Re: What ASN.1 got right

Nico Williams <nico@cryptonector.com> Wed, 03 March 2021 00:23 UTC

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Date: Tue, 2 Mar 2021 18:23:31 -0600
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From: Nico Williams <nico@cryptonector.com>
To: Michael Thomas <mike@mtcc.com>
Cc: Phillip Hallam-Baker <phill@hallambaker.com>, IETF Discussion Mailing List <ietf@ietf.org>
Subject: Re: What ASN.1 got right
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On Tue, Mar 02, 2021 at 04:17:28PM -0800, Michael Thomas wrote:
> > Now, maybe you have something different in mind.
> 
> I'm talking about the server side sshd just fetching the associated ssh keys
> with the user trying to log in, maybe with some authz sprinkled in for finer
> granularity. It could be LDAP, it could whatever you want. I don't know how
> configurable sshd is, so that might limit your choices.

I wouldn't want to do this.  It's much more complex than the client
sending a certificate.

And getting their public key(s) (they will almost certainly have more
than one, and many ephemeral) into the directory is the equivalent of
getting a certificate issued.  So you're not saving anything, and you're
adding complexity, and if you're using LDAP you're not even getting rid
of x.500 or ASN.1.

> I'm just using LDAP as an example of a well known corpro directory. It could
> be anything. It just needs to be something online that can store the name
> public key(s) binding so that the sshd can see if they should allow that
> user/key to log in.

It can't be anything.  It has to be standard-enough.

> > The client is also a relying party though, since it has to authenticate
> > the server.
>
> If you care about that, I suppose. I think most people do the leap of faith
> and known_hosts ignores the problem.

I very much care about that.  Certainly in a corporate network.

> I don't see how doing nothing at all on the client can be "infinitely
> easier" than doing a lot of something else. [...]

It's not nothing.  New keys?  Update the directory.  Same complexity as
getting keys certified, only worse because the online CA only needs to
be online when you want new keys / certs, but the directory has to be
online any time you want to use those keys.

> Is anybody using PKINIT?

Yes.

Nico
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