website/site/blog/2021-05-19-gnupg-quickstart.md

# GnuPG Quickstart

I love GPG and the way it works. I know there are many that complain
about it because it has flaws. My stance on this is that I prefer
battle-tested software with known flaws to something with unknown flaws.

Anyway, this should get you started with GnuPG

## Prerequisites

Install gpg and pinentry.

<pre>
# pkg_add gnupg pinentry
</pre>

## You need a Key

If you want to lock and unlock stuff, you need a key. This is how you 
get to one:

<pre>
$ gpg --generate-key
</pre>

Hop through the wizard until you see these lines:

<pre>
pub   rsa3072 2021-05-19 [SC] [expires: 2023-05-19]
      BA696588D9A04AD9F70DA33EC54733F6DBECC2C1
uid                      John Doe &lt;j.doe@example.com&gt;
sub   rsa3072 2021-05-19 [E] [expires: 2023-05-19]
</pre>

If you see an error like:
    gpg: agent_genkey failed: Permission denied

Add the following entry and try again.

<pre>
$ echo "allow-loopback-pinentry" &gt;&gt; ~/.gnupg/gpg-agent.conf
</pre>

Congratulations, you got yourself a GPG Key. This long gibberish is your 
full GPG Key ID. Most of the time, you can simply use the last 8 
characters. So the short version of this GPG Key is DBECC2C1.

You can set it as default key, so it's used to encrypt stuff when no
explicit key is given.

<pre>
$ echo "default-key DBECC2C1" &gt;&gt; ~/.gnupg/gpg.conf
</pre>

## Share the key with your people

If you want someone to be able to encrypt something for you, send him or 
her the output of:

<pre>
$ gpg --export -a DBECC2C1
</pre>

You can also use your email address instead of the Key ID, if you have
only one key with it. This key is public. So put it on some webspace and
add a link to your email header or signature.

## Upload the key so people can find it (optional)

You can also upload your key to a key server. For this, configure a 
keyserver:

<pre>
$ echo "keyserver hkps://keys.openpgp.org" &gt;&gt;  ~/.gnupg/gpg.conf
</pre>

Then send your key to it:

<pre>
$ gpg --send-keys DBECC2C1
</pre>

## You got a key from someone

Add a key from someone else to gnupg, so you can use it to encrypt data 
for this person. If the key is on your harddrive, use:

<pre>
$ gpg --import &lt;pubkeyfile.asc&gt;
</pre>

The file ending here is kind of undefined. Some call it .asc, .gpg, .pub
or .key. If the key is on a key server, you can import it like so:

<pre>
$ gpg --recv-key 52BE43BA
</pre>

This would import my key. You can look at it now with:

<pre>
$ gpg --list-keys 52BE43BA
</pre>

## Encrypt a file

This encrypts the file plain.txt with the public key DBECC2C1.

<pre>
$ gpg --encrypt -r DBECC2C1 file.txt
</pre>

Now you have file.txt.gpg, which is the encrypted version

## Decrypt a file

GnuPG automaticall figures out what key it can use to decrypt a file. So 
this will output the content of file.txt on the terminal. If you want 
to save the output in a file, add -o file.txt.

<pre>
$ gpg -d file.txt.gpg 
$ gpg -d file.txt.gpg -o file.txt
</pre>

## Choose a better password prompt (optional)

You can change the way gpg asks for the password:

<pre>
$ cat ~/.gnupg/gpg-agent.conf
[...]
pinentry-program /usr/local/bin/pinentry-curses
[...]
</pre>

Options are:

  - pinentry (sometimes also called pinentry-tty)
  - pinentry-curses
  - pinentry-gtk2: pkg_add pinentry-gtk2
  - pinentry-gnome3: pkg_add pinentry-gnome3
  - pinentry-dmenu: https://github.com/ritze/pinentry-dmenu

*Note: If you use a console pinentry program and want to use gpg with a
GUI tool (like thunderbird), the password prompt will be invisible and
gpg/thunderbird will freeze.*

Makes sense, doesn't it?

## Start GPG Agent for password caching (optional)

Put this in your .kshrc or .bashrc:

<pre>
export GPG_TTY=$(tty)
gpg-connect-agent /bye
</pre>

## Make a Backup (not so optional)

There is no handholding cloud or support team you can call when you 
messed up or deleted your key. So back it up safely.

Either you backup your ~/.gnugp directory, or you export the secret 
keys and backup them safely.

<pre>
$ gpg --export-secret-keys -a DBECC2C1 &gt; gpg_key_backup.sec
</pre>

Seriously, don't skip this step.

## Configure Mutt (optional)

Install mutt with the gpgme flavor. Gpgme is the "new way" of handling 
gpg in mutt.

<pre>
# pkg_add mutt--gpgme
</pre>

If you're not on OpenBSD, check with `mutt -v` if it was compiled with
the `--enable-gpgme` option. Then enable it in mutt.

<pre>
$ cat ~/.muttrc
[...]
crypt_use_gpgme = yes
[...]
</pre>

In the mutt compose view, you can now select Security Options.

<pre>
        From: c0dev0id &lt;c0@example.com&gt;
          To: j.doe@example.com
          Cc:
         Bcc:
     Subject: Hello my friend
    Reply-To:
         Fcc: =Sent
    Security: Sign, Encrypt (PGP/MIME)
     Sign as: &lt;default&gt;
</pre>

You can change the setting with the key "p", which should bring up a
selection menu.

    PGP (e)ncrypt, (s)ign, sign (a)s, (b)oth, s/(m)ime or (c)lear?

*That's it! GPG is not difficult. You need to know a few bits, but these are not
more difficult than many other things we do on a daily basis.*