Split a secret among people you trust
A password, a document, a photo. Split it into parts and decide how many are needed to get it back — one part on its own reveals nothing at all.
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What is it
A cryptographic algorithm that splits a secret into multiple parts called shares. Only a minimum number of shares — the threshold — can reconstruct the original secret.
For example, split a secret into 5 shares with a 3-of-5 threshold. Any 3 shares recover the secret; fewer than 3 reveal nothing at all. This is called information-theoretic security.
Use Cases
Leave your accounts, documents and photos to your heirs so that they can only recover them together. Nobody holds the whole thing, not even the lawyer.
The master password of your manager, the root account of a company, the domain registrar. What one person alone should not be able to use, and one person alone should not be able to lose.
Deeds, policies, a .zip with everything together. The file is encrypted and only its key gets split, so the encrypted file can live anywhere.
Split your 12 or 24 words with SLIP-39, the standard Trezor reads. The parts are not a private format of ours: any compatible implementation recovers them.
How It Works
Type or paste any text — a seed phrase, password, private key, or any sensitive data you want to protect.
Choose how many total shares to create and the minimum threshold needed to reconstruct the secret.
Each share is a self-contained string. Distribute them to trusted people, devices, or secure locations.
Features
All cryptographic operations happen in your browser. Your secret never leaves your device — no servers, no uploads, no tracking.
Uses Galois Field arithmetic over GF(2^8), the same mathematics behind proven implementations of Shamir's Secret Sharing scheme.
Each part carries its own index, threshold and checksum, so a mistyped part is caught the moment you paste it instead of years later.
Install as a Progressive Web App and use it without internet. Perfect for air-gapped environments and secure setups.
Security
ShamirVault is designed with a zero-trust architecture. We can't see your data because it never reaches us.
FAQ
Shamir's Secret Sharing (SSS) is a cryptographic algorithm invented by Adi Shamir in 1979. It splits a secret into multiple parts called shares. Only a minimum number of shares (the threshold) can reconstruct the original secret. For example, you can split a secret into 5 shares where any 3 can recover it, but 2 or fewer reveal absolutely nothing.
Use ShamirVault to split your Bitcoin seed phrase into multiple shares using Shamir's Secret Sharing. Choose a threshold (e.g., 3-of-5) so that any 3 shares can recover your seed, but fewer cannot. Distribute shares to trusted locations or people. Unlike simply cutting a seed phrase in half, Shamir splitting provides information-theoretic security — fewer shares than the threshold reveal zero information about the original seed.
Yes. ShamirVault runs 100% in your browser. No data is ever sent to a server. The tool uses standard GF(256) Galois Field arithmetic for the Shamir scheme, which is mathematically proven secure. You can verify this by using the tool offline or in an air-gapped environment. The app carries no ads and no analytics. It does load its typefaces from Google Fonts and check for a minimum version on startup; neither of those carries your secret, and the privacy policy lists exactly what leaves your device.
Multisig (multi-signature) is a Bitcoin protocol feature that requires multiple keys to authorize a transaction. Shamir Secret Sharing splits a single secret (like a private key or seed phrase) into parts. They are complementary: you can use Shamir splitting to back up each key in a multisig setup, providing an extra layer of security for key recovery.
Yes. ShamirVault is a Progressive Web App (PWA) that can be installed on your device and used without an internet connection. This makes it ideal for air-gapped environments where maximum security is required for splitting sensitive secrets like Bitcoin seed phrases or private keys.