We propose a novel and totally decentralized strategy for private and secure data exchange in peer-to-peer systems. Our scheme is particularly appealing for point-to-point exchanges and use zero-knowledge mechanisms to preserve privacy. Furthermore, we show how to plug our private and secure data exchange module in existing publish/subscribe architectures. Our proposal enriches the original system with security and privacy making it resilient to a broad class of attacks (e.g. brute-force, eavesdroppers, man-in-the middle or malicious insiders). Additionally, the original properties of the publish/subscribe system are preserved without any degradation. A nice feature of our proposal is the reduce message cost: only one extra message is sent for every message sent in the original system. Note that our contribution is more conceptual than experimental and can be easily exploited by new emergent areas such as P2P Internet Games or Social Networks where a major trend is to achieve a secure and private communication without relying on any fixed infrastructure or centralized authority.