End-to-end encryption for direct messages

So, the title briefly explains what I want to do.

I want to implement end-to-end AES256-bit encryption for direct messages. This means that only the player sending and the player receiving can view the message in unencrypted form, or if it's a group direct message, all of the members of the group can view the message in unencrypted form. Staff and third-party services will be unable to view direct conversations, unless necessary.

As stipulated by our Privacy Statement, we refuse to sell or grant third-parties access to your personal information or direct conversations. Staff will have limited access to direct conversations and personal information. To ensure compliance with the GDPR (General Data Protection Regulation) that applies to users within European regions, we are required to implement appropriate technical security measures to keep your information secure.

Another quick side note if it's helpful, all requests processed through our servers are encrypted with TLS encryption and a proxy server for security.

I'm wondering, would this be possible to implement with a simple Java plugin?

Thanks in advance.

Sincerely,
TurtlesBeast23