Crypto

JavaScript · Reference cheat sheet

📋 Overview

Node.js node:crypto provides hashing, HMAC, random bytes, UUIDs, and more (ciphers, key derivation). Prefer the built-in module over ad-hoc hashing. For passwords use a dedicated KDF (scrypt, pbkdf2, or argon2 via libs) — not raw createHash.

import crypto from "node:crypto";

🔧 Core concepts

• createHash(algo): one-way digest (sha256, sha512, md5…). Chain .update().digest().
• randomUUID(): RFC 4122 v4 UUID string (cryptographically strong).
• randomBytes(n): n cryptographically strong random bytes (Buffer); sync or callback/promise forms.
• createHmac(algo, key): keyed hash for integrity with a secret.
• Timing-safe compare: timingSafeEqual(a, b) for secrets/hashes (same length required).

💡 Examples

import crypto from "node:crypto";

const hash = crypto.createHash("sha256").update("hello", "utf8").digest("hex");

const id = crypto.randomUUID(); // '3b9f…'

const buf = crypto.randomBytes(16);
const token = buf.toString("hex");

const hmac = crypto
  .createHmac("sha256", process.env.SECRET ?? "dev")
  .update("payload")
  .digest("hex");

// Promise API (Node 15+)
import { randomBytes, randomUUID } from "node:crypto";
const bytes = await randomBytes(32);

function sha256FileBuffer(buf) {
  return crypto.createHash("sha256").update(buf).digest("hex");
}

// Compare digests safely
const a = Buffer.from(hash, "hex");
const b = Buffer.from(hash, "hex");
crypto.timingSafeEqual(a, b); // true

// Password hashing sketch — prefer scrypt
const salt = crypto.randomBytes(16);
const key = crypto.scryptSync("password", salt, 64);

⚠️ Pitfalls

• md5 / sha1 are broken for security — use only for checksums if required.
• Never store passwords as plain sha256(password); use salted slow KDFs.
• timingSafeEqual throws if lengths differ — check length first or pad carefully.
• Math.random() is not crypto-safe; use randomBytes / randomUUID.
• Streaming large inputs: call .update() multiple times, then .digest() once.

🔗 Related

• Buffer — digests and random bytes as Buffers
• fs — hash file contents
• process — secrets via process.env
• Stream — hash while piping
• encode — encoding helpers adjacent to hex/base64