How to achieve data interconnection through bridging?

How to bridge for data interconnection?

In a series of articles, encryption researcher Blockingtrick McCorry explores the relationship between bridges and rollups. This article further introduces how bridge protocols link the blockchain world, mainly focusing on how users can move their assets from one database to another and discussing several different verification methods.

A bridge can be seen as a communication protocol between sending and receiving parties. All communication protocols aim to provide the following properties: timely delivery, where messages can be received by the receiver as soon as possible; integrity, where complete message content is delivered; and authentication, where the receiver can verify that the message was indeed initiated by the sender. As a communication protocol, a bridge does not aim to protect the privacy of messages; its main concern is whether the receiver can trust the authenticity of the message, i.e., the proof process.

1) Enforcing correct proofs (Nomad): Institutions still need to prove the authenticity of messages, but if they attempt to cheat, they may be punished immediately. Nomad is an example of implementing this method, which assumes a validating institution and a vetoing institution. The validating institution prevents malicious behavior by locking shares, and the vetoing institution must be appointed before the protocol is instantiated. Nomad has three stages: message approval, message broadcasting, and veto opportunity.

2) Checking consensus protocol consistency (SPV): Allows the receiving smart contract on database B to trust the protocol generated by the consensus protocol on database A. To achieve this, the consensus protocol must be light client-friendly by default. The Bitcoin whitepaper refers to this as the Simplified Payment Verification (SPV) mode. SPV allows users to verify that they have received currency without verifying and storing a copy of the entire Bitcoin database. The process of SPV includes: cryptographic proof, checking the longest chain, inclusion proof, and trust. SPV can serve as the basis for building a light client bridge, allowing a smart contract on another blockchain to understand the content of the Bitcoin database.