## Cryptology ePrint Archive: Report 2013/401

Functional Signatures and Pseudorandom Functions

Elette Boyle and Shafi Goldwasser and Ioana Ivan

Abstract: In this paper, we introduce \emph{functional digital signatures} and \emph{pseudorandom functions}.

In a functional signature scheme, in addition to a master signing key that can be used to sign any message, there are \emph{signing keys for a function} $f$, which allow one to sign any message in the range of $f$. We show applications of functional signatures to construct succinct non-interactive arguments and delegation schemes. We give several general constructions for this primitive based on different computational hardness assumptions, and describe the trade-offs between them in terms of the assumptions they require and the size of the signatures.

In a functional pseudorandom function, in addition to a master secret key that can be used to evaluate the pseudorandom function $F$ on any point in the domain, there are additional \emph{secret keys for a function} $f$, which allow one to evaluate $F$ on any $y$ for which there exists an $x$ such that $f(x)=y$. This implies the ability to delegate keys per function $f$ for computing a pseudorandom function $F$ on points $y$ for which $f(y)=1$. We define and provide a sample construction of a functional pseudorandom function family for the prefix-fixing function family. }

Category / Keywords:

Date: received 18 Jun 2013, last revised 29 Jun 2013

Contact author: ioanai at mit edu

Available format(s): PDF | BibTeX Citation

[ Cryptology ePrint archive ]