I'm making a project in Java and Python that includes sending an encrypted string from one to the other. I can get the languages to understand each other and fully de-crypt / encrypt strings. However I was talking to somebody and was told that I am not being totally secure. I am using AES encryption for the project. Part of the problem is that I am distributing the software and need to come up with an effective way and secure way of making sure both the server side know the IV and 'Secret Key'. Right now the same string will always encrypt to be the same result. If I could change those two factors they would be different, so 2 users with the same password won't have the same encrypted password. Please do keep in mind that the server only needs to manage one account.
I appreciate your responses, and thank you very much ahead of time!