A modular tech stack to build a scalable, interoparable and privacy-preserving protocol

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Multi-layer Protocol

Execution Layer

Blockchains and legacy data sources

As a multi-chain ecosystem, Topos interoperates execution layers, called subnets. The system can handle arbitrarily many subnets deployed permissionessly. The protocol makes near-zero assumption as to the internal structure of subnets: natively built for blockchains made with Subnet DevKits, the ecosystem is designed to seamlessly integrate any type of new and existing blockchains and, to a greater extent, all data systems.

Certification Layer

Universal Certification Interface (UCI)

The abstraction over the execution layer is made possible by means of a common interface, a shared language spoken by all subnets to interact with each other. The Universal Certification Interface lays the foundation for subnet authentication and state transitions validity, and is at the core of Topos.

Settlement Layer

Transmission Control Engine (TCE)

The Transmission Control Engine sets the groundwork for Topos cross-subnet communication. Moving away from common consensus-based solutions, the engine implements an asynchronous reliable broadcast primitive to prevent equivocation (e.g., double spend) on certificates exchanged between subnets, and is supported by a network of dedicated nodes that can unlimitedly scale.

How does the TCE work?

Unlimited scalability

With quadratic message complexity, traditional BFT algorithms are limited by significantly higher settlement latency as the number of system participants increases, hence validating groups cannot exceed a few hundred participants. Topos's leaderless reliable broadcast primitive has a logarithmic per-node message complexity, and thus allows the TCE network to scale unlimitedly.


Certificates—data structures defined in UCI to support cross-subnet communication—do not commute for a given sending subnet, i.e., they are totally ordered. On the other hand, those of different subnets do commute. Causal ordering of certificates is what allows Topos to rely on a reliable causal broadcast primitive in place of stronger primitives such as consensus.

Full asynchrony

Topos's reliable broadcast primitive is fully asynchronous as there is no upper bound on the delivery time of certificates and no synchronized clocks. Its correctness does not depend on any timing assumptions, unlike synchronous systems which are vulnerable to adversaries delaying messages to slow down honest participants. This leads to a considerably more robust protocol.

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