Re: [Tcpcrypt] Initial questions

Joe Touch <touch@isi.edu> Thu, 19 June 2014 18:35 UTC

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Date: Thu, 19 Jun 2014 11:35:06 -0700
From: Joe Touch <touch@isi.edu>
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Subject: Re: [Tcpcrypt] Initial questions
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On 6/19/2014 11:23 AM, ianG wrote:
> On 19/06/2014 18:55 pm, Joe Touch wrote:
...
> When did TCP have this 'urgent decision' ?  If it happened several years
> after 1996, then what you have is a forewarning that was ignored.  If it
> was after 2004, well, no amount of warning will do, and algorithmic
> agility is a crutch that should be stripped away in order to focus
> attention.

2004 was the first practical attack on MD5; the first draft of TCP-AO 
was 2007. It took another three years for the IETF sausage mill to 
generate a final result.

Given that TCP-AO was used mostly for router security, and nobody had 
reported a successful MD5-based attack in the wild, that's not bad IMO.

The primary problem with TCP MD5 was that it wasn't algorithm-agile.

...
>> That's why TCP-AO included two 'must implement' algorithms from the
>> start, and why it's important to do so here as well.
>
> I'd like to see some historical evidence of when this actually made a
> difference?  Yes, we understand the idea.  But we now have 20 years of
> experience in Internet protocols.  We have data.  What does the data say
> about algorithmic agility, in the field?

You're arguing two points at the same time.

1) use one algorithm

	I've already pointed out how that's dangerous; it prevents
	pre-deploying a backup when a given algorithm is deprecated.

2) don't have algorithm agility

	This is counter to your earlier post. If you consider
	that any one algorithm won't last forever, then ultimately
	we'll want a solution that can support different algorithms.

I don't like either of the above, but they're separate points.

Joe