Spooky encryption and its applications

Yevgeniy Dodis, Shai Halevi, Ron D. Rothblum, Daniel Wichs

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Consider encrypting n inputs under n independent public keys. Given the ciphertexts {ci = Encpki (xi)}i, Alice outputs ciphertexts c’1,…, c‘n that decrypt to y1,…, yn respectively. What relationships between the xi’s and yi’s can Alice induce? Motivated by applications to delegating computations, Dwork et al. [11] showed that a semantically secure scheme disallows signaling in this setting, meaning that yi cannot depend on xj for j ≠ i. On the other hand if the scheme is homomorphic then any local (component-wise) relationship is achievable, meaning that each yi can be an arbitrary function of xi. However, there are also relationships which are neither signaling nor local. Dwork et al. asked if it is possible to have encryption schemes that support such “spooky” relationships. Answering this question is the focus of our work. Our first result shows that, under the LWE assumption, there exist encryption schemes supporting a large class of “spooky” relationships, which we call additive function sharing (AFS) spooky. In particular, for any polynomial-time function f, Alice can ensure that y1,…, yn are random subject to ∑n i=1 yi = f(x1,…, xn). For this result, the public keys all depend on common public randomness. Our second result shows that, assuming sub-exponentially hard indistinguishability obfuscation (iO) (and additional more standard assumptions), we can remove the common randomness and choose the public keys completely independently. Furthermore, in the case of n = 2 inputs, we get a scheme that supports an even larger class of spooky relationships. We discuss several implications of AFS-spooky encryption. Firstly, it gives a strong counter-example to a method proposed by Aiello et al. [1] for building arguments for NP from homomorphic encryption. Secondly, it gives a simple 2-round multi-party computation protocol where, at the end of the first round, the parties can locally compute an additive secret sharing of the output. Lastly, it immediately yields a function secret sharing (FSS) scheme for all functions. We also define a notion of spooky-free encryption, which ensures that no spooky relationship is achievable. We show that any nonmalleable encryption scheme is spooky-free. Furthermore, we can construct spooky-free homomorphic encryption schemes from SNARKs, and it remains an open problem whether it is possible to do so from falsifiable assumptions.

Original languageEnglish (US)
Title of host publicationAdvances in Cryptology - 36th Annual International Cryptology Conference, CRYPTO 2016, Proceedings
EditorsMatthew Robshaw, Jonathan Katz
PublisherSpringer Verlag
Number of pages30
ISBN (Print)9783662530146
StatePublished - 2016
Event36th Annual International Cryptology Conference, CRYPTO 2016 - Santa Barbara, United States
Duration: Aug 14 2016Aug 18 2016

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Other36th Annual International Cryptology Conference, CRYPTO 2016
Country/TerritoryUnited States
CitySanta Barbara

ASJC Scopus subject areas

  • Theoretical Computer Science
  • General Computer Science


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