Subject: | Don't assume that gpg is installed and available |
You currently use gpg pretty much blindly from what I can see.
What you probably should do is to at the very least put a check into
your Makefile.PL to confirm in advance that gpg is installed and tell
the installer to go and install gpg first (assuming GPG is compulsory).
The system call to use gpg looks relatively clean, but you might want to
look into IPC::Run3, which is basically a cross-platform equivalent of
system.