I'm working on encrypting a web application's cookie. Using symmetric AES/CBC, I encrypt the cookie data before writing it out, and then decrypt it when reading it back in - the standard stuff.
The problem is that people may use load balancers to host this web app. For that reason, the secret key used to encrypt cookie data cannot be randomized - it must always be the same so that one load-balance server can decrypt a cookie that was written out by another load-balance server.
This means my secret key is much easier to crack than if the secret key was randomized. Right now I use "PBKDF2WithHmacSHA1" to derive the secret key using a non-random salt. Do you think that's acceptable? Is there any way to make it definitively more secure in this case? Thanks for your insights.