const ivLen = crypto.cipherivLength('des-ede3-ofb') // => 8
const keyLen = crypto.cipherkeyLength('des-ede3-ofb') // => 24

'use strict'

const assert = require('assert').strict
const crypto = require('crypto')

const SALT = 'foobar'

function genKey(alg) {
	const keyLen = 24 // => crypto.cipherkeyLength(alg)
	const hash = crypto.createHash('sha256').update(SALT).digest()
	return hash.slice(0, keyLen)
}

function encrypt(value, alg = 'des-ede3-ofb') {
	const ivLen = 8 // => crypto.cipherivLength(alg)
	const iv = crypto.randomBytes(ivLen)
	const key = genKey(alg)
	const cipher = crypto.createCipheriv(alg, key, iv, {authTagLength: ivLen})
	const encryptedUpdate = cipher.update(value)
	const encryptedFinal = cipher.final()
	const encrypted = Buffer.concat([encryptedUpdate, encryptedFinal], encryptedUpdate.byteLength + encryptedFinal.byteLength)
	return [encrypted, iv]
}

function decrypt([encrypted, iv], alg = 'des-ede3-ofb') {
	const ivLen = iv.byteLength
	const key = genKey(alg)
	const cipher = crypto.createDecipheriv(alg, key, iv, {authTagLength: ivLen})
	const decryptedUpdate = cipher.update(encrypted)
	const decryptedFinal = cipher.final()
	return Buffer.concat([decryptedUpdate, decryptedFinal], decryptedUpdate.byteLength + decryptedFinal.byteLength)
}

// Testing
const input = 'test'
const output = decrypt(encrypt(input)).toString('utf8')
assert.strictEqual(input, output) // => OK