Crypt functions in Python that mimic Java's PBEWithMD5AndDES algorithm to produce a DES key

cryptutil.py

"""Mimic Java's PBEWithMD5AndDES algorithm to produce a DES key

Closely based in https://stackoverflow.com/a/44509919
"""

import base64
import re

from Crypto.Cipher import DES
from Crypto.Hash import MD5


def init_crypt_functions():
    password = b'0725W_37B610++MKLE7#@0PPY310'
    salt = b'\xA9\x9B\xC8\x32\x56\x35\xE3\x03'
    iterations = 1000

    hasher = MD5.new()
    hasher.update(password)
    hasher.update(salt)
    result = hasher.digest()

    for i in range(1, iterations):
        hasher = MD5.new()
        hasher.update(result)
        result = hasher.digest()

    def encrypt(data):
        # Pad plaintext per RFC 2898 Section 6.1
        padding = 8 - len(data) % 8
        data += chr(padding) * padding

        des = DES.new(result[:8], DES.MODE_CBC, result[8:16])

        encrypted = des.encrypt(data)
        return base64.b64encode(encrypted).decode('UTF-8')

    def decrypt(data):
        encrypted = base64.b64decode(data)

        des = DES.new(result[:8], DES.MODE_CBC, result[8:])

        decrypted = des.decrypt(encrypted)

        # Remove padding
        padding = decrypted[-1]
        pattern = br'%s{%d}$' % (padding.to_bytes(1, 'little'), padding)
        decrypted, subs = re.subn(pattern, b'', decrypted)

        # Check if padding is valid
        if subs != 1:
            raise ValueError("decryption error: %d" % subs)

        return decrypted

    return encrypt, decrypt


encrypt, decrypt = init_crypt_functions()
del init_crypt_functions