Secret Splitter (Shamir)
Split a secret into shares so only a group of them together can rebuild it.
How to use the Secret Splitter (Shamir)
- Type the secret, then choose how many shares to make and how many are needed to rebuild it.
- Press Split. Copy each share or save them as separate files.
- Give the shares to different people or store them in different places.
- To recover, open the Rebuild tab and paste or open enough shares, in any order.
About this tool
Some secrets are too important to keep in one place and too dangerous to copy freely: the recovery phrase for a crypto wallet, the master password of a family password manager, the code to a safe. Shamir secret sharing solves this. It turns one secret into several shares and lets you set a threshold, for example any three of five. Three shares together rebuild the secret exactly; two shares, or one, reveal nothing about it, not even a hint.
Each share made here carries a checksum, so a single mistyped character is caught and reported rather than silently producing the wrong secret. Shares also carry a set code that ties them to one split, and the rebuilt secret is checked against a hidden fingerprint, so mixing shares from two different splits, or an altered share, is detected. If you paste a spare share, the tool can even point out which share is the bad one.
Plan for real life when you choose the numbers. A threshold of two out of three survives the loss of any one share. Three out of five lets two shares go missing while still requiring a small group to act together. Write down who holds which share, and test a rebuild before you destroy the original.
Frequently asked questions
Is Shamir secret sharing actually secure?
Yes. It is a long-established method with a mathematical proof: below the threshold, every possible secret is equally likely. The weak points are practical, such as storing too many shares in one place, so spread them out.
Can I rebuild the secret on another website or app?
Shares made here use this tool's own text format, which includes checksums. Keep a link to this page, or save a copy of the page to your computer, so you can always rebuild. The format starts with a version number, so future versions of the tool can still read today's shares.
Why are shares longer than my secret?
The secret is padded to hide its exact length, and each share adds its number, the threshold, a set code and a checksum. A share is a little longer than the secret but stays a single line you can copy or print.
Should I print the shares?
Paper is a good choice for long-term storage because it cannot be hacked remotely. Print or write each share on a separate sheet and store the sheets in separate secure places.
Does my secret ever leave this page?
No. Splitting and rebuilding run in your browser using its built-in secure random number generator. The secret is never stored, logged or sent, and the page works offline once loaded.