> ## Documentation Index
> Fetch the complete documentation index at: https://docs.zerokeyusb.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Flashing Protocol (WebTool)

> The WebTool now acts as a simple loader that transfers the pre-signed binary to the device and manages the reboot.

## WebTool: A Secure Loader

The **WebTool** (the browser-based flasher) no longer calculates security features; it only acts as a transfer interface.

### 📥 Input Files

The WebTool should only receive **binary files (`*.bin`) that have already been pre-signed** by the Offline Signer Tool.

* The file contains the application code **PLUS** the 28-byte Security Footer.

### 🔄 Transfer Protocol

The flashing process follows the traditional USB CDC protocol, treating the signed file as a single complete *payload*:

1. **Start:** The WebTool sends `HELLO` and then `ERASE APP` to clear the application space.
2. **Writing:** The WebTool sends the entire **signed file** in *chunks* using the command `WRITE addr len crc32` and the binary *payload*.
3. **Finalization:** The `DONE` command is sent.
4. **Activation:** The Bootloader receives the data, writes it to Flash (including the footer in its final location), and reboots.

### ⏱️ Timeout Management

To ensure the flashing process does not fail prematurely if unauthorized firmware is loaded, the WebTool waits for an extended period:

* **Increased Delay:** The final waiting time after sending `DONE` has been extended to **20 seconds**.
* **Purpose:** This time covers the 15-second delay imposed by the Bootloader if the authenticity check fails, ensuring the USB connection is not cut before the device can reboot or enter waiting mode.

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