kmzi3_8sem

from asn1 import Encoder, Decoder, Numbers
from Cryptodome.Random import get_random_bytes
from Cryptodome.Random.random import randint
from Cryptodome.Util.number import getPrime, inverse, GCD
from Cryptodome.Cipher import AES
from Cryptodome.Util.Padding import pad, unpad

CONST_MENU = "Enter command number:\n" \
             "1 - Encrypt file\n" \
             "2 - Decrypt user's file\n" \
             "3 - Exit\n"
CONST_X = 88

# AES key generation
def generate_aes_key():
    #return get_random_bytes(32)
    AES_key = b'\x8e\x10l\x0f\x11w\xbc\xb4\xef\xf3\xe2\xf8\xe1\x1f \xe5~\xa6s\x1f\xack\x06 ^KkDc\x15\xa8\x88'
    return AES_key


# Read file data
def read_data(filename):
    data = b''
    try:
        with open(filename, "rb") as inp:
            for line in inp:
                data += line
    except FileNotFoundError:
        print("File not found\n")
    return data


# Encrypt data
def encrypt_input(filename, aes_key):
    iv = 16 * b' '
    input_data = b''
    input_data = read_data(filename)
    cipher = AES.new(aes_key, AES.MODE_CBC, iv)
    cipher_text = cipher.encrypt(pad(input_data, 16))
    return cipher_text


# ElGamal params
def generate_params():
    G = list()
    a = getPrime(8, randfunc=get_random_bytes)
    p = getPrime(1024, randfunc=get_random_bytes)
    tmp = 1
    G.append(tmp)
    for i in range(0, p):
        tmp *= a
        if tmp > p:
            break
        G.append(tmp)
    b = G[CONST_X]
    return [a, p, G, b]


# ElGamal already generated params
# ASN1 format
def write_asn1_file(cipher):
    f = Encoder()
    f.start()
    f.enter(Numbers.Sequence)
    f.enter(Numbers.Set)
    f.enter(Numbers.Sequence)
    f.write(b'\x80\x01\x02\x01', Numbers.OctetString)
    f.write(b'Encoded file with El Gamal', Numbers.UTF8String)
    f.enter(Numbers.Sequence)
    f.write(cipher[3], Numbers.Integer)
    f.leave()
    f.enter(Numbers.Sequence)
    f.write(cipher[5], Numbers.Integer)
    f.write(cipher[4], Numbers.Integer)
    f.leave()
    f.enter(Numbers.Sequence)
    f.write(cipher[1], Numbers.Integer)
    f.write(cipher[0], Numbers.Integer)
    f.leave()
    f.leave()
    f.leave()
    f.enter(Numbers.Sequence)
    f.write(b'\x10\x82', Numbers.OctetString)
    f.write(len(cipher[6]), Numbers.Integer)
    f.leave()
    f.leave()
    f.write(cipher[6])
    with open("encrypted.txt", "wb") as enc:
        enc.write(f.output())


# ElGamal encryption
def encrypt_data(filename):
    aes_key = generate_aes_key()
    m = int.from_bytes(aes_key, byteorder="big")
    encrypted_data = encrypt_input(filename, aes_key)
    #crypto_params = generate_params()
    crypto_params = return_const_params()
    y = 213132
    counter = 2
    a = crypto_params[0]
    b = crypto_params[3]
    while counter < y:
        a = a * crypto_params[0] % crypto_params[1]
        b = b * crypto_params[0] % crypto_params[1]
        counter += 1
    c = m * b % crypto_params[1]
    cipher = list()
    cipher.append(a)
    cipher.append(c)
    x = 1
    while a != b:
        a = a * crypto_params[0] % crypto_params[1]
        x += 1
    #print(x)
    #print(c)
    #print(a)
    cipher.append(x)
    cipher.append(crypto_params[3])
    cipher.append(crypto_params[0])
    cipher.append(crypto_params[1])
    cipher.append(encrypted_data)
    write_asn1_file(cipher)
    print("File was successfully encrypted!")
    return cipher


# AES decryption
def decrypt_text(aes_key, text):
    iv = 16 * b' '
    cipher = AES.new(aes_key, AES.MODE_CBC, iv)
    plain_text = cipher.decrypt(text)
    plain_text = unpad(plain_text, 16)
    return plain_text

# ElGamal decryption
def decrypt_data(filename):
    data = read_data(filename)
    f = Decoder()
    f.start(data)
    f.enter()
    f.enter()
    f.enter()
    value = f.read()
    value = f.read()
    f.enter()
    value = f.read()[1]
    f.leave()
    f.enter()
    param = list()
    value1 = f.read()[1]
    value2 = f.read()[1]
    param.append(value2)
    param.append(value1)
    f.leave()
    f.enter()
    c = f.read()[1]
    a = f.read()[1]
    f.leave()
    f.leave()
    f.leave()
    f.enter()
    length = f.read()
    val = f.read()
    f.leave()
    f.leave()
    text = f.read()[1]
    i = 1
    while i != CONST_X:
        i += 1
        a = a * param[0] % param[1]
    m = c * inverse(a, param[1]) % param[1]
    m = m.to_bytes((m.bit_length() // 8), byteorder="big")
    plain_text = decrypt_text(m, text)
    with open("decrypted.txt", "wb") as res:
        res.write(plain_text)
    print("File was successfully decrypted!")


# Get user's filename
def get_filename(op_type):
    return input("Enter filename for " + op_type + ": ")


# main func
def main():
    while 1:
        user_choice = int(input(CONST_MENU))
        if user_choice == 1:
            encrypt_data(get_filename("encryption"))
            break
        elif user_choice == 2:
            decrypt_data(get_filename("decryption"))
            break
        elif user_choice == 3:
            return


main()