✗ chdist apt precise update                        
Ign:1 http://archive.ubuntu.com/ubuntu precise InRelease
Get:2 http://archive.ubuntu.com/ubuntu precise Release [49.6 kB]
Get:3 http://archive.ubuntu.com/ubuntu precise Release.gpg [198 B]
Ign:3 http://archive.ubuntu.com/ubuntu precise Release.gpg
Reading package lists... Done  
W: GPG error: http://archive.ubuntu.com/ubuntu precise Release: The following signatures were invalid: 630239CC130E1A7FD81A27B140976EAF437D05B5
E: The repository 'http://archive.ubuntu.com/ubuntu precise Release' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.