[crypto] Fwd: CWG Schedule 13 Sep

[R. Hirschfeld]

-------- Original Message --------
Subject: CWG Schedule 13 Sep
Date: 2024-09-09 10:04
 From: "Guarise Vieira, Heloise" <h.guarise.vieira at tue.nl>
To:

Dear Crypto Working Group Participant,

Find below the schedule for our meeting this Friday, 13 September, at 
the Kargadoor, in Utrecht.

Let me know if I can further assist you.

Best regards.


10:45h
Access Structure Hiding Verifiable Tensor Designs
Suprita Talnikar

The field of verifiable secret sharing schemes was introduced by Verheul 
et al. and has evolved over time, including well-known examples by 
Feldman and Pedersen. Stinson made advancements in combinatorial 
design-based secret sharing schemes in 2004. Desmedt et al. introduced 
the concept of frameproofness in 2021, while recent research by Sehrawat 
et al. in 2021 focuses on LWE-based access structure hiding verifiable 
secret sharing with malicious-majority settings. Furthermore, Roy et al. 
combined the concepts of reparable threshold schemes by Stinson et al. 
and frameproofness by Desmedt et al. in 2023, to develop extendable 
tensor designs built from balanced incomplete block designs, and also 
presented a frameproof version of their design.
This talk explores ramp-type verifiable secret sharing schemes, and the 
application of hidden access structures in such cryptographic protocols. 
Inspired by Sehrawat et al.'s access structure hiding scheme, we develop 
an $\epsilon$-almost access structure hiding scheme, which is verifiable 
as well as frameproof. We detail how the concept $\epsilon$-almost 
hiding is important for incorporating ramp schemes, thus making a 
fundamental generalisation of this concept.

11:30h - coffee break

11:45h
On Broadcast and Identifiability in MPC
Divya Ravi

TBD

12:30h lunch

14:00h
New Limits of Provable Security and Applications to ElGamal Encryption
Sven Schäge
We provide new results showing that ElGamal encryption cannot be proven 
CCA1-secure – a long-standing open problem in cryptography. Our result 
follows from a very broad, meta-reduction-based impossibility result on 
random self-reducible relations with efficiently re-randomizable 
witnesses. The techniques that we develop allow, for the first time, to 
provide impossibility results for very weak security notions where the 
challenger outputs fresh challenge statements at the end of the security 
game. This can be used to finally tackle encryption-type definitions 
that have remained elusive in the past. We show that our results have 
broad applicability by casting several known cryptographic setups as 
instances of random self-reducible and re-randomizable relations. These 
setups include general semi-homomorphic PKE and the large class of 
certified homomorphic one-way bijections. As a result, we also obtain 
new impossibility results for the IND-CCA1 security of the PKEs of 
Paillier and Damgard–Jurik, and many one-more inversion assumptions like 
the one-more DLOG or the one-more RSA assumption.

14:45h coffee break

15:00h
Towards post-quantum secure PAKE
Silvia  Ritsch

ABSTRACT: Password-based authenticated key exchange (PAKE) protocols 
allow two parties to establish a secure session key using a shared 
password. Unlike traditional methods, PAKE does not require a public-key 
infrastructure (PKI) and is designed to be secure even if the password 
is weak. We revisit OCAKE (ACNS 23), a method for constructing PAKE 
generically using key encapsulation mechanisms (KEMs), including 
post-quantum KEMs like KYBER. The original paper left open the challenge 
of proving security against quantum attackers. To address this, we 
provide a game-based security proof in the BPR model (EUROCRYPT 2000), 
which is a crucial step towards a comprehensive post-quantum security 
proof. Finally, we explore current PQC KEMs that can be integrated into 
our protocol, supported by a proof-of-concept implementation and runtime 
benchmarks.

15:45h end of activities
--

[Image]

Heloise Vieira, PhD
Discrete Mathematics Cluster, Project Leader
Department of Mathematics and Computer Science
Phone number +31 (0)402474864

De Zaale, Eindhoven
05 MetaForum, MF 6.101