The Portal bridge is an application built on top of Wormhole. When users bridge tokens through Portal, the origin token gets locked in a smart contract on the source chain and a new Portal wrapped token gets minted on the destination chain. The user can then swap those wrapped tokens for the native tokens on the destination chain. The bridge uses special validator nodes called Guardians to enable cross-chain transfers. Any transfer on Portal must be validated by at least two-thirds of the Guardians, with each Guardian having an equal weight in the validation process. The Portal bridge charges a bridge fee for facilitating the cross-chain transfer of assets. This fee is minuscule at only about $0.0001 per transaction.
The Guardian nodes continuously monitor the transfer activity on the bridge; when a transfer request is detected, the nodes verify the request, register it, and locks the sender's native tokens on the source chain. The Guardians then mint the same amount of native tokens on the destination chain. The network of Guardians consist of 19 trusted institutional staking service providers that have been actively involved in Solana staking.
The Portal bridge is as secure as the trusted group of Guardians. These special validators are external to any blockchains which makes it risker and prone to centralization especially as the 19 validators are also validators for the Solana network. The bridge was previously exploited in February 2022 when a hacker was able to bypass the verification process by injecting a spoofed Guardian signature by generating a fake signature to drain 120K ETH on Ethereum and effectively making the WETH on Solana worthless.
