Ubuntu Extras keyring error [duplicate]

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.

You can automatically import all missing GPG keys using:

sudo add-apt-repository ppa:nilarimogard/webupd8
sudo apt-get update
sudo apt-get install launchpad-getkeys
sudo launchpad-getkeys