dkcDfQVQ

1import base64
2import hashlib
3
4from Crypto.Cipher import AES
5
6
7class DecryptParameters:
8    # The block size to be used while padding
9    BS = 16
10
11    def __init__(self, secret_key, iv_key):
12        """Initialises the Class with the parameters passed.
13
14        :param secret_key:
15        The secret key to use in the symmetric cipher.
16        It must be 16 bytes long
17        :type secret_key: string
18
19        :param iv_key:
20        The initialization vector key to use in the symmetric cipher.
21        It must be 16 bytes long
22        :type iv_key: string
23        """
24
25        # Hash the secret key
26        self.secret_key_hash = hashlib.sha256(secret_key.encode()).hexdigest()[:32]
27
28        # Hash the IV Key
29        self.iv_hash = hashlib.sha256(iv_key.encode()).hexdigest()[:16]
30
31    def un_pad(self, string):
32        """Removes extra bytes formally inserted for strings less than the block size
33
34        :param string:
35        The string value of the text to be un padded
36        :type string: string
37
38        :return: string
39        """
40        return string[:-ord(string[len(string) - 1:])]
41
42    def decrypt(self, encrypted_string):
43        """Decrypts the encoded string passed with the IV and secret key passed while initializing this class
44
45        :param encrypted_string:
46        The string to be decrypted
47        :type encrypted_string: string
48
49        :return: string: Decrypted string
50        """
51        cipher = AES.new(self.secret_key_hash.encode(), AES.MODE_CBC, self.iv_hash.encode())
52
53        string = base64.b64decode(base64.b64decode(encrypted_string))
54        string = cipher.decrypt(string)
55
56        return self.un_pad(string.decode())