RSAScriptRuben_V2.py

#!usr/bin/python3
import random
from fractions import gcd

__author__="Wylleman Ruben"
__version__="Version 2"



def inputnumbers():
  '''
  # input: manual !! prime integer value
  # creates: global variable p (int)
             global variable q (int)

  This function will take care of the input and make this input available
  for futur functions. 
  It will also check the validity (integer and prime number) of the numbers put in by the user.
  '''
  global p
  global q
  print("1) Select Primes")
  try:
    p = int(input("p = "))  # we are assuming the number put in is integer and try to parse it and we will catch the error if it is not.
  except ValueError:
      print()
      print("PLEASE ENTER A VALID PRIME INTEGER")
      print()
      inputnumbers()
      pass
  try:
    q = int(input("q = ")) # we are assuming the number put in is integer and try to parse it and we will catch the error if it is not.
  except ValueError:
      print()
      print("PLEASE ENTER A VALID PRIME INTEGER")
      print()
      inputnumbers()
      pass
  
  if is_prime_number(p) == False:
      print()
      print("!! INTEGER p IS NOT A PRIME NUMBER !!")
      print()
      inputnumbers()
  if is_prime_number(q) == False:
      print("!! INTEGER q IS NOT A PRIME NUMBER !!")
      print()
      inputnumbers()
    


def calcmodulus(a,b):
  '''
  # input: prime a, prime b
  # creates: global variable n

  this functions will calculate the modulus from 2 prime numbers

  '''
  global n
  n = a * b
  print('modulus n = p * q = {}'.format (n))

def calcphi(a,b):
  '''
  # input: prime a, prime b
  # creates: global variable phi

  this functions calculates the phi value from 2 prime numbers
  for RSA calculation
  '''
  global phi
  phi=(a-1)*(b-1)
  print('phi = (p-1) * (q-1) = {} '.format (phi))

def Select_e(a):
  '''
  # input: phi
  # creates: global variable e

  this function will calculate a value for e to work with the input phi.
  '''
  global e
  e = random.randrange(1,a)
  g = gcd(e,a) 
  while g != 1:
    e = random.randrange(1,a)
    g = gcd (e,a)
  print("choose public key e: {}".format (e))
  print("[*] {} and {} have no common factors except 1".format(e,a))

def find_d(a,b):
  '''
  # input: the value for e, the value for phi
  # creates: global variable d

  this function will find a value for d to use RSA encryption
  '''
  global d
  d = 1
  temp = (a*d)-1
  while temp % b != 0:   
    d = d+1
    temp = (a*d)-1
  print("computed private key d = {}".format (d))
  calc=(e*d)%b
  print("[*] {} * {} mod {} = {}".format (a,d,b,calc))
 
def encrypt(a):
  '''
  # input: message to encrypt
  # returns: encrypted message as string

  this function will encrypt a message using the generated public key and return  it's output
  '''
  output = a ** e % n
  print("encrypted message c = m ** e % n = {}".format(output))
  return output

def decrypt(a):
  '''
  # input: message to decrypt (string)
  # returns: decrypted message (string)

  this function will decrypt the message using the private key generated 
  in this  script. the decrypted message will return as output.
  '''
  output = a ** d % n
  print ("decrypted message mm = c ** d % n = {}".format(output))
  return output

def test(a,b):
  '''
  # input: message before encryption (m), message after decryption (mm)

  this function will test the functionality of this script.
  '''
  if a == b:
    print("is m == mm ? ... OK working example")
  else:
    print("is m == mm ? ... ERROR, RSA code faulty")


def is_prime_number(x):
  if x >= 2:
    for y in range(2,x):
            if not ( x % y ):
                return False
  else:
    return False
  return True

def check_value_m(x,mod):
    if x > mod:
        return False
    else:

        return True



def main():
  '''
  This is the main script for the RSA calculation.
  '''
  inputnumbers()
  print()
  calcmodulus(p,q)
  calcphi(p,q)
  print()
  Select_e(phi)
  print()
  find_d(e,phi)
  print()
  m=int(input("Select message m: "))
  if check_value_m(m,n) == False:
      print()
      print("please enter a value smaller than the modulus {}" .format(n) )
      print()
      m=int(input("Select message m:  "))
  print()
  m_enc=encrypt(m)
  mm=decrypt(m_enc)
  print()
  test(m,mm)


if __name__ == "__main__":
    main()