GPG Guide

Guide on creating and using GPG keys

WIP (Ctrl-S's job)

Guide for securely creating a PGP keyset. Currently most available smartcards support a maximum of 2048 bit RSA keys. Some smartcards support longer keys. This guide will use 2048 bit RSA keys for as much security as is currently practical.


Preparation

  • Determine where you want to store your secret keys.
  • I suggest in a subfolder on each USB drive.

e.g.
'/media/ubuntu/keystore01/gpg.ctrl-s.2020-02-12'
'/media/ubuntu/keystore02/gpg.ctrl-s.2020-02-12'
'/media/ubuntu/keystore03/gpg.ctrl-s.2020-02-12'

  • Decide how long you want the keys to remain valid.
  • It is supposed to be possible to increase this time at a later time, bot I don't know how this shit works yet.
  • Command notation quickref:
## Double hash symbol(##) This is a comment, just for you to read.
$ nano somefile.txt ## <- Dollar sign ($) That was a command in BASH running as a normal user.
$ sudo nano somefile.txt ## <- That was a regular user using sudo to run a command as root.
# nano somefile.txt ## <- Single hash (#) sign -That was running a command a root.
## (The root account is a superuser with complete authority over the system.)
gpg> help ## <- That was a command inside the gpg program's subshell.


Buy stuff

You will need:

  • 1X Computer.
  • 1X (boot)USB flash drive 16GB+ (32GB+ USB3+ preferred).
  • 3X (keystore) USB flash drive.
  • 1X Pen/pencil.
  • 3X Pieces of paper.
  • 1+ Smartcard(s) that support PGP/GPG. (e.g. Yubico Yubikey 5 USB authenticator)


Create Ubuntu LiveUSB Environment

  • Have a USB flash drive (32GB+ USB3+ preferred).
  • Download latest ubuntu desktop ISO. Available from: https://ubuntu.com/download/desktop
  • Have a ubuntu linux environment to install the liveusb from.
  • Install the drive creation tools:
$ sudo add-apt-repository universe
$ sudo add-apt-repository ppa:mkusb/ppa
$ sudo apt-get update
$ sudo apt install --install-recommends mkusb mkusb-nox usb-pack-efi

Find out what storage devices are connected:

$ lsblk
  • Figure out which device is your flash drive.

e.g. /dev/sdh


Write a persistant Ubuntu LiveUSB Environment to the flash drive

  1. Press the windows key on your keyboard to bring up the ubuntu app search screen.
  2. type mkusb
  3. Run the mkusb tool by clicking on it.
  1. Choose: i - "Install (make a boot device)".
  2. Choose: p - "Persistent live – only Debian and Ubuntu".
  3. Select the ubuntu ISO file on your machine.
  4. Select the device that matches your USB drive to install onto.
  5. Choose just: "usb-pack-efi (default grub from ISO file)"
  6. Tell the program how much space to give to the liveUSB ubuntu install for it's own storage, about half of the disk should do (4GB+).
  7. Confirm everything is correct, as continuing with incorrect settings may destroy your data.
  8. If everything is correct, select "go" and click "go".
  9. Wait for the program to write to the USB drive.
  10. Choose: "Quit"
  11. Choose: "Quit"
  12. Press return in the console windows to exit it.

Your USB drive should now be ready to boot from.


Boot liveUSB

  1. Have machine powered off.
  2. Insert bootable USB drive.
  3. Hold F2 while powering on machine until BIOS menun shows up.
  4. Choose to boot from the USB drive.
  5. Ubuntu bootloader should autoselect persistant liveusb
  6. Let machine boot into persistant liveusb
  7. Ubuntu desktop environment should be displayed on your computer.

Update liveUSB software

Open a terminal window by pressing the three keys simultaneously: Ctrl-Alt-T Run the following commands: Check how much free space you have:

 $ df -h

You should see a line containting /media/ubuntu/casper-rw, and it should have at least 1GB of space free. If this is not the case, you probably did not succeed with the previous steps. This alternative command should show only the disk partition we are interested in:

 $ df -h | grep casper-rw

Enable extra apt repositories: (You will need an internet connection for this part.)

$ sudo add-apt-repository universe
$ sudo add-apt-repository multiverse
## Update installed software:
$ sudo apt update # Update information about what software packages are available.
$ sudo apt upgrade -y # Upgrade to the latest available version of installed packages.


Enable smartcard support. (generic)

(You will need an internet connection for this part.)

$ sudo apt-get install scdaemon # This package does all the smartcard communication!
$ sudo systemctl start pcscd 
$ sudo systemctl enable pcscd
$ gpg --card-edit list # Test by looking for connected cards

This is an example of expected output with a yubikey 5 with values removed for confidentiality:

$ gpg --card-edit list

Reader ...........: [REMOVED]
Application ID ...: [REMOVED]
Version ..........: 3.4
Manufacturer .....: Yubico
Serial number ....: [REMOVED]
Name of cardholder: [not set]
Language prefs ...: [not set]
Sex ..............: unspecified
URL of public key : [not set]
Login data .......: [not set]
Signature PIN ....: not forced
Key attributes ...: rsa2048 rsa2048 rsa2048
Max. PIN lengths .: 127 127 127
PIN retry counter : 3 0 3
Signature counter : 0
KDF setting ......: on
Signature key ....: [none]
Encryption key....: [none]
Authentication key: [none]
General key info..: [none]

gpg/card>

Remove machine from network

  • Remove all network cables from the machine.
  • Turn off all wifi devices on the machine.
  • Test by running:
$ ping 8.8.8.8
  • You should fail to connect.

Generate keys

  •  !!! BE OFFLINE !!!

GPG Secret keys

  • Create master as demonstrated in the following example:
$  gpg --full-gen-key
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.

Please select what kind of key you want:
   (1) RSA and RSA (default)
   (2) DSA and Elgamal
   (3) DSA (sign only)
   (4) RSA (sign only)
Your selection? 1
RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (3072) 4096
Requested keysize is 4096 bits
Please specify how long the key should be valid.
         0 = key does not expire
      <n>  = key expires in n days
      <n>w = key expires in n weeks
      <n>m = key expires in n months
      <n>y = key expires in n years
Key is valid for? (0) 0
Key does not expire at all
Is this correct? (y/N) y

GnuPG needs to construct a user ID to identify your key.

Real name: fakename
Email address: [email protected]
Comment: fake person comment
You selected this USER-ID:
    "fakename (fake person comment) <[email protected]>"

Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? o
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.
gpg: key BEBEAAF16847B703 marked as ultimately trusted
gpg: directory '/home/pi/.gnupg/openpgp-revocs.d' created
gpg: revocation certificate stored as '/home/pi/.gnupg/openpgp-revocs.d/196CBE3A87E329179CC27B5CBEBEAAF16847B703.rev'
public and secret key created and signed.

pub   rsa4096 2020-02-12 [SC]
      196CBE3A87E329179CC27B5CBEBEAAF16847B703
uid                      fakename (fake person comment) <[email protected]>
sub   rsa4096 2020-02-12 [E]
  • This master key should be 4096 bits in size.
  • When asked: "Please select what kind of key you want:"
    • Choose: "(1) RSA and RSA (default)"
  • When asked: What keysize do you want?
    • Choose: 4096
  • When asked: "Please specify how long the key should be valid."
    • Choose: 0 = key does not expire
  • A hexadecimal 'name' for the key you just generated should be displayed in the console.

Select it, and copy the text to the clipboard by right-clicking the highlighted text and choosing "copy".

    • In the example this keyname was 196CBE3A87E329179CC27B5CBEBEAAF16847B703


Create subkeys for actual use

  • One subkey for each of: Encrypt, Authenticate, Sign
  • These subkeys should each be 2048 bits in size so they can fit onto all common smartcards.
  • (To create subkeys as shown you must use the --expert command-line argument)
$ gpg --expert --edit-key KEYNAME
  • Example of creating subkeys:
$ gpg --expert --edit-key 196CBE3A87E329179CC27B5CBEBEAAF16847B703
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 key is available.

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
sec  rsa4096/BEBEAAF16847B703
     created: 2020-02-12  expires: never       usage: SC
     trust: ultimate      validity: ultimate
ssb  rsa4096/2975948F8F5E65F7
     created: 2020-02-12  expires: never       usage: E
[ultimate] (1). fakename (fake person comment) <[email protected]>

gpg> key 1 ## Selecting the automatically-generated subkey to delete it.

sec  rsa4096/BEBEAAF16847B703
     created: 2020-02-12  expires: never       usage: SC
     trust: ultimate      validity: ultimate
ssb* rsa4096/2975948F8F5E65F7
     created: 2020-02-12  expires: never       usage: E
[ultimate] (1). fakename (fake person comment) <[email protected]>

gpg> delkey ## Deleting the automatically-generated subkey.
Do you really want to delete this key? (y/N) y

sec  rsa4096/BEBEAAF16847B703
     created: 2020-02-12  expires: never       usage: SC
     trust: ultimate      validity: ultimate
[ultimate] (1). fakename (fake person comment) <[email protected]>

gpg> addkey ## Adding a subkey to "Sign" (1/3)...
Please select what kind of key you want:
   (3) DSA (sign only)
   (4) RSA (sign only)
   (5) Elgamal (encrypt only)
   (6) RSA (encrypt only)
   (7) DSA (set your own capabilities)
   (8) RSA (set your own capabilities)
  (10) ECC (sign only)
  (11) ECC (set your own capabilities)
  (12) ECC (encrypt only)
  (13) Existing key
Your selection? 8

Possible actions for a RSA key: Sign Encrypt Authenticate
Current allowed actions: Sign Encrypt

   (S) Toggle the sign capability
   (E) Toggle the encrypt capability
   (A) Toggle the authenticate capability
   (Q) Finished

Your selection? e

Possible actions for a RSA key: Sign Encrypt Authenticate
Current allowed actions: Sign

   (S) Toggle the sign capability
   (E) Toggle the encrypt capability
   (A) Toggle the authenticate capability
   (Q) Finished

Your selection? q
RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (3072) 4096
Requested keysize is 4096 bits
Please specify how long the key should be valid.
         0 = key does not expire
      <n>  = key expires in n days
      <n>w = key expires in n weeks
      <n>m = key expires in n months
      <n>y = key expires in n years
Key is valid for? (0) 0
Key does not expire at all
Is this correct? (y/N) y
Really create? (y/N) y
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.

sec  rsa4096/BEBEAAF16847B703
     created: 2020-02-12  expires: never       usage: SC
     trust: ultimate      validity: ultimate
ssb  rsa4096/203E068632D2C436
     created: 2020-02-12  expires: never       usage: S
[ultimate] (1). fakename (fake person comment) <[email protected]>

gpg> addkey ## Adding a subkey to "Encrypt" (2/3)...
Please select what kind of key you want:
   (3) DSA (sign only)
   (4) RSA (sign only)
   (5) Elgamal (encrypt only)
   (6) RSA (encrypt only)
   (7) DSA (set your own capabilities)
   (8) RSA (set your own capabilities)
  (10) ECC (sign only)
  (11) ECC (set your own capabilities)
  (12) ECC (encrypt only)
  (13) Existing key
Your selection? 8

Possible actions for a RSA key: Sign Encrypt Authenticate
Current allowed actions: Sign Encrypt

   (S) Toggle the sign capability
   (E) Toggle the encrypt capability
   (A) Toggle the authenticate capability
   (Q) Finished

Your selection? s

Possible actions for a RSA key: Sign Encrypt Authenticate
Current allowed actions: Encrypt

   (S) Toggle the sign capability
   (E) Toggle the encrypt capability
   (A) Toggle the authenticate capability
   (Q) Finished

Your selection? q
RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (3072) 4096
Requested keysize is 4096 bits
Please specify how long the key should be valid.
         0 = key does not expire
      <n>  = key expires in n days
      <n>w = key expires in n weeks
      <n>m = key expires in n months
      <n>y = key expires in n years
Key is valid for? (0) 0
Key does not expire at all
Is this correct? (y/N) y
Really create? (y/N) y
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.

sec  rsa4096/BEBEAAF16847B703
     created: 2020-02-12  expires: never       usage: SC
     trust: ultimate      validity: ultimate
ssb  rsa4096/203E068632D2C436
     created: 2020-02-12  expires: never       usage: S
ssb  rsa4096/96F8E1C255A68B9D
     created: 2020-02-12  expires: never       usage: E
[ultimate] (1). fakename (fake person comment) <[email protected]>

gpg> addkey ## Adding a subkey to "Authenticate" (3/3)...
Please select what kind of key you want:
   (3) DSA (sign only)
   (4) RSA (sign only)
   (5) Elgamal (encrypt only)
   (6) RSA (encrypt only)
   (7) DSA (set your own capabilities)
   (8) RSA (set your own capabilities)
  (10) ECC (sign only)
  (11) ECC (set your own capabilities)
  (12) ECC (encrypt only)
  (13) Existing key
Your selection? 8

Possible actions for a RSA key: Sign Encrypt Authenticate
Current allowed actions: Sign Encrypt

   (S) Toggle the sign capability
   (E) Toggle the encrypt capability
   (A) Toggle the authenticate capability
   (Q) Finished

Your selection? s

Possible actions for a RSA key: Sign Encrypt Authenticate
Current allowed actions: Encrypt

   (S) Toggle the sign capability
   (E) Toggle the encrypt capability
   (A) Toggle the authenticate capability
   (Q) Finished

Your selection? e

Possible actions for a RSA key: Sign Encrypt Authenticate
Current allowed actions:

   (S) Toggle the sign capability
   (E) Toggle the encrypt capability
   (A) Toggle the authenticate capability
   (Q) Finished

Your selection? a

Possible actions for a RSA key: Sign Encrypt Authenticate
Current allowed actions: Authenticate

   (S) Toggle the sign capability
   (E) Toggle the encrypt capability
   (A) Toggle the authenticate capability
   (Q) Finished

Your selection? q
RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (3072) 4096
Requested keysize is 4096 bits
Please specify how long the key should be valid.
         0 = key does not expire
      <n>  = key expires in n days
      <n>w = key expires in n weeks
      <n>m = key expires in n months
      <n>y = key expires in n years
Key is valid for? (0) 0
Key does not expire at all
Is this correct? (y/N) y
Really create? (y/N) y
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.

sec  rsa4096/FEEDB00BCODEBEEF
     created: 2020-02-12  expires: never       usage: SC
     trust: ultimate      validity: ultimate
ssb  rsa4096/203E068632D2C436
     created: 2020-02-12  expires: never       usage: S
ssb  rsa4096/96F8E1C255A68B9D
     created: 2020-02-12  expires: never       usage: E
ssb  rsa4096/43685156C4472A6B
     created: 2020-02-12  expires: never       usage: A
[ultimate] (1). fakename (fake person comment) <[email protected]>

gpg>save ## You MUST enter the save command for the keys to be kept!
$ ## Finished creating the subkeys.

Store keys to backup drives

  •  !!! BE OFFLINE !!!
  • Create a folder to store our secret keys:
$ mkdir -vp '/medua/ubuntu/keystore01/gpg.ctrl-s.2020-02-01'
  • Change to the folder where we want to save the keys to:
$ cd '/medua/ubuntu/keystore01/gpg.ctrl-s.2020-02-01'
  • Secret keys:
$ gpg --output KEYNAME-DATE.masterkeys.txt --export-secret-keys --armor KEYNAME
$ gpg --output KEYNAME-DATE.subkeys.txt --export-secret-subkeys --armor KEYNAME
  • Public keys:
$ gpg --export --armor KEYNAME > KEYNAME-DATE.public.key
  • Revocation certificate:
$ gpg --output KEYNAME-DATE.revocation-certificate.asc --gen-revoke KEYNAME
  • SSH public key
$ date; gpg --output "FEEDB00BCODEBEEF-1970JAN01.ssh-remote.key" --armour --export-ssh-key FEEDB00BCODEBEEF


Exporting SSH key

How to generate the ssh public key to put onto a remote server.

$ date; gpg --output "FEEDB00BCODEBEEF-1970JAN01.ssh-remote.key" --armour --export-ssh-key FEEDB00BCODEBEEF


Smartcards

Reset smartcard to factory settings and erase stored GPG keys

  •  ! ONLY TESTED ON Yubikey 5 !
  •  ! USE AT OWN RISK !
  • I don't know if doing a factory reset will affect other functions of your smartcard, such as FIDO, FIDO2, PIV, OTP, etc.
$ date; gpg --card-edit # Begin editing the smartcard.
gpg/card> help # Show commands list.

## Inspect card to be sure it's the one you intend to reset:
gpg/card> list # "list all available data"

gpg/card> admin # Enable card admin commands.
gpg/card> help # Show commands list.

## Perform factory reset on smartcard to bring it to a known-good state
gpg/card> factory-reset # "factory-reset  destroy all keys and data"
## Confirm that you want to reset the card
>y
>yes
## Confirm card has been reset by inspection:
gpg/card> list # "list all available data"
gpg/card>quit

Set the smartcard PIN, adminPIN, & reset code

  • The PIN, AdminPIN, and ResetCode can be alphanumerical passphrases.
 (a-z, A-Z, 0-9, space, etc.)
  • "PIN" - Day-to-day use.
  • "Admin PIN" - Load new key onto card.
  • "Reset Code" - Reset PIN attempts counter.
  • The Default yubikey "PIN" is "123456"
  • The Default Yubikey "Admin PIN" apin is "12345678"
  • Begin editing the smartcard.
$ date; gpg --card-edit # Begin editing the smartcard.
gpg/card> admin
  • Set PIN
gpg/card> passwd # "menu to change or unblock the PIN"
>"1 - change PIN"
  • Set admin PIN (used for installing secret key to card)
gpg/card> passwd # "menu to change or unblock the PIN"
>3 - change Admin PIN
  • Set the Recovery Code (Used for resetting retry counter for PIN)
gpg/card> passwd # "menu to change or unblock the PIN"
>4 - set the Reset Code

Smartcard PIN codes

  • You need to set two PIN codes for your smartcard.


A user PIN and an admin PIN

  • Generate a random number to use as a PIN for your smartcard

(apg is a linux tool to generate random passwords https://linux.die.net/man/1/apg )

## apg (Password generator program)
## -a 1 (Use supplied parameters)
## -M N (Use numerals only)
## -m 10 (Minimum 8 characters long)
## -x 10 (Maximum 8 characters long)
$ apg -a 1 -M N -m 8 -x 8
86187171
65856553
45100116
18826756
02283057
10274420
  • Write down the user PIN code on your paper.

User PIN: USER-PIN-HERE
The user PIN is required to use the stored keys.

  • Write down the admin PIN code on your paper.

admin PIN: ADMIN-PIN-HERE
The admin pin is used to edit the card.

  • Store copies of these codes in safe places where you will not lose them and nobody can read them.
  • You will not be able to use the smartcard without the correct code.
  • Change the smartcard's user PIN.
$ gpg --card-edit
gpg/card> admin ## Card admin menu.
gpg/card> passwd ## Change card password(s).
gpg/card> 1 ## 1 - change PIN.
gpg/card> q ## Exit PIN edit submenu.
gpg/card> list ## Display card information.
gpg/card> quit ## Exit GPG.
  • Change the smartcard's admin PIN
$ gpg --card-edit
gpg/card> admin ## Card admin menu.
gpg/card> passwd ## Change card password(s).
gpg/card> 3 ## 3 - change Admin PIN.
gpg/card> q ## Exit PIN edit submenu.
gpg/card> list ## Display card information.
gpg/card> quit ## Exit GPG.

Reload the secret key and subkeys from the backup file

This is required if you want to prepare more than one smartcard.

Delete GPG keystore

  • Do not do this unless you are sure you have successfully backed up your keys.
  • To install the same key to additional smartcards, it must be reloaded from the file again.
  • It MAY be needed to delete the key from GPG's keystore for reimport?
$ date; gpg --delete-secret-keys FEEDB00BCODEBEEF # Forget/erase secret key from GPG keystore.
$ date; gpg --delete-keys FEEDB00BCODEBEEF # Forget/erase public key from GPG keystore.
$ date; rm -rf ~/.gnupg/ # Erase GPG keystore alltogether.

Import secret key from file

$ cd "/path/to/my/key/backup/dir/" # Go to the directory where we have the key files.
$ date; gpg --import FEEDB00BCODEBEEF.1970JAN01.public.key # Import your publickey from file.
$ date; gpg --allow-secret-key-import --import FEEDB00BCODEBEEF-20200530.masterkeys.txt # Import your secretkey from file into local keystore (You should be asked for the secretkey password at this point).
$ date; gpg --allow-secret-key-import --import FEEDB00BCODEBEEF-20200530.subkeys.txt

Set imported secretkey to maximum trust level

  • It is required to set the trust level to ultimate to put it on a smartcard.
$ date; gpg --edit-key FEEDB00BCODEBEEF
gpg>trust # Edit trust level for the key.
gpg>trust>5 # "5 = I trust ultimately"
gpg>trust>y # Confirm absolute trust
gpg>save # Save changes and exit GPG.

Move the key to smartcard

  •  !!! BE OFFLINE !!!
  • Insert your smartcard device.
  • Transfer each of the three subkeys to the smartcard (Sign, Encrypt, Authenticate)
$ gpg --card-edit
gpg>key 1 ## Toggle select for the key at position 1 in the list.
gpg> keytocard # Send the key to the smartcard.
gpg>key 1 ## Toggle select for the key at position 1 in the list.
$ gpg --card-edit
gpg>key 2 ## Toggle select for the key at position 2 in the list.
gpg> keytocard # Send the key to the smartcard.
gpg>key 2 ## Toggle select for the key at position 2 in the list.
$ gpg --card-edit
gpg>key 3 ## Toggle select for the key at position 3 in the list.
gpg> keytocard # Send the key to the smartcard.
gpg>key 3 ## Toggle select for the key at position 3 in the list.
  • To add the key to another smartcard, you must import it from the backup.
$ gpg --import KEYNAME-DATE.masterkeys.txt
$ gpg --import KEYNAME-DATE.subkeys.txt
$ gpg --edit-key KEYNAME
gpg> trust ## Edit the trust level for this key.
gpg> 5 ## Assign ultimate trust to our own key.
gpg> y ## Confirm the trust setting.

Erase keys from liveusb

  •  !!! BE OFFLINE !!!
  • Remove the GPG keystore as an added precaution.
$ rm -rf ~/.gnupg*

Setup public key side

Copy and paste the text in the ssh-remote.key file from the earlier steps into the `~/.ssh/authorized_keys` file on the machine you intend to connect to.


Set up key on machine we want to SSH to

Open the authorized_keys for your user account and paste in the SSH key (Created earlier in this guide as "FEEDB00BCODEBEEF-1970JAN01.ssh-remote.key")

$ mkdir -vp ~/.ssh/ ; touch ~/.ssh/authorized_keys; # Create authorized_keys if it does not exist.
$ nano ~/.ssh/authorized_keys # Edit authorized_keys file

Using multiple cards

This command tells GPG to associate keys it has with copies of those keys on a connected smartcard. The same command works on both Linux and Windows.

$ gpg-connect-agent "scd serialno" "learn --force" /bye
> gpg-connect-agent "scd serialno" "learn --force" /bye

https://github.com/drduh/YubiKey-Guide#using-multiple-keys


WSL (Windows Subsystem for Linux)

  •  ! WIP !

Getting SSH to work in WSL. https://github.com/drduh/YubiKey-Guide#using-multiple-keys https://github.com/vuori/weasel-pageant

  • Download and extract weasel-pagent to somewhere convenient on the windows side.
https://github.com/vuori/weasel-pageant/releases

Place this line in your .bashrc file

$ nano ~./bashrc
# Make GNUPG / GPG work with windows smartcards weasel-pageant 
eval $(<location where you unpacked the zip>/weasel-pageant -rb -a $HOME/.weasel-pageant.sock)

Reload the config from the updated file:

$ source ~/.bashrc

Add entry to the ~/.ssh/config file:

nano ~/.ssh/config
ForwardAgent yes
RemoteForward /root/.gnupg/S.gpg-agent.ssh $HOME/.weasel-pageant.sock
$ chmod 600 ~/.ssh/config ; chown $USER ~/.ssh/config # Ensure you have the correct owner and permissions for the config file.

Test if it works:

$ ssh-add -l

If it is working it will show your key in the list it gives.

if you get the erro : chmod 600 ~/.ssh/config

Automating on Windows

Save the following script to a .bat file. (e.g. `C:\scripts\gpg_refresh.bat`)

@echo off 
rem gpg_refresh.bat
rem Check if our key is on an attached smartcard and associate it if so.
gpg-connect-agent "scd serialno" "learn --force" /bye
  • Press the start button on your keyboard to open the start menu.
  • Type "schedule", "Task Scheduler" should appear as a search result in the start menu.
  • Open Task Scheduler.
  • In the section on the right of the window (Under the heading "Actions") select "Create Task".
  • Set the Name to `Check and Update GPG smartcards`
  • Set the description to `Tell GPG to compare its keys against smartcards, and link any that match.`
    • "Name" : "1 hour"
    • "Description" : "1 hour"
    • "Security options" -> "Run whether user is logged on or not" : Selected. (Hides command window when task runs)
    • "Security options" -> "Do not store password. The task will only have access to local computer resources." : Selected. (Prevents requiring user's password to be entered to set up task.)
  • This task must be running using your user account, so that the instance of GPG associated with your account is acted on.
    • "Configure for:": "Windows 10"
  • Click on the "Triggers" tab at the top of the window then click the "New" button
  • In the "New Trigger" window that opens:
    • "Begin the task": `On a schedule`
    • Settings -> "Daily" selected.
    • Settings -> "Start": Set a value in the next hour or so.
    • Settings -> "Recur every" [ ] days: "1"
    • "Advanced setings" -> "Repeat task every": Box checked.
    • "Advanced setings" -> "Repeat task every" : "1 hour"
    • "Advanced setings" -> "for a duration of" : "1 day"
    • "Advanced setings" -> "Expire": Box unchecked. (Never expire)
    • "Advanced setings" -> "Enabled": Box checked.
  • Click "OK" once these settings are set.
  • Click on the "Actions" tab at the top of the window then click the "New" button
  • In the "New Action" window that opens:
    • "Settings` -> "Action": "Start a program"
    • "Settings" -> "Program/script" : The path to the .bat file.
  • Click "OK" once these settings are set.
  • Click "OK" in the "Create Task" window.

https://stackoverflow.com/questions/4249542/run-a-task-every-x-minutes-with-windows-task-scheduler

https://www.howtogeek.com/tips/how-to-run-a-scheduled-task-without-a-command-window-appearing/

Troubleshooting

To kill running background GPG:

gpg-connect-agent killagent /bye # Kill GPG.

To start background GPG:

gpg-connect-agent /bye # Start GPG.

To inspect connected card(s?):

gpg --card-status # Inspect smartcard.

Sources

Guide to set up Ubuntu on a USB flash drive (Full persistant install to USB drive):

https://www.howtogeek.com/howto/14912/create-a-persistent-bootable-ubuntu-usb-flash-drive/

  • Guide to write Ubuntu installer to USB drive (Does not support software install wituout modifications, see other guide):

https://ubuntu.com/tutorials/try-ubuntu-before-you-install#1-getting-started

  • Ubuntu download page:

https://ubuntu.com/download/desktop

  • Guides to set up a Yubikey device:

https://support.yubico.com/support/solutions/articles/15000006420-using-your-yubikey-with-openpgp

https://withinboredom.info/blog/2017/11/18/signing-commits-ssh-with-yubikey-and-windows/

https://zeos.ca/post/2018/gpg-yubikey5/

  • Yubikey troubleshooting pages:

https://support.yubico.com/support/solutions/articles/15000014892-troubleshooting-gpg-no-such-device-

  • GPG key import/export:

https://unix.stackexchange.com/questions/184947/how-to-import-secret-gpg-key-copied-from-one-machine-to-another

https://msol.io/blog/tech/back-up-your-pgp-keys-with-gpg/

  • Other guides:

https://github.com/tomlowenthal/documentation/blob/master/gpg/smartcard-keygen.md

https://blogs.fsfe.org/jens.lechtenboerger/2013/04/19/how-to-set-up-your-fellowship-card/

https://gist.github.com/ageis/14adc308087859e199912b4c79c4aaa4

https://spin.atomicobject.com/2013/11/24/secure-gpg-keys-guide/

https://support.yubico.com/support/solutions/articles/15000006420-using-your-yubikey-with-openpgp

https://www.linode.com/docs/security/authentication/gpg-key-for-ssh-authentication/

https://0day.work/using-a-yubikey-for-gpg-and-ssh/

https://xladius.com/opsec/2018/06/25/using-yubikeys-for-openpgp

https://oychang.com/posts/gpg/notes-on-yubikey-neo.html

https://github.com/drduh/YubiKey-Guide

  • Misc of interest:

https://www.dongleauth.info/

https://www.dongleauth.info/dongles/

https://www.nitrokey.com/documentation/installation

https://www.nitrokey.com/documentation/frequently-asked-questions-faq#how-to-use-the-nitrokey-with-multiple-computers

https://www.fsij.org/doc-gnuk/gnuk-passphrase-setting.html#

https://security.stackexchange.com/questions/45094/smart-card-gnupg-what-is-stored-in-my-keyring-how-to-adopt-smart-card

https://stackoverflow.com/questions/46689885/how-to-get-public-key-from-an-openpgp-smart-card-without-using-key-servers

https://www.gnupg.org/howtos/card-howto/en/smartcard-howto-single.html

https://crypto.stackexchange.com/questions/43223/are-additional-pgp-subkeys-still-needed-for-smartcards

https://stackoverflow.com/questions/48016033/how-do-i-encrypt-an-email-using-a-yubikey