Hash & Encryption Algorithms Cheat Sheet

Practical Snippet

Key points: (1) choose by purpose — CRC32 or xxHash for integrity, SHA-256 or better for adversarial cases, and never a general hash for passwords; (2) hand-rolled hash(secret + data) is vulnerable to length extension, so use crypto.createHmac for any keyed operation; (3) password storage needs a salted KDF with a cost parameter (Argon2id, bcrypt, scrypt, PBKDF2) because general hashes are fast enough for GPUs to brute force billions per second; (4) compare any token or signature with timingSafeEqual to avoid a timing side channel; (5) migrate legacy hashes progressively by upgrading to KDF format on successful login.

import { createHash, createHmac, randomBytes, scryptSync, timingSafeEqual } from 'crypto'

// ① 按用途选算法
const BY_PURPOSE = {
  integrity:  'sha256',   // 校验数据是否被改（可配 HMAC）
  signature:  'sha256',   // 对抗性场景：碰撞必须难构造
  password:   null,       // 🔴 密码绝不用 createHash，走 KDF
  dedup:      'xxhash64', // 仅做分片/去重，可以快
}

// ② 内容指纹：数据量大时可只取前 8 字节十六进制
function fingerprint(data, algo = 'sha256') {
  const hex = createHash(algo).update(data).digest('hex')
  return hex.slice(0, 16)   // 16 字符 = 64 bit，亿级条目碰撞率可接受
}

// ③ 🔴 密钥场景必须用 HMAC，不能自己拼 hash(secret + data)
function mac(data, secret) {
  return createHmac('sha256', secret).update(data).digest()
}
// ❌ 有长度扩展攻击：
//   const bad = createHash('sha256').update(secret + data).digest('hex')
//   攻击者可算出 hash(secret + data + padding + extra) 的合法值

// ④ 密码存储：用 KDF + 随机盐，绝不用 sha256
function hashPassword(password) {
  const salt = randomBytes(16)
  const key = scryptSync(password, salt, 64, { N: 16384, r: 8, p: 1 })
  return { salt: salt.toString('hex'), key: key.toString('hex') }
}
function verifyPassword(password, stored) {
  const key = scryptSync(password, Buffer.from(stored.salt, 'hex'), 64, { N: 16384, r: 8, p: 1 })
  // 定长比较，防时序侧信道
  return timingSafeEqual(key, Buffer.from(stored.key, 'hex'))
}

// ⑤ 常量时间比较：任何 token / 签名校验都要用
function safeEqual(a, b) {
  const ba = Buffer.from(a), bb = Buffer.from(b)
  return ba.length === bb.length && timingSafeEqual(ba, bb)
}

// ⑥ 迁移旧哈希：登录成功时升级为 KDF
function upgradeIfNeeded(password, legacyMd5) {
  const mine = createHash('md5').update(password).digest('hex')
  if (!safeEqual(mine, legacyMd5)) return null
  return hashPassword(password)   // 登录时顺手换成 KDF 格式