/**
* @file Multi-factor Derived Key Setup
* @copyright Multifactor, Inc. 2022–2025
*
* @description
* Validate and setup a configuration for a multi-factor derived key
*
* @author Vivek Nair (https://nair.me) <[email protected]>
*/
const defaults = require('../defaults')
const crypto = require('crypto')
const { v4: uuidv4 } = require('uuid')
const { hkdfSync } = require('crypto')
const share = require('../secrets/share').share
const xor = require('buffer-xor')
const { argon2id } = require('hash-wasm')
const MFKDFDerivedKey = require('../classes/MFKDFDerivedKey')
/**
* Validate and setup a configuration for a multi-factor derived key
*
* @example
* // setup 16 byte 2-of-3-factor multi-factor derived key with a password, HOTP code, and UUID recovery code
* const setup = await mfkdf.setup.key([
* await mfkdf.setup.factors.password('password'),
* await mfkdf.setup.factors.hotp({ secret: Buffer.from('hello world') }),
* await mfkdf.setup.factors.uuid({ id: 'recovery', uuid: '9b1deb4d-3b7d-4bad-9bdd-2b0d7b3dcb6d' })
* ], {threshold: 2, size: 16})
*
* // derive key using 2 of the 3 factors
* const derive = await mfkdf.derive.key(setup.policy, {
* password: mfkdf.derive.factors.password('password'),
* hotp: mfkdf.derive.factors.hotp(365287)
* })
*
* setup.key.toString('hex') // -> 34d20ced439ec2f871c96ca377f25771
* derive.key.toString('hex') // -> 34d20ced439ec2f871c96ca377f25771
*
* @param {Array.<MFKDFFactor>} factors - Array of factors used to derive this key
* @param {Object} [options] - Configuration options
* @param {string} [options.id] - Unique identifier for this key; random UUIDv4 generated by default
* @param {number} [options.size=32] - Size of derived key, in bytes
* @param {number} [options.threshold] - Number of factors required to derive key; factors.length by default (all required)
* @param {Buffer} [options.salt] - Cryptographic salt; generated via secure PRG by default (recommended)
* @returns {MFKDFDerivedKey} A multi-factor derived key object
* @author Vivek Nair (https://nair.me) <[email protected]>
* @since 0.8.0
* @async
* @memberOf setup
*/
async function key (factors, options) {
if (!Array.isArray(factors)) throw new TypeError('factors must be an array')
if (factors.length === 0) throw new RangeError('factors must not be empty')
options = Object.assign(Object.assign({}, defaults.key), options)
const policy = {
$schema: 'https://mfkdf.com/schema/v1.0.0/policy.json'
}
// id
if (options.id === undefined) options.id = uuidv4()
if (typeof options.id !== 'string') {
throw new TypeError('id must be a string')
}
if (options.id.length === 0) throw new RangeError('id must not be empty')
policy.$id = options.id
// size
if (!Number.isInteger(options.size)) {
throw new TypeError('key size must be an integer')
}
if (!(options.size > 0)) throw new RangeError('key size must be positive')
policy.size = options.size
// threshold
if (options.threshold === undefined) options.threshold = factors.length
if (!Number.isInteger(options.threshold)) {
throw new TypeError('threshold must be an integer')
}
if (!(options.threshold > 0)) {
throw new RangeError('threshold must be positive')
}
if (!(options.threshold <= factors.length)) {
throw new RangeError('threshold cannot be greater than number of factors')
}
policy.threshold = options.threshold
// salt
if (options.salt === undefined) {
options.salt = crypto.randomBytes(policy.size)
}
if (!Buffer.isBuffer(options.salt)) {
throw new TypeError('salt must be a buffer')
}
policy.salt = options.salt.toString('base64')
// check factor correctness
for (const factor of factors) {
// type
if (typeof factor.type !== 'string') {
throw new TypeError('factor type must be a string')
}
if (factor.type.length === 0) {
throw new RangeError('factor type must not be empty')
}
// id
if (typeof factor.id !== 'string') {
throw new TypeError('factor id must be a string')
}
if (factor.id.length === 0) {
throw new RangeError('factor id must not be empty')
}
// data
if (!Buffer.isBuffer(factor.data)) {
throw new TypeError('factor data must be a buffer')
}
if (factor.data.length === 0) {
throw new RangeError('factor data must not be empty')
}
// params
if (typeof factor.params !== 'function') {
throw new TypeError('factor params must be a function')
}
}
// id uniqueness
const ids = factors.map((factor) => factor.id)
if (new Set(ids).size !== ids.length) {
throw new RangeError('factor ids must be unique')
}
// generate secret key material
const secret = crypto.randomBytes(policy.size)
const key = Buffer.from(
await argon2id({
password: secret,
salt: Buffer.from(policy.salt, 'base64'),
hashLength: policy.size,
parallelism: 1,
iterations: 2,
memorySize: 32
})
)
const shares = share(secret, policy.threshold, factors.length)
// process factors
policy.factors = []
const outputs = {}
const theoreticalEntropy = []
const realEntropy = []
for (const [index, factor] of factors.entries()) {
// stretch to key length via HKDF/SHA-512
const share = shares[index]
theoreticalEntropy.push(factor.data.byteLength * 8)
realEntropy.push(factor.entropy)
const salt = crypto.randomBytes(policy.size)
let stretched = Buffer.from(
hkdfSync('sha256', factor.data, salt, '', policy.size)
)
if (Buffer.byteLength(share) > policy.size) {
stretched = Buffer.concat([
Buffer.alloc(Buffer.byteLength(share) - policy.size),
stretched
])
}
const pad = xor(share, stretched)
const params = await factor.params({ key })
outputs[factor.id] = await factor.output()
policy.factors.push({
id: factor.id,
type: factor.type,
pad: pad.toString('base64'),
params,
salt: salt.toString('base64')
})
}
const result = new MFKDFDerivedKey(policy, key, secret, shares, outputs)
theoreticalEntropy.sort((a, b) => a - b)
const theoretical = theoreticalEntropy
.slice(0, policy.threshold)
.reduce((a, b) => a + b, 0)
realEntropy.sort((a, b) => a - b)
const real = realEntropy
.slice(0, policy.threshold)
.reduce((a, b) => a + b, 0)
result.entropyBits = {
theoretical: Math.min(policy.size * 8, theoretical),
real: Math.min(policy.size * 8, real)
}
return result
}
module.exports.key = key