signature verification error for wine - index files failed to download - changing mirror doesn't help

When I sudo apt-get update I get the error shown below.

W: An error occurred during the signature verification. 
The repository is not updated and the previous index files will be used. 
GPG error: https://dl.winehq.org/wine-builds/ubuntu bionic InRelease: 
The following signatures couldn't be verified
 because the public key is not available: NO_PUBKEY 76F1A20FF987672F
W: Failed to fetch https://dl.winehq.org/wine-builds/ubuntu/dists/bionic/InRelease
The following signatures couldn't be verified
 because the public key is not available: NO_PUBKEY 76F1A20FF987672F
W: Some index files failed to download. They have been ignored, or old ones used instead.

So I go ahead and change my mirror as suggested by this Ask Ubuntu answer. Then I restart the computer. And I still get the same error above when I sudo apt-get update.

Let's try and reinstall the keys.

$ wget -nc https://dl.winehq.org/wine-builds/Release.key && sudo apt-key add Release.key
File ‘Release.key’ already there; not retrieving. OK

And I might as well ping -c3 archive.ubuntu.com and my packet loss is 0%. What else do I need to do?

Solution 1:

As of 2018-12-19 08:07 there is a new winehq.key keyfile as mentioned here.

Download the new repository key and add it to the list of trusted keys:

cd /tmp
wget -nc https://dl.winehq.org/wine-builds/winehq.key
sudo apt-key add winehq.key
sudo apt update

As mentioned by @jason-hunter in a comment, apt update will ask if you accept the changes in the repository, whereas apt-get update will show an error and fail.

Solution 2:

Note that after adding the new keyfile, it is better to use apt update rather than apt-get update, as it will prompt you to accept the changes.

So in full:

wget -nc https://dl.winehq.org/wine-builds/winehq.key && sudo apt-key add winehq.key && sudo apt update