Network Working Group                                            E. Lear
Internet-Draft                                             Cisco Systems
Intended status: Informational                            March 09, 2021
Expires: September 10, 2021

             Deep Thoughts on Network Onboarding Challenges


   With various onboarding methods being built out, one aspect that has
   been overlooked is the trust relationship between the deployment and
   the manufacturer.  This document asks questions about how that trust
   should be established, and how it can be leveraged.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Device Provisioning Protocol  . . . . . . . . . . . . . .   2
     1.2.  Bootstrapping Remote Key Infratructure (BRSKI)  . . . . .   3
   2.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Resale and Transfer . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Choices, Choices  . . . . . . . . . . . . . . . . . . . .   5
   4.  Beware too much mechanism . . . . . . . . . . . . . . . . . .   6
   5.  This is really only about network onboarding  . . . . . . . .   6
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Appendix A.  Changes from Earlier Versions  . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   A number of network onboarding technologies are currently beginning
   to mature in the market place.  The questions they all seek to answer
   are these:

   o  How does the device know that it should join a particular network?

   o  How does the network know that it should trust a particular

   Let's examine two protocols to understand how these questions are
   answered and what questions may also be interesting to ask.  We will
   begin with looking at the Wifi Alliance's Device Provisioning
   Protocol, and then take a gander at Bootstrapping Remote Secure Key
   Infrastructure (BRSKI)[I-D.ietf-anima-bootstrapping-keyinfra], with a
   quick review of the operation model of each.  We focus our attention
   to zero touch provisioning.

   Zero touch provisioning in this context means that the device
   receives network credentials that it will use to bidirectionally
   authenticate with an appropriate network without any human direction
   or validation at the time that the device is first powered at the

1.1.  Device Provisioning Protocol

   As is described in its specification, Device Provisioning Protocol or
   DPP makes use of a public/private key pair.  The private key is
   stored in the device, and the public key is provided to the user out
   of band.

   In the current specification, either side may initiate communciation,
   but for battery saving reasons, it is generally preferred that the

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   endpoint initiate, and thus be in a position to disable its
   transceiver at other times.

   Several validations then take place.  The network is able to prove to
   the endpoint that it has the correct public key, and the device is
   able to prove to the network that it has the correct private key.
   Thus, mutual authentication has taken place.  The next exchange
   allows for appropriate credentials to be provisioned in the device,
   such as a trust anchor or an SAE password.

   As previously mentioned, the public key is provided to the user out
   of band.  In this sense, the public key is effectively a password, in
   that anyone who holds it may onboard the device.  If the user would
   ned to scan the public key from a QR code or via OCR, we would not
   call such a step "hands free".  If the user needs to agree to
   onboarding a device at the time it is enabled, then here again we
   would not call this "hands free".

   This leaves one additional possibility: communication of the public
   key via electronic means for the device having been deployed.  The
   DPP standard doesn't discuss this method.  This may provide a means
   for zero-touch deployment.  In this context, we might consider the
   device that receives and stores public keys a form of a registrar.

   While Internet connectivity is not required for DPP to function on
   its own, transmission of an public key would require some
   connectivity at some point.

   The assumed endstate in all of this is that the device will be able
   to authenticate to the network without the Internet being available.
   While this may not be important in some cases, such as with devices
   whose applications require Internet availability to function, it
   would will be critical for other cases, such as disconnected
   environments with critical control functions.

1.2.  Bootstrapping Remote Key Infratructure (BRSKI)

   BRSKI's flow is somewhat different.  In this case, the endpoint sends
   a voucher request to a registrar in the local deployment, who adorns
   the request with is public key information.  This request is then
   forwarded to the device's manufacturer, who can take whatever choices
   it will to determine whether the device belongs in a particular local
   deployment.  Those choices include:

   o  Nothing.  It can just sign the voucher request, logging the

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   o  Validation that a particular device belongs in a particular

   The first step is problematic for wireless deployments because a
   device would simply join the first network it heard, if it could
   authenticate, and there is no reason to believe that the first
   network would be the correct network.

   The second step is not standardized.  It is possible that an out-of-
   band introduction is taking place on the first transaction, but that
   would not be a zero-touch flow.

   At some point, the deployment must also assign establish that the
   device belongs on its network.  This too is not specified by the

2.  Discussion

   In the case of both BRSKI and DPP, once the device is onboarded by
   the network, no Internet connectivity is required.  This is
   important, as a matter of resiliency.

   BRSKI and DPP barely differ the gaps they have to get to zero-touch
   provisioning.  In BRSKI's case, it's about establishing trust between
   the registrar and the manufacturer, a one time affair, and then then
   later the registrar having some reason to believe that particular
   device belongs within a deployment.  In the case of DPP, once one
   decides that keys are going to be delivered in advance, whatever
   service receives them has to have been introduced to the service
   sending them.

   One could perhaps envision a system in which credentials are
   transmitted at time of sale to a registrar.  In the case of BRSKI,
   this would involve careful configuration of voucher requests, in
   which the voucher is "nonceless", but yet bound to a particular

   This leads us to another concern.

3.  Resale and Transfer

   We should assume that device ownership and use will change over time.
   This presents some additional problems.  We assume, for purposes of
   this discussion that both DPP and BRSKI have some form of a registrar
   function.  We also assume that zero-touch may or may not require a
   device reset (a'la pin in the hole, type).

   There are several ways to think about this problem:

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   o  seller transmits something to the buyer registrar as part of a

   o  seller provides buyer an artifact as part of a sale.

   o  original manufacturer records the sale.

   o  original manufacturer simply notes the transfer.

   Let's dispense with the last option.  It suffers all the same
   wireless problems as the original case.  Therefore, it is not further
   considered in this discussion.

   If the seller transmits something to the buyer registrar as part of a
   transaction, this means that the seller must have identified the
   buyer registrar.  That in itself may be a trick.  If the seller
   provides the buyer with an artifact, the buyer must do something with
   it.  Both of these methods suffer a particular problem: if the
   original owner went out of business, there is no chance for any
   transfer to take place.

   If the original manufacturer records the sale, this means that the
   new owner would have to either know to query the manufacturer, or
   that the manufacturer would have enough information to send an
   appropriate credential to the new owner.  This _also_ means that the
   manufacturer is still in business.

3.1.  Choices, Choices

   The above models are not necessarily mutually exclusive.  That is, it
   might be possible to rely on automated means when they exist, and
   otherwise rely on less automated means when they do not exist.  This
   is somewhat problematic for BRSKI, in that somehow or another a
   voucher needs to be generated.

   Alternatively we might ponder an additional actor whose role it is to
   safeguard transfer credentials in the form of an escrow agent.  The
   existence of such an actor introduces a number of questions:

   o  How would the buyer know to use a particular escrow agent?

   o  Is there an incentive model that would bring such an agent into
      creation?  After all, someone has to pay for such a service.

   o  How is transaction privacy maintained (or is _that_ how the
      service gets paid for)?

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   Another model, and the author writes this with great trepidation, is
   the use of Merkle trees to record a transaction.  This has the
   benefit of being able to establish previous ownership, but has the
   risks that the previous owner is no longer in existence to provide an
   assertion that the device has transfered.  On the third hand, perhaps
   a claim by a known party is enough.  Such transactions have privacy
   implications as well, and there has to be an incentive model to
   maintain a distributed ledger.

4.  Beware too much mechanism

   As this area of work advances, there will be the temptation to add a
   vast amount of mechanism.  The previous supposition of the use of
   Merkel trees is a great example of just that.  From an IoT device
   standpoint, it's all but interolerable.  We are, after all, talking
   about a codespace that is generally considered to be constrainted.

5.  This is really only about network onboarding

   But that may not be the only problem.  Rekeying will occasionally
   happen for various reasons.  How this takes places will depend on the
   authentication mechanism used in a deployment.  If EAP-TLS or TEAP
   are used, the presumption is that there will be an EST server or
   similar available for credential renewal.

   For private shared keys, there currently is no great answer to this

6.  Normative References

              Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
              and K. Watsen, "Bootstrapping Remote Secure Key
              Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
              keyinfra-45 (work in progress), November 2020.

              Fries, S., Brockhaus, H., Lear, E., and T. Werner,
              "Support of asynchronous Enrollment in BRSKI (BRSKI-AE)",
              draft-ietf-anima-brski-async-enroll-01 (work in progress),
              January 2021.

Appendix A.  Changes from Earlier Versions

   Draft -00:

   o  Initial revision

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Author's Address

   Eliot Lear
   Cisco Systems
   Richtistrasse 7
   Wallisellen  CH-8304

   Phone: +41 44 878 9200

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