Split your secret.
Break a secret into N pieces. Choose how many (M) are required to put it back together. Below that threshold, even all the partial pieces combined reveal nothing. It's not encryption: the maths makes partial knowledge mathematically impossible.
Secret to split
Threshold
Enter shares
Paste each share on a separate line. You need at least M shares.
How Shamir's Secret Sharing works.
Your secret becomes a coefficient in a random polynomial of degree M−1. Each share is a single point on that curve. With M points, the curve (and your secret) reconstructs exactly. With M−1 points, infinitely many curves fit, so your secret is information-theoretically secure. Not just hard to guess. Mathematically unrecoverable.
In practice: give one share to your lawyer, one to your partner, one to a safety deposit box, one to a sealed envelope at home, one to a trusted friend abroad. You set the threshold. If a share is lost or someone is compromised, you stay safe as long as M valid shares survive.
Not your control file's encryption layer. Shamir doesn't replace encryption. The shares themselves are unencrypted points on a curve. Combine the two: encrypt your seed phrase deniably with Protect, then split the resulting control file with Shamir.
Use cases.
Crypto inheritance
Split your control file 3-of-5. Give shares to your lawyer, partner, trusted friend, safe deposit box, and a sealed letter. If something happens to you, any 3 can reconstruct access.
Multi-party custody
A fund requires 2-of-3 signers to access cold storage. Split the deny.sh control file the same way. No single party can decrypt alone.
Geographic distribution
Store shares in different countries. A seizure in one jurisdiction can't compromise the secret. You need shares from multiple locations.
Dead man's switch
Give M-1 shares to people you trust. Keep the final share yourself. If you become unreachable, a time-locked share release completes the set.
Everything stays on your device.
Splitting and combining happen entirely in your browser. Nothing is transmitted. Pair this with seed phrase protection: encrypt first, then split the control file.