One document matched: draft-ietf-radext-populating-eapidentity-01.txt
Differences from draft-ietf-radext-populating-eapidentity-00.txt
RADIUS Extensions Working Group S. Winter
Internet-Draft RESTENA
Updates: 3748 (if approved) July 08, 2016
Intended status: Best Current Practice
Expires: January 9, 2017
Considerations regarding the correct use of EAP-Response/Identity
draft-ietf-radext-populating-eapidentity-01
Abstract
There are some subtle considerations for an EAP peer regarding the
content of the EAP-Response/Identity packet when authenticating with
EAP to an EAP server. This document describes two such
considerations and suggests workarounds to the associated problems.
One of these workarounds is a new requirement for EAP peers that the
use of UTF-8 is required for the content of EAP-Response/Identity
(which updates RFC3748).
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 January 9, 2017.
Copyright Notice
Copyright (c) 2016 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
(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
Winter Expires January 9, 2017 [Page 1]
Internet-Draft Populating EAP-Response/Identity July 2016
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 . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Problem Statement . . . . . . . . . . . . . . . . . . . . 2
1.2. Taxonomy of identities in EAP . . . . . . . . . . . . . . 3
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. EAP-Response/Identity: Effects on EAP type negotiation . . . 5
3. Character (re-)encoding may be required . . . . . . . . . . . 6
4. Recommendations for EAP peer implementations . . . . . . . . 7
5. Privacy Considerations . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 9
1. Introduction
1.1. Problem Statement
An Extensible Authentication Protocol (EAP, [RFC3748]) conversation
between an EAP peer and an EAP server starts with an (optional)
request for identity information by the EAP server (EAP-Request/
Identity) followed by the peer's response with identity information
(EAP-Response/Identity). Only after this identity exchange are EAP
types negotiated.
EAP-Response/Identity is sent before EAP type negotiation takes
place, but it is not independent of the later-negotiated EAP type.
Two entanglements between EAP-Response/Identity and EAP methods'
notions of a user identifier are described in this document.
1. The choice of identifier to send in EAP-Response/Identity may
have detrimental effects on the subsequent EAP type negotiation.
2. Using identifiers from the preferred EAP type without thoughtful
conversion of character encoding may have detrimental effects on
the outcome of the authentication.
The following two chapters describe each of these issues in detail.
The last chapter contains recommendations for implementers of EAP
peers to avoid these issues.
Winter Expires January 9, 2017 [Page 2]
Internet-Draft Populating EAP-Response/Identity July 2016
1.2. Taxonomy of identities in EAP
The notion of identity occurs numerous times in the EAP protocol
stack (EAP-Response/Identity, Outer identity, method-specific
identity, tunneled identity). This document uses the following
terminology when discussing EAP identities.
o User Identifier: Each EAP method has a means to identify the user
or machine that tries to authenticate. There are no restrictions
on the format or encoding of this identifier. The user identifier
is often also referred to as "method-specific identity". If an
EAP method distinguishes between the user identifier and a realm
identifier (see next bullet), then the user identifier is also
often referred to as the "inner/true/real identity".
o Realm Identifier: Some EAP methods allow privacy-preserving
enhancements where a string is sent which is actually not
necessarily related to the user or machine that tries to
authenticate. This identifier is often also referred to as "outer
identity" or "roaming identity" or "anonymous outer identity".
There is often a relationship between the realm identifier and the
user identifier (e.g. they often share the same NAI realm suffix);
but this is not a requirement. There are no restrictions on the
format or encoding of the realm identifier. Realm identifiers are
either
* explicitly configured (e.g. string input UI in EAP peer: "Outer
Identity")
* implicitly configured by copying the actual user identifier
* implicitly configured by copying the NAI realm of the user
identifier and prefixing it non-configurably with a fixed
privacy-preserving local username part like "anonymous" or the
empty string (see [RFC7542])
* configured in a mixed way, e.g. using a explicit string input
UI for the local part of the realm identifier and combining it
implicitly with a copy of the NAI realm part of the user
identifier
o EAP-Response/Identity: a string representing the user or machine
that tries to authenticate, used outside the EAP method-specific
context for the entire EAP conversation. There can be only one
EAP-Response/Identity per EAP conversation, even if that
conversation could negotiate more than one EAP method to
authenticate with. As per [RFC3748] there is no encoding
requirement on EAP-Response/Identity (which this document changes:
Winter Expires January 9, 2017 [Page 3]
Internet-Draft Populating EAP-Response/Identity July 2016
the encoding MUST be UTF-8). In AAA protocol routing contexts,
the content of EAP-Response/Identity is often used for request
routing purposes. EAP-Response/Identity is chosen from the set:
* all realm identifiers from all configured EAP types supporting
the notion of a realm identifier
* all user identifiers from all configured EAP types without the
notion of a realm identifier
Several EAP types in a local configuration may share the same user
and/or realm identifiers. The set of identifiers for EAP-Response
/Identity may thus contain fewer elements than there are
configured EAP types in a local configuration. One of the two
problems addressed in this document stems from this fact: the set
of identifiers may contain more than one element. The resulting
EAP-Response/Identity always routes all configured EAP types to
only one destination, even if different EAP types would need
routing to different destinations.
o User-Name: when using EAP in AAA protocol contexts (e.g. RADIUS
[RFC2865], Diameter [RFC6733]), this additional identifier is
created outside the EAP peer (typically in a pass-through
authenticator) by copying EAP-Response/Identity content to the AAA
protocol's User-Name attribute. There is no format requirement on
User-Name, but there is an encoding requirement: the string MUST
be UTF-8 encoded. One of the two problems addressed in this
document stems from this fact: EAP-Response/Identity does not have
an encoding requirement, nor does it carry meta-information about
the encoding used - and yet, it needs to be coerced into a UTF-8
encoding.
o Further identifiers: Some EAP methods establish an EAP session
inside EAP (e.g. PEAP first establishes a TLS tunnel using a realm
identifier, and then starts an EAP exchange inside the tunnel).
This being a new, independent EAP session, it contains its own
EAP-Response/Identity, can invoke EAP method negotiation with
different (inner) EAP types (this happens e.g. with EAP-FAST and
its configurable choice of EAP-GTC or EAP-MSCHAPv2 inside the
inner EAP session), and those inner EAP methods then have their
own user identifiers. Where the inner EAP method itself supports
the notion of realm identifiers, another identifier could be
configured. For the purposes of this document, none of those
details are considered and the process by which the (outer) EAP
method selects its user identifier is left entirely to that EAP
type. This document does not consider the (inner) EAP-Response/
Identity in scope; the recommendations in this document to not
apply to such (inner) occurences of EAP-Response/Identity.
Winter Expires January 9, 2017 [Page 4]
Internet-Draft Populating EAP-Response/Identity July 2016
1.3. Requirements Language
In this document, several words are used to signify the requirements
of the specification. 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]
2. EAP-Response/Identity: Effects on EAP type negotiation
Assuming the EAP peer's EAP type selection is not the trivial case
(i.e. it has more than one configured EAP type for a given network or
application, and needs to make a decision which one to use), an issue
arises when the configured EAP types are not all configured with the
same realm identifier (or user identifier for EAP types not
supporting the notion of a realm identifier).
Issue: if the identifiers in the set of configured EAP types differ
(e.g. have a different [RFC7542] "realm" portion), and the
authenticator does not send identity selection hints as per
[RFC7542], then EAP type negotiation may be limited to those EAP
types which are terminated in the same EAP server. The reason for
that is because the information in the EAP-Response/Identity is used
for request routing decisions and thus determines the EAP server - a
given realm identifier may be routed to a server which exclusively
serves the corresponding EAP types. Negotiating another EAP type
from the set of configured EAP types during the running EAP
conversation is then not possible.
Example:
Assume an EAP peer is configured to support two EAP types:
o EAP-AKA' [RFC5448] with user identifier imsi@mnc123.mcc123.3gpp-
network.org; the configuration is set up to authenticate only to
* cellular networks
* Wi-Fi Passpoint networks which advertise support for the MNC
123 and MCC 123
The EAP server for this EAP type is in a host under control of the
3GPP consortium
o EAP-TTLS [RFC5281] with user identifier "john@realm.example" and
realm identifier "@realm.example"; the configuration is set up to
authenticate only to
Winter Expires January 9, 2017 [Page 5]
Internet-Draft Populating EAP-Response/Identity July 2016
* Wi-Fi networks with the SSID "eduroam"
* Wi-Fi Passpoint networks which advertise support for the
roaming consortium 00-1B-C5-04-60 (the eduroam consortium)
* wired ethernet
The EAP server for this EAP type is in a host under control of the
eduroam consortium
The user approaches a Passpoint Wi-Fi hotspot with SSID "arbitrary"
which emits a beacon advertising support for the MNC 123/MCC 123 AND
for the consortium identifier 00-1B-C5-04-60. The local
configuration thus yields two different EAP type candidates for
authentication to the network. Unbeknownst to the user's device, the
credit with the 3G provider is fully depleted and the user will be
unable to authenticate with his EAP-AKA' credentials. Using his
identifier of the roaming consortium eduroam (see also [RFC7593]), he
could authenticate with EAP-TTLS and his john@realm.example user
identifier. Identity selection hints are not sent.
Consequence: If the EAP peer consistently chooses the
imsi@mnc123.mcc123.3gpp-network.org user identifier as choice for its
initial EAP-Response/Identity, requests will always be routed to the
3GPP consortium EAP server, and the user will be consistently and
perpetually rejected, even though in possession of a valid credential
for the hotspot.
An EAP peer should always try all options to authenticate. As the
example above shows, it may not be sufficient to rely on EAP method
negotiation alone to iterate through all configured EAP types and
come to a conclusive outcome of the authentication attempt. Multiple
new EAP authentications, each using an EAP-Response/Identity from a
different element of the set of realm identifiers, may be required to
fully iterate through the list of usable identities.
3. Character (re-)encoding may be required
The user identifiers as configured in the EAP method configuration
are not always suited as realm identifiers to choose as EAP-Response/
Identity: EAP methods define the encoding of their method-specific
outer identities at their leisure; in particular, the chosen encoding
may or may not be UTF-8.
It is not the intention of EAP, as a mere method-agnostic container
which simply carries EAP types, to restrict an EAP method's choice of
encoding of user identifiers. However, there are restrictions in
what should be contained in the EAP-Response/Identity: EAP is very
Winter Expires January 9, 2017 [Page 6]
Internet-Draft Populating EAP-Response/Identity July 2016
often carried over a AAA protocol (e.g over RADIUS as per [RFC3579]).
The typical use for the contents of EAP-Response/Identity inside AAA
protocols like RADIUS [RFC2865] and Diameter [RFC6733] is to copy the
content of EAP-Response/Identity into a "User-Name" attribute; the
encoding of the User-Name attribute is required to be UTF-8. EAP-
Response/Identity does not carry encoding information itself, so a
conversion between a non-UTF-8 encoding and UTF-8 is not possible for
the AAA entity doing the EAP-Response/Identity to User-Name copying.
Consequence: If an EAP method's user identifier is not encoded in
UTF-8, and if the EAP peer verbatimly uses that user identifier for
its EAP-Response/Identity field, then the AAA entity is forced to
violate its own specification because it has to, but can not use
UTF-8 for its own User-Name attribute. If the EAP method supports a
separate realm identifier in a non UTF-8 character set, and the EAP
peer verbatimly uses that realm identifier for its EAP-Response/
Identity field, then the same violation occurs.
This jeopardizes the subsequent EAP authentication as a whole;
request routing may fail, lead to a wrong destination or introduce
routing loops due to differing interpretations of the User-Name in
EAP pass-through authenticators and AAA proxies.
4. Recommendations for EAP peer implementations
Where realm identifiers or user identifiers between multiple
configured EAP types in an EAP peer differ, the EAP peer can not rely
on the EAP type negotiation mechanism alone to provide useful
results. If an EAP authentication gets rejected, the EAP peer SHOULD
re-try the authentication using a different EAP-Response/Identity
than before. The EAP peer SHOULD try all possible EAP-Response/
Identity contents from the entire set of configured EAP types before
declaring final authentication failure.
EAP peers need to maintain state on the encoding of the configured
user identifiers and realm identifiers which are used in their local
EAP type configuration. When constructing an EAP-Response/Identity
from the set of available identifiers, they MUST (re-)encode the
corresponding identifier as UTF-8 and use the resulting value for the
EAP-Response/Identity.
Where an EAP method supports privacy-preserving realm identifiers,
those SHOULD be configured for user privacy reasons. For deployments
of such EAP types, these realm identifiers MUST be in the the format
Network Access Identifier (NAI), see [RFC7542] if the realm
identifiers are expected to become used beyond the scope of a single,
closed enterprise. Even in such closed environments, the NAI format
is RECOMMENDED. The RECOMMENDED format for the local part of the
Winter Expires January 9, 2017 [Page 7]
Internet-Draft Populating EAP-Response/Identity July 2016
realm identifier is the empty string; where this is not possible the
suggested alternative is the string "anonymous".
5. Privacy Considerations
Because the EAP-Response/Identity content is not encrypted, the
backtracking to a new EAP-Response/Identity will systematically
reveal all configured identifiers to intermediate passive listeners
on the path between the EAP peer and the EAP server (until one
authentication round succeeds).
This additional leakage of identity information is not very
significant though, because where privacy is considered important,
the additional option for separate privacy-preserving realm
identifiers which is present in most modern EAP methods can and
should be used.
If the EAP peer implementation is certain that all EAP types will be
terminated at the same EAP server (e.g. with a corresponding
configuration option) then the iteration over all identities can be
avoided, because EAP type negotiation is then sufficient.
If a choice of which identity information to disclose needs to be
made by the EAP peer, when iterating through the list of identifiers
the EAP peer SHOULD
o in first priority honour a manually configured order of preference
of EAP types, if any
o in second priority try EAP types in order of less leakage first;
that is, EAP types with a privacy-preserving realm identifier that
differs from the user identifier should be tried before other EAP
types which would reveal the corresponding actual user
identifiers.
6. Security Considerations
The security of an EAP conversation is determined by the EAP method
which is used to authenticate. This document does not change the
actual authentication with an EAP method, and all the security
properties of the chosen EAP method remain. The format requirements
(character encoding) and operational considerations (re-try EAP with
a different EAP-Response/Identity) do not lead to new or different
security properties.
Winter Expires January 9, 2017 [Page 8]
Internet-Draft Populating EAP-Response/Identity July 2016
7. IANA Considerations
There are no IANA actions in this document.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", RFC
2865, June 2000.
[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication
Dial In User Service) Support For Extensible
Authentication Protocol (EAP)", RFC 3579, September 2003.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
3748, June 2004.
[RFC5281] Funk, P. and S. Blake-Wilson, "Extensible Authentication
Protocol Tunneled Transport Layer Security Authenticated
Protocol Version 0 (EAP-TTLSv0)", RFC 5281, August 2008.
[RFC5448] Arkko, J., Lehtovirta, V., and P. Eronen, "Improved
Extensible Authentication Protocol Method for 3rd
Generation Authentication and Key Agreement (EAP-AKA')",
RFC 5448, May 2009.
[RFC6733] Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
"Diameter Base Protocol", RFC 6733, October 2012.
[RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, DOI
10.17487/RFC7542, May 2015,
<http://www.rfc-editor.org/info/rfc7542>.
[RFC7593] Wierenga, K., Winter, S., and T. Wolniewicz, "The eduroam
Architecture for Network Roaming", RFC 7593, DOI 10.17487/
RFC7593, September 2015,
<http://www.rfc-editor.org/info/rfc7593>.
Winter Expires January 9, 2017 [Page 9]
Internet-Draft Populating EAP-Response/Identity July 2016
Author's Address
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.
Winter Expires January 9, 2017 [Page 10]
| PAFTECH AB 2003-2026 | 2026-04-23 18:51:20 |