Python Bytes & Lists & Encryption

Question

I'm using Fernet to encrypt my data with this implementation. Let's assume that I have these three data:

data = [fernet.encrypt("Hello".encode()), fernet.encrypt("Stack".encode()), fernet.encrypt("Overflow".encode())]

After this operation, Python automatically converts bytes to string, and I'm writing them to a csv file. When I need to decrypt them like:

fernet.decrypt(data)

It gives me an error like you can only decrypt only bytes etc. I also checked that my data in the csv file is already bytes but string form.

b'gAAAAABiVUw5BzOkOv3VxlV5xa57Iaf0R4dzPbgsrnheAME8uYeslCZfTx9GeyRWe7l9VMM-gdDXiPZ4zsAXoXkG6T1dyXH6EztcqirrPhXX3YCt65_3xXvykVTDPdbEXs51cHvR-3HH'

Answer 1

An end-to-end usage example for encoding, writing to text, reading, and decoding.

The Fernet documentation can be referenced here.

from cryptography.fernet import Fernet

# Auto-generate a secret key.
key = Fernet.generate_key()
f = Fernet(key)

# Encode the string 'Hello' and encrypt.
encoded = f.encrypt('Hello'.encode())

This creates a bytestring (a bytes object) as:

b'gAAAAABiVVOOeO-hUG2QaKCVOyshntpbqVbxnexIVsFr7ttBGmKhHlDeM7jkTCjPPGphZxbh4D15X82pts3hKes12DjzwI8_jQ=='

Write, read and decrypt:

# Write the *decoded* encrypted string to a TXT file.
with open('/tmp/encoded.txt', 'w') as fh:
    fh.write(encoded.decode())
    
# Read the encrypted string from TXT file.
with open('/tmp/encoded.txt') as fh:
    encoded = fh.read()
    
# Encode the string, pass through fernet for decryption, 
# and decode the bytes output.
f.decrypt(encoded.encode()).decode()

Output:

'Hello'

Answer 2

fernet.encrypt returns bytes (I assume, you're not being specific which implementation you're using, I'm guessing this one). .decode() them to a string. Then your CSV will contain "gAAA...", not "b'gAAA...'". When reading those again from the CSV, .encode() the string before passing it to fernet.decrypt.

• fernet.encrypt returns bytes
• bytes.decode() turns bytes into str
• CSV wants str
• str.encode() turns str into bytes
• fernet.decrypt wants bytes