Giới thiệu về mã hóa / giải mã tệp

// Derive encryption key from password
async function deriveKey(password, salt) {
  const encoder = new TextEncoder();
  const keyMaterial = await crypto.subtle.importKey(
    'raw',
    encoder.encode(password),
    'PBKDF2',
    false,
    ['deriveBits', 'deriveKey']
  );

  return crypto.subtle.deriveKey(
    {
      name: 'PBKDF2',
      salt: salt,
      iterations: 600000,  // High iteration count
      hash: 'SHA-256'
    },
    keyMaterial,
    { name: 'AES-GCM', length: 256 },
    false,
    ['encrypt', 'decrypt']
  );
}

// Encrypt file data
async function encryptFile(fileData, password) {
  const salt = crypto.getRandomValues(new Uint8Array(16));
  const iv = crypto.getRandomValues(new Uint8Array(12));
  const key = await deriveKey(password, salt);

  const encrypted = await crypto.subtle.encrypt(
    { name: 'AES-GCM', iv: iv },
    key,
    fileData
  );

  return { encrypted, salt, iv };
}