How to get public key for http://ppa.launchpad.net

If you come across this error after yunning aptitude update

1. W: GPG error: http://ppa.launchpad.net intrepid Release: The following signatures couldn't be verified because the public key is not available:
2. NO_PUBKEY 7D2C7A23BF810CD5
3. W: You may want to run apt-get update to correct these problems

due to a missing GPG key do the following to correct the problem

1. gpg --keyserver subkeys.pgp.net --recv 7D2C7A23BF810CD5

Replace the key number “7D2C7A23BF810CD5″ with the one included in your error message

1. gpg --export --armor 7D2C7A23BF810CD5 | sudo apt-key add -

After that, the key will be added to a list and the error will not reappear.