Ark: Offchain Transaction Batching in Bitcoin

Computer Science > Distributed, Parallel, and Cluster Computing [Submitted on 20 May 2026] Ark: Offchain Transaction Batching in Bitcoin Pim Keer, Matteo Maffei, Marco Argentieri, Andrew Camilleri, Zeta Avarikioti Bitcoin is the cryptocurrency with the largest market capitalisation, but its widespread adoption is fundamentally limited by the scalability constraints of its consensus algorithm, which requires every transaction to be confirmed onchain. To address this, several Layer-2 scalability solutions have been proposed to move payments offchain -- most notably, the Lightning Network. However, their deployment remains hindered by cumbersome setup requirements: users must lock funds onchain to participate and engage in complex auxiliary protocols (e.g., for channel rebalancing, top-ups, and routing). Other solutions, like payment pools, sidechains and rollups, cannot be implemented in a non-custodial way on Bitcoin due to its limited scripting capabilities, or require all protocol participants to update the offchain state. In this work, we present Ark, the first Bitcoin-compatible commit-chain. Ark enables offchain transactions of virtual UTXOs (VTXOs), through an untrusted operator who aggregates them into succinct onchain commitments. A distinctive feature of Ark is its ease of deployment: users can receive offchain payments without locking any funds beforehand and Ark state updates can be performed only requiring the users involved in that update. We formally define the Ark protocol and prove its security. During this process, we identified two attacks affecting the testnet implementation, which we responsibly disclosed and proposed fixes for, which have been now integrated into the mainnet implementation. Our experimental evaluation demonstrates that Ark can commit onchain to batches of arbitrarily many VTXOs with a constant-sized footprint of approximately 200 vB. Cooperative exits add one output per user, while unilateral exits require \mathcal{O}(\log n) transactions of roughly 150 vB per VTXO for a batch of n VTXOs. Comments: 32 pages (13 for main paper), 4 figures Subjects: Distributed, Parallel, and Cluster Computing (cs.DC); Cryptography and Security (cs.CR) Cite as: arXiv:2605.20952 [cs.DC]   (or arXiv:2605.20952v1 [cs.DC] for this version)   https://doi.org/10.48550/arXiv.2605.20952 Focus to learn more Submission history From: Pim Keer [view email] [v1] Wed, 20 May 2026 09:40:20 UTC (255 KB) Access Paper: view license Current browse context: cs.DC < prev   |   next > new | recent | 2026-05 Change to browse by: cs cs.CR References & Citations NASA ADS Google Scholar Semantic Scholar Export BibTeX Citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the Explorer?) Connected Papers Toggle Connected Papers (What is Connected Papers?) Litmaps Toggle Litmaps (What is Litmaps?) scite.ai Toggle scite Smart Citations (What are Smart Citations?) Code, Data, Media Demos Related Papers About arXivLabs Which authors of this paper are endorsers? | Disable MathJax (What is MathJax?)