Description
Forward-secure signatures (FSS) prevent forgeries for past time periods when an attacker obtains full access to the signer's storage. To simplify the integration of these primitives into standard security architectures, Boyen, Shacham, Shen and Waters recently introduced the concept of forward-secure signatures with untrusted updates where private keys are additionally protected by a second factor (derived from a password). Key updates can be made on encrypted version of signing keys so that passwords only come into play for signing messages.<br/> The scheme put forth by Boyen et al. relies on bilinear maps and does not require the random oracle. The latter work also suggested the integration of untrusted updates in the Bellare-Miner forward-secure signature and left open the problem of endowing other existing FSS systems with the same second factor protection. We solve this problem by showing how to adapt the very efficient generic construction of Malkin, Micciancio and Miner (MMM) to untrusted update environments. More precisely, our modified construction - which does not use random oracles either - obtains a forward-secure signature with untrusted updates from any 2-party multi-signature in the plain public key model. In combination with Bellare and Neven's multi-signatures, our generic method yields implementations based on standard assumptions such as RSA, factoring or the hardness of computing discrete logarithms. Like the original MMM scheme, it does not require to set a bound on the number of time periods at key generation.
Prochains exposés
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Some applications of linear programming to Dilithium
Orateur : Paco AZEVEDO OLIVEIRA - Thales & UVSQ
Dilithium is a signature algorithm, considered post-quantum, and recently standardized under the name ML-DSA by NIST. Due to its security and performance, it is recommended in most use cases. During this presentation, I will outline the main ideas behind two studies, conducted in collaboration with Andersson Calle-Vierra, Benoît Cogliati, and Louis Goubin, which provide a better understanding of[…] -
Wagner’s Algorithm Provably Runs in Subexponential Time for SIS^∞
Orateur : Johanna Loyer - Inria Saclay
At CRYPTO 2015, Kirchner and Fouque claimed that a carefully tuned variant of the Blum-Kalai-Wasserman (BKW) algorithm (JACM 2003) should solve the Learning with Errors problem (LWE) in slightly subexponential time for modulus q = poly(n) and narrow error distribution, when given enough LWE samples. Taking a modular view, one may regard BKW as a combination of Wagner’s algorithm (CRYPTO 2002), run[…]-
Cryptography
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CryptoVerif: a computationally-sound security protocol verifier
Orateur : Bruno Blanchet - Inria
CryptoVerif is a security protocol verifier sound in the computational model of cryptography. It produces proofs by sequences of games, like those done manually by cryptographers. It has an automatic proof strategy and can also be guided by the user. It provides a generic method for specifying security assumptions on many cryptographic primitives, and can prove secrecy, authentication, and[…]-
Cryptography
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Structured-Seed Local Pseudorandom Generators and their Applications
Orateur : Nikolas Melissaris - IRIF
We introduce structured‑seed local pseudorandom generators (SSL-PRGs), pseudorandom generators whose seed is drawn from an efficiently sampleable, structured distribution rather than uniformly. This seemingly modest relaxation turns out to capture many known applications of local PRGs, yet it can be realized from a broader family of hardness assumptions. Our main technical contribution is a[…]-
Cryptography
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