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from Crypto.Util.number import (
bytes_to_long,
getPrime,
long_to_bytes,
getRandomNBitInteger,
)
import random
import hashlib
from math import gcd
import socketserver
KEYSIZE = 512
WELCOME = "welcome to my funny challenge !!! Can you guess right 32 times in a row? "
String = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890abcdefghijklmnopqrstuvwxyz"
def exgcd(a, b):
if b == 0:
return 1, 0, a
else:
x, y, q = exgcd(b, a % b)
x, y = y, (x - (a // b) * y)
return x, y, q
def invert(a,p):
x, y, q = exgcd(a,p)
if q != 1:
raise Exception("No solution.")
else:
return (x + p) % p
def lcm(a,b):
return a*b // gcd(a,b)
def proof_of_work():
STR = "".join([String[random.randint(0, len(String) - 1)] for _ in range(16)])
HASH = hashlib.sha256(STR.encode()).hexdigest()
return STR[:4], STR[4:], HASH
def keygen():
p, q = getPrime(KEYSIZE), getPrime(KEYSIZE)
n = p * q
g = n + 1
LAMBDA = lcm(p - 1, q - 1)
_key = open("key", "r").read()
key = []
for i in _key.split("\n"):
for j in i[1:-1].split(" "):
if int(j) not in key:
key.append(int(j))
assert len(key) == 80
assert key[0] == 119 and key[1] == 241 and key[2] == 718 and key[3] == 647
return n, g, LAMBDA, key
def enc(n, g, m):
while 1:
r = random.randint(2, n - 1)
if gcd(r, n) == 1:
break
c = (pow(g, m, n ** 2) * pow(r, n, n ** 2)) % (n ** 2)
return c
def dec(n, g, LAMBDA, c):
L1 = (pow(c, LAMBDA, n ** 2) - 1) // n
L2 = (pow(g, LAMBDA, n ** 2) - 1) // n
m = (invert(L2, n) * L1) % n
return m
class server(socketserver.BaseRequestHandler):
def _recv(self):
data = self.request.recv(1024)
return data.strip()
def _send(self, msg, newline=True):
if isinstance(msg, bytes):
msg += b"\n"
else:
msg += "\n"
msg = msg.encode()
self.request.sendall(msg)
def handle(self):
print("Service start.")
START, END, HASH = proof_of_work()
self._send("SHA-256(?+{}) == {}".format(END, HASH))
RCV = self._recv().decode()
if RCV != START:
return
flag = open("flag", "rb").read()
self._send(WELCOME)
for _ in range(32):
self._send("round " + str(_+1))
n, g, LAM, KEY = keygen()
self._send("Step 1 - KeyGen. This is my public key.")
self._send("n = " + str(n))
self._send("g = " + str(g))
self._send(
"Step 2 - Phase 1. Now, you can give me one ciphertexts,I will return the corresponding plaintext."
)
self._send("Please give me one decimal ciphertext.")
cipher = int(self._recv().decode())
plaintext = str(dec(n, g, LAM, cipher))
self._send("This is the corresponding plaintext.")
self._send(plaintext)
self._send(
"Step 3 - Challenge. Now, you must give me two decimal plaintexts(m0,m1), I will encry them and return a ciphertext randomly"
)
self._send("Give me m0.")
plaintext1 = int(self._recv().decode())
self._send("Give me m1.")
plaintext2 = int(self._recv().decode())
if (
plaintext1 <= 2
or plaintext2 <= 2
or len(bin(plaintext1)) != len(bin(plaintext2))
):
return
R = 2 * random.randint(0, 39)
I = random.randint(0, 1)
cipher1 = enc(n, g, plaintext1 * plaintext2 * KEY[R])
cipher2 = enc(n, g, plaintext1 * plaintext2 * KEY[R + 1])
self._send("This is a ciphertext.")
self._send(str([cipher1, cipher2][I]))
self._send(
"Step 4 - Phase 2. Now, you can give me some ciphertexts,I will return the corresponding plaintext.But you can not give me the ciphertext that I give you in step 3."
)
self._send("Please give me one decimal ciphertext ")
cipher = int(self._recv().decode())
plaintext = str(dec(n, g, LAM, cipher))
if int(plaintext) == plaintext1 * plaintext2 * KEY[R] or int(plaintext) == plaintext1 * plaintext2 * KEY[R+1]:
return
self._send("This is the corresponding plaintext.")
self._send(plaintext)
self._send(
"Step 5 - Guess. You must tell me which ciphertext was I give you in step 3, 0 or 1(m0 -> c0 , m1 -> c1)?"
)
Guess = int(self._recv().decode())
if Guess == I:
self._send("Good! You are right")
else:
self._send("Sorry!")
return
self._send(flag)
class ForkedServer(socketserver.ThreadingMixIn, socketserver.TCPServer):
pass
if __name__ == "__main__":
HOST, PORT = "0.0.0.0", 10001
server = ForkedServer((HOST, PORT), server)
server.allow_reuse_address = True
server.serve_forever()
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