public void CreateFile(string path)
    {
        Task<byte[]> headerTask = CreateHeaderAsync();
        Task<byte[]> filesTask = CombineFilesAsync();
        byte[] header = headerTask.Result;
        byte[] files = filesTask.Result;

        byte[] combined = new byte[header.Length + files.Length];
        Buffer.BlockCopy(header, 0, combined, 0, header.Length);
        Buffer.BlockCopy(files, 0, combined, header.Length, files.Length);

        Task.Factory.StartNew(() => File.WriteAllBytes(path, combined));
    }

    private Task<byte[]> CreateHeaderAsync()
    {
        return Task.Factory.StartNew(() =>
        {
            StringBuilder sb = new StringBuilder();
            int position = 0;
            foreach (ByteFile file in _files)
            {
                sb.Append(file + "?" + position + Environment.NewLine);
                position += file.Length;
            }
            return Encoding.UTF8.GetBytes(sb + "--header_end--" + Environment.NewLine);
        });
    }

    private Task<byte[]> CombineFilesAsync()
    {
        return Task.Factory.StartNew(() =>
        {
            ByteFile[] arrays = _files.ToArray();

            byte[] rv = new byte[arrays.Sum(a => a.Length)];
            int offset = 0;
            foreach (ByteFile t in arrays)
            {
                var array = Encryption.EncryptBytes(t.Content, "password");
                var array = t.Content;

                Buffer.BlockCopy(array, 0, rv, offset, array.Length);
                offset += array.Length;
            }
            return rv;
        });
    }