International Association
for Cryptologic Research

We study homomorphic authenticated encryption, where privacy

and authenticity of data are protected simultaneously. We define homomorphic versions

of various security notions for privacy and authenticity, and investigate

relations between them. In particular, we show that it is possible to

give a natural definition of IND-CCA for homomorphic authenticated encryption, unlike

the case of homomorphic encryption. Also, we construct a homomorphic

authenticated encryption scheme supporting arithmetic circuits on $\\ZZ_Q$

for smooth modulus $Q$, which is chosen-ciphertext secure both for privacy

and authenticity. Our scheme is based on the error-free approximate GCD assumption.