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bug#34125: Installation script needs to be secured with a gpg signature

From: Ricardo Wurmus
Subject: bug#34125: Installation script needs to be secured with a gpg signature
Date: Tue, 22 Jan 2019 08:18:09 +0100
User-agent: mu4e 1.0; emacs 26.1

Hi Björn,

> I was looking at the installation video from Laura (not yet public) and
> wondered about that:
> We just download the installation script:
> $ wget https://.../guix-install.sh
> Then we go on directly executing that script.
> Shouldn't that be save-garded by a PGP-signature too?

I don’t know.

> Because if it is not, the user could be tricked into a script that
> downloads a "bad" Guix installation tarball.

To avoid having the user tricked we use HTTPS.  At least the users will
know that this file comes from the official project website.

A user who is tricked into downloading a script from a malicious site
could just as well download a matching signature from somewhere else, so
the script body itself should be signed.  We can’t sign the whole file
because the first line must be the shebang — unless we forgo the shebang
and the “chmod +x” instruction and ask people to execute it with “sudo
bash guix-install.sh”.  “gpg --clear-sign” adds a block of text before
and after the file, which would be a syntax error in a shell script.

We are probably stuck with having a separate signature file.  I don’t
know if it’s worth doing when HTTPS is used to fetch the script from an
authoritative source.

> That's what we are always
> criticising about others wget-scripts that install whatever to the user.

The criticism is aimed at “curl | sudo bash” instructions that execute
scripts off the Internet without prior inspection as root.


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