Re: Is fast variant of Paillier insecure?



Amit <amitabh123@xxxxxxxxx> wrote:
Kristian, what did you mean when you said 'There are other minor
applications of such moduli'? Can you describe some application?

n = (2as+1)(2bs+1) = pq. Let g have order ab, let h have order s.

s can be prime or composite. If s only has small prime factors,
you can compute discrete logs to base h.

You then get a nice additively homomorphic cryptosystem where the public
key is (n,g,h), the private key is (n,ab), and you encrypt messages
as g^r h^m. To decrypt, compute c^ab, find the discrete logarithm x,
then find the message as x*(ab)^{-1} mod s.

That's a minor application if I ever saw one.

--
Kristian Gjøsteen
.