Permissionless, trustless cross-chain bridging without Oracles.

TL;DR;

• Existing bridging protocols are NOT trustless; instead, they are built on Oracle-based systems, making them dependent on complex, unverifiable, and untraceable security mechanisms.
• These systems rely on 3rd parties, making them permissioned, opaque, and complex.
• Adding new networks to Oracle-based systems can compromise the protocol's or the integrator's entire security.
• We challenge this approach by introducing PreHTLC, an improved version of HTLC that addresses practicality issues with atomic swaps like secret management and claim transactions on the destination chain.
• Atomic swaps are widely regarded as the most secure method of asset exchange.
• The proposed protocol is permissionless and has agnostic security attributes.
• The protocol supports multi-hop transactions, allowing bridging between chains that don't have direct liquidity provider connections.
• We demonstrate how new networks and integrators can connect to the protocol.
• We release the protocol’s spec and initial implementation for Bitcoin, EVM, Starknet, TON, Solana, and Sui/Aptos.
• Finally, we are launching the Alpha version to try out.

1. Introduction

The cryptocurrency ecosystem is rapidly expanding, with new chains emerging, including L1s, L2s, side-chains, and app-chains. We envision a future where thousands of these chains exist to scale the capacity of blockchain technology to billions of users. However, this necessary proliferation creates a significant challenge: seamless asset movement across chains. This challenge also hampers the development of new chains as the user onboarding process becomes a vital issue.

2. The Bridging Protocols

Most blockchain networks are isolated by design, meaning there is no native way to transmit information from one to another. Bridging protocols are designed to overcome that isolation. They typically use Oracle-based systems to transfer and validate information across chains. Once the state is confirmed on the source chain, the information is relayed to the destination chain, where the value transfer is executed.

<aside> 💡 We use the term “Oracle-based systems” to collectively describe various solutions, from optimistic Oracles (Across) to separate settlement chains with their own relayers (Wormhole) and so-called verification networks (Stargate—LayerZero). Regardless of the specific approach, their core function is to act as an Oracle, localizing external information through 3rd parties.

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3. Limitations of Existing Bridging Approaches

While the approach with Oracles seems reasonable (and widely adopted), it introduces several significant challenges:

• Permissioned: New networks must convince Oracle infrastructure providers to support them.