Renewing GPG Keys on Yubikey

Mitchell Caisse - January 13, 2022 - 3 mins read

gpg
yubikey

When I setup my GPG keys on my Yubikey I set the expiration of the keys to be two years and forgot all about it. Until recently when the keys hit the two-year mark and expired. I had of course forgotten how exactly I set up the keys initially and how to renew them. After some research and experimenting with the gpg2 commands, I was able to renew them.

I decided I would document the process for when this inevitably happens again in two years.

Renewing the expired keys

First we will need to get the ID of the keys we will be renewing. There are two ways to do this:
- With your Yubikey plugged in you can run gpg2 --card-status. This will print out information about the card, including the keys on it.
- You can also run gpg2 --list-secret-keys. This will list all the gpg keys that you have the private key for.
From the output of these commands, you will want to copy of the ID from the main key. The main key is identified by having sec in the first column. The ID will be the sequence of hexadecimal numbers next to it.
```
sec  rsa4096/A32231B41FCC3E18
     created: 2020-01-12  expires: 2024-01-13  usage: SC  
     card-no: 0006 06645024
     trust: unknown       validity: unknown
sub  rsa4096/06F83DE8FBEBF491
     created: 2020-01-12  expires: 2024-01-13  usage: S   
sub  rsa4096/455A454783C762BD
     created: 2020-01-12  expires: 2024-01-13  usage: A   
ssb  rsa4096/3CA276AA203A53E2
     created: 2020-01-12  expires: 2024-01-13  usage: E   
     card-no: XXXX XXXXXXXX
[ unknown] (1). Mitchell Caisse <[email protected]>
```
For example, in the above A32231B41FCC3E18 is the id of my main key and 06F83DE8FBEBF491 is the id of the first sub key.
Now that we have the ID of the main key we can run gpg2 --edit-key <<key-id>> to start editing the key. This will drop us into an interactive shell. If you want to explore a bit typing help will list all available commands, list will print out the key information, and quit will exit.
To renew the key enter expire This will open a prompt to enter how long the key should be valid for, with examples of the accepted options. 2y means the key will expire 2 years from now.
However, that only extends the validity of the main key, you will need to repeat the process for each sub key that you have.
- First you will need to select the sub key, which you can do by typing key <index> or key <<sub-key-id>> where index is the index of the key in the list and sub-key-id is the id of the key to select. Running the command again will deselect the key. You can select multiple keys at a time.
- After your desired sub keys are selected, repeat the process in step 3 to new the keys. Note: When you run list any selected keys will have an asterisk (*) next to them.
Finally, to save the changes and quit type save

The expiration date of your key(s) are now updated and valid once again. You might want to share your updated, which to do so you’ll need to export the key.

Which you can do by running:

gpg2 --armor --export <<key-id>> > public_key.gpg