# Shamir secret sharing — split & reconstruct, no upload

> Free Shamir secret sharing tool: split a secret into shares with a recovery threshold, then reconstruct it from the minimum number of shares — all in your browser, no upload.

Split a text secret into several shares where only a chosen threshold are needed to rebuild it, then reconstruct the original from that minimum. The math runs in your browser, so the secret and its shares never leave your device.

Some secrets are too important to keep in one place and too important to lose — a master key, a crypto seed phrase, a break-glass password. Shamir's scheme resolves that tension: split the secret into shares so that a threshold subset can rebuild it, but any smaller group learns nothing at all.

That lets you distribute trust — three of five executives, two of three engineers — with a mathematical guarantee rather than a policy. Store the shares apart, and losing one or two doesn't lock you out.

For protecting a file directly rather than a text secret, use AES file encrypt, and to store the resulting shares, keep them in a Password Desk vault.

## How to

1. **Enter the secret.** Paste the text you want to protect — a key, seed phrase, or password.
2. **Set shares & threshold.** Choose how many shares to create and how many are required to recover.
3. **Distribute.** Hand each share to a different person or store them separately.
4. **Reconstruct.** Later, combine any threshold-many shares to restore the secret.

## FAQ

### How does Shamir secret sharing work?

The secret becomes a point on a polynomial; each share is another point. Any threshold-many points define the polynomial and recover the secret, while fewer reveal nothing about it.

### What threshold should I pick?

Balance safety and resilience: a 3-of-5 scheme survives losing two shares yet needs three to collude. Lower thresholds recover more easily; higher ones resist compromise better.

### What happens if some shares are lost?

As long as at least the threshold number of shares survive, the secret reconstructs perfectly. Below the threshold, it's unrecoverable — which is exactly the security guarantee.

### Are my secret and shares uploaded?

No. Splitting and reconstruction are computed locally in your browser, so neither the original secret nor any share is ever transmitted.


## Related tools

- [AES file encrypt](https://www.safepaper.app/security/file-encrypt)
- [Password strength](https://www.safepaper.app/security/password-strength)
- [Password Generator](https://www.safepaper.app/passwords/password-generator)
- [Hash & checksum](https://www.safepaper.app/security/hash-verify)

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Canonical HTML: https://www.safepaper.app/security/shamir
Markdown: https://www.safepaper.app/security/shamir.md

There is no upload endpoint — your files are processed in this browser tab. Open your network tab and check.