Why we cannot wait for better post-quantum signature algorithms
As Eric Rescorla wrote 
in 2024 
 
 You go to war with the algorithms you have, not the ones you wish you had 

dr. Bas Westerbaan
Recent content on dr. Bas Westerbaan
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Hybrid Signature Troubles
It seems like a no-brainer to deploy PQ/T hybrid signatures instead
of post-quantum signatures on its own. However, on closer inspection,
hybrids come with a serious drawback: they increase the number of options
and tempt reuse of existing infrastructure. Because of this
they delay agreement on what to deploy.
Thus especially in more fragmented ecosystems,
supporting…
Cloudflare targets 2029 for full post-quantum security
For a decade now I’ve worked on migrating to PQC.
All this time I thought we’d have at least until 2035.
Moving deadlines is rough, but that’s what you gotta do when
circumstances change.
Factoring is not a good benchmark to track Q-day
If quantum computers were such an imminent threat, why haven’t they factored
any number larger than 15 yet?
State of the post-quantum Internet in 2025
PQC is a fast moving field. A lot has happened in the last 20 months.
High time for an update to the 2024 overview, to take another look
where we are with the migration and what to expect for the coming years.
Keeping the Internet fast and secure: introducing Merkle Tree Certificates
Cloudflare is launching an experiment with Chrome to evaluate fast,
scalable, and quantum-ready Merkle Tree Certificates, all without
degrading performance or changing WebPKI trust relationships.
Private SCT Auditing, Revisited
We revisit the problem of private SCT auditing given the recent
advances in PIR and changes to the certificate transparency ecosystem.
A look at the latest post-quantum signature standardization candidates
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
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
We propose X-Wing, a concrete, simple and IND-CCA secure
PQ/T hybrid KEM based on X25519 and ML-KEM.
Post-Quantum Privacy Pass via Post-Quantum Anonymous Credentials
We show how to construct a practical post-quantum
anonymous credential scheme.
Merkle Tree Certificates
Large post-quantum signatures force us to rethink
the WebPKI. While we’re at it, we simplify transparency.
NIST's Pleasant Post-Quantum Surprise
I discuss the impact on the Web of NIST’s choices for post-quantum algorithms.
Sizing Up Post Quantum Signatures
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
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
Are there nice assumptions on a category such that any such category
must be a category of quantum types with quantum programs between them?
Implementing and measuring KEMTLS
We compare performance of PQ KEMTLS against other TLS variants
on the drand system.
Don't throw your nonces out with the bathwater
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
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
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
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
It’s known that affine and relevant monads preserve respectively drop
and dup equations. We prove a converse.
A characterization of ordered abstract probabilities
We prove a Representation Theorem for \(\omega\)-complete effect monoids.
The universal property of infinite direct sums in C*- and W*-categories
The title says it all.
Pure maps between Euclidean Jordan Algebras
We propose a definition of purity for positive linear maps between
Euclidean Jordan Algebras.
Doctoral thesis: Dagger and Dilation in the Category of Von Neumann Algebras
A mathematical study of quantum computing, concentrating on two
related, but independent topics.
Picture-perfect Quantum Key Distribution
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.
Solving Binary MQ with Grover's algorithm
We explicitly construct oracles to solve binary MQ,
which is the underlying hard problem of many proposed post-quantum
cryptographic schemes.
Paschke Dilations
We generalize Stinespring’s Dilation Theorem to
arbitrary completely positive normal
maps between von Neumann algebra’s.
A universal property for sequential measurement
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.
An Introduction to Effectus Theory
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.
Quotient–Comprehension Chains
A universal property for \( A \mapsto \sqrt{B} A \sqrt{B} \)
appears in a chain of adjunctions.
States of Convex Sets
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.
Unordered tuples in Quantum Computation
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.
A Kochen-Specker system has at least 22 vertices
A Kochen-Specker system has at least 22 vertices.
Statman's Hierarchy Theorem
A simplification and slight extension of Statman’s Hierarchy
Theorem.
Sequential product on effect logics
An investigation of the sequential product on predicates
in the framework of Jacobs.
On effective undecidability and Post's problem
We introduce several notions of effective undecidability and show they
are equivalent to previously investigated notions of completeness
and creativity.