6th_rsa_v2_normal_assignment.py

# 1. Set p, q
# 2. n = p * q
# 3. phi(n) = (p - 1) * (q - 1)
# 4. find e: gcd(phi(n), e) = 1, 1 < e < phi(n)
# 5. find d: e * d mod phi(n) = 1, 1 < d < phi(n)
# 6. decrypt
# 7. encrypt

# import math
from math import gcd

def setting(p: int, q: int):
    n = p * q
    phi_n = (p-1) * (q-1)
    e = find_e(phi_n)
    d = find_d(phi_n, e)
    
    return n, e, d
    
def find_e(phi_n: int):
    e = 0
    for i in range(2, phi_n):
        if gcd(phi_n, i) == 1:
            e = i
            break
            
    return e        
    
def find_d(phi_n: int, e: int):
    d = 0
    for i in range(2, phi_n):
        if (e * i) % phi_n == 1:
            d = i
            break
            
    return d        

def encrypt(plain_text: list, pub_key: list):
    # c = p^e mod n
    cipher_bytes = []
    
    for i in plain_bytes:
        cipher_bytes.append((i ** pub_key[1]) % pub_key[0])
        
    return cipher_bytes    
        
def decrypt(cipher_list: str, pri_key: list):
    # p = c^d mod n
    # to_list
    cipher_bytes = [ord(x) for x in cipher_list]
    plain_bytes = []
    
    for i in cipher_list:
        plain_bytes.append((i ** pri_key[1]) % pri_key[0])
        
    plain_text = "".join([chr(x) for x in plain_bytes])
    
    return plain_text    
    
if __name__=="__main__":
    p = 11
    q = 13
    n, e, d = setting(p, q)
    
    pub_key = [n, e]
    pri_key = [n, d]
    
    cipher = "0x4d765050762d2162592d1512043e813e6e6e"
    
    plain = decrypt(cipher, pri_key)
    
    hex_to_decimal = []
    for i in plain:
        hex_to_decimal.append("{:02x}".format(i))
    
    hex_text = "0x" + "".join(hex_to_decimal)   
    
    plain = decrypt(cipher, pri_key)
    print(plain)