Add encrypt_text/decrypt_text function using aes256 algorithm (2.1.5)

[xsellier]

This merge request should fix this issue #1969

• Tested using the following gdscript

  var encrypt_key = 'supersecretkey'
  var original_string = {
    test = 'aAáäç,©./:\'[p',
    test2 = 156,
    as56 = '©ç9865321898#@!$%6&'
  }

  var encrypted_string = original_string.to_json().encrypt_text(encrypt_key)
  var decrypted_string = encrypted_string.decrypt_text(encrypt_key)

  print('original_string: %s' % [original_string])
  print('encrypted_string: %s' % [encrypted_string])
  print('decrypted_string: %s' % [decrypted_string])

I'm using it for large amount of json, and it works flawlessly

[i80and]

I have no right to jump in here as just a rando, but this looks like it's implementing ECB?

At minimum you want to implement CBC: https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Cipher_Block_Chaining_(CBC)

In CBC mode, each block of plaintext is XORed with the previous ciphertext block before
being encrypted. This way, each ciphertext block depends on all plaintext blocks processed
up to that point. To make each message unique, an initialization vector must be used in the
first block.

[xsellier]

@i80and You are right it is ECB. Since only ECB is implemented and already used by Godot Engine, I will keep going using AES ECB. Plus CBC is not implemented in Godot Engine.

Feel free to open another issue to be able to use another encryption algorithm (here is why CBC is way better than ECB)

[akien-mga]

This should be implemented in the master branch too. As I expect there will be quite some bikeshedding there, I'll merge this one in the meantime for 2.1. Users of this method should not expect forward compatibility when porting their projects to 3.x.

[xsellier]

@akien-mga Do you want me to port it to the mater branch ? (as is)

[akien-mga]

Yeah that would be good to start the discussion. Maybe we won't have as much bikeshedding as I fear and will be able to merge it as is :D