Decentralized PGP Keys with WKD
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After creating a PGP key, it is common to distribute it to various keyservers. However, anyone can upload to these keyservers impersonating someone else. One solution is to use a decentralized identities approach, however, if your email is on your own domain that you tell every soul about, why not have your own website host the key? This is where the Web Key Directory (WKD) protocol comes in.
Setting up WKD
To start we need to create a new folder on our webserver:
mkdir .well-known/openpgpkey/hu
In it, add an empty policy file
touch .well-known/openpgpkey/hu/policy
Now we need to add our key to the folder. The key needs to be stored in the file named after the email’s WKD hash. We can get this hash through the following command:
gpg --with-wkd-hash --fingerprint brozek@brandonrozek.com
Replacing my email with yours. At the current moment, this returns the following for me:
pub ed25519 2022-12-14 [SC] [expires: 2023-12-14]
5F37 830B FA46 FF78 81F4 7AC7 8DF7 9C3D C5FC 658A
uid [ultimate] Brandon Rozek <brozek@brandonrozek.com>
o1dbwkdx683fduwgzmrbwa3yip41frdn@brandonrozek.com
uid [ultimate] Brandon Rozek <hello@brandonrozek.com>
im4cc8qhazwkfsi65a8us1bc5gzk1o4p@brandonrozek.com
The string starting witho1dbwk is the WKD hash for brozek@brandonrozek.com and the string starting with im4cc8qh is the WKD hash for hello@brandonrozek.com.
Let’s store that hash in $WKD
export WKD="o1dbwkdx683fduwgzmrbwa3yip41frdn"
The WKD specification says to upload the non-armored (binary) version of our key.
gpg --no-armor --export brozek@brandonrozek.com > .well-known/openpgpkey/hu/$WKD
After uploading it to our webserver, it needs to be configured with the right content type and access control headers.
In Nginx:
location /.well-known/openpgpkey {
default_type application/octet-stream;
add_header Access-Control-Allow-Origin "*";
}
Now we can check our setup using the website:
https://metacode.biz/openpgp/web-key-directory
Using WKD
Many applications currently support WKD, though I’ll show how we can use gpg to search for someone’s key.
gpg --auto-key-locate wkd --locate-key brozek@brandonrozek.com
This will not only locate but import the key into our keystore.
With WKD, we didn’t have to trust anyone but the DNS provider in order to retrieve the key. The biggest downside with this approach, however, is that most people do not have an email on their own domain. Since nowadays, many people use gmail as their primary provider, they will have to fallback to using a different approach for distributing their keys.