Great Wall

Yuri da Silva Villas Boas

Applied cryptographer · coercion-resistant Bitcoin self-custody
author of BIP-450 · Great Wall

Self-custody advice tells you to hide, deny, and keep a decoy. All three are bets on what the attacker believes. None of them has ever been assessed as what it is: a security mechanism whose entire strength depends on the adversary's ignorance.

Papers

Both open access, both free, neither behind a signup. Each DOI resolves to the current version.

The Deadly Race 10.5281/zenodo.22018891 Any custody scheme which, through a wrench attack, yields a feasible-but-unfinished path to the funds turns you into racer for the same balance, hence manufacturing an incentive for killing you. The paper establishes a design criterion you can apply to your own setup: the attack must clearly succeed or clearly fail, never become a race.
The Denial Spiral 10.5281/zenodo.22778480 Where "Don't tell anyone you own Bitcoin." is commonplace, anyone's denial, truthfull or otherwise becomes utterly unconvincing. Paper dives in community's crisis of prolonged wrench attacks and its recalcitrance on methods reliant on ignorance, stupidity and gullibility of wrench attackers.

Both build on Jameson Lopp's public registry of physical attacks.

Standards

BIP-450 — Formosa
A forwards- and backwards-compatible expansion of BIP-39 that maps seed entropy onto grammatical sentences instead of word lists. In the Bitcoin standards repository. Reference implementation.

Projects

Great Wall
Coercion-resistant self-custody through Tacit Knowledge-Based Authentication: memory-held entropy navigated against a user-specific perturbation of a fractal. Kerckhoffian and coercion-resistant at the same time. The implementation is a prototype. Do not put savings behind it yet.
BTC-D20
A printable kit for generating a BIP-39 seed with a 20-sided die, in four languages. Entropy you watch happen, no electronic RNG anywhere. Finished, and needs nothing to keep working.
Research
The threat model, the cost analysis, and the registry coding behind the papers.
SRVB · LVBsig
Earlier cryptographic work.

Self-custody audit

I read the arrangement you already have — hardware wallet, passphrase, multisig, decoy, inheritance plan, whatever there is — and answer four questions in a closed report.

  1. Is your security based on a secret trick? Does it depend on the attacker not knowing what you do, and how you do it?
  2. Once your devices and secrets are seized, could the attacker spend right away, or only eventually? "Eventually" means you are still a competing racer for the same balance.
  3. Is your custody strictly individual? Can anyone else do something that stops you reaching your own coins?
  4. Does it depend on particular objects in particular places? And do you own those places?

I never ask for your seed, your balances, your addresses or where you live. The audit works on the shape of your arrangement, not its contents. An auditor of coercion resistance who collected holder data would be assembling exactly the list the papers condemn, and data that was never with me cannot be seized from me.

What I will not do is build a decoy with denial training. It is the most requested service and the only one I refuse, for the whole argument of The Denial Spiral.

The four questions in full, and what the report contains →

The course

Five live sessions on coercion-resistant self-custody, cohorts of 6 to 12, every session ending at a keyboard. The textbook, slides and syllabus are already free and public; what's sold is the room. It's a pilot, and the first cohort's job is partly to break it.

The five sessions, who it's for, and how to join →

Support

Great Wall, BTC-D20, BIP-450 and the papers are MIT or Apache-2.0, and that does not change: no "pro" version, no feature unlocked by payment, no priority queue for donors. What is sold is time, not software.

Support takes Lightning and on-chain, with no signup and nothing expected in return. What has actually shipped is logged and dated in git history that anyone can audit: DELIVERED.md.

Selected writing

The series — posts on coercion resistance and the physical-attack registry, each in several languages, drafted in the open at great-wall-posts.