Vulnerability Development mailing list archives
Re: Covert Channels
From: Dragos Ruiu <dr () kyx net>
Date: Sun, 20 Oct 2002 05:17:21 +0000
On Fri, 18 Oct 2002 14:41:25 -0400 (EDT) Michal Zalewski <lcamtuf () dione ids pl> wrote:
On Fri, 18 Oct 2002, Ofir Arkin wrote:There are protocols which you CAN perfectly understand and distinguish between legit and not legit traffic.No, because, as I stated, this is not an either-or distinction. Simply put, the presence or abstence of a legitimate traffic, or a specific nature (sequence, target, type) of legitimate traffic can establish a covert channel. ICMP ping with no payload, normalized options, etc, can considered be a legitimate traffic, assuming your policy allows pings. Yet the fact the host is pinged three times, as opposed to two, may establish a covert information flow (practical for some purposes, not practical for others).
To reinforce Michal's statement and to further contradict Ofir and all the would be covert channel filter advocates: You will _never_ be able to screen all covert channels. You can modulate information (albeit slowly) for instance by _not_ pinging in a predetermined fashion. I am reminded of the old "ladies dress code" where spies modulated/encoded/signalled information by having lady messengers wear certain colors/styles of outfits. Uhm you should then force everyone (especially pretty ladies :-) go nude to avoid this possibility... :-P (On second thought this might not be so good it would mean ugly old fat guys would have to go nude too :-) Same thing applies to packets. The only way to block a potential covert channel is to disable the communications link altogether. Blocking covert channels may be futile, but detection is another matter :-). Subverting the covert channel to disinform is left as an excercise for the reader. -- --dr pgpkey: http://dragos.com/dr-dursec.asc 0 = 1 , for large values of zero and small values of one.
Current thread:
- Covert Channels Jeremy Junginger (Oct 16)
- Re: Covert Channels kam (Oct 16)
- Re: Covert Channels Valdis . Kletnieks (Oct 17)
- RE: Covert Channels Ofir Arkin (Oct 18)
- RE: Covert Channels Michal Zalewski (Oct 18)
- Re: Covert Channels David Litchfield (Oct 18)
- Re: Covert Channels Michal Zalewski (Oct 18)
- RE: Covert Channels Ofir Arkin (Oct 19)
- RE: Covert Channels Michal Zalewski (Oct 19)
- Re: Covert Channels Dragos Ruiu (Oct 21)
- Re: Covert Channels Roland Postle (Oct 22)
- Re: Covert Channels Valdis . Kletnieks (Oct 17)
- Re: Covert Channels kam (Oct 16)
- RE: Covert Channels Roland Postle (Oct 21)
- Re: Covert Channels Roland Postle (Oct 17)
- RE: Covert Channels Jeff Nathan (Oct 19)
- RE: Covert Channels Dom De Vitto (Oct 19)