Subject: Re: [Bitcoin-development] Anti DoS for tx replacement

From: Peter Todd <[email-masked]>
Date: Thu, 18 Apr 2013 05:28:24 -0400

On Thu, Apr 18, 2013 at 05:04:44AM -0400, Peter Todd wrote:
> An attack still shuts down useful tx replacement though. For instance in
> the adjusting payments example an attacker sets up a legit adjusting
> payment channel, does a bunch of adjustments, and then launches their
> attack. They broadcast enough adjustments that their adjustment session
> looks like part of an attack, and then don't have to pay for the full
> adjusted amount.

...and actually, that's not a problem if the defender is online, because
they can just broadcast the highest sequence numbered tx, which blocks
further broadcasts by the attacker. You still need some way of
distinguishing the two acts, by time is probably fine, but it'd make a
real attack difficult.

Of course, regardless you are still asking nodes to set aside however
many KB/second to tx replacement transactions, and they're all going to
use different settings, which makes overall network convergence
impossible to guarantee as legit replacement transactions outnumber
non-legit ones. Any protocol requiring the broadcast of more than one or
two replacements, either normally or against an attacker, just isn't
going to be reliable. But many don't, so they're probably doable.

But lets see some working code first...

-- 
'peter'[:-1]@petertodd.org