Why Polygon (MATIC) Prefers to Distrust Chains for AggLayer Security

• Polygon has unveiled a novel solution to bolster the security of its interoperability layer.
• The unveiled solution relies on distrust.
• Beyond security, Polygon believes that the new solution could serve as a boon for its multichain vision.

Crypto users are often wary of blockchain interoperability solutions, the would-be armored trucks of crypto, because of how vulnerable they typically are to exploits and how frequently they are targeted because of the amount of assets flowing through them.

These fears have, however, not dissuaded Polygon (MATIC) Labs, the builders of the popular Ethereum scaling solution, from embarking on the ambitious roadmap of connecting as many chains to Ethereum as possible through its unified AggLayer bridge. The team’s security solution for this unified bridge has recently been unveiled: “pessimistic proofs .”

Can this novel concept ensure the safety of funds transferred across the AggLayer?

How Polygon’s (MATIC) Pessimistic Proofs Work

Introduced on Tuesday, May 28, Polygon Labs described pessimistic proofs as a “cryptographic guarantee” that allows chains to share a bridge without additional trust assumptions. In simple terms, it provides an assurance that everything is above board on connected chains before asset transfers are allowed.

The naming of the zero-knowledge proof comes from its base assumption: “All chains are unreliable and can’t play nice with one another.” It starkly contrasts the Optimistic bridging approach, which assumes that nodes are honest and the transmitted data is valid unless proven otherwise.

The pessimistic proof aims to ensure that no chain tries to withdraw more assets than they have in deposits. The proof system achieves this by checking three key parameters. These parameters include the state of the chain when a transaction is initiated, the chain’s accounting, and the accounting of all connected chains. 

If everything checks out, a valid proof is generated, allowing the transaction to occur. Through this method, Polygon intends to ensure that a breach of one chain does not lead to a network-wide threat.

Meanwhile, beyond security, Polygon Labs has tipped pessimistic proofs to serve as a boon for overall AggLayer adoption.

Pessimistic Proofs to Open the AggLayer to Non-ZK Chains?

As Polygon Labs highlights, the pessimistic code is written in Rust, a widely used programming language. At the same time, the firm explains that the proof will be generated using Succinct Labs’ SP1, a zkVM solution powered by Polygon’s Plonky 3 prover. SP1 allows developers to generate proofs for different consensus mechanisms. 

As explained by Polygon Labs, SP1’s capabilities will allow Non-ZK chains to join the AggLayer, which could be a significant boon to the network’s multichain goals. At the time of writing, at least three chains already leverage the Polygon interoperability solution to enjoy shared liquidity. These chains include OKX’S X Layer, Astar zkEVM , and Polygon zkEVM .

On the Flipside

• The effectiveness of pessimistic proofs in preventing exploits has yet to be battle-tested.

Why This Matters 

Blockchain bridge exploits have accounted for most of the largest exploits in crypto history. As a bridge intending to connect multiple blockchains, including Ethereum, the AggLayer will likely also become a target for hackers looking to make a large haul in one fell swoop. Pessimistic proofs, however, look to foil any such efforts.

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