Date: Sat, 21 Mar 2015 20:30:09 -0700 From: Russ Allbery <eagle@...ie.org> To: oss-security@...ts.openwall.com Subject: Re: CVE for Kali Linux Daniel Micay <danielmicay@...il.com> writes: > It would be much better to provide the download via HTTPS from a domain > that's HSTS preloaded and ideally has some level of key pinning. We are > all well aware that few users are going to go through a manual process > on the command-line to verify the download, especially if they're on > Windows as they won't have the commands that are being used. Unless you do certificate pinning, I don't see how this adds much meaningful security. Commercial CAs at the level of browser verification of server certificates are a bad joke. You should assume that a moderately sophisticated attacker can get a valid brower-acceptable certificate for any web site they choose, particularly given the number of opportunities attackers have to insert new root CAs into the user's browser store. (Sometimes even preinstalled on the factory-shipped computer.) I think the approach Debian takes here has some real merit, although it would still be a good idea to offer https downloads just for privacy reasons (it's hard to do so just because of the way the mirror network and the commercial CA world work). Because the downloads are over HTTP, everyone goes "wait, what?" and looks for the *actual* security, which, provided you can get a good bootstrap of the initial public PGP keys, is quite a bit better than just TLS verification of the server. As opposed to seeing TLS and assuming that adds meaningful verification of the server, which is dubious. And that approach has the significant advantage that, because it uses proper public key cryptography, anyone can mirror the packages and you don't have to care where you got the packages from or establishing a full trust chain for them. You only have to do that for the published signing key, and then verify the signatures, which apt does for you. This is a pretty huge advantage, since it means that large organizations can just mirror the repository with rsync, and any apt client can be pointed to the mirror without needing to configure any new keys and while getting the same level of security validation. The problem, of course, is how to do the bootstrap, and that's where the original post came in. The ISO images presumably (like Debian's) include the pre-installed repository signing keys, so known-good ISO images are a way to bootstrap the security of subsequent downloads. But this requires actually verifying the ISO signatures in some meaningful way, which is hard for the average user to do, since there isn't any pre-existing trust relationship that one can easily leverage. -- Russ Allbery (eagle@...ie.org) <http://www.eyrie.org/~eagle/>
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