Description
Authentication protocols, run between a prover and a verifier, allow the verifier to check the legitimacy of the prover. A legitimate prover should always authenticate (the correctness requirement), while illegitimate parties (adversaries) should not authenticate (the soundness or impersonation resistance requirement). Secure authentication protocols thwart most Man-in-the-Middle (MIM) attacks, such as replays, but they do not prevent relay attacks , where a coalition of two adversaries, a leech and a ghost , forwards messages between an honest verifier and an honest, far-away prover so as to let the illegitimate ghost authenticate.<br/> Distance-bounding protocols strengthen the security of authentication so as to prevent pure relaying, by enabling the verifier to upper-bound his distance to the prover. This is done by adding a number of time-critical challenge-response rounds, where bits are exchanged over a fast channel; the verifier measures the challenge-response roundtrip and compares it to a time-based proximity bound. There are four attacks such protocols should prevent: mafia fraud, where a MIM adversary tries to authenticate in the presence of a far-away (honest) prover, without purely relaying messages (the clock prevents this); terrorist fraud, where the prover is dishonest and helps the MIM adversary authenticate insofar as this help does not give the adversary any advantage for future (unaided) authentication; distance fraud, where a far-away prover wants to prove he is within the verifier's proximity; and (lazy-round) impersonation security, requiring a degree of impersonation security even for the exchanges that are not timed. Constructing distance-bounding protocols is a highly non-trivial task, since often providing security against one requirement creates a vulnerability with respect to a different requirement. I propose to describe how to construct distance-bounding protocols which are probably secure and also guarantee the prover's privacy.
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[…] -
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
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