An overview of bridges

The article argues that bridges between blockchains should be understood as a way to pass messages between databases, and it examines how trust in the bridge's attestation process can be reduced. It describes human-operated bridges, in which trusted authorities fetch, sign and attest to messages, as the easiest to deploy but the hardest to secure at scale. It then presents the Nomad Protocol as an accountable approach, in which an endorsement authority signs messages and can be slashed by Database A for signing unendorsed messages, while a veto authority must be trusted to cancel false messages within a fixed 30-minute window. The article goes on to describe light-client verification, citing Bitcoin's Simplified Payment Verification mode from its white paper.