PGP setup with smartcard (Yubikey)
Smartcard commands
This is a guide to setup a PGP key with a Yubikey and to create a backup of the keys. The guide is written for MacOS but if you take security seriously, please consider using a dedicated offline Linux machine with Tails OS (GPG commands are mostly the same).
Preliminary steps
brew install gnupg pinentry-mac ykman
export EMAIL="exemple@exemple.com"
echo $EMAIL
Generate pgp keys and create a backup folder
Create backup folder:
mkdir ~/Documents/mykeys
cd ~/Documents/mykeys
Create the master password and the admin pin:
openssl rand -base64 32 > passphrase.txt
openssl rand -base64 32 > adminpin.txt
Create configuration files:
gpg --list-keys
echo "default-cache-ttl 60\nmax-cache-ttl 120\npinentry-program /opt/homebrew/bin/pinentry-mac" > ~/.gnupg/gpg-agent.conf
gpg-connect-agent /bye
echo "reader-port Yubico Yubi" > ~/.gnupg/scdaemon.conf
gpgconf --reload scdaemon
Generate the master key:
gpg --expert --full-generate-key
gpg (GnuPG) 2.4.3; Copyright (C) 2023 g10 Code GmbH
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
(2) DSA and Elgamal
(3) DSA (sign only)
(4) RSA (sign only)
(7) DSA (set your own capabilities)
(8) RSA (set your own capabilities)
(9) ECC (sign and encrypt) *default*
(10) ECC (sign only)
(11) ECC (set your own capabilities)
(13) Existing key
(14) Existing key from card
Your selection? 8
Possible actions for this RSA key: Sign Certify Encrypt Authenticate
Current allowed actions: Sign Certify Encrypt
(S) Toggle the sign capability
(E) Toggle the encrypt capability
(A) Toggle the authenticate capability
(Q) Finished
Your selection? s
Possible actions for this RSA key: Sign Certify Encrypt Authenticate
Current allowed actions: Certify Encrypt
(S) Toggle the sign capability
(E) Toggle the encrypt capability
(A) Toggle the authenticate capability
(Q) Finished
Your selection? e
Possible actions for this RSA key: Sign Certify Encrypt Authenticate
Current allowed actions: Certify
(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
GnuPG needs to construct a user ID to identify your key.
Real name: simon
Email address: s.glatre@gmail.com
Comment:
You selected this USER-ID:
"simon <s.glatre@gmail.com>"
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.
gpg: directory '/Users/simon/.gnupg/openpgp-revocs.d' created
gpg: revocation certificate stored as '/Users/simon/.gnupg/openpgp-revocs.d/B897195F0C977FD64539A7DCCC749C9B694007E4.rev'
public and secret key created and signed.
pub rsa4096 2024-01-31 [C]
B897195F0C977FD64539A7DCCC749C9B694007E4
uid simon <s.glatre@gmail.com>
Generate the subkeys:
gpg --expert --edit-key $EMAIL
gpg (GnuPG) 2.4.3; Copyright (C) 2023 g10 Code GmbH
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.
sec rsa4096/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: ultimate validity: ultimate
[ultimate] (1). simon <s.glatre@gmail.com>
gpg> addkey
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
(14) Existing key from card
Your selection? 4
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) 2y
Key expires at Ven 30 jan 11:03:28 2026 CET
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/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: ultimate validity: ultimate
ssb rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
[ultimate] (1). simon <s.glatre@gmail.com>
gpg> addkey
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
(14) Existing key from card
Your selection? 6
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) 2y
Key expires at Ven 30 jan 11:03:54 2026 CET
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/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: ultimate validity: ultimate
ssb rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
ssb rsa4096/E4B84DE860069A6B
created: 2024-01-31 expires: 2026-01-30 usage: E
[ultimate] (1). simon <s.glatre@gmail.com>
gpg> addkey
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
(14) Existing key from card
Your selection? 8
Possible actions for this 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? =a
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) 2y
Key expires at Ven 30 jan 11:04:34 2026 CET
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/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: ultimate validity: ultimate
ssb rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
ssb rsa4096/E4B84DE860069A6B
created: 2024-01-31 expires: 2026-01-30 usage: E
ssb rsa4096/E41FCDFD84F9D4F0
created: 2024-01-31 expires: 2026-01-30 usage: A
[ultimate] (1). simon <s.glatre@gmail.com>
gpg> save
Check the result:
gpg --list-public-keys
gpg --list-secret-keys
Backup the keys and useful public information:
gpg --armor --export-secret-keys $EMAIL > master.asc
gpg --gen-revoke $EMAIL > revoke.asc
gpg --armor --export-secret-subkeys $EMAIL > sub.asc
gpg --fingerprint --fingerprint $EMAIL > fingerprints.txt
gpg --armor --export $EMAIL > pub.asc
cp -r ~/.gnupg ./gnupg.backup
Setup the Yubikey
Insert the Yubikey and check that it is recognized:
gpg --card-status
Transfer the subkeys to the Yubikey:
gpg --edit-key $EMAIL
gpg (GnuPG) 2.4.3; Copyright (C) 2023 g10 Code GmbH
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.
sec rsa4096/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: ultimate validity: ultimate
ssb rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
ssb rsa4096/E4B84DE860069A6B
created: 2024-01-31 expires: 2026-01-30 usage: E
ssb rsa4096/E41FCDFD84F9D4F0
created: 2024-01-31 expires: 2026-01-30 usage: A
[ultimate] (1). simon <s.glatre@gmail.com>
gpg> key 1
sec rsa4096/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: ultimate validity: ultimate
ssb* rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
ssb rsa4096/E4B84DE860069A6B
created: 2024-01-31 expires: 2026-01-30 usage: E
ssb rsa4096/E41FCDFD84F9D4F0
created: 2024-01-31 expires: 2026-01-30 usage: A
[ultimate] (1). simon <s.glatre@gmail.com>
gpg> keytocard
Please select where to store the key:
(1) Signature key
(3) Authentication key
Your selection? 1
sec rsa4096/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: ultimate validity: ultimate
ssb* rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
ssb rsa4096/E4B84DE860069A6B
created: 2024-01-31 expires: 2026-01-30 usage: E
ssb rsa4096/E41FCDFD84F9D4F0
created: 2024-01-31 expires: 2026-01-30 usage: A
[ultimate] (1). simon <s.glatre@gmail.com>
Note: the local copy of the secret key will only be deleted with "save".
gpg> key 1
sec rsa4096/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: ultimate validity: ultimate
ssb rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
ssb rsa4096/E4B84DE860069A6B
created: 2024-01-31 expires: 2026-01-30 usage: E
ssb rsa4096/E41FCDFD84F9D4F0
created: 2024-01-31 expires: 2026-01-30 usage: A
[ultimate] (1). simon <s.glatre@gmail.com>
gpg> key 2
sec rsa4096/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: ultimate validity: ultimate
ssb rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
ssb* rsa4096/E4B84DE860069A6B
created: 2024-01-31 expires: 2026-01-30 usage: E
ssb rsa4096/E41FCDFD84F9D4F0
created: 2024-01-31 expires: 2026-01-30 usage: A
[ultimate] (1). simon <s.glatre@gmail.com>
gpg> keytocard
Please select where to store the key:
(2) Encryption key
Your selection? 2
sec rsa4096/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: ultimate validity: ultimate
ssb rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
ssb* rsa4096/E4B84DE860069A6B
created: 2024-01-31 expires: 2026-01-30 usage: E
ssb rsa4096/E41FCDFD84F9D4F0
created: 2024-01-31 expires: 2026-01-30 usage: A
[ultimate] (1). simon <s.glatre@gmail.com>
Note: the local copy of the secret key will only be deleted with "save".
gpg> key 2
sec rsa4096/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: ultimate validity: ultimate
ssb rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
ssb rsa4096/E4B84DE860069A6B
created: 2024-01-31 expires: 2026-01-30 usage: E
ssb rsa4096/E41FCDFD84F9D4F0
created: 2024-01-31 expires: 2026-01-30 usage: A
[ultimate] (1). simon <s.glatre@gmail.com>
gpg> key 3
sec rsa4096/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: ultimate validity: ultimate
ssb rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
ssb rsa4096/E4B84DE860069A6B
created: 2024-01-31 expires: 2026-01-30 usage: E
ssb* rsa4096/E41FCDFD84F9D4F0
created: 2024-01-31 expires: 2026-01-30 usage: A
[ultimate] (1). simon <s.glatre@gmail.com>
gpg> keytocard
Please select where to store the key:
(3) Authentication key
Your selection? 3
sec rsa4096/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: ultimate validity: ultimate
ssb rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
ssb rsa4096/E4B84DE860069A6B
created: 2024-01-31 expires: 2026-01-30 usage: E
ssb* rsa4096/E41FCDFD84F9D4F0
created: 2024-01-31 expires: 2026-01-30 usage: A
[ultimate] (1). simon <s.glatre@gmail.com>
Note: the local copy of the secret key will only be deleted with "save".
gpg> save
Harden the Yubikey by changing the pin and the admin pin, remember that the admin pin is in adminpin.txt, use a memorable password for the pin:
gpg --change-pin
gpg: OpenPGP card no. D2760001240100000006177802720000 detected
1 - change PIN
2 - unblock PIN
3 - change Admin PIN
4 - set the Reset Code
Q - quit
Your selection? 1
PIN changed.
1 - change PIN
2 - unblock PIN
3 - change Admin PIN
4 - set the Reset Code
Q - quit
Your selection? 3
PIN changed.
1 - change PIN
2 - unblock PIN
3 - change Admin PIN
4 - set the Reset Code
Q - quit
Your selection? q
Continue the hardening by setting requiering physical touch on the Yubikey when signing, encrypting or authenticating:
ykman openpgp info
ykman openpgp keys set-touch sig on
ykman openpgp keys set-touch enc on
ykman openpgp keys set-touch aut on
ykman openpgp info
Recreate a fresh environment, with no private information
Reset gpg:
rm -r ~/.gnupg
gpg --list-public-keys
echo "default-cache-ttl 60\nmax-cache-ttl 120\npinentry-program /opt/homebrew/bin/pinentry-mac" > ~/.gnupg/gpg-agent.conf
gpg-connect-agent /bye
echo "reader-port Yubico Yubi" > ~/.gnupg/scdaemon.conf
gpgconf --reload scdaemon
Import the public key and create stubs for the private keys:
gpg --import pub.asc
gpg --list-public-keys
gpg --list-secret-keys
gpg --card-status
gpg --list-secret-keys
Trust your own key with ultimate trust using the “trust” command in gpg:
gpg --edit-key $EMAIL
gpg (GnuPG) 2.4.3; Copyright (C) 2023 g10 Code GmbH
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 rsa4096/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: unknown validity: unknown
ssb rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
card-no: 0006 17780272
ssb rsa4096/E4B84DE860069A6B
created: 2024-01-31 expires: 2026-01-30 usage: E
card-no: 0006 17780272
ssb rsa4096/E41FCDFD84F9D4F0
created: 2024-01-31 expires: 2026-01-30 usage: A
card-no: 0006 17780272
[ unknown] (1). simon <s.glatre@gmail.com>
gpg> trust
pub rsa4096/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: unknown validity: unknown
ssb rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
card-no: 0006 17780272
ssb rsa4096/E4B84DE860069A6B
created: 2024-01-31 expires: 2026-01-30 usage: E
card-no: 0006 17780272
ssb rsa4096/E41FCDFD84F9D4F0
created: 2024-01-31 expires: 2026-01-30 usage: A
card-no: 0006 17780272
[ unknown] (1). simon <s.glatre@gmail.com>
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 rsa4096/CC749C9B694007E4
created: 2024-01-31 expires: never usage: C
trust: ultimate validity: unknown
ssb rsa4096/8BAE7179A13643CB
created: 2024-01-31 expires: 2026-01-30 usage: S
card-no: 0006 17780272
ssb rsa4096/E4B84DE860069A6B
created: 2024-01-31 expires: 2026-01-30 usage: E
card-no: 0006 17780272
ssb rsa4096/E41FCDFD84F9D4F0
created: 2024-01-31 expires: 2026-01-30 usage: A
card-no: 0006 17780272
[ unknown] (1). simon <s.glatre@gmail.com>
Please note that the shown key validity is not necessarily correct
unless you restart the program.
gpg> save
Key not changed so no update needed.
Encrypt the backup folder
Keep a copy of pub.asc in your documents, you will need it later. Optionally, publish it on a keyserver for others to find it easily.
Use the veracrpyt GUI or LUKS to create the encrypted backup. The password to encrypt the backup must be strong and new.
Delete the mykeys folder when the backup is done.
Test the setup
cd ~/Documents
echo "Privacy is the power to selectively reveal oneself to the world. - Eric Hughes" > message.txt
gpg --encrypt --armor --recipient $EMAIL -o encrypted.asc message.txt
gpg --decrypt encrypted.asc
gpg --armor --clearsign -o signed.asc message.txt
gpg --verify signed.asc
Add SSH support
Add ssh support:
echo "enable-ssh-support" >> ~/.gnupg/gpg-agent.conf
gpgconf --kill gpg-agent
Replace ssh-agent with gpg-agent by adding to ~/.zshrc:
export SSH_AUTH_SOCK="$(gpgconf --list-dirs agent-ssh-socket)"