crypto

#!/usr/bin/python3.8
import os, sys
from getpass import getpass
from Crypto.Cipher import AES
from Crypto.Hash import SHA256
from Crypto import Random

secureRandom = Random.new()

def Main():
  if len(sys.argv) != 4: # commands: ./crypto -enc file2encrypt.txt cipher | ./crypto -dec ./cipher plaintext
      raise Exception("There is a missing argument(s). Try again")

  mode = sys.argv[1] # options: -erc | -dec
  input = sys.argv[2] # -enc: it is the file will be encrypted | -dec: it is the generated cipher file
  out = sys.argv[3] # -enc: it is the generated cipher file name | -dec: it is the generated plaintext from cipher
  password = getpass("Password:") #

  if mode == '-enc':
    hmac = calcDigest(password)
    encryptFile(hmac, input, out)
  elif mode == '-dec':
    hmac = calcDigest(password)
    decryptFile(hmac, input, out)
  else:
    raise Exception('There is no such mode for this program. You can only encrypt (-enc) or decrypt(-dec) a file')

def encryptFile(key, fileName, outputFile):
    with open(fileName , 'rb') as fileWillBeEncrypted:
        IV = secureRandom.read(16)
        AESBlockCipher = AES.new(key, AES.MODE_CBC, IV)
        fileSize = str(os.stat(fileName).st_size).zfill(16)

        with open(outputFile, 'wb') as cipher:
            cipher.write(fileSize.encode('utf-8'))
            cipher.write(IV)
            fileInStringFormat = fileWillBeEncrypted.read()
            if len(fileInStringFormat) % 16 != 0:
                fileInStringFormat += b' ' * (16 - (len(fileInStringFormat) % 16))
            cipher.write(AESBlockCipher.encrypt(fileInStringFormat))

def decryptFile(key, filename, outputFile):
    with open(filename, 'rb') as cipher:
        fileSize = int(cipher.read(16))
        IV = cipher.read(16)
        AESBlockCipher = AES.new(key, AES.MODE_CBC, IV)

        with open(outputFile, 'wb') as plainText:
            plainText.write(AESBlockCipher.decrypt(cipher.read()))

def calcDigest(password):
    hash = SHA256.new(password.encode('utf-8'))
    password = secureRandom.read(16) # deleting the password after generate the digest
    return hash.digest()

if __name__ == '__main__': Main()