To improve speech communication in noisy and reverberant environments, an increased interest is shown to develop algorithms that make efficiently use of acoustic wireless sensor networks (WSNs). The processors and sensors forming these WSNs can be owned by multiple users. Sending private data across such a WSN can lead to severe privacy and security issues and may limit its acceptance. Using the advantages of WSNs, while guaranteeing people's privacy, requires therefore to share processors and data in a privacy preserving manner. In this paper we raise attention to the problem of privacy and security for distributed speech enhancement and propose the new paradigm of privacy preserving distributed beamforming. Using cryptographic techniques, particularly homomorphic encryption, we demonstrate how distributed beamforming techniques can be computed in a privacy preserving manner in the encrypted domain.