I have installed debian jessie from unetbootin pendrive and without network drivers. After booting from HDD, I have added mounted pendrive to apt sources (with file:// prefix). I have two problems.
- gnome-shell and other packages are not available from official mirrors (but are found on pendrive)
- apt warns that packages in pendrive are not secure
I expected to expected to find GPG keys somewhere on pendrive and that they somehow passed verification during installation. How does this process work, so that I can fix it?