Encrypting data with a public key in Node.js

The updated public/private decrypt and encryption module is URSA. The node-rsa module is outdated.

This Node module provides a fairly complete set of wrappers for the RSA public/private key crypto functionality of OpenSSL.

npm install ursa

I tested this in Node.js 10, you can use encrypt/decrypt functions (small changes on Jacob's answer):

const crypto = require('crypto')
const path = require('path')
const fs = require('fs')

function encrypt(toEncrypt, relativeOrAbsolutePathToPublicKey) {
  const absolutePath = path.resolve(relativeOrAbsolutePathToPublicKey)
  const publicKey = fs.readFileSync(absolutePath, 'utf8')
  const buffer = Buffer.from(toEncrypt, 'utf8')
  const encrypted = crypto.publicEncrypt(publicKey, buffer)
  return encrypted.toString('base64')
}

function decrypt(toDecrypt, relativeOrAbsolutePathtoPrivateKey) {
  const absolutePath = path.resolve(relativeOrAbsolutePathtoPrivateKey)
  const privateKey = fs.readFileSync(absolutePath, 'utf8')
  const buffer = Buffer.from(toDecrypt, 'base64')
  const decrypted = crypto.privateDecrypt(
    {
      key: privateKey.toString(),
      passphrase: '',
    },
    buffer,
  )
  return decrypted.toString('utf8')
}

const enc = encrypt('hello', `public.pem`)
console.log('enc', enc)

const dec = decrypt(enc, `private.pem`)
console.log('dec', dec)

---

For the keys you can generate them with

const { writeFileSync } = require('fs')
const { generateKeyPairSync } = require('crypto')

function generateKeys() {
  const { privateKey, publicKey } = generateKeyPairSync('rsa', {
    modulusLength: 4096,
    publicKeyEncoding: {
      type: 'pkcs1',
      format: 'pem',
    },
    privateKeyEncoding: {
      type: 'pkcs1',
      format: 'pem',
      cipher: 'aes-256-cbc',
      passphrase: '',
    },
  })

  writeFileSync('private.pem', privateKey)
  writeFileSync('public.pem', publicKey)
}

Use the node-rsa module. Here's a link to the test.js file that demonstrates usage.

A library is not necessary. Enter crypto.

Here's a janky little module you could use to encrypt/decrypt strings with RSA keys:

var crypto = require("crypto");
var path = require("path");
var fs = require("fs");

var encryptStringWithRsaPublicKey = function(toEncrypt, relativeOrAbsolutePathToPublicKey) {
    var absolutePath = path.resolve(relativeOrAbsolutePathToPublicKey);
    var publicKey = fs.readFileSync(absolutePath, "utf8");
    var buffer = Buffer.from(toEncrypt);
    var encrypted = crypto.publicEncrypt(publicKey, buffer);
    return encrypted.toString("base64");
};

var decryptStringWithRsaPrivateKey = function(toDecrypt, relativeOrAbsolutePathtoPrivateKey) {
    var absolutePath = path.resolve(relativeOrAbsolutePathtoPrivateKey);
    var privateKey = fs.readFileSync(absolutePath, "utf8");
    var buffer = Buffer.from(toDecrypt, "base64");
    var decrypted = crypto.privateDecrypt(privateKey, buffer);
    return decrypted.toString("utf8");
};

module.exports = {
    encryptStringWithRsaPublicKey: encryptStringWithRsaPublicKey,
    decryptStringWithRsaPrivateKey: decryptStringWithRsaPrivateKey
}

I would recommend not using synchronous fs methods where possible, and you could use promises to make this better, but for simple use cases this is the approach that I have seen work and would take.