Description
Adaptive oblivious transfer (OT) is a protocol where a sender initially commits to a database M_1, …, M_N. Then, a receiver can query the sender up to k times with private indexes ρ_1, …, ρ_k so as to obtain M_{ρ_1}, …, M_{ρ_k} and nothing else. Moreover, for each i ∈ [k], the receiver’s choice ρ_i may depend on previously obtained messages {M_{ρ_j}}_{j< i} . Oblivious transfer with access control (OT-AC) is a flavor of adaptive OT where database records are protected by distinct access control policies that specify which credentials a receiver should obtain in order to acces each M_i. So far, all known OT-AC protocols only support access policies made of conjunctions or rely on ad hoc assumptions in pairing-friendly groups (or both). In this paper, we provide an OT-AC protocol where access policies may consist of any branching program of polynomial length, which is sufficient to realize any access policy in NC^1. The security of our protocol is proved under the Learning-with-Errors (LWE) and Short-Integer-Solution (SIS) assumptions. As a result of independent interest, we provide protocols for proving the correct evaluation of a committed branching program on a committed input. This is joint work with Benoît Libert, San Ling, Khoa Nguyen and Huaxiong Wang.
Next sessions
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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[…] -
TBD
Speaker : Maria Corte-Real Santos - ENS Lyon
TBD-
Cryptography
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