Paper 2024/197

Alba: The Dawn of Scalable Bridges for Blockchains

Giulia Scaffino, TU Wien
Lukas Aumayr, TU Wien
Mahsa Bastankhah, Princeton University
Zeta Avarikioti, TU Wien
Matteo Maffei, TU Wien

Over the past decade, cryptocurrencies have garnered attention from academia and industry alike, fostering a diverse blockchain ecosystem and novel applications. The inception of bridges improved interoperability, enabling asset transfers across different blockchains to capitalize on their unique features. Despite their surge in popularity and the emergence of Decentralized Finance (DeFi), trustless bridge protocols remain inefficient, either relaying too much information (e.g., light-client-based bridges) or demanding expensive computation (e.g., zk-based bridges). These inefficiencies arise because existing bridges securely prove a transaction's on-chain inclusion on another blockchain. Yet this is unnecessary as off-chain solutions, like payment and state channels, permit safe transactions without on-chain publication. However, existing bridges do not support the verification of off-chain payments. This paper fills this gap by introducing the concept of Pay2Chain bridges that leverage the advantages of off-chain solutions like payment channels to overcome current bridges' limitations. Our proposed Pay2Chain bridge, named Alba, facilitates the efficient, secure, and trustless execution of conditional payments or smart contracts on a target blockchain based on off-chain events. Alba, besides its technical advantages, enriches the source blockchain's ecosystem by facilitating DeFi applications, multi-asset payment channels, and optimistic stateful off-chain computation. We formalize the security of Alba against Byzantine adversaries in the UC framework and complement it with a game theoretic analysis. We further introduce formal scalability metrics to demonstrate Alba’s efficiency. Our empirical evaluation confirms Alba efficiency in terms of communication complexity and on-chain costs, with its optimistic case incurring only twice the cost of a standard Ethereum transaction of token ownership transfer.

Available format(s)
Cryptographic protocols
Publication info
BlockchainBridgesInteroperabilityPayment ChannelsCryptocurrenciesDistributed LedgersDeFi
Contact author(s)
giulia scaffino @ tuwien ac at
lukas aumayr @ tuwien ac at
mhs bastankhah @ princeton edu
georgia avarikioti @ tuwien ac at
matteo maffei @ tuwien ac at
2024-02-12: approved
2024-02-09: received
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Creative Commons Attribution


      author = {Giulia Scaffino and Lukas Aumayr and Mahsa Bastankhah and Zeta Avarikioti and Matteo Maffei},
      title = {Alba: The Dawn of Scalable Bridges for Blockchains},
      howpublished = {Cryptology ePrint Archive, Paper 2024/197},
      year = {2024},
      note = {\url{}},
      url = {}
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