shamirs-secret-sharing-example.js

import sss from 'shamirs-secret-sharing'

const { crypto } = window
const u8ToB64 = u8 => Buffer.from(u8).toString('base64')
const b64toU8 = b64 => Buffer.from(b64, 'base64')

async function sssDemo() {
  const keypair = await crypto.subtle.generateKey(
    {
      name: 'RSA-OAEP',
      modulusLength: 4096,
      publicExponent: new Uint8Array([1, 0, 1]),
      hash: 'SHA-256'
    },
    true,
    ['encrypt', 'decrypt']
  )
  const pubKeyJWK = await crypto.subtle.exportKey('jwk', keypair.publicKey)
  const privKeyJWK = await crypto.subtle.exportKey('jwk', keypair.privateKey)
  const privKeyStr = JSON.stringify(privKeyJWK)
  const secretBuffer = Buffer.from(privKeyStr)
  console.log({ secretBuffer })
  const allFragments = sss.split(secretBuffer, { shares: 3, threshold: 2 }).map(u8ToB64)
  console.log({ allFragments }) // only 2 of these 3 fragments are required to recover the original private key
  const twoFragments = allFragments.slice(0, 2).reverse()
  const recovered = sss.combine(twoFragments.map(b64toU8))
  const recoveredPrivKeyJWK = JSON.parse(recovered.toString())
  console.log({ recoveredPrivKeyJWK })
}

sssDemo()