An eDRAM-Based In-Situ-Computing Processor for Homomorphic Encryption Evaluation on the Edge

This work presents an in-situ-computing accelerator for homomorphic encryption (HE) evaluation on the edge, with eight eDRAM-based in-situ HE processing cores integrated with RISC-V CPU and HE-specialized NoC. The key features are: (1) the architecture-level fusion with customized ISA chains HE operators, avoiding excessive intermediate ciphertext movements; (2) the circuit-level fusion of eDRAM bitcells and dynamic digital datapath enables energy-efficient in-memory HE evaluation with high storage density; (3) intra-/inter-core hybrid automorphism network greatly reduces communication overheads. The silicon prototype in 28 nm CMOS achieves $2.33 \mathrm{Mb} / \mathrm{mm}^{2} \mathrm{HE}$ storage density, with peak energy efficiency of 329 nJ/NTT at 4096-points-19-bit and 15.1 classification per second with a linear support vector machine in CKKS-RNS scheme, exceeding previously reported ASIC works and CPUs.