Shamir Secret Sharing
Split a secret into shares: any threshold of them rebuilds it, and fewer reveal nothing about its contents, only its length. Runs in your browser.
Any 3 of 5 shares required to reconstruct
Enter a secret and click Split to generate shares
All splitting and reconstruction happens in your browser using GF(256) finite field arithmetic. This tool doesn't store your secret or its shares, or send them to a server.
Shamir Secret Sharing FAQ
What do Threshold and Shares mean here?
Shares is how many pieces the tool hands you, and Threshold is how many of those have to come back together to rebuild the secret. The tool opens at 3 of 5. Threshold starts at 2 and cannot exceed the current share count, and Shares tops out at 10 and cannot fall below the current threshold, so the two sliders bound each other.
Why do fewer shares than the threshold reveal nothing about the contents?
Every byte of the secret gets its own polynomial over GF(256): the byte itself is the constant term, and the remaining coefficients come from the Web Crypto random generator. Hold one share fewer than the threshold and each of the 256 possible values for that byte is matched by exactly one polynomial of degree below the threshold, so every value stays equally likely. That is information-theoretic secrecy, not a hard computation, so more time or a faster machine buys nothing. The one thing a share does give away is length, because a share is the same number of bytes as the secret.
What can I use this for?
Splitting a master password, an encryption key or a recovery seed across several custodians. Split a database master key among five engineers at a threshold of three, and any three can recover it while no two can read anything at all.
Do the generated shares survive leaving the page?
No. Nothing is saved, so a reload, the Clear button, or switching to Reconstruct and back all discard them — changing mode navigates to the other URL, which rebuilds the tool from scratch. Copy the set before you do any of those. The page cannot clear your clipboard, so a share you already copied stays there until you overwrite it. Splitting the same secret again draws fresh coefficients and produces an independent set, and shares from two runs cannot be mixed even though both rebuild the same secret.
Need to share secrets securely?
Use CredenShare to deliver sensitive data with end-to-end encryption, expiration controls, and full audit logging.