Ubuntu apt update funktioniert nicht - GPG signatures invalid Error?

Hey! Wenn ich versuche, auf Ubuntu den apt update Befehl auszuführen, bekomme ich einen sehr langen Error:

tux@cruggserver:~$ sudo apt-get update
Ign:1 http://archive.ubuntu.com/ubuntu precise InRelease
Hit:2 http://archive.ubuntu.com/ubuntu precise Release
Get:3 http://archive.ubuntu.com/ubuntu precise-updates InRelease [55,7 kB]
Get:4 http://archive.ubuntu.com/ubuntu precise-security InRelease [55,7 kB]
Get:5 http://archive.ubuntu.com/ubuntu precise-backports InRelease [55,7 kB]
Get:6 http://archive.ubuntu.com/ubuntu precise Release.gpg [198 B]
Err:3 http://archive.ubuntu.com/ubuntu precise-updates InRelease
  The following signatures were invalid: 630239CC130E1A7FD81A27B140976EAF437D05B5
Err:4 http://archive.ubuntu.com/ubuntu precise-security InRelease
  The following signatures were invalid: 630239CC130E1A7FD81A27B140976EAF437D05B5
Err:5 http://archive.ubuntu.com/ubuntu precise-backports InRelease
  The following signatures were invalid: 630239CC130E1A7FD81A27B140976EAF437D05B5
Ign:6 http://archive.ubuntu.com/ubuntu precise Release.gpg
Reading package lists... Done
W: GPG error: http://archive.ubuntu.com/ubuntu precise-updates InRelease: The following signatures were invalid: 630239CC130E1A7FD81A27B140976EAF437D05B5
E: The repository 'http://archive.ubuntu.com/ubuntu precise-updates InRelease' 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.
W: GPG error: http://archive.ubuntu.com/ubuntu precise-security InRelease: The following signatures were invalid: 630239CC130E1A7FD81A27B140976EAF437D05B5
E: The repository 'http://archive.ubuntu.com/ubuntu precise-security InRelease' 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.
W: GPG error: http://archive.ubuntu.com/ubuntu precise-backports InRelease: The following signatures were invalid: 630239CC130E1A7FD81A27B140976EAF437D05B5
E: The repository 'http://archive.ubuntu.com/ubuntu precise-backports InRelease' 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.
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.

Ich habe schon sehr vieles im Internet probiert, jedoch hat nichts geklappt.

Linux, Ubuntu, apt-get, GPG
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