It all depends on what are the powers your attackers have. If your attackers can monitor the whole web, inject packets as he wish and control every computer in

It all depends on what are the powers your attackers have. If your attackers can monitor the whole web, inject packets as he wish and control every computer in the world - there probably isn't any way to offer secrecy. On the other hand, if we're talking about an adversary with a more limited capabilities - maybe he can access only 50% of the computers in the world and that cannot crack encryption at will - Than there are papers talking about theoretically sound systems that can give you anonymity with very high reliability.