Let's assume I have a string that I'm generating on the server and sending to the client (browser/app) which is to be treated as opaque by the client.
I want to obfuscate the string so it's reasonably difficult for an attacker to guess or modify the contents of the string. But, it also needs to be fast because I have to obfuscate and de-obfuscate it a lot on the server.
What existing and well-known algorithms/mechanisms exist for implementing such obfuscation? It should be reasonably difficult for an attacker to uncover but I guess it doesn't matter too much if it is uncovered or modified.
I'd prefer to not use encryption algorithms because they tend to be slow (in my mind anyway).
I did look at schemes like Base64 but that's too easy to reverse and modify by an attacker. Encryption schemes like RSA/AES would solve the issue but performing such operations is costly.