Failed to verify signature archive-contents.sig

[Seth Hoenig]

After freshly installing the emacs25-nox package, the very first command I ran was

> M-x list-packages

Which immediately produced this error.

Failed to verify signature archive-contents.sig:
No public key for 066DAFCB81E42C40 created at 2020-02-10T16:05:02-0600 using RSA
Command output:
gpg: Signature made Mon 10 Feb 2020 04:05:02 PM CST
gpg: using RSA key C433554766D3DDC64221BFAA066DAFCB81E42C40
gpg: Can't check signature: No public key

I have no .emacs or .emacs.d configured - this is a 100% fresh "apt install" of emacs25-nox.

I would expect Emacs packaged with Ubuntu to be bundled with a valid key!

Also, none of the instructions on the internet actually work on getting this fixed!

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: emacs25-nox 25.2+1-6
ProcVersionSignature: Ubuntu 5.3.0-28.30~18.04.1-generic 5.3.13
Uname: Linux 5.3.0-28-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.9
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Mon Feb 10 20:26:51 2020
InstallationDate: Installed on 2019-12-29 (43 days ago)
InstallationMedia: Ubuntu 18.04.3 LTS "Bionic Beaver" - Release amd64 (20190805)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: emacs25
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[apt-ghetto (apt-ghetto)]

I had the same issue with emacs-nox, but I have installed it on Windows 10 inside of WSL2 with Ubuntu 18.04.

I was able to workaround the issue with:
gpg --homedir ~/.emacs.d/elpa/gnupg --keyserver hkps://keyserver.ubuntu.com:443 --receive-keys 066DAFCB81E42C40

After successfully importing the key, a package-refresh-contents worked fine.