Goal: Ensure no single location or person holds the full seed/private key while maintaining durable, tamper-resistant backups.
Quick Steps
- Open 4 safety-deposit boxes at different banks (banks - not branches), ideally in different jurisdictions or geographic areas.
- Two can be in one location, and the other two in a second city / location.
- Prepare steel plates (corrosion-resistant stainless steel or dedicated crypto plates designed for mnemonic/seed stamping).
- Stamp your seed keys (mnemonic or private key fingerprint) into the steel plates using plate-stamping tools.
- Divide your key(s) in half. Put half the seed keys on one plate and the other half on the second plate. (Copy A and Copy B).
- Do this again. You now have two copies of your keys - with half of each key on its own plate.
- Test recovery: In a secure environment, reassemble plates from copies (use non-production keys first, i.e., a test wallet) to confirm you can
reconstruct the seed and access funds. Do this before relying on the system.
- Distribute halves across the 4 boxes so no single box contains a full copy of the seed. Example distribution:
- Box 1: A first half
- Box 2: A second half
- Box 3: B first half
- Box 4: B second half
(This ensures two separate copies are split and each box only contains a partial piece.)
- Place one key set in one geographic area and the other key set in a separate area.
- Document the scheme in Safeinity. Record which bank and box number holds which piece.
Practical Hardening Details & Best Practices
- No digital photos / no cloud copies: Never photograph or scan stamped plates.
- Never put your keys in any digital format other than KeePassXC, or on your hardened laptop or a hardware wallet.
- Avoid writing the full seed in the same location as passphrase: If you use a BIP-39 passphrase,
store it separately (different box or trusted holder) - never co-locate.
- Legal & access planning: Ensure the right people (or executor) can lawfully access boxes when needed; This is What
Safeinity and your will is for.
- Chain of custody: Keep records of who had access during stamping and transport.
Use a trusted courier or do it yourself; do not mail plates.
- Periodically verify (every 1-3 years): Banks change policies; check boxes and confirm plates intact.
- Keep plate materials durable: Choose stainless steel or dedicated crypto metal (e.g., Cryptosteel, Billfodl) rated for
corrosion, fire, and time.
Safer / More Complex Alternative
Use Safeinity's key sharding and a threshold scheme (e.g., 2-of-3, 3-of-5) to divide the key into shares. Store shares in
separate deposit boxes or with trusted custodians. Advantages: flexible quorum, better resilience, and no brittle physical-halving mistakes.
Note: many people are irresponsible with keys. Some of the people you give shards to will probably lose them. Make sure
they understand the importance of their shard, and make the threshold low enough to ensure your key can be reconstructed (e.g., 5-of-10). Describe
how to use the shards and about Safeinity in your will.
For extremely large holdings, consider building a shielded enclosure / Faraday cage and only accessing your hardened laptop
and Safeinity from within it. This protects against electronic theft.
Warnings / Gotchas
- If you split badly, you can permanently lose funds. Plan, test, and document recovery precisely.
- Banks will refuse access without the right paperwork. Plan legal access (will, executor). Obviously do not put the seed/passphrase in the will.
- Physical theft vs. coercion: A safety deposit box has few physical attack vectors, but is subject to coercion attacks.
- Safeinity is working on a new service to mitigate coercion risk. This will include your required physical presence and retired FBI agents. It will not be cheap.