root@PiHole:~# apt-get install --allow-unauthenticated gnupg2
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
ncurses-base : Breaks: libtinfo5 (< 6.1) but 6.0+20160213-1ubuntu1 is to be installed
E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.
root@PiHole:~# apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 3B4FE6ACC0B21F32 40976EAF437D05B5
E: gnupg, gnupg2 and gnupg1 do not seem to be installed, but one of them is required for this operation
root@PiHole:~# apt-get update --allow-insecure-repositories
Get:1

xenial InRelease [247 kB]
Get:2

xenial-updates InRelease [99.8 kB]
Get:3

xenial-backports InRelease [97.4 kB]
Get:4

xenial InRelease [11.5 kB]
Get:5

xenial-security InRelease [99.8 kB]
Ign:1

xenial InRelease
Ign:2

xenial-updates InRelease
Ign:3

xenial-backports InRelease
Ign:4

xenial InRelease
Ign:5

xenial-security InRelease
Fetched 555 kB in 0s (1161 kB/s)
Reading package lists... Done
W: GPG error:

xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: The repository 'http://archive.ubuntu.com/ubuntu xenial InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error:

xenial-updates InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: The repository 'http://archive.ubuntu.com/ubuntu xenial-updates InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error:

xenial-backports InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: The repository 'http://archive.ubuntu.com/ubuntu xenial-backports InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error:

xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: The repository 'http://archive.canonical.com/ubuntu xenial InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error:

xenial-security InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: The repository 'http://archive.ubuntu.com/ubuntu xenial-security InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.