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Date: Thu, 13 Mar 2014 16:37:26 -0400
From: Patrick Mylund Nielsen <>
To: "" <>
Subject: Re: [PHC] "Why I Don't Recommend Scrypt"

On Thu, Mar 13, 2014 at 4:31 PM, Tony Arcieri <> wrote:

> On Thu, Mar 13, 2014 at 1:09 PM, Patrick Mylund Nielsen <
>> wrote:
>> What I'm saying is you have exactly the same problems with any other kind
>> of request a user can make. You can DDoS a website simply by doing regular
>> login requests but with random (and non-existing) usernames, too.
> If you can leverage a slow PHF, the attack becomes far more asymmetrical
> in terms of what it costs the attacker versus the resulting impact on your
> system.
> I am honestly curious: Has the compute overhead ever actually impacted
>> anyone who had more general DDoS protections?
> There's no such thing as a "general DDoS protection" any more than there
> is a general solution to someone taking down your power grid. You must
> consider every aspect of the request pipeline from your upstream PoPs to
> your backend applications, and the solutions you implement at each step of
> the way apply to every part of your application. Every part of the request
> pipeline is vulnerable in different ways.
> You need to armor your upstream PoPs via automated BGP flowspec
> directives, ensure an attacker can't exhaust the capacity of your HTTP
> routing mesh, and ensure that your backend apps can't spin indefinitely on
> slow endpoints. There are no general solutions to this. None.

When I say general protection I'm not implying that there is a One Way to
prevent DDoS: I am saying that there are mechanisms to combat a DDoS that
work equally well for a DDoS being performed through a username, contact
form, or password field.

I understand what you are saying, but I am completely unconvinced that this
hypothetical attack is any reason whatsoever that we should discourage
people from strengthening their password digests. (Not to mention most
companies won't *ever* have a DDoS problem!) Where is the evidence?

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