Upgrading to functional encryption

Saikrishna Badrinarayanan, Dakshita Khurana, Amit Sahai, Brent Waters

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


The notion of Functional Encryption (FE) has recently emerged as a strong primitive with several exciting applications. In this work, we initiate the study of the following question: Can existing public key encryption schemes be “upgraded” to Functional Encryption schemes without changing their public keys or the encryption algorithm? We call a public-key encryption scheme with this property to be FE-compatible. Indeed, assuming ideal obfuscation, it is easy to see that every CCA-secure public-key encryption scheme is FE-compatible. Despite the recent success in using indistinguishability obfuscation to replace ideal obfuscation for many applications, we show that this phenomenon most likely will not apply here. We show that assuming fully homomorphic encryption and the learning with errors (LWE) assumption, there exists a CCA-secure encryption scheme that is provably not FE-compatible. We also show that a large class of natural CCA-secure encryption schemes proven secure in the random oracle model are not FE-compatible in the random oracle model. Nevertheless, we identify a key structure that, if present, is sufficient to provide FE-compatibility. Specifically, we show that assuming sub-exponentially secure iO and sub-exponentially secure one way functions, there exists a class of public key encryption schemes which we call Special-CCA secure encryption schemes that are in fact, FE-compatible. In particular, each of the following popular CCA secure encryption schemes (some of which existed even before the notion of FE was introduced) fall into the class of Special-CCA secure encryption schemes and are thus FE-compatible: 1.[CHK04] when instantiated with the IBE scheme of [BB04].2.[CHK04] when instantiated with any Hierarchical IBE scheme.3.[PW08] when instantiated with any Lossy Trapdoor Function.

Original languageEnglish (US)
Title of host publicationTheory of Cryptography - 16th International Conference, TCC 2018, Proceedings
EditorsStefan Dziembowski, Amos Beimel
Number of pages30
ISBN (Print)9783030038069
StatePublished - 2018
Externally publishedYes
Event16th Theory of Cryptography Conference, TCC 2018 - Panaji, India
Duration: Nov 11 2018Nov 14 2018

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume11239 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference16th Theory of Cryptography Conference, TCC 2018

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Computer Science(all)


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