/**
* @file Secret Sharing
* @copyright Multifactor 2022 All Rights Reserved
*
* @description
* Divide a secret into shares using various methods
*
* @author Vivek Nair (https://nair.me) <[email protected]>
*/
const crypto = require('crypto')
const xor = require('buffer-xor')
const secrets = require('secrets.js-34r7h')
/**
* K-of-N secret sharing. Uses bitwise XOR for k=n, Shamir's Secret Sharing for 1 < K < N, and direct secret sharing for K = 1.
*
* @example
* // share secret using 2-of-3 shares
* const shares = mfkdf.secrets.share(Buffer.from('hello world'), 2, 3) // -> [Buffer, Buffer, Buffer]
*
* // recover secret using 2 shares
* const secret = mfkdf.secrets.combine([shares[0], null, shares[2]], 2, 3)
* secret.toString() // -> hello world
*
* // recover original 3 shares
* const recover = mfkdf.secrets.recover([shares[0], null, shares[2]], 2, 3) // -> [Buffer, Buffer, Buffer]
*
* @param {Buffer} secret - The secret value to be shared
* @param {number} k - The threshold of shares required to reconstruct the secret
* @param {number} n - The number of shares to generate
* @returns {Array.<Buffer>} An array of N shares as Buffers
* @author Vivek Nair (https://nair.me) <[email protected]>
* @since 0.8.0
* @memberOf secrets
*/
function share (secret, k, n) {
if (!Buffer.isBuffer(secret)) throw new TypeError('secret must be a buffer')
if (secret.length === 0) throw new RangeError('secret must not be empty')
if (!Number.isInteger(n)) throw new TypeError('n must be an integer')
if (!(n > 0)) throw new RangeError('n must be positive')
if (!Number.isInteger(k)) throw new TypeError('k must be an integer')
if (!(k > 0)) throw new RangeError('k must be positive')
if (k > n) throw new RangeError('k must be less than or equal to n')
if (k === 1) { // 1-of-n
return Array(n).fill(secret)
} else if (k === n) { // n-of-n
const shares = []
let lastShare = Buffer.from(secret)
for (let i = 1; i < n; i++) {
const share = crypto.randomBytes(secret.length)
lastShare = xor(lastShare, share)
shares.push(share)
}
shares.push(lastShare)
return shares
} else { // k-of-n
secrets.init(Math.max(Math.ceil(Math.log(n + 1) / Math.LN2), 3))
const shares = secrets.share(secret.toString('hex'), n, k, 0)
return shares.map(share => {
const components = secrets.extractShareComponents(share)
if (components.data.length % 2 === 1) components.data = '0' + components.data
return Buffer.from(components.data, 'hex')
})
}
}
module.exports.share = share