OpenPGP smartcard under GNOME on Debian 10 Buster

Debian buster is almost released, and today I celebrate midsummer by installing (a pre-release) of it on my Lenovo X201 laptop. Everything went smooth, except for the usual issues with smartcards under GNOME. I use a FST-01G running Gnuk, but the same issue apply to all OpenPGP cards including YubiKeys. I wrote about this problem for earlier releases, read Smartcards on Debian 9 Stretch and Smartcards on Debian 8 Jessie. Some things have changed – now GnuPG‘s internal ccid support works, and dirmngr is installed by default when you install Debian with GNOME. I thought I’d write a new post for the new release.

After installing Debian and logging into GNOME, I start a terminal and attempt to use the smartcard as follows.

jas@latte:~$ gpg --card-status
gpg: error getting version from 'scdaemon': No SmartCard daemon
gpg: OpenPGP card not available: No SmartCard daemon
jas@latte:~$ 

The reason is that the scdaemon package is not installed. Install it as follows.

jas@latte:~$ sudo apt-get install scdaemon

After this, gpg --card-status works. It is now using GnuPG’s internal CCID library, which appears to be working. The pcscd package is not required to get things working any more — however installing it also works, and you might need pcscd if you use other applications that talks to the smartcard.

jas@latte:~$ Reader ...........: Free Software Initiative of Japan Gnuk (FSIJ-1.2.14-67252015) 00 00
Application ID ...: D276000124010200FFFE672520150000
Version ..........: 2.0
Manufacturer .....: unmanaged S/N range
Serial number ....: 67252015
Name of cardholder: Simon Josefsson
Language prefs ...: sv
Sex ..............: man
URL of public key : https://josefsson.org/key-20190320.txt
Login data .......: jas
Signature PIN ....: inte tvingad
Key attributes ...: ed25519 cv25519 ed25519
Max. PIN lengths .: 127 127 127
PIN retry counter : 3 3 3
Signature counter : 710
KDF setting ......: off
Signature key ....: A3CC 9C87 0B9D 310A BAD4  CF2F 5172 2B08 FE47 45A2
      created ....: 2019-03-20 23:40:49
Encryption key....: A9EC 8F4D 7F1E 50ED 3DEF  49A9 0292 3D7E E76E BD60
      created ....: 2019-03-20 23:40:26
Authentication key: CA7E 3716 4342 DF31 33DF  3497 8026 0EE8 A9B9 2B2B
      created ....: 2019-03-20 23:40:37
General key info..: [none]
jas@latte:~$ 

As before, using the key does not work right away:

jas@latte:~$ echo foo|gpg -a --sign
gpg: no default secret key: No public key
gpg: signing failed: No public key
jas@latte:~$ 

This is because GnuPG does not have the public key that correspond to the private key inside the smartcard.

jas@latte:~$ gpg --list-keys
jas@latte:~$ gpg --list-secret-keys
jas@latte:~$ 

You may retrieve your public key from the clouds as follows. With Debian Buster, the dirmngr package is installed by default so there is no need to install it. Alternatively, if you configured your smartcard with a public key URL that works, you may type “retrieve” into the gpg --card-edit interactive interface. This could be considered slightly more reliable (at least from a self-hosting point of view), because it uses your configured URL for retrieving the public key rather than trusting clouds.

jas@latte:~$ gpg --recv-keys "A3CC 9C87 0B9D 310A BAD4  CF2F 5172 2B08 FE47 45A2"
gpg: key D73CF638C53C06BE: public key "Simon Josefsson <simon@josefsson.org>" imported
gpg: marginals needed: 3  completes needed: 1  trust model: pgp
gpg: depth: 0  valid:   2  signed:   0  trust: 0-, 0q, 0n, 0m, 0f, 2u
gpg: next trustdb check due at 2019-10-22
gpg: Total number processed: 1
gpg:               imported: 1
jas@latte:~$ 

Now signing with the smart card works! Yay! Btw: compare the output size with the output size in the previous post to understand the size advantage with Ed25519 over RSA.

jas@latte:~$ echo foo|gpg -a --sign
-----BEGIN PGP MESSAGE-----

owGbwMvMwCEWWKTN8c/ddRHjaa4khlieP//S8vO5OkpZGMQ4GGTFFFkWn5nTzj3X
kGvXlfP6MLWsTCCFDFycAjARscUM/5MnXTF9aSG4ScVa3sDiB2//nPSVz13Mkpbo
nlzSezowRZrhn+Ky7/O6M7XljzzJvtJhfPvOyS+rpyqJlD+buumL+/eOPywA
=+WN7
-----END PGP MESSAGE-----

As before, encrypting to myself does not work smoothly because of the trust setting on the public key. Witness the problem here:

jas@latte:~$ echo foo|gpg -a --encrypt -r simon@josefsson.org
gpg: 02923D7EE76EBD60: There is no assurance this key belongs to the named user

sub  cv25519/02923D7EE76EBD60 2019-03-20 Simon Josefsson <simon@josefsson.org>
 Primary key fingerprint: B1D2 BD13 75BE CB78 4CF4  F8C4 D73C F638 C53C 06BE
      Subkey fingerprint: A9EC 8F4D 7F1E 50ED 3DEF  49A9 0292 3D7E E76E BD60

It is NOT certain that the key belongs to the person named
in the user ID.  If you *really* know what you are doing,
you may answer the next question with yes.

Use this key anyway? (y/N) 
gpg: signal Interrupt caught ... exiting

jas@latte:~$

You update the trust setting with the gpg --edit-key command. Take note that this is not the general way of getting rid of the “There is no assurance this key belongs to the named user” warning — using a ultimate trust setting is normally only relevant for your own keys, which is the case here.

jas@latte:~$ gpg --edit-key simon@josefsson.org
gpg (GnuPG) 2.2.12; Copyright (C) 2018 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Secret subkeys are available.

pub  ed25519/D73CF638C53C06BE
     created: 2019-03-20  expires: 2019-10-22  usage: SC  
     trust: unknown       validity: unknown
ssb  cv25519/02923D7EE76EBD60
     created: 2019-03-20  expires: 2019-10-22  usage: E   
     card-no: FFFE 67252015
ssb  ed25519/80260EE8A9B92B2B
     created: 2019-03-20  expires: 2019-10-22  usage: A   
     card-no: FFFE 67252015
ssb  ed25519/51722B08FE4745A2
     created: 2019-03-20  expires: 2019-10-22  usage: S   
     card-no: FFFE 67252015
[ unknown] (1). Simon Josefsson <simon@josefsson.org>

gpg> trust
pub  ed25519/D73CF638C53C06BE
     created: 2019-03-20  expires: 2019-10-22  usage: SC  
     trust: unknown       validity: unknown
ssb  cv25519/02923D7EE76EBD60
     created: 2019-03-20  expires: 2019-10-22  usage: E   
     card-no: FFFE 67252015
ssb  ed25519/80260EE8A9B92B2B
     created: 2019-03-20  expires: 2019-10-22  usage: A   
     card-no: FFFE 67252015
ssb  ed25519/51722B08FE4745A2
     created: 2019-03-20  expires: 2019-10-22  usage: S   
     card-no: FFFE 67252015
[ unknown] (1). Simon Josefsson <simon@josefsson.org>

Please decide how far you trust this user to correctly verify other users' keys
(by looking at passports, checking fingerprints from different sources, etc.)

  1 = I don't know or won't say
  2 = I do NOT trust
  3 = I trust marginally
  4 = I trust fully
  5 = I trust ultimately
  m = back to the main menu

Your decision? 5
Do you really want to set this key to ultimate trust? (y/N) y

pub  ed25519/D73CF638C53C06BE
     created: 2019-03-20  expires: 2019-10-22  usage: SC  
     trust: ultimate      validity: unknown
ssb  cv25519/02923D7EE76EBD60
     created: 2019-03-20  expires: 2019-10-22  usage: E   
     card-no: FFFE 67252015
ssb  ed25519/80260EE8A9B92B2B
     created: 2019-03-20  expires: 2019-10-22  usage: A   
     card-no: FFFE 67252015
ssb  ed25519/51722B08FE4745A2
     created: 2019-03-20  expires: 2019-10-22  usage: S   
     card-no: FFFE 67252015
[ unknown] (1). Simon Josefsson <simon@josefsson.org>
Please note that the shown key validity is not necessarily correct
unless you restart the program.

gpg> quit
jas@latte:~$

Confirm gpg --list-keys indicate that the key is now trusted, and encrypting to yourself should work.

jas@latte:~$ gpg --list-keys
/home/jas/.gnupg/pubring.kbx
----------------------------
pub   ed25519 2019-03-20 [SC] [expires: 2019-10-22]
      B1D2BD1375BECB784CF4F8C4D73CF638C53C06BE
uid           [ultimate] Simon Josefsson <simon@josefsson.org>
sub   ed25519 2019-03-20 [A] [expires: 2019-10-22]
sub   ed25519 2019-03-20 [S] [expires: 2019-10-22]
sub   cv25519 2019-03-20 [E] [expires: 2019-10-22]

jas@latte:~$ gpg --list-secret-keys
/home/jas/.gnupg/pubring.kbx
----------------------------
sec#  ed25519 2019-03-20 [SC] [expires: 2019-10-22]
      B1D2BD1375BECB784CF4F8C4D73CF638C53C06BE
uid           [ultimate] Simon Josefsson <simon@josefsson.org>
ssb>  ed25519 2019-03-20 [A] [expires: 2019-10-22]
ssb>  ed25519 2019-03-20 [S] [expires: 2019-10-22]
ssb>  cv25519 2019-03-20 [E] [expires: 2019-10-22]

jas@latte:~$ echo foo|gpg -a --encrypt -r simon@josefsson.org
gpg: checking the trustdb
gpg: marginals needed: 3  completes needed: 1  trust model: pgp
gpg: depth: 0  valid:   1  signed:   0  trust: 0-, 0q, 0n, 0m, 0f, 1u
gpg: next trustdb check due at 2019-10-22
-----BEGIN PGP MESSAGE-----

hF4DApI9fuduvWASAQdA4FIwM27EFqNK1I5eZERaZVDAXJDmYLZQHjZD8TexT3gw
7SDaeTLm7s0QSyKtsRugRpex6eSVhfA3WG8fUOyzbNv4o7AC/TQdhZ2TDtXZGFtY
0j8BRYIjVDbYOIp1NM3kHnMGHWEJRsTbtLCitMWmLdp4C98DE/uVkwjw98xEJauR
/9ZNmmvzuWpaHuEJNiFjORA=
=tAXh
-----END PGP MESSAGE-----
jas@latte:~$ 

The issue with OpenSSH and GNOME Keyring still exists as in previous releases.

jas@latte:~$ ssh-add -L
The agent has no identities.
jas@latte:~$ echo $SSH_AUTH_SOCK 
/run/user/1000/keyring/ssh
jas@latte:~$ 

The trick we used last time still works, and as far as I can tell, it is still the only recommended method to disable the gnome-keyring ssh component. Notice how we also configure GnuPG’s gpg-agent to enable SSH daemon support.

jas@latte:~$ mkdir ~/.config/autostart
jas@latte:~$ cp /etc/xdg/autostart/gnome-keyring-ssh.desktop ~/.config/autostart/
jas@latte:~$ echo 'Hidden=true' >> ~/.config/autostart/gnome-keyring-ssh.desktop 
jas@latte:~$ echo enable-ssh-support >> ~/.gnupg/gpg-agent.conf 

Log out of GNOME and log in again. Now the environment variable points to gpg-agent’s socket, and SSH authentication using the smartcard works.

jas@latte:~$ echo $SSH_AUTH_SOCK 
/run/user/1000/gnupg/S.gpg-agent.ssh
jas@latte:~$ ssh-add -L
ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAILzCFcHHrKzVSPDDarZPYqn89H5TPaxwcORgRg+4DagE cardno:FFFE67252015
jas@latte:~$ 

Topics for further discussion and research this time around includes:

  1. Should scdaemon (and possibly pcscd) be pre-installed on Debian desktop systems?
  2. Could gpg --card-status attempt to import the public key and secret key stub automatically? Alternatively, some new command that automate the bootstrapping of a new smartcard.
  3. Should GNOME keyring support smartcards?
  4. Why is GNOME keyring used by default for SSH rather than gpg-agent?
  5. Should gpg-agent default to enable the SSH daemon?
  6. What could be done to automatically infer the trust setting for a smartcard based private key?

Thanks for reading and happy smartcarding!

Installing Gnuk on FST-01G running NeuG

The FST-01G device that you order from the FSF shop runs NeuG. To be able to use the device as a OpenPGP smartcard, you need to install Gnuk. While Niibe covers this on his tutorial, I found the steps a bit complicated to follow. The following guides you from buying the device to getting a FST-01G running Gnuk ready for use with GnuPG.

Once you have received the device and inserted it into a USB port, your kernel log (sudo dmesg) will show something like the following:

[628772.874658] usb 1-1.5.1: New USB device found, idVendor=234b, idProduct=0004
[628772.874663] usb 1-1.5.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[628772.874666] usb 1-1.5.1: Product: Fraucheky
[628772.874669] usb 1-1.5.1: Manufacturer: Free Software Initiative of Japan
[628772.874671] usb 1-1.5.1: SerialNumber: FSIJ-0.0
[628772.875204] usb-storage 1-1.5.1:1.0: USB Mass Storage device detected
[628772.875452] scsi host6: usb-storage 1-1.5.1:1.0
[628773.886539] scsi 6:0:0:0: Direct-Access     FSIJ     Fraucheky        1.0  PQ: 0 ANSI: 0
[628773.887522] sd 6:0:0:0: Attached scsi generic sg2 type 0
[628773.888931] sd 6:0:0:0: [sdb] 128 512-byte logical blocks: (65.5 kB/64.0 KiB)
[628773.889558] sd 6:0:0:0: [sdb] Write Protect is off
[628773.889564] sd 6:0:0:0: [sdb] Mode Sense: 03 00 00 00
[628773.890305] sd 6:0:0:0: [sdb] No Caching mode page found
[628773.890314] sd 6:0:0:0: [sdb] Assuming drive cache: write through
[628773.902617]  sdb:
[628773.906066] sd 6:0:0:0: [sdb] Attached SCSI removable disk

The device comes up as a USB mass storage device. Conveniently, it contain documentation describing what it is, and you identify the version of NeuG it runs as follows.

jas@latte:~/src/gnuk$ head /media/jas/Fraucheky/README 
NeuG - a true random number generator implementation (for STM32F103)

							  Version 1.0.7
							     2018-01-19
						           Niibe Yutaka
				      Free Software Initiative of Japan

To convert the device into the serial-mode that is required for the software upgrade, use the eject command for the device (above it came up as /dev/sdb): sudo eject /dev/sdb. The kernel log will now contain something like this:

[628966.847387] usb 1-1.5.1: reset full-speed USB device number 27 using ehci-pci
[628966.955723] usb 1-1.5.1: device firmware changed
[628966.956184] usb 1-1.5.1: USB disconnect, device number 27
[628967.115322] usb 1-1.5.1: new full-speed USB device number 28 using ehci-pci
[628967.233272] usb 1-1.5.1: New USB device found, idVendor=234b, idProduct=0001
[628967.233277] usb 1-1.5.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[628967.233280] usb 1-1.5.1: Product: NeuG True RNG
[628967.233283] usb 1-1.5.1: Manufacturer: Free Software Initiative of Japan
[628967.233286] usb 1-1.5.1: SerialNumber: FSIJ-1.0.7-67252015
[628967.234034] cdc_acm 1-1.5.1:1.0: ttyACM0: USB ACM device

The strings NeuG True RNG and FSIJ-1.0.7 suggest it is running NeuG version 1.0.7.

Now both Gnuk itself and reGNUal needs to be built, as follows. If you get any error message, you likely don’t have the necessary dependencies installed.

jas@latte:~/src$ git clone https://salsa.debian.org/gnuk-team/gnuk/neug.git
jas@latte:~/src$ git clone https://salsa.debian.org/gnuk-team/gnuk/gnuk.git
jas@latte:~/src$ cd gnuk/src/
jas@latte:~/src/gnuk/src$ git submodule update --init
jas@latte:~/src/gnuk/src$ ./configure --vidpid=234b:0000
...
jas@latte:~/src/gnuk/src$ make
...
jas@latte:~/src/gnuk/src$ cd ../regnual/
jas@latte:~/src/gnuk/regnual$ make
jas@latte:~/src/gnuk/regnual$ cd ../../

You are now ready to flash the device, as follows.

jas@latte:~/src$ sudo neug/tool/neug_upgrade.py -f gnuk/regnual/regnual.bin gnuk/src/build/gnuk.bin 
gnuk/regnual/regnual.bin: 4544
gnuk/src/build/gnuk.bin: 113664
CRC32: 931cab51

Device: 
Configuration: 1
Interface: 1
20000e00:20005000
Downloading flash upgrade program...
start 20000e00
end   20001f00
# 20001f00: 31 : 196
Run flash upgrade program...
Wait 3 seconds...
Device: 
08001000:08020000
Downloading the program
start 08001000
end   0801bc00
jas@latte:~/src$ 

Remove and insert the device and the kernel log should contain something like this:

[629120.399875] usb 1-1.5.1: new full-speed USB device number 32 using ehci-pci
[629120.511003] usb 1-1.5.1: New USB device found, idVendor=234b, idProduct=0000
[629120.511008] usb 1-1.5.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[629120.511011] usb 1-1.5.1: Product: Gnuk Token
[629120.511014] usb 1-1.5.1: Manufacturer: Free Software Initiative of Japan
[629120.511017] usb 1-1.5.1: SerialNumber: FSIJ-1.2.14-67252015

The device can now be used with GnuPG as a smartcard device.

jas@latte:~/src/gnuk$ gpg --card-status
Reader ...........: 234B:0000:FSIJ-1.2.14-67252015:0
Application ID ...: D276000124010200FFFE672520150000
Version ..........: 2.0
Manufacturer .....: unmanaged S/N range
Serial number ....: 67252015
Name of cardholder: [not set]
Language prefs ...: [not set]
Sex ..............: unspecified
URL of public key : [not set]
Login data .......: [not set]
Signature PIN ....: forced
Key attributes ...: rsa2048 rsa2048 rsa2048
Max. PIN lengths .: 127 127 127
PIN retry counter : 3 3 3
Signature counter : 0
Signature key ....: [none]
Encryption key....: [none]
Authentication key: [none]
General key info..: [none]
jas@latte:~/src/gnuk$ 

Congratulations!

OpenPGP Smartcards and GNOME

The combination of GnuPG and a OpenPGP smartcard has been implemented and working for almost a decade. I recall starting to use it when I received a FSFE Fellowship card in 2006. Today I’m using a YubiKey NEO. Sadly there has been some regressions when using them under GNOME recently. I reinstalled my laptop with Debian Jessie (beta2) recently, and now took the time to work through the issue and write down a workaround.

To work with GnuPG and smartcards you install GnuPG agent, scdaemon, pscsd and pcsc-tools. On Debian you can do it like this:

apt-get install gnupg-agent scdaemon pcscd pcsc-tools

Use the pcsc_scan command line tool to make sure pcscd recognize the smartcard before continuing, if that doesn’t recognize the smartcard nothing beyond this point will work. The next step is to make sure you have the following line in ~/.gnupg/gpg.conf:

use-agent

Logging out and into GNOME should start gpg-agent for you, through the /etc/X11/Xsession.d/90gpg-agent script. In theory, this should be all that is required. However, when you start a terminal and attempt to use the smartcard through GnuPG you would get an error like this:

jas@latte:~$ gpg --card-status
gpg: selecting openpgp failed: unknown command
gpg: OpenPGP card not available: general error
jas@latte:~$

The reason is that the GNOME Keyring hijacks the GnuPG agent’s environment variables and effectively replaces gpg-agent with gnome-keyring-daemon which does not support smartcard commands (Debian bug #773304). GnuPG uses the environment variable GPG_AGENT_INFO to find the location of the agent socket, and when the GNOME Keyring is active it will typically look like this:

jas@latte:~$ echo $GPG_AGENT_INFO 
/run/user/1000/keyring/gpg:0:1
jas@latte:~$ 

If you use GnuPG with a smartcard, I recommend to disable GNOME Keyring’s GnuPG and SSH agent emulation code. This used to be easy to achieve in older GNOME releases (e.g., the one included in Debian Wheezy), through the gnome-session-properties GUI. Sadly there is no longer any GUI for disabling this functionality (Debian bug #760102). The GNOME Keyring GnuPG/SSH agent replacement functionality is invoked through the XDG autostart mechanism, and the documented way to disable system-wide services for a normal user account is to invoke the following commands.

jas@latte:~$ mkdir ~/.config/autostart
jas@latte:~$ cp /etc/xdg/autostart/gnome-keyring-gpg.desktop ~/.config/autostart/
jas@latte:~$ echo 'Hidden=true' >> ~/.config/autostart/gnome-keyring-gpg.desktop 
jas@latte:~$ cp /etc/xdg/autostart/gnome-keyring-ssh.desktop ~/.config/autostart/
jas@latte:~$ echo 'Hidden=true' >> ~/.config/autostart/gnome-keyring-ssh.desktop 
jas@latte:~$ 

You now need to logout and login again. When you start a terminal, you can look at the GPG_AGENT_INFO environment variable again and everything should be working again.

jas@latte:~$ echo $GPG_AGENT_INFO 
/tmp/gpg-dqR4L7/S.gpg-agent:1890:1
jas@latte:~$ echo $SSH_AUTH_SOCK 
/tmp/gpg-54VfLs/S.gpg-agent.ssh
jas@latte:~$ gpg --card-status
Application ID ...: D2760001240102000060000000420000
...
jas@latte:~$ ssh-add -L
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDFP+UOTZJ+OXydpmbKmdGOVoJJz8se7lMs139T+TNLryk3EEWF+GqbB4VgzxzrGjwAMSjeQkAMb7Sbn+VpbJf1JDPFBHoYJQmg6CX4kFRaGZT6DHbYjgia59WkdkEYTtB7KPkbFWleo/RZT2u3f8eTedrP7dhSX0azN0lDuu/wBrwedzSV+AiPr10rQaCTp1V8sKbhz5ryOXHQW0Gcps6JraRzMW+ooKFX3lPq0pZa7qL9F6sE4sDFvtOdbRJoZS1b88aZrENGx8KSrcMzARq9UBn1plsEG4/3BRv/BgHHaF+d97by52R0VVyIXpLlkdp1Uk4D9cQptgaH4UAyI1vr cardno:006000000042
jas@latte:~$ 

That’s it. Resolving this properly involves 1) adding smartcard code to the GNOME Keyring, 2) disabling the GnuPG/SSH replacement code in GNOME Keyring completely, 3) reorder the startup so that gpg-agent supersedes gnome-keyring-daemon instead of vice versa, so that people who installed the gpg-agent really gets it instead of the GNOME default, or 4) something else. I don’t have a strong opinion on how to solve this, but 3) sounds like a simple way forward.