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Reflow crypto: digital product passports for the circular economy

Today I feel light and grateful: light for finally publishing something I’ve worked on for the past 2 years and grateful because this is an outstanding achievement that could only be attained with the help of my colleagues at

A pre-print of our paper is freely available: “Reflow: Zero Knowledge Multi Party Signatures with Application to Distributed Authentication

Also mirrored at Arxiv and SAO/NASA ADS, versioned source on github/DYNE

Reflow signatures are based on the work we did in the DECODE project with colleagues at UCL: we built a privacy-by-design signature scheme on top of Coconut credentials (yes, the stuff that got Facebook/Libra so interested).

All Reflow crypto is fully implemented in free and open source code using Zenroom which makes it easy for mathematicians to review what is inside Zencode language statements as well for engineers to integrate it in existing applications.

What REFLOW is for?

The Reflow project is an EU Horizon 2020 innovation action running through 2019 and 2022 which aims to enable the transition of European cities towards circular and regenerative practices.

More specifically, REFLOW uses Fab Labs and makerspaces as catalyzers of a systemic change in urban and peri-urban environments, which enable, visualize and regulate “four freedoms”: free movement of materials, people, (technological) knowledge and commons, in order to reduce materials consumption, maximize multifunctional use of (public) spaces and envisage regenerative practices. The project will provide best practices aligning market and government needs in order to create favorable conditions for the public and private sector to adopt circular economy practices.

REFLOW is creating new circular economy business models within six pilot cities: Amsterdam, Berlin, ClujNapoca, Milan, Paris and Vejle and assess their social, environmental and economic impact, by enabling active citizen involvement and systemic change to re-think the current approach to material flows in cities.

This paper and the free and open source software referenced sit at the core of the innovative developments in Reflow’s technical work-package and implement a novel signature scheme for material passports whose integrity, provenance and portability is granted by means of provable cryptography.

We need this because if we want to recycle more we need to have a clear picture of material flows coming in and out of our cities, as well a way to track the life-span of each material.

Think of material passports as sort of “barcodes” that cannot be counterfeit and do contain the whole history of materials and components part of an object. Here we explain the material passport use-case a bit.

What else can we do with Reflow crypto

Well, quite a lot considering it is all quite modular and configurable. In the paper we analyze 4 base functions:

  1. Credential based and anonymous multi-signature and decentralized verification scaling up to thousands of participants.
  2. Need-to-know application for multiple participants to sign complex documents without distributing the entire document to everyone
  3. Advanced Disposable-ID scenarios augmented with multi-signature
  4. Last not least the material passport, more generally consisting of a system to authenticate fairly complex graph data structures

And so Reflow crypto is a core building block for what we are envisioning to be the future of the so called Industry 4.0:

In a not so distant future we’ll see objects being produced and marketed as the remixing of open and distributed design contributions: the main challenge for this market will be to fairly redistribute the wealth to all contributors while keeping track of them while respecting their privacy.

A lesson about what can we do with crypto

Its not a mystery that I’m involved in crypto since more than 10 years now

So let me conclude that I’m very proud today to present this work, which is not yet another coin to accumulate or mine, nor a system that needs a lot of energy to run (look at our benchmarks!) but a sincere and collective effort to use cryptography and math for the aims of a green and sustainable agenda.



-- is a non-profit foundation and free software foundry established in 1999 with the mission of increasing environmental sustainability, inter-disciplinarity and freedom of expression. It connects an online community in which art, science and technology meet open source.

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