dchain/client-app/lib/crypto.ts

/**
 * Cryptographic operations for DChain messenger.
 *
 * Ed25519  — transaction signing (via TweetNaCl sign)
 * X25519   — Diffie-Hellman key exchange for NaCl box
 * NaCl box — authenticated encryption for relay messages
 */

import nacl from 'tweetnacl';
import { decodeUTF8, encodeUTF8 } from 'tweetnacl-util';
import { getRandomBytes } from 'expo-crypto';
import type { KeyFile } from './types';

// ─── PRNG ─────────────────────────────────────────────────────────────────────
// TweetNaCl looks for window.crypto which doesn't exist in React Native/Hermes.
// Wire nacl to expo-crypto which uses the platform's secure RNG natively.
nacl.setPRNG((output: Uint8Array, length: number) => {
  const bytes = getRandomBytes(length);
  for (let i = 0; i < length; i++) output[i] = bytes[i];
});

// ─── Helpers ──────────────────────────────────────────────────────────────────

export function hexToBytes(hex: string): Uint8Array {
  if (hex.length % 2 !== 0) throw new Error('odd hex length');
  const bytes = new Uint8Array(hex.length / 2);
  for (let i = 0; i < bytes.length; i++) {
    bytes[i] = parseInt(hex.slice(i * 2, i * 2 + 2), 16);
  }
  return bytes;
}

export function bytesToHex(bytes: Uint8Array): string {
  return Array.from(bytes).map(b => b.toString(16).padStart(2, '0')).join('');
}

// ─── Key generation ───────────────────────────────────────────────────────────

/**
 * Generate a new identity: Ed25519 signing keys + X25519 encryption keys.
 * Returns a KeyFile compatible with the Go node format.
 */
export function generateKeyFile(): KeyFile {
  // Ed25519 for signing / blockchain identity
  const signKP = nacl.sign.keyPair();

  // X25519 for NaCl box encryption
  // nacl.box.keyPair() returns Curve25519 keys
  const boxKP = nacl.box.keyPair();

  return {
    pub_key:     bytesToHex(signKP.publicKey),
    priv_key:    bytesToHex(signKP.secretKey),
    x25519_pub:  bytesToHex(boxKP.publicKey),
    x25519_priv: bytesToHex(boxKP.secretKey),
  };
}

// ─── NaCl box encryption ──────────────────────────────────────────────────────

/**
 * Encrypt a plaintext message using NaCl box.
 * Sender uses their X25519 secret key + recipient's X25519 public key.
 * Returns { nonce, ciphertext } as hex strings.
 */
export function encryptMessage(
  plaintext:        string,
  senderSecretHex:  string,
  recipientPubHex:  string,
): { nonce: string; ciphertext: string } {
  const nonce      = nacl.randomBytes(nacl.box.nonceLength);
  const message    = decodeUTF8(plaintext);
  const secretKey  = hexToBytes(senderSecretHex);
  const publicKey  = hexToBytes(recipientPubHex);

  const box = nacl.box(message, nonce, publicKey, secretKey);
  return {
    nonce:      bytesToHex(nonce),
    ciphertext: bytesToHex(box),
  };
}

/**
 * Decrypt a NaCl box.
 * Recipient uses their X25519 secret key + sender's X25519 public key.
 */
export function decryptMessage(
  ciphertextHex:    string,
  nonceHex:         string,
  senderPubHex:     string,
  recipientSecHex:  string,
): string | null {
  try {
    const ciphertext = hexToBytes(ciphertextHex);
    const nonce      = hexToBytes(nonceHex);
    const senderPub  = hexToBytes(senderPubHex);
    const secretKey  = hexToBytes(recipientSecHex);

    const plain = nacl.box.open(ciphertext, nonce, senderPub, secretKey);
    if (!plain) return null;
    return encodeUTF8(plain);
  } catch {
    return null;
  }
}

// ─── Ed25519 signing ──────────────────────────────────────────────────────────

/**
 * Sign arbitrary data with the Ed25519 private key.
 * Returns signature as hex.
 */
export function sign(data: Uint8Array, privKeyHex: string): string {
  const secretKey = hexToBytes(privKeyHex);
  const sig = nacl.sign.detached(data, secretKey);
  return bytesToHex(sig);
}

/**
 * Sign arbitrary data with the Ed25519 private key.
 * Returns signature as base64 — this is the format the Go blockchain node
 * expects ([]byte fields are base64 in JSON).
 */
export function signBase64(data: Uint8Array, privKeyHex: string): string {
  const secretKey = hexToBytes(privKeyHex);
  const sig = nacl.sign.detached(data, secretKey);
  return bytesToBase64(sig);
}

/** Encode bytes as base64. Works on Hermes (btoa is available since RN 0.71). */
export function bytesToBase64(bytes: Uint8Array): string {
  let binary = '';
  for (let i = 0; i < bytes.length; i++) {
    binary += String.fromCharCode(bytes[i]);
  }
  return btoa(binary);
}

/**
 * Verify an Ed25519 signature.
 */
export function verify(data: Uint8Array, sigHex: string, pubKeyHex: string): boolean {
  try {
    return nacl.sign.detached.verify(data, hexToBytes(sigHex), hexToBytes(pubKeyHex));
  } catch {
    return false;
  }
}

// ─── Address helpers ──────────────────────────────────────────────────────────

/** Truncate a long hex address for display: 8...8 */
export function shortAddr(hex: string, chars = 8): string {
  if (hex.length <= chars * 2 + 3) return hex;
  return `${hex.slice(0, chars)}…${hex.slice(-chars)}`;
}