Paper 2022/592

Chaghri --- an FHE-friendly Block Cipher

Tomer Ashur, KU Leuven, Eindhoven University of Technology
Mohammad Mahzoun, Eindhoven University of Technology
Dilara Toprakhisar, KU Leuven

The Recent progress in practical applications of secure computation protocols has also attracted attention to the symmetric-key primitives underlying them. Whereas traditional ciphers have evolved to be efficient with respect to certain performance metrics, advanced cryptographic protocols call for a different focus. The so called arithmetic complexity is viewed through the number and layout of non-linear operations in the circuit implemented by the protocol. Symmetric-key algorithms that are optimized with respect to this metric are said to be algebraic ciphers. Previous work targeting ZK and MPC protocols delivered great improvement in the performance of these applications both in lab and in practical use. Interestingly, despite its apparent benefits to privacy-aware cloud computing, algebraic ciphers targeting FHE did not attract similar attention. In this paper we present Chaghri, an FHE-friendly block cipher enabling efficient transciphering in BGV-like schemes. A complete Chaghri circuit can be implemented using only 16 multiplications, 32 Frobenius automorphisms and 32 rotations, all arranged in a depth-32 circuit. Our HElib implemention achieves a throughput of 0.26 seconds-per-bit which is 65% faster than AES in the same setting.

Available format(s)
Secret-key cryptography
Publication info
Published elsewhere. ACM CCS 2022
FHEalgebraic ciphers
Contact author(s)
tomer ashur @ esat kuleuven be
m mahzoun @ tue nl
dilara toprakhisar @ esat kuleuven be
2023-03-29: last of 3 revisions
2022-05-17: received
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      author = {Tomer Ashur and Mohammad Mahzoun and Dilara Toprakhisar},
      title = {Chaghri --- an FHE-friendly Block Cipher},
      howpublished = {Cryptology ePrint Archive, Paper 2022/592},
      year = {2022},
      note = {\url{}},
      url = {}
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