Python3でOpenSSLで暗号化したファイルを復号する

Python3を使ってOpenSSLで暗号化したファイルを復号する方法。

結構ありそうなシチュエーションだけど、ファイルの復号・暗号となると文献が少なくちょっと苦労したのでメモ。

開発環境は以下。
・Python3.7.3
・Windows10
・必要なパッケージは随時 pip install で入れる

importはこんな感じに書く。（あくまで例）

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

OpenSSLで暗号化されたファイルの復号

@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()

こんどは暗号化。

ファイルをOpenSSL方式で暗号

@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()