Decrypt files encrypted with OpenSSL with Python 3

How to decrypt a file encrypted with OpenSSL using Python3.

It's a situation that seems quite likely, but when it comes to decrypting and encrypting files, there aren't many documents, so I made a note.

The development environment is as follows. ・ Python 3.7.3 ・ Windows 10 ・ Install necessary packages with pip install at any time.

Import is written like this. (Example)

import binascii
import io
from hashlib import sha256
from Crypto.Cipher import AES
from Crypto import Random

Decrypting files encrypted with OpenSSL

@classmethod
def decrypt(self,infile, expf, key_length=32):
    """
    Decrypt the file.

    Parameters
    ----------
    infile : string
        File path before decryption
    expf : string
        File path after decryption
    key_length : int
        key_length

    Returns
        None
    -------
    """

    # Divide password hashed by sha256 to first half  and second half ,set to key and iv. This is OpenSSL specifications.
    key = binascii.unhexlify('E1B85B27D6BCB05846C18E6A48F118E8')
    iv = binascii.unhexlify('9F0C0587140DE9FB3359F8370D0DBA08')

    in_file  = open( infile , 'rb' )
    out_file = open( expf , 'wb' )

    bs = AES.block_size

    cipher = AES.new(self.key, AES.MODE_CBC, self.iv)
    next_chunk = ''
    finished = False
    while not finished:
        chunk, next_chunk = next_chunk, cipher.decrypt(in_file.read(1024 * bs))
        if len(next_chunk) == 0:
            padding_length = chunk[-1]
            chunk = chunk[:-padding_length]
            finished = True

        if type(chunk) is str:
            wk = chunk.encode('utf-8')
        elif type(chunk) is bytes:
            wk = chunk
        else:
            wk = chunk
    
        out_file.write(wk)

    # file close
    in_file.close()
    out_file.close()

Encrypt files with OpenSSL

@classmethod
def encrypt(self,in_file, out_file,  key_length=32):
    """
    Encrypt the file.

    Parameters
    ----------
    in_file : string
        File path before encryption
    out_file : string
        File path before encryption
    key_length : int
        key_length
    Returns
        None
    -------
    """

    # Divide password hashed by sha256 to first half  and second half ,set to key and iv. This is OpenSSL specifications.
    key = binascii.unhexlify('E1B85B27D6BCB05846C18E6A48F118E8')
    iv = binascii.unhexlify('9F0C0587140DE9FB3359F8370D0DBA08')

    in_file  = open( in_file , 'rb' )
    out_file = open( out_file , 'wb' )

    bs = AES.block_size

    cipher = AES.new(self.key, AES.MODE_CBC, self.iv)

    finished = False
    while not finished:
        chunk = in_file.read(1024 * bs)
        if len(chunk) == 0 or len(chunk) % bs != 0:
            padding_length = (bs - len(chunk) % bs) or bs
            chunk += padding_length * bytes([padding_length])
            finished = True
        out_file.write(cipher.encrypt(chunk))
    
    # file close
    in_file.close()
    out_file.close()