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Monday, April 6, 2026 2:45 pm - 3:45 pm EDT (GMT -04:00)

Graphs and Matroids - Eileen Robinson-Coloring claw-free graphs of bounded codegree

Speaker: Eileen Robinson
Affiliation: Université libre de Bruxelles
Room: MC 5479

Abstract:We define the codegree of a given graph as the maximum number of neighbors that any two distinct vertices have in common.

In 2002, V. Vu proposed that for a given graph, its chromatic number should never be too much larger than its codegree, provided that its codegree is not too small as a proportion of its maximum degree.
Tuesday, April 7, 2026 2:30 pm - 3:30 pm EDT (GMT -04:00)

Algebraic and enumerative combinatorics seminar-Ashleigh Adams-Promotion, plane partitions, partial evaluations, and webs

Speaker: Ashleigh Adams
Affiliation: North Dakota State University
Location: MC 6029

Abstract: Webs are graphical objects that give a tangible, combinatorial way to compute and classify tensor invariants. Recently, Gaetz, Pechenik, Pfannerer, Striker, and Swanson (arXiv:2306.12501) found a rotation-invariant web basis for SL₄, as well as its quantum deformation U_q(sl₄), and a bijection between move equivalence classes of SL₄-webs and fluctuating tableaux such that web rotation corresponds to tableau promotion. They also found a bijection between the set of plane partitions in an a×b×c box and a benzene move equivalence class of SL₄-webs by determining the corresponding oscillating tableau. In this talk, I will similarly find the oscillating tableaux corresponding to plane partitions in certain symmetry classes by characterizing them via certain lattice words. A dynamical action on tableaux, called promotion, corresponds to rotation of SL₄-webs. I will show how promotion of certain subtableaux aligns with rotation of their respective webs. I will also show that this correspondence maps through a projection to either SL₂ or SL₃ webs. Moreover, this projection is exactly a partial evaluation of webs. This talk will be given through the lens of the combinatorics of webs and tableaux. Some of this work is joint with Jessica Striker.

There will be a pre-seminar presenting relevant background at the beginning graduate level starting at 1:30pm.

Friday, April 10, 2026 10:30 am - 11:30 am EDT (GMT -04:00)

Crypto Reading Group - Elnaz Hessami Pilehrood-Shadowfax: Hybrid Security and Deniability for AKEMs

Speaker:

 Elnaz Hessami Pilehrood
Affiliation: University of Waterloo
Location: MC 6029

Abstract:As cryptographic protocols transition to post-quantum security, most adopt hybrid solutions combining classical and post-quantum assumptions. This shift often sacrifices efficiency, compactness, or even security. One such property is deniability, which enables users to plausibly deny authorship of potentially incriminating messages. While classical protocols like X3DH key agreement (used in Signal and WhatsApp) provide deniability, post-quantum protocols like PQXDH and Apple’s iMessage with PQ3 do not. This work addresses this gap by investigating how to efficiently preserve deniability in post-quantum protocols. Specifically, we propose two hybrid schemes for authenticated key encapsulation mechanisms (AKEMs). The first is a black-box construction that preserves deniability when both constituent AKEMs are deniable. The second is Shadowfax, a non-black-box AKEM that achieves hybrid security, integrating a classical non-interactive key exchange, a post-quantum key encapsulation mechanism, and a post-quantum ring signature. Shadowfax satisfies deniability in both dishonest and honest receiver settings, relying on statistical security in the former and on a single pre- or post-quantum assumption in the latter. Finally, we provide several portable implementations of Shadowfax. When instantiated with standardised components (ML–KEM and Falcon), Shadowfax yields ciphertexts of 1 728 bytes and public keys of 2 036 bytes, with encapsulation and decapsulation costs of 1.8M and 0.7M cycles on an Apple M1 Pro.