Randomized decryption (RD) mode of operation for homomorphic cryptography - increasing encryption, communication and storage efficiency

Consider a client who wants to outsource storage and computation of sensitive information to a not fully trusted third party. Secure computation algorithms like homomorphic encryption are typically used to solve this issue, but introduce overhead through randomization and thus ciphertext expansion. Furthermore, encryption may be infeasible for small, resource constrained devices. We present a mode of operation for homomorphic cryptographic systems such that pseudo-random values are decrypted and used as a pseudo one time pad to construct a stream cipher. As a result efficient encryption, transmission and storage of sensitive data, is achieved. Most importantly, the resulting ciphertexts can be trivially transformed into an homomorphic encryption of the concealed data. The resulting scheme is proven to be as secure as the underlying pseudo-random number generator and homomorphic cryptographic system. A performance evaluation shows the benefits and costs of our approach.