Peer-to-peer (P2P) systems, and client-server type storage and computation outsourcing constitute some of the major applications that the next generation cloud schemes will address. Since these applications are just emerging, it is the perfect time to design them with security and privacy in mind. Furthermore, considering the high-churn characteristics of such systems, the cryptographic protocols employed must be efficient and scalable. This book shows that cryptography can be used to efficiently and scalably provide security and privacy for the next generation cloud systems. The three main application areas presented are P2P file sharing/distribution systems, cloud computation mechanisms and outsourced storage schemes. In all these settings, we present cryptographic protocols that guarantee fairness, correctness, security against malicious participants, and privacy of the honest parties executing the protocol. Lastly, we show that all our solutions are efficient and scalable by presenting results from the "Brownie Cashlib" library we implemented, with an appendix containing a comprehensive pseudocode listing. The source code and documentation of Cashlib is freely available online.