Four Ways to Forge a Bundle My Own Verifier Calls Clean: Refusal-Site Mutation Testing of an Evidence-Bundle Verifier

arXiv:2608.26183v1 Announce Type: cross Abstract: I built a protocol whose premise is that a stranger can re-run my claims offline and get the same answer.

An outside engineer audited it and broke it: a bundle whose headline numbers were false verified clean, the cheapest forgery four bytes.

I merged his fix, then pointed my own instruments at the fixed verifier and found the same defect four more times, in places his audit did not reach. The cheapest is one capital letter. The unifying defect is not cryptographic or exotic: a check that reports success along a path where it never examined anything. Vacuous pass is a working label, not a discovery; Section 4 names the literatures already occupying it.

So I stopped collecting anecdotes and measured. At f59fb62, under the extraction rule of Section 6, the verifier exposes 112 refusal sites; 75 could be deleted with the whole suite and every tamper fixture still green, a score of 0.330. Three of the four hand-found forgeries fall in surviving classes; the fourth is an obligation with no refusal site.

Scored alone, the sixteen-fixture corpus built to prove the verifier can refuse catches 10. Testing the refusals themselves took it to 0.941, then to 1.000 at 92e4548 over a grown population of 146 sites; those denominators differ and the series between them is non-monotone, so Section 7.5 carries all eleven, not just the five rows of Table 2.

Fixing the four found defects instead moved 37/112 to 39/119, leaving the pre-existing sites at 37. Seven times during this study my own measuring tools reported success while measuring nothing; four were built to detect this class, and one returned a perfect 1.000.

Every number here is self-measured on a system I wrote, over a registry that is a closed loop of my own repositories; the one external data point is the audit of Section 2.2. That is stated here rather than buried: it is the paper's credibility, not a caveat.