How do I encrypt and decrypt a string in python?

in stackoverflow ∙ 3 mins read ∙ Tags: Python, Python-3.x, Encryption

How do I encrypt and decrypt a string in python?

  1. Question by David
  2. Answer by Milovan Tomašević
    1. Encrypt Data
    2. Encrypt a Message
    3. Below is a full working example of encrypting a message :
    4. Decrypt Data

Question by David

I have been looking for sometime on how to encrypt and decrypt a string. But most of it is in 2.7 and anything that is using 3.2 is not letting me print it or add it to a string.

So what I’m trying to do is the following:

mystring = "Hello stackoverflow!"
encoded = encode(mystring,"password")
print(encoded)

jgAKLJK34t3g (a bunch of random letters)

decoded = decode(encoded,"password")
print(decoded)

Hello stackoverflow!

Is there anyway of doing this, using python 3.X and when the string is encoded it’s still a string, not any other variable type.

Answer by Milovan Tomašević

Encrypt Data

First, we need to install the cryptography library:

pip3 install cryptography

  • From the cryptography library, we need to import Fernet and start generating a key - this key is required for symmetric encryption/decryption.

  • To generate a key, we call the generate_key() method.
    • We only need to execute the above method once to generate a key.

      You need to keep this key in a safe place. If you lose the key, you won’t be able to decrypt the data that was encrypted with this key.

  • Once we have generated a key, we need to load the key with load_key()

Encrypt a Message

This is a three step process:

  1. encode the message
  2. initialize the Fernet class
  3. pass the encoded message to encrypt() method

Below is a full working example of encrypting a message :

from cryptography.fernet import Fernet

def generate_key():
    """
    Generates a key and save it into a file
    """
    key = Fernet.generate_key()
    with open("secret.key", "wb") as key_file:
        key_file.write(key)

def load_key():
    """
    Load the previously generated key
    """
    return open("secret.key", "rb").read()

def encrypt_message(message):
    """
    Encrypts a message
    """
    key = load_key()
    encoded_message = message.encode()
    f = Fernet(key)
    encrypted_message = f.encrypt(encoded_message)

    print(encrypted_message)

if __name__ == "__main__":
    # generate_key() # execute only once 
    encrypt_message("Hello stackoverflow!")

output:

b'gAAAAABgLX7Zj-kn-We2BI_c9NQhEtfJEnHUVhVqtiqjkDi5dgJafj-_8QUDyeNS2zsJTdBWg6SntRJOjOM1U5mIxxsGny7IEGqpVVdHwheTnwzSBlgpb80='

Decrypt Data

To decrypt the message, we just call the decrypt() method from the Fernet library. Remember, we also need to load the key as well, because the key is needed to decrypt the message.

from cryptography.fernet import Fernet

def load_key():
    """
    Load the previously generated key
    """
    return open("secret.key", "rb").read()

def decrypt_message(encrypted_message):
    """
    Decrypts an encrypted message
    """
    key = load_key()
    f = Fernet(key)
    decrypted_message = f.decrypt(encrypted_message)

    print(decrypted_message.decode())

if __name__ == "__main__":
    decrypt_message(b'gAAAAABgLX7Zj-kn-We2BI_c9NQhEtfJEnHUVhVqtiqjkDi5dgJafj-_8QUDyeNS2zsJTdBWg6SntRJOjOM1U5mIxxsGny7IEGqpVVdHwheTnwzSBlgpb80=')

output:

Hello stackoverflow!

Your password is in the secret.key in a form similar to the password below:

B8wtXqwBA_zb2Iaz5pW8CIQIwGSYSFoBiLsVz-vTqzw=

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