Partially Homomorphic Encryption
Partially homomorphic encryption (PHE) supports unlimited homomorphic evaluation of only one operation (addition or multiplication), e.g., RSA (multiplication) and Paillier (addition).
Purpose
It provides efficient homomorphic computation for aggregation scenarios needing a single operation, such as encrypted vote tallying and encrypted counting.
Mechanism
RSA: E(m1)·E(m2) mod n = E(m1·m2) (multiplicative); Paillier: E(m1)·E(m2) mod n^2 = E(m1+m2) (additive); ElGamal is multiplicatively homomorphic. One operation only, with no limit on count.
Use cases
- Encrypted electronic voting
- Privacy-preserving summation
- Encrypted data aggregation