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MAK Crypto Seminar: Chen Yuan and Oriol Farras

Two talks. Thursday 10 October 2019, at 11. Campus Nord UPC, Building C3, Room 204a (2nd floor). 1. Towards Optimal Robust Secret Sharing with Security Against a Rushing Adversary (Chen Yuan) 2. Secret-Sharing Schemes for General Access Structures (Oriol Farras)

Quan
10/10/2019 de 11:00 a 13:00 (Europe/Madrid / UTC200)
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Campus Nord UPC, Building C3, Room 204a (2nd floor)
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Two talks in this session:

 

TALK #1:

By: Chen Yuan, CWI Amsterdam
Title: Towards Optimal Robust Secret Sharing with Security Against a Rushing Adversary

Abstract: Robust secret sharing enables the reconstruction of a secret-shared message in the presence of up to t (out of n) incorrect shares. The most challenging case is when n = 2t + 1, which is the largest t for which the task is still possible, up to a small error probability and with some overhead in the share size. In this work,we propose a new robust secret sharing scheme that offers full security against a rushing adversary. We also answer the open question posed by Cevallos et al.(Eurocrypt 2012) who proposed a scheme with overhead of O(n+K) and asked whether the linear dependency on n was necessary or not.

This is a joint work with Serge Fehr.

 

TALK #2:

By: Oriol Farras, URV Tarragona
Title: Secret-Sharing Schemes for General Access Structures

Abstract: A secret-sharing scheme allows some authorized sets of parties to reconstruct a secret; the collection of authorized sets is called the access structure. For over 30 years, it was known that any (monotone) collection of authorized sets can be realized by a secret-sharing scheme whose shares are of size $2^{n−o(n)}$ and until recently no better scheme was known. In a recent breakthrough, Liu and Vaikuntanathan (STOC 2018) reduced the share size to $O(2^{0.994n})$. We improved the general construction, obtaining a share size $O(2^{0.892n})$. For the special case of linear secret-sharing schemes, we get an exponent of $0.942$ (compared to $0.999$ of Liu and Vaikuntanathan).

This result was included in the paper "Secret-Sharing Schemes for General and Uniform Access Structures", a joint work with Benny Applebaum, Amos Beimel, Oded Nir and Naty Peter presented in Eurocrypt 2019.

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