A seed phrase is a contradiction: one copy gets lost, many copies each add risk. This page cuts a secret into several parts so that any required K of them put it back together, while fewer say nothing about it. Three parts with three people you trust, any two restore it — and none of them alone can do anything.
Everything is computed in the browser: neither the secret nor the parts go anywhere.
Neither the secret nor the parts go anywhere: all the mathematics is computed in this tab.
Shamir’s scheme. Each byte of the secret is hidden in a polynomial: the constant term equals the byte itself, the other coefficients are random, and the degree is one less than the threshold. Part number x — is the value of the polynomial at the point x. Through any K points there passes exactly one polynomial of the required degree, so K parts give the original byte unambiguously. Through K−1 points there pass infinitely many such polynomials, and every constant term is equally likely — which is why fewer parts say nothing at all.
Everything is computed in the field GF(256) — the same one inside AES. Bytes stay bytes, the parts come out short, and writing them on paper is realistic.
The most workable arrangement for keeping things at home is three parts with a threshold of two. One with you, one with a relative, one in a safe deposit box or with a second person you trust. Lose yours and you restore it from the remaining two. Have one stolen and the thief has nothing, not even a hint.
What not to do: keep two parts in one place (that is the same as keeping a single copy), and set the threshold equal to the number of parts (then losing any part is losing the secret).
Nearby: a seed phrase checker, encrypt a file with a password and encrypt text.
No secrets, no parts, no passwords — just as there are no visit logs in the VPN itself. There is nothing to hand over on request.
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