Since spinning out from the ICF at the start of the year, we’ve been hard at work on a number of projects aligned with our mission of verifiable distributed systems and organizations. Here we’ll provide an update on each of them.


Verification Driven Development

A primary focus of our efforts at Informal is to define an explicit process for engineering distributed systems that involves specification, verification, and implementation in a co-ordinated manner. We believe that specification and verification should not be an after thought, but should be built into the architecture itself. We call this approach “Verification Driven Development” (VDD).

Formal verification techniques are rapidly maturing. Model checking with TLA+ has been taken up across AWS engineering teams. Theorem proving is being used to secure operating systems and compilers. Compilers and static analysis tools are catching an increasing scope of real program bugs.

In the long term, we suspect that VDD will include a careful mix of these different approaches to verification. In the short term, we’re focused on specification and model checking with TLA+. We’re also developing our own model checker for TLA+, called Apalache, to overcome limitations with the default model checker, TLC.

In a future blog post, we will go into much more detail about why we’ve chosen to focus on model checking, how we foresee TLA+ models being integrated with actual code, and what role other verification techniques will play.

In the meantime, we’re developing a template guide for writing English and TLA+ specs for distributed systems protocols and implementations. The guide is in an early prototype phase and will be revamped and improved as we integrate it into our own specification, verification, and implementation efforts. We hope it will be useful to others in their efforts to employ more rigorous development processes.

Tendermint Fast Sync

In the past, Informal Systems engineers have played pivotal roles in the Tendermint Core codebase. While Tendermint Core is the world-leading implementation of Byzantine Fault Tolerant consensus, aspects of its architecture have made it difficult to test, maintain, improve, and verify the core protocols. We designed a simplified architecture, based on finite state machines with less concurrency, and implemented it for the Fast Sync protocol, or “blockchain reactor”, which enables new nodes, or a node that has been offline for a while, to quickly download all the missing blocks. The new implementation is dubbed v2.

As part of this effort, we wrote a detailed English and TLA+ specification for the Fast Sync protocol that can be found here. The specification was written according to the VDD guidelines, and basic verification was completed. In performing this work, we discovered a vulnerability in the protocol and proposed a straight forward fix.

If you are designing and/or implementing a distributed systems protocol, please get in touch with us - we’d love to discuss how we can help you with similar kinds of analysis.

Tendermint Light Client

Informal Systems has taken over maintenance of the tendermint-rs library, originally developed by Tony Arcieri as part of the Tendermint KMS. We plan to build out a complete implementation of the Tendermint system over two years, starting with the Light Client. The Light Client is a protocol for securely syncing with the blockchain using a minimal amount of information. It is the foundation of the IBC protocol for secure communication between two blockchains.

Last year, members of our team researched the light client, establishing a taxonomy of attacks and discovering new ones. We have since written TLA+ specifications for the light client, performed some initial verification, and completed an initial implemention in Rust. We are currently reworking both the specification and the implementation to improve their verifiability.

We also spent some time over the past few months cleaning up the tendermint-rs repository and updating it for compatibility with the latest version of Tendermint Core. If you’re interested in interacting with Tendermint components in Rust, please check it out!.

IBC Connection and Relayer

The InterBlockchain Communication protocol, or IBC, is the hallmark of the Cosmos Network, allowing arbitrary blockchains to communicate with one another. Over the last year, members of our team played a significant role in developing the English specification of IBC. While there is now a functioning implementation of IBC in Golang, we have begun an effort to formally specify the protocol in TLA+, and to implement it in Rust.

IBC can be thought of as mostly analogous to TCP, which underlies the modern internet. Like computers using TCP, blockchains using IBC can establish connections to one another over which they can communicate by sending packets. While TCP operates over a network of routers connected via the physical infrastructure of the internet, IBC operates over a set of relayers, nodes which monitor the blockchains and relay packets (and proofs) from one blockchain to another.

We have begun with TLA+ specifications of the connection handshake and the relayer. We hope that this effort will help put the IBC protocol on a more formal footing, making it more accessible and appealing to other organizations and researchers.

We’re also working towards a full implementation of a relayer in Rust, to complement the one developed by the Iqlusion team in Go. In the longer term, we expect to implement the complete IBC protocol in Rust, enabling Cosmos applications written in Rust to benefit from interoperability with other Cosmos blockchains.

Apalache - Symbolic Model Checker for TLA+

Part of the power of using TLA+ to specify systems and properties is the ability to use the built in model checker, TLC, to exhaustively search the state space of the system and verify its properties. While TLC has been heavily optimized over the years, its approach of explicitly enumerating states means the run time can be exponential in the size of the model. In practice, this means that systems can only be verified for very small numbers (3 or 4) of nodes.

To improve over this approach, we’ve been developing a symbolic model checker for TLA+, called Apalache, which can greatly accelerate certain verification tasks. Rather than explicitly enumerate states like TLC, Apalache translates the TLA+ specification and properties to a logic understood by Z3, the powerful SMT solver; it uses a more symbolic representation to more efficiently explore a model and verify its properties. For more information on how Apalache works, see the paper.

Over the past few months, we’ve made major improvements to Apalache, culminating in the v0.6.0 release. Much of this work has focused on transitioning the tool from an academic project to an industrial one - usability improvements, integration with the TLA+ toolbox, and fixes to run on real world specifications. If you’re familiar with TLA+ and frustrated with the run-times of TLC, we encourage you to give Apalache a spin! Of course, if you run into any trouble, please open an issue!

PlainText Tooling

Our mission at Informal is to bring verifiability not just to distributed systems, but also to distributed organizations. In this regard, we’ve been working on tools that adopt best practices from software engineering - like plain text, version control, and continuous integration - and apply these practices to the management of corporations, including our own. We refer to these efforts more generally as PlainText Tooling, as they have as a primary focus the representation of data in human and machine readable plaintext. Over the past few months, we’ve been working on two plaintext projects in particular.

The first is a tool for generating legal contracts from a plaintext template and a parameters file. This grew out of frustration from working with Word documents and tracking changes, both in the parameters and the templates. Our current implementation uses LaTeX as a templating language to enable arbitrary formatting, but we’re still experimenting with markdown and its variants. The tool allows you to define a template with a set of variables, and then to instantiate and sign a contract using the parameters in a short TOML file. If you’ve ever found yourself frustrated with current approaches to legal contracts, please check it out and provide feedback!

The second project is a grants management pipeline built on top of Gitlab, designed primarily for use by the Interchain Foundation to manage its grants program. Our goal is to provide a low-cost and flexible solution for grant management and other submission based processes, like hiring, that lend themselves toward transparency and the use of open tools. While the tooling is not yet open-sourced, we expect to open components of it over the year. If you might be interested in using such a tool for your own funding program or hiring pipeline, please let us know by emailing us!

Research Collaborations

Informal Systems maintains an active research program, collaborating with leading scientists in academia and other organizations around the world. Together, we are conducting fundamental research at the intersection of formal verification and distributed systems.

In collaboration with researchers at EPFL, we’re verifying Tendermint protocols like the light client and improving the fork accountability protocol. With researchers at TU Wien, TU Munich, INRIA, and the University of Sydney, we’re collaborating to improve techniques for model checking Byzantine Fault Tolerant protocols. With researchers at USI, we’re exploring gossip based consensus algorithms. And much more. We will be providing more detail on these collaborations in future blog posts. If you’re interested in our research program or collaborating with Informal, please reach out.


We’re excited about the early progress we’ve made over the last few months and about what’s ahead for the next few as we further our mission of verifiable distributed systems and organizations. To stay in-touch, subscribe to our newsletter and follow us on twitter.

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