BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Drupal iCal API//EN X-WR-CALNAME:Events items teaser X-WR-TIMEZONE:America/Toronto BEGIN:VTIMEZONE TZID:America/Toronto X-LIC-LOCATION:America/Toronto BEGIN:DAYLIGHT TZNAME:EDT TZOFFSETFROM:-0500 TZOFFSETTO:-0400 DTSTART:20260308T070000 END:DAYLIGHT BEGIN:STANDARD TZNAME:EST TZOFFSETFROM:-0400 TZOFFSETTO:-0500 DTSTART:20261101T060000 END:STANDARD END:VTIMEZONE BEGIN:VEVENT UID:6af97ef3b3d33 DTSTART;TZID=America/Toronto:20261116T150000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20261116T160000 URL:https://uwaterloo.ca/combinatorics-and-optimization/events/graphs-and-m atroids-cece-henderson-hypergraph-nash-williams SUMMARY:Graphs and Matroids | Cece Henderson\, On the Hypergraph Nash-Willi ams'\nConjecture CLASS:PUBLIC DESCRIPTION:SPEAKER:\n Cece Henderson\n\nAFFILIATION:\n University of Water loo\n\nROOM:\n MC 6029\n\nABSTRACT: The study of combinatorial designs in cludes some of the\noldest questions at the heart of combinatorics. In a b reakthrough\nresult of 2014\, Keevash proved the longstanding Existence Co njecture\nby showing the existence of (n\,q\,r)-Steiner systems (equivalen tly\nK_q^r-decompositions of K_n^r) for all large enough n satisfying the\ nnecessary divisibility conditions. Meanwhile\, in recent decades\,\nincre mental progress has been made on the celebrated Nash-Williams'\nConjecture of 1970\, which posits that any large enough\,\ntriangle-divisible graph on n vertices with minimum degree at least\n3n/4 admits a triangle decompo sition. In 2021\, Glock\, Kühn\, and\nOsthus proposed a generalization of these results by conjecturing a\nhypergraph version of the Nash-Williams' Conjecture\, where their\nproposed minimum degree K_q^r-decomposition thr eshold is motivated by\nhypergraph Turán theory. By using the recently de veloped method of\nrefined absorption and establishing a non-uniform Turá n theory\, we\ntie the K_q^r-decomposition threshold to its fractional rel axation.\nCombined with the best-known fractional decomposition threshold from\nDelcourt\, Lesgourgues\, and Postle\, this dramatically closes the g ap\nbetween what was known and the above conjecture. This talk is based on \njoint work with Luke Postle. DTSTAMP:20261115T094419Z END:VEVENT BEGIN:VEVENT UID:6af97ef3b74c7 DTSTART;TZID=America/Toronto:20261124T163000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20261124T175000 URL:https://uwaterloo.ca/combinatorics-and-optimization/events/cryptography -seminar-rolfe-schmidt-making-signal-protocol SUMMARY:Cryptography Seminar | Rolfe Schmidt\, Making the Signal Protocol\n Quantum Safe: Where We Are and What’s Next CLASS:PUBLIC DESCRIPTION:SPEAKER:\n Rolfe Schmidt\n\nAFFILIATION:\n Signal\n\nLOCATION:\ n United College\, Room 105\n\nABSTRACT: In 2023 Signal deployed PQXDH\, a small change to the\nhandshake that protects new conversations against adversaries who\nrecord traffic today and decrypt it with a future quantum computer.\nTwo gaps remain: post-compromise security in the ratchet and\n authentication in the handshake both still rely on elliptic curves.\nThis talk describes how we closed the first and how we plan to close\nthe secon d.\n\nIn the first part\, we look at the challenge of building a post-quan tum\nratcheted messaging protocol in a bandwidth-constrained setting\, and \nbuild up Signal’s Sparse Post-Quantum Ratchet\, deployed in 2025\,\nst ep by step through a series of simpler protocols.\n\nIn the second part\, we look ahead to a new handshake that completes\nthe transition of Signal ’s 1:1 messaging with hybrid\, deniable\nauthentication. While the post- quantum ratchet feels like an\nengineering variation on the classical one\ , the post-quantum key\nagreement takes a very different shape. Our need t o save bandwidth\nstill drives plenty of engineering\, including Merkle tr ees\, Falcon\nsignature recovery modes\, and context-specific optimization s.\n\nI’ll close with open questions and a brief look at what it will ta ke\nto make the rest of the Signal app quantum safe. DTSTAMP:20261115T094419Z END:VEVENT BEGIN:VEVENT UID:6af97ef3b81e9 DTSTART;TZID=America/Toronto:20261119T143000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20261119T153000 URL:https://uwaterloo.ca/combinatorics-and-optimization/events/algebraic-an d-enumerative-combinatorics-seminar-andy-zucker SUMMARY:Algebraic and Enumerative Combinatorics Seminar | Andy Zucker\, The \nordering property and topological dynamics CLASS:PUBLIC DESCRIPTION:SPEAKER:\n Andy Zucker\n\nAFFILIATION:\n University of Waterloo \n\nLOCATION:\n MC 5417\n\nABSTRACT: A 1976 theorem of Nesetril and Rodl proves that the class\nof k-clique-free finite graphs has the ordering pro perty. In this\ntalk\, we will define the ordering property and give a pro babilistic\nargument that it holds. We then discuss how a 2005 paper of Ke chris\,\nPestov\, and Todorcevic applies the ordering property to topologi cal\ndynamics.\n\nThere will be a pre-seminar presenting relevant backgrou nd at\nbeginning graduate level starting at 1:30pm in MC 5417. DTSTAMP:20261115T094419Z END:VEVENT BEGIN:VEVENT UID:6af97ef3b8de9 DTSTART;TZID=America/Toronto:20261116T110000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20261116T120000 URL:https://uwaterloo.ca/combinatorics-and-optimization/events/combopt-read ing-group-mehrdad-sohrabi-approximating-graphic SUMMARY:CombOpt Reading Group | Mehrdad Sohrabi\, Approximating graphic TSP by\nb-matchings CLASS:PUBLIC DESCRIPTION:SPEAKER:\n\nMehrdad Sohrabi\n\nAFFILIATION:\n University of Wat erloo\n\nROOM:\n MC 6029\n\nABSTRACT: We are going to talk about approxim ating graphic TSP\, which\nis a variant of TSP where the distances come fr om shortest paths\nbetween vertices of an undirected graph. We will talk a bout Mömke and\nSvensson’s approach\, which used matchings to improve t he\napproximation ratio\, and also our recent generalization that uses\nb- matchings. This is joint work with Levent Tunçel and Swati Gupta. DTSTAMP:20261115T094419Z END:VEVENT BEGIN:VEVENT UID:6af97ef3b99b6 DTSTART;TZID=America/Toronto:20261120T153000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20261120T163000 URL:https://uwaterloo.ca/combinatorics-and-optimization/events/tutte-colloq uium-andy-zucker-survey-structural-ramsey-theory SUMMARY:Tutte Colloquium | Andy Zucker\, A survey of structural Ramsey theo ry CLASS:PUBLIC DESCRIPTION:SPEAKER:\n Andy Zucker\n\nAFFILIATION:\n University of Waterloo \n\nLOCATION:\n MC 5501\n\nABSTRACT: Ramsey's celebrated theorem has two forms — an infinite\nversion and a finite one. A natural way to try to g eneralize the\ntheorem is to color substructures of a given structure\, ra ther than\njust subsets of a given set. A 1977 theorem of Nesetril and Rod l\nprovides a sweeping generalization of the finite version of Ramsey's\nt heorem to all relational free-amalgamation classes of finite\nstructures. For the infinite version\, things get much more\ncomplicated. While a 2022 theorem of mine proves a generalization of\nthe infinite version for fini tely-constrained binary free-amalgamation\nclasses\, the result in full ge nerality is false dropping either the\nfinite-constraint assumption or the binary assumption. Time\npermitting\, I will discuss joint work with Joey Lakerdas-Gayle\ndiscussing some of the strange things that can happen for \ninfinitely-constrained binary free-amalgamation classes.    DTSTAMP:20261115T094419Z END:VEVENT BEGIN:VEVENT UID:6af97ef3ba5b3 DTSTART;TZID=America/Toronto:20261118T100000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20261118T110000 URL:https://uwaterloo.ca/combinatorics-and-optimization/events/crypto-readi ng-group-quantum-computing-jonas-janneck-camryn SUMMARY:Crypto Reading Group on quantum computing | Jonas Janneck & Camryn\ nSteckel\, The Quantum-Accessible Random Oracle Model CLASS:PUBLIC DESCRIPTION:SPEAKER:\n Jonas Janneck & Camryn Steckel\n\nAFFILIATION:\n Uni versity of Waterloo\n\nROOM:\n MC 5501\n\nABSTRACT: A lot of classical co nstructions are proven secure the\nrandom oracle model. With quantum adver saries\, it is necessary to\nconsider a quantum-accessible model allowing the adversary to query\nthe oracle with quantum states. In this talk\, we define such an\noracle and show its implications on classical security pr oofs. We will\npresent an example separating the classical and quantum-acc essible\nrandom oracle models using a scheme that is secure when the adver sary\nis given classical access to the random oracle\, but is insecure whe n\nthey can make quantum oracle queries. We further define history-free\nr eductions and show that there is a general lifting result allowing to\narg ue security in the quantum random oracle model when there is a\nreduction in the classical setting. As an example for this technique\nwe will show h ow to prove the security of signatures following the\nFull Domain Hash par adigm. DTSTAMP:20261115T094419Z END:VEVENT BEGIN:VEVENT UID:6af97ef3bb0e4 DTSTART;TZID=America/Toronto:20261112T143000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20261112T153000 URL:https://uwaterloo.ca/combinatorics-and-optimization/events/algebraic-an d-enumerative-combinatorics-seminar-zachary SUMMARY:Algebraic and Enumerative Combinatorics Seminar | Zachary Hamaker\, \nSchubert polynomial formulas via degeneration CLASS:PUBLIC DESCRIPTION:SPEAKER:\n Zachary Hamaker\n\nAFFILIATION:\n University of Flor ida\n\nLOCATION:\n MC 5417\n\nABSTRACT: Schubert polynomials are monomial positive representatives\nfor the classes of Schubert varieties in the co mplete flag variety. As\nsuch\, they are a key tool for computation in Sch ubert calculus\, an\narea of enumerative algebraic geometry. There are sev eral\ncombinatorial proofs of the monomial positivity of Schubert\npolynom ials\, but the first geometric explanation came much later in\nfoundationa l work of Knutson and Miller. In this talk\, I will discuss\nhow to unders tand combinatorial formulas for Schubert polynomials via\nGrobner degenera tion. This includes the Knutson-Miller work as well as\nrelated results by Klein-Weigandt and some work in progress. Results\nof mine presented come from two projects\, one joint with Oliver\nPechenik and Anna Weigandt\, t he other with Gabe Udell and Tianyi Yu.\n\nThere will be a pre-seminar pre senting relevant background at\nbeginning graduate level starting at 1:30p m in MC 5417. DTSTAMP:20261115T094419Z END:VEVENT BEGIN:VEVENT UID:6af97ef3bbbc0 DTSTART;TZID=America/Toronto:20261109T150000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20261109T160000 URL:https://uwaterloo.ca/combinatorics-and-optimization/events/graphs-and-m atroids-jim-geelen-introduction-rotas-basis SUMMARY:Graphs and Matroids | Jim Geelen\, An introduction to Rota’s Basi s\nConjecture CLASS:PUBLIC DESCRIPTION:SPEAKER:\n Jim Geelen\n\nAFFILIATION:\n University of Waterloo\ n\nROOM:\n MC 6029\n\nABSTRACT: I will give a turorial-style talk on Rota ’s Basis\nConjecture focusing on an old result\, due independently to Hu ang and\nRota and to Onn\, who \"all-but proved\" Rota’s Basis Conjectur e for\nreal-representable matroids. DTSTAMP:20261115T094419Z END:VEVENT BEGIN:VEVENT UID:6af97ef3bc6d1 DTSTART;TZID=America/Toronto:20261113T153000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20261113T163000 URL:https://uwaterloo.ca/combinatorics-and-optimization/events/tutte-colloq uium-kateryna-tatarko-reverse-isoperimetric SUMMARY:Tutte Colloquium | Kateryna Tatarko\, The reverse isoperimetric pro blem\nfor intersections of balls CLASS:PUBLIC DESCRIPTION:SPEAKER:\n Kateryna Tatarko\n\nAFFILIATION:\n University of Wat erloo\n\nLOCATION:\n MC 5501\n\nABSTRACT: The classical isoperimetric pro blem states that the\nEuclidean ball has the largest volume among all conv ex bodies of a\nfixed surface area. What if we ask for the smallest volume instead?\nWithout additional constraints\, the volume can be arbitrarily small.\nWe will discuss this reverse question for the intersections of bal ls\nof fixed radius\, the class of convex bodies for which the question\nb ecomes meaningful. In particular\, we will show that a lens\, the\ninterse ction of two balls\, minimizes the volume for a prescribed\nsurface area i n this class.  DTSTAMP:20261115T094419Z END:VEVENT BEGIN:VEVENT UID:6af97ef3bd273 DTSTART;TZID=America/Toronto:20261111T100000 SEQUENCE:0 TRANSP:TRANSPARENT DTEND;TZID=America/Toronto:20261111T110000 URL:https://uwaterloo.ca/combinatorics-and-optimization/events/crypto-readi ng-group-quantum-computing-huanhuan-chen-bruce SUMMARY:Crypto Reading Group on quantum computing | Huanhuan Chen & Bruce X u\,\nClassical Security Proofs\, Game Hopping and the Random Oracle Model CLASS:PUBLIC DESCRIPTION:SPEAKER:\n Huanhuan Chen &Bruce Xu\n\nAFFILIATION:\n Universit y of Waterloo\n\nROOM:\n MC 5501\n\nABSTRACT: This talk introduces fundam ental techniques for proving\nsecurity in classical cryptography\, with an emphasis on game hopping\nand the random oracle model. We will discuss ho w security arguments\nare structured as sequences of games and how the ran dom oracle model\nsimplifies the analysis of cryptographic constructions. As a first\nexample\, we will examine how a random oracle can be used to c onstruct\na secure pseudorandom function (PRF) and subsequently a message\ nauthentication code (MAC). As a second example\, we will explore the\nrol e of the random oracle in the Fujisaki–Okamoto transformation and\nits s ecurity proof. DTSTAMP:20261115T094419Z END:VEVENT END:VCALENDAR