Faster SeaSign signatures through improved rejection sampling

Thomas Decru, Lorenz Panny, Frederik Vercauteren

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We speed up the isogeny-based "SeaSign'' signature scheme recently proposed by De Feo and Galbraith. The core idea in SeaSign is to apply the "Fiat–Shamir with aborts'' transform to the parallel repeated execution of an identification scheme based on CSIDH. We optimize this general transform by allowing the prover to not answer a limited number of said parallel executions, thereby lowering the overall probability of rejection. The performance improvement ranges between factors of approximately 4.4 and 65.7 for various instantiations of the scheme, at the expense of roughly doubling the signature sizes.
Original languageEnglish
Number of pages14
JournalIACR Cryptology ePrint Archive
Issue number2018/1109
Publication statusPublished - 2018


  • cryptographic protocols
  • Isogeny-based cryptography, signatures, SeaSign, rejection sampling, group actions


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