Python UnicodeDecodeError: 'utf-8' codec can't decode byte

Question

First, I'm sorry, there's so many questions regarding this issue, and I drowned in so many answers, but I still don't get it, because my code works just if I write to the file(?)

So, why this works:

# encrypt and write to file    
    data_to_encrypt = "mytext" 
    data = data_to_encrypt.encode('utf-8')
    ciphered_bytes = cipher_encrypt.encrypt(data)
    ciphered_data = ciphered_bytes
    print(ciphered_data)

    with open(fileConfigBIN, "wb") as binary_file:
        binary_file.write(ciphered_data)

# read the file and decrypt
    with open(fileConfigBIN, "rb") as binary_file:
        data1 = binary_file.read()
        print(data1)
        deciphered_bytes = cipher_decrypt.decrypt(data1)
        decrypted_data = deciphered_bytes.decode('utf-8')
        print(decrypted_data)

Output:

b'\xa0U\xee\xda\xa8R'

b'\xa0U\xee\xda\xa8R'

mytext

But just by commenting the write to file (the file still there with the same information):

    #data_to_encrypt = "mytext" 
    #data = data_to_encrypt.encode('utf-8')
    #ciphered_bytes = cipher_encrypt.encrypt(data)
    #ciphered_data = ciphered_bytes
    #print(ciphered_data)

    #with open(fileConfigBIN, "wb") as binary_file:
    #    binary_file.write(ciphered_data)

    with open(fileConfigBIN, "rb") as binary_file:
        data1 = binary_file.read()
        print(data1)
        deciphered_bytes = cipher_decrypt.decrypt(data1)
        decrypted_data = deciphered_bytes.decode('utf-8')
        print(decrypted_data)

I get this:

b'\xa0U\xee\xda\xa8R'

Exception in Tkinter callback Traceback (most recent call last): File "C:\Users...................\Python37-32\lib\tkinter__init__.py", line 1705, in call return self.func(*args) File "C:\Users\Fabio\source.............", line 141, in AbrirConfig decrypted_data = deciphered_bytes.decode('utf-8') UnicodeDecodeError: 'utf-8' codec can't decode byte 0xdd in position 1: invalid continuation byte

The read code is using the same file as the commented part save it!

I tried to save and read in 'latin-1', 'ISO-8859-1' and others.. it give no errors, but returns just strange characters

Using Python 3.7

Thank's in advance!

EDIT:

Full working minimal code:

from Crypto.Cipher import AES

fileConfigBIN = "data.dat"

key = b'\x16\x18\xed\x1c^\xaaGN\rl\xc0]\xf0t=\xd0\xdc]t\xaf\xb2\x12,\xe6\xfc\xd6\x11-\x10\xb4\xb1\x0b'
cipher_encrypt = AES.new(key, AES.MODE_CFB)
iv = cipher_encrypt.iv
cipher_decrypt = AES.new(key, AES.MODE_CFB, iv=iv)

def Encrypt():
    data_to_encrypt = "MyTextToEncrypt" 
    data = data_to_encrypt.encode('utf-8')
    ciphered_bytes = cipher_encrypt.encrypt(data)
    ciphered_data = ciphered_bytes

    with open(fileConfigBIN, "wb") as binary_file:
        binary_file.write(ciphered_data)
        print("CRYPTED DATA SAVED TO FILE: ", str(ciphered_data))

def Decrypt():
    with open(fileConfigBIN, "rb") as binary_file:
        data1 = binary_file.read()
        print("DATA READ FROM FILE: ", data1)
        deciphered_bytes = cipher_decrypt.decrypt(data1)
        decrypted_data = deciphered_bytes.decode('utf-8')
        print("DECRYPTED DATA: ", decrypted_data)

Encrypt() #comment this function to show the problem
print('---------------------')
Decrypt()

I did it guys! Thanks to @Hoenie insight, for every encryption, I store the iv value and use it to decrypt when needed. If happens to need to encrypt again, it save another iv value and so on... Thanks thanks!

Only you know what `cipher_decrypt` and `cipher_encrypt` are, and how they were initialized. If you don't show a complete working example then we can't run it and find out what the problem is. All that I can say is that decryption is failing and returning garbage data. — President James K. Polk, Feb 14 '20 at 01:16
cp1252 when I just decrypt returns like.. †“m]Û&{r¿ÉÞY%Œè . What am I missing here? — Ken Sowyer, Feb 14 '20 at 02:26

score 0 · Accepted Answer · answered Feb 14 '20 at 03:12

Ok, it seems this does have nothing to do with encoding/decoding. You need to create a new cipher object, because it can only be used once.

def Decrypt():
    cipher_decrypt = AES.new(key, AES.MODE_CFB, iv=iv)   # <-- add this
    with open(fileConfigBIN, "rb") as binary_file:
        data1 = binary_file.read()
        print("DATA READ FROM FILE: ", data1)
        deciphered_bytes = cipher_decrypt.decrypt(data1)
        decrypted_data = deciphered_bytes.decode('utf-8')
        print("DECRYPTED DATA: ", decrypted_data)

In the source code: GitHub

A cipher object is stateful: once you have decrypted a message you cannot decrypt (or encrypt) another message with the same object.

Thanks to: https://stackoverflow.com/a/54082879/7547749

That kinda works! I put the first iv value that was generated in the encryptation in the "iv=" and now I can decrypt. BUT, I can encrypt again.. thanks dude! That helped! — Ken Sowyer, Feb 14 '20 at 03:44

Python UnicodeDecodeError: 'utf-8' codec can't decode byte

1 Answers1