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A Bitcoin developer by the name of Burak recently unveiled Ark, a Layer 2 protocol designed to enable fast and secure transactions. According to a post on the Bitcoin dev mailing list, Ark offers an alternative scaling approach that allows users to send and receive funds without liquidity constraints, making it easier for recipients to get paid without an onboarding setup. Unlike other Layer 2 solutions like Lightning, Ark does not require the opening and closing of channels, reducing the on-chain footprint significantly.

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The protocol operates using virtual UTXOs (vTXOs), which are short-lived notes that expire after four weeks. When a payment is made, existing vTXOs are redeemed, and new ones are created. The anonymity of coin ownership is improved by restricting vTXO values to a range of sats values. Users can acquire vTXOs from others or use a process called lifting, which allows them to lift their on-chain UTXOs off the chain for virtual UTXOs.

The protocol introduces an intermediary called the Ark Service Provider (ASP), which serves as a liquidity provider, CoinJoin coordinator and Lightning service provider. ASPs create rapid, blinded CoinJoin sessions every five seconds, known as pools, which ensure the atomicity of payment schedules. Recipients can claim their funds through a txlock condition that requires the connector outpoint to remain unchanged.

Ark’s integration with the Lightning Network allows users to attach HTLCs (or PTLCs) to a pool transaction, enabling interoperability between the two protocols. Multiple ASPs can be used to pay Lightning invoices from different vTXO sources using multi-part payments. Payments on Ark are credited every five seconds, allowing users to spend their zero-conf vTXOs immediately without waiting for on-chain confirmations.

The developer behind Ark highlighted the protocol’s potential for future extensions and improvements. A hypothetical data manipulation opcode could disincentivize double-spending, and users could forge an ASP’s signature to reclaim their vTXOs in case of a double-spend. Overall, Ark offers a promising solution for efficient and secure off-chain transactions on the Bitcoin network.

For more information on Ark and its technical details, curious users are encouraged to visit