I understand that using a salt makes it harder to find cleartext using rainbow tables - but in that scenario the clear text is structured / low entropy. If my clear text is generated randomly, then is there any benefit to using a salt?
The problem I am trying to solve is that of encrypting http session data serverside. I don't want to persist the decryption key on the server, hence currently I am storing separate cookies for the session identifier and the encryption key at the client. But it occurred to me that if I just stored a single value (the decryption key) at the client, then use the hash of that key as the session identifier, then (in principle) the key cannot be derived from the information stored at the server.