Abstract
We revisit constructions of asymmetric primitives from obfuscation and give simpler alternatives. We consider public-key encryption, (hierarchical) identity-based encryption ((H)IBE), and predicate encryption. Obfuscation has already been shown to imply PKE by Sahai and Waters (STOC’14) and full-fledged functional encryption by Garg et al. (FOCS’13). We simplify all these constructions and reduce the necessary assumptions on the class of circuits that the obfuscator needs to support. Our PKE scheme relies on just a PRG and does not need any puncturing.
Our IBE and bounded HIBE schemes convert natural key-delegation mechanisms from (recursive) applications of puncturable PRFs to IBE and HIBE schemes. Our most technical contribution is an unbounded HIBE, which uses (public-coin) differing-inputs obfuscation for circuits and whose proof relies on a pebbling-based hybrid argument by Fuchsbauer et al. (ASIACRYPT’14). All our constructions are anonymous, support arbitrary inputs, and have compact keys and ciphertexts.
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Notes
- 1.
Although the proof of this construction is somewhat complex, the construction itself is relatively simple given that it achieves an unbounded number of levels.
- 2.
- 3.
Since our construction relies on public-coin diO, it must be hard to find a differing input even when given the coins used to sample the circuits (whose obfuscations should be indistinguishable). As a hash collision results in a differing input, it must be hard to find one even given the coins used to sample the hash function.
- 4.
Note that this is not the case if we only use one encryption of 1 (i.e. if we remove \(h_{21}\) and \(h_{22}\)).
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Acknowledgments
Farshim was supported by the European Research Council under the European Community’s Seventh Framework Programme (FP7/ 2007–2013 Grant Agreement no. 339563 - CryptoCloud). Fuchsbauer is supported by the Vienna Science and Technology Fund (WWTF) through project VRG18-002; work done while at Inria and supported by the French ANR Project ANR-16-CE39-0002 EfTrEC. Passelègue was supported in part from a DARPA/ARL SAFEWARE award, NSF Frontier Award 1413955, NSF grants 1619348, 1228984, 1136174, and 1065276, BSF grant 2012378, a Xerox Faculty Research Award, a Google Faculty Research Award, an equipment grant from Intel, and an Okawa Foundation Research Grant.
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Farshim, P., Fuchsbauer, G., Passelègue, A. (2020). Simpler Constructions of Asymmetric Primitives from Obfuscation. In: Bhargavan, K., Oswald, E., Prabhakaran, M. (eds) Progress in Cryptology – INDOCRYPT 2020. INDOCRYPT 2020. Lecture Notes in Computer Science(), vol 12578. Springer, Cham. https://doi.org/10.1007/978-3-030-65277-7_32
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