Shamir Secret Sharing Online | Split & Recover Secrets (GF(256))

This tool implements Shamir's Secret Sharing over GF(256) — the same finite field used in AES encryption. Split a secret into N shares where any K (threshold) shares can reconstruct the original via Lagrange polynomial interpolation, but fewer than K shares reveal absolutely nothing — providing information-theoretic security stronger than any computational scheme. All computation runs 100% in your browser.

Threshold Security Reference

How different (K, N) configurations affect security and recoverability:

Code Examples

Implement Shamir's Secret Sharing programmatically:

// JavaScript (GF(256) arithmetic)
// Each byte of the secret is split independently.
// For byte b, construct random polynomial f(x) where f(0) = b.
// Share i gets value f(i). Recover via Lagrange interpolation at x=0.

// Using a well-audited library:
import { share, combine } from 'shamir-secret-sharing'

const secret = new TextEncoder().encode('my secret')
const shares = share(secret, 3, 5)  // 3-of-5 threshold
const recovered = combine(shares.slice(0, 3))  // any 3 shares

# Python (secret-sharing library)
from secret_sharing import split_and_recover

shares = split_and_recover('my secret', 3, 5)
recovered = split_and_recover(shares[:3])  # any 3 shares

Security Notes

• Information-theoretic security — fewer than K shares provide zero information about the secret, regardless of computational power.
• Distribute shares physically — never store multiple shares in the same location or transmit them over the network.
• Use K=ceil(N/2)+1 or higher — ensures no single party can reconstruct alone and majority consensus is required.
• Test recovery before relying on it — always verify you can reconstruct the secret from K shares before distributing them.

Related Tools

Looking for a different approach to secret backup? The BIP39 Mnemonic Validator works with crypto seed phrases. To understand the entropy strength of your secrets, try the Entropy Calculator. For encrypting data before splitting, the AES Encrypt/Decrypt tool adds an extra layer of protection.