Peer-to-Peer (P2P) networking has recently gained significant acceptance as an emerging model for communications and computation. P2P networks are evolving as an advanced distributed computing model with a strong emphasis on decentralization, self-organization, heterogeneity, and autonomy of the peers. These features allow researchers to design and build highly adaptive, robust, scalable and dynamic P2P networks. Although P2P networking has its technological roots tracing back through decades of designing distributed information systems, contemporary applications in P2P systems exhibit that it is an effective way to build internet based applications that connect millions of users across the world without dependence on specially deployed servers. Homomorphic Encryption is used to secure the cloud data and allow access to authorized users to perform each and every single task online while the data is in its encrypted state. This book deals with trust and security management using homomorphic encryption and encrypted QR codes for Peer-to-Peer networks.