Function elgamal::add_ciphertexts

pub fn add_ciphertexts(
    lhs: Ciphertext,
    rhs: Ciphertext
) -> Result<Ciphertext, Error>

Elgamal ciphertexts under the same encryption key enjoy an additive homomorphism, i.e. if c1 = Enc(ek, m1) and c2 = Enc(pk, m2), then we can define an addition operation + such that Dec(dk, c1 + c2) = m1 + m2.

The addition is defined as componentwise application of the group operation on the pairs of group elements that make up ciphertexts.