example using node.js crypto API with aes-256-gcm

crypto-aes-256-gcm-demo.js

const buffer = require('buffer');
const crypto = require('crypto');

// Demo implementation of using `aes-256-gcm` with node.js's `crypto` lib.
const aes256gcm = (key) => {
  const ALGO = 'aes-256-gcm';

  // encrypt returns base64-encoded ciphertext
  const encrypt = (str) => {
    // The `iv` for a given key must be globally unique to prevent
    // against forgery attacks. `randomBytes` is convenient for
    // demonstration but a poor way to achieve this in practice.
    //
    // See: e.g. https://csrc.nist.gov/publications/detail/sp/800-38d/final
    const iv = new Buffer(crypto.randomBytes(12), 'utf8');
    const cipher = crypto.createCipheriv(ALGO, key, iv);

    // Hint: Larger inputs (it's GCM, after all!) should use the stream API
    let enc = cipher.update(str, 'utf8', 'base64');
    enc += cipher.final('base64');
    return [enc, iv, cipher.getAuthTag()];
  };

  // decrypt decodes base64-encoded ciphertext into a utf8-encoded string
  const decrypt = (enc, iv, authTag) => {
    const decipher = crypto.createDecipheriv(ALGO, key, iv);
    decipher.setAuthTag(authTag);
    let str = decipher.update(enc, 'base64', 'utf8');
    str += decipher.final('utf8');
    return str;
  };

  return {
    encrypt,
    decrypt,
  };
};

const KEY = new Buffer(crypto.randomBytes(32), 'utf8');

const aesCipher = aes256gcm(KEY);

const [encrypted, iv, authTag] = aesCipher.encrypt('hello, world');
const decrypted = aesCipher.decrypt(encrypted, iv, authTag);

console.log(decrypted); // 'hello, world'

I did not implemented it, and stick to the CBC variant for now. Also, I'm not an expert and don't dear to advice anything.

Most applications should consider using the new KeyObject API instead of passing keys as strings or 
Buffers due to improved security features. -https://nodejs.org/api/crypto.html#class-keyobject

e.g. generateKey('aes', { length: 256 }

Most applications should consider using the new KeyObject API instead of passing keys as strings or 
Buffers due to improved security features. -https://nodejs.org/api/crypto.html#class-keyobject

e.g. generateKey('aes', { length: 256 }

crypto.generateKey('aes', { length: 256 }) - What exactly do you want to replace with this?