This is what happens when you have a repository that makes HTTP->HTTPS redirection in your sources.lists, and you didn't have apt-transport-https installed: # apt-get update E: The method driver /usr/lib/apt/methods/https could not be found. N: Is the package apt-transport-https installed? It didn't tell me which repository causes the problem, but oh well... Let's try to install apt-transport-https: # apt-get install apt-transport-https Reading package lists... Done Building dependency tree Reading state information... Done The following NEW packages will be installed: apt-transport-https (1.0.6) 0 upgraded, 1 newly installed, 0 to remove and 3 not upgraded. Need to get 0 B/132 kB of archives. After this operation, 221 kB of additional disk space will be used. WARNING: The following packages cannot be authenticated! apt-transport-https Install these packages without verification? [y/N] E: Some packages could not be authenticated This is rather user-unfriendly. Why does a problem with one repository cause authentication warnings for an unrelated repository?