Error actualizando un Raspberry PI

 pi@raspberrypi ~ $ sudo apt-get update
.....
.....

Fetched 473 B in 21s (22 B/s)
Reading package lists... Done

A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://archive.raspberrypi.org wheezy Release: The following signatures were invalid: BADSIG 82B129927FA3303E Raspberry Pi Archive Signing Key

W: Failed to fetch http://archive.raspberrypi.org/debian/dists/wheezy/Release
W: Some index files failed to download. They have been ignored, or old ones used instead.
pi@raspberrypi ~ $


Si esta actualizando un Raspberry Pi Model B+, y tiene un error como el anterior debe ejecutar los siguientes pasos:

sudo apt-get install aptitude
sudo aptitude -o Acquire::http::No-Cache=True -o Acquire::BrokenProxy=true update
sudo apt-get clean
cd /var/lib/apt
sudo mv lists lists.old
sudo mkdir -p lists/partial
sudo apt-get clean
sudo apt-get update


Notas y Referencias:

•  Solución obtenida del foro de Raspberry Pi Problems with ap-get update. Please Help 
• Updating and Upgrading Raspbian