On the security of Domingo-Ferrer's homomorphic cryptosystem against ciphertext-only attack

The paper proposes an analysis of the security of the Domingo-Ferrer's homomorphic encryption scheme against the ciphertext-only attack. This cryptosystem provides a good counterexample to the equivalence hypothesis of ciphertext-only attack and known plaintext attack on encryption schemes, that are homomorphic over the residue ring modulo a hardly-factorizable number.