Hi, Mark

> On 3 Jul 2016, at 9:08 PM, Mark McFadden <[email protected]> wrote:

<snip />

> 3) The Internet Draft Currently under consideration is not the best starting 
> point as it assumes that post-quantum pre-shared keys are the preferred 
> solution for quantum resistance. This is not obviously the case; there are a 
> number of drawbacks with the suggested system:

I think this misstates the problem that the draft is trying to solve. The draft 
is not a solution to the problem of authenticating peers in a world where 
adversaries have quantum computers. The draft is a solution to the problem of 
authenticating peers *using pre-shared keys* in such a world. There may be 
different solutions for authenticating peers with other credentials. 

In general, someone deploying an IKE/IPsec solution can choose what credentials 
to deploy. So the system administrator for the Elbonian foreign office may 
decide to deploy NTRU keys to each embassy. Or ECDSA keys. Or pre-shared 
secrets. Or short passwords.

As implementers, we don’t get to decide this. Our implementations are required 
to support whatever credentials the users either already have or wish to 
deploy. If quantum resistance becomes a requirement, implementers like me will 
need to support pre-shared keys in a quantum safe way, and it is up to this 
working group to provide a method of doing just that.

Of course, I as an implementer may decide that I don’t want to solve this 
because maybe I think quantum resistance is not an important requirement, or 
because I don’t believe people are actually using pre-shared keys. Similarly, 
the WG may decide that solving the quantum resistant PSK method is not 
important enough to work on. Or that this particular solution to this problem 
is not the right one.

However, with my vendor hat on, I know that PSKs are used extensively (and 
nobody’s asking me whether this is a good idea or not), and I have heard that 
some users are beginning to ask questions about quantum resistance.So I believe 
that there is a problem to solve here. 

Yoav

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