@localnerve/hmac-symmetric

hmac-symmetric

A library for simple symmetric encryption with HMAC digests

Summary

A zero dependency node library with basic functions for using symmetric encryption with HMAC digests. A a simple, small, configurable, and reusable set of functions for payload integrity and authentication.

TLDR; Skip to the example...

Applications

This is a general purpose library that can be used in any application where an HMAC'd symmetrically encrypted payload is useful. Here's a quick reminder of a couple of useful applications for this library:

1. Bot Mitigation
   When the payload is a simple timestamp, roundtripping (get at the beginning and send at the end of input) can be used to force bots to take a "human" amount of time to submit a form or field. This is a deal breaker for any serious bot network. In my experience, this is the biggest step you can take to destroy bots and maintain user trust, but you have to procure/measure an accurate minimum human usage time.
2. Integrity and Authenticity
   The base function of a hashcode is to ensure payload integrity (that it has been unaltered). When combined with a shared secret (HMAC), this also ensures authtenticity. If there are services on your network that will receive a data block that originated from the a trusted source, this can be used to verify the integrity and authenticity of that data block, no matter how many hands it went through in between.

API

This library uses the environment variables

• HS_HMAC_SECRET
• HS_ENCRYPTION_KEY

As the default source for keys for cryptographic functions.
For more information see:

1. For HMAC secret key
2. For Encryption/Decryption key
3. And caveats for using strings as inputs for cryptographic APIs

To NOT use environment variables, supply options hmacSecret and encryptionKey.

Methods this library exports:

encryptAndDigest

Symmetrically encrypt data and generate an HMAC digest for it.
encryptAndDigest (input [, options]) : { payload, digest }

• {String|Buffer|TypedArray|DataView} input - The data to encrypt
• {Object} [options] - Optional options for generateHmac and symmetricEncrypt
• Returns {Object} with payload and digest properties for the encrypted payload and the hmac digest.

decryptAndTest

Symmetrically decrypt data and test it's HMAC digest against an original.
decryptAndTest (originalDigest, encryptedInput [, options]) : { ok, decrypted }

• {String} originalDigest - The original hmac digest to test against.
• {String} encryptedInput - The encrypted input data string.
• {Object} [options] - Optional options for generateHmac and symmetricDecrypt
• Returns {Object} with ok and decrypted properties for the test result and the decrypted payload.

generateHmac

Generate an HMAC digest using the HMAC secret.
generateHmac (input [, options]) : String

• {String|Buffer|TypedArray|DataView} input - Input data.
• {Object} [options] - Optional options.
• {String} [options.inputEncoding] - Applied if input is a String. Default 'utf8'.
• {String} [options.hmacAlgo] - Algo used to create HMAC. Default 'sha256'.
• {String} [options.hmacSecret] - Secret to use. Defaults to environment variable HS_HMAC_SECRET.
• Returns {String} of a hex encoded HMAC digest.

symmetricEncrypt

Symmetrically encrypt the input using an encryption key.
symmetricEncrypt (input [, options]) : String

• {String|Buffer|TypedArray|DataView} input - The data to encrypt.
• {Object} [options] - Optional options.
• {String} [options.encryptionAlgo] - Symmetric cipher algo, defaults to 'aes-256-cbc'.
• {String} [options.encryptionKey] - Symmetric cipher key. Defaults to environment variable HS_ENCRYPTION_KEY.
• {String} [options.inputEncoding] - Encoding if the input is a String. Defaults to 'utf8'.
• Returns {String} hex encoded encryption of the input.

symmetricDecrypt

Symmetrically decrypt an encrypted input using an encryption key.
symmetricDecrypt (input [, options]) : String

• {String} input - The encrypted data.
• {Object} [options] - Optional options.
• {String} [options.encryptionAlgo] - Symmetric cipher algo, defaults to 'aes-256-cbc'.
• {String} [options.encryptionKey] - Symmetric cipher key. Defaults to environment HS_ENCRYPTION_KEY.
• {Boolean} [options.outputBuffer] - true to return the Buffer result, false to convert buffer to string. Defaults to false.
• Returns {String|Buffer} for the decrypted data as requested.

HSError

The class used by this library to throw errors.
Useful for determining hmac-symmetric specific error source.
class HSError, constructor (hsErrorType, originalError)

HSError.HSE_HMAC

Error property hseType will be equal to HSError.HSE_HMAC if error occurred during HMAC generation.

HSError.HSE_ENCRYPT

Error property hseType will be equal to HSError.HSE_ENCRYPT if error occurred during encryption.

HSError.HSE_DECRYPT

Error property hseType will be equal to HSError.HSE_DECRYPT if error occurred during decryption.

Example

Encryption/decryption usage with top level helper API using hmacSecret and encryptionKey (instead of using environment variables HS_HMAC_SECRET and HS_ENCRYPTION_KEY).

import crypto from 'node:crypto';
import { HSError, encryptAndDigest, decryptAndTest } from '@localnerve/hmac-symmetric';

// Create demo input and phony keys for demo only.
const input = 'hello world';
const hmacSecret = crypto.randomBytes(32);
const encryptionKey = crypto.randomBytes(32);  
console.log(input);
  // hello world

try {
  const encrypted = encryptAndDigest(input, {
    hmacSecret,
    encryptionKey
  });
  console.log(encrypted);
    // {
    //   digest: 'd3d6a6f1b2723f001c8c4ff4b28d0b310899c5eefbdbece184d62fcd8a4d712e',
    //   payload: '1f59ccab850189d7906db63f7f087d0f:957c9fe80c93033a8f9a9de0c0d73729'
    // }

  const decrypted = decryptAndTest(encrypted.digest, encrypted.payload, {
    hmacSecret,
    encryptionKey
  });
  console.log(decrypted);
    // { 
    //   ok: true,
    //   decrypted: 'hello world'
    // }

} catch (e) {
  console.log(e.hseType);
    // HSE_HMAC, HSE_ENCRYPT, or HSE_DECRYPT
  console.log('hmac error', e.hseType === HSError.HSE_HMAC);
  console.log('encryption error', e.hseType === HSError.HSE_ENCRYPT);
  console.log('decryption error', e.hseType === HSError.HSE_DECRYPT);
}

LICENSE

• BSD 3-Clause, Alex Grant, LocalNerve, LLC