Recently I got lots of GPG errors and tried the following methods at various stages:

1. sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3E5C1192
2. sudo apt-get install -reinstall ubuntu-extras-keyring (For Ubuntu Extras only)

3. gpg –keyserver keyserver.ubuntu.com –recv 3E5C1192
gpg –export –armor 3E5C1192 | sudo apt-key add -
sudo apt-get update

4. sudo aptitude -o Acquire::http::No-Cache=True -o Acquire::BrokenProxy=true update

5. sudo -i
apt-get clean
cd /var/lib/apt
mv lists lists.old
mkdir -p lists/partial
apt-get clean
apt-get update

I again got BADSIG error for extras.ubuntu.com today. So, I'm really at a loss what's causing this error to occur time and again. I really want to solve this problem once and for all.