Université de Neuchâtel/Swiss National Science Foundation
ENG
CIRCULA / SNSF RESEARCH PROGRAMME
EXPIRY-AWARE SYSTEM DESIGN FOR BLOCKCHAINS
Expiry and renewal in blockchain systems
CIRCULA studies how blockchains’ shared state, validation rules and verifiable history
provide a programmable environment in which expiry and renewal can be formalised and
evaluated. The research programme connects a formal model, an executable ledger
prototype and reproducible experiments to study the effects, costs and limits of these
mechanisms, including what information, if any, remains useful for verification or
recovery after expiry.
Choose the initial expiry, the request time and the proposed new expiry. Apply the values to update the comparison.
THE IDEAS BEHIND CIRCULA
Key concepts
From distributed systems and blockchain programmability to expiry, renewal and questions about what remains afterwards.
Distributed ledger technology (DLT)
A shared record maintained across multiple network participants, who use agreed rules to validate and synchronize updates.
Programmability
Rules encoded in the protocol or in smart contracts determine how ledger operations are validated and executed. This is the programmable context in which CIRCULA studies expiry.
Expiry
A boundary after which an operation is no longer valid; its records may remain according to the system’s design.
Evidence
Information that may support understanding or verification after expiry. Its availability and usefulness are research questions.
A distinction that matters – Expiry changes validity; what remains afterwards depends on the system’s design.
Four connected work packages move from understanding existing lifetime rules to
formalising, building and testing expiry-aware ledger designs. Evidence Atlas, Semantic
Reference, Proof of Concept and Evaluation Bench each provide an artefact for the next
stage.
Four connected work packages, with evaluation feeding back into the design.
Universities, research groups, companies and institutions are welcome to propose
collaborations, discuss use cases or express interest in CIRCULA. Tell us where your
expertise and our research could meet.
Hosted at Université de Neuchâtel, Switzerland, CIRCULA connects a local research team
with international partners through a four-year programme funded by the Swiss National
Science Foundation.
Host university
Université de Neuchâtel
The host university and the home of CIRCULA’s core research team.
Based in Neuchâtel, Switzerland, with a programme open to international collaboration.
CIRCULA studies how blockchains’ shared state, validation rules and verifiable history
provide a programmable environment in which expiry and renewal can be formalised and
evaluated. The research programme connects a formal model, an executable ledger
prototype and reproducible experiments to study the effects, costs and limits of these
mechanisms, including what information, if any, remains useful for verification or
recovery after expiry.
Choose the initial expiry, the request time and the proposed new expiry. Apply the values to update the comparison.
THE IDEAS BEHIND CIRCULA
Key concepts
From distributed systems and blockchain programmability to expiry, renewal and questions about what remains afterwards.
Distributed ledger technology (DLT)
A shared record maintained across multiple network participants, who use agreed rules to validate and synchronize updates.
Programmability
Rules encoded in the protocol or in smart contracts determine how ledger operations are validated and executed. This is the programmable context in which CIRCULA studies expiry.
Expiry
A boundary after which an operation is no longer valid; its records may remain according to the system’s design.
Evidence
Information that may support understanding or verification after expiry. Its availability and usefulness are research questions.
A distinction that matters – Expiry changes validity; what remains afterwards depends on the system’s design.
Four connected work packages move from understanding existing lifetime rules to
formalising, building and testing expiry-aware ledger designs. Evidence Atlas, Semantic
Reference, Proof of Concept and Evaluation Bench each provide an artefact for the next
stage.
Four connected work packages, with evaluation feeding back into the design.
Universities, research groups, companies and institutions are welcome to propose
collaborations, discuss use cases or express interest in CIRCULA. Tell us where your
expertise and our research could meet.
Hosted at Université de Neuchâtel, Switzerland, CIRCULA connects a local research team
with international partners through a four-year programme funded by the Swiss National
Science Foundation.
Host university
Université de Neuchâtel
The host university and the home of CIRCULA’s core research team.
Based in Neuchâtel, Switzerland, with a programme open to international collaboration.
CIRCULA: Expiry-Aware System Design for Blockchains
CIRCULA studies expiry and renewal in the programmable environment provided by blockchains’ shared state, validation rules and verifiable history. The research programme develops formal semantics, a minimal prototype and reproducible experiments to assess effects and costs, including whether useful information remains for verification or recovery after expiry. Inspired by circulation and its Latin root circulus (“circle”), the name evokes the lifecycle of digital claims and rights: validity, expiry and possible renewal.[1]
THE SCIENTIFIC AIM
Lifetime rules as a design choice
Blockchains commonly retain records and verification state after an operation is completed or a right becomes inactive. Lifetime rules already exist as timeouts, timelocks and retention policies, but their assumptions, enforcement layers and recovery requirements are often studied separately.
CIRCULA connects these questions in one fixed technical context: native ledger-level operations with expiry-conditioned validity and renewal. It asks which designs preserve correctness and auditability, how much persistence can be bounded, and what new verification, recovery or operator costs arise.
THE WIDER PERSPECTIVE
Auditability and recovery
Expiry changes validity. The research will examine what information is retained, discarded or becomes unavailable, and under which conditions verification, contestation or recovery remain possible.
CIRCULA investigates the availability and usefulness of information that may remain after expiry.
THE CONCEPTUAL FRAMEWORK
Key concepts
The foundations explain how nodes maintain a shared ledger. The validity concepts describe what CIRCULA will model, implement and evaluate.
Foundations
Distributed systems
Independent computers coordinate over a network, where messages can be delayed and individual nodes can fail.
Blockchain
A shared ledger that groups transactions into blocks linked by cryptographic hashes, so participants can verify the order and history.
Consensus
A protocol for nodes to agree on a shared result, such as which transactions enter the ledger and in what order.
Programmability
Rules encoded in the protocol or in smart contracts determine how ledger operations are validated and executed. This is the programmable context in which CIRCULA studies expiry.
Validity and evidence
Validity interval
The period in which a ledger operation meets its lifetime conditions. Its start, end and notion of time must be specified.
Expiry transition
The transition from valid to expired at a defined boundary. The system’s design determines how historical records are handled.
Renewal rule
An authorized operation that changes or extends a validity interval. Timing, permissions and late renewal need explicit semantics.
Evidence after expiry
Records or proofs that may remain after validity ends. CIRCULA will assess what is available and whether it supports verification or recovery.
Enforcement layer
The part of the system that checks lifetime conditions. CIRCULA investigates ledger-native enforcement and its costs and guarantees.
Audit and recovery
The ability to investigate past states, explain expiry decisions and support recovery while preserving a transparent historical record.
Persistence, growth and circulation
Coin Metrics snapshots compare infrastructure growth and holdings patterns for Bitcoin, Ethereum and USDC on Ethereum at the end of 2018 and 2025. Together, they show how growing ledger records coexist with concentration and dormancy, motivating explicit lifetime rules, bounded retention and recovery-aware archival.[2]
Infrastructure growth
Read each row from 2018 to 2025; the final column gives relative growth. Ledger size is a cumulative data proxy in GB; addresses and transactions are cumulative counts in millions; smart contracts are an end-of-period stock. People can use multiple addresses, and an address can represent multiple people. Growth rates use the underlying series before rounding, so very small displayed starting values can produce large percentages.
Infrastructure growth
Asset
Metric
End-2018
End-2025
Change (%)
BTC
Ledger size proxy (GB, cumulative)
198.11
710.27
+258.5%
New addresses (millions, cumulative)
470.36
1,499.19
+218.7%
Transactions (millions, cumulative)
368.69
1,290.96
+250.1%
ETH
Ledger size proxy (GB, cumulative)
69.02
1,411.29
+1944.8%
New addresses (millions, cumulative)
73.44
388.79
+429.4%
Smart contracts (millions, end-of-period)
9.05
63.36
+600.0%
Transactions (millions, cumulative)
368.81
3,163.55
+757.8%
USDC on ETH
New addresses (millions, cumulative)
0.02
25.80
+116545.5%
Transactions (millions, cumulative)
0.05
146.39
+295302.2%
Holdings and circulation
The left group shows shares of supply; the right group shows the implied USD value of those holdings in billions. Both “Change” columns report relative percentage changes; percentage points measure the absolute difference between shares. For example, Ethereum’s top-address share falls from 99.82% to 69.37%: a drop of 30.45 percentage points, or 30.5% relative to 2018.
Holdings and circulation
Asset
Indicator
Share of supply (%)
Implied value (USD bn)
2018
2025
Change (%)
2018
2025
Change (%)
BTC
Top 10% of addresses
98.94%
98.83%
-0.1%
63.68
1,727.28
+2612.4%
On exchanges
8.79%
12.46%
+41.7%
5.66
217.71
+3746.9%
Asset dormancy
98.57%
97.93%
-0.6%
63.44
1,711.45
+2597.7%
ETH
Top 10% of addresses
99.82%
69.37%
-30.5%
13.59
249.85
+1737.9%
On exchanges
16.95%
11.78%
-30.5%
2.31
42.44
+1738.5%
Asset dormancy
91.45%
90.19%
-1.4%
12.45
324.82
+2508.3%
USDC on ETH
Top 10% of addresses
99.99%
99.85%
-0.1%
0.25
51.63
+20491.1%
On exchanges
45.17%
20.61%
-54.4%
0.11
10.66
+9308.7%
Asset dormancy
68.96%
68.70%
-0.4%
0.17
35.52
+20442.9%
What the comparison reveals
20.4×
Ledger data expands
Ethereum’s ledger-size proxy rises from 69.02 to 1,411.29 GB, about 20.4 times its 2018 level. This growing historical footprint motivates studying bounded persistence alongside audit and recovery requirements.
97.93%
Dormancy remains high
Bitcoin’s dormancy indicator is still 97.93% in 2025, compared with 98.57% in 2018. Infrastructure growth can coexist with persistent inactivity, inviting further investigation into its relationship with circulation.
16.95% → 11.78%
Shares and values differ
Ethereum’s exchange-held share drops from 16.95% to 11.78%, while its implied value rises from USD 2.31 to 42.44 billion. A lower supply share can still have a higher dollar value: the two groups answer different questions.
These snapshots describe trends. Establishing any causal effect of expiry would require further research. Concentration, exchange holdings and dormancy depend on custody, address reuse and accounting. Missing infrastructure metrics are inapplicable or unavailable as comparable series; cumulative counts and end-of-period stocks remain distinct.
Research questions
Four questions connect lifetime semantics, enforcement placement, measurable gains and costs, and bounded downstream validation. RQ1–RQ3 form the technical core; RQ4 considers only designs that pass its correctness, auditability and recovery gates.
RQ1
Semantics
What does a lifetime rule mean?
Specify validity, expiry, renewal, auditability and recovery under explicit assumptions about time, triggering, finality and bounded persistence. The aim is to give each lifecycle event an unambiguous meaning that formal and executable models can test.
RQ2
Placement
Where should the rule live?
Compare enforcement at the system, contract, wallet or service layer. A placement is retained only if it preserves the stated invariants and passes boundary conformance tests; higher-layer conditioning remains a possible outcome when native enforcement is not technically viable.
RQ3
Evaluation
What are the gains and costs?
Under controlled expiry-sensitive workloads, compare bounded-persistence gains with additional verification, recovery and operator costs. Use explicit non-expiring or higher-layer baselines, and judge results against scenario-specific cost envelopes and measurement uncertainty.
RQ4
Deployability
Which designs can be deployed?
For designs that pass the technical gates, examine which enforcement layers remain admissible under transparency, auditability, recovery and due-process constraints. Validation stays within the fixed project context; regulated-payment references set the boundaries of the comparison.
From question to evidence
Research method and work packages
The project follows a semantics-to-evidence pipeline. An evidence map fixes assumptions and baselines; formal and executable semantics define the checks; a bounded prototype demonstrates retained placements; controlled experiments compare their behaviour, costs and limits.
Fixed technical context
Native ledger-level operations with expiry-conditioned validity and renewal
Read from the fixed technical context through the research questions to the four linked outputs. Each work package shows its RQ coverage; evaluation feeds back into semantics and baselines. The prototype connects consensus, tokenomics and the expiry ledger.
WP1 / PLANNED WORK
Lifetime rules and enforcement layers
Document existing lifetime rules: what expires, which layer enforces the rule, and
which assumptions it needs. The atlas provides the evidence and comparison boundaries
for later work.
All research staff begin with this common framing.
Formalise issuance, transfer, expiry, renewal, contestation, settlement and recovery.
Model what information is retained or discarded and under which assumptions
verification or recovery is possible. Develop a deterministic executable reference and
conformance scenarios.
The model states its assumptions about time and finality.
Implement the selected semantics in a minimal node or small testbed. Examine
expiry-aware primitives and bounded persistence, and test which verification or
recovery interfaces can be supported after expiry.
Conformance checks determine which designs proceed to evaluation.
PLANNED OUTPUT
CIRCULA Proof of Concept
Bounded prototype · Conformance checks · Audit and recovery interfaces
WP4 / PLANNED WORK
Controlled comparisons with baselines
Compare selected designs with explicit baselines under controlled workloads. Measure
persistence, verification and recovery costs; examine institutional and adoption
constraints in the selected contexts.
Report uncertainty, limitations and negative results.
Evaluation is part of an internal scientific review cycle. Conformance failures revise semantics or implementation choices; experiments can refine baselines, observables and deployment boundaries. Only designs meeting correctness, auditability and recovery requirements proceed. Versioned research artefacts document those decisions.
CIRCULA connects research findings with the evidence, software and methods behind them. Four planned artefacts carry the work from an evidence atlas to executable semantics, a prototype and controlled evaluation. This page brings together those artefacts, publications, public releases and project milestones as the programme progresses.
From programme to results
Research artefacts
Each work package produces a distinct, connected artefact. The atlas frames the questions; the reference defines the rules; the prototype implements retained designs; the evaluation bench supplies controlled comparisons. These are planned outputs, with public materials linked when available.
WP1Planned
Evidence Atlas
Annotated evidence maps existing lifetime mechanisms, their enforcement layers and assumptions. The atlas establishes the taxonomy and comparison boundaries used by subsequent work packages.
A formal model and executable reference describe validity, expiry and renewal, including assumptions about retained information and possible verification or recovery. Invariants and conformance scenarios make implementations comparable against explicit rules.
A bounded ledger prototype implements selected lifetime rules and enforcement placements. Conformance checks and audit and recovery interfaces connect its behaviour to the semantic reference.
Controlled workloads compare designs with explicit baselines, measuring persistence, verification and recovery costs. Versioned configurations, datasets and analysis materials make the comparisons reproducible and their limits inspectable.
Project publications and public releases will be listed as they become available. Each entry will connect a finding or implementation to its supporting research artefact, so readers can follow both the result and how it was obtained.
Release records will identify the version, research questions, assumptions, baselines and interpretation limits. Links to repositories, archived datasets, configurations and licences will make the supporting materials easy to find and reuse.
Version & identifier
Research questions
Assumptions & baselines
Reproduction materials
Licence & archive
Project milestones
Project updates
Public milestones document the programme’s progress, from funding approval and launch to research releases. Announcements appear alongside the results they introduce, keeping the project’s context and supporting evidence together.
PROJECT ANNOUNCEMENT
CIRCULA receives
SNSF Project Funding approval.
Hosted at Université de Neuchâtel, CIRCULA will study expiry and renewal in the programmable context of blockchain systems through formal semantics, prototypes and controlled evaluation.
Blockchain and distributed systems research at Université de Neuchâtel, Switzerland.
Two open PhD positions
The provisional application deadline is 01.12.2026. Expected start: 01.02.2027. Contact
the project team for applications and enquiries.
The Institute of Computer Science invites applications for two fully funded PhD positions
within CIRCULA – Expiry-Aware System Design for Blockchains, a four-year
project funded by the Swiss National Science Foundation.
The first PhD focuses on the technical design, implementation and evaluation of
expiry-aware distributed systems.
Formal and executable modelling of expiry, renewal and recovery.
Blockchain and distributed-system protocol design, consensus, ledger and state
management.
Conformance testing and machine-checkable properties.
Minimal single- or multi-node prototypes and controlled experimentation.
Performance, networking, storage and resource analysis; reproducible cluster and
cloud workflows.
Relevant backgrounds include distributed systems, blockchain, computer systems,
networking, software engineering, formal methods and security. AI-enabled systems,
AI-assisted testing, modern cryptography and quantum-safe technologies are welcome
where relevant to the research direction.
PHD 2 / DEPLOYABILITY
Blockchain deployability, digital economy & socio-technical validation.
The second PhD focuses on deployability and quantitative validation of expiry-aware
mechanisms, including economic, operational and institutional constraints.
Operationalising blockchain and digital-asset use cases.
Translating real-world constraints into explicit system assumptions and measurable
variables.
Defining scenarios, baselines, enforcement layers and evaluation methods.
Studying auditability, recovery, transparency and contestability.
Quantitative analysis of incentives, market organisation, adoption and digital-asset
behaviour.
Agent-based modelling, simulation and data-driven validation.
Relevant backgrounds include computer science, data science, computational economics,
information systems, financial engineering, computational social science, digital
assets and fintech. Digital economics, cryptoeconomics, financial infrastructures,
autonomous agents and AI-supported simulation are particularly relevant.
Research environment
Research software, distributed-system experimentation, formal modelling, quantitative
analysis and cluster/cloud deployment. University infrastructure includes GPU- and
SGX/TDX-capable resources.
Familiarity with a selection of these technologies and a willingness to develop further skills are welcome.
Candidate profile
A Master Degree in Computer Science, or strongly related one, is required. We look for
strong analytical skills, programming and/or quantitative research experience, the
ability to work independently and discuss methods and findings within the research team,
an interest in experimental reproducibility, and strong written and spoken English.
Nice to have: French at CEFR B2 level or above.
Applicants may indicate a preference for PhD 1 or PhD 2, or state that they have no
preference and wish to be considered for both.
Application materials
Combine all application materials into one PDF and email it to
valerio.schiavoni@unine.ch with the subject “CIRCULA PhD Application”. Use this exact
subject for your application.
CV and motivation letter describing research interests and, if applicable, the
preferred PhD profile.
Academic transcripts and Master’s thesis or equivalent research, if available.
Publications, preprints, software or GitHub/GitLab projects, if applicable.
A time-bounded assignment may combine open questions, a compact technical task, problem
analysis and a personal research idea. Standard development and AI-assisted tools may be
used with substantial use disclosed; candidates must explain and defend their
submission.
