The eduroam architecture for network roaming
draft-wierenga-ietf-eduroam-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 7593.
Expired & archived
|
|
|---|---|---|---|
| Authors | Klaas Wierenga , Stefan Winter , Tomasz Wolniewicz | ||
| Last updated | 2013-04-18 (Latest revision 2012-10-15) | ||
| RFC stream | (None) | ||
| Formats | |||
| IETF conflict review | conflict-review-wierenga-ietf-eduroam, conflict-review-wierenga-ietf-eduroam, conflict-review-wierenga-ietf-eduroam, conflict-review-wierenga-ietf-eduroam, conflict-review-wierenga-ietf-eduroam, conflict-review-wierenga-ietf-eduroam | ||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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| IESG | IESG state | Became RFC 7593 (Informational) | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-wierenga-ietf-eduroam-00
Network Working Group K. Wierenga
Internet-Draft Cisco Systems
Intended status: Informational S. Winter
Expires: April 18, 2013 RESTENA
T. Wolniewicz
Nicolaus Copernicus University
October 15, 2012
The eduroam architecture for network roaming
draft-wierenga-ietf-eduroam-00.txt
Abstract
This document describes the architecture of the eduroam service for
federated (wireless) network access in academia. The combination of
802.1X, EAP and RADIUS that is used in eduroam provides a secure,
scalable and deployable service for roaming network access. The
successful deployment of eduroam over the last decade in the
educational sector may serve as an example for other sectors, hence
this document. In particular the initial architectural and standards
choices and the changes that were prompted by operational experience
are highlighted.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 18, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Notational Conventions . . . . . . . . . . . . . . . . . . 4
1.3. Design Goals . . . . . . . . . . . . . . . . . . . . . . . 4
2. Classic Architecture . . . . . . . . . . . . . . . . . . . . . 6
2.1. Authentication . . . . . . . . . . . . . . . . . . . . . . 6
2.1.1. 802.1X . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.2. EAP . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Federation Trust Fabric . . . . . . . . . . . . . . . . . 8
2.2.1. RADIUS . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Issues with initial Trust Fabric . . . . . . . . . . . . . . . 11
3.1. Server Failure Handling . . . . . . . . . . . . . . . . . 11
3.2. No error condition signalling . . . . . . . . . . . . . . 12
3.3. Routing table complexity . . . . . . . . . . . . . . . . . 13
3.4. UDP Issues . . . . . . . . . . . . . . . . . . . . . . . . 14
3.5. Insufficient payload encryption . . . . . . . . . . . . . 15
4. Enhanced Architecture . . . . . . . . . . . . . . . . . . . . 17
4.1. Federation Trust Fabric . . . . . . . . . . . . . . . . . 17
4.1.1. RADIUS with TLS . . . . . . . . . . . . . . . . . . . 17
4.1.2. Dynamic Discovery . . . . . . . . . . . . . . . . . . 18
5. Abuse prevention and incident handling . . . . . . . . . . . . 19
5.1. Incident Handling . . . . . . . . . . . . . . . . . . . . 19
5.2. Operator Name . . . . . . . . . . . . . . . . . . . . . . 20
5.3. Chargeable User Identifier . . . . . . . . . . . . . . . . 21
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 22
6.1. Collusion of RPs . . . . . . . . . . . . . . . . . . . . . 22
6.2. Exposing user credentials . . . . . . . . . . . . . . . . 22
6.3. Track location of users . . . . . . . . . . . . . . . . . 22
7. Security Considerations . . . . . . . . . . . . . . . . . . . 23
7.1. Man in the middle and Tunneling Attacks . . . . . . . . . 23
7.2. Denial of Service Attacks . . . . . . . . . . . . . . . . 23
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.1. Normative References . . . . . . . . . . . . . . . . . . . 25
9.2. Informative References . . . . . . . . . . . . . . . . . . 26
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 29
Appendix B. Changes . . . . . . . . . . . . . . . . . . . . . . . 30
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31
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1. Introduction
In 2002 the European Research and Education community set out to
create a network roaming service for students and employees in
academia [eduroam-start]. Now over 10 years later this service has
grown to more than 5000 service locations, serving millions of users
in all continents with the exception of Antarctica.
This memo serves to explain the considerations for the design of
eduroam as well as to document operational experience and resulting
changes that led to IETF standardization effort like for example
RADIUS over TCP [RFC6613] and RADIUS with TLS [RFC6614] and that
promoted alternative use of RADIUS like in Abfab
[I-D.ietf-abfab-arch]. Whereas the eduroam service is limited to
academia, the eduroam architecture can easily be reused in other
environments.
1.1. Terminology
XXX This document uses identity management and privacy terminology
from [I-D.hansen-privacy-terminology]. In particular, this document
uses the terms Identity Provider, Service Provider and identity
management.
1.2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
1.3. Design Goals
The guiding design considerations of eduroam were as follows:
- Unique identification of users at the edge of the network
In order to determine whether a user has the right to use the network
resources the user needs to be identified. Furthermore, in case of
abuse of the resources, there is a requirement to be able to identify
the user. Lastly, it should not be possible for a person to
impersonate someone else or take over their identity.
- Enable (trusted) guest use:
In order to enable roaming it should be possible for users of
participating institutions to get seamless access to the networks of
other institutions that participate in the service.
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- Scalable
The infrastructure that is created should scale to a large number of
users and organizations without requiring a lot of coordination and
other administrative procedures (possibly after initial set up).
Specifically, it should not be necessary to go through an
administrative process when a user visits another organization.
- Easy to install and use
It should not be very complicated to participate in the roaming
infrastructure as that may inhibit wide scale adoption. In
particular, there should be no or easy client installation and one-
off configuration.
- Secure and privacy preserving
Whereas it is impossible to create a secure system in the absolute
sense, it is important to have a system that strikes a good balance
between ease of use and security. One important design criteria has
been that there needs to be a security association between the end-
user and their home organization, so no exposure of credentials to a
third party. In particular, it should be possible for participating
organizations to set their own requirements for the quality of
authentication of users without the need for the infrastructure as a
whole to implement the same standard.
- Standards based
In an infrastructure in which many thousands of organizations
participate it is obvious that it should be possible to use equipment
from different vendors, therefore it is important to base the
infrastructure on open standards.
These considerations have led to an architecture based on:
o 802.1X ([dot1X-standard])as port based authentication framework
using
o EAP ([RFC3748]) for integrity and confidentially protected
transport of credentials and a
o RADIUS ([RFC2865]) hierarchy as trust fabric.
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2. Classic Architecture
Federations, like eduroam, implement essentially two types of trust.
The trust relation between an end-user and the Identity Provider
(IdP, operated by the home organization of the user) and between the
IdP and the Service Provider (SP, in eduroam the operator of the
network at the visited location). In eduroam the establishment of
the trust relation between user and IdP is through mutual
authentication. IdPs and SP establish trust through the use of a
RADIUS hierarchy.
These two forms of trust in turn provide the transitive trust that
makes the SP allow the use of its network resources.
2.1. Authentication
Authentication in eduroam is achieved by using a combination of IEEE
802.1X [dot1X-standard] and EAP [RFC4372].
2.1.1. 802.1X
By using the 802.1X [dot1X-standard] framework for port-based network
authentication, organizations that offer network access (SPs) for
visiting (and local) eduroam users can make sure that only authorized
users get access. The user (or rather the user's supplicant) sends
an access request to the authenticator (wireless access point or
switch) at the SP, the authenticator forwards the access request to
the authentication server of the SP which in turn proxies the request
through the RADIUS hierarchy to the authentication server of the
user's home organization (the IdP, see below).
In order for users to be aware of the availability of the eduroam
service, an SP that offers wireless network access MUST broadcast the
SSID 'eduroam', unless that conflicts with the SSID of another
eduroam SP, in which case an SSID starting with "eduroam-" MAY be
used. To protect user data confidentiality eduroam SPs IEEE 802.11
wireless networks MUST support WPA2+AES, and MAY additionally support
WPA/TKIP as a courtesy to users of legacy hardware.
2.1.2. EAP
The use of the Extensible Authentication Protocol (EAP) [RFC4372]
serves 2 purposes. In the first place a proper chosen EAP-method
allows for integrity and confidentiality protected transport of the
user credentials to the home organization. Secondly, by having all
RADIUS servers transparently proxy access requests regardless of the
EAP-method inside the RADIUS packet, the choice of EAP-method is
between the 'home' organization of the user and the user, in other
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words, in principle every authentication form that can be carried
inside EAP can be used in eduroam, as long as they adhere to the
policy with regards to security properties.
+-----+
/ \
/ \
/ \
/ \
,----------\ | | ,---------\
| SP | | eduroam | | IdP |
| +----+ trust fabric +---+ |
`------+---' | | '-----+---'
| | | |
| \ / |
| \ / |
| \ / |
| \ / |
+----+ +-----+ +----+
| |
| |
+---+--+ +--+---+
| | | |
+-+------+-+ ___________________________ | |
| | O__________________________ ) +------+
+----------+
Host (supplicant) EAP tunnel Authentication server
Figure 1: Tunneled EAP
Proxying of access requests is based on the outer identity in the
EAP-message. Those outer identities MUST be of the form
something@realm, where the realm part is the domain name of the
domain that the IdP belongs to. In order to preserve privacy,
participating organizations MUST deploy EAP-methods that provide
mutual authentication. For EAP methods that support outer identity,
anonymous outer identities are recommended. Most commonly used in
eduroam are the so-called tunneled EAP-methods that first create a
server authenticated TLS tunnel through which the user credentials
are transmitted.
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2.2. Federation Trust Fabric
The eduroam federation trust fabric is based on RADIUS. RADIUS trust
is based on shared secrets between RADIUS peers. In eduroam any
RADIUS message originating from a trusted peer is implicitly assumed
to originate from a member of the romaing consortium.
2.2.1. RADIUS
The eduroam trust fabric is based on a proxy hierarchy of RADIUS
servers, loosely based on the DNS hierarchy. That is, the
organizational RADIUS servers agree on a shared secret with the
national servers and the national servers agree on a shared secret
with the root server. Access requests are routed through a chain of
RADIUS proxies towards the home organization of the user, and the
access accept (or reject) follows the same path back.
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+-------+
| |
| . |
| |
+---+---+
/ | \
+----------------/ | \---------------------+
| | |
| | |
| | |
+--+---+ +--+--+ +----+---+
| | | | | |
| .edu | . . . | .nl | . . . | .ac.uk |
| | | | | |
+--+---+ +--+--+ +----+---+
/ | \ | \ |
/ | \ | \ |
/ | \ | \ |
+-----+ | +-----+ | +------+ |
| | | | | |
| | | | | |
+---+---+ +----+---+ +----+---+ +--+---+ +-----+----+ +-----+-----+
| | | | | | | | | | | |
|utk.edu| |utah.edu| |case.edu| |hva.nl| |surfnet.nl| |soton.ac.uk|
| | | | | | | | | | | |
+----+--+ +--------+ +--------+ +------+ +----+-----+ +-----------+
| |
| |
+--+--+ +--+--+
| | | |
+-+-----+-+ | |
| | +-----+
+---------+
user: paul@surfnet.nl surfnet.nl Authentication server
Figure 2: eduroam RADIUS hierarchy
Routing of access requests to the home IdP is done based on the realm
part of the outer identity. For example, when user paul@surfnet.nl
of SURFnet (surfnet.nl) tries to gain wireless network access at the
University of Tennessee at Knoxville (utk.edu) the following happens:
o Paul's supplicant transmits an EAP access request to the Access
Point (Authenticator) at UTK with outer identity say
anonymous@surfnet.nl
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o The Access Point forwards the EAP message to its Authentication
Server (the UTK RADIUS server)
o The UTK RADIUS server checks the realm to see if it is a local
realm, since it isn't the request is proxied to the .edu RADIUS
server
o The .edu RADIUS server verifies the realm, and since it is not a
in a .edu subdomain it proxies the request to the root server
o The root RADIUS server proxies the request to the .nl RADIUS
server
o The .nl RADIUS server proxies the request to the surfnet.nl server
o The surfnet.nl RADIUS server decapsulates the EAP message and
verifies the user credentials
o The surfnet.nl RADIUS server informs the utk.edu server of the
outcome of the authentication request (accept or deny) by proxying
the outcome through the RADIUS hierarchy in reverse order.
o The UTK RADIUS server instructs the UTK Access Point to either
accept or deny access based on the outcome of the authentication.
Note: The depiction of the root RADIUS server is a simplification of
reality. In reality the root server is distributed over 3 continents
and each maintains a list of top level realms a specific root server
is responsible for. So in reality, for intercontinental roaming
there is an extra proxy step from one root server to the other
involved.
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3. Issues with initial Trust Fabric
While the hierarchical RADIUS architecture in the previous section
has served as the basis for eduroam Operations for an entire decade,
the exponential growth of authentications is expected to lead to
performance and operations bottlenecks on the aggregation proxies.
The following sections describe some of the shortcomings, and the
resulting conclusions.
3.1. Server Failure Handling
In eduroam, authentication requests for roaming users are statically
routed through pre-configured proxies. The number of proxies varies:
in a national roaming case, the number of proxies is typically 1 or 2
(some countries deploy regional proxies, which are in turn aggregated
by a national proxy); in international roaming, 3 or 4 proxy servers
are typically involved (the number may be higher along some routes).
RFC2865 [RFC2865] does not define a failover algorithm. In
particular, the failure of a server needs to be deducted from the
absence of a reply. Operational experience has shown that this has
detrimental effects on the infrastructure and end user experience:
1. Authentication failure: the first user whose authentication path
is along a newly-failed server will experience a long delay and
possibly timeout
2. Wrongly deducted states: since the proxy chain is longer than 1
hop, a failure further down in the authentication path is
indistinguishable from a failure in the next hop.
3. Inability to determine recovery of a server: only a "live"
authentication request sent to a server which is believed
inoperable can lead to the discovery that the server is in
working order again. This issue has been resolved with RFC5997
[RFC5997].
The second point can have significant impact on the operational state
of the system in a worst-case scenario: Imagine one realm's home
server being inoperable. A user from that realm is trying to roam
internationally and tries to authenticate. The RADIUS server on the
hotspot location will assume its own national proxy is down, because
it does not reply. That national server, being perfectly alive, in
turn will assume that the international aggregation proxy is down;
which in turn will believe the home country proxy national server is
down. None of these assumptions are true. Worse yet: should any of
these servers trigger a failover to a redundant backup RADIUS server,
it will still not receive a reply, because the request will still be
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routed to the same defunct home server. Within a short time, all
redundant aggregation proxies might be considered defunct by their
preceding hop.
In the absence of proper next-hop state derivation, some interesting
concepts have been introduced by eduroam participants; the most
noteworthy being a failover logic which considers up/down states not
per next-hop RADIUS peer, but instead per realm (See [
http://wiki.eduroam.cz/dead-realm/docs/dead-realm.html ] for
details). As of recent, RFC5997 [RFC5997] implementations and
cautious failover parameters make such a worst-case scenario very
unlikely to happen, but are still an important issue to consider.
3.2. No error condition signalling
The RADIUS protocol lacks signalling of error conditions, and the
IEEE 802.1X protocol does not allows to convey extended failure
reasons to the end-user's device. For eduroam, this creates issues
in a twofold way:
o The home server may have an operational problem, for example if
its authentication decisions depend on an external data source
such as ActiveDirectory or an SQL server, and if these external
dependencies are out of order. If the RADIUS interface is still
functional, there are two options how to reply to an Access-
Request which can't be serviced due to such error conditions:
1. Do Not Reply: the inability to reach a conclusion can be
treated by not replying to the request. The upside of this
approach is that the end-user's software doesn't come to wrong
conclusions and won't give unhelpful hints such as "maybe your
password is wrong". The downside is that intermediate proxies
may come to wrong conclusions because their downstream RADIUS
server isn't responding.
2. Reply with Reject: in this option, the inability to reach a
conclusion is treated like an authentication failure. The
upside of this approach is that intermediate proxies maintain
a correct view on the reachability state of their RADIUS peer.
The downside is that EAP supplicants on end-user devices often
react with either false advice ("your password is wrong") or
even trigger permanent configuration changes (e.g. the Windows
built-in supplicant will delete the credential set from its
registry, prompting the user for their password on the next
connection attempt). The latter case of Windows is a source
of significant helpdesk activity; users may have forgotten
their password after initially storing it, but are suddenly
prompted again.
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o There have been epic discussions in the eduroam community which of
the two approaches is more appropriate; but they were not
conclusive.
o Similar considerations as above apply when an intermediate proxy
does not receive a reply from a downstream RADIUS server. The
proxy may either choose not to reply to the original request,
leading to retries and its upstream peers coming to wrong
conclusions about its own availability; or it may decide to reply
with Access-Reject to indicate its own liveliness, but again with
implications for the end user.
The ability to send Status-Server watchdog requests is only of use
reactively if a downstream server doesn't reply. The active link-
state monitoring of the TCP connection with e.g. RADIUS/TLS gives a
clearer indication whether there is an alive RADIUS peer, but does
not solve the defunct backend problem. An explicit ability to send
Error-Replies, on the RADIUS (for other RADIUS peer information) and
EAP level (for end-user supplicant information), would alleviate
these problems but is currently not available.
3.3. Routing table complexity
The aggregation of RADIUS requests based on the structure of the
user's realm implies that realms ending with the same top-level
domain are routed to the same server; i.e. to a common administrative
domain. While this is true for ccTLDs, which map into national
eduroam federations, it is not true for realms residing in gTLDs.
Realms in gTLDs were historically discouraged because the automatic
mapping "realm ending" -> "eduroam federation's server" could not be
applied. However, with growing demand from eduroam realm
administrators, it became necessary to create exceptional entries in
the forwarding rules; such realms need to be mapped on a realm-by-
realm basis to their eduroam federations. Example: "kit.edu" needs
to be routed to the German federation server; "iu.edu" neeeds to be
routed to the U.S.A. federation server.
While the ccTLDs occupied only approx. 50 routing entries in total
(and has a upper bound of approx. 200), the potential size of the
routing table becomes virtually unlimited if it needs to accomodate
all individual entries in .edu, .org, etc.
In addition to that, all these routes need to be synchronised between
three international root servers, and the updates needed to be
applied manually to RADIUS server configuration files. The frequency
of the required updates made this approach fragile and error-prone as
the number of entries grew.
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3.4. UDP Issues
RADIUS is based on UDP, which was a reasonable choice when its main
use was with simple PAP requests which required only exactly one
packet exchange in each direction.
When transporting EAP over RADIUS, the EAP conversations requires
multiple round-trips; depending on the total payload size, 8-10
round-trips are not uncommon. The loss of a single UDP packet will
lead to user-visible delays and might result in servers being marked
as dead due to the absence of a reply. The proxy path in eduroam
consists of several proxies, all of which introduce a tiny packet
loss probability; i.e. the more proxies are needed, the higher the
failure rate is going to be.
For some EAP types, depending on the exact payload size they carry,
RADIUS servers and/or supplicants may choose to fill as much EAP data
into a single RADIUS packet as the supplicant's layer 2 medium allows
for, typically 1500 Bytes. In that case, the RADIUS encapsulation
around the EAP-Message will itself also exceed 1500 Byte size which
in turn means the UDP datagram which carries the RADIUS packet will
need to be fragmented on the IP layer. While this is not a problem
in theory, practice has shown evidence of misbehaving firewalls which
erroneously discard non-first UDP fragments, which ultimately leads
to a denial of service for users with such EAP types and that
specific configuration.
One EAP type proved to be particularly problematic: EAP-TLS. While
it is possible to configure the EAP server to send smaller chunks of
EAP payload to the supplicant (e.g. 1200 Bytes, to allow for another
300 Bytes of RADIUS overhead without fragmentation), very often the
supplicants which send the client certificate do not expose such a
configuration detail to the user. Consequently, when the client
certificate is beyond 1500 Bytes in size, the EAP-Message will always
make use of the maximum possible layer-2 chunk size, which introduces
the fragmentation on the path EAP peer -> EAP server.
The operational experience regarding EAP-TLS leads to the following
RECOMMENDATION: EAP supplicants should either make the maximum EAP
chunk size configurable OR use cautious values regarding the EAP
chunk size (e.g. max. 1200 Bytes per chunk, even if the layer 2
medium provides foresaw more space).
Both of the previously mentioned sources of errors (packet loss,
fragment discard) are hard to diagnose and can lead to significant
user frustration for the affected users.
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3.5. Insufficient payload encryption
The RADIUS protocol's design foresaw only the encryption of select
RADIUS attributes, most notably User-Password. With EAP methods
conforming to the requirements of RFC4017, the user's credential is
not transmitted using the User-Password attribute, and stronger
encryption than the one for RADIUS' User-Password is in use
(typically TLS).
Still, the use of EAP does not encrypt all personally identifiable
details of the user session. In particular, the user's computing
device can be identified by inspecting the Calling-Station-ID
attribute; and the user's location may be derived from observing NAS-
IP-Address, NAS-Identifier or Operator-Name attributes. Since these
attributes are not encrypted, even IP-layer third parties can harvest
the corresponding data. In a worst-case scenario, this enables the
creation of mobility profiles.
These profiles are not necessarily linkable to an actual user because
EAP allows for the use of anonymous outer identities and protected
credential exchanges. However, practical experience has shown that
many users neglect to configure their supplicants in a privacy-
preserving way. Worse, for EAP-TLS users, the use of EAP-TLS
identity protection is not usually implemented and cannot be used.
In eduroam, concerned individuals and IdPs which use EAP-TLS are
using pseudonymous client certificates to provide for better privacy.
One way out, at least for EAP types involving a username, is to
pursue the creation and deployment of pre-configured supplicant
configuration which makes all the required settings in user devices
prior to their first connection attempt; this depends heavily on the
remote configuration possibilities of the supplicants though.
A further threat involves the verification of the EAP server's
identity. Even though the cryptographic foundation, TLS tunnels, is
sound, there is a weakness in the supplicant configuration: many
users do not understand or are willing to invest time into the
inspection of server certificates or the installation of a trusted
CA. As a result, users may easily be tricked into connecting to an
unauthorized EAP server, ultimately leading to a leak of their
credentials to that unauthorized third party.
Again, one way out of this particular threat is to pursue the
creation and deployment of pre-configured supplicant configuration
which makes all the required settings in user devices prior to their
first connection attempt.
Note: there are many different and vendor-proprietary ways to pre-
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configure a device with the necessary EAP parameters (examples
include Apple, Inc's "mobileconfig" and Microsoft's "EAPHost" XML
schema). Some manufacturers even completely lack any means to
distribute EAP configuration data. We believe there is value in
defining a common EAP configuration meta data format which could be
used across manufacturers; ideally leading to a situation where any
IEEE 802.1X network end-user merely needs to apply this configuration
file to configure any of his devices securely with the required
connection properties.
Another possible threat involves transport of user-specific
attributes in a Reply-Message. If, for example, a RADIUS server
sends back a hypothetical RADIUS Vendor-Specific-Attribute "User-Role
= Student of Computer Science" (e.g. for consumption of a SP RADIUS
server and subsequent assignment into a "student" VLAN), this
information would also be visible for third parties and could be
added to the mobility profile.
The only way out to mitigate all information leakage to third parties
is by protecting the entire RADIUS packet payload so that IP-layer
third parties can not extract privacy-relevant information. RFC2865
RADIUS does not offer this possibility though.
Note: This operational experience of eduroam could be taken as a
guideline for supplicant implementers to leave sufficient space in
transmitted packets.
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4. Enhanced Architecture
The operational difficulties with an ever increasing number of
participants as documented in the previous section have led to a
number of changes to the eduroam architecture that in turn have, as
mentioned in the introduction, led to standardization effort.
Note: The enhanced architecture components are fully backwards
compatible with the existing installed base, and is in fact gradually
replacing those parts of it where problems may arise.
4.1. Federation Trust Fabric
Whereas the user authentication using 802.1X and EAP has remained
unchanged (i.e. no need for end-users to change any configurations),
the issues as reported above have resulted in a major overhaul of the
way EAP messages are transported from the RADIUS server of the SP to
that of the IdP and back. The two fundamental changes are the use of
TCP instead of UDP and reliance on TLS instead of shared secrets
between RADIUS peers.
4.1.1. RADIUS with TLS
The deficiencies of RADIUS over UDP as described in Section 3.4
warranted a search for a replacement of RFC2865 [RFC2865] for the
transport of EAP. By the time this need was understood, the
designated successor protocol to RADIUS, Diameter [RFC3588], was
already specified by the IETF. However, within the operational
constraints of eduroam:
o reasonably cheap to deploy on many administrative domains
o supporting NASREQ Application
o supporting EAP Application
o supporting Diameter Redirect
o supporting validation of authentication requests of the most
popular EAP types (EAP-TTLS, PEAP, and EAP-TLS)
o possibility to retrieve these credentials from popular backends
such as Microsoft ActiveDirectory, MySQL
no single implementation could be found. In addition to that, no
Wireless Access Points at the disposal of eduroam participants
supported Diameter, nor did any of the manufacturers have a roadmap
towards Diameter support. This led to the open question of lossless
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translation from RADIUS to Diameter and vice versa; a question not
satisfactorily answered by NASREQ.
After monitoring the Diameter implementation landscape for a while,
it became clear that a solution with better compatibility and a
plausible upgrade path from the existing RADIUS hierarchy was needed.
The eduroam community actively engaged in the IETF towards the
specification of several enhancements to RADIUS to overcome the
limitations mentioned in Section 3. The outcome of this process was
[RFC6614] and [I-D.ietf-radext-dynamic-discovery].
With its use of TCP instead of UDP, and with its full packet
encryption, while maintaining full packet format compatibility with
RADIUS/UDP, RADIUS/TLS [RFC6614] allows to upgrade any given RADIUS
link in eduroam without the need of a "flag day".
In a first upgrade phase, the classic eduroam hierarchy (forwarding
decision taken by inspecting the realm) remains intact. That way,
RADIUS/TLS merely enhances the underlying transport of the RADIUS
datagrams. But this already provides some key advantages:
o explicit peer reachability detection using long-lived TCP sessions
o protection of user credentials and all privacy-relevant RADIUS
attributes
RADIUS/TLS connections for the static hierarchy could be realised
with the TLS-PSK operation mode (which effectively provides a 1:1
replacement for RADIUS/UDP's "shared secrets"), but since this
operation mode is not widely supported as of yet, all RADIUS/TLS
links in eduroam are secured by TLS with X.509 certificates from a
set of accredited CAs.
This first deployment phase does not yet solve the routing table
complexity problem (see (Section 3.3); this aspect is covered by
introducing dynamic discovery for RADIUS/TLS servers.
4.1.2. Dynamic Discovery
XXX
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5. Abuse prevention and incident handling
Since the eduroam service is a confederation of autonomous networks,
there is little justification for transferring accounting information
from the visited site to any other in general, or in particular to
the home organization of the user. Accounting in eduroam is
therefore considered to be a local matter of the visited site. The
eduroam compliance statement ([eduroam-compliance]) in fact specifies
that accounting traffic SHOULD NOT be forwarded.
The static routing infrastructure of eduroam acts as a filtering
system blocking accounting traffic from misconfigured local RADIUS
servers. Proxy servers are configured to terminate accounting
request traffic by answering to Accounting-Requests with an
Accounting-Response in order to prevent the retransmission of
orphaned Accounting-Request messages.
Roaming creates accounting problems identified by [RFC4372]
(Chargeable User Identity). Since the NAS can only see the (likely
anonymous) outer identity of the user, it is impossible to correlate
usage with a specific user (who may use multiple devices). A NAS
that supports Chargeable User Identity can request additional
information - Chargeable-User-Identity and if this is supplied by the
authenticating RADIS server in the Access-Accept message, this value
will then be added to corresponding Access-Request packets. While
eduroam does not have any charging mechanisms, it may still be
desirable to identify traffic originating from one particular user.
One of the reasons is to prevent abuse of guest access by users
living nearby university campuses. Chargeable User Identity supplies
the perfect answer to this problem, however at the moment of writing,
to our knowledge only one hardware vendor (Meru Networks) implements
RFC4372 on their Access Points. For all other vendors, requesting
the Chargeable-User-Identity attribute needs to happen on the RADIUS
server to which the Access Point is connected to. Currently, the
RADIUS servers FreeRADIUS and Radiator can be retrofitted with the
ability to do this.
5.1. Incident Handling
10 years of experience with eduroam have not exposed any serious
incident. This may be taken as evidence for proper security design
and awareness of users that they are identifiable, acts as an
effective deterrent.
For example the European eduroam policy [eduroam-policy] describes
incident scenarios and actions to be taken, in this document we
present the relevant technical issues.
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The first action in the case of an incident is to block the user's
access to eduroam at the visited site. Since the roaming user's true
identity is likely hidden behind an anonymous/fake outer identity,
the visited site can only rely on the realm of the user. Without
cooperation from the user's home institution, the visited
institution's options are limited to blocking authentications from
the entire realm, which may be considered as too harsh. On the other
hand, the home institution has only the possibility of blacking the
user's authentication entirely, thus blocking this user from
accessing eduroam in all sites. This may also be seen as a too harsh
an action, especially since visited and home sites could differ in
interpreting the user's actions. Introduction of support for
Operator-Name and Chargeable-User-Identity (see below) to eduroam can
significantly improve the situation.
5.2. Operator Name
The Operator-Name attribute is defined in [RFC5580] as a means of
unique identification of the access site.
The Proxy infrastructure of eduroam makes it impossible for home
sites to tell where their users roam to. While this may be seen as a
positive aspect enhancing user's privacy, it also makes user support,
roaming statistics and blocking offending user's access to eduroam
significantly harder.
Sites participating in eduroam are encouraged to add the Operator-
Name attribute using the REALM namespace, i.e. sending a realm name
under control of the given site.
The introduction of Operator-Name in eduroam has identified one
operational problem - the identifier 126 assigned to this attribute
has been previously used by some vendors for their specific purposes
and has been included in attribute dictionaries of several RADIUS
server distributions. Since the syntax of this hijacked attribute
had been set to Integer, this introduces a syntax clash with the the
RFC definition (OctetString). Operational tests in eduroam have
shown that servers using the Integer syntax for attribute 126 may
either truncate the value to 4 octets or even drop the entire RADIUS
packet (thus making authentication impossible). The eduroam
monitoring and eduroam test tools try to locate problematic sites.
When a visited site sends its Operator-Name value, it creates a
possibility for the home sites to set up conditional blocking rules,
depriving certain users of access to selected sites. Such action
will cause much less concern then blocking users from all of eduroam.
In eduroam the Operator Name is also used for the generation of
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Chargeable User Identity values.
The addition of Operator-Name is a straightforward configuration of
the RADIUS server and may be easily introduced on a large scale.
5.3. Chargeable User Identifier
The Chargeable-User-Identity (CUI) attribute is defined by RFC4372
[RFC4372] as an answer to accounting problems caused by the use of
anonymous identity in some EAP methods. In eduroam the primary use
of CUI is in incident handling, but it can also enhance local
accounting.
The eduroam policy requires that a given user's CUI generated for
requests originating form different sites should be different (to
prevent collusion attacks). The eduroam policy thus mandates that a
CUI request be accompanied by the Operator-Name attribute, which is
used as one of the inputs for the CUI generation algorithm. The
Operator-Name requirement is considered to be the "business
requirement" described in Section 2.1 of RFC4372 [RFC4372] and hence
conforms to the RFC.
When eduroam started considering using CUI, there were no NAS
implementations, therefore the only solution was moving all CUI
support to the RADIUS server.
CUI request generation requires only the addition of NUL CUI
attributes to outgoing Access-Requests, however the real strength of
CUI comes with accounting. Implementation of CUI based accounting in
the server requires that the authentication and accounting RADIUS
servers used directly by the NAS are actually the same or at least
have access to a common source of information. Upon processing of an
Access-Accept the authenticating RADIUS server must store the
received CUI value together with the device's Calling-Station-Id in a
temporary database. Upon receipt of an Accounting-Request, the
server needs to update the packet with the CUI value read from the
database.
A wide introduction of CUI support in eduroam will significantly
simplify incident handling at visited sites. Introducing local, per-
user access restriction will be possible. Visited sites will also be
able to notify the home site about the introduction of such a
restriction, pointing to the CUI value an thus making it possible for
the home site to identify the user. When the user reports the
problem at his home support, the reason will be already known.
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6. Privacy Considerations
XXX
6.1. Collusion of RPs
XXX
6.2. Exposing user credentials
XXX
6.3. Track location of users
XXX
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7. Security Considerations
This section addresses only security considerations associated with
the use of eduroam. For considerations relating to 802.1X, RADIUS
and EAP in general, the reader is referred to the respective
specification and to other literature.
7.1. Man in the middle and Tunneling Attacks
XXX
7.2. Denial of Service Attacks
XXX
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8. IANA Considerations
There are no IANA Considerations
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9. References
9.1. Normative References
[I-D.hansen-privacy-terminology]
Hansen, M., Tschofenig, H., and R. Smith, "Privacy
Terminology", draft-hansen-privacy-terminology-03 (work in
progress), October 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)",
RFC 3748, June 2004.
[RFC4279] Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites
for Transport Layer Security (TLS)", RFC 4279,
December 2005.
[RFC4372] Adrangi, F., Lior, A., Korhonen, J., and J. Loughney,
"Chargeable User Identity", RFC 4372, January 2006.
[RFC5176] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
Aboba, "Dynamic Authorization Extensions to Remote
Authentication Dial In User Service (RADIUS)", RFC 5176,
January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5247] Aboba, B., Simon, D., and P. Eronen, "Extensible
Authentication Protocol (EAP) Key Management Framework",
RFC 5247, August 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC5580] Tschofenig, H., Adrangi, F., Jones, M., Lior, A., and B.
Aboba, "Carrying Location Objects in RADIUS and Diameter",
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RFC 5580, August 2009.
[RFC5997] DeKok, A., "Use of Status-Server Packets in the Remote
Authentication Dial In User Service (RADIUS) Protocol",
RFC 5997, August 2010.
[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:
Extension Definitions", RFC 6066, January 2011.
[RFC6613] DeKok, A., "RADIUS over TCP", RFC 6613, May 2012.
[RFC6614] Winter, S., McCauley, M., Venaas, S., and K. Wierenga,
"Transport Layer Security (TLS) Encryption for RADIUS",
RFC 6614, May 2012.
9.2. Informative References
[I-D.ietf-abfab-arch]
Howlett, J., Hartman, S., Tschofenig, H., Lear, E., and J.
Schaad, "Application Bridging for Federated Access Beyond
Web (ABFAB) Architecture", draft-ietf-abfab-arch-03 (work
in progress), July 2012.
[I-D.ietf-radext-dtls]
DeKok, A., "DTLS as a Transport Layer for RADIUS",
draft-ietf-radext-dtls-02 (work in progress), July 2012.
[I-D.ietf-radext-dynamic-discovery]
Winter, S. and M. McCauley, "NAI-based Dynamic Peer
Discovery for RADIUS/TLS and RADIUS/DTLS",
draft-ietf-radext-dynamic-discovery-04 (work in progress),
June 2012.
[MD5-attacks]
Black, J., Cochran, M., and T. Highland, "A Study of the
MD5 Attacks: Insights and Improvements", October 2006,
<http://www.springerlink.com/content/40867l85727r7084/>.
[RFC3539] Aboba, B. and J. Wood, "Authentication, Authorization and
Accounting (AAA) Transport Profile", RFC 3539, June 2003.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
[RFC4107] Bellovin, S. and R. Housley, "Guidelines for Cryptographic
Key Management", BCP 107, RFC 4107, June 2005.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
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(TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks",
RFC 4953, July 2007.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011.
[RFC6421] Nelson, D., "Crypto-Agility Requirements for Remote
Authentication Dial-In User Service (RADIUS)", RFC 6421,
November 2011.
[dot1X-standard]
IEEE, "IEEE std 802.1X-2010", February 2010, <http://
standards.ieee.org/getieee802/download/802.1X-2010.pdf>.
[eduroam-compliance]
Trans-European Research and Education Networking
Association, "eduroam compliance statement", 2011, <http:/
/www.eduroam.org/downloads/docs/
eduroam_Compliance_Statement_v1_0.pdf>.
[eduroam-homepage]
Trans-European Research and Education Networking
Association, "eduroam Homepage", 2007,
<http://www.eduroam.org/>.
[eduroam-policy]
Trans-European Research and Education Networking
Association, "European eduroam policy", 2011, <http://
www.eduroam.org/downloads/docs/
GN3-12-194_eduroam-policy-%20for-
signing_ver2%204_18052012.pdf>.
[eduroam-start]
Wierenga, K., "Initial proposal for (now) eduroam", 2002,
<http://www.terena.org/activities/tf-mobility/
start-of-eduroam.pdf>.
[geant2] Delivery of Advanced Network Technology to Europe,
"European Commission Information Society and Media:
GEANT2", 2008, <http://www.geant2.net/>.
[radsec-whitepaper]
Open System Consultants, "RadSec - a secure, reliable
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RADIUS Protocol", May 2005,
<http://www.open.com.au/radiator/radsec-whitepaper.pdf>.
[radsecproxy-impl]
Venaas, S., "radsecproxy Project Homepage", 2007,
<http://software.uninett.no/radsecproxy/>.
[terena] TERENA, "Trans-European Research and Education Networking
Association", 2008, <http://www.terena.org/>.
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Appendix A. Acknowledgments
The authors would like to thank the participants in the TERENA Task
Force on Mobility and Network Middleware as well as the Geant project
for their reviews and contributions.
The eduroam trademark is registered by TERENA.
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Appendix B. Changes
This section to be removed prior to publication.
o 00 Initial Revision.
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Authors' Addresses
Klaas Wierenga
Cisco Systems
Haarlerbergweg 13-19
Amsterdam 1101 CH
The Netherlands
Phone: +31 20 357 1752
Email: klaas@cisco.com
Stefan Winter
Fondation RESTENA
6, rue Richard Coudenhove-Kalergi
Luxembourg 1359
Luxembourg
Phone: +352 424409 1
Fax: +352 422473
Email: stefan.winter@restena.lu
URI: http://www.restena.lu.
Tomasz Wolniewicz
Nicolaus Copernicus University
pl. Rapackiego 1
Torun
Poland
Phone: +48-56-611-2750
Fax: +48-56-622-1850
Email: twoln@umk.pl
URI: http://www.home.umk.pl/~twoln/
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