On Mon, Mar 30, 2009 at 5:10 PM, "Plüm, Rüdiger, VF-Group" <[email protected]> wrote: >> -----Ursprüngliche Nachricht----- >> Von: Paul Querna >> Gesendet: Montag, 30. März 2009 17:04 >> An: [email protected] >> Betreff: Re: [PROPOSAL] mod_cloudbeat >> >> On Mon, Mar 30, 2009 at 4:45 PM, Jim Jagielski >> <[email protected]> wrote: >> > >> > On Mar 29, 2009, at 11:43 AM, Paul Querna wrote: >> >> >> >> URL Authentication is done by computing an randomly seeded >> md5 signature >> >> of: >> >> seed + "$"+ MD5(seed + shared_secret + uri) >> >> This is base64 encoded, and placed in a 'X-Cloudbeat-Auth' header. >> >> >> > >> > Thinking outloud here... The idea I think is to ensure that >> > the X-Cloudbeat-Auth defines an authenticated server, using >> > the fact that it knows the shared secret. But how does the >> > above do that? Say for example that A and B known to each >> > other and B is sending X-Cloudbeat-Auth. This is easy to >> > find out, of course. So I setup B' to send the exact same >> > header and apply a DoS to B causing it to drop/hang/whatever. >> > Won't A just see B' as B, maybe thinking that it had a >> > momentary glitch and came back? It seems to me that we need >> > some sort of IP:port knowledge in there as well. >> >> In my mind, URL includes the IP/port, so you shouldn't be able to DoS >> it this way. I guess I should of been clearer by what I meant with >> URL. >> >> I was thinking about this more, and we should also change the hash to >> sha1, considering it only takes a few days to find md5 collisions if >> you have enough playstation 3s: >> seed + "$"+ sha1(seed + shared_secret + ip ":"+ port + URI) > > Which IP do you use here? The one from the client that sends the request? > Furthermore we should include a timestamp as we are very vulnerable against > replay attacks otherwise.
Server A wants to talk to B. We include server B's IP in the hash that Server A sends to B. (this prevents B without knowledge of the secret from doing a replay). I dislike adding a timestamp as it tends to make the protocols more brittle, but maybe int(current unix timestamp / 2 days in seconds) would allow boxes out of sync, but prevent long term replay and hash reuse. Thanks, Paul
