Paper 2019/986

Outpost: A Responsive Lightweight Watchtower

Majid Khabbazian, Tejaswi Nadahalli, and Roger Wattenhofer


In the context of second layer payments in Bitcoin, and specifically the Lightning Network, we propose a design for a lightweight watchtower that does not need to store signed justice transactions. We alter the structure of the opening and commitment transactions in Lightning channels to encode justice transactions as part of the commitment transactions. With that, a watchtower just needs to watch for specific cheating commitment transaction IDs on the blockchain and can extract signed justice transactions directly from these commitment transactions that appear on the blockchain. Our construction saves an order of magnitude in storage over existing watchtower designs. In addition, we let the watchtower prove to each channel that it has access to all the data required to do its job, and can therefore be paid-per-update.

Available format(s)
Publication info
Published elsewhere. AFT '19: Proceedings of the first ACM conference on Advances in Financial Technologies
Contact author(s)
tejaswin @ ethz ch
2019-09-02: received
Short URL
Creative Commons Attribution


      author = {Majid Khabbazian and Tejaswi Nadahalli and Roger Wattenhofer},
      title = {Outpost: A Responsive Lightweight Watchtower},
      howpublished = {Cryptology ePrint Archive, Paper 2019/986},
      year = {2019},
      note = {\url{}},
      url = {}
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