attiny-pass-key — USB Password Typer for Digispark / ATtiny85

Open-source ATtiny85 firmware that turns a Digispark into a USB HID keyboard that automatically types a pre-configured password when plugged in.

attiny-pass-key is a tiny, single-sketch Arduino firmware for the Digispark / ATtiny85 microcontroller. It emulates a USB keyboard (USB HID) and types a password for you the moment the board is plugged into any computer — no drivers, no software, no manual typing. Think of it as a DIY USB password dongle or auto-typer built on cheap, widely available hardware.

Table of Contents

• Why use attiny-pass-key?
• Purpose
• How It Works
• Features
• Tools Used
• Getting Started
• Build and Upload
• Releases
• Project Structure
• Keywords

Why use attiny-pass-key?

Typing a password by hand can be a pain — especially when you don't have a keyboard connected directly to the device you want to access, or when you use a passphrase so long and complex that retyping it every time is a hassle. attiny-pass-key solves this by typing the password for you over USB.

⚠️ THIS PROJECT IS MADE FOR EDUCATIONAL PURPOSES ONLY. USE AT YOUR OWN RISK.

Purpose

This project is designed for the ATtiny microcontroller (specifically the Digispark / ATtiny85) to implement a passkey system. It acts as a USB keyboard device that automatically types a configured password when plugged in. This makes entering long passphrases effortless on machines where typing them is impractical — a convenience tool, not a security one.

How It Works

Once plugged in, the device waits about a second, types the configured password followed by Enter into whatever window currently has focus, then blinks the on-board LED indefinitely.

Features

• Automated Password Entry: Types a pre-configured password via USB HID the moment the board is plugged in.
• Plug-and-Play USB Keyboard: Enumerates as a standard USB HID keyboard — works on Windows, macOS, and Linux with no extra drivers or software.
• Compact Codebase: A single Arduino sketch optimized for the resource-constrained ATtiny85 microcontroller.
• Configurable Password: Set your password via an environment variable, injected into the firmware at compile time.
• Cheap, Accessible Hardware: Runs on the low-cost Digispark / ATtiny85 board.

Tools Used

• Arduino CLI: For building and uploading firmware.
• mise: For task management and tool versioning.
• ATtiny85 / Digispark: The target hardware platform.
• Digistump's DigiKeyboard library: USB HID functionality (vendored from the Digistump platform, referenced by path in sketch.yaml).

Getting Started

Prerequisites

• mise: This project uses mise to manage dependencies and tasks. Install it by following the installation guide.
• Hardware: A Digispark or ATtiny85 development board.

Setup

1. Clone the repository:

git clone https://github.com/lmarqs/attiny-pass-key.git
cd attiny-pass-key

2. Install Tools: Run mise install to download the required version of arduino-cli and other tools defined in mise.toml.

mise install

3. Initialize Environment: Run the setup task to configure the Arduino core and libraries.

mise run setup

This command will:

• Create a .env file from .env.example if it doesn't exist.
• Update the Arduino core and library indexes.

4. Configure Password: Open the .env file and set your desired password in the ATTINY_PASS_KEY_PASSWORD variable.

ATTINY_PASS_KEY_PASSWORD="your_secure_password_here"

Build and Upload

This project uses mise tasks to simplify the build process.

1. Compile the Firmware:

mise run arduino:compile

This compiles the sketch and injects the password from your .env file.

2. Upload to Device:

mise run arduino:upload

Connect your Digispark/ATtiny85 when prompted (or within the 60-second timeout window typical for Micronucleus bootloaders).

3. All-in-one (Optional):

mise run arduino:run

Runs compile + upload + monitor in sequence.

Note: With DigiKeyboard, the Digispark enumerates as an HID-only device (V-USB provides no CDC serial), so mise run arduino:monitor will typically find no serial port — this sketch produces no serial output.

Releases

Every push to main triggers a CI build that publishes a build-<sha> GitHub release with the build output. Release artifacts are compiled without a .env, so the firmware contains the default_password fallback — to embed your own password, build locally as described above.

Project Structure

• attiny-pass-key.ino: The main Arduino sketch containing the logic.
• mise.toml: Configuration for mise, defining tools and tasks (compile, upload, setup).
• arduino-cli.yaml: Configuration file for arduino-cli.
• sketch.yaml: Defines the board profile (FQBN) and platform dependencies.
• .env: Stores sensitive configuration like the password (do not commit this file).
• .arduino/: Local sandboxed Arduino environment (platforms, tools, build output — gitignored), created by the setup and compile tasks.

Keywords

ATtiny85, Digispark, USB HID keyboard, password typer, auto-type password, USB password dongle, Arduino firmware, ATtiny microcontroller, micronucleus bootloader, DigiKeyboard, arduino-cli, mise, embedded firmware, HID emulation, USB rubber ducky alternative, keystroke injection, AVR.