Setting Up a PGP Webkey Directory

#pgp #gpg #wkd #security

A little while ago, a friend on IRC asked me how I set up a PGP webkey directory on my website. For those that don’t know, a webkey directory is a method to find keys through gpg’s --locate-key command. This allows people to find my key using this command:

gpg --locate-key p.spek@tyil.nl

This is a very user-friendly way for people to get your key, as compared to using long IDs.

This post will walk you through setting it up on your site, so you can make your key more easily accessible to other people.

Set up the infrastructure

For a webkey directory to work, you simply need to have your key available at a certain path on your website. The base path for this is .well-known/openpgpkey/.

mkdir -p .well-known/openpgpkey

The webkey protocol will check for a policy file to exist, so you must create this too. The file can be completely empty, and that’s exactly how I have it.

touch .well-known/openpgpkey/policy

The key(s) will be placed in the hu directory, so create this one too.

mkdir .well-known/openpgpkey/hu

Adding your PGP key

The key itself is just a standard export of your key, without ASCII armouring. However, the key does need to have its file name in a specific format. Luckily, you can just show this format with gpg’s --with-wkd-hash option.

gpg --with-wkd-hash -k p.spek@tyil.nl

This will yield output that may look something like this:

pub   rsa4096/0x7A6AC285E2D98827 2018-09-04 [SC]
      Key fingerprint = 1660 F6A2 DFA7 5347 322A  4DC0 7A6A C285 E2D9 8827
uid                   [ultimate] Patrick Spek <p.spek@tyil.nl>
                      i4fxxwcfae1o4d7wnb5bop89yfx399yf@tyil.nl
sub   rsa2048/0x031D65902E840821 2018-09-04 [S]
sub   rsa2048/0x556812D46DABE60E 2018-09-04 [E]
sub   rsa2048/0x66CFE18D6D588BBF 2018-09-04 [A]

What we’re interested in is the uid line with the hash in the local-part of the email address, which would be i4fxxwcfae1o4d7wnb5bop89yfx399yf@tyil.nl. For the filename, we only care about the local-part itself, meaning the export of the key must be saved in a file called i4fxxwcfae1o4d7wnb5bop89yfx399yf.

gpg --export 0x7A6AC285E2D98827 > .well-known/openpgpkey/hu/i4fxxwcfae1o4d7wnb5bop89yfx399yf

Configuring your webserver

Lastly, your webserver may require some configuration to serve the files correctly. For my blog, I’m using lighttpd, for which the configuration block I’m using is as follows.

$HTTP["url"] =~ "^/.well-known/openpgpkey" {
	setenv.add-response-header = (
		"Access-Control-Allow-Origin" => "*",
	)
}

It may be worthwhile to note that if you do any redirection on your domain, such as adding www. in front of it, the key lookup may fail. The error message given by gpg on WKD lookup failures is… poor to say the least, so if anything goes wrong, try some verbose curl commands and ensure that the key is accessible at the right path in a single HTTP request.

Wrapping up

That’s all there’s to it! Adding this to your site should be relatively straightforward, but it may be a huge convenience to anyone looking for your key. If you have any questions or feedback, feel free to reach out to me!