Polygon's Proof of Stake (PoS) Bridge is the canonical smart contract to move assets to and from Polygon's PoS sidechain. Assets are locked on the source chain and minted on Polygon.

Bridge

Polygon PoS Bridge

Protocol Code Quality

Protocol Maturity

Protocol Design

Risk Rating

yellow

Average

* [Documentation](https://docs.polygon.technology/docs/develop/ethereum-polygon/pos/getting-started) 
 * Auditors 
 	* [Certik](https://github.com/maticnetwork/pos-portal) 
 * Please see our [FAQ on experienced auditors](https://help.exponential.fi/en/articles/6381015-what-are-experienced-auditors)

Exploit/Hacks

Unknown

* [Website](https://wallet.polygon.technology/bridge/)  
 * Token: MATIC  
 * Tags: Bridge

Info

Key Metrics

Information


- Code reviewed by at least one experienced auditor; [Certik](https://github.com/maticnetwork/pos-portal) audited in July 2020
- Public team promotes accountability
- No documented protocol hacks since launch

green


- Core protocol launched in 2020; maturity over 2 years minimizes technical risk as smart contracts are amongst the most battle-tested
- Top 1% by total value locked reduces risk
- Centralized governance increases risk
- Low voting power concentration reduces risk


- No concerns identified
- Externally verified bridge system that is reliant on an external set of validators who have to post collateral that gets burned in case of malicious activities; this system does not guarantee user funds will be reimbursed
- The Polygon PoS Bridge is managed by the Polygon PoS chain team, which increases how much oversight the bridge receives as it is key to the well-functioning of the Polygon chain

Risk Assessment

Offers an easy way to quickly transfer ERC-20 tokens to the Polygon network.

What we like

Requires more trust assumptions as its consensus mechanism relies on extrernal, trusted validators. Malicious actions can result in loss of user funds.

What we like less

Offers you a simple way to transfer your crypto assets from Ethereum to Polygon to access decentralized applications with lower gas fees and faster transaction speeds.

What it means for you

Summary

#### How Polygon PoS bridge works
The Polygon PoS bridge supports the transfer of ERC-20 tokens and is the recommended option for most users. Deposits on the PoS bridge are completed almost instantly but withdrawals may take a while to confirm. When bridging tokens to Polygon, the tokens are locked on Ethereum with the same number of tokens minted on Polygon. When bridging back to Ethereum, the pegged tokens on Polygon are burned and the Ethereum assets are then unlocked.
#### What is the consensus mechanism?
The PoS bridge uses a Proof-of-Stake (PoS) consensus algorithm to secure its network. Polygon relies on a set of external validators who run full nodes, produce blocks, validate and participate in consensus. Validators must stake a certain amount of MATIC tokens which are at risk of getting slashed in case of any malicious actions like double signing. The bridge mechanism requires at least two-thirds of the validators to agree on the locked token event on Ethereum to mint the corresponding token amount on Polygon.
#### Risks of using the Polygon PoS bridge
The Polygon PoS bridge requires greater trust assumptions as it is secured by a set of external validators who must post bond as collateral. The bridge contract also retains admin authority and is controlled by a 5/8 multisig wallet. Among the eight signers, four are Polygon co-founders, and the other four are key members from Polygon DeFi projects. Owners of the contract can upgrade and replace the contract at any time (without a timelock period), which means the multisig can withdraw all user assets in the contract.