Aggregated Blockchains: A New Thesis

Edited 02/23/2024

tl;dr:

• The unified bridge for AggLayer is live
• Monolithic → Modular → Aggregated
• Aggregation synthesizes the benefits of both integrated (monolithic) and modular architectures using ZK technology
• The AggLayer brings uniform cryptographic security and atomic composability across aggregated chains without sacrificing sovereignty
• Devs can connect any L1 or L2 chain to the AggLayer, building a Web3 network that feels like a single chain with unified liquidity and practically unlimited scalability

Blockchains today don’t look or feel like the Internet. Instead of a unified, highly scalable network, users face scaling limitations and bad UX due to fragmented liquidity and state. Unfortunately, the ever-increasing list of new chains being launched has compounded the problem. This environment is reminiscent of the pre-Internet era, siloed and lacking interoperability. We need to do better.

To solve these challenges, Polygon Labs researchers and engineers have designed the aggregation layer, a novel solution to unify the whole of Web3. Like the invention of TCP/IP, which created a seamlessly unified Internet, the aggregation layer, or AggLayer, unites a divided blockchain landscape into a web of ZK-secured L1 and L2 chains that feels like a single chain. 

The AggLayer is a decentralized protocol that does two things:

1. It aggregates ZK proofs from all connected chains.
2. It ensures safety for near-instant [atomic] cross-chain transactions.

If you want an early in-the-weeds technical explainer to understand how the AggLayer will work, read the documentation here.

The AggLayer is the next evolutionary step of blockchain design, improving on the currently prevailing approaches, namely monolithic and modular.

AggLayer, live 

Today, the first essential components of the AggLayer are live. Right now, the only protocol connected is Polygon zkEVM, while other chains are working to plug into the AggLayer soon. This is just the first step toward an aggregated blockchain network that will, when complete, enable near-instant, secure chain-to-chain transactions. 

The live components of the AggLayer that Polygon zkEVM has connected to are: 

• A unified bridge to Ethereum, enabling cross-chain transactions
• A bridgeAndCall() library of solidity contracts to help craft these transactions

From the perspective of Ethereum, all rollups are simply smart contracts holding a state root with a bunch of assets, plus a verifier that says what can go in and out. In a normal multichain L2 ecosystem, there are many bridges to Ethereum—a bridge for every chain. That means that even in “unified” multichain L2 ecosystems, to transfer assets between chains, without using a third-party bridging service, requires a withdrawal to Ethereum—which, in the case of an optimistic chain, requires a seven-day delay.

The AggLayer’s unified bridge, live today, changes this: There is only a single bridge contract on Ethereum for all connected chains. Where we see a multiplicity, Ethereum will see a single contract. Each chain will have a local copy of the unified bridge root, enabling cross-chain transactions that don’t require withdrawing to Ethereum or the security risks of third-party bridges.

This early AggLayer release also contains a bridgeAndCall() Solidity library, which means developers can program logic that executes calls on a different chain. Not only can users transfer assets between chains (bridge), but they can also trigger contracts on a different chain after the asset has arrived (call). 

So putting this together, what can actually be done with AggLayer this early? 

A user on soon-to-be-connected AggChain1 who holds DAI can buy an NFT on Polygon zkEVM, without having to first bridge funds to Polygon zkEVM. From the end user’s perspective, this will feel like using a single chain. Initially, there will be high latency. But as the AggLayer evolves, its singular goal is to lower that latency as much as possible, with future iterations of the AggLayer later this year dropping the time substantially, and an end state of near-instant cross-chain transactions. The point is that with the AggLayer, users can interact with dApps without needing to know that they are accessing another chain.

The bridgeAndCall() feature enables users to send assets and then participate in activity on another chain. Let’s say Alice is an Ethereum user and sees a character’s skin on a gaming chain built with Polygon CDK that she wants to buy—and she wants to buy it first by swapping ETH to MATIC on Polygon zkEVM because it has deeper liquidity than the Polygon CDK chain. 

Alice can bridge to Polygon zkEVM, perform a swap, and then purchase the skin on the gaming chain—all in one transaction. From Alice’s perspective, this would feel simple, like a single environment. 

This is only the beginning. But it is an important beginning. These first components are the necessary underpinning for the rest of the work to follow. The AggLayer is the next evolutionary step of blockchain design, improving on the currently prevailing approaches, namely monolithic and modular.

Monolithic → Modular → Aggregated

A quick tour of the history of blockchain architecture shows the need to evolve towards aggregated blockchains. 

In the beginning, there were the monoliths (i.e., integrated chains).

Monolithic chains run with nodes responsible for consensus, data availability, and execution, and they also serve as a settlement layer. Such an ecosystem is unified and interoperable by design; however, it has fundamental limits. Those limits come in the way of scalability, security, and decentralization tradeoffs. As scalability increases, the hardware requirements for validators increase, resulting in greater centralization and less security. Even the most efficient chains eventually result in state bloat (storing too much data) and state contention (processing too many transactions that touch the same state), which means performance degrades over time. In addition, monolithic chains do not offer meaningful customizability or sovereignty for ecosystem participants. 

To address these challenges, devs began to tinker with modular architectures, and for good reason: a modular framework solves a ton of problems inherent to monolithic systems. Modularity results in many chains running independently and in parallel, each maintaining sovereignty. It allows for much higher scalability and multiplicity of chain design—from VMs to decentralization to privacy profiles.

But modularity alone, as an evolution from monolithic chains, leads to fragmentation across liquidity and users; it creates multi-chain ecosystems that either require awkward and inefficient bridging, or sacrificing chain sovereignty.

There will be no mass adoption with siloed liquidity and users.

The solution to the monolithic-versus-modular dilemma is a new category of blockchain design: Aggregation.

Aggregation offers the sovereignty and scale of modular architectures, as well as the unified liquidity and UX of a monolithic system, synthesizing these two approaches into something novel.

AggLayer Advantages

As a central component of Polygon 2.0, the AggLayer will use ZK proofs to create a seamless, aggregated environment that feels like a single chain–even as each chain in the ecosystem remains sovereign. 

This enables near-instant, atomic transactions, unifies liquidity across the ecosystem, creates capital efficiency, and dramatically improves UX.

• For L1s and L2s connected to AggLayer: Maintain full sovereignty but also get to tap into a huge pool of unified liquidity, making it easy to bootstrap liquidity.

• For dApp developers: Reach users in aggregate. Even if your dApp is on a different chain, users from other chains will be able to interact with it, without cumbersome bridging UX. Seamless cross-chain transactions mean true growth and access to users of the aggregated network. 
• ‍For end users: UX that is like the Internet. A single environment that doesn’t require cumbersome and frequent bridging.

In the end state of AggLayer, end users will be able to execute cross-chain atomic transactions in < 1 second.

What’s next?

Now that the first component of the AggLayer is live, developers at Polygon Labs are focused on bringing all other components of the AggLayer. The next iteration, expected later this year, will be focused entirely on increasing the speed of finality + the synchronizer, to run messages between chains as fast as possible. 

Excited to learn more? In the next few weeks, we’ll have deep dives into the most important components of the AggLayer, including: proof aggregation, optimistic confirmations, and atomic cross-chain transactions. 

Tune into the blog and our social channels to keep up with updates about the Polygon ecosystem.

Together, we can build an equitable future for all through the mass adoption of Web3.

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