Somewhat Homomorphic Encryption
Somewhat homomorphic encryption (SHE) supports evaluating circuits of bounded depth on ciphertexts; noise grows with depth, and decryption fails past a threshold.
Purpose
It provides limited homomorphic computation for lightweight scenarios that need no bootstrapping, far outperforming FHE — the intermediate form on the way to FHE.
Mechanism
Ciphertexts carry noise that grows multiplicatively with each multiplication. SHE supports low-depth circuits (e.g., a few multiplications); past the noise bound, bootstrapping is required to upgrade to FHE. BFV/CKKS operate as SHE before bootstrapping.
Use cases
- Low-depth encrypted computation
- CKKS approximate arithmetic
- The pre-bootstrapping stage of FHE