summary [was: vnc and security]

W. Brian Blevins brian.blevins "at" tridia.com
Wed, 20 Jun 2001 14:00:31 +0000


Jeff,

Jeff Walker wrote:
> 
> Looks like the problem with the Tridia viewer was me.  I tried it again and
> didn't have any trouble, so I don't know what the problem was.  Sorry for
> the false error report.

Error reports are a great way for developers to find problems in
open source.  The only reason I understand the protocol level
encoding behavior is from looking at the source code.

> >
> 
> Indeed that was with the Tridia viewer, which is the one I use.  What I did
> was use the "connection options..." dialog to change the encoding on the
> fly.  (sorry for the lack of clarity)

Ah, so the viewer is running on Win32.  I still think the server would
log an error for an unknown encoding.  However, if I recall correctly,
the Win32 viewer builds a list of all possible encodings.  The user
selected encoding is simply placed at the beginning of the list and
therefore given priority by the server.  If the server can not do that
encoding, it will fall back to one of the others.  This means that
selecting zlib in the TridiaVNC viewer will most likely not result in
raw encoding against an AT&T server.  You would probably get hextile
in that case.

> 
> I'm seeing some strange things when I connect by hand to the server.  I
> believe I am using the same viewer, but when I connect by hand, I get
> "ignoring unknown encoding type", but I am specifying hextile, and that is
> what I get.  Strange.  Usually, I use a dos batch program to run the viewer
> (the same viewer) with a "config" option and I pass it settings saved from a
> previous run.

As mentioned above, the Win32 viewer builds a list of all encodings, from 0
to 5 or 6.  RFB encoding #3 is no longer supported by any of the current
servers.  So you will often see an error message in the server logs about an
unknown encoding #3 when a Win32 viewer is connecting.  This is normal.

The config option may prevent the entire list behavior, I'm not sure.

> 
> I guess part of the problem might just be that I don't know what type of
> server I am using.  I know that I patched it to fix a problem that someone
> on the list gave me, to fix a problem when the mouse cursor moves via an X
> app, the vnc was moving it back.  So I am reluctant to use a vanilla server,
> but I may experiment with that when I have more time.

If you get an unknown encoding error in the log file for zlib (encoding #6),
then you likely have an AT&T server.

-- 
Brian 
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