In a hybrid peer-to-peer (P2P) system, some operations are intentionally centralized, such as indexing of peers? files. We present several protocols to achieve mutual communication anonymity between an information requester and a provider in a hybrid P2P information-sharing environment with trusted index servers such that neither the requester, nor the provider can identify each other, and no other peers can identify the two communicating parties with certainty. Some existing protocols provide solutions to achieve mutual anonymity in pure P2P systems without any trusted central controls. Compared with two representative protocols, our proposed mutual anonymity protocols improve efficiency by utilizing trusted third parties and aiming at both reliability and low-cost. We show that with some limited central support, our protocols can accomplish the goals of anonymity, efficiency, and reliability. We have evaluated our techniques in a browser-sharing environment. We show that the average increase in response time caused by our protocols is trivial, and these protocols show advantages over existing protocols in a hybrid P2P system.