dr. Bas Westerbaan

Publications and notes

• 2025
• Private SCT Auditing, Revisited

  published with Lena Heimberger and dr. Chris Patton [ eprint · talk ]

  We revisit the problem of private SCT auditing given the recent advances in PIR and changes to the certificate transparency ecosystem.

• 2024
• A look at the latest post-quantum signature standardization candidates

  published with dr. Luke Valenta [ blog ]

  We take another look at the current landscape of post-quantum signature schemes, and share some relevant surprising statistics on the median number of bytes transferred over a connection on the web.

• The state of the post-quantum Internet

  published [ blog ]

  We take measure of where we are in the migration, and what to expect for the coming years.

• X-Wing: The Hybrid KEM You've been Looking For

  submitted with dr. Manuel Barbosa, Deirdre Connolly, João Diogo Duarte, Aaron Kaiser, dr. Peter Schwabe, and dr. Karoline Varner [ eprint · I-D ]

  We propose X-Wing, a concrete, simple and IND-CCA secure PQ/T hybrid KEM based on X25519 and ML-KEM.

• 2023
• Post-Quantum Privacy Pass via Post-Quantum Anonymous Credentials

  submitted with Guru-Vamsi Policharla, dr. Armando Faz-Hernández, and dr. Chris Wood [ eprint · code · demo · slides (rwc2023) ]

  We show how to construct a practical post-quantum anonymous credential scheme.

• Merkle Tree Certificates for TLS

  drafting with David Benjamin and Devon O'Brien [ I-D ]

  Large post-quantum signatures force us to rethink the WebPKI. While we’re at it, we get rid of X.509 and simplify transparency.

• 2022
• NIST's Pleasant Post-Quantum Surprise

  published [ blog ]

  I discuss the impact on the Web of NIST’s choices for post-quantum algorithms.

• 2021
• Sizing Up Post Quantum Signatures

  published [ blog · forum ]

  How much room does TLS have for the big post-quantum signatures? We had a look at Cloudflare: it’s tight.

• A Concrete Treatment of Efficient Continuous Group Key Agreement via Multi-Recipient PKEs

  accepted (CCS) with Keitaro Hashimoto, dr. Shuichi Katsumata, dr. Eamonn Postlethwaite, and dr. Thomas Prest [ eprint · code ]

  We proposed chained CmPKE, a Continuous Group Key Agreement and their underlying efficient Post-Quantum Multi-Recipient KEMs based on Kyber, NTRU LPRime, Frodo and SIKE.

• A computer scientist's reconstruction of quantum theory

  invited with dr. John van de Wetering [ eprint ]

  Are there nice assumptions on a category such that any such category must be a category of quantum types with quantum programs between them? (more)

• Implementing and measuring KEMTLS

  accepted with Sofía Celi, dr. Armando Faz-Hernández, Nick Sullivan, Goutam Tamvada, dr. Luke Valenta, dr. Thom Wiggers, and dr. Chris Wood [ eprint ]

  We compare performance of PQ KEMTLS against other TLS variants on the drand system.

• 2020
• Don't throw your nonces out with the bathwater

  short note with Amber Sprenkels [ eprint ]

  We suggest a small change to the Dilithium signature scheme that allows reusing computation between aborted attempts for a speed-up in signing time.

• The three types of normal sequential effect algebras

  published with dr. Bram Westerbaan and dr. John van de Wetering [ arXiv · quantum ]

  We show that any normal SEA splits as the direct sum of a complete Boolean algebra, a convex normal SEA and a so-called almost-convex normal SEA.

• Sign in finite fields

  short note with dr. Bram Westerbaan [ eprint ]

  We show that there is a consistent choice of square root in a finite field \(\mathbb{F}_{p^k}\) for odd prime \(p \neq 1\) and \(k\neq 0\) if and only if \(k\) is odd.

• Dichotomy between deterministic and probabilistic models in countably additive effectus theory

  accepted with dr. Kenta Cho and dr. John van de Wetering [ arXiv · video ]

  A non-trivial σ-effectus with normalization has as scalars either {0,1} or [0,1]. When states and predicates are separating, then it must embed into the category Boolean algebras (in the first case) and into the category of Banach order-unit spaces in the second case.

• Preservation of Equations by Monoidal Monads

  published with dr. Louis Parlant, dr. Jurriaan Rot, and prof. Alexandra Silva [ arXiv · LIPIcs ]

  It’s known that affine and relevant monads preserve respectively drop and dup equations. We prove a converse.

• 2019
• A characterization of ordered abstract probabilities

  accepted with dr. Bram Westerbaan and dr. John van de Wetering [ arXiv · video ]

  We prove a Representation Theorem for \(\omega\)-complete effect monoids. (more)

• The universal property of infinite direct sums in C*- and W*-categories

  published with dr. Tobias Fritz [ ACS · arXiv ]

  The title says it all.

• 2018
• Pure maps between Euclidean Jordan Algebras

  published with dr. Bram Westerbaan and dr. John van de Wetering [ arXiv · EPTCS ]

  We propose a definition of purity for positive linear maps between Euclidean Jordan Algebras. (more)

• Doctoral thesis: Dagger and Dilation in the Category of Von Neumann Algebras

  awarded [ arXiv ]

  A mathematical study of quantum computing, concentrating on two related, but independent topics. (more)

• 2017
• Picture-perfect Quantum Key Distribution

  submitted with dr. Aleks Kissinger and dr. Sean Tull [ arXiv ]

  We give a new way to bound the security of QKD using only the diagrammatic behavior of complementary observables and essential uniqueness of purification for quantum channels. (more)

• 2016
• Solving Binary MQ with Grover's algorithm

  published with dr. Peter Schwabe [ preprint · LNCS ]

  We explicitly construct oracles to solve binary MQ, which is the underlying hard problem of many proposed post-quantum cryptographic schemes.

• Paschke Dilations

  published with dr. Bram Westerbaan [ arXiv · EPTCS · video · slides ]

  We generalize Stinespring’s Dilation Theorem to arbitrary completely positive normal maps between von Neumann algebra’s. (more)

• A universal property for sequential measurement

  published with dr. Bram Westerbaan [ journal (JMP) ]

  We study the sequential product, the operation \(p * q = \sqrt{p} q \sqrt{p}\) on the set of effects of a von Neumann algebra that represents sequential measurement of first \(p\) and then \(q\). We give four axioms which completely determine the sequential product.

• 2015
• An Introduction to Effectus Theory

  done with dr. Kenta Cho, prof. Bart Jacobs, and dr. Bram Westerbaan [ arXiv ]

  Effectus theory is a new branch of categorical logic that aims to capture the essentials of quantum logic, with probabilistic and Boolean logic as special cases. (more)

• Quotient–Comprehension Chains

  published with dr. Kenta Cho, prof. Bart Jacobs, and dr. Bram Westerbaan [ preprint · EPTCS ]

  A universal property for \( A \mapsto \sqrt{B} A \sqrt{B} \) appears in a chain of adjunctions.

• 2014
• States of Convex Sets

  published with prof. Bart Jacobs and dr. Bram Westerbaan [ preprint · LNCS · slides ]

  State spaces in probabilistic and quantum computation are convex sets, that is, Eilenberg–Moore algebras of the distribution monad. This article studies some computationally relevant properties of convex sets. (more)

• Unordered tuples in Quantum Computation

  published with dr. Robert Furber [ preprint · EPTCS · video · slides ]

  The star-algebra \( M_2 \otimes M_2 \) models a pair of qubits. We show in detail that \( M_3 \oplus \mathbb{C} \) models an unordered pair of qubits. Then we use the late 19th century Schur-Weyl duality, to characterize the star-algebra that models an unordered n-tuple of d-level quantum systems. (more)

• A Kochen-Specker system has at least 22 vertices

  published with dr. Sander Uijlen [ preprint · EPTCS · journal · data · sourcecode · video · slides ]

  A Kochen-Specker system has at least 22 vertices. (more)

• Statman's Hierarchy Theorem

  published with dr. Bram Westerbaan, Rutger Kuyper, Carst Tankink, Remy Viehoff, and prof. Henk Barendregt [ LMCS · preprint ]

  A simplification and slight extension of Statman’s Hierarchy Theorem. (more)

• 2013
• Sequential product on effect logics

  done supervised by prof. Bart Jacobs [ pdf ]

  An investigation of the sequential product on predicates in the framework of Jacobs.

• 2012
• On effective undecidability and Post's problem

  done supervised by dr. Wim Veldman [ pdf · arXiv ]

  We introduce several notions of effective undecidability and show they are equivalent to previously investigated notions of completeness and creativity.