Re: What ASN.1 got right

Michael Thomas <mike@mtcc.com> Wed, 03 March 2021 00:43 UTC

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Subject: Re: What ASN.1 got right
To: Nico Williams <nico@cryptonector.com>
Cc: Phillip Hallam-Baker <phill@hallambaker.com>, IETF Discussion Mailing List <ietf@ietf.org>
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From: Michael Thomas <mike@mtcc.com>
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Date: Tue, 2 Mar 2021 16:43:10 -0800
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On 3/2/21 4:23 PM, Nico Williams wrote:
>
>> 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.

Huh? It's a bit of configuration on the server side that is probably 
captured in provisioning systems. And client provisioning -- which is 
what certs imply -- is extremely problematic. How do I get a client ssh 
cert onto my phone's ssh app, for example? Not having to change client 
behavior or provisioning significantly simplifies the problem.

> 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.
Not having to do anything at all on the client is a significant savings. 
I would much rather the help desk cost of nothing different than taking 
calls on how to install the ssh certs on exotic and not so exotic clients.
>
>> 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.

It's orthogonal to the client side authentication problem though.

>
>> 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.

Uploading a new public keys is the ~same for both. Downloading a client 
cert is a whole lot of something. And if your corpro directory is down, 
you are already in a world of hurt. The advantage of offline 
verification in the age of 24/7 internet is very niche.


>
>> Is anybody using PKINIT?
> Yes.

Where? In any volume?

Mike