[FFmpeg-devel] Fix NTP time in RTCP SR packets

Reimar Döffinger Reimar.Doeffinger
Fri Feb 15 12:02:21 CET 2008

On Fri, Feb 15, 2008 at 11:30:36AM +0100, Luca Abeni wrote:
> Reimar D?ffinger wrote:
> > Uh, as I understand it, this sends out the local time with usec
> > precision. The server sure as hell does not know that, and it could e.g.
> > be used to guess values if someone uses a stupid random number
> > generator, system/network load and other things.
> > IOW this is one of the things everyone planning a side-channel attack
> > just dreams of.
> I do not fully understand the problem here, but I believe you
> because I am no expert in security.
> I am just surprised, because you are basically saying that all
> the RTSP server in the world have security problems (I checked
> a lot of implementations, and they all properly fill the NTP
> field).

These things are not in general exploitable, esp. not in away that can
be generalized to take over lots of servers.
But it does allow to get additional information about a PC, which will
always weaken security.
side-channel attacks are always a fickly thing and it is rather unlikely
that someone will actually be affected by one, but I still do not like
things that make it easier - mostly since I can't avoid the feeling that
this is there because someone was too lazy to think of a good solution
instead of a quick hack.
Also, the examples that I have for using this only make it easier to
exploit an already given weakness (bad random number generator,
detecting a wrong local time that would allow to use expired
So to summarize: I do not want to claim that this is a security problem
itself, but I feel like it might weaken the security and confidentiality
of the system as a whole and ease exploiting existing problems, thus I
do not feel good with it being enabled by default. 

Reimar D?ffinger

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