@article{5887, abstract = {Cryptographic security is usually defined as a guarantee that holds except when a bad event with negligible probability occurs, and nothing is guaranteed in that bad case. However, in settings where such failure can happen with substantial probability, one needs to provide guarantees even for the bad case. A typical example is where a (possibly weak) password is used instead of a secure cryptographic key to protect a session, the bad event being that the adversary correctly guesses the password. In a situation with multiple such sessions, a per-session guarantee is desired: any session for which the password has not been guessed remains secure, independently of whether other sessions have been compromised. A new formalism for stating such gracefully degrading security guarantees is introduced and applied to analyze the examples of password-based message authentication and password-based encryption. While a natural per-message guarantee is achieved for authentication, the situation of password-based encryption is more delicate: a per-session confidentiality guarantee only holds against attackers for which the distribution of password-guessing effort over the sessions is known in advance. In contrast, for more general attackers without such a restriction, a strong, composable notion of security cannot be achieved.}, author = {Demay, Gregory and Gazi, Peter and Maurer, Ueli and Tackmann, Bjorn}, issn = {0926227X}, journal = {Journal of Computer Security}, number = {1}, pages = {75--111}, publisher = {IOS Press}, title = {{Per-session security: Password-based cryptography revisited}}, doi = {10.3233/JCS-181131}, volume = {27}, year = {2019}, } @article{6515, abstract = {We give non-degeneracy criteria for Riemannian simplices based on simplices in spaces of constant sectional curvature. It extends previous work on Riemannian simplices, where we developed Riemannian simplices with respect to Euclidean reference simplices. The criteria we give in this article are in terms of quality measures for spaces of constant curvature that we develop here. We see that simplices in spaces that have nearly constant curvature, are already non-degenerate under very weak quality demands. This is of importance because it allows for sampling of Riemannian manifolds based on anisotropy of the manifold and not (absolute) curvature.}, author = {Dyer, Ramsay and Vegter, Gert and Wintraecken, Mathijs}, issn = {1920-180X}, journal = {Journal of Computational Geometry }, number = {1}, pages = {223–256}, publisher = {Carleton University}, title = {{Simplices modelled on spaces of constant curvature}}, doi = {10.20382/jocg.v10i1a9}, volume = {10}, year = {2019}, } @inproceedings{6528, abstract = {We construct a verifiable delay function (VDF) by showing how the Rivest-Shamir-Wagner time-lock puzzle can be made publicly verifiable. Concretely, we give a statistically sound public-coin protocol to prove that a tuple (N,x,T,y) satisfies y=x2T (mod N) where the prover doesn’t know the factorization of N and its running time is dominated by solving the puzzle, that is, compute x2T, which is conjectured to require T sequential squarings. To get a VDF we make this protocol non-interactive using the Fiat-Shamir heuristic.The motivation for this work comes from the Chia blockchain design, which uses a VDF as akey ingredient. For typical parameters (T≤2 40, N= 2048), our proofs are of size around 10K B, verification cost around three RSA exponentiations and computing the proof is 8000 times faster than solving the puzzle even without any parallelism.}, author = {Pietrzak, Krzysztof Z}, booktitle = {10th Innovations in Theoretical Computer Science Conference}, isbn = {978-3-95977-095-8}, issn = {1868-8969}, location = {San Diego, CA, United States}, publisher = {Schloss Dagstuhl - Leibniz-Zentrum für Informatik}, title = {{Simple verifiable delay functions}}, doi = {10.4230/LIPICS.ITCS.2019.60}, volume = {124}, year = {2019}, } @inproceedings{6565, abstract = {In this paper, we address the problem of synthesizing periodic switching controllers for stabilizing a family of linear systems. Our broad approach consists of constructing a finite game graph based on the family of linear systems such that every winning strategy on the game graph corresponds to a stabilizing switching controller for the family of linear systems. The construction of a (finite) game graph, the synthesis of a winning strategy and the extraction of a stabilizing controller are all computationally feasible. We illustrate our method on an example.}, author = {Kundu, Atreyee and Garcia Soto, Miriam and Prabhakar, Pavithra}, booktitle = {5th Indian Control Conference Proceedings}, isbn = {978-153866246-5}, location = {Delhi, India}, publisher = {IEEE}, title = {{Formal synthesis of stabilizing controllers for periodically controlled linear switched systems}}, doi = {10.1109/INDIANCC.2019.8715598}, year = {2019}, } @inproceedings{6628, abstract = {Fejes Tóth [5] and Schneider [9] studied approximations of smooth convex hypersurfaces in Euclidean space by piecewise flat triangular meshes with a given number of vertices on the hypersurface that are optimal with respect to Hausdorff distance. They proved that this Hausdorff distance decreases inversely proportional with m 2/(d−1), where m is the number of vertices and d is the dimension of Euclidean space. Moreover the pro-portionality constant can be expressed in terms of the Gaussian curvature, an intrinsic quantity. In this short note, we prove the extrinsic nature of this constant for manifolds of sufficiently high codimension. We do so by constructing an family of isometric embeddings of the flat torus in Euclidean space.}, author = {Vegter, Gert and Wintraecken, Mathijs}, booktitle = {The 31st Canadian Conference in Computational Geometry}, location = {Edmonton, Canada}, pages = {275--279}, title = {{The extrinsic nature of the Hausdorff distance of optimal triangulations of manifolds}}, year = {2019}, }