Web3 is currently a very fragmented place. Crosschain transactions are mostly reserved for only the most battle hardened degens. Application developers arguably have it worse as they are forced to deploy their apps and tokens across multiple networks, just to access users and liquidity that have been pooled into silos. Bridges between chains have security vulnerabilities, can be unreliable and result in a cumbersome and confusing multistep process for users. While Web3 remains in this fragmented state, its progress will be limited. Vital developer resources are being eaten up while they could instead be spent building user-centric applications that surpass centralized Web2 alternatives.
In an ideal scenario, developers should only have to deploy applications and tokens once using optimal tech for their specific project, then freely interoperate with other ecosystems, all with minimal set up or maintenance. Developers would only need to create and maintain a single deployment, reducing overheads while continuing to access free flowing liquidity and contributing new services for users from different networks. Decentralized governance would operate seamlessly, no matter where token holders had bridged their assets. Then there are the multiple use cases that would be unlocked in a seamlessly connected ecosystem. Avail has laid the foundation for this interconnected ecosystem, and it will take a huge step forward with the upcoming Nexus upgrade that introduces interoperability and a ZK execution runtime to the Avail Network.
What is Avail Nexus?
Avail Nexus provides a set of apps that run on a versatile ZK execution runtime to simplify interoperability between ZK, Optimistic and Sovereign Blockchains so that developers can build crosschain applications without maintaining deployments across different networks, or navigating disjointed interoperability solutions. The end result is that users can seamlessly interact with connected apps without needing to bridge tokens between them.
ZK, Optimistic and Sovereign chains will be able to freely interoperate with each other via the interoperability apps built on Avail Nexus. While chains do not need to be built on Avail DA to use Avail Nexus, there are benefits that come from doing so. The interoperability apps enable developers to select a trust model, and Avail Nexus will execute based on that trust model.
Interoperability is a huge problem that needs to be resolved for all blockchains, and it’s specifically relevant to Avail. The reason being, is that deploying L2s, Appchains, dApps and Rollups on Avail DA today is very straightforward. Avail DA provides a horizontally scalable architecture that can support an arbitrarily large number of blockchains on top without encountering throughput constraints or high costs. The architecture enables blockchains to execute transactions independently of other chains on Avail DA. The end result is multiple blockchains executing transactions in parallel, with transaction data availability, block ordering and consensus handled by the Avail Blockchain. Having isolated channels for execution on top is great for scalability as you can keep adding more and more applications to it, then as the demand for data availability capacity increases, Avail DA can expand its capacity to accommodate by increasing the block size. The problem arises however, when these applications want to share liquidity or interoperate with one another, and we end up in a situation where fragmentation has only been further increased.
Avail Nexus solves this by enabling L1s, L2s, Appchains, dApps and Rollups to freely interoperate with one another both within and beyond Avail, whether they have been built as a ZK, Optimistic or Sovereign blockchain.
How Does Avail Nexus Work?
Avail Nexus will have multiple interoperability apps to support a wide variety of crosschain transactions. Developers will be able to select an interoperability model via the Avail Nexus API, and the Nexus runtime will support the apps.
The different transaction types include:
- ZK Interop App for highly secure trust minimized transactions.
- TEE Interop App for trust-minimized transactions that rely on secure hardware.
- OP Interop App for rapid crosschain transactions that rely on economic security.
The apps making up Avail Nexus handle settlement slightly differently, as shown in the table below.
Avail Nexus Architecture
The Avail Nexus architecture consists of the following key components.
- Messaging Layer: This is what most developers will interact with. It provides a fast intent based model and a slower but safer state root option.
- Avail Nexus Adapter: This makes it so that ZK chains built using any ZK chain stack are compatible with the Avail Nexus Runtime, and the Messaging Layer.
- Avail Nexus Runtime: This is where state roots are assembled and aggregate proofs generated.
- Avail Nexus Verifier: This is responsible for verifying state changes.
Expanding this out, we see how Avail Nexus would support a fully interoperable network where multiple apps/chains can verify crosschain messages.
Nexus Runtime
The Nexus Runtime is a new, additional component that will be added to the Avail tech stack with the Nexus upgrade. It’s a light but expansive execution layer that will initially support the Nexus interop apps. However, any program that can be proven by RISC Zero, SP1 or any supported zkVM can run on the Nexus Runtime and settle to the Nexus Verifier.
The Nexus Runtime, which sits off the Avail base layer, will send a succinct proof to the Nexus Verifier. Doing this adds minimal load to the Avail chain, ensuring that it remains highly scalable even with the addition of a native, ZK proven execution environment.
With the ability to verify execution proofs for Avail native rollups, support for DAS and the interoperability capability offered by the Nexus Interop apps, this upgrade makes Avail a full-feature, rollup-centric blockchain.
ZK-Interop App
The ZK-Interop App provides the highest security guarantees for crosschain transactions between ZK chains built on Avail DA, as it is the most trust-minimized option. The Avail Light Client will enable any network participant to independently verify crosschain transactions without reliance on third party providers.
At its core, the ZK-Interop App verifies and aggregates state proofs from multiple chains into a single ZK proof. Users can then verify the aggregated ZK proof with the Avail Light Client to verify the state of all participating chains. This is an optimal architecture for crosschain transactions, as every user within a decentralized network from individuals to institutions could independently verify transactions with the certainty that comes from running a full node, all without needing to trust any individual or entity.
As blockchains have evolved, trusted entities have emerged to fill important roles within networks moving onchain verification further away from end users. ZK execution and Data Availability Sampling help correct this. The ZK-Interop App leverages both, enabling users to verify crosschain transactions on devices they already own like phones and laptops, by taking full advantage of the Avail Light Client.
This benefit can be extended to verifying execution of Avail native ZK chains also, as the Avail Nexus proof could be used to verify state proofs even when no cross-chain transactions are present. This is because the app verifies the state proofs of connected chains and aggregates them into a single, succinct proof that verifies the state of all participating chains.
User Verified Transactions
The best way to ensure a transaction is valid in a blockchain network is to run a full node. In doing so, we can be sure of the following:
- Execution Correctness: We need to know if all state transitions were done correctly. A full node does this by re-executing every transaction to ensure it was executed as per the agreed State Transition Function (STF).
- Correct Transaction Order: State transitions might be executed correctly, but full nodes must also verify they were executed in the correct order. A full node can verify the consensus of the protocol to ensure the order of the blockchain is the correct order.
- Data Availability: A blockchain is only decentralized if others can participate. For others to participate the data required to arrive at the latest state, needs to be publicly available. If a full-node can re-execute the STF to arrive at the current state, then it can be certain that the transaction data is available as a result.
Most blockchains are unable to give these guarantees to users unless they are willing to invest the time and resources to deploy a full node. All of this changes with the ZK Interop App.
When deploying a blockchain on the Avail Network today, Avail’s Light Client already verifies validator consensus for block ordering, and data availability (DA) without reliance on a full node. DA is verified using the same techniques earmarked in Ethereum’s full Danksharding roadmap, validity proofs based on KZG polynomial commitments and Data Availability Sampling. The missing piece that will unlock the equivalent power of a full node, is execution correctness. Execution correctness will be verified by the light client through an aggregated ZK proof. This turns phones, laptops and even the browser into a trust-minimized verifier with full node guarantees.
Development Status
The ZK-Interop App has two Avail native rollup chains built on ZKsync’s ZK Stack, transacting with each other. The state root of the source chain is sent to the ZK-Interop App which is verified. At this point a proof will be generated, which the destination chain can quickly and easily verify.
The repo for the current ZK-Interop App POC is public and will be extended to support additional ZK tech stacks in the future.
TEE-Interop App
The TEE-Interop App uses Trusted Execution Environments (TEE) that protect code and data from malicious actors by running on secure hardware. The TEE-Interop App verifies state from participating chains and generates cryptographic attestations that are used for settling transactions.
TEEs are commonly used for protecting sensitive data in Web2 like biometrics and for securing mobile payments like Apple Pay. TEEs secure both data and code by running within a secure area of a main processor, on specialized hardware, that enforces robust security and makes them resistant to software attacks.
The TEE-Interop App generates attestations using Ternoa’s Trusted Execution Environment to verify state updates and provide attestations to settle transactions. The TEE-Interop App is a good middle ground that uses secure enclaves to offer quick settlement times.
Development Status
The TEE-Interop app is being developed in collaboration with Ternoa, and the testnet will be deployed in the imminent future.
OP-Interop App
The OP-Interop App optimistically enables fast and efficient cross-chain transactions for connected chains. It is built on the ERC-7683 standard and uses solvers to fulfill crosschain transactions in a few seconds or less.
When a user initiates a crosschain transaction with the OP-Interop App, an intent is issued based on the ERC-7683 standard. The intent acts like an order ticket that solvers compete to fill. The solver role will be decentralized to the community over time so that community operators, like those running on Symbiotic for example, could run as solvers for Avail Nexus transactions.
Solvers get rewarded for fulfilling intents quickly and efficiently. To deter them from behaving maliciously, solvers are required to submit a bond which can be slashed. This economic incentive mechanism, while introducing some trust assumptions, enables crosschain transactions to be fulfilled in a few seconds or less.
The OP-Interop App will provide additional guarantees like dispute resolution and insurance in the case of a rollback. This is currently under development.
Development Status
The initial version of the OP-Interop App has interoperability working between two chains built on a custom rollup stack using Reth ExEx using Avail DA, and going through an EVM settlement layer. Orders are generated through the ERC-7683 intents standard and filled by a solver. The order’s inclusion and fill verification is done using Incremental Merkle Trees.
The End Game With Avail Nexus
As the ecosystem matures with ZK proofs getting faster, increased DA capacity, accessible shared security and alt-VMs coming online, it’s clearer than ever that no single monolithic blockchain, no matter how well it’s vertically optimized, will have the capacity to handle the value exchange for every user on the internet. Nor will developers choose to limit their choice to a handful of options, when they can instead have the flexibility to select specific technologies for a particular project, but all of it needs to work together. This is the future that Avail is building for.
If the not too distant future consists of multiple, interoperable blockchains, then having an abundance of trust-minimized data availability capacity is a foundational step to enabling this. Interoperability between these chains then needs to be smooth and flexible enough to allow for different use cases and user journeys, along with facilitating connections to external chains in a trust minimized way.
Avail Nexus couples a powerful ZK execution runtime on top of Avail DA, with apps to facilitate interoperability between different types of chains, such as an Optimistic rollup interoperating with a ZK rollup. This capability extends to both Avail native rollups and external chains too. By leveraging the different interoperability apps within Avail Nexus, developers will be able to build custom solutions that meet the needs of different applications and users, all without sacrificing scalability.
ZK rollups on Avail offer the most trust-minimized interoperability, as every user running a light client can independently verify transactions without relying on any other entity. For applications and users that prioritize trust minimization, this will be their preferred choice.
For faster cross-chain transactions, the OP-Interop App provides an alternative with additional trust assumptions, while the TEE-Interop offers a safe middle ground by utilizing secure hardware.
All of these interop apps come together to provide a future where all connected chains, both native to Avail and outside, interoperate freely. Maintaining multiple app deployments across different networks will quickly become a thing of the past as liquidity and users begin flowing freely throughout an interconnected ecosystem. Avail Nexus will generate a single aggregated proof to verify the state of all participating chains and provide fertile ground for the next generation of connected blockchain apps.
Build With Avail Nexus
Join the builders connecting the ecosystem and start building on Avail Nexus. If you’d like to inquire about being an Avail Nexus launch partner, please reach out to business@availproject.org with a brief description of your project or application.
You can begin experimenting with the initial version of the ZK Interop App, including these Nexus examples, and ask questions, or provide feedback on the design in the Avail Forum and follow Avail on X for updates.
