> On Feb 9, 2015, at 4:03 AM, Paul Wouters <p...@nohats.ca> wrote: > > On Sun, 8 Feb 2015, Yaron Sheffer wrote: > >> I think we've come a full circle. We now have a proposal that makes >> proof-of-work more deterministic for each type of client (which I find very >> useful). But the weaker clients will always lose, no matter what POW >> solution we choose. This has been a problem with this proposal from day one >> and it's a limitation that we as a group need to decide whether to accept or >> not. > > I'm not yet convinced this proposal will provide a working solution to > the DDOS problem.
Hi, Paul “solution” is hard. Whatever we do, an attacker with unlimited resources can throw more at us. We could block all regular initiations under load, allowing only RFC 5723 resumptions. But this allows an attacker to force us into this mode and effectively deny service to all initiators that don’t have a saved session. So instead we can allow resumptions and also make it more costly for the attacker to mount the attack on regular initiations. Even an easy puzzle, one that my 1.2 GHz single-core ARMv5 with C code can solve in a second is much harder than just the return routability that COOKIE provides. The draft has text about how to make these puzzles a weapon of last resort, so legitimate users hardly ever need to solve them, but even setting the puzzle difficulty to something a strong desktop can do 20 times a second, it’s still better than the two other alternatives: allow the strong desktop to create 1000 half-open SAs in a second, or entirely block the subnet from which the desktop seems to come. Yoav _______________________________________________ IPsec mailing list IPsec@ietf.org https://www.ietf.org/mailman/listinfo/ipsec
