Subkeys renewing/expiring strategy

[nect]

Hello Ingo,

Thank you for your reply.

>You will still have to upload the updated key to every website you use.
So,
> you don't gain much if anything with this approach.

You are totally right, I didn't think of that.
In any case, this begs the question: is it better (best practice if you
want) to have many expired subkeys in your keyring or constantly bumping
the expiry date of one of your subkeys (without creating new ones every
time)?

> Encryption and authentication subkeys are useless for a commit
> signing key, but you may of course use your key also for other purposes

I made those just to be sure in case I will need them.
Is it better to have authoring and encrypting subkeys with an unlimited
expiry? Or is it better to not create them at all until you need them?

>"Trust" is usually bound to the primary key. Expired subkeys shouldn't
matter.

Thank you for clarifying that.

> Since I use this key exclusively for commit signing, I can
> simply replace it with a completely different key if I change my mind.

About this, how do you deal-or plan of dealing- with past commits signed
with a now expired key?
I created on year ago a test repo with only one commit, signed with my now
expired subkey.
Checking that commit's signature now shows an alert saying that the key is
expired (in red).
While this is correct, I guess that some users or services may see expired
signatures as invalid, even though they are valid and I just superseded
them with newer subkeys.

I can think of two choices: either resign all your past commits every time
your subkey expires, or ignore the fact that old commits were signed with
expired subkeys.
So, I was wondering if extending the expiry is the better way to deal with
this, since you avoid showing any alert for old commits.

Regards

On Tue, Oct 11, 2022, 7:44 PM Ingo Klöcker <kloecker at kde.org> wrote:

> On Dienstag, 11. Oktober 2022 17:23:49 CEST nect via Gnupg-users wrote:
> > I started using gpg relatively recently (1 year or so), mainly for
> > signing git commits, and I am far from mastering it.
> >
> > Since I was struggling to choose a strategy for expiring/renewing my
> > subkeys (more details below) I decided to seek expert advice (hopefully
> > this is the right place).
>
> I'm far from being an expert.
>
> > At the moment, I have my primary key (with no expiry) stored on a
> > offline drive.
> > I created the key 1 year ago, alongside a set of subkeys whose expiry
> > was due in 1 year.
> > Since they recently expired, I created another triplet of subkeys (sign,
> > author, encrypt) and started using them instead of the old ones.
>
> For signing git commits I recently created an OpenPGP key with a
> certify-only
> primary key (with long validity period) and a signing subkey (which
> expires
> next year). Encryption and authentication subkeys are useless for a commit
> signing key, but you may of course use your key also for other purposes.
>
> This commit signing key is certified with my main key.
>
> > Now, when I was doing this I realized that this strategy is not
> > particularly good, especially in the long run,
> > since you have to recreate every year (or 2) the new subkeys and let the
> > old ones expire (losing some trust?).
>
> "Trust" is usually bound to the primary key. Expired subkeys shouldn't
> matter.
>
> > Also, uploading the new keys to every website that you use (eg GitLab)
> > is quite the annoying chore.
> >
> > So, I was wondering what's the best strategy I can use to keep my
> > (sub)keys valid without compromising on security.
> > Is bumping the expiry date every year or so a better solution?
>
> You will still have to upload the updated key to every website you use.
> So,
> you don't gain much if anything with this approach.
>
> > Also, are subkeys with unlimited expiry bad, or am I just being carried
> > away?
>
> The advantage of an expiring key is that you can simply let it expire to
> make
> it invalid (for signatures created after the expiration date). On the
> other
> hand, if you don't lose access to the primary key, then you can still
> change
> the expiry of a subkey with unlimited validity if you decide to expire it.
> The
> downside of setting the expiration date in retrospect is that you need to
> send
> the updated key everywhere. And people may still use the outdated version
> without expiry.
>
> I'm going to experiment with 1-year-validity of the signing subkeys of my
> commit signing key. Since I use this key exclusively for commit signing, I
> can
> simply replace it with a completely different key if I change my mind.
>
> Regards,
> Ingo
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