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One of the frequently performed computing tasks is public key encryption and decryption. Rust and C++ code vastly outperforms JavaScript code in these tasks. In this tutorial, let's use pure Rust implementation of the RSA algorithm as an example to show how to perform public key encryption and decryption in a Node.js web service.

The following Rust functions perform the encryption and decryption tasks.

• The generate_key_pair() function creates a random public / private key pair of specified length. The generated RSAKeyPair is serialized into a JSON string and returned to the JavaScript caller.

• The encrypt() function takes a RSAPublicKey in serialized JSON format, and a byte array message. It encrypts the message and returns the result as a byte array.

• The decrypt() function takes a RSAPrivateKey in serialized JSON format, and an encrypted byte array message. It decrypts the message and returns the result as a byte array.

use wasm_bindgen::prelude::*;
use rsa::{PublicKey, RSAPublicKey, RSAPrivateKey, PaddingScheme};
use rand::rngs::OsRng;
use serde::{Serialize, Deserialize};
​
#[derive(Serialize, Deserialize)]
struct RSAKeyPair {
  rsa_private_key: RSAPrivateKey,
  rsa_public_key: RSAPublicKey
}
​
​
#[wasm_bindgen]
pub fn generate_key_pair (bits: i32) -> String {
  let mut rng = OsRng;
  let private_key = RSAPrivateKey::new(&mut rng, bits as usize).expect("failed to generate a key");
  let public_key = private_key.to_public_key();
  let key_pair = RSAKeyPair {rsa_private_key: private_key, rsa_public_key: public_key};
  return serde_json::to_string(&key_pair).unwrap();
}
​
#[wasm_bindgen]
pub fn decrypt (pk: &str, data: &[u8]) -> Vec<u8> {
  let private_key: RSAPrivateKey = serde_json::from_str(pk).unwrap();
  return private_key.decrypt(PaddingScheme::PKCS1v15, data).expect("failed to decrypt");
}
​
#[wasm_bindgen]
pub fn encrypt (pk: &str, data: &[u8]) -> Vec<u8> {
  let mut rng = OsRng;
  let public_key: RSAPublicKey = serde_json::from_str(pk).unwrap();
  return public_key.encrypt(&mut rng, PaddingScheme::PKCS1v15, data).expect("failed to encrypt");
}

The Javascript host application calls the Rust functions as follows. It first calls the Rust generate_key_pair() function to generate the key pair, and then saves the generated public and private keys respectively. It then uses the public key to encrypt a string message, and then use the private key to decrypt that message. The keys are serialized into JSON strings before passing to the Rust functions.

const { generate_key_pair, encrypt, decrypt } = require('../pkg/rsa_example_lib.js');
​
var kp = JSON.parse(generate_key_pair(2048));
var public_key = kp['rsa_public_key'];
var private_key = kp['rsa_private_key'];
​
var msg = "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks";
var enc_data = encrypt(JSON.stringify(public_key), encoder.encode(msg));
var dec_data = decrypt(JSON.stringify(private_key), enc_data);
console.log(decoder.decode(dec_data));

The RSA example is simple but provides substantial performance benefits when you run many public key encryption and decryption operations.

For a more complex example of public key encryption and decryption, please see our Recrypt-as-a-Service repo. It is a scalable approach for individuals to control access to private data without shared secrets or storing secrets (e.g., private keys) on a centralized service. As a part of the workflow, the web service needs to perform large amounts of proxy encryption using public keys. Rust and WebAssembly are ideally suited for this.