Crossroads: A Smart Contract Layer for Chain-Abstracted Assets

2026-07-07

AI Summary

This work addresses the fragmentation of blockchain assets by proposing a universal chain abstraction model that maps multi-chain assets into a unified ERC-20 representation on a single backend chain via a smart contract layer, enabling seamless cross-chain interoperability. The design employs a threshold signature committee and a pluggable oracle system—supporting zkBridge, TEE, or hybrid modes—combined with chain-specific finality verification and an optimistic fast-access mechanism. This approach guarantees strong finality while, for the first time, providing completeness for unilateral user withdrawals. Moreover, it allows permissionless, modular integration of new chains. A prototype implementation has been validated on Bitcoin, Ethereum, and Solana, successfully supporting applications such as universal wallets, cross-chain staking and lending, private payments, and privatized asset management.

Abstract

This paper introduces Crossroads, a smart contract layer for chain-abstracted assets. In Crossroads, assets from nearly any chain are represented on a single backend blockchain as ERC-20 tokens. As a result, any asset can participate in smart-contract-based exchange, lending, or privacy applications on a single unified platform. So while Crossroads offers cross-chain bridging, a common, partial approach to alleviating the fragmentation of the blockchain ecosystem today, this is just one service within Crossroads' general-purpose chain-abstraction model. Crossroads relies on key encumbrance: a threshold signing committee holds encumbered keys controlling assets on each integrated chain, signing transactions only as authorized by smart contracts on the backend blockchain. Asset movements are fee-efficient, as ownership changes are recorded on the backend blockchain and users may set the transaction fee for withdrawals. Crossroads enables permissionless, modular integration of new blockchains using pluggable oracles with flexible design options (zkBridge, TEE-based, hybrid). Asset deposits into Crossroads benefit from strong, chain-specific finalization guarantees, minimizing the risk of reorg attacks. Unlike existing bridges, however, third-party smart contracts in Crossroads can provide fast, optimistic access to funds before finalization completes. We prove that Crossroads satisfies soundness: given an honest quorum of signing committee members, any user can unilaterally generate a withdrawal transaction transferring their net balance to an account on an integrated blockchain. We implement a proof of concept across multiple public blockchains: Bitcoin, Ethereum, and Solana. We catalog a range of applications enabled by Crossroads, including universal wallets, cross-chain staking and lending, privacy-preserving payments, and private management of public blockchain assets.

Problem

• cross-chain
• asset fragmentation
• blockchain interoperability
• chain abstraction
• smart contracts

Innovation

• chain abstraction
• threshold signing committee
• pluggable oracles
• cross-chain assets
• smart contract layer