sudo apt-get update
Get:1 http://de.archive.ubuntu.com trusty InRelease [54.9 kB]  
Ign http://de.archive.ubuntu.com trusty InReleaselib/apt/lists/partial/de.archive.ubuntu.com_ubuntu_dists_trusty_InRelease into data and signature failed
E: GPG error: http://de.archive.ubuntu.com trusty InRelease: Clearsigned file isn't valid, got 'NODATA' (does the network require authentication?)