mirror of
https://github.com/tillitis/tillitis-key1.git
synced 2024-12-21 13:44:59 -05:00
136 lines
5.3 KiB
Markdown
136 lines
5.3 KiB
Markdown
# System Description
|
|
|
|
## Purpose and Revision
|
|
|
|
The purpose of this document is to provide a description of the
|
|
Tillitis TKey. What it is, what is supposed to be used for, by whom,
|
|
where and possible use cases. The document also provides a functional
|
|
level description of features and components of the TKey.
|
|
|
|
Finally, the document acts as a requirement description. For the
|
|
requirements, the document follows
|
|
[RFC2119](https://datatracker.ietf.org/doc/html/rfc2119) to indicate
|
|
requirement levels.
|
|
|
|
The described functionality and requirements applies to version 1 of
|
|
the TKey (TK1)
|
|
|
|
The intended users of this document are:
|
|
- Implementors of the TKkey hardware, firmware and SDKs
|
|
- Developers of secure applications for the TKey
|
|
- Technically skilled third parties that wants to understand the
|
|
TKey
|
|
|
|
|
|
## Introduction
|
|
The TKey is a USB-connected, RISC-V based application platform. The
|
|
purpose of the TKey is to provide a secure environment
|
|
for applications that provides some security functionality needed by the
|
|
device user. Some examples of such security functionality are:
|
|
|
|
- TOTP token generators
|
|
- Signing oracles
|
|
- SSH login dongles
|
|
|
|
|
|
### Measured Based Security
|
|
The key, unique feature of the TKey is that it measures the secure
|
|
application when the application is being loaded onto the device. The
|
|
measurement (a hash digest), combined with a Unique Device Secret
|
|
(UDS) is used to derive a base secret for the application.
|
|
|
|
The consequence of this is that if the application is altered,
|
|
the base secret derived will also change. Conversely, if the keys
|
|
derived from the base secret are the same as the last time the
|
|
application was loaded onto the same device, the application can
|
|
be trusted not to have been altered.
|
|
|
|
Note that since the UDS is per-device unique, the same application
|
|
loaded onto another TKey device will derive a different set of keys.
|
|
This ties keys to a specific device.
|
|
|
|
The derivation can also be combined with a User Supplied Secret
|
|
(USS). This means that keys derived are both based on something the user
|
|
has - the specific device, and something the user knows (the USS). And
|
|
the derived can be trusted because of the measurement being used
|
|
by the derivation, thereby verifying the intergrity od the application.
|
|
|
|
|
|
### Assets
|
|
The TKey store and use the following assets internally:
|
|
|
|
- UDS - Unique Device Secret. 256 bits. Provisioned and stored during
|
|
device manufacturing. Never to be replaced during the life time of
|
|
a given device. Used to derive application secrets. Must never leave
|
|
the device. Tillitis will NOT store a copy of the UDS. Can be read
|
|
by firmware once between power cycling
|
|
|
|
- UDI - Unique Device ID. 64 bits. Provisioned and stored during
|
|
device manufacturing. Only accessible by FW. Never to be replaced or
|
|
altered during the life time of a given device. May be copied,
|
|
extracted, read from the device.
|
|
|
|
- CDI - Compound Device Identity. Dervied by the FW when an application
|
|
is loaded using the UDS and the application binary. Used by the
|
|
application to derive secrets, keys as needed. The CDI should never
|
|
be exposed outside of the application_fpga
|
|
|
|
|
|
Additionally the following asset could be provided from the host:
|
|
|
|
- USS - User Supplied Secret. May possibly be replaced many times.
|
|
Supplied from the host to the device. Should not be revealed to a
|
|
third party.
|
|
|
|
|
|
### Subsystems and Components
|
|
The TKey as a project, system and secure application platform
|
|
consists of a number of subsystems and components, modules, support
|
|
libraries etc. Roughly these can be divided into:
|
|
|
|
- TKey boards. PCB designs including schematics, Bill of Material (BOM)
|
|
and layout, as needed for development, production and and general usage
|
|
of the TKey devices
|
|
|
|
- TKey programmer. SW, PCB designs including schematics, Bill of
|
|
Material (BOM) and layout, as needed for development, production
|
|
and and provisioning, programming general usage
|
|
|
|
- USB to UART controller. FW for the MCU implementing the USB host
|
|
interface on the TKey
|
|
|
|
- application_fpga. FPGA design with cores including CPU and memory that
|
|
implements the secure application platform
|
|
|
|
- application_fpga FW. The base software running on the CPU as needed to
|
|
boot, load applications, measure applications, dderive base secret etc
|
|
|
|
- One or more applications loaded onto the application_fpga to provide
|
|
some functionality to the user of the host
|
|
|
|
- host side application loader. Software that talks to the FW in the
|
|
application_fpga to load a secure application
|
|
|
|
- host side boot, management. Support software to boot, authenticate
|
|
the TKey device connected to a host
|
|
|
|
- host side secure application. Software that communicates with the
|
|
secure application running in the application_fpga as needed to solve
|
|
a security objective
|
|
|
|
- application_fpga FW SDK. Tools, libraries, documentation and examples
|
|
to support development of the application_fpga firmware
|
|
|
|
- secure application SDK. Tools, libraries, documentation and examples
|
|
to support development of the secure applications to be loaded onto
|
|
the application_fpga
|
|
|
|
- host side secure application SDK. Tools, libraries, documentation and
|
|
examples to support development of the host applications
|
|
|
|
|
|
## References
|
|
More detailed information about the software running on the device
|
|
(referred to firmware, SDK, and secure application), can be found in
|
|
the [software document](software.md).
|