One of the biggest concerns for many applications in cloud computing lies in
data privacy. A potential solution to this problem is homomorphic encryption
(HE), which supports certain operations directly over the ciphertexts.
Conventional HE schemes, however, exhibit significant performance overhead and
are hardly applicable to real-world applications. This paper presents Rache, a
caching optimization for accelerating the performance of HE schemes. The key
insights of Rache include (i) caching some homomorphic ciphertexts before
encrypting the large volume of plaintexts; (ii) expanding the plaintexts into a
summation of powers of radixes; and (iii) constructing the ciphertexts with
only homomorphic addition. The extensive evaluation shows that Rache exhibits
almost linear scalability and outperforms Paillier by orders of magnitude.