Setting up OpenPGP Web Key Directory (WKD)

Sunday, February 5, 2023

gpgopenpgpWKD

Quick note on OpenPGP Web Key Directory (WKD). The GnuPG wiki states:

A Web Key Directory (WKD) provides an easy way to provide and get the current public key for a given email address through HTTPS. Thus it is infrastructure to improve the user experience for exchanging secure emails and files. – https://wiki.gnupg.org/WKD

It basically means it becomes simple to manage your gpg key yourself on your own server. So people can easily add your gpg key with one command: gpg --locate-keys email@domain.tld. They key will be automatically found.

For this to work, there are 2 solutions:

  • Implementing a Web Key Service (WKS): Allow to manage multiple keys for the same domain
  • Hosting a Web Key Directory (WKD): Manage a simple flat structure files “manually” to manage keys of the domain

In this post, I’m setting up Web Key Directory (WKD), not Web Key Service (WKS). WKS is a more advanced configuration that is usefull in case you want to manage many domains and/or many email addresses. In my use case, for the rdi55.pl domain I only manage 1 email address (bac@). In this case, setting up WKD is way easier and faster.

The documentation says:

The Web Key Directory is the HTTPS directory from which keys can be fetched. The Web Key Service is a tool / protocol to automatically publish and update keys in the Web Key Directory. It is optional to reduce the administrative effort of a Web Key Directory. – https://wiki.gnupg.org/WKD

To setup WKD, the documentation indicates:

The hu directory has to be published on your server as https://openpgpkey.example.com/.well-known/openpgpkey/example.com/hu/ (or https://example.com/.well-known/openpgpkey/hu/ if openpgpkey.example.com is not resolvable via DNS).

So I decided to use the non subdomain option (https://example.com/.well-known/openpgpkey/hu/) for extra simplicity.

Following the gnupg wiki for installing WKD, as my gpg version is newer than 2.2.12, I can use the gpg-wks-client command to help:

mkdir /path/to/domain.tld/.well-known/opengpgkey && cd /path/to/domain.tld/ # Creating our working directory
chmod o-rw .well-known/openpgpkey # Set the right permission, otherwise the gpg-wks-client command will fail
gpg --list-options show-only-fpr-mbox -k mail@domain.tld | gpg-wks-client -v --install-key

Result:

gpg-wks-server: gpg: Quantité totale traitée : 1
gpg-wks-server: using key with user id 'User <mail@domain.tld>'
gpg-wks-server: gpg: Quantité totale traitée : 1
gpg-wks-server: directory '.well-known/openpgpkey/domain.tld' created
gpg-wks-server: directory '.well-known/openpgpkey/domain.tld/hu' created
gpg-wks-server: policy file '.well-known/openpgpkey/domain.tld/policy' created
gpg-wks-server: key XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX published for 'mail@domain.tld'
.
└── .well-known
    └── openpgpkey
        └── domain.tld
            ├── hu
            │   └── yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
            └── policy

Because I’m using the solution without the openpgpkey subdomain, it means that the tree is incorrect. I shouldn’t have domain.tld directory within openpgpkey but directly the hu directory. Let’s move things around:

cd .well-known/openpgpkey
mv domain.tld/* ./
rmdir domain.tld

Now, the tree is:

.
└── .well-known
    └── openpgpkey
        ├── hu
        │   └── yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
        └── policy

Now I just need to scp the .well-known directory to the web server.

For the root of the directory, as I’m not using this domain for an actual site, I just created a basic html file that redirects to my main site bacardi55.io:

<!DOCTYPE html>
<html>
  <head>
    <meta http-equiv="refresh" content="3; url='https://bacardi55.io'" />
  </head>
  <body>
    <p>Nothing here, please go to <a href="https://bacardi55.io">my blog</a>.</p>
  </body>
</html>

And voilà, this should normally allow anyone to use gpg --locate-key with my email bac -at- rdi55.pl.


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