Asymmetric Encryption using Nodejs Crypto module

A library is not necessary. Enter crypto.

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

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

const encryptStringWithRsaPublicKey = function (toEncrypt, relativeOrAbsolutePathToPublicKey) {
  const absolutePath = path.resolve(relativeOrAbsolutePathToPublicKey);

  const publicKey = fs.readFileSync(absolutePath, "utf8");
  const buffer = Buffer.from(toEncrypt);
  const encrypted = crypto.publicEncrypt(publicKey, buffer);

  return encrypted.toString("base64");
};

const decryptStringWithRsaPrivateKey = function (toDecrypt, relativeOrAbsolutePathtoPrivateKey) {
  const absolutePath = path.resolve(relativeOrAbsolutePathtoPrivateKey);

  const privateKey = fs.readFileSync(absolutePath, "utf8");
  const buffer = Buffer.from(toDecrypt, "base64");
  const 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.