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@cypher-nullbyte
Forked from ErbaAitbayev/rsa.py
Created September 14, 2020 05:59
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Simple Python RSA for digital signature with hashing implementation. For hashing SHA-256 from hashlib library is used.
import random
from hashlib import sha256
def coprime(a, b):
while b != 0:
a, b = b, a % b
return a
def extended_gcd(aa, bb):
lastremainder, remainder = abs(aa), abs(bb)
x, lastx, y, lasty = 0, 1, 1, 0
while remainder:
lastremainder, (quotient, remainder) = remainder, divmod(lastremainder, remainder)
x, lastx = lastx - quotient*x, x
y, lasty = lasty - quotient*y, y
return lastremainder, lastx * (-1 if aa < 0 else 1), lasty * (-1 if bb < 0 else 1)
#Euclid's extended algorithm for finding the multiplicative inverse of two numbers
def modinv(a, m):
g, x, y = extended_gcd(a, m)
if g != 1:
raise Exception('Modular inverse does not exist')
return x % m
def is_prime(num):
if num == 2:
return True
if num < 2 or num % 2 == 0:
return False
for n in range(3, int(num**0.5)+2, 2):
if num % n == 0:
return False
return True
def generate_keypair(p, q):
if not (is_prime(p) and is_prime(q)):
raise ValueError('Both numbers must be prime.')
elif p == q:
raise ValueError('p and q cannot be equal')
n = p * q
#Phi is the totient of n
phi = (p-1) * (q-1)
#Choose an integer e such that e and phi(n) are coprime
e = random.randrange(1, phi)
#Use Euclid's Algorithm to verify that e and phi(n) are comprime
g = coprime(e, phi)
while g != 1:
e = random.randrange(1, phi)
g = coprime(e, phi)
#Use Extended Euclid's Algorithm to generate the private key
d = modinv(e, phi)
#Return public and private keypair
#Public key is (e, n) and private key is (d, n)
return ((e, n), (d, n))
def encrypt(privatek, plaintext):
#Unpack the key into it's components
key, n = privatek
#Convert each letter in the plaintext to numbers based on the character using a^b mod m
numberRepr = [ord(char) for char in plaintext]
print("Number representation before encryption: ", numberRepr)
cipher = [pow(ord(char),key,n) for char in plaintext]
#Return the array of bytes
return cipher
def decrypt(publick, ciphertext):
#Unpack the key into its components
key, n = publick
#Generate the plaintext based on the ciphertext and key using a^b mod m
numberRepr = [pow(char, key, n) for char in ciphertext]
plain = [chr(pow(char, key, n)) for char in ciphertext]
print("Decrypted number representation is: ", numberRepr)
#Return the array of bytes as a string
return ''.join(plain)
def hashFunction(message):
hashed = sha256(message.encode("UTF-8")).hexdigest()
return hashed
def verify(receivedHashed, message):
ourHashed = hashFunction(message)
if receivedHashed == ourHashed:
print("Verification successful: ", )
print(receivedHashed, " = ", ourHashed)
else:
print("Verification failed")
print(receivedHashed, " != ", ourHashed)
def main():
p = int(input("Enter a prime number (17, 19, 23, etc): "))
q = int(input("Enter another prime number (Not one you entered above): "))
#p = 17
#q=23
print("Generating your public/private keypairs now . . .")
public, private = generate_keypair(p, q)
print("Your public key is ", public ," and your private key is ", private)
message = input("Enter a message to encrypt with your private key: ")
print("")
hashed = hashFunction(message)
print("Encrypting message with private key ", private ," . . .")
encrypted_msg = encrypt(private, hashed)
print("Your encrypted hashed message is: ")
print(''.join(map(lambda x: str(x), encrypted_msg)))
#print(encrypted_msg)
print("")
print("Decrypting message with public key ", public ," . . .")
decrypted_msg = decrypt(public, encrypted_msg)
print("Your decrypted message is:")
print(decrypted_msg)
print("")
print("Verification process . . .")
verify(decrypted_msg, message)
main()
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