Paper 2014/897
Leveled Fully Homomorphic Signatures from Standard Lattices
Sergey Gorbunov, Vinod Vaikuntanathan, and Daniel Wichs
Abstract
In a homomorphic signature scheme, a user Alice signs some large dataset $x$ using her secret signing key and uploads the signed data to an untrusted remote server. The server can then run some computation $y=f(x)$ over the signed data and homomorphically derive a short signature $\sigma_{f,y}$ certifying that $y$ is the correct output of the computation $f$. Anybody can verify the tuple $(f, y, \sigma_{f,y})$ using Alice's public verification key and become convinced of this fact without having to retrieve the entire underlying data. In this work, we construct the first (leveled) fully homomorphic signature schemes that can evaluate arbitrary circuits over signed data. Only the maximal depth $d$ of the circuits needs to be fixed apriori at setup, and the size of the evaluated signature grows polynomially in $d$, but is otherwise independent of the circuit size or the data size. Our solution is based on the (subexponential) hardness of the small integer solution (SIS) problem in standard lattices and satisfies full (adaptive) security. In the standard model, we get a scheme with large public parameters whose size exceeds the total size of a dataset. In the randomoracle model, we get a scheme with short public parameters. In both cases, the schemes can be used to sign many different datasets. The complexity of verifying a signature for a computation $f$ is at least as large as that of computing $f$, but can be amortized when verifying the same computation over many different datasets. Furthermore, the signatures can be made contexthiding so as not to reveal anything about the data beyond the outcome of the computation. These results offer a significant improvement in capabilities and assumptions over the best prior homomorphic signature schemes, which were limited to evaluating polynomials of constant degree. As a building block of independent interest, we introduce a new notion called homomorphic trapdoor functions (HTDF) which conceptually unites homomorphic encryption and signatures. We construct HTDFs by relying on the techniques developed by Gentry et al. (CRYPTO '13) and Boneh et al. (EUROCRYPT '14) in the contexts of fully homomorphic and attributebased encryptions.
Note: This is a merged version of Eprint 2014/463 and 2014/451, with additional results.
Metadata
 Available format(s)
 Category
 Foundations
 Publication info
 Preprint. MINOR revision.
 Keywords
 Homomorphic SignaturesLatticesOutsourcing Computation
 Contact author(s)
 sergeyg @ mit edu
 History
 20141107: last of 3 revisions
 20141030: received
 See all versions
 Short URL
 https://ia.cr/2014/897
 License

CC BY
BibTeX
@misc{cryptoeprint:2014/897, author = {Sergey Gorbunov and Vinod Vaikuntanathan and Daniel Wichs}, title = {Leveled Fully Homomorphic Signatures from Standard Lattices}, howpublished = {Cryptology {ePrint} Archive, Paper 2014/897}, year = {2014}, url = {https://eprint.iacr.org/2014/897} }