Internet DRAFT - draft-friel-anima-brski-over-802dot11
draft-friel-anima-brski-over-802dot11
Network Working Group O. Friel
Internet-Draft E. Lear
Intended status: Informational J. Henry
Expires: April 21, 2019 Cisco
M. Richardson
Sandelman Software Works
October 18, 2018
BRSKI over IEEE 802.11
draft-friel-anima-brski-over-802dot11-00
Abstract
This document outlines the challenges associated with implementing
Bootstrapping Remote Secure Key Infrastructures over IEEE 802.11 and
IEEE 802.1x networks. Multiple options are presented for discovering
and authenticating to the correct IEEE 802.11 SSID. This draft is a
discussion document and no final recommendations are made on the
recommended approaches to take. However, the advantages and
downsides of each possible method are evaluated.
Status of This Memo
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This Internet-Draft will expire on April 21, 2019.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Discovery and Authentication Design Considerations . . . . . 5
2.1. Incorrect SSID Discovery . . . . . . . . . . . . . . . . 5
2.1.1. Leveraging BRSKI MASA . . . . . . . . . . . . . . . . 5
2.1.2. Relying on the Network Administrator . . . . . . . . 6
2.1.3. Requiring the Network to Demonstrate Knowledge of
Device . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. IEEE 802.11 Authentication Mechanisms . . . . . . . . . . 7
2.2.1. Authentication Signaling Considerations . . . . . . . 8
2.2.2. IP Address Assignment Considerations . . . . . . . . 8
2.3. Client and Server Implementations . . . . . . . . . . . . 8
3. Potential SSID Discovery and Validation Mechanisms . . . . . 9
3.1. Well-known BRSKI SSID . . . . . . . . . . . . . . . . . . 10
3.2. IEEE 802.11aq . . . . . . . . . . . . . . . . . . . . . . 11
3.3. IEEE 802.11 Vendor Specific Information Element . . . . . 12
3.4. Reusing Existing IEEE 802.11u Elements . . . . . . . . . 12
3.5. IEEE 802.11u Interworking Information - Internet . . . . 13
3.6. Define New IEEE 802.11u Extensions . . . . . . . . . . . 13
3.7. Wi-Fi Protected Setup . . . . . . . . . . . . . . . . . . 14
3.8. Define and Advertise a BRSKI-specific AKM in RSNE . . . . 14
3.9. Wi-Fi Device Provisioning Profile . . . . . . . . . . . . 15
4. Potential Mutual Validation Options . . . . . . . . . . . . . 16
4.1. MAC Address Validation method . . . . . . . . . . . . . . 16
4.2. Vendor Token Validation method . . . . . . . . . . . . . 16
4.3. Device Token Validation method . . . . . . . . . . . . . 17
4.4. Infrastructure Response Filtering . . . . . . . . . . . . 17
4.5. Infrastructure Validation Method . . . . . . . . . . . . 17
5. Potential Authentication Options . . . . . . . . . . . . . . 18
5.1. Unauthenticated and Unencrypted or OWE Pre-BRSKI and EAP-
TLS Post-BRSKI . . . . . . . . . . . . . . . . . . . . . 19
5.2. DPP Pre-BRSKI and EAP-TLS post-BRSKI . . . . . . . . . . 19
5.3. PSK or SAE Pre-BRSKI and EAP-TLS Post-BRSKI . . . . . . . 19
5.4. MAC Address Bypass Pre-BRSKI and EAP-TLS Post-BRSKI . . . 20
5.5. EAP-TLS Pre-BRSKI and EAP-TLS Post-BRSKI . . . . . . . . 20
5.6. New DPP BRSKI mechanism . . . . . . . . . . . . . . . . . 21
5.7. New TEAP BRSKI mechanism . . . . . . . . . . . . . . . . 21
5.8. New IEEE 802.11 Authentication Algorithm for BRSKI and
EAP-TLS Post-BRSKI . . . . . . . . . . . . . . . . . . . 24
5.9. New IEEE 802.1X EAPOL-Announcements to encapsulate BRSKI
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and EAP-TLS Post-BRSKI . . . . . . . . . . . . . . . . . 25
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
7. Security Considerations . . . . . . . . . . . . . . . . . . . 25
7.1. Client side exposure . . . . . . . . . . . . . . . . . . 26
7.2. Infrastructure side exposure . . . . . . . . . . . . . . 26
8. Informative References . . . . . . . . . . . . . . . . . . . 27
Appendix A. IEEE 802.11 Primer . . . . . . . . . . . . . . . . . 28
A.1. IEEE 802.11i . . . . . . . . . . . . . . . . . . . . . . 28
A.2. IEEE 802.11u . . . . . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction
Bootstrapping Remote Secure Key Infrastructures (BRSKI)
[I-D.ietf-anima-bootstrapping-keyinfra] describes how a device can
bootstrap against a local network using an Initial Device Identity
X.509 [IEEE802.1AR] IDevID certificate that is pre-installed by the
vendor on the device in order to obtain an [IEEE802.1AR] LDevID. The
BRSKI flow assumes the device can obtain an IP address, and thus
assumes the device has already connected to the local network.
Further, the draft states that BRSKI use of IDevIDs:
allows for alignment with [IEEE802.1X] network access control
methods, its use here is for Pledge authentication rather than
network access control. Integrating this protocol with network
access control, perhaps as an Extensible Authentication Protocol
(EAP) method (see [RFC3748], is out-of-scope.
The draft does not describe any mechanisms for how an [IEEE802.11]
enabled device would discover and select a suitable [IEEE802.11] SSID
when multiple SSIDs are available. A typical deployment scenario
could involve a device begin deployed in a location were twenty or
more SSIDs are being broadcast, for example, in a multi-tenanted
building or campus where multiple independent organizations operate
[IEEE802.11] networks.
In order to reduce the administrative overhead of installing new
devices, it is desirable that the device will automatically discover
and connect to the correct SSID without the installer having to
manually provision any network information or credentials on the
device. It is also desirable that the device does not discover,
connect to, and automatically enroll with the wrong network as this
could result in a device that is owned by one organization connecting
to the network of a different organization in a multi-tenanted
building or campus.
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Additionally, as noted above, the BRSKI draft does not describe how
BRSKI could potentially align with [IEEE802.1X] authentication
mechanisms.
This document outlines multiple different potential mechanisms that
would enable a bootstrapping device to choose between different
available [IEEE802.11] SSIDs in order to associate and execute the
BRSKI flow. This document also outlines several options for how
[IEEE802.11] networks enforcing [IEEE802.1X] authentication could
enable the BRSKI flow, and describes the required device behaviour.
This document presents both [IEEE802.11] mechanisms and Wi-Fi
Alliance (WFA) mechanisms. An important consideration when
determining what the most appropriate solution to device onboarding
should be is what bodies need to be involved in standardisation
efforts: IETF, IEEE and/or WFA.
1.1. Terminology
IEEE 802.11u: an amendment to the IEEE 802.11-2007 standard to add
features that improve interworking with external networks.
ANI: Autonomic Networking Infrastructure
ANQP: Access Network Query Protocol
AP: IEEE 802.11 Access Point
CA: Certificate Authority
EAP: Extensible Authentication Protocol
EST: Enrollment over Secure Transport
HotSpot 2.0 / HS2.0: An element of the Wi-Fi Alliance Passpoint
certificatoin program that enables cell phones to automatically
discover capabilities and enroll into IEEE 802.11 guest networks
(hotspots).
IE: Information Element
IDevID: Initial Device Identifier
LDevID: Locally Significant Device Identifier
OI: Organization Identifier
MASA: BRSKI Manufacturer Authorized Signing Authority service
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SSID: IEEE 802.11 Service Set Identifier
STA: IEEE 802.11 station
WFA: Wi-Fi Alliance
WLC: Wireless LAN Controller
WPA/WPA2: Wi-Fi Protected Access / Wi-Fi Protected Access version 2
WPS: Wi-Fi Protected Setup
2. Discovery and Authentication Design Considerations
2.1. Incorrect SSID Discovery
As will be seen in the following sections, there are several
discovery scenarios where the device can choose an incorrect SSID and
attempt to join the wrong network. For example, the device is being
deployed by one organization in a multi-tenant building, and chooses
to connect to the SSID of a neighbor organization. The device is
dependent upon either detecting that the other networks are unwanted
candidates, or upon the incorrect networks rejecting its BRSKI
enrollment attempt. It is possible that the device could end up
enrolled with the wrong network. It is also possible that the device
will waste time before identifying and joining the correct network.
2.1.1. Leveraging BRSKI MASA
2.1.1.1. Prevention
BRSKI allows optional sales channel integration which could be used
to ensure only the "correct" network can claim the device. In
theory, this could be achieved if the BRSKI MASA service has explicit
knowledge of the network where every single device will be deployed.
After connecting to the incorrect SSID and possibly authenticating to
the network, the device would present network TLS information in its
voucher-request, and the MASA server would have to reject the request
based on this network TLS information and not issue a voucher. The
device could then reject that SSID and attempt to bootstrap against
the next available SSID.
This could possibly be acheieved via sales channel integration, where
devices are tracked through the supply chain all the way from
manufacturer factory to target deployment network operator. In
practice, this approach may be challenging to deploy as it may be
extremely difficult to implement this tightly coupled sales channel
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integration and ensure that the MASA actually has accurate deployment
network information.
An alternative to sales channel integration is to provide the device
owners with a, possibly authenticated, interface or API to the MASA
service whereby they would have to explicitly claim devices prior to
the MASA issuing vouchers for that device. There are similar
problems with this approach, as there could be a complex sales and
channel partner chain between the MASA service operator and the
device operator who owns and deploys the device. This could make
exposure of APIs by the MASA operator to the device operator
untenable.
2.1.1.2. Detection
If a device connects to the wrong network, the correct network
operator could detect this incorrect association after the fact by
integration with MASA and checking audit logs for the device. The
MASA audit logs should indicate all networks that have been issued
vouchers for a specific device. This mechanism also relies on the
correct network operator having a list, bill or materials, or similar
of all device identities that should be connecting to their network
in order to check MASA logs for devices that have not come online,
but are known to be physically deployed.
2.1.2. Relying on the Network Administrator
An obvious mechanism is to rely on network administrators to be good
citizens and explicitly reject devices that attempt to bootstrap
against the wrong network. This is not guaranteed to work for two
main reasons:
o Some network administrators will configure an open policy on their
network. Any device that attempts to connect to the network will
be automatically granted access.
o Some network administrators will be bad actors and will accept the
onboarding of devices that they do not own but that are in range
of their networks.
2.1.3. Requiring the Network to Demonstrate Knowledge of Device
Technologies such as the WFA Easy Connect (also known as Device
Provisioning Profile [DPP]) require that a network provisoining
entity demonstrates knowledge of device information such as the
device's bootstrapping public key prior to the device attempting to
connect to the network. This gives a higher level of confidence to
the device that it is connecting to the correct SSID. These
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mechanisms could leverage a key that is printed on the device label,
or included in a sales channel bill of materials. The security of
these types of key distribution mechanisms relies on keeping the
device label or bill of materials content from being compromised
prior to device installation.
[IEEE802.11] also includes several advertisement mechanisms that
could allow the device to exchange information with the wireless
infrastructure. Examples are provided throughout this text. Such
exchange can be added to, or integrated with, the standard
[IEEE802.11] discovery mechanisms to allow the device to discard the
networks that would not provide information showing that the network
knows the device. Similarly, the network could reject the
association of devices that would fail to show particular indicators
related to their credentials.
2.2. IEEE 802.11 Authentication Mechanisms
[IEEE802.11i] allows an SSID to advertise different authentication
mechanisms via the AKM Suite list in the RSNE. A very brief
introduction to [IEEE802.11i] is given in the appendices. An SSID
could advertise PSK or [IEEE802.1X] authentication mechanisms. When
a network operator needs to enforce two different authentication
mechanisms, one for pre-BRSKI devices and one for post-BRSKI devices,
the operator has four options:
o configure two SSIDs with the same SSID string value, each one
advertising a different authentication mechanism
o configure two different SSIDs, each with its own SSID string
value, with each one advertising a different authentication
mechanism
o configure a single SSID, advertising two different authentication
mechansim in the RSNE
o configure a single SSID, advertising a general authentication
mechanism in the RSNE, and particular additional authentication
options in some other information element.
If devices have to be flexible enough to handle two of more of these
options, then this adds complexity to the device firmware and
internal state machines. Similarly, if network infrastructure (APs,
WLCs, AAAs) potentially needs to support all options, then this adds
complexity to network infrastructure configuration flexibility,
software and state machines. Consideration must be given to the
practicalities of implementation for both devices and network
infrastructure when designing the final bootstrap mechanism and
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aligning [IEEE802.11], [IEEE802.1X] and BRSKI protocol interactions.
As such, a mechanism that allows for the coexistence of pre-BRSKI and
post-BRSKI authentication on the same SSID is likely to be preferred.
2.2.1. Authentication Signaling Considerations
Devices should be flexible enough to handle potential options defined
by any final draft. When discovering a pre-BRSKI SSID, the device
should also discover the authentication mechanisms enforced by the
SSID. If the device supports the authentication mechanism being
advertised, then the device can connect to the SSID in order to
initiate the BRSKI flow. For example, the device may support
[IEEE802.1X] as a pre-BRSKI authentication mechanism, but may not
support PSK as a pre-BRSKI authentication mechanism.
Once the device has completed the BRKSI flow and has obtained an
LDevID, a mechanism is needed to tell the device which SSID to use
for post-BRSKI network access. This may be the same SSID as the pre-
BRSKI SSID, or another SSID. The decision in whether to onboard
devices through the production SSID or use an onboarding and
provisioning SSID that is different from the production SSID is
dependent on individual organisation networking and security
architectures. As such, the mechanism by which the post-BRSKI SSID
is advertised to the device, if that SSID is different from the pre-
BRSKI SSID, is out-of-scope of this version of this document.
2.2.2. IP Address Assignment Considerations
If a device has to perform two different authentications, one for
pre-BRSKI and one for post-BRSKI, network policy will typically
assign the device to different VLANs for these different stages, and
may assign the device different IP addresses depending on which
network segment the device is assigned to. This could be true even
if a single SSID is used for both pre-BRSKI and post-BRSKI
connections. Therefore, the bootstrapping device may need to
completely reset its network connection and network software stack,
and obtain a new IP address between pre-BRSKI and post-BRSKI
connections.
2.3. Client and Server Implementations
When evaluating all possible SSID discovery mechanisms and
authentication mechanisms outlined in this document, consideration
must be given to the complexity of the required client and server
implementation and state machines. Consideration must also be given
to the network operator configuration complexity if multiple
permutations and combinations of SSID discovery and network
authentication mechanisms are possible.
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3. Potential SSID Discovery and Validation Mechanisms
This section outlines multiple different mechanisms that could
potentially be leveraged that would enable a bootstrapping device to
choose between multiple different available [IEEE802.11] SSIDs. The
discovery mechanism needs to include the following steps:
o A process for the bootstrapping device that has not completed the
bootstrapping process, and that it is at a stage where such
process is needed before further connection
o A process for the Wi-Fi infrastructure to signal that it can
perform bootstrapping
o A process for the bootstrapping device and the infrastructure to
validate each other request. This step includes, for the
bootstrapping device, discriminating between two SSIDs in range.
This step may also include, for the Wi-Fi infrastructure,
validating the bootstrapping device's request (before accepting
it).
The discovery options outlined in this document include:
o Well-known BRSKI SSID
o [IEEE802.11aq]
o [IEEE802.11] Vendor Specific Information Element
o Reusing Existing [IEEE802.11u] Elements
o [IEEE802.11u] Interworking Information - Internet
o Define New [IEEE802.11u] Extensions
o Wi-Fi Protected Setup
o Define and Advertise a BRSKI-specific AKM in RSNE
o Wi-Fi Device Provisioning Profile
These mechanisms are described in more detail in the following
sections.
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3.1. Well-known BRSKI SSID
A standardized naming convention for SSIDs offering BRSKI services is
defined such as:
o BRSKI%ssidname
Where:
o BRSKI: is a well-known prefix string of characters. This prefix
string would be baked into device firmware.
o %: is a well known delimiter character. This delimiter character
would be baked into device firmware.
o ssidname: is the freeform SSID name that the network operator
defines.
Device manufacturers would bake the well-known prefix string and
character delimiter into device firmware. Network operators
configuring SSIDs which offer BRSKI services would have to ensure
that the SSID of those networks begins with this prefix. On
bootstrap, the device would scan all available SSIDs and look for
ones with this given prefix.
If multiple SSIDs are available with this prefix, then the device
could simply round robin through these SSIDs and attempt to start the
BRSKI flow on each one in turn until it succeeds.
This mechanism suffers from the limitations outlined in Section 2.1 -
it does nothing to prevent a device enrolling against an incorrect
network.
Another issue with defining a specific naming convention for the SSID
is that this may require network operators to have to deploy a new
SSID. In general, network operators attempt to keep the number of
unique SSIDs deployed to a minimum as each deployed SSID eats up a
percentage of available air time and network capacity. A good
discussion of SSID overhead and an SSID overhead [calculator] is
available.
Additionally, a third issue with this mechanism is that the
bootstrapping SSID might be different from the production SSID. As
such, using this mechanism may force a network operator to maintain
an SSID (with the overhead concerns detailed above) just for
occasional boostrapping events. The SSID could be enabled only when
bootstrapping events are expected, but this manual operation does not
scale very well (and ignores cases where devices need to re-bootstrap
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or are introduced into the network individually at unpredictable
intervals). Keeping the SSID enabled at all times consumes airtime
for low added value outside of the bootstrapping events.
3.2. IEEE 802.11aq
[IEEE802.11aq] is an amedment to the [IEEE802.11] Standard that was
published in August 2018. [IEEE802.11aq] defines new elements that
can be included in [IEEE802.11] Beacon, Probe Request and Probe
Response frames, and defines new elements for ANQP frames.
The extensions allow an AP to broadcast support for backend services,
where allowed services are those registered in the [IANA] Service
Name and Transport Protocol Port Number Registry. The services can
be advertised in [IEEE802.11] elements that include either:
o SHA256 hashes of the registered service names
o a bloom filter of the SHA256 hashes of the registered service
names
Bloom filters simply serve to reduce the size of Beacon and Probe
Response frames when a large number of services are advertised. If a
bloom filter is used by the AP, and a device discovers a potential
service match in the bloom filter, then the device can query the AP
for the full list of service name hashes using newly defined ANQP
elements.
If BRSKI were to leverage [IEEE802.11aq], then a BRSKI service would
need to be defined in [IANA].
[IEEE802.11aq] describes two types of exchanges. An unsollicited
Preassociation Discovery (PAD) procedure, where the AP advertises
services reachable through the AP, and a sollicited method, where the
PAD is initated by the unassociated client attempting to discover a
service offered through the AP and SSID. The unsollictited PAD
method could be leveraged to advertise support for BRSKI. This
mechanism suffers from the limitations outlined in Section 2.1 - it
does nothing to prevent a device enrolling against an incorrect
network.
The sollicited method could be used by the device to query about
general BRSKI support, or to request information about specific BRSKI
modes or options. This method could be used to overcome the
Section 2.1 issue.
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3.3. IEEE 802.11 Vendor Specific Information Element
[IEEE802.11] defines Information Element (IE) number 221 for carrying
Vendor Specific information. The purpose of this document is to
define an SSID discovery mechanism that can be used across all
devices and vendors, so use of this IE is not an appropriate long
term solution.
3.4. Reusing Existing IEEE 802.11u Elements
[IEEE802.11u] defines mechanisms for interworking. An introduction
to [IEEE802.11u] is given in the appendices. Existing IEs in
[IEEE802.11u] include:
o Roaming Consortium IE (RCOI)
o NAI Realm IE
These existing IEs could be used to advertise a well-known, logical
service that devices implicitly know to look for. This may be
implemented in the spirit of the 802.11u logic, where the NAI or the
RCOI point to a specific set of service providers. This could also
be implemented as a variation where the NAI or the RCOI point to a
specific service, with no specific service provider identified in the
IE.
In the case of NAI Realm, a well-known service name such as
"_bootstrapks" could be defined and advertised in the NAI Realm IE.
In the case of Roaming Consortium, a well-known Organization
Identifier (OI) could be defined and advertised in the Roaming
Consortium IE.
Device manufacturers would bake the well-known NAI Realm or Roaming
Consortium OI into device firmware. Network operators configuring
SSIDs which offer BRSKI services would have to ensure that the SSID
offered this NAI Realm or OI. On bootstrap, the device would scan
all available SSIDs and use ANQP to query for NAI Realms or Roaming
Consortium OI looking for a match.
The key concept with this proposal is that BRSKI uses a well-known
NAI Realm name or Roaming Consortium OI more as a logical service
advertisement rather than as a backhaul internet provider
advertisement. This is conceptually very similar to what
[IEEE802.11aq] is attempting to achieve.
Leveraging NAI Realm or Roaming Consortium would not require any
[IEEE802.11] specification changes, and could be defined by this IETF
draft with the strings suggested above for NAI. However, the RCOI
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has the format of a MAC address, and would need to be allocated by
the IEEE. In the case where specific vendors would implement a
specific NAI or RCOI, identifying both the vendor or vendor
consortium and support for BRSKI, new NAI and RCOI would need to be
defined by these vendors. Although the Wireless Broadband Alliance
(WBA) keeps a Next generation Hotspot (NGH) registry of known RCOIs
and NAIs, there is no official and exahsutive published repository of
these values.
In addition to BRSKI support, as the NAI Realm includes advertising
the EAP mechanism required, if a new EAP-BRSKI were to be defined,
then this could be advertised. Devices could then scan for an NAI
Realm that enforced EAP-BRSKI, and ignore the realm name.
This mechanism suffers from the limitations outlined in Section 2.1 -
it does nothing to prevent a device enrolling against an incorrect
network.
Additionally, as the IEEE is attempting to standardize logical
service advertisement via [IEEE802.11aq], [IEEE802.11aq] would seem
to be the more appropriate option than overloading an existing IE.
However, it is worth noting that configuration of 802.11u IEs is
commonly supported today by Wi-Fi infrastructure vendors, and this
mechanism may be suitable for demonstrations or proof-of-concepts.
3.5. IEEE 802.11u Interworking Information - Internet
It is possible that an SSID may be configured to provide unrestricted
and unauthenticated internet access. This could be advertised in the
Interworking Information IE by including:
o internet bit = 1
o ASRA bit = 0
If such a network were discovered, a device could attempt to use the
BRSKI well-known vendor cloud Registrar. Possibly this could be a
default fall back mechanism that a device could use when determining
which SSID to use. However, this mechanism suffers from the
limitations outlined in Section 2.1 - it does nothing to prevent a
device enrolling against an incorrect network. Additionally, this
mechanism does not provide any information about local BRSKI support.
3.6. Define New IEEE 802.11u Extensions
Of the various elements currently defined by [IEEE802.11u] for
potentially advertising BRSKI, NAI Realm and Roaming Consortium IE
are the two existing options that are a closest fit, as outlined
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above. Another possibility that has been suggested in the IETF
mailers is defining an extension to [IEEE802.11u] specifically for
advertising BRSKI service capability. Any extensions should be
included in Beacon and Probe Response frames so that devices can
discover BRSKI capability without the additional overhead of having
to explicitly query using ANQP. ANQP queries could be used to
provide additional information, such as vendor support.
[IEEE802.11aq] appears to be the proposed mechanism for generically
advertising any service capability, provided that service is
registered with [IANA]. It is probably a better approach to
encourage adoption of [IEEE802.11aq] and register a service name for
BRSKI with [IANA] rather than attempt to define a completely new
BRSKI-specific [IEEE802.11u] extension.
3.7. Wi-Fi Protected Setup
Wi-Fi Protected Setup (WPS) only works with Wi-Fi Protected Access
(WPA) and WPA2 when in Personal Mode. WPS does not work when the
network is in Enterprise Mode enforcing [IEEE802.1X] authentication.
WPS is intended for consumer networks and does not address the
security requirements of enterprise or IoT deployments.
Additionally, WPS relies on three methods (button push, PIN or NFC),
none of which scale easily in an enterprise environement.
3.8. Define and Advertise a BRSKI-specific AKM in RSNE
[IEEE802.11i] introduced the RSNE element which allows an SSID to
advertise multiple authentication mechanisms. A new Authentication
and Key Management (AKM) Suite could be defined that indicates the
STA can use BRSKI mechanisms to authenticate against the SSID. The
authentication handshake could be an [IEEE802.1X] handshake, possibly
leveraging an EAP-BRSKI mechanism, the key thing here is that a new
AKM is defined and advertised to indicate the specific BRSKI-capable
EAP method that is supported by [IEEE802.1X], as opposed to the
current [IEEE802.1X] AKMs which give no indication of the supported
EAP mechanisms. It is clear that such method would limit the SSID to
BRSKI-supporting clients. This would require an additional SSID
specifically for BRSKI clients. As such, this solution also suffers
from the limitations mentioned about additional overhead.
Additionally, this mechanism suffers from the limitations outlined in
Section 2.1 - it does nothing to prevent a device attempting to
enroll against an incorrect network.
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3.9. Wi-Fi Device Provisioning Profile
The [DPP] specification, also known as Wi-Fi Easy Connect, defines
how an entity that is already trusted by a network can assist an
untrusted entity in enrolling with the network. The description
below assumes the [IEEE802.11] network is in infrastructure mode.
DPP introduces multiple key roles including:
o Configurator: A logical entity that is already trusted by the
network that has capabilities to enroll and provision devices
called Enrollees. A Configurator may be a STA or an AP.
o Enrollee: A logical entity that is being provisioned by a
Configurator. An Enrollee may be a STA or an AP.
o Initiator: A logical entity that initiates the DPP Authentication
Protocol. The Initiator may be the Configurator or the Enrollee.
o Responder: A logical entity that responds to the Initiator of the
DPP Authentication Protocol. The Responder may be the
Configurator or the Enrollee.
In the DPP model, a common Configurator and Initiator is an app
running on a trusted smartphone. This process is manual, and each
device is treated individually. In order to support a plug and play
model for installation of a large number devices, where each device
is simply powered up for the first time and automatically discovers
the Wi-Fi network without the need for a helper or supervising
application, then this implies that the AP must perform the role of
the Configurator and the device or STA performs the role of Enrollee.
Note that the AP may simply proxy DPP messages through to a backend
WLC, but from the perspective of the device, the AP is the
Configurator.
The DPP specification also mandates that the Initiator must be
bootstrapped the bootstrapping public key of the Responder. For
BRSKI purposes, the DPP bootstrapping public key will be the
[IEEE802.1AR] IDevID of the device. As the boostrapping device
cannot know in advance the bootstrapping public key of a specific
operators network, this implies that the Configurator must take on
the role of the Initiator. Therefore, the AP must take on the roles
of both the Configurator and the Initiator.
At boot time, the device does not know which AP or which SSID is
likely to provide DPP services. In the DPP model, the Configurator
advertizes a special Authentication and Key Management (AKM) mode,
DPP. Announcing this mode outside of onboarding windows might result
in regular, non-DPP clients to fail to associate to a network which
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AKM they do not recognize. As such, it is preferable that the DPP
process be started after the device establishes a link with the
access point. Therefore, DPP is likely not the best process to
identify a supporting access point. Additionally, this mechanism
suffers from the limitations outlined in Section 2.1 - it does
nothing to prevent a device attempting to enroll against an incorrect
network.
4. Potential Mutual Validation Options
When the bootstrapping device determines that one or more APs or
SSIDs are available that provide support for BRSKI, with one or more
of the mechanisms listed in section 3, then the device needs to
determine which is the correct SSID. At the same time, an AP
receiving signals from a bootstrapping device may need to verify if
the need to determine if the device is attempting to connect the the
correct network. In essence, this joint requirement means that BRSKi
could be started immediately after the discovery phase. A case of
mistaken identity (device attempting to join the wrong network) can
be resolved with a round robin process, where the device fails the
BRSKI process on the attempted network, then attempts BRSKi against
the next candidate network. However, this process may result in
wasted airtime and possible security exposure where an operator
attempts to capture information about neighboring bootstrapping
devices.
4.1. MAC Address Validation method
An alternative to the round robin mode is a primary selection mode
where the device and the AP exchange mutual signs of knowledge about
each other. This could be achieved using the standard 802.11
process, where the device would send a probe request using its real
MAC address. This MAC address could be known to a central database
and validated by the wireless infrastructure. This method has the
merit of being simple. However, it is more and more common for
devices with simple network stacks to use locally administered (and
temporal) MAC addresses. This method only validates the device (not
the infrastructure).
4.2. Vendor Token Validation method
An alternative to the MAC address method is to use a token, placed in
an extension Information Element of the device probe request frame.
This token would identify the device vendor. A limitation of this
method is that, in some cases, neighboring networks may bootstrap
devices from the same vendor. This method validates the vendor, but
not the device. It also does not validate the infrastructure. It
can be used as a coarse initial filtering mechanism.
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4.3. Device Token Validation method
An alternative to the vendor token is to use a unique identifier for
the device. However, as the transaction is exposed to eavesdropping,
this method exposes the toke. As such, the token should not be an
element that can be compromised. The token can be the MAC address,
if the device uses locally administered addresses for its probe
requests. This method only validates the device (not the
infrastructure).
4.4. Infrastructure Response Filtering
When additional filtering is required, the infrastructure may
validate the additiomal information provided by the device, and
either respond, if the additional information is computed to match
the infrastructure knowledge, or ignore the request (no probe
response) if the additional information does not match the
infrastructure knowledge.
In some cases, the AP may not be able to access the database locally,
and may need to forward the request (including the additional
information provided by the device) to another system. In this case,
the AP may respond with a frame that includes a GAS comeback value.
This value indicates a delay after which the device should ask the
question again. In that interval, the AP will query the
infrastructure to obtain the additional iformation required. After
expiration of the comeback interval, the device may send the probe
request again, and the AP may respond or ignore the request, or
request more time. It is understood that the device would accept a
limited number of comeback requests (for example 3) and a limited
comeback interval (for example no more than 3 seconds).
4.5. Infrastructure Validation Method
It is expected, when the device adds information to its probe
request, that the infrastructure should only respond to those devices
that have been validated by the infrastructure system. However, some
systems may not be able to respond in time and may be configured to
accept all requests. Additionally, bad actors may decide to accept
any request. There may therefore be a need to mandate the
infrastructure to return information that indicates proof of
knowledge of the device. The following modes are envisioned:
o When the device uses its MAC address, or expresses its MAC address
in an information element contained in the probe request, the
infrastructure may be able to express its knowledge of the device
servial number, and mention this serial number in the probe
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response. As it may be needed to protect the serial number at
this stage, the serial number could be encoded in a bloom filter.
o When the device uses a vendor token, the AP can only reply with
another token identifying the same vendor, as the device itself is
not known.
5. Potential Authentication Options
When the bootstrapping device determines which SSID to connect to,
there are multiple potential options available for how the device
authenticates with the network while bootstrapping. Several options
are outlined in this section. This list is not exhaustive.
At a high level, authentication can generally be split into two
phases using two different credentials:
o Pre-BRSKI: The device can use its [IEEE802.1AR] IDevID to connect
to the network while executing the BRSKI flow
o Post-BRSKI: The device can use its [IEEE802.1AR] LDevID to connect
to the network after completing BRSKI enrollment
The authentication options outlined in this document include:
o Unauthenticated Pre-BRSKI and EAP-TLS Post-BRSKI
o DPP Pre-BRSKI and EAP-TLS Post-BRSKI
o PSK or SAE Pre-BRSKI and EAP-TLS Post-BRSKI
o MAC Address Bypass Pre-BRSKI and EAP-TLS Post-BRSKI
o EAP-TLS Pre-BRSKI and EAP-TLS Post-BRSKI
o New DPP BRSKI mechanism
o New TEAP BRSKI mechanism
o New [IEEE802.11] Authentication Algorithm for BRSKI and EAP-TLS
Post-BRSKI
o New [IEEE802.1X] EAPOL-Announcements to encapsulate BRSKI prior to
EAP-TLS Post-BRSKI
These mechanisms are described in more detail in the following
sections. Note that any mechanisms leveraging [IEEE802.1X] are
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[IEEE802.11] MAC layer authentication mechanisms and therefore the
SSID must advertise WPA2 capability.
When evaluating the multiple authentication options outlined below,
care and consideration must be given to the complexity of the
software state machine required in both devices and services for
implementation.
5.1. Unauthenticated and Unencrypted or OWE Pre-BRSKI and EAP-TLS Post-
BRSKI
The device connects to an unauthenticated network pre-BRSKI. The
device connects to a network enforcing EAP-TLS post-BRSKI. The
device uses its LDevID as the post-BRSKI EAP-TLS credential.
In the pre-BRSKI phase, the device may establish a secure connection
with the AP using WPA3 to protect the BRSKI exchange from
eavesdroppers. The pre-BRSKi phase can be protected, but is not
authenticated.
5.2. DPP Pre-BRSKI and EAP-TLS post-BRSKI
The device can be provisioned with DPP for the pre-BRSKI phase,
receiving the SSID value and optionally a temporal PSK. It should be
noted that the device at that point is not untampered anymore.
However, the configuration is temporal and limited. In a WPA3
network, when DPP from a mobile (e.g. smartphone) is used, the DPP
process may provision the SSID and leave the device to use OWE for
its connection to the AP.
Alternatively, when DPP is processed through the AP in an automated
fashion, the AP first establishes an OWE connection with the device.
Through this encrypted connection, the AP provides the SSID and the
temporal PSK value.
5.3. PSK or SAE Pre-BRSKI and EAP-TLS Post-BRSKI
The device connects to a network enforcing PSK pre-BRSKI. If DPP is
not used, the PSK may be factory-set (default PSK) or provisioned by
direct action on the device. Neither of these modes is preferred as
factory-defauls are weak and direct interaction with the device does
not allow for massive automated bootstrapping. After the PSK-based
pre-BRSKI connection, the device connects to a network enforcing EAP-
TLS post-BRSKI. The device uses the LDevID obtained via BRSKI as the
post-BRSKI EAP-TLS credential.
When the device connects to the post-BRSKI network that is enforcing
EAP-TLS, the device uses its LDevID as its credential. The device
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should verify the certificate presented by the server during that
EAP-TLS exchange against the trusted CA list it obtained during
BRSKI.
If the [IEEE802.1X] network enforces a tunneled EAP method, for
example [RFC7170], where the device must present an additional
credential such as a password, the mechanism by which that additional
credential is provisioned on the device for post-BRSKI authentication
is out-of-scope of this version of this document. NAI Realm may be
used to advertise the EAP methods being enforced by an SSID. It is
to be determined if guidelines should be provided on use of NAI Realm
for advertising EAP method in order to streamline BRSKI.
5.4. MAC Address Bypass Pre-BRSKI and EAP-TLS Post-BRSKI
Many AAA server state machine logic allows for the network to
fallback to MAC Address Bypass (MAB) when initial authentication
against the network fails. If the device does not present a valid
credential to the network, then the network will check if the
device's MAC address is whitelisted. If it is, then the network may
grant the device access to a network segment that will allow it to
complete the BRSKI flow and get provisioned with an LDevID. Once the
device has an LDevID, it can then reauthenticate against the network
using its EAP-TLS and its LDevID.
5.5. EAP-TLS Pre-BRSKI and EAP-TLS Post-BRSKI
The device connects to a network enforcing EAP-TLS pre-BRSKI. The
device uses its IDevID as the pre-BRSKI EAP-TLS credential. The
device connects to a network enforcing EAP-TLS post-BRSKI. The
device uses its LDevID as the post-BRSKI EAP-TLS credential.
When the device connects to a pre-BRSKI network that is enforcing
EAP-TLS, the device uses its IDevID as its credential. The device
should not attempt to verify the certificate presented by the server
during that EAP-TLS exchange, as it has not yet discovered the local
domain trusted CA list.
When the device connects to the post-BRSKI network that is enforcing
EAP-TLS, the device uses its LDevID as its credential. The device
should verify the certificate presented by the server during that
EAP-TLS exchange against the trusted CA list it obtained during
BRSKI.
Again, if the post-BRSKI network enforces a tunneled EAP method, the
mechanism by which that second credential is provisioned on the
device is out-of-scope of this version of this document.
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5.6. New DPP BRSKI mechanism
BRSKI can be integrated into the DPP choreography, in three modes:
o When a local commissioning tool is used (e.g. application on a
mobile device), the standard DPP process is used for the
configurator to establish a trusted connection to the enrolee (the
bootstrapping device), over Bluetoot, NFC, Wi-Fi or other means
defined by DPP. The configurator then provision the boostrapping
device with the target SSID, but also installs on the device the
TrustAnchor. The bootstrapping device then connects to the target
SSID using EAP-BRSKI (EST). The query is relayed to the
registrar, which validates the device identity. An EAP-Success
message is then returned to the access point.
o When the commissioning tool is not mobile and not interacting
directly with the bootstrapping device, identifiers for the device
may be fed into an authentication database (e.g. serial number,
MAC address, DPP key, device-specific factory-set PSK or other).
Upon device request (probe request with request for network proof
of knowledge), the AP retrieves one or more of these parameters
from the authentication database, and uses them to provide proof
of knowledge to the device. Once trust is established, a temporal
trusted link is established between the device and the AP (using
DPP parameters or OWE) and the AP provisions the device with the
SSID. The device then connects to the target SSID using EAP-BRSKI
as above.
o When the authentication server has reachability to the MASA
server, the process above is started. As the device conencst to
the target SSID, its identity is not only validated by the
authentication server, but the authentication server also
initiates a voucher request to the MASA server. The exchange
between the bootstrapping device and the authentication server,
now in possession of the voucher, continues as per
[I-D.ietf-anima-bootstrapping-keyinfra].
5.7. New TEAP BRSKI mechanism
New TEAP TLVs are defined to transport BRSKI messages inside an outer
EAP TLS tunnel such as TEAP [RFC7170]. [I-D.lear-eap-teap-brski]
outlines a proposal for how BRSKI messages could be transported
inside TEAP TLVs. At a high level, this enables the device to obtain
an LDevID during the Layer 2 authentication stage. This has multiple
advantages including:
o avoids the need for the device to potentially connect to two
different SSIDs during bootstrap
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o the device only needs to handle one authentication mechanism
during bootstrap
o the device only needs to obtain one IP address, which it obtains
after BRSKI is complete
o avoids the need for the device to have to disconnect from the
network, reset its network stack, and reconnect to the network
o potentially simplifies network policy configuration
There are two suboptions to choose from when tunneling BRSKI messages
inside TEAP:
o define new TLVs for transporting BRSKI messages inside the TEAP
tunnel
o define a new EAP BRSKI method type that is tunneled within the
outer TEAP method
This section assumes that new TLVs are defined for transporting BRSKI
messages inside the TEAP tunnel and that a new EAP BRSKI method type
is not defined.
The device discovers and connects to a network enforcing TEAP. A
high level TEAP with BRSKI extensions flow would look something like:
o Device starts the EAP flow by sending the EAP TLS ClientHello
message
o EAP server replies and includes CertificateRequest message, and
may specify certificate_authorities in the message
o if the device has an LDevID and the LDevID issuing CA is allowed
by the certificate_authorities list (i.e. the issuing CA is
explicitly included in the list, or else the list is empty) then
the device uses its LDevID to establish the TLS tunnel
o if the device does not have an LDevID, or certificate_authorities
prevents it using its LDevID, then the device uses its IDevID to
establish the TLS tunnel
o if certificate_authorities prevents the device from using its
IDevID (and its LDevID if it has one) then the device fails to
connect
The EAP server continues with TLS tunnel establishment:
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o if the device certificate is invalid or expired, then the EAP
server fails the connection request.
o if the device certificate is valid but is not allowed due to a
configured policy on the EAP server, then the EAP server fails the
connection request
o if the device certificate is accepted, then the EAP server
establishes the TLS tunnel and starts the tunneled EAP-BRSKI
procedures
At this stage, the EAP server has some policy decisions to make:
o if network policy indicates that the device certificate is
sufficient to grant network access, whether it is an LDevID or an
IDevID, then the EAP server simply initiates the Crypto-Binding
TLV and 'Success' Result TLV exchange. The device can now obtain
an IP address and connect to the network.
o the EAP server may instruct the device to initialise a full BRSKI
flow. Typically, the EAP server will instruct the device to
initialize a BRSKI flow when it presents an IDevID, however, the
EAP server may instruct the device to initialize a BRSKI flow even
if it presented a valid LDevID. The device sends all BRSKI
messages, for example 'requestvoucher', inside the TLS tunnel
using new TEAP TLVs. Assuming the BRSKI flow completes
successfully and the device is issued an LDevID, the EAP server
completes the exchange by initiating the Crypto-Binding TLV and
'Success' Result TLV exchange.
Once the EAP flow has successfully completed, then:
o network policy will automatically assign the device to the correct
network segment
o the device obtains an IP address
o the device can access production service
It is assumed that the device will automatically handle LDevID
certificate reenrolment via standard EST [RFC7030] outside the
context of the EAP tunnel.
An item to be considered here is what information is included in
Beacon or Probe Response frames to explicitly indicate that
[IEEE802.1X] authentication using TEAP supporting BRSKI extensions is
allowed. Currently, the RSNE included in Beacon and Probe Response
frames can only indicate [IEEE802.1X] support.
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5.8. New IEEE 802.11 Authentication Algorithm for BRSKI and EAP-TLS
Post-BRSKI
[IEEE802.11] supports multiple authentication algorithms in its
Authentication frame including:
o Open System
o Shared Key
o Fast BSS Transition
o Simultaneous Authentication of Equals
Shared Key authentication is used to indicate that the legacy WEP
authentication mechanism is to be used. Simultaneous Authentication
of Equals is used to indicate that the Dragonfly-based shared
passphrase authentication mechanism introduced in [IEEE802.11s] is to
be used. One thing that these two methods have in common is that a
series of handshake data exchanges occur between the device and the
AP as elements inside Authentication frames, and these Authentication
exchanges happen prior to [IEEE802.11] Association.
It would be possible to define a new Authentication Algorithm and
define new elements to encapsulate BRSKI messages inside
Authentication frames. For example, new elements could be defined to
encapsulate BRSKI requestvoucher, voucher and voucher telemetry JSON
messages. The full BRSKI flow completes and the device gets issued
an LDevID prior to associating with an SSID, and prior to doing full
[IEEE802.1X] authentication using its LDevID.
The high level flow would be something like:
o SSID Beacon / Probe Response indicates in RSNE that it supports
BRSKI based Authentication Algorithm
o SSIDs could also advertise that they support both BRSKI based
Authentication and [IEEE802.1X]
o device discovers SSID via suitable mechanism
o device completes BRSKI by sending new elements inside
Authentication frames and obtains an LDevID
o device associates with the AP
o device completes [IEEE802.1X] authentication using its LDevID as
credential for EAP-TLS or TEAP
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5.9. New IEEE 802.1X EAPOL-Announcements to encapsulate BRSKI and EAP-
TLS Post-BRSKI
[IEEE802.1X] defines multiple EAPOL packet types, including EAPOL-
Announcement and EAPOL-Announcement-Req messages. EAPOL-Annoncement
and EAPOL-Announcement-Req messages can include multiple TLVs.
EAPOL-Annoncement messages can be sent prior to starting any EAP
authentication flow. New TLVs could be defined to encapsulate BRSKI
messages inside EAPOL-Announcement and EAPOL-Announcement-Req TLVs.
For example, new TLVs could be defined to encapsulate BRSKI
requestvoucher, voucher and voucher telemetry JSON messages. The
full BRSKI flow could complete inside EAPOL-Announcement exchanges
prior to sending EAPOL-Start or EAPOL-EAP messages.
The high level flow would be something like:
o SSID Beacon / Probe Response indicates somehow in RSNE that it
supports [IEEE802.1X] including BRSKI extensions.
o device connects to SSID and completes standard Open System
Authentication and Association
o device starts [IEEE802.1X] EAPOL flow and uses new EAPOL-
Announcement frames to encapsulate and complete BRSKI flow to
obtain an LDevID
o device completes [IEEE802.1X] authentication using its LDevID as
credential for EAP-TLS or TEAP
6. IANA Considerations
This document has no IANA actions.
7. Security Considerations
The mechanisms described in this document rely on BRSKI. As such,
the same security considerations are applicable to this document as
they are in [I-D.ietf-anima-bootstrapping-keyinfra].
Additionally, the Wireless LAN presents a unique DOS attack vector,
as endpoints contend for the shared medium on a completely
egalitarian basis with the AP. This means that any wireless device
could potentially monopolize the air by constantly sending frames.
This would prevent the bootstrapping device, or the infrastrcuture,
to complete their exchange and would make the BRSKI process fail.
This risk is inherent to the nature of 802.11 transmissions, and can
only be mitigated by physical access control to the cell area. Such
attack is also easily detected.
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Also, initial exchanges between the bootstrapping device and the AP
are not protected. Whenever a unicast communication is initiated
between a bootstrapping device and an AP in an attempt to start
active bootstrapping or provisioning, the link should first be
protected whenever possible, for example with OWE.
7.1. Client side exposure
The discovery mechanism imposes that the bootstrapping device and the
infrastructure must exchange messages to be aware of each other's
existence. If these messages are generic, then the bootstrapping
device has no mechanism to distinguish the correct SSID from a
neighboring SSID. The bootstrapping device then is faced with two
options:
o Try all possible SSIDs in a round-robin fashion. By doing so, the
bootstrapping device will potentially expose parameters to the
wrong SSID and infrastructure. Although such exposure is unlikely
tor esult in device compromission, it will still expose
unnecessarily device parameters to the wrong network. As such, it
is recommended that a pre-BRSKI filtering mechanism be implemented
to avoid this exposure, conducting the bootstrapping device to
only start the BRSKI process with an SSID that has been confirmed
to be a likely correct candidate.
o When the boostrapping device attempts to proceed to an SSID
filtering, it may need to expose parameters to allow for the
infrastructure to respond and provide a proof of knowledge. If
this mechanism is implemented, the bootstrapping device should
only expose information that is not sufficient to acquire complete
knwledge of the bootstrapping device. For example, the
bootstrapping device should not send both its serial number and
MAC address, but should only expose an element that has low
security value (such as a MAC address), and only in scenarios
where the infrastructure has to respond with another element that
will confirm to the bootstrapping device that it is communicating
with the correct infrastructure.
7.2. Infrastructure side exposure
The general choreography of 802.11 networks imply that the
infrastructure advertizes capabilities and support for specific
features through beacons and probe responses. As such, the AP is
likely to have to expose its support for BRSKI. This exposure is not
a security concern.
When the infrastructure is requested to provide bre-BRSKI proof of
knowledge, it has to process a frame received from an unknown
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candidate device and either respond (if the device is found to be
known), delay the response (if additional processing is needed) or
ignore the request. Each of these behaviors may be tested by a rogue
device in an attempt to gain information about the wireless
infrastructure. It is therefore recommended that the proof of
knowledge test should only focus on parameters specific to a
particular device, and not to parameters generally applicable to
multiple devices (for example parameters that would apply to multiple
devices of one or more vendors).
8. Informative References
[calculator]
Revolution Wi-Fi, "SSID Overhead Calculator", n.d.,
<http://www.revolutionwifi.net/revolutionwifi/p/
ssid-overhead-calculator.html>.
[DPP] Wi-Fi Alliance, "Wi-Fi Device Provisioning Protocol",
n.d., <https://www.wi-fi.org/file/wi-fi-device-
provisioning-protocol-dpp-draft-technical-specification-
v0023>.
[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
S., and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
keyinfra-16 (work in progress), June 2018.
[I-D.lear-eap-teap-brski]
Lear, E., Friel, O., and N. Cam-Winget, "Bootstrapping Key
Infrastructure over EAP", draft-lear-eap-teap-brski-01
(work in progress), October 2018.
[IANA] Internet Assigned Numbers Authority, "Service Name and
Transport Protocol Port Number Registry", n.d.,
<https://www.iana.org/assignments/service-names-port-
numbers/service-names-port-numbers.xhtml>.
[IEEE802.11]
IEEE, ., "Wireless LAN Medium Access Control (MAC) and
Physical Layer (PHY) Specifications", 2016.
[IEEE802.11aq]
IEEE, ., "802.11 Amendment 5 Pre-Association Discovery",
2017.
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[IEEE802.11i]
IEEE, ., "802.11 Amendment 6 Medium Access Control (MAC)
Security Enhancements", 2004.
[IEEE802.11s]
IEEE, ., "802.11 Amendment 10 Mesh Networking", 2011.
[IEEE802.11u]
IEEE, ., "802.11 Amendment 9 Interworking with External
Networks", 2011.
[IEEE802.1AR]
IEEE, ., "Secure Device Identity", 2017.
[IEEE802.1X]
IEEE, ., "Port-Based Network Access Control", 2010.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, Ed., "Extensible Authentication Protocol
(EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
<https://www.rfc-editor.org/info/rfc3748>.
[RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The
Network Access Identifier", RFC 4282,
DOI 10.17487/RFC4282, December 2005,
<https://www.rfc-editor.org/info/rfc4282>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/info/rfc7030>.
[RFC7170] Zhou, H., Cam-Winget, N., Salowey, J., and S. Hanna,
"Tunnel Extensible Authentication Protocol (TEAP) Version
1", RFC 7170, DOI 10.17487/RFC7170, May 2014,
<https://www.rfc-editor.org/info/rfc7170>.
Appendix A. IEEE 802.11 Primer
A.1. IEEE 802.11i
802.11i-2004 is an IEEE standard from 2004 that improves connection
security. 802.11i-2004 is incorporated into 802.11-2014. 802.11i
defines the Robust Security Network IE which includes information on:
o Pairwise Cipher Suites (WEP-40, WEP-104, CCMP-128, etc.)
o Authentication and Key Management Suites (PSK, 802.1X, etc.)
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The RSN IEs are included in Beacon and Probe Response frames. STAs
can use this frame to determine the authentication mechanisms offered
by a particular AP e.g. PSK or 802.1X.
A.2. IEEE 802.11u
802.11u-2011 is an IEEE standard from 2011 that adds features that
improve interworking with external networks. 802.11u-2011 is
incorporated into 802.11-2016.
STAs and APs advertise support for 802.11u by setting the
Interworking bit in the Extended Capabilities IE, and by including
the Interworking IE in Beacon, Probe Request and Probe Response
frames.
The Interworking IE includes information on:
o Access Network Type (Private, Free public, Chargeable public,
etc.)
o Internet bit (yes/no)
o ASRA (Additional Step required for Access - e.g. Acceptance of
terms and conditions, On-line enrollment, etc.)
802.11u introduced Access Network Query Protocol (ANQP) which enables
STAs to query APs for information not present in Beacons/Probe
Responses.
ANQP defines these key IEs for enabling the STA to determine which
network to connect to:
o Roaming consortium IE: includes the Organization Identifier(s) of
the roaming consortium(s). The OI is typically provisioned on
cell phones by the SP, so the cell phone can automatically detect
802.11 networks that provide access to its SP's consortium.
o 3GPP Cellular Network IE: includes the Mobile Country Code (MCC)
and Mobile Network Code (MNC) of the SP the AP provides access to.
o Network Access Identifier Realm IE: includes [RFC4282] realm names
that the AP provides access to (e.g. wifi.service-provider.com).
The NAI Realm IE also includes info on the EAP type required to
access that realm e.g. EAP-TLS.
o Domain name IE: the domain name(s) of the local AP operator. Its
purpose is to enable a STA to connect to a domain operator that
may have a roaming agreement with STA's Service Provider.
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STAs can use one or more of the above IEs to make a suitable decision
on which SSID to pick.
HotSpot 2.0 is an example of a specification built on top of 802.11u
and defines 10 additional ANQP elements using the standard vendor
extensions mechanisms defined in 802.11. It also defines a HS2.0
Indication element that is included in Beacons and Probe Responses so
that STAs can immediately tell if an SSID supports HS2.0.
Authors' Addresses
Owen Friel
Cisco
Email: ofriel@cisco.com
Eliot Lear
Cisco
Email: lear@cisco.com
Jerome Henry
Cisco
Email: jerhenry@cisco.com
Michael Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
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