Problem

I was trying to configure an Arch Linux virtual machine with Vagrant + Virtual Box and ran the following commands:

mkdir archlinux
cd archlinux
vagrant init archlinux/archlinux
vagrant up

After the vagrant box was downloaded and the virtual machine was configured and up running, I logged in:

vagrant ssh

The first thing I did was to upgrade the system by running:

sudo pacman -Syyu

After all the packages were downloaded, it asked me to import some PGP keys:

:: Import PGP key 3B94A80E50A477C7, "Jan Alexander Steffens (heftig) <heftig@archlinux.org>"? [Y/n]
:: Import PGP key 3B94A80E50A477C7, "Jan Alexander Steffens (heftig) <heftig@archlinux.org>"? [Y/n]

and it gave me the following error with every single package:

error: archlinux-keyring: signature from "Christian Hesse <eworm@archlinux.org>" is unknown trust
:: File /var/cache/pacman/pkg/archlinux-keyring-20200603-1-any.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
Do you want to delete it? [Y/n]

The latest version of the Arch Linux box was released on June 3rd and this error also occurred with some previous versions released this year, even when I was trying to install any package.

Solution

There's an answer to a post in the Manjaro Linux Forum suggesting that the error can be fixed by running the following commands:

sudo rm -r /etc/pacman.d/gnupg
sudo pacman -Sy gnupg archlinux-keyring manjaro-keyring
sudo pacman-key --init
sudo pacman-key --populate archlinux manjaro 
sudo pacman-key --refresh-keys 
sudo pacman -Sc

But running sudo pacman -Sy gnupg archlinux-keyring manjaro-keyring will give the same error and the manjaro-keyring package is not necessary as well as manjaro in sudo pacman-key --populate archlinux manjaro, as we're running Arch Linux. So the steps to follow are:

sudo rm -r /etc/pacman.d/gnupg
sudo pacman-key --init
sudo pacman-key --populate archlinux 
sudo pacman-key --refresh-keys
sudo pacman -Sy gnupg archlinux-keyring 
sudo pacman -Sc

After that we can upgrade the system or install a package as usual.