--- title: "Shamir Secret Sharing - Split and Recover | CanDoYa" description: "Split a secret into threshold shares with Shamir secret sharing, then recover it from any sufficient subset. Runs locally in your browser." url: https://candoya.com/tools/secret-sharing-shamir/ locale: en type: browser-tool --- # Shamir Secret Sharing Online Category: Developer ## What is Shamir secret sharing? Shamir secret sharing divides a secret into multiple independent shares and sets a threshold for recovery. In a 3-of-5 setup, any three shares rebuild the original text, while one or two cannot reconstruct its content. This tool creates and combines shares locally in your browser. The tool encodes your UTF-8 text with a checksum, then evaluates a fresh random polynomial for every byte in the finite field GF(256). Each share carries its set ID and threshold settings so mixed sets are rejected. No account is needed, and the tool does not upload your input. This page uses a documented CanDoYa share format rather than a cryptocurrency wallet standard. It is suitable for general text secrets, but it does not create SLIP-0039 mnemonic shares. ## How to use it 1. **Enter the secret** - Type or paste up to 64 KiB of text. Use the visibility control if you need to check it. 2. **Choose the threshold** - Set the total number of shares and how many different shares recovery should require. 3. **Create and separate the shares** - Copy or download the generated strings, then store each share in a genuinely separate place. 4. **Verify recovery** - Switch to recovery, paste any threshold-sized subset with one share per line, and confirm the original text returns exactly. ## Who it's for - **Teams protecting an emergency credential** can require several trusted people to cooperate before access is restored. - **Individuals backing up a recovery code** can store shares in separate physical locations without leaving the whole secret in one place. - **Families and executors planning digital access** can distribute recovery authority while avoiding a single holder with complete access. - **Developers testing threshold workflows** can generate deterministic-format text shares and verify subset recovery in the browser. ## Expert note A 3-of-5 threshold tolerates the loss of two shares, but storing all five together defeats the distribution benefit. Test recovery with the exact subset you plan to keep before deleting the original. ## Frequently asked questions ### Is my secret uploaded? No. Splitting and recovery run inside your browser, and this tool does not send the secret or shares to a server. For highly sensitive material, use a trusted device, load the page first, disconnect from the network, and close the tab after you verify recovery. ### Is this Shamir secret sharing tool free? Yes. You can create and recover threshold shares without an account, payment, or usage meter. The tool supports text secrets up to 64 KiB and creates between 2 and 10 shares in one set. ### How many shares can I create? You can create 2 to 10 shares and require any number from 2 through the total. A 2-of-3 setup favors simple recovery, while 3-of-5 adds more distribution and still tolerates two missing shares. ### Can fewer than the threshold recover the secret? No. With fresh, uniformly random polynomial coefficients, fewer than the required number of shares cannot reconstruct the secret content. Share strings do expose metadata such as the payload length. Duplicate copies of one share do not help because recovery needs different share indexes. ### What happens if a share is changed or mixed with another set? The tool rejects shares with different set identifiers or settings. It also checks the reconstructed text with a checksum, which catches accidental edits in normal use. The checksum is not a digital signature and does not protect against deliberate forgery. ### Are these shares compatible with SLIP-0039 wallets? No. The cdy-shamir-v1 format is designed for text handled by this tool and is not SLIP-0039. Do not import these strings into a hardware wallet. Keep the complete share strings and access to this tool for later recovery. ### Which threshold should I choose? Choose the smallest threshold that prevents one person or location from becoming a single point of failure, then make enough total shares to survive realistic loss. A 3-of-5 setup is a practical starting point, but the right choice depends on who stores each share. ## Related tools - [AES Encrypt and Decrypt](https://candoya.com/tools/aes-encrypt-decrypt/) - [Password Generator](https://candoya.com/tools/password-generator/) - [PBKDF2 Derive](https://candoya.com/tools/pbkdf2-derive/) - [RSA Key Pair Generator](https://candoya.com/tools/rsa-key-pair-generator/) - [SHA-256 Hash Generator](https://candoya.com/tools/sha-256-hash/) --- *Markdown edition of , published for AI agents and other automated readers. Index of key pages: .*