Users of Swiss-based Bitcoin-only app Relai are set to unlock Lightning payment functionality following the integration of Blockstream’s Greenlight solution.

An announcement shared with Cointelegraph unpacked details of the collaboration, which entails Blockstream’s Lightning-as-a-service solution being integrated into Relai’s Bitcoin-only wallet platform.

Greenlight’s functionality is set to allow 100,000 Relai users to make low-cost Bitcoin (BTC) payments using the Lightning network while maintaining control of their private keys. The integration of Greenlight also means that Relai does not have to build and maintain its bespoke Lightning infrastructure.

Blockstream rolled out Greenlight in June 2023 as an alternative service for developers and platforms to provide fast, low-fee Bitcoin payments. The service hinges on using Blockstream’s infrastructure while preserving user control over private keys.

Custodial solutions are an alternative option that offers quick onboarding and convenience, but these typically compromise security and privacy guarantees for users. Non-custodial solutions prioritize security and privacy but require more technical and operational resources.

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Greenlight’s approach to enable custodial Lightning splits nodes into smaller components that operate separately. Using Core Lightning as the base implementation, Greenlight makes all operations involving private keys performed on a user's device as the signer. The remainder of the node and operational needs run on Blockstream’s infrastructure.

Blockstream built its signer on the Validating Lightning Signer (VLS) project to ensure end-to-end verification. This means only users can initiate operations involving their funds, not the infrastructure operator or anyone with similar control or access.

The design is similar to hardware wallets, where a user has a client interface and signer, while the wallet provider operates a Bitcoin node that connects to the network. User-controlled elements can initiate payments and sign invoices while Blockstream runs the node.

Relai was founded in 2020, with a sole focus on Bitcoin trading and custody. The app has generated over $300 million in trading volume over the past four years.  Relai's decision to onboard Lightning payments comes off the heels of some of the biggest exchanges looking to improve their 

Coinbase, the largest exchange operator in the United States, announced that it would integrate Bitcoin Lightning payments into its offering in September 2023. CEO Brian Armstrong cited Bitcoin’s position as the most important asset in the cryptocurrency ecosystem and that the functionality would help facilitate faster and cheaper BTC transactions.

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