my_RSA

"""https://www.khanacademy.org/computing/computer-science/cryptography

https://www.youtube.com/watch?v=qfgYfyyBRcY

https://www.youtube.com/watch?v=kYasb426Yjk"""
import prime_chooser
import Sieve_of_Eratosthenes
import math

p=int()
q=int()
e=int()
d=int() #d= mod inverse of e
n=int()
phi=int()

def make_pl():
    """makes the primes list. Used in find_k_d_e()."""
    primes_list=list(Sieve_of_Eratosthenes.sieve_using_set_and_ranges(100000))
    primes_list.sort()
    while primes_list[0]<math.log(n,2):
        del(primes_list[0])
    return primes_list

def choose_primes_n_phi():
    """this is totally good"""
    global p
    global q
    global n
    global phi
    q=prime_chooser.prime_Chooser(2**124)
    p=prime_chooser.prime_Chooser(2**120)
    n=q*p
    phi=((p-1)*(q-1))
    return

def extendedEuclid(a, b):
    """return a tuple of three values: x, y and z, such that x is
    the GCD of a and b, and x = y * a + z * b
    https://www.youtube.com/watch?v=kYasb426Yjk"""
    if a == 0:
        return b, 0, 1
    else:
        g, y, x = extendedEuclid(b % a, a)
        return g, x - (b // a) * y, y

def gcd(a,b):
    """totally good"""
    if b==0:
        return a
    else:
        return gcd(b,a%b)

        
    
def find_k_d_e():
    global k
    global d
    global e
    primes_list=make_pl()
    for i in primes_list:
        if gcd((phi),i)==1:
            e=i
            x,y,z=extendedEuclid(phi, e)
            #x= gcd of a and b=y*a+z*b
            if z>=0:
                d=z
            else:
                d=phi+z 
            return
            
    
    return "wrong"

def find_everything():
    choose_primes_n_phi()
    find_k_d_e()

find_everything()
    
    

def encrypt(m):
    """takes a number m (message) and encrypts by raising it to e and taking
it modulo n"""
    c=pow(m,e,n)
    return c

def decrypt(c):
    """takes and encrypted number (e) and decrypts it"""
    m=pow(c,d,n)
    return m

def convertToNumber (s):
    """http://stackoverflow.com
/questions/31701991/string-of-text-to-unique-integer-method Thank you poke"""
    return int.from_bytes(s.encode(), 'little')
def convertFromNumber (n):
    """Thanks again poke"""
    return n.to_bytes(math.ceil(n.bit_length() / 8), 'little').decode()
def decrypt_to_text(c):
    d=decrypt(c)
    t=convertFromNumber(d)
    return t
def rsa():
    t=input('give a string to encrypt')
    m=convertToNumber(t)
    c=encrypt(m)
    k=int(input('enter 0 to decrypt, enter 1 to return encrypted number'))
    if k==0:
        print(decrypt_to_text(c))
        #print(s)
    elif k==1:
        return c
if __name__ == '__main__':
    rsa()