Re: [Iot-onboarding] BRSKI-EST and TLS Unique ID check

"M. Ranganathan" <mranga@gmail.com> Sat, 04 April 2020 21:02 UTC

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From: "M. Ranganathan" <mranga@gmail.com>
Date: Sat, 4 Apr 2020 17:02:11 -0400
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To: Dan Harkins <dharkins@lounge.org>
Cc: iot-onboarding@ietf.org
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Subject: Re: [Iot-onboarding] BRSKI-EST and TLS Unique ID check
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On Sat, Apr 4, 2020 at 1:51 PM Dan Harkins <dharkins@lounge.org> wrote:
>
>
>    Hi Ranga,
>
>    This check does proof-of-possession of the private key. I think it's
> very important.


Hi Dan,

This check just ensures that the CSR was generated by same entity that
established the connection with the EST server (i.e. it is not
proxying a request for another party). It is checking if the CSR
password is the TLS unique ID.

In BRSKI EST, the way I understand it, the pledge creates a persistent
HTTPS connection with the registrar / EST server.
In doing so it presents its certificate and is challenged for proof or
possession of the corresponding private key (TLS handshake).

It now uses that private key to sign the CSR. The server in this case
has the corresponding public key and can verify the
CSR. Proof of possession of private key has already been established
above. If the client (pledge) tears down the Connection
prior to doing this, the EST server would remove its public keys and
therefore verification would fail. Hence I thought this check
is redundant for BRSKI / EST.

The one thing this does not accomplish is guarding against replay
attacks (a previously signed CSR could
be replayed) which the TLS unique ID guards against. Is this really an
issue in BRSKI EST? It could
only be replayed by the same party that generated the CSR in the first
place due to the persistent connection requirement.

Second, what can be done if TLS Unique ID is not supported (e.g. TLS 1.3)?

Thanks,

Ranga

>
>    regards,
>
>    Dan.
>
> On 4/3/20 9:45 AM, M. Ranganathan wrote:
> > Hello,
> >
> > The EST spec says that if the password on a simpleenroll CSR exists
> > then that password should match the tls unique identifier of the HTTPS
> > connection (section 3.5).
> >
> > Given that BRSKI establishes a persistent HTTPS connection, is this
> > check even required?
> >
> > I looked at draft-richardson-anima-registrar-considerations but I
> > could not find anything about this so I would appreciate some
> > clarification.
> >
> > Thanks,
> >
> > Ranga
> >
> >
> >
>
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-- 
M. Ranganathan