Breaking down Bitcoin bridges: Insights from RootstockLabs

Bitcoin bridging has long been a technical and philosophical challenge, while other blockchain networks have embraced interoperability with relative ease.

This difficulty arises from Bitcoin’s intentionally strict consensus rules and limited scripting language, which makes crosschain transactions cumbersome despite the demand for decentralized bridges. 

Over the years, Bitcoin Virtual Machine (BitVM) protocols have been developed to address these limitations. Still, they come with trade-offs, including increased complexity and reduced decentralization.

In an exclusive interview with Cointelegraph, Sergio Lerner, science specialist at RootstockLabs, discussed the limitations of past approaches and the potential of Bitcoin (BTC) bridging for the broader decentralized finance (DeFi) space.

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Limitations of Bitcoin

Bitcoin’s scripting language, while reliable and secure, was not built to support the complex computations necessary for validating crosschain transactions.

“Bitcoin did not have a language expressive enough to support [decentralized bridges],” Lerner explained. This constraint has historically limited efforts to build fully decentralized and trust-minimized bridges.

While BitVM protocols address some of these challenges by introducing disputable computing to verify complex computations on Bitcoin, Lerner noted that early versions were inefficient:

“The original white paper left many questions unanswered. So by creating BitVMX, together with RootstockLabs and Fairgate Labs, we took the challenge to improve it.”

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Are the trade-offs worth it?

BitVM protocols often depend on trusted parties or external committees to monitor and validate disputes on the network. This introduces new security assumptions and reduces Bitcoin’s decentralization.

“A limitation of every BitVM protocol is that it needs covenants for Bitcoin, and without covenants, they must emulate them with a committee that co-signs a set of transactions,” Lerner said.

This approach requires at least one committee member to act honestly to maintain system security.

“This limitation does not exist in two-party protocols based on BitVMX, such as payment channels,” Lerner said. “It only arises when the protocol must provide an open service to other unknown parties.”

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Scaling Bitcoin bridges

Despite the challenges, Lerner emphasized that BitVMX offers an alternative method for Bitcoin bridging, enabling participation in broader blockchain applications.

The RootstockLabs science specialist said that BitVMX “is currently the cheapest and most resource-efficient disputable computing protocol for Bitcoin,” making it a candidate for building validating bridges for the network.

Still, Lerner acknowledged the need for rigorous testing and careful deployment to avoid risks, adding that any team rushing to deploy a BitVM-based system without proper testing “will be playing with users’ money.”

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