.bit_length() = ')) | |
| print('enc = {}'.format(enc)) | |
| print('p = {}'.format(p)) | |
| if p % 4 != 1: | |
| print('failed') | |
| exit() | |
| F = GF(p) | |
| n = F(-1) | |
| t = n.sqrt() | |
| if str(t).startswith('sqrt'): | |
| print('failed') | |
| exit() | |
| t = int(t) | |
| print('t = {}'.format(t)) | |
| key = [] # lowest first | |
| for i in range((bitsize + 1) // 2): | |
| con.sendlineafter('a = ', str(t).encode()) | |
| con.sendlineafter('b = ', str(p - t).encode()) | |
| con.sendlineafter('c = ', str(p - 1).encode()) | |
| con.sendlineafter('d = ', b'1337') # Not used | |
| x = int(con.recvlineafter('x = ')) | |
| y = int(con.recvlineafter('y = ')) | |
| z = int(con.recvlineafter('z = ')) # Not used | |
| print('x = {}'.format(x)) | |
| print('y = {}'.format(y)) | |
| print('z = {}'.format(z)) | |
| if 1 ^^ x <= 1: | |
| b1 = 1 ^^ x | |
| elif (p - 1) ^^ x <= 1: | |
| b1 = (p - 1) ^^ x | |
| elif t ^^ x <= 1: | |
| b1 = t ^^ x | |
| elif (p - t) ^^ x <= 1: | |
| b1 = (p - t) ^^ x | |
| else: | |
| print('failed') | |
| exit() | |
| if 1 ^^ y <= 1: | |
| b2 = 1 ^^ y | |
| elif (p - 1) ^^ y <= 1: | |
| b2 = (p - 1) ^^ y | |
| elif t ^^ y <= 1: | |
| b2 = t ^^ y | |
| elif (p - t) ^^ y <= 1: | |
| b2 = (p - t) ^^ y | |
| else: | |
| print('failed') | |
| exit() | |
| print('b1 = {}'.format(b1)) | |
| print('b2 = {}'.format(b2)) | |
| key.append(b1) | |
| key.append(b2) | |
| key.reverse() | |
| print(''.join(map(str, key))) |
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| from base64 import b64decode | |
| from Crypto.Cipher import AES | |
| from Crypto.Util.number import long_to_bytes | |
| key_n = 0b1011110110101000111010101110100101011111111111011000100111100001110101010011100010101011010111100000100111101011100101010110100101100111100010000100011100101001100000010011111000010100101100100010010110011010111110110110111101110110111100001111111001101000 | |
| key = long_to_bytes(key_n) | |
| enc = b64decode('VpD9EOCUAfDYWp1OV1+pFLY/8M29GIay0mXFLTzfVKlGxHFF2yRC38WXlH63/0Kz') | |
| print(len(enc)) | |
| iv = enc[0:16] | |
| c = enc[16:] | |
| print(len(iv)) | |
| print(len(c)) | |
| aes = AES.new(key=key, mode=AES.MODE_CBC, iv=iv) | |
| flag = aes.decrypt(c) | |
| print(flag) |
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