Marcin Pawlowski 57be929af7

blend: minimum release interval, and jitter vs clock under a timing attack ...

Two release designs at a MATCHED delay budget, so they differ only in how they
delay: clock (batch at free-running ticks, the existing model) and jitter (each
message waits its own exponential draw, mean set equal to the clock residual).
Plus min_blend_delay, which forbids intervals shorter than it.

Minimum interval -- a negative result, and provably so. A zero-length gap is
instantaneous, so it never covers an arrival and is never sampled by the residual
or by the size-biased interval. Excluding it therefore leaves the mean hold
exactly unchanged, and with it blending and linkability; what it does change is
E[S], the gap between release opportunities. Confirmed analytically and in
simulation: 1.168s vs 1.167s at M=3.

Timing attack -- the effective anonymity set of a release (perplexity of the
observer posterior over which arrival produced it), plus MAP success, the chance
its single best guess is right. The second matters because perplexity flatters a
heavy tail: an exponential never fully excludes an old arrival, so it can look
unlinkable while still being guessed correctly.

At the baseline rate BOTH designs fail almost completely -- MAP success 0.98-0.99,
effective set ~1. A relay handles so little traffic that in->out matching is
trivial, which follows directly from the mixing~0 result. Traffic, not delay, is
what buys timing protection.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

2026-08-06 18:00:00 +02:00

..

blend

blend: minimum release interval, and jitter vs clock under a timing attack

2026-08-06 18:00:00 +02:00

tsi

Item 16: the revenue-optimal adversary is not the estimator's worst case

2026-08-06 14:54:52 +02:00