MFRC522 Saving objects

So as a small personal project, I wired up the MFRC52 reader/writer and got some python code to read and write to tags.

Then I decided that I should not leave basic strings on the tags. Anybody with a reader would be able to read the card contents. So I am attempting to encrypt the string being sent to the card.

I managed to save an encrypted object to the card by writing bytes to the card. It required some tweaking of the SimpleMRFRC522 library. However, when it comes to decoding, I can't seem to get it to decode correctly.

My understanding of this is that the reading portion is expecting a string when the reading the card. However the reader returns bytes and the SimpleMFRC522 just won't accept this.

On to my question, either I get a better MFRC522 library (which I haven't been able to find) or is there a string to string encryption library available? I think there should be such a library for example in email encryption. I have not been able to find an encryption library that can do this for me though. Any suggestions?