What happens if I lose a share?

Nothing, as long as you still hold the threshold number. That redundancy is the reason to produce more shares than you require — five shares needing three tolerates two losses without any drama.

Do fewer shares than the threshold leak part of the secret?

No. This is information-theoretic rather than computational security: below the threshold every possible secret of that length remains equally consistent with what you hold. More computing power does not help, and neither will a future one.

Is a share as sensitive as the secret?

Less so, but not harmless. A share reveals the length of the secret, and it is one of the pieces an attacker needs. Store each one as carefully as you would a password, just in different places.

Can I use this for a crypto wallet seed phrase?

It is one of the strongest reasons to use it, and the one caution is the obvious one: test the recovery before you rely on it. Split the phrase, combine a threshold subset on the matching page, and check you get the same words back before you destroy anything.

Why not just split the password into three pieces myself?

Because each piece would give away part of the answer and shorten the guess. Holding two-thirds of a password is a colossal advantage to an attacker. Holding two of three shares is no advantage whatsoever.

Split a Secret Into Shares

Shamir's scheme — any M of N shares rebuild it, fewer reveal nothing.

Everything runs inside your browser. Your files never leave your device.

Input

Result

The result appears here as you type.

Ask about Split a Secret Into Shares

Questions about what this tool does, which option to pick, or what it can and cannot handle.

The question you type here is sent to an AI provider to be answered — your files and whatever you put in the tool above are not, and the assistant cannot see them. Answers are generated and can be wrong. The tool itself is not guessing: it runs deterministic code on your device.

About the Split a Secret Into Shares

Some secrets are too important to keep in one place and too important to copy. A master password, a crypto wallet recovery phrase, the root credentials for a company's infrastructure. Storing one copy risks losing it; storing several copies multiplies the chance one is stolen.

Shamir's Secret Sharing resolves that properly rather than by compromise. It splits the secret into any number of shares and sets a threshold: bring that many back together and the original is reconstructed exactly. Bring fewer and you learn nothing at all — not part of it, not its structure, nothing beyond the length. That is not a claim about how hard the mathematics is to break. Below the threshold, every possible secret of that length remains exactly as likely as every other, so there is nothing to attack.

The mechanism is a polynomial over a finite field. To require three shares, the tool builds a degree-two polynomial whose constant term is your secret byte and whose other coefficients are random, then hands out points on that curve. Three points determine a parabola uniquely; two points lie on infinitely many, which is precisely why two shares tell you nothing. Each byte of your secret gets its own polynomial with fresh random coefficients.

Three of five is the usual arrangement and a sensible default: you can lose two shares to a house fire or a failed drive and still recover, while an attacker needs to compromise three separate locations. Give them to different people, or put them in different places, and keep a note of the threshold — a set of shares with no record of how many are needed is a puzzle you have set yourself.

How to use it

1Type or paste the secret — a password, a recovery phrase, a key. Anything that fits in text works.
2Choose how many shares to produce and how many of them are needed to rebuild it.
3Optionally add a label, which is prefixed to each share so you can tell one set apart from another later.
4Distribute the shares to genuinely separate places. Two shares in the same drawer are one share for every purpose that matters.
5Record the threshold somewhere with the shares, and destroy this page's output by closing the tab.

Questions

What happens if I lose a share?: Nothing, as long as you still hold the threshold number. That redundancy is the reason to produce more shares than you require — five shares needing three tolerates two losses without any drama.
Do fewer shares than the threshold leak part of the secret?: No. This is information-theoretic rather than computational security: below the threshold every possible secret of that length remains equally consistent with what you hold. More computing power does not help, and neither will a future one.
Is a share as sensitive as the secret?: Less so, but not harmless. A share reveals the length of the secret, and it is one of the pieces an attacker needs. Store each one as carefully as you would a password, just in different places.
Can I use this for a crypto wallet seed phrase?: It is one of the strongest reasons to use it, and the one caution is the obvious one: test the recovery before you rely on it. Split the phrase, combine a threshold subset on the matching page, and check you get the same words back before you destroy anything.
Why not just split the password into three pieces myself?: Because each piece would give away part of the answer and shorten the guess. Holding two-thirds of a password is a colossal advantage to an attacker. Holding two of three shares is no advantage whatsoever.