Towards Stronger Functional Signatures
Preprint, 2021

Functional digital Signatures (FS) schemes introduced by Boyle, Goldwasser and Ivan (PKC 2014) provide
a method to generate fine-grained digital signatures in which a master key-pair $(\msk,\mvk)$ is used to
generate a signing secret-key $\sk_\function$ for a function $f$ that allows to sign any message $\msg$
into the message $f(\msg)$ and signature $\sigma$.
The verification algorithm takes the master verification-key $\mvk$ and checks that the signature $\sigma$
corresponding to $f(\msg)$ is valid.
In this paper, we enhance the FS primitive by introducing a function public-key $\pk_f$ that acts as
a commitment for the specific signing key $\sk_f$. This public-key is used during the verification
phase and guarantees that the message-signature pair is indeed the result generated by employing the specific key $\sk_f$
in the signature phase, a property not achieved by the original FS scheme.

This enhanced FS scheme is defined as Strong Functional Signatures (SFS) for which we define
the properties of unforgeability as well as the function hiding property.
Finally, we provide an unforgeable, function hiding SFS instance in the random oracle model based
on Boneh-Lynn-Shacham signature scheme (ASIACRYPT 2001) and Fiore-Gennaro's publicly verifiable
computation scheme (CCS 2012).

Verifiable Computation

Function Privacy

Functional Signatures


Carlo Brunetta

Chalmers, Data- och informationsteknik, Nätverk och system

Bei Liang

Chalmers, Data- och informationsteknik, Nätverk och system

Aikaterini Mitrokotsa

Chalmers, Data- och informationsteknik, Nätverk och system

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Vetenskapsrådet (VR) (2014-4845), 2015-01-01 -- 2018-12-31.



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