On Wed, May 21, 2014 at 5:48 AM, Jason A. Donenfeld <ja...@zx2c4.com> wrote: > Temporary work around is to hard code IPs into NTP.
It'd be neat to do the following: (1) Do a DNS lookup for NTP servers, fetching DNSSec information. (2) If a signature/clock sync issue is the only barrier to validating the response, still use the response for the next couple steps. (3) Fetch time from the NTP servers, but only use it to validate the DNS response signatures. (4) If the signature now checks out, sync the local clock to the data. Code could ship minimum timestamps to accept in step #3, thereby ensuring that malicious, replayed responses are never older than the release itself. This is superior to shipping fixed IPs because this algorithm ensures the IPs are *at least* as fresh as the release rather than *exactly* as fresh as the release. It's a shame that there's no provision in DNSSec for a server creating custom-signed responses based on a client nonce, just for this sort of case. That would only require the ability to generate one-time values, even if it's just a MAC address plus a counter. Might be an easy way to DoS attack DNS servers, though, by breaking through caches and forcing lots of signing work. Wouldn't work with servers supporting only offline signing, either. _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel