Re: [Iot-onboarding] [Secdispatch] DANE IOT proposed outcome

[Shumon Huque <[e-mail]>]

On Tue, Nov 17, 2020 at 1:53 PM Ash Wilson <[e-mail]> wrote:

>
> It's called "public" keys ;-)) But indeed, DNS makes it easier for
>> discovery of public keys == identities
>> of devices. And their names. I am probably more worried about the
>> publicity of names.
>>
>
> Good point. There are a few areas we should be mindful of as we proceed.
>   Knowing the device's name is a sure way to access the public key, if the
> public key is in DNS. But you must first know (or guess) the device's name.
> Not putting unnecessary information in a certificate is a good way to
> lessen the impact of a guessed device name.
>   Don't put device certificates into CT logs. Unless there's a good reason
> that's completely escaping me... that's a surefire way to signal the size
> of your fleet, together with whatever metadata the certificates contain.
> This is a risk that has nothing to do with making DANE work for Client ID
> or cert discovery use cases, but it's worth mentioning. DANE makes the
> certificate discoverable, without making the fleet easily enumerable.
>   Passive DNS might be a vector for fleet enumeration, but it has its own
> challenges.
>   Let's ensure that the TLS implementation does a good job of protecting
> the dane_clientid field. I think that's where we may have an opportunity
> for discovery by packet capture, if it passes in plaintext. Discovery via
> this method would provide a source and destination IP/NAT address as well
> as an identity name, which could be used for certificate discovery. If we
> pass the dane_clientid encrypted, this vector is mitigated.
>

Just to elaborate on this point, with TLS 1.3 it should be possible to
fully protect the dane_clientid. In the next revision of the draft we will
move the use of the extension into the CertificateRequest and Certificate
messages which are both encrypted. TLS 1.2 on the other hand, will be a
challenge: ClientHello extensions and the client's Certificate message are
both in the clear (and ECH is not being designed for 1.2).

Shumon.