Encypting and Decrypting

Python Help
1

So I am working on a project for school in which I need to make a code to encrypt and decrypt text seperatly from eachother. My current code works to encrypt and decrypt at the same time but I can’t seem to get it working seperatly.
My code:


from cryptography.fernet import Fernet
 
# we will be encryting the below string.
message =input("Give your message: ")
 
# generate a key for encryptio and decryption
# You can use fernet to generate
# the key or use random key generator
# here I'm using fernet to generate key
 
key = Fernet.generate_key()
 
# Instance the Fernet class with the key
 
fernet = Fernet(key)
 
# then use the Fernet class instance
# to encrypt the string string must must
# be encoded to byte string before encryption
encMessage = fernet.encrypt(message.encode())
 
print("original string: ", message)
print("encrypted string: ", encMessage)
 
# decrypt the encrypted string with the
# Fernet instance of the key,
# that was used for encrypting the string
# encoded byte string is returned by decrypt method,
# so decode it to string with decode methods
decMessage = fernet.decrypt(encMessage).decode()
 
print("decrypted string: ", decMessage)

Does anyone know how to seperate this?

2

Hi Thomas,
If you mean by separate: to have a script for encryption and one for decryption, then you’ll have
to think where you ‘store’ the encrypted message or: how to transfer the message from one script
to another. Storing it into a file is the most obvious.
Nacho

3

Hi Thomas, and welcome!

I’m sorry, I don’t understand what you mean by encrypting and decrypting
“at the same time”. It looks like different times to me:

First you encrypt:

encMessage = fernet.encrypt(message.encode())
print("original string: ", message)
print("encrypted string: ", encMessage)

Then later you decrypt:

decMessage = fernet.decrypt(encMessage).decode()
print("decrypted string: ", decMessage)

Can you explain in more detail what you are trying to do?

4

Hello,

I’m trying to get a seperate script for encryting and decrypting. So if I were to send an email with a text that I have encrypted that the receiver can decrypt it with a seperate decryption script.

5

Hello,

Would this stll be possible to do if I were to need it to send emails to others. So I encrypt it, send the file and then they decrypt it again with a separate decryption script?

6

Fernet.generate_key() creates a new random key every time you call the function. You need to save and transfer the key somehow.

7

Hello Christian,

Would it be possible to make the code create a file that saves the key and the encrypted message that can be sent through mail? The receiver gets the file, downloads it and runs it through a similar code that decrypts the message. Is this possible or will I need a different code for this?

8

If you store the key and the encrypted message together, then anyone who
receives the message can just use the key to decrypt the message. The
level of security is effectively zero. Is that what you intend?

9

Yeah I just need to be able to send emails that are encrypted that others can decrypt, don’t really care about security since it is just a concept and will not be used as an actual way of sending information.

10

Okay, with the understanding that this is totally insecure and
just suitable for playing around, you could try this:

# Untested.
key = Fernet.generate_key()
fernet = Fernet(key)
encMessage = fernet.encrypt(message.encode())
with open("secret_message", "w") as f:
    f.write(key)
    f.write(encMessage)

You may need to encode or decode either the key or message.

I’m assuming that the key is a fixed length, let’s assume it is 128
characters, so when you want to decrypt it:

with open("secret_message", "r") as f:
    message = f.read()
key = message[:128]
message = message[128:]

I hope this points you in the right direction.

11

Thank you for the code, I just tested it but I get the error:
Traceback (most recent call last):
File “main.py”, line 8, in
f.write(key)
TypeError: write() argument must be str, not bytes

Is there a way to maybe get f.write(key) back to a string instead of bytes?

12

And one other question, I am currently working with Replit, only this can’t seem to make files on my pc so I can’t really test if the files work. What is a good programme that works with pc files to write this code in?

13

Like the error message says, you are writing the file in text mode (i.e. representing textual characters with a given text encoding, like ASCII or UTF-8), but encMesssage and key are binary data, just a sequence of bytes (in particular, note that you use .encode() on the input message to convert it to bytes, and decode() on the decrypted message to convert it back to text).

To fix this, replace "w" in your open call with "wb". Similarly, when you open it, you want to read it in as bytes, so use "rb" instead of "r".

If you want the full nitty-gritty, you can read the official unicode tutorial, though you may want to look for something more introductory if you find it too complex.