DiffieHellmanKeyExchange.py

# N = RandomPrime[{2^1020, 2^1025}]
# G = PrimitiveRoot[N]
import random

N = 450399019389671650452249084921759078761980896382890703798228170622215717666353
G = 3

def msgToNumber(msg):
    total = 0
    for i in range(len(msg)):
        c = msg[i]
        offset = 8 * (len(msg) - i - 1)
        total += (ord(c) << offset)
    return total

def numberToMsg(number):
    msg = []
    while number > 0:
        c_num = number & 0b11111111
        number = number >> 8
        msg.append(chr(c_num))
    return "".join(list(reversed(msg)))

# Alice and Bob choose private numbers
x = random.randrange(2**16, 2**18)
y = random.randrange(2**16, 2**18)
print("x:", x)
print("y:", y)

# Alice and Bob calculate exchange values
R1 = (G**x) % N
R2 = (G**y) % N
print("R1:", R1)
print("R2:", R2)

# R1 and R2 are exchanged and used to calculate
# K1, K2 where K1 == K2
K1 = (R2**x) % N
K2 = (R1**y) % N
print("K1:", K1)

# Plain text Message
msg = "Your secret message!"
print("msg:", msg)

# Message encrypted and sent by Alice
c = msgToNumber(msg) ^ K1
print("c:", c)

# Bob decrypts message and reads it
d = numberToMsg(c ^ K2)
print("d:", d)