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February 11, 2017 15:45
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RSA implementation in python
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# !usr/bin/python | |
# coding: utf-8 | |
# author: mdubourg001 : https://github.com/mdubourg001 | |
import random | |
import base64 | |
import struct | |
import sys | |
from random import randrange | |
def is_prime(n, k=30): | |
if n <= 3: | |
return n == 2 or n == 3 | |
neg_one = n - 1 | |
s, d = 0, neg_one | |
while not d & 1: | |
s, d = s+1, d>>1 | |
assert 2 ** s * d == neg_one and d & 1 | |
for i in range(k): | |
a = randrange(2, neg_one) | |
x = pow(a, d, n) | |
if x in (1, neg_one): | |
continue | |
for r in range(1, s): | |
x = x ** 2 % n | |
if x == 1: | |
return False | |
if x == neg_one: | |
break | |
else: | |
return False | |
return True | |
def randprime(N=10**8): | |
p = 1 | |
while not is_prime(p): | |
p = randrange(N) | |
return p | |
def pgcd(a,b) : | |
while a%b != 0 : | |
a, b = b, a%b | |
return b | |
def rand_e(): | |
e = 3 | |
while True: | |
e += 1 | |
if ((random.randint(1, 1000) % 42) == 0) and pgcd(e, fn) == 1: | |
return e | |
return e | |
def multinv(modulus, value): | |
x, lastx = 0, 1 | |
a, b = modulus, value | |
while b: | |
a, q, b = b, a // b, a % b | |
x, lastx = lastx - q * x, x | |
result = (1 - lastx * modulus) // value | |
if result < 0: | |
result += modulus | |
assert 0 <= result < modulus and value * result % modulus == 1 | |
return result | |
def print_encoded(ascii_arr): | |
toprint = "" | |
for nb in ascii_arr: | |
toprint += str(nb) | |
print ("Your encoded message is: " + toprint) | |
def encode(message): | |
# return a list containing (ascii_value_of_char**e % n) | |
to_return = [] | |
for c in message: | |
# fast exponentiation using pow | |
to_return.append(pow(ord(c), e, n)) | |
return to_return | |
def decode(ascci_msg): | |
result = "" | |
for nb in ascci_msg: | |
result += chr(pow(nb, d, n)) | |
return result | |
p = randprime(2**512) | |
q = randprime(2**512) | |
n = p * q | |
fn = (p-1) * (q-1) | |
e = rand_e() | |
d = multinv(fn, e) | |
if len(sys.argv) > 1: | |
m = sys.argv[1] | |
else: | |
m = "bonjour je suis le message a chiffrer puis a dechiffrer" | |
# public key is the couple (e, n) but conventionnaly b64 encoded | |
print ("Your b64 encoded public key is: \n\n %s, %s \n\n\n" % (base64.b64encode(str(e)), base64.b64encode(str(n)))) | |
# private key is the couple (d, n) but n is known in public key | |
print ("Your b64 encoded private key is \n\n%s \n\n\n" % (base64.b64encode(str(d)))) | |
crypt = encode(m) | |
#print_encoded(crypt) | |
print ("Your decoded message is " + decode(crypt)) |
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