tillitis-key/README.md

# Tillitis Key

## Introduction

Tillitis Key (TKey) is a new kind of USB security token. What makes
the TKey unique is that it allows a user to load and run applications on
the device, while still providing security. This allow for open-ended,
flexible usage. Given the right application, the TKey can support use
cases such as SSH login, Ed25519 signing, Root of Trust, FIDO2, TOTP,
Passkey, and more.

During the load operation, the device measures the application
(calculates a cryptographic hash digest over it) before running
it on the open hardware security processor. This measurement
is similar to [TCG DICE](https://trustedcomputinggroup.org/work-groups/dice-architectures/).

Each Tkey device contains a Unique Device Secret (UDS), which
together with the application measurement, and an optional
user-provided seed, is used to derive key material unique to each
application. This guarantees that if the integrity of the application
loaded onto the device has been tampered with, the correct keys
needed for an authentication will not be generated.

Key derivation with a user-provided seed allows users to build and
load their own apps, while ensuring that each app loaded will have
its own cryptographic identity, and can also be used for authentication
towards different services.

The Tkey platform is based around a 32-bit RISC-V processor and has
128 KB of RAM. The current firmware is designed to load an app that is
up to 100 KB in size, and gives it a stack of 28 KB. A smaller app may
move itself in memory to get larger continuous memory.

All of the Tkey software, firmware, FPGA Verilog source code, schematics
and PCB design files are open source. Like all trustworthy security software
and hardware should be. This in itself makes it different, as other
security tokens utilize at least some closed source hardware for its
security-critical operations.

![Tillitis Key 1 PCB, first implementation](doc/images/mta1-usb-v1.jpg)
*The TK1 PCB, the first implementation of the TKey.*


## Documentation

### Getting started
* [Quickstart](doc/quickstart.md) to program the TKey
* [Toolchain setup](doc/toolchain_setup.md)
* [Release Notes](doc/release_notes.md)

### In-depth technical information
* [System Description](doc/system_description/system_description.md)
* [Threat Model](doc/threat_model/threat_model.md)
* [Framing Protocol](doc/framing_protocol/framing_protocol.md)
* [Boards](doc/system_description/boards.md)
* [Firmware](doc/system_description/firmware.md)
* [Software](doc/system_description/software.md)

Note that development is ongoing. For example, changes might be made
to the measuring and derivation of key material, causing the
public/private keys of a signer app to change. To avoid unexpected
changes, please use a tagged release. Read the [Release
Notes](doc/release_notes.md) to keep up to date with changes and new
releases.

Applications and host programs that communicate with the apps are kept
in this repository: https://github.com/tillitis/tillitis-key1-apps


## About this repository

This repository contains hardware, software and utilities written as
part of the TKey. It is structured as monolithic repository, or
"monorepo", where all components live in one repository.


## Licensing

See [LICENSES](./LICENSES/README.md) for more information about
the projects' licenses.

All contributors must adhere to the [Developer Certificate of Origin](dco.md).