Paper 2022/180

Towards Globally Optimized Hybrid Homomorphic Encryption - Featuring the Elisabeth Stream Cipher

Orel Cosseron, École Normale Supérieure de Lyon, Télécom ParisTech
Clément Hoffmann, Université Catholique de Louvain
Pierrick Méaux, University of Luxembourg
François-Xavier Standaert, Université Catholique de Louvain

Hybrid Homomorphic Encryption (HHE) reduces the amount of computation client-side and band- width usage in a Fully Homomorphic Encryption (FHE) framework. HHE requires the usage of specific sym- metric schemes that can be evaluated homomorphically efficiently. In this paper, we introduce the paradigm of Group Filter Permutator (GFP) as a generalization of the Improved Filter Permutator paradigm introduced by M ́eaux et al. From this paradigm, we specify Elisabeth , a family of stream cipher and give an instance: Elisabeth-4 . After proving the security of this scheme, we provide a Rust implementation of it and ensure its performance is comparable to state-of-the-art HHE. The true strength of Elisabeth lies in the available opera- tions server-side: while the best HHE applications were limited to a few multiplications server-side, we used data sent through Elisabeth-4 to homomorphically evaluate a neural network inference. Finally, we discuss the improvement and loss between the HHE and the FHE framework and give ideas to build more efficient schemes from the Elisabeth family

Note: Corrected small affiliation mistake

Available format(s)
Secret-key cryptography
Publication info
A minor revision of an IACR publication in ASIACRYPT 2022
homomorphic encryption hybrid homomorphic encryption Elisabeth stream-ciphers Group Filter Permutator TFHE
Contact author(s)
orel cosseron @ ens-lyon fr
clement hoffmann @ uclouvain be
pierrick meaux @ uni lu
fstandae @ uclouvain be
2022-09-21: last of 4 revisions
2022-02-20: received
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Creative Commons Attribution


      author = {Orel Cosseron and Clément Hoffmann and Pierrick Méaux and François-Xavier Standaert},
      title = {Towards Globally Optimized Hybrid Homomorphic Encryption - Featuring the Elisabeth Stream Cipher},
      howpublished = {Cryptology ePrint Archive, Paper 2022/180},
      year = {2022},
      note = {\url{}},
      url = {}
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