How to encrypt data on the user's local machine?

Question

Encryption

I have:

• Open source lua script that runs locally on the user's machine and works with sensitive data (passwords, logins from game accounts)
  
• Recent leak of one of the script developers under the same platform as me. (he just leaked jsons of users with passwords to the network)
  

How to encrypt user passwords so that they can then be decrypted into the original string?
Salt can be stolen (since the script is open source), dynamically how to generate, and most importantly - store, salt is also not an option, the algorithm will be stolen.
One option is to encrypt on the side (server), but there are two problems:

• The script does not pay for itself in any way and is completely free, there is no money for the server
  
• Users are unlikely to trust encryption on the side.
  

Answer 1

No way (with such a formulation of the problem)

Answer 2

0. Learn the basics. For starters, at least this wiki
will allow you not to write such nonsense

Salt can be stolen (since the script is open source), dynamically how to generate, and most importantly - store, salt is also not an option, the algorithm will be stolen.

1. Find recognized leaders in the field. They are all open source btw
2. Read their code
3. Take a couple of crypto courses