BillTracker/services/encryptionService.js

'use strict';

const crypto = require('crypto');

const ALGORITHM = 'aes-256-gcm';
const IV_BYTES   = 12;
const TAG_BYTES  = 16;

// Returns a stable 256-bit key. Prefers TOKEN_ENCRYPTION_KEY env var (power-user
// override); otherwise auto-generates a random key on first startup and persists
// it in the settings table so it survives restarts without any manual config.
function getKey() {
  const envRaw = process.env.TOKEN_ENCRYPTION_KEY || '';
  if (envRaw) {
    const buf = Buffer.from(envRaw, 'utf8');
    if (buf.length < 32) throw new Error('TOKEN_ENCRYPTION_KEY must be at least 32 bytes');
    return crypto.createHash('sha256').update(buf).digest();
  }

  // Lazy-require to avoid circular dependency at module load time
  const { getSetting, setSetting } = require('../db/database');
  let stored = getSetting('_auto_encryption_key');
  if (!stored) {
    stored = crypto.randomBytes(48).toString('hex');
    setSetting('_auto_encryption_key', stored);
  }
  return crypto.createHash('sha256').update(stored, 'utf8').digest();
}

// No-op now that the key is always available — kept for call-site compatibility
function assertEncryptionReady() {}

function encryptSecret(plaintext) {
  const key = getKey();
  const iv  = crypto.randomBytes(IV_BYTES);
  const cipher = crypto.createCipheriv(ALGORITHM, key, iv, { authTagLength: TAG_BYTES });
  const ct = Buffer.concat([cipher.update(plaintext, 'utf8'), cipher.final()]);
  const tag = cipher.getAuthTag();
  return `${iv.toString('hex')}:${tag.toString('hex')}:${ct.toString('hex')}`;
}

function decryptSecret(stored) {
  const parts = stored.split(':');
  if (parts.length !== 3) throw new Error('Invalid encrypted secret format');
  const [ivHex, tagHex, ctHex] = parts;
  const key     = getKey();
  const iv      = Buffer.from(ivHex, 'hex');
  const tag     = Buffer.from(tagHex, 'hex');
  const ct      = Buffer.from(ctHex, 'hex');
  const decipher = crypto.createDecipheriv(ALGORITHM, key, iv, { authTagLength: TAG_BYTES });
  decipher.setAuthTag(tag);
  return Buffer.concat([decipher.update(ct), decipher.final()]).toString('utf8');
}

module.exports = { assertEncryptionReady, encryptSecret, decryptSecret };