Do you know if there exists any keystream algorithms where in which, given an input key, you can request from the algorithm something like "give me slot 433"?
Let me clarify,
so a typical keystream you seed with some key and then are able to request sequential bytes. In my particular application I want to encrypt 8Kbytes xored against a keystream but have it so it can be randomly read and written to. So I guess it would be like a key-block cipher or something like that. I don't fancy re-implementing crypto so I'm wondering if such a technique exists out there.