Description
The problem of computing the zeta function of a variety over a finite field has attracted considerable interest in recent years, motivated in part by an application in cryptography. (In less fancy language, the problem is just to compute the number of solutions to a system of polynomial equations over a finite field.) I will discuss a new algorithm for computing zeta functions which is based upon relative p-adic cohomology. The idea is that to compute the zeta function of a single projective hypersurface, say , one puts it in a one-dimensional family of hypersurfaces. As one moves through this family, the zeta function varies in a manner which is controlled by a differential equation. One can arrange matters so that one fibre in the family has an easily computed zeta function. By solving the differential equation locally around this fibre, and using a form of analytic continuation, one can now recover the zeta function of any fibre in the family. In particular, one gets the zeta function of the original hypersurface! The key point is that because the `deformation' from the original hypersurface to the easy one is one-dimensional, the complexity of this approach is largely independent of the dimension of the hypersurface. In fact, one gets a uniform dependence on the input size over all dimensions. This contrasts starkly with existing approaches, whose performance deteriorates as the dimension increases. I believe the talk should be of interest to both cryptographers and p-adic cohomologists.
Next sessions
-
Efficient zero-knowledge proofs and arguments in the CL framework
Speaker : Agathe Beaugrand - Institut de Mathématiques de Bordeaux
The CL encryption scheme, proposed in 2015 by Castagnos and Laguillaumie, is a linearly homomorphic encryption scheme, based on class groups of imaginary quadratic fields. The specificity of these groups is that their order is hard to compute, which means it can be considered unknown. This particularity, while being key in the security of the scheme, brings technical challenges in working with CL,[…] -
Constant-time lattice reduction for SQIsign
Speaker : Sina Schaeffler - IBM Research
SQIsign is an isogeny-based signature scheme which has recently advanced to round 2 of NIST's call for additional post-quantum signatures. A central operation in SQIsign is lattice reduction of special full-rank lattices in dimension 4. As these input lattices are secret, this computation must be protected against side-channel attacks. However, known lattice reduction algorithms like the famous[…] -
Circuit optimisation problems in the context of homomorphic encryption
Speaker : Sergiu Carpov - Arcium
Fully homomorphic encryption (FHE) is an encryption scheme that enables the direct execution of arbitrary computations on encrypted data. The first generation of FHE schemes began with Gentry's groundbreaking work in 2019. It relies on a technique called bootstrapping, which reduces noise in FHE ciphertexts. This construction theoretically enables the execution of any arithmetic circuit, but[…] -
Cycles of pairing-friendly abelian varieties
Speaker : Maria Corte-Real Santos - ENS Lyon
A promising avenue for realising scalable proof systems relies on the existence of 2-cycles of pairing-friendly elliptic curves. More specifically, such a cycle consists of two elliptic curves E/Fp and E’/Fq that both have a low embedding degree and also satisfy q = #E(Fp) and p = #E’(Fq). These constraints turn out to be rather restrictive; in the decade that has passed since 2-cycles were first[…]-
Cryptography
-