I cannot get my SCR3310 smart card reader to work in Ubuntu 20.04.2, despite installing cackey, pcsc_scan and the DOD certificates

Many device access problems can be resolved through group membership changes.

Specifically, if ls -l shows that the group permissions (the second "rwx" triplet) is "rw" (e.g."-rw-rw----"), then, adding oneself to the group that owns the device will grant rw access.

Here's how:

device="/dev/whatever"
sudo adduser $USER $(stat -c "%G" $device)

This allows you membership in the group that can rw the device, but there is one more step.

To make all your processes members of the new group, logout and login. Group memberships are set up at login time.

To create a single process in the new group (for testing, prior to logout/login):

newgrp $(stat -c "%G" $device)  

or, just type the group name. See man newgrp.

I've had issues using the "latest" cackey on 20.04 (however I'm running KDE). For some reason I've only bean able to get the version 7.5.1 for Debian to work using the instructions from MiltaryCAC.com

You can download 7.5.1 here: cackey_0.7.5-1_amd64.deb

Install with sudo dpkg -i cackey_0.7.5-1_amd64.deb

That said, the KDE package manager "updates" cackey frequently, and breaks it. So I have to keep version 7.5.1 install file and reinstall it after I log in, fortunately I don't have to redo any of the other install steps, just run the command above BEFORE you open any web browsers. It's a bit of a hack but works.