On Wed, 16 Jun 2010, Dan McGee wrote:
On Wed, Jun 16, 2010 at 6:08 PM, Dimitrios Apostolou <jimis@xxxxxxx> wrote:
Hey, what do you think about this way of verifying packages?
On Tue, 15 Jun 2010, Dimitrios Apostolou wrote:
On another note, an easy but maybe a bit costly way to avoid any MITM
tampering to packages, is serve *.md5 files for every package through a
trusted HTTPS host. Then everyone can query that single host and check if
the package he got from a mirror is safe.
Costs: A little more traffic by serving hash files to everyone plus the
cost of the certificate from a CA. Is the income Arch receives from ads and
schwag enough for such a simple solution?
Let me explain it a bit more:
Pacman downloads package-1.tar.xz from a random mirror.
It then fetches:
https://sums.archlinux.org/exactly/the/same/path/package-1.tar.xz.sha1
Pacman should then know whether the connection to sums.archlinux.org was
tampered, since the certificate is signed from a CA in ca-bundle.crt. So if
the two hashes match, the package is safe (as safe as the archlinux
server...)
That way any type of file can be verified (packages, db files, PKGBUILDs,
patches etc) provided that its cryptographic hash is in that HTTPS host.
Obviously to be able to verify db files, they need a timestamp appended to
them, e.g. core-YYYYMMDDHHMM.tar.gz. That necessary change is perhaps the
most difficult part of this proposal.
If too many small files is a problem, maybe the whole db.tar.gz can be
served (at the cost of a higher bandwidth utilisation).
This solution doesn't use package signing nor a web-of-trust. It simply
piggybacks on the tried and true HTTPS mechanism. Primary advantage is the
lack of complexity which makes it easy to understand and implement.
What do you think?
I think that someone could blow this apart. I break in, touch a
package of my choosing without telling anyone, and update the checksum
file. Bam- everyone's systems are fucked and the developers never knew
because you didn't do anything both cryptographically secure and
verifiable, you just added some indirection to the process.
HTTPS is both cryptographically correct and verifiable. The case you
mention is if someone breaks the one end, that must be guarded most.
The danger is there everywhere, on the web-of-trust case someone that
broke into a dev's machine and got the key, can sign anything he wants and
serve it to the user, who would know? On the distro-wide key case, it's
like someone stealing that key, and be able to serve/sign everything.
Here, we don't have a key to keep safe, but a server. So it needs special
attention about who has access and how hashes are submitted (although
HTTPS can secure this process too). But I admit that keeping a server safe
is a bit harder than keys, if that was your point.
Dimitris
-Dan
