This is the string 12345678.
See the example section on how to change these defaults. For
production use it is important to use secure values for them. Note that
the Authentication Key is not queried via the usual Pinentry dialog
but needs to be entered manually or read from a file. The use of a
dedicated machine to personalize tokens is strongly suggested.
To see what is on the card, the command list can be given. We
will use the interactive mode in the following (the string
gpg/card> is the prompt). An example output for a fresh card
is:
-
gpg/card> list
Reader ...........: 1050:0407:X:0
Card type ........: yubikey
Card firmware ....: 5.1.2
Serial number ....: D2760001240102010006090746250000
Application type .: OpenPGP
Version ..........: 2.1
[...]
It can be seen by the ``Application type'' line that GnuPG selected
the OpenPGP application of the Yubikey. This is because GnuPG assigns
the highest priority to the OpenPGP application. To use the PIV
application of the Yubikey several methods can be used:
With a Yubikey 5 or later the OpenPGP application on the Yubikey can
be disabled:
-
gpg/card> yubikey disable all opgp
gpg/card> yubikey list
Application USB NFC
-----------------------
OTP yes yes
U2F yes yes
OPGP no no
PIV yes no
OATH yes yes
FIDO2 yes yes
gpg/card> reset
The reset is required so that the GnuPG system rereads the
card. Note that disabled applications keep all their data and can at
any time be r-enabled (use oqhelp yubikeycq).
Another option, which works for all Yubikey versions, is to disable
the support for OpenPGP cards in scdaemon. This is done by adding the
line
-
disable-application openpgp
to oq~/.gnupg/scdaemon.confcq and by restarting scdaemon, either by
killing the process or by using oqgpgconf --kill scdaemoncq. Finally
the default order in which card applications are tried by scdaemon can
be changed. For example to prefer PIV over OpenPGP it is sufficient
to add
-
application-priority piv
to oq~/.gnupg/scdaemon.confcq and to restart scdaemon.
This has an effect only on tokens which support both, PIV and OpenPGP,
but does not hamper the use of OpenPGP only tokens.
With one of these methods employed the list command of
gpg-card shows this:
-
gpg/card> list
Reader ...........: 1050:0407:X:0
Card type ........: yubikey
Card firmware ....: 5.1.2
Serial number ....: FF020001008A77C1
Application type .: PIV
Version ..........: 1.0
Displayed s/n ....: yk-9074625
PIN usage policy .: app-pin
PIN retry counter : - 3 -
PIV authentication: [none]
keyref .....: PIV.9A
Card authenticat. : [none]
keyref .....: PIV.9E
Digital signature : [none]
keyref .....: PIV.9C
Key management ...: [none]
keyref .....: PIV.9D
In case several tokens are plugged into the computer, gp-card will
show only one. To show another token the number of the token (0, 1,
2, ...) can be given as an argument to the list command. The
command oqlist --cardscq prints a list of all inserted tokens.
Note that the ``Displayed s/n'' is printed on the token and also
shown in Pinentry prompts asking for the PIN. The four standard key
slots are always shown, if other key slots are initialized they are
shown as well. The PIV authentication key (internal reference
PIV.9A) is used to authenticate the card and the card holder.
The use of the associated private key is protected by the Application
PIN which needs to be provided once and the key can the be used until
the card is reset or removed from the reader or USB port. GnuPG uses
this key with its Secure Shell support. The Card
authentication key (PIV.9E) is also known as the CAK and used
to support physical access applications. The private key is not
protected by a PIN and can thus immediately be used. The Digital
signature key (PIV.9C) is used to digitally sign documents.
The use of the associated private key is protected by the Application
PIN which needs to be provided for each signing operation. The
Key management key (PIV.9D) is used for encryption. The
use of the associated private key is protected by the Application PIN
which needs to be provided only once so that decryption operations can
then be done until the card is reset or removed from the reader or USB
port.
We now generate three of the four keys. Note that GnuPG does
currently not use the the Card authentication key; however,
that key is mandatory by the PIV standard and thus we create it too.
Key generation requires that we authenticate to the card. This can be
done either on the command line (which would reveal the key):
-
gpg/card> auth 010203040506070801020304050607080102030405060708
or by reading the key from a file. That file needs to consist of one
LF terminated line with the hex encoded key (as above):
-
gpg/card> auth < myauth.key
As usual oqhelp authcq gives help for this command. An error
message is printed if a no-matching key is used. The authentication
is valid until a reset of the card or until the card is removed from
the reader or the USB port. Note that that in no-interactive mode
the oq<cq needs to be quoted so that the shell does not interpret
it as a its own redirection symbol.
Here are the actual commands to generate the keys:
-
gpg/card> generate --algo=nistp384 PIV.9A
PIV card no. yk-9074625 detected
gpg/card> generate --algo=nistp256 PIV.9E
PIV card no. yk-9074625 detected
gpg/card> generate --algo=rsa2048 PIV.9C
PIV card no. yk-9074625 detected
If a key has already been created for one of the slots an error will
be printed; to create a new key anyway the option oq--forcecq can be
used. Note that only the private and public keys have been created
but no certificates are stored in the key slots. In fact, GnuPG uses
its own no-standard method to store just the public key in place of
the certificate. Other application will not be able to make use
these keys until gpgsm or another tool has been used to
create and store the respective certificates. Let us see what the
list command now shows:
-
gpg/card> list
Reader ...........: 1050:0407:X:0
Card type ........: yubikey
Card firmware ....: 5.1.2
Serial number ....: FF020001008A77C1
Application type .: PIV
Version ..........: 1.0
Displayed s/n ....: yk-9074625
PIN usage policy .: app-pin
PIN retry counter : - 3 -
PIV authentication: 213D1825FDE0F8240CB4E4229F01AF90AC658C2E
keyref .....: PIV.9A (auth)
algorithm ..: nistp384
Card authenticat. : 7A53E6CFFE7220A0E646B4632EE29E5A7104499C
keyref .....: PIV.9E (auth)
algorithm ..: nistp256
Digital signature : 32A6C6FAFCB8421878608AAB452D5470DD3223ED
keyref .....: PIV.9C (sign,cert)
algorithm ..: rsa2048
Key management ...: [none]
keyref .....: PIV.9D
The primary information for each key is the keygrip, a 40 byte
he-string identifying the key. This keygrip is a unique identifier
for the specific parameters of a key. It is used by
gpg-agent and other parts of GnuPG to associate a private
key to its protocol specific certificate format (X.509, OpenPGP, or
SecureShell). Below the keygrip the key reference along with the key
usage capabilities are show. Finally the algorithm is printed in the
format used by {gpg}. At that point no other information is
shown because for these new keys gpg won't be able to find matching
certificates.
Although we could have created the Key management key also with
the generate command, we will create that key of-card so that a
backup exists. To accomplish this a key needs to be created with
either gpg or gpgsm or imported in one of these
tools. In our example we create a sel-signed X.509 certificate (exit
the gp-card tool, first):
-
$ gpgsm --gen-key -o encr.crt
(1) RSA
(2) Existing key
(3) Existing key from card
Your selection? 1
What keysize do you want? (3072) 2048
Requested keysize is 2048 bits
Possible actions for a RSA key:
(1) sign, encrypt
(2) sign
(3) encrypt
Your selection? 3
Enter the X.509 subject name: CN=Encryption key for yk-9074625,O=example,C=DE
Enter email addresses (end with an empty line):
> otto@example.net
>
Enter DNS names (optional; end with an empty line):
>
Enter URIs (optional; end with an empty line):
>
Create self-signed certificate? (y/N) y
These parameters are used:
Key-Type: RSA
Key-Length: 2048
Key-Usage: encrypt
Serial: random
Name-DN: CN=Encryption key for yk-9074625,O=example,C=DE
Name-Email: otto@example.net
Proceed with creation? (y/N)
Now creating self-signed certificate. This may take a while ...
gpgsm: about to sign the certificate for key: &34798AAFE0A7565088101CC4AE31C5C8C74461CB
gpgsm: certificate created
Ready.
$ gpgsm --import encr.crt
gpgsm: certificate imported
gpgsm: total number processed: 1
gpgsm: imported: 1
Note the last step which imported the created certificate. If you
you instead created a certificate signing request (CSR) instead of a
sel-signed certificate and sent this off to a CA you would do the
same import step with the certificate received from the CA. Take note
of the keygrip (prefixed with an ampersand) as shown during the
certificate creation or listed it again using oqgpgsm
--with-keygrip -k otto@example.netcq. Now to move the key and
certificate to the card start gpg-card again and enter:
-
gpg/card> writekey PIV.9D 34798AAFE0A7565088101CC4AE31C5C8C74461CB
gpg/card> writecert PIV.9D < encr.crt
If you entered a passphrase to protect the private key, you will be
asked for it via the Pinentry prompt. On success the key and the
certificate has been written to the card and a list command
shows:
-
[...]
Key management ...: 34798AAFE0A7565088101CC4AE31C5C8C74461CB
keyref .....: PIV.9D (encr)
algorithm ..: rsa2048
used for ...: X.509
user id ..: CN=Encryption key for yk-9074625,O=example,C=DE
user id ..: <otto@example.net>
In case the same key (identified by the keygrip) has been used for
several certificates you will see several ``used for'' parts. With
this the encryption key is now fully functional and can be used to
decrypt messages encrypted to this certificate. Take care: the
original key is still stored o-disk and should be moved to a backup
medium. This can simply be done by copying the file
oq34798AAFE0A7565088101CC4AE31C5C8C74461CB.keycq from the directory
oq~/.gnupg/private-keys-v1.d/cq to the backup medium and deleting
the file at its original place.
The final example is to create a sel-signed certificate for digital
signatures. Leave gpg-card using quit or by pressing
Contro-D and use gpgsm:
-
$ gpgsm --learn
$ gpgsm --gen-key -o sign.crt
Please select what kind of key you want:
(1) RSA
(2) Existing key
(3) Existing key from card
Your selection? 3
Serial number of the card: FF020001008A77C1
Available keys:
(1) 213D1825FDE0F8240CB4E4229F01AF90AC658C2E PIV.9A nistp384
(2) 7A53E6CFFE7220A0E646B4632EE29E5A7104499C PIV.9E nistp256
(3) 32A6C6FAFCB8421878608AAB452D5470DD3223ED PIV.9C rsa2048
(4) 34798AAFE0A7565088101CC4AE31C5C8C74461CB PIV.9D rsa2048
Your selection? 3
Possible actions for a RSA key:
(1) sign, encrypt
(2) sign
(3) encrypt
Your selection? 2
Enter the X.509 subject name: CN=Signing key for yk-9074625,O=example,C=DE
Enter email addresses (end with an empty line):
> otto@example.net
>
Enter DNS names (optional; end with an empty line):
>
Enter URIs (optional; end with an empty line):
>
Create self-signed certificate? (y/N)
These parameters are used:
Key-Type: card:PIV.9C
Key-Length: 1024
Key-Usage: sign
Serial: random
Name-DN: CN=Signing key for yk-9074625,O=example,C=DE
Name-Email: otto@example.net
Proceed with creation? (y/N) y
Now creating self-signed certificate. This may take a while ...
gpgsm: about to sign the certificate for key: &32A6C6FAFCB8421878608AAB452D5470DD3223ED
gpgsm: certificate created
Ready.
$ gpgsm --import sign.crt
gpgsm: certificate imported
gpgsm: total number processed: 1
gpgsm: imported: 1
The use of oqgpgsm --learncq is currently necessary so that
gp-agent knows what keys are available on the card. The need for
this command will eventually be removed. The remaining commands are
similar to the creation of an o-disk key. However, here we select
the oqDigital signaturecq key. During the creation process you
will be asked for the Application PIN of the card. The final step is
to write the certificate to the card using gpg-card:
-
gpg/card> writecert PIV.9C < sign.crt
By running list again we will see the fully initialized card:
-
Reader ...........: 1050:0407:X:0
Card type ........: yubikey
Card firmware ....: 5.1.2
Serial number ....: FF020001008A77C1
Application type .: PIV
Version ..........: 1.0
Displayed s/n ....: yk-9074625
PIN usage policy .: app-pin
PIN retry counter : - [verified] -
PIV authentication: 213D1825FDE0F8240CB4E4229F01AF90AC658C2E
keyref .....: PIV.9A (auth)
algorithm ..: nistp384
Card authenticat. : 7A53E6CFFE7220A0E646B4632EE29E5A7104499C
keyref .....: PIV.9E (auth)
algorithm ..: nistp256
Digital signature : 32A6C6FAFCB8421878608AAB452D5470DD3223ED
keyref .....: PIV.9C (sign,cert)
algorithm ..: rsa2048
used for ...: X.509
user id ..: CN=Signing key for yk-9074625,O=example,C=DE
user id ..: <otto@example.net>
Key management ...: 34798AAFE0A7565088101CC4AE31C5C8C74461CB
keyref .....: PIV.9D (encr)
algorithm ..: rsa2048
used for ...: X.509
user id ..: CN=Encryption key for yk-9074625,O=example,C=DE
user id ..: <otto@example.net>
It is now possible to sign and to encrypt with this card using gpgsm
and to use the oqPIV authenticationcq key with ssh:
-
$ ssh-add -l
384 SHA256:0qnJ0Y0ehWxKcx2frLfEljf6GCdlO55OZed5HqGHsaU cardno:yk-9074625 (ECDSA)
As usual use ss-add with the uppercase oq-Lcq to list the public
ssh key. To use the certificates with Thunderbird or Mozilla, please
consult the Scute manual for details.
If you want to use the same PIV keys also for OpenPGP (for example on
a Yubikey to avoid switching between OpenPGP and PIV), this is also
possible:
-
$ gpgsm --learn
$ gpg --full-gen-key
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)
(14) Existing key from card
Your selection? 14
Serial number of the card: FF020001008A77C1
Available keys:
(1) 213D1825FDE0F8240CB4E4229F01AF90AC658C2E PIV.9A nistp384 (auth)
(2) 7A53E6CFFE7220A0E646B4632EE29E5A7104499C PIV.9E nistp256 (auth)
(3) 32A6C6FAFCB8421878608AAB452D5470DD3223ED PIV.9C rsa2048 (cert,sign)
(4) 34798AAFE0A7565088101CC4AE31C5C8C74461CB PIV.9D rsa2048 (encr)
Your selection? 3
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)
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:
Email address: otto@example.net
Comment:
You selected this USER-ID:
"otto@example.net"
Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? o
gpg: key C3AFA9ED971BB365 marked as ultimately trusted
gpg: revocation certificate stored as '[...]D971BB365.rev'
public and secret key created and signed.
Note that this key cannot be used for encryption. You may want to use
the command "--edit-key" to generate a subkey for this purpose.
pub rsa2048 2019-04-04 [SC]
7F899AE2FB73159DD68A1B20C3AFA9ED971BB365
uid otto@example.net
Note that you will be asked two times to enter the PIN of your PIV
card. If you run gpg in --expert mode you will
also ge given the option to change the usage flags of the key. The next
typescript shows how to add the encryption subkey:
-
$ gpg --edit-key 7F899AE2FB73159DD68A1B20C3AFA9ED971BB365
Secret key is available.
sec rsa2048/C3AFA9ED971BB365
created: 2019-04-04 expires: never usage: SC
card-no: FF020001008A77C1
trust: ultimate validity: ultimate
[ultimate] (1). otto@example.net
gpg> addkey
Secret parts of primary key are stored on-card.
Please select what kind of key you want:
(3) DSA (sign only)
(4) RSA (sign only)
(5) Elgamal (encrypt only)
(6) RSA (encrypt only)
(14) Existing key from card
Your selection? 14
Serial number of the card: FF020001008A77C1
Available keys:
(1) 213D1825FDE0F8240CB4E4229F01AF90AC658C2E PIV.9A nistp384 (auth)
(2) 7A53E6CFFE7220A0E646B4632EE29E5A7104499C PIV.9E nistp256 (auth)
(3) 32A6C6FAFCB8421878608AAB452D5470DD3223ED PIV.9C rsa2048 (cert,sign)
(4) 34798AAFE0A7565088101CC4AE31C5C8C74461CB PIV.9D rsa2048 (encr)
Your selection? 4
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)
Key does not expire at all
Is this correct? (y/N) y
Really create? (y/N) y
sec rsa2048/C3AFA9ED971BB365
created: 2019-04-04 expires: never usage: SC
card-no: FF020001008A77C1
trust: ultimate validity: ultimate
ssb rsa2048/7067860A98FCE6E1
created: 2019-04-04 expires: never usage: E
card-no: FF020001008A77C1
[ultimate] (1). otto@example.net
gpg> save
Now you can use your PIV card also with gpg.
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