Tor installation error - SIGNATURE VERIFICATION FAILED

Installing Tor bundle from Ubuntu Software center on 16.04.

I have searched for similar cases. But only found one post, that was marked as a duplicate... But, it doesn't tell you where the duplicate is OR what the title of the duplicate is. And, I couldn't find it anywhere.

When starting the Tor Browser from the system menu (I am currently using the MATE distro of 16.04) It starts a "download" of the Tor browser. (Which is already installed from the USC...?) And, once it is finished with that, about five minutes later, I get "SIGNATURE VERIFICATION FAILED - You might be under attack, or there might just be a networking problem."

OK, So, I deactivate UFW, and the firewall on my router... then click "start" to retry the download... Now, with NO firewall active, another five minutes later, I receive the same error.

The purpose for using TOR is that I want to use an application called RetroShare with family and friends on other continents. The app requires a TOR "secrethidden space" and it's X.onion address in order to work. But, I cannot for the life of me figure out what the problem is with this TOR Browser. Documentation is (intentionally?) cryptic. It says to "do XYZ" with no hint whatsoever HOW to do XYZ or what it even means to "do XYZ".

Anyway, I have tried to follow reasonable methodology as far as I am able. But, the failures provide no clue as to what steps need to be taken to avoid the error happening over and over again. If it isn't firewall, I have no clue how to proceed.

This is due to an outdated key for verifying the torbrowser-launcher download. Try:

gpg --homedir "$HOME/.local/share/torbrowser/gnupg_homedir/" --refresh-keys --keyserver pgp.mit.edu

This worked fine in my case and I was able to successfully launch the tor browser.

Duplicate: https://unix.stackexchange.com/questions/341513/torbrowser-signature-verification-fails-a-glitch-or-an-attack/341519

It's fixed in the latest version of torbrowser-launcher. Add the author's PPA to get the update:

sudo add-apt-repository ppa:micahflee/ppa

Try the following:

gpg --homedir "$HOME/.local/share/torbrowser/gnupg_homedir" --refresh-keys --keyserver keyserver.ubuntu.com

It worked for me on ubuntu 16.04