## Cryptology ePrint Archive: Report 2014/487

**GGHLite: More Efficient Multilinear Maps from Ideal Lattices**

*Adeline Langlois and Damien Stehle and Ron Steinfeld*

**Abstract: **The GGH Graded Encoding Scheme, based on ideal lattices, is the first plausible approximation to a cryptographic multilinear map. Unfortunately, using the security analysis in the original paper, the scheme requires very large parameters to provide security for its underlying encoding re-randomization process. Our main contributions are to formalize, simplify and improve the efficiency and the security analysis of the re-randomization process in the GGH construction. This results in a new construction that we call GGHLite. In particular, we first lower the size of a standard deviation parameter of the re-randomization process of the original scheme from exponential to polynomial in the security parameter. This first improvement is obtained via a finer security analysis of the
drowning step of re-randomization, in which we apply the
Rényi divergence instead of the conventional statistical distance as a measure of distance between distributions. Our second improvement is to reduce the number of randomizers needed from $\Omega(n \log n)$ to $2$, where $n$ is the dimension of the underlying ideal lattices. These two contributions allow us to decrease the bit size of the public parameters from $O(\lambda^5 \log \lambda)$ for the
GGH scheme to $O(\lambda \log^2 \lambda)$ in GGHLite, with respect to the security parameter $\lambda$ (for a constant multilinearity parameter $\kappa$).

**Category / Keywords: **public-key cryptography / multilinear maps

**Original Publication**** (with minor differences): **IACR-EUROCRYPT-2014

**Date: **received 19 Jun 2014

**Contact author: **adeline langlois at ens-lyon fr

**Available format(s): **PDF | BibTeX Citation

**Version: **20140623:130643 (All versions of this report)

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