Sorry for some reason I didn't see the posts past SS lol. When you have a distributed system you can start to do what you are talking about pretty easily. One thing you could do is called 'Encrypted Keyword Search' Encrypted Keyword Search involves a set of servers holding encrypted documents, they are queried by clients with keywords (that the servers can not see), they search the encrypted documents (which they cannot actually see the plaintext of) for the keywords, and then they supply all of the resulting hits to the clients (without the servers being able to determine which of the documents they are supplying to the clients). This is a very advanced sort of cryptosystem that is actually built up by incorporating many different techniques.