gnuk/README

Gnuk - An Implementation of USB Cryptographic Token for GnuPG

							    Version 2.2
							     2024-04-20
							   Niibe Yutaka
				      Free Software Initiative of Japan

Release Notes
=============

This is the release of Gnuk, version 2.2, which has major clean up
from Gnuk 1.2.  Many (questionable) features have been removed.

It has supports of Ed25519 and X25519 (ECDH on Curve25519).  It also
has experimental support of Ed448 and X448.

It supports the KDF-DO feature.  You need to prepare the KDF-DO on
your token by the card-edit/kdf-setup command of GnuPG.

With FST-01SZ and GNU/Linux emulation, experimental ack button support
is available for test.


What's Gnuk?
============

Gnuk is an implementation of USB cryptographic token for GNU Privacy
Guard.  Gnuk supports OpenPGP card protocol version 3, and it runs on
STM32F103 processor (and its compatible).

I wish that Gnuk will be a developer's soother who uses GnuPG.  I have
been nervous of storing secret key(s) on usual secondary storage.
There is a solution with OpenPGP card, but it is not the choice for
me, as card reader is not common device.  With Gnuk, this issue will
be solved by a USB token.

Please look at the graphics of "gnuk.svg" for the software name.  My
son used to be with his NUK(R), always, everywhere.  Now, I am with a
USB Cryptographic Token by "Gnuk", always, everywhere.


FAQ
===

Q0: How Gnuk USB Token is superior than other solutions (OpenPGP
    card 2.0/3.3/3.4, YubiKey, etc.) ?
    https://www.g10code.de/p-card.html
    https://www.yubico.com/
A0: Good points of Gnuk are:
    * If you have skill of electronics and like DIY, you can build
      Gnuk Token cheaper (see Q8-A8).
    * You can study Gnuk to modify and to enhance.  For example, you
      can implement your own authentication method with some sensor
      such as an acceleration sensor.
    * It is "of Free Software"; Gnuk is distributed under GPLv3+,
	    "by Free Software"; Gnuk development requires only Free Software
				(GNU Toolchain, Python, etc.), 
	    "for Free Software"; Gnuk supports GnuPG.

Q1: What kind of key algorithm is supported?
A1: Gnuk version 2.1 supports Ed25519, Ed448, X25519 and X448.

Q2: How long does it take for digital signing?
A2: It takes less than a second for ECC.

Q3: What's your recommendation for target board?
A3: Orthodox choice is Olimex STM32-H103.
    FST-01SZ (Flying Stone Tiny 01 SZ) is available for sale, and it
    is a kind of the best choice, hopefully.  If you have a skill of
    electronics, STM32 Nucleo F103 is the best choice for experiment.

Q4: What's version of GnuPG are you using?
A4: In Debian GNU/Linux system, I use GnuPG modern 2.4.1.

Q5: What's version of pcscd and libccid are you using?
A5: I don't use them, pcscd and libccid are optional, you can use Gnuk
    Token without them.

Q6: What kinds of hardware is required for development?
A6: You need a target board plus a JTAG/SWD debugger.  If you just
    want to test Gnuk for target boards with DfuSe, JTAG debugger is
    not the requirement.  Note that for real use, you need JTAG/SWD
    debugger to enable flash ROM protection.

Q7: How much does it cost?
A7: Olimex STM32-H103 plus ARM-USB-TINY-H cost 70 Euro or so.

Q8: How much does it cost for DIY version?
A8: STM32 Nucleo F103 costs about $10 USD.

Qd: Do you know a good SWD debugger to connect FST-01 or something?
Ad: ST-Link/V2 is cheap one.  We have a tool/stlinkv2.py as flash ROM
    writer program.  STM32 Nucleo F103 comes with the valiant of
    ST-Link/V2.  Note that the firmware of ST-Link/V2 is proprietary.
    So, in case of transparency matters, ST-Link/V2 would not be your
    choice.
    I care transparency for our process of manufacturing FST-01SZ (and
    better control by Free Software, in general), thus, I develop
    BBG-SWD, SWD debugger by BeagleBone Green.
    I use ST-Link/V2 for daily development.  For serious task like
    flashing product, I use BBG-SWD.


Tested features
===============

Gnuk is tested by test suite.  Please see the "tests" directory.

	* Personalization of the card
	  * Changing Login name, URL, Name, Sex, Language, etc.
	* Password handling (PW1, RC, PW3)
	* Key import for three types:
	  * key for digital signing
	  * key for decryption
	  * key for authentication
	* PSO: Digital Signature
	* PSO: Decipher
	* INTERNAL AUTHENTICATE
	* Changing value of password status bytes (0x00C4): forcesig
	* Card holder certificate (read)
	* Removal of keys
	* Key generation on device side
	* Overriding key import

Original features of Gnuk, tested manually lightly:

	* OpenPGP card serial number setup
	* Card holder certificate (write by UPDATE BINARY)
	* Upgrading with "EXTERNAL AUTHENTICATE" by reGNUal


Targets
=======

We use Olimex STM32-H103 board and Flying Stone Tiny 01 (FST-01).

With DfuSe support, STBee is also our targets.  But this target with
DfuSe is for experiment only, because it is impossible for DfuSe to
disable read from flash.  For real use, please consider killing DfuSe
and enabling read protection using JTAG debugger.


Build system and Host system
============================

Makefile is written for GNU make.  You need Bash 4.x for configure.

If your bash is not installed as /bin/bash, you need to run configure
script prepending 'bash' before './configure'.

Some tools are written in Python.  If your Python is not installed as
/usr/bin/python, please prepend 'python' or 'python3' for your command
invocation.  I use Python 3.11, PyUSB 1.2.2, CFFI 1.15.1.


Source code
===========

Gnuk source code is under src/ directory.

Note that SHA-2 hash function implementation, src/sha256.c, is based
on the original implementation by Dr. Brian Gladman.  See:

  https://web.archive.org/web/20140314032610/http://gladman.plushost.co.uk/oldsite/cryptography_technology/sha/index.php


License
=======

It is distributed under GNU General Public Licence version 3 or later
(GPLv3+).  Please see src/COPYING.

Please note that it is distributed with external source code too.
Please read relevant licenses for external source code as well.

The author(s) of Gnuk expect users of Gnuk will be able to access the
source code of Gnuk, so that users can study the code and can modify
if needed.  This doesn't mean person who has a Gnuk Token should be
able to access everything on the Token, regardless of its protections.
Private keys, and other information should be protected properly.


External source code
====================

Gnuk is distributed with external source code.

* chopstx/  -- Chopstx 2.5

  We use Chopstx as the kernel for Gnuk.

  Chopstx is distributed under GPLv3+ (with a special exception).


USB vendor ID and product ID (USB device ID)
============================================

When you have a vendor ID and assign a product ID for Gnuk, edit the
file GNUK_USB_DEVICE_ID and add an entry for yours.  In this case,
please contact Niibe, so that it is listed to the file in the official
release of the source code.

When you are modifing Gnuk and installing the binary to device, you
should replace the vendor string and serial number to yours (in the
file GNUK_USB_DEVICE_ID and SERIALNO of the script of src/configure),
so that users can see it's not by original vendor, and it is modified
version.

FSIJ allows you to use USB device ID of FSIJ (234b:0000) for devices
with Gnuk under one of following conditions:

  * For everyone for experimental purpose:

    - You must not distribute a binary with FSIJ's USB device ID, but
      must use the binary by yourself only for your experiment.  Note
      that "Distributing binary" includes distributing a device which
      holds the binary.

  * For general individuals:

    - You must use your Gnuk device with a card serial number which is
      *not* by FSIJ.  Easy one would be a card serial number generated
      by chip unique ID.

  * For individuals with explicit permission from FSIJ.

    - You should have an assigned card serial number by FSIJ,
      please use that number for your device.
      (There a file 'GNUK_SERIAL_NUMBER' in the official release.)

FSIJ could give companies or business entities "second source
manufacturer" license to use USB device ID of FSIJ for devices with
unmodified version of Gnuk, provided they support Free Software and
respect users' freedom for computing.  Please ask FSIJ for the
license.

Otherwise, companies which want to distribute Gnuk devices, please use
your own USB vendor ID and product ID.  Please replace vendor string
and possibly product string to yours, when you modify Gnuk.


Host Requirements
=================

For GNU/Linux, PC/SC service is an option, you can use GnuPG's
internal CCID driver instead.  If you chose using PC/SC service,
libccid version >= 1.3.11 is recommended for GNU/Linux.


How to compile
==============

You need GNU toolchain and newlib for 'arm-none-eabi' target.

On Debian we can install the packages of gcc-arm-none-eabi
and its friends.  I'm using:

	binutils-arm-none-eabi	2.41.90.20240115-1+23
	gcc-arm-none-eabi 	15:13.2.rel1-2
	picolibc-arm-none-eabi	1.8.6-2
	gdb-multiarch 		13.2-1

Change directory to `src':

  $ cd gnuk-VERSION/src

Then, run `configure':

  $ ./configure --vidpid=<VID:PID>

Here, you need to specify USB vendor ID and product ID.  For FSIJ's,
it's: --vidpid=234b:0000 .  Please read section 'USB vendor ID and
product ID' above.


Then, type:

  $ make

Then, we will have "gnuk.elf" under src/build directory.

If you are not the authorized vendor, please never distribute this
file of "gnuk.elf", which includes VID:PID in the image.  If you would
like to distribute the image (for example, to check if it's
reproducible or not), the file "gnuk-no-vidpid.elf" is the one with no
VID:PID.


How to install
==============

Olimex STM32-H103 board
-----------------------

If you are using Olimex JTAG-Tiny, type following to invoke OpenOCD
and write "gnuk.elf" to Flash ROM:

  $ openocd -f interface/ftdi/olimex-jtag-tiny.cfg \
            -f board/olimex_stm32_h103.cfg \
            -c "program build/gnuk.elf verify reset exit"

Command invocation is assumed in src/ directory.


Flying Stone Tiny 01
--------------------

If you are using Flying Stone Tiny 01, you need a SWD writer.

OpenOCD 0.12.0 supports ST-Link/V2.  We can use it like:

  $ openocd -f interface/stlink.cfg -f target/stm32f1x.cfg \
            -c "program build/gnuk.elf verify reset exit"


STBee
-----

Note that this is only for your experiment; Your private key materials
on the board can be accessed by DfuSe.

Reset the board with "USER" switch pushed.  Type following to write
to flash:

  # cd ../tool
  # ./dfuse.py ../src/build/gnuk.hex

Then, reset the board.


How to protect flash ROM
========================

To protect, invoke OpenOCD like (for FST-01):

  $ openocd -f interface/stlink.cfg -f target/stm32f1x.cfg \
            -c init -c "reset halt" -c "stm32f1x lock 0" -c reset -c exit

After power-off / power-on sequence, the contents of flash ROM cannot
be accessible from JTAG debugger.

Unprotecting is:

  $ openocd -f interface/stlink.cfg -f target/stm32f1x.cfg \
            -c init -c "reset halt" -c "stm32f1x unlock 0" -c reset -c exit

Upon unprotection, flash is erased.

Note that it would be still possible for some implementation of DfuSe
to access the contents, even if it's protected.  If you really want to
protect, killing DfuSe and accessing by JTAG debugger is recommended.


(Optional) Configure serial number and X.509 certificate
========================================================

This is completely optional.

For this procedure, you need python and pyscard (python-pyscard
package in Debian) or PyUSB (python-usb package in Debian).

(1) [pyscard] Stop scdaemon
    [PyUSB] Stop the pcsc daemon.

If scdaemon is running, please kill it, or you will get "Smartcard
Exception" by "Sharing violation".

  $ gpg-connect-agent "SCD KILLSCD" "SCD BYE" /bye

In case of PyUSB tool, you need to stop pcscd.

  # systemctl stop pcscd


(2) [Optional] Write card holder certificate

If you have card holder certificate binary file, you can do:

  $ ../tool/gnuk_put_binary_usb.py ../../<YOUR-CERTIFICATE>.bin
  ../../<YOUR-CERTIFICATE>.bin: <LENGTH-OF-YOUR-CERTIFICATE>
  Updating card holder certificate
  ...


How to run
==========

Testing Gnuk
------------

Type following command to see Gnuk runs:

  $ gpg --card-status


Besides, there is a functionality test under tests/ directory.  See
tests/README.


Personalize the Token, import keys, and change the password
-----------------------------------------------------------

You can personalize the token, putting your information like: Name,
Login name, Sex, Languages, URL.  To do so, GnuPG command is:

  $ gpg --card-edit

Note that the factory setting of user password is "123456" and admin
password is "12345678" as the specification.

It is recommended to create your keys on your host computer, and
import them to Gnuk Token.  After you create your keys (they must be
supported ones by Gnuk Token), you can import them.

Gnuk supports key generation, but this feature should be considered
experimental.

For detail, please see documentation under doc/.  You can see the HTML
version at: https://www.fsij.org/doc-gnuk/


How to debug
============

We can use GDB.

  $ arm-none-eabi-gdb gnuk.elf


Inside GDB, we can connect OpenOCD by:

  (gdb) target remote localhost:3333

or

  (gdb) target extended-remote localhost:3333


You can see the output of PCSCD:

  # /etc/init.d/pcscd stop
  # LIBCCID_ifdLogLevel=7 /usr/sbin/pcscd --debug --foreground


You can observe the traffic of USB using "usbmon".  See the file:
linux/Documentation/usb/usbmon.txt


Firmware update
===============

See doc/note/firmware-update.


Git Repositories
================

Please use: https://salsa.debian.org/gnuk-team/gnuk/

You can get it by:
 
    $ git clone https://salsa.debian.org/gnuk-team/gnuk/gnuk.git

It's also available at: www.gniibe.org
You can browse at: https://git.gniibe.org/cgit/gnuk/gnuk.git/

I put Chopstx as a submodule of Git.  Please do this:

    $ git submodule update --init


Information on the Web
======================

For more information, please visit: https://www.fsij.org/gnuk/

Please see the FST-01 support pages:

    https://www.gniibe.org/category/fst-01.html

Please consider to join Gnuk-users mailing list:

    https://lists.gnupg.org/mailman/listinfo/gnuk-users



Your Contributions
==================

FSIJ welcomes your contributions.  Please assign your copyright
to FSIJ (if possible), as I do.


Foot note
==========

* NUK(R) is a registered trademark owend by MAPA GmbH, Germany.
--