Data Encryption

data-encryption.js

import { bytesToHex, hexToBytes, bytesToUtf8, utf8ToBytes } from '@noble/ciphers/utils';
import { randomBytes } from '@noble/ciphers/webcrypto';
import { secp256k1 } from '@noble/curves/secp256k1';
import { xchacha20poly1305 } from '@noble/ciphers/chacha';

// Encrypting data
function encryptWithPublicKey(publicKey, plaintext) {
  // Generate a random ephemeral private key
  const ephemeralPrivateKey = secp256k1.utils.randomPrivateKey();
  
  // Derive the ephemeral public key
  const ephemeralPublicKey = secp256k1.getPublicKey(ephemeralPrivateKey);

  // Compute shared secret using ECDH
  const sharedSecret = secp256k1.getSharedSecret(ephemeralPrivateKey, publicKey);

  // Use a key derivation step to create a 256-bit key for XChaCha20
  const encryptionKey = sharedSecret.slice(0, 32); // First 32 bytes of the shared secret

  // Create a random 192-bit nonce (24 bytes)
  const nonce = randomBytes(24);

  // Encrypt the plaintext with XChaCha20-Poly1305
  const cipher = xchacha20poly1305(encryptionKey, nonce);
  const ciphertext = cipher.encrypt(new TextEncoder().encode(plaintext));

  return {
    ephemeralPublicKey, // Include ephemeral public key for decryption
    nonce, // Include nonce for decryption
    ciphertext,
  };
}

// Decrypting data
function decryptWithPrivateKey(privateKey, encryptedData) {
  const { ephemeralPublicKey, nonce, ciphertext } = encryptedData;

  // Compute shared secret using ECDH
  const sharedSecret = secp256k1.getSharedSecret(privateKey, ephemeralPublicKey);

  // Use a key derivation step to create a 256-bit key for XChaCha20
  const encryptionKey = sharedSecret.slice(0, 32); // First 32 bytes of the shared secret

  // Decrypt the ciphertext with XChaCha20-Poly1305
  const cipher = xchacha20poly1305(encryptionKey, nonce);
  const plaintext = cipher.decrypt(ciphertext);

  return new TextDecoder().decode(plaintext);
}

const receiverPrivateKey = secp256k1.utils.randomPrivateKey();
const receiverPublicKey = secp256k1.getPublicKey(receiverPrivateKey);

const receiverPrivateKeyHex = bytesToHex(receiverPrivateKey);
const receiverPublicKeyHex = bytesToHex(receiverPublicKey);

console.log('Private Key:', receiverPrivateKeyHex);
console.log('Public Key:', receiverPublicKeyHex);

const plaintext = 'Hello, XChaCha20-Poly1305!';
console.log('Plaintext:', plaintext);

const encryptedData = encryptWithPublicKey(receiverPublicKey, plaintext);

const encryptedDataHex = {
    ephemeralPublicKey: bytesToHex(encryptedData.ephemeralPublicKey),
    nonce: bytesToHex(encryptedData.nonce),
    ciphertext: bytesToHex(encryptedData.ciphertext),
};
console.log('Encrypted Data:', encryptedDataHex);

const decryptedData = decryptWithPrivateKey(receiverPrivateKey, encryptedData);
console.log('Decrypted Data:', decryptedData);