What is Polygon cross-chain bridge?

Polygon is a Layer2 network designed to solve Ethereum's throughput and sovereignty challenges.

Although Ethereum is the most popular platform for blockchain development, its low throughput makes it unsuitable for some applications. Polygon is a decentralized Ethereum scaling platform that enables developers to build scalable user-friendly dApps with low transaction fees without sacrificing security. Polygon offers application-specific, Ethereum-compatible sidechains that combine the scalability and independence of standalone chains with the community and security of Ethereum. Polygon's vision is to build the blockchain Internet of Ethereum.

Cross-chain bridge

Polygon has a trustless two-way bridge that realizes a two-way cross-chain channel between Polygon and Ethereum, allowing users to transfer funds (deposit) and return (withdraw) from Ethereum without third-party risk and market liquidity limit. If you want to transfer funds from Ethereum to Polygon, you must go through Polygon Bridge, and Polygon Bridge works through a locking and minting mechanism. On Polygon, users can choose to use two 'bridges': PoS Bridge and Plasma Bridge.

PoS Bridge and Plasma Bridge mainly contain two functions: Deposit and Withdrawals. Among them, Deposit refers to transferring the user's assets on Ethereum to Polygon, and Withdrawals refers to withdrawing assets from Polygon to Ethereum. Both PoS Bridge and Plasma Bridge use two-way peg technology (Two-way Peg). Its working principle is that when transferring assets from Ethereum to Polygon, the tokens on Ethereum will first be mapped to Polygon. In this way, when a user deposits from Ethereum to Polygon, these tokens on Ethereum will be locked first, and at this time, the same number of mapped tokens on Polygon will be minted. When tokens are withdrawn from Polygon to Ethereum, these mapped tokens on Polygon will be destroyed, and tokens on Ethereum will be unlocked accordingly.

The difference between PoS Bridge and Plasma Bridge is mainly in security, deposit and withdrawal time, and supported protocol standards. In terms of security: Plasma Bridge inherits security from the Ethereum main chain; while PoS Bridge uses the same set of validators and pledged MATIC to protect the security of the chain itself. In terms of withdrawal time: when users transfer assets across chains, the PoS bridge deposit time is 7-8 minutes, and the withdrawal time is 45 minutes to 3 hours (only one checkpoint interval is required); while the Plasma storage time is 3-5 minutes , but the redemption process takes 7 days to complete. Supported token protocols: PoS bridge supports multiple standards such as ETH, ERC20, ERC721 and ERC1155, while Plasma only supports three types, including: ETH, ERC20, ERC721.

Eight expansion solutions

There has always been a huge market for solutions to Ethereum's scaling problems. Polygon has been committed to solving the expansion problem of Ethereum. By providing a general framework to create expansion solutions compatible with Ethereum, it has a complete set of Ethereum expansion solutions. Let's take stock of some mature expansion solutions on Polygon.

1 Polygon PoS

Polygon Proof of Stake (POS) is the most mature scaling solution in web3 and the best way to start web3 projects for global users.

Polygon PoS is an Ethereum sidechain compatible with EVM (Ethereum Virtual Machine). Unprecedented transaction speed and cost savings are achieved through solutions utilizing sidechains for transaction processing. At the same time, POS uses the Plasma bridge framework and a decentralized proof-of-stake (POS) validator network to ensure the security of assets.

2 Polygon zkEVM

Polygon zkEVM is the first open source zkProver to provide full EVM opcode equivalence and Ethereum security. The original project was named Hermez, and it was renamed Polygon zkEVM after Hermez was acquired by Polygon in August 2021. In V God's EVM compatibility level classification, the current Polygon zkEVM is tied for the third level with Scroll, surpassing other ZK Rollups, and is at the forefront of the current ZK Rollup in terms of EVM compatibility.

3 Polygon Avail

Polygon Avail is a general-purpose, scalable, data-availability-centric blockchain for standalone and off-chain scaling solutions.

4 Polygon Edge

Polygon Edge is a modular and scalable framework for building private or public Ethereum-compatible blockchain networks. It is guided by the principles of modular architecture and provides Ethereum compatibility to the network.

5 Polygon Nightfall

Polygon Nightfall is an Optimistic Rollup designed to reduce the cost of transferring ERC20, ERC721 and ERC1155 tokens privately. It uses Optimistic Rollup to reduce transaction fees and zero-knowledge proofs for privacy. The Optimistic Rollup contract is deployed on Ethereum (layer 1). Proposers roll up transactions into blocks and submit them to the Optimistic contract. The challenger submits fraud proofs for any invalid blocks to the same contract. All information required to perform private transfers resides in the client, without relying on any off-chain third parties.

6 Polygon Miden

Polygon Miden is a layer 2 scaling solution for Ethereum. Miden relies on zero-knowledge technology (zk-STARKs) to 'roll up' thousands of layer 2 transactions into a single Ethereum transaction, increasing throughput and reducing transaction fees. At the heart of Polygon Miden is the Miden VM: a Turing-complete STARK-based virtual machine that provides a level of security and supports advanced features not currently available on Ethereum.

7 Polygon Zero

Polygon Zero uses the speed of Plonky2 to achieve a more scalable and decentralized ZK L2. It offers rollup and validation modes, enabling users to achieve higher throughput and lower fees. What differentiates Polygon Zero from other ZK scaling solutions is the power of Plonky2, which generates ZK proofs faster than any other existing technology. Plonky2 supports efficient recursive proof generation, allowing Polygon Zero to scale horizontally, meaning that the throughput of the protocol is not limited by the weakest node on the network, but only by the total amount of computation available.

8 Polygon Supernets

Polygon Supernets provide end-to-end services for building and supporting private blockchains. Eliminates the complexity of blockchain development without maintaining blockchain infrastructure.