Functional encryption for cascade automata (Extended abstract)

Dan Brownstein, Shlomi Dolev, Niv Gilboa

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


We introduce a functional encryption scheme based on the security of bilinear maps for the class of languages accepted by extended automata. In such an automaton, n DFAs, each with at most q states, are linked in a cascade such that the first DFA receives the input to the system and a feedback symbol from the last DFA, and in each transition the i-th DFA, i = 1,..., n, both performs its own transition and outputs a symbol that acts as the input for DFA number i+1 mod n. The state of the whole system is an n-tuple consisting of the state of each component DFA. Our work extends the work of Waters (Crypto’12) by replacing a single DFA with a cascade. Although both models accept all regular languages, a cascade automata reduces the number of states and therefore the key size for certain regular languages by an exponential factor. In both systems, a message m is encrypted with a word w and can be decrypted only by a key that is associated with an automaton that accepts w. Our scheme has key size O(nq2) and all its other efficiency measures including the ciphertext length, encryption and decryption times are linear in the length of w. As an example of the additional power that a cascade provides, we show a construction of a cascade that accepts a word in a regular language only if it is accompanied by a standard public key signature on that word. Our work improves on alternative approaches using functional encryption for general circuits or programs, by either being based on weaker assumptions, i.e. bilinear maps, or by being more efficient.

Original languageEnglish
Title of host publicationStabilization, Safety and Security of Distributed Systems - 17th International Symposium, SSS 2015, Proceedings
EditorsAndrzej Pelc, Alexander A. Schwarzmann
PublisherSpringer Verlag
Number of pages15
ISBN (Print)9783319217406
StatePublished - 1 Jan 2015
Event17th International Symposium on Stabilization, Safety and Security of Distributed Systems, SSS 2015 - Edmonton, Canada
Duration: 18 Aug 201521 Aug 2015

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


Conference17th International Symposium on Stabilization, Safety and Security of Distributed Systems, SSS 2015


  • Functional encryption

ASJC Scopus subject areas

  • Theoretical Computer Science
  • General Computer Science


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