Hierarchical Functional Encryption

Zvika Brakerski and Gil Segev

Abstract

Functional encryption provides fine-grained access control for encrypted data, allowing each user to learn only specific functions of the encrypted data. We study the notion of \emph{hierarchical} functional encryption, which augments functional encryption with \emph{delegation} capabilities, offering significantly more expressive access control. We present a {\em generic transformation} that converts any general-purpose public-key functional encryption scheme into a hierarchical one without relying on any additional assumptions. This significantly refines our understanding of the power of functional encryption, showing (somewhat surprisingly) that the existence of functional encryption is equivalent to that of its hierarchical generalization. Instantiating our transformation with the existing functional encryption schemes yields a variety of hierarchical schemes offering various trade-offs between their delegation capabilities (i.e., the depth and width of their hierarchical structures) and underlying assumptions. When starting with a scheme secure against an unbounded number of collusions, we can support \emph{arbitrary} hierarchical structures. In addition, even when starting with schemes that are secure against a bounded number of collusions (which are known to exist under rather minimal assumptions such as the existence of public-key encryption and shallow pseudorandom generators), we can support hierarchical structures of bounded depth and width.

Available format(s)
Category
Public-key cryptography
Publication info
Preprint. MINOR revision.
Keywords
functional encryption
Contact author(s)
zvika brakerski @ weizmann ac il
History
2016-09-15: revised
See all versions
Short URL
https://ia.cr/2015/1011

CC BY

BibTeX

@misc{cryptoeprint:2015/1011,
author = {Zvika Brakerski and Gil Segev},
title = {Hierarchical Functional Encryption},
howpublished = {Cryptology ePrint Archive, Paper 2015/1011},
year = {2015},
note = {\url{https://eprint.iacr.org/2015/1011}},
url = {https://eprint.iacr.org/2015/1011}
}

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