Paper 2023/1818

On Instantiating Unleveled Fully-Homomorphic Signatures from Falsifiable Assumptions

Romain Gay, IBM Research - Zurich
Bogdan Ursu, Consensys

We build the first unleveled fully homomorphic signature scheme in the standard model. Our scheme is not constrained by any a-priori bound on the depth of the functions that can be homomorphically evaluated, and relies on subexponentially-secure indistinguishability obfuscation, fully-homomorphic encryption and a non-interactive zero-knowledge (NIZK) proof system with composable zero-knowledge. Our scheme is also the first to satisfy the strong security notion of context-hiding for an unbounded number of levels, ensuring that signatures computed homomorphically do not leak the original messages from which they were computed. All building blocks are instantiable from falsifiable assumptions in the standard model, avoiding the need for knowledge assumptions. The main difficulty we overcome stems from the fact that bootstrapping, which is a crucial tool for obtaining unleveled fully homomorphic encryption (FHE), has no equivalent for homomorphic signatures, requiring us to use novel techniques.

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Publication info
Published by the IACR in PKC 2024
fully homomorphic signaturesfully homomorphic encryptionnon-interactive zero-knowledgeobfuscation
Contact author(s)
rga @ zurich ibm com
bogdanursuoffice @ gmail com
2024-01-23: revised
2023-11-24: received
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      author = {Romain Gay and Bogdan Ursu},
      title = {On Instantiating Unleveled Fully-Homomorphic Signatures from Falsifiable Assumptions},
      howpublished = {Cryptology ePrint Archive, Paper 2023/1818},
      year = {2023},
      note = {\url{}},
      url = {}
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