Efficient implementation of LowMC in HElib

Abstract

LowMC is a symmetric block cipher designed for fully homomorphic encryption. This thesis focuses on Martin Albrecht’s implementation of the cipher in the FHE library HElib, and how his implementation can be improved when encrypting a single plaintext. We have succeeded in getting faster encryption by changing the packing of the plaintext bits and focusing on a rotation-based linear layer. When only encrypting a single plaintext Albrecht’s implementation takes 217.17 seconds, while our alternative implementation takes 11.53 seconds.