The Future Is Private Compute Through Homomorphic Encryption

There's a range of algorithms that support homomorphism.

https://en.m.wikipedia.org/wiki/ElGamal_encryption

ElGamal is very simple and supports multiplicative homomorphism. If you do it over an elliptic curve, this changes to additive.

Another is NTRU, but it's naturally addictively homomorphic.

https://en.wikipedia.org/wiki/NTRUEncrypt

The values are added modulus 3 though so I'm not aware of any applications for it.

For example, adding cipher texts of the plaintexts [1,2,0,0] and [1,1,0,1] results in [2,0,0,1]