> Is this actually all the way technically correct? As far as I know, there is no requirement that the trust chains for server certificates and client certificates are in any way related. It seems to me that it would be perfectly possible for the DoD to use its own entirely private client certificate infrastructure but to still have the server certificate use something resembling an ordinary root certificate.

I think you're right that it's possible in principle for a Web server to enforce use of DoD CAC (enforcing the client cert being in the DoD PKI) without itself using a DoD PKI cert on the server side.

That said there's little benefit to it, users who haven't jumped through hoops to install DoD root CA certs won't typically be able to get their browsers to present them to the remote server in the first place, and if we're willing to jump through those hoops then there's no good reason for the DoD server not to have a DoD PKI cert.

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amluto 2 hours ago | parent [-]

I've never used one of the DoD smartcards, but I can certainly imagine the DoD wanting a user of one of these smartcards to be able to use it with a COTS client device to authenticate themselves.

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mpyne an hour ago | parent [-]

Sure, people do that all the time. After they run "InstallRoot" to install DoD root certs on their COTS device, that is. I'm honestly not sure any major browser will allow you to use a client smartcard without having the smartcard's certificate chain to the trust store used by the browser so this part seems unavoidable.

FWIW I just tested it and yes you can run a web server using a commercial server cert that enforces client PKI tied to the client having a DoD PKI cert. It works just fine.

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amluto 20 minutes ago | parent [-]

> I'm honestly not sure any major browser will allow you to use a client smartcard without having the smartcard's certificate chain to the trust store used by the browser so this part seems unavoidable.

It’s been a while, but I’ve used file-backed client certs issued by a private CA in an ordinary browser without installing anything into the trust store, and it worked fine. I don’t see why a client cert using PKCS11 or any other store would work any differently. Why would the browser want to verify a certificate chain at all?

	▲	mpyne 6 minutes ago \| parent [-]
		I'm really just talking about the browser trusting the user cert itself. I've done the softcert thing myself before, I forget if it used commercial root CA or not but it did work. I guess you could flag the leaf (user) cert as ultimately trusted and that should be fine, but if the browser doesn't see that trust notation, and does see an intermediate CA, it's going to try to pull that back to a trusted root. One way or the other the user will have to fiddle with browser settings to make a CAC work, either to tell the browser to trust their cert explicitly, or to have the browser trust DoD certs.