15:00
Wave: A New Family of Trapdoor Preimage Sampleable Functions Based on Codes
It is a long-standing open problem to build an efficient and secure digital signature scheme based on the hardness of decoding a linear code which could compete with widespread schemes like DSA or RSA. The latter signature schemes are broken by a quantum computer with Shor’s algorithm. Code-based schemes could provide a valid quantum resistant replacement. We present here Wave the first « hash-and-sign » code-based signature scheme which strictly follows the GPV strategy which ensures universal unforgeability. It uses the family of ternary generalized $(U, U+V)$ codes. Our algorithm produces uniformly distributed signatures through a suitable rejection sampling (one rejection every 3 or 4 signatures). Furthermore, our scheme enjoys efficient signature and verification algorithms. Typically, for 128 bits of classical security, signatures are in the order of 10 thousand bits long and the public key is in the order of one megabyte.
p-Adic Asai L-functions of Bianchi modular forms
Abstract
The Asai (or twisted tensor) L-function attached to a Bianchi modular form is the 'restriction to the rationals' of the standard L-function. Introduced by Asai in 1977, subsequent study has linked its special values to the arithmetic of the corresponding form. In this talk, I will discuss joint work with David Loeffler in which we construct a p-adic Asai L-function -- that is, a measure on Z_p* that interpolates the critical values L^As(f,chi,1) -- for ordinary weight 2 Bianchi modular forms. We use a new method for constructing p-adic L-functions, using Kato's system of Siegel units to build a 'Betti analogue' of an Euler system, building on algebraicity results of Ghate. I will start by giving a brief introduction to p-adic L-functions and Bianchi modular forms, and if time permits, I will briefly mention another case where the method should apply, that of non-self-dual automorphic representations for GL(3).