We redesigned Thunderbolt, the Bitcoin payment protocol we are building at Nubit, several times over the past year. At a few points, that meant going back to the beginning. The market was rough, too. This was a long way from finishing a design and spending the rest of the year implementing it.
Now the paper has been accepted at ACM CCS, a major computer-security research conference, for its 2026 edition. The code is open source, so other people can read and run it.
Changing the design of a payment system means reopening questions you had hoped to settle. Who needs to be online? What does the person receiving the payment have to do? Can they finish later? You can describe a transfer in one sentence, then spend a great deal of time trying to make that sentence true under the conditions people will use it in.
Thunderbolt lets ownership of bitcoin move without putting every transfer on the blockchain. The sender and recipient can complete their parts at different times. That sounds compact now. Reaching a design that we could explain, defend, and build took repeated revisions.
The paper (Wen et al., 2026) makes the central invariant explicit: the shares controlling a Bitcoin output change while the on-chain public key stays fixed. Correctness and security depend on showing that these updates agree, under the paper’s stated assumption about how many committee members may be corrupted. That is the research content behind the user-facing promise that the recipient can finish later.
There is a practical cost to each of those revisions. The explanation changes along with the software. You have to make sure the paper still describes what the code does, and that you have not kept relying on an assumption from a version you abandoned. Meanwhile, the people following the project need a clear account of what it has become.
With v1.0.0, that account is available for other people to examine. They can read the paper, run the software, and ask questions about specific choices. After a year of changing the design ourselves, we have put the implementation in their hands.