draft-ietf-mip4-rfc3012bis-04.txt   draft-ietf-mip4-rfc3012bis-05.txt 
Network Working Group Charles E. Perkins Network Working Group Charles E. Perkins
Internet-Draft Nokia Research Center Internet-Draft Nokia Research Center
Expires: December 19, 2005 Pat R. Calhoun Expires: August 3, 2006 Pat R. Calhoun
Black Storm Networks Cisco Systems, Inc.
Jayshree. Bharatia Jayshree. Bharatia
Nortel Networks Nortel Networks
June 17, 2005 January 30, 2006
Mobile IPv4 Challenge/Response Extensions (revised) Mobile IPv4 Challenge/Response Extensions (revised)
draft-ietf-mip4-rfc3012bis-04.txt draft-ietf-mip4-rfc3012bis-05.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
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have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on December 19, 2005. This Internet-Draft will expire on August 3, 2006.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2006).
Abstract Abstract
Mobile IP, as originally specified, defines an authentication Mobile IP, as originally specified, defines an authentication
extension (the Mobile-Foreign Authentication extension) by which a extension (the Mobile-Foreign Authentication extension) by which a
mobile node can authenticate itself to a foreign agent. mobile node can authenticate itself to a foreign agent.
Unfortunately, that extension does not provide the foreign agent any Unfortunately, that extension does not provide the foreign agent any
direct guarantee that the protocol is protected from replays, and direct guarantee that the protocol is protected from replays, and
does not allow for the use of existing techniques (such as CHAP) for does not allow for the use of existing techniques (such as CHAP) for
authenticating portable computer devices. authenticating portable computer devices.
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extension. This new extension is provided so that a mobile node can extension. This new extension is provided so that a mobile node can
supply credentials for authorization using commonly available AAA supply credentials for authorization using commonly available AAA
infrastructure elements. This Authorization-enabling extension MAY infrastructure elements. This Authorization-enabling extension MAY
co-exist in the same Registration Request with Authentication co-exist in the same Registration Request with Authentication
extensions defined for Mobile IP Registration by RFC3344. This extensions defined for Mobile IP Registration by RFC3344. This
document obsoletes RFC3012. document obsoletes RFC3012.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Mobile IP Agent Advertisement Challenge Extension . . . . . . 6 2. Mobile IP Agent Advertisement Challenge Extension . . . . . . 6
2.1 Handling of Solicited Agent Advertisements . . . . . . . . 6 2.1. Handling of Solicited Agent Advertisements . . . . . . . . 6
3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 Mobile Node Processing for Registration Requests . . . . . 8 3.1. Mobile Node Processing of Registration Requests . . . . . 8
3.2 Foreign Agent Processing for Registration Requests . . . . 9 3.2. Foreign Agent Processing of Registration Requests . . . . 9
3.3 Foreign Agent Processing for Registration Replies . . . . 11 3.2.1. Foreign Agent Algorithm for Tracking Used
3.4 Home Agent Processing for the Challenge Extensions . . . . 12 Challenges . . . . . . . . . . . . . . . . . . . . . . 11
3.5 Mobile Node Processing for Registration Replies . . . . . 12 3.3. Foreign Agent Processing of Registration Replies . . . . . 11
4. Mobile-Foreign Challenge Extension . . . . . . . . . . . . . . 15 3.4. Home Agent Processing of Challenge Extensions . . . . . . 13
5. Generalized Mobile IP Authentication Extension . . . . . . . . 16 3.5. Mobile Node Processing of Registration Replies . . . . . . 13
6. Mobile-AAA Authentication subtype . . . . . . . . . . . . . . 18 4. Mobile-Foreign Challenge Extension . . . . . . . . . . . . . . 14
7. Reserved SPIs for Mobile IP . . . . . . . . . . . . . . . . . 19 5. Generalized Mobile IP Authentication Extension . . . . . . . . 15
8. SPIs for RADIUS AAA Servers . . . . . . . . . . . . . . . . . 20 6. Mobile-AAA Authentication subtype . . . . . . . . . . . . . . 17
9. Configurable Parameters . . . . . . . . . . . . . . . . . . . 21 7. Reserved SPIs for Mobile IP . . . . . . . . . . . . . . . . . 18
10. Error Values . . . . . . . . . . . . . . . . . . . . . . . . 22 8. SPIs for RADIUS AAA Servers . . . . . . . . . . . . . . . . . 19
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . 23 9. Configurable Parameters . . . . . . . . . . . . . . . . . . . 20
12. Security Considerations . . . . . . . . . . . . . . . . . . 24 10. Error Values . . . . . . . . . . . . . . . . . . . . . . . . . 21
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 25 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
14. Normative References . . . . . . . . . . . . . . . . . . . . 25 12. Security Considerations . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 26 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24
A. Change History . . . . . . . . . . . . . . . . . . . . . . . . 27 14. Normative References . . . . . . . . . . . . . . . . . . . . . 24
B. Verification Infrastructure . . . . . . . . . . . . . . . . . 30 Appendix A. Change History . . . . . . . . . . . . . . . . . . . 25
C. Message Flow for FA Challenge Messaging with Mobile-AAA Appendix B. Verification Infrastructure . . . . . . . . . . . . . 26
Extension . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Appendix C. Message Flow for FA Challenge Messaging with
D. Message Flow for FA Challenge Messaging with MN-FA Mobile-AAA Extension . . . . . . . . . . . . . . . . 28
Authentication . . . . . . . . . . . . . . . . . . . . . . . . 34 Appendix D. Message Flow for FA Challenge Messaging with
E. Foreign Agent Algorithm for Tracking Used Challenges . . . . . 35 MN-FA Authentication . . . . . . . . . . . . . . . . 30
Intellectual Property and Copyright Statements . . . . . . . . 37 Appendix E. Example Pseudo-Code for Tracking Used Challenges . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32
Intellectual Property and Copyright Statements . . . . . . . . . . 33
1. Introduction 1. Introduction
Mobile IP defines the Mobile-Foreign Authentication extension to Mobile IP defines the Mobile-Foreign Authentication extension to
allow a mobile node to authenticate itself to a foreign agent. Such allow a mobile node to authenticate itself to a foreign agent. Such
authentication mechanisms are mostly external to the principal authentication mechanisms are mostly external to the principal
operation of Mobile IP, since the foreign agent can easily route operation of Mobile IP, since the foreign agent can easily route
packets to and from a mobile node whether or not the mobile node is packets to and from a mobile node whether or not the mobile node is
reporting a legitimately owned home address to the foreign agent. reporting a legitimately owned home address to the foreign agent.
Unfortunately, that extension does not provide the foreign agent any Unfortunately, that extension does not provide the foreign agent any
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Registration Request that allow a foreign agent to use challenge/ Registration Request that allow a foreign agent to use challenge/
response mechanism to authenticate the mobile node. Furthermore, an response mechanism to authenticate the mobile node. Furthermore, an
additional authentication extension, the Mobile-AAA authentication additional authentication extension, the Mobile-AAA authentication
extension, is provided so that a mobile node can supply credentials extension, is provided so that a mobile node can supply credentials
for authorization using commonly available AAA infrastructure for authorization using commonly available AAA infrastructure
elements. The foreign agent may be able to interact with an AAA elements. The foreign agent may be able to interact with an AAA
infrastructure (using protocols outside the scope of this document) infrastructure (using protocols outside the scope of this document)
to obtain a secure indication that the mobile node is authorized to to obtain a secure indication that the mobile node is authorized to
use the local network resources. use the local network resources.
1.1 Terminology 1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
This document uses the term Security Parameters Index (SPI) as This document uses the term Security Parameters Index (SPI) as
defined in the base Mobile IP protocol specification [RFC3344]. All defined in the base Mobile IP protocol specification [RFC3344]. All
SPI values defined in this document refer to values for the SPI as SPI values defined in this document refer to values for the SPI as
defined in that specification. defined in that specification.
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message. The challenge is selected by the foreign agent to provide message. The challenge is selected by the foreign agent to provide
local assurance that the mobile node is not replaying any earlier local assurance that the mobile node is not replaying any earlier
registration request. Eastlake, et al. [RFC1750] provides more registration request. Eastlake, et al. [RFC1750] provides more
information on generating pseudo-random numbers suitable for use as information on generating pseudo-random numbers suitable for use as
values for the challenge. values for the challenge.
Note that the storage of different Challenges received in Agent Note that the storage of different Challenges received in Agent
Advertisements from multiple foreign agents is implementation Advertisements from multiple foreign agents is implementation
specific and hence, out of scope for this specification. specific and hence, out of scope for this specification.
2.1 Handling of Solicited Agent Advertisements 2.1. Handling of Solicited Agent Advertisements
When a foreign agent generates an Agent Advertisement in response to When a foreign agent generates an Agent Advertisement in response to
a Router Solicitation [RFC1256], some additional considerations come a Router Solicitation [RFC1256], some additional considerations come
into play. According to the Mobile IP base specification [RFC3344], into play. According to the Mobile IP base specification [RFC3344],
the resulting Agent Advertisement may be either multicast or unicast. the resulting Agent Advertisement may be either multicast or unicast.
If the solicited Agent Advertisement is multicast, it MUST NOT If the solicited Agent Advertisement is multicast, it MUST NOT
generate a new Challenge value and update its window of remembered generate a new Challenge value and update its window of remembered
advertised Challenges. It must instead re-use the most recent of the advertised Challenges. It must instead re-use the most recent of the
CHALLENGE_WINDOW Advertisement Challenge values. CHALLENGE_WINDOW Advertisement Challenge values (Section 9).
If the agent advertisement is unicast back to the soliciting mobile If the agent advertisement is unicast back to the soliciting mobile
node, it MUST be handled as follows: If the challenge most recently node, it MUST be handled as follows: If the challenge most recently
unicast to the soliciting mobile node has not been previously used unicast to the soliciting mobile node has not been previously used
(as defined in Section 1.1), it SHOULD be repeated in the newly (as defined in Section 1.1), it SHOULD be repeated in the newly
issued unicast agent advertisement, otherwise a new challenge MUST be issued unicast agent advertisement, otherwise a new challenge MUST be
generated and remembered as the most recent challenge issued to the generated and remembered as the most recent challenge issued to the
mobile node. For further discussion of this, see Section 12. mobile node. For further discussion of this, see Section 12.
3. Operation 3. Operation
This section describes modifications to the Mobile IP registration This section describes modifications to the Mobile IP registration
process [RFC3344] which may occur after the foreign agent issues a process [RFC3344] which may occur after the foreign agent issues a
Mobile IP Agent Advertisement containing the Challenge on its local Mobile IP Agent Advertisement containing the Challenge on its local
link. See Appendix C for a diagram showing the canonical message link. See Appendix C for a diagram showing the canonical message
flow for messages related to the processing of the foreign agent flow for messages related to the processing of the foreign agent
challenge values. challenge values.
3.1 Mobile Node Processing for Registration Requests 3.1. Mobile Node Processing of Registration Requests
Retransmission behavior for Registration Requests is identical to Retransmission behavior for Registration Requests is identical to
that specified in Mobile IP specification [RFC3344]. A retransmitted that specified in Mobile IP specification [RFC3344]. A retransmitted
Registration Request MAY use the same Challenge value as given in the Registration Request MAY use the same Challenge value as given in the
original Registration Request. original Registration Request.
Whenever the Agent Advertisement contains the Challenge extension, if Whenever the Agent Advertisement contains the Challenge extension, if
the mobile node does not have a security association with the foreign the mobile node does not have a security association with the foreign
agent, then it MUST include the Challenge value in a Mobile-Foreign agent, then it MUST include the Challenge value in a Mobile-Foreign
Challenge extension to the Registration Request message. If, on the Challenge extension to the Registration Request message. If, on the
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chosen as CHAP_SPI (see Section 9), then the mobile node specifies chosen as CHAP_SPI (see Section 9), then the mobile node specifies
CHAP-style authentication [RFC1994] using MD5 [RFC1321]. CHAP-style authentication [RFC1994] using MD5 [RFC1321].
In either case, the Mobile-Foreign Challenge extension followed by In either case, the Mobile-Foreign Challenge extension followed by
one of the above specified authentication extensions MUST follow the one of the above specified authentication extensions MUST follow the
Mobile-Home Authentication extension, if present. Mobile-Home Authentication extension, if present.
A mobile node MAY include the Mobile-AAA Authentication extension in A mobile node MAY include the Mobile-AAA Authentication extension in
the Registration Request when the mobile node registers directly with the Registration Request when the mobile node registers directly with
its home agent (using a co-located care-of address). In this case, its home agent (using a co-located care-of address). In this case,
if the mobile node uses an SPI value of CHAP_SPI (Section 8) in the the mobile node uses an SPI value of CHAP_SPI (Section 8) in the MN-
MN-AAA Authentication extension, the mobile node MUST include the AAA Authentication extension and MUST NOT include the Mobile-Foreign
Mobile-Foreign Challenge extension prior to the Mobile-AAA Challenge extension. Also, replay protection for the Registration
Authentication extension. The mechanism used by the mobile node to Request in this case is provided by the Identification field defined
obtain the Challenge value in this case is outside the scope of this by [RFC3344].
document.
3.2 Foreign Agent Processing for Registration Requests 3.2. Foreign Agent Processing of Registration Requests
Upon receipt of the Registration Request, if the foreign agent has Upon receipt of the Registration Request, if the foreign agent has
issued a Challenge as part of its Agent Advertisements, and it does issued a Challenge as part of its Agent Advertisements, and if it
not have a security association with the mobile node, then the does not have a security association with the mobile node, then the
foreign agent SHOULD check that the Mobile-Foreign Challenge foreign agent SHOULD check that the Mobile-Foreign Challenge
extension exists, and that it contains a challenge value previously extension exists, and that it contains a challenge value previously
unused by the mobile node. This ensures that the mobile node is not unused by the mobile node. This ensures that the mobile node is not
attempting to replay a previous advertisement and authentication. In attempting to replay a previous advertisement and authentication. In
this case, if the Registration Request does not include a challenge this case, if the Registration Request does not include a Challenge
extension, the foreign agent MUST send a Registration Reply with the extension, the foreign agent MUST send a Registration Reply with the
Code field set to set to MISSING_CHALLENGE. In this document, Code field set to set to MISSING_CHALLENGE.
whenever the foreign agent is required to reject a Registration
Request, it MUST put the given code in the usual Code field of the
Registration Reply, unless the Registration Reply has already been
received from the home agent. In this case the foreign agent MUST
preserve the value of the Code field set by the home agent and MUST
put its own rejection code only in the Status field of the FA Error
extension (defined in [FAERR]).
If a mobile node retransmits a Registration Request with the same If a mobile node retransmits a Registration Request with the same
Challenge extension, and the foreign agent still has a pending Challenge extension, and the foreign agent still has a pending
Registration Request record in effect for the mobile node, then the Registration Request record in effect for the mobile node, then the
foreign agent forwards the Registration Request to the Home Agent foreign agent forwards the Registration Request to the Home Agent
again. The foreign agent SHOULD check that the mobile node is again. The foreign agent SHOULD check that the mobile node is
actually performing a retransmission, by verifying that the relevant actually performing a retransmission, by verifying that the relevant
fields of the retransmitted request (including, if present, the fields of the retransmitted request (including, if present, the
mobile node NAI Extension [RFC2794]) are the same as represented in mobile node NAI Extension [RFC2794]) are the same as represented in
the visitor list entry for the pending Registration Request (section the visitor list entry for the pending Registration Request (section
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Request unless it was offered in the last Registration Reply or Request unless it was offered in the last Registration Reply or
unicast Agent Advertisement sent to the mobile node, or else unicast Agent Advertisement sent to the mobile node, or else
advertised as one of the last CHALLENGE_WINDOW (see Section 9) advertised as one of the last CHALLENGE_WINDOW (see Section 9)
Challenge values inserted into the immediately preceding Agent Challenge values inserted into the immediately preceding Agent
advertisements. If the Challenge is not one of the recently advertisements. If the Challenge is not one of the recently
advertised values, the foreign Agent SHOULD send a Registration Reply advertised values, the foreign Agent SHOULD send a Registration Reply
with Code value UNKNOWN_CHALLENGE (see Section 10). The foreign with Code value UNKNOWN_CHALLENGE (see Section 10). The foreign
agent MUST maintain the last challenge used by each mobile node that agent MUST maintain the last challenge used by each mobile node that
has registered using any one of the last CHALLENGE_WINDOW challenge has registered using any one of the last CHALLENGE_WINDOW challenge
values. This last challenge value can be stored as part of the values. This last challenge value can be stored as part of the
mobile node's registration records. Also, see Appendix E for a mobile node's registration records. Also, see Section 3.2.1 for a
possible algorithm that can be used to satisfy this requirement. possible algorithm that can be used to satisfy this requirement.
Furthermore, the foreign agent MUST check that there is either a Furthermore, the foreign agent MUST check that there is either a
Mobile-Foreign, or a Mobile-AAA Authentication extension after the Mobile-Foreign, or a Mobile-AAA Authentication extension after the
Challenge extension. Any registration message containing the Challenge extension. Any registration message containing the
Challenge extension without either of these authentication extensions Challenge extension without either of these authentication extensions
MUST be silently discarded. If the registration message contains a MUST be silently discarded. If the registration message contains a
Mobile-Foreign Authentication extension with an incorrect Mobile-Foreign Authentication extension with an incorrect
authenticator that fails verification, the foreign agent MAY send a authenticator that fails verification, the foreign agent MAY send a
Registration Reply to the mobile node with Code value Registration Reply to the mobile node with Code value
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in the message, or if an NAI extension is included indicating that in the message, or if an NAI extension is included indicating that
the mobile node belongs to a different administrative domain, the the mobile node belongs to a different administrative domain, the
foreign agent may take actions outside the scope of this protocol foreign agent may take actions outside the scope of this protocol
specification to carry out the authentication of the mobile node. If specification to carry out the authentication of the mobile node. If
the registration message contains a Mobile-AAA Authentication the registration message contains a Mobile-AAA Authentication
extension with an incorrect authenticator that fails verification, extension with an incorrect authenticator that fails verification,
the foreign agent MAY send a Registration Reply to the mobile node the foreign agent MAY send a Registration Reply to the mobile node
with Code value FA_BAD_AAA_AUTH. If the Mobile-AAA Authentication with Code value FA_BAD_AAA_AUTH. If the Mobile-AAA Authentication
Extension is present in the Registration Request, the foreign agent Extension is present in the Registration Request, the foreign agent
MUST NOT remove the Mobile-AAA Authentication Extension and the MUST NOT remove the Mobile-AAA Authentication Extension and the
Mobile-Foreign Challenge Extension from the Registration Request. Mobile-Foreign Challenge extension from the Registration Request,
Appendix C provides an example of an action that could be taken by a before forwarding to the home agent. Appendix C provides an example
foreign agent. of an action that could be taken by a foreign agent.
In the event that the Challenge extension is authenticated through In the event that the Challenge extension is authenticated through
the Mobile-Foreign Authentication extension and the Mobile-AAA the Mobile-Foreign Authentication extension and the Mobile-AAA
Authentication extension is not present, the foreign agent MAY remove Authentication extension is not present, the foreign agent MAY remove
the Challenge Extension from the Registration Request without the Challenge extension from the Registration Request without
disturbing the authentication value computed by the mobile node for disturbing the authentication value used for the computation. If the
use by the AAA or the home agent. If the Mobile-AAA Authentication Mobile-AAA Authentication extension is present and a security
extension is present and a security association exists between the association exists between the foreign agent and the home agent, the
foreign agent and the home agent, the Mobile-Foreign Challenge Mobile-Foreign Challenge extension and the Mobile-AAA Authentication
extension and the Mobile-AAA Authentication extension MUST precede extension MUST precede the Foreign-Home Authentication extension.
the Foreign-Home Authentication extension.
If the foreign agent does not remove the Challenge extension, then
the foreign agent SHOULD store the Challenge value as part of the
pending registration request list [RFC3344]. Also, if the
Registration Reply coming from the home agent does not include the
Challenge Extension, the foreign agent SHOULD NOT reject the
Registration Request message. If the Challenge Extension is present
in the Registration Reply, it MUST be the same Challenge value that
was included in the Registration Request. If the Challenge value
differs in the Registration Reply received from the home agent, the
foreign agent MUST insert an FA Error extension with Status value
HA_WRONG_CHALLENGE in the Registration Reply sent to the mobile node
(see Section 10).
If the foreign agent does remove the Challenge extension and If the foreign agent does remove the Challenge extension and
applicable authentication from the Registration Request message, then applicable authentication from the Registration Request message, then
it SHOULD insert the Identification field from the Registration it SHOULD store the Identification field from the Registration
Request message along with its record-keeping information about the Request message as part of its record-keeping information about the
particular mobile node in order to protect against replays. particular mobile node in order to protect against replays.
3.3 Foreign Agent Processing for Registration Replies 3.2.1. Foreign Agent Algorithm for Tracking Used Challenges
If the foreign agent maintains a large CHALLENGE_WINDOW, it becomes
more important for scalability purposes to efficiently compare
incoming challenges against the set of Challenge values which have
been advertised recently. This can be done by keeping the Challenge
values in order of advertisement, and by making use of the mandated
behavior that mobile nodes MUST NOT use Challenge values which were
advertised before the last advertised Challenge value that the mobile
node has attempted to use. The pseudo-code in Appendix E
accomplishes this objective. The maximum amount of total storage
required by this algorithm is equal to Size*(CHALLENGE_WINDOW +
(2*N)), where N is the current number of mobile nodes for which the
foreign agent is storing challenge values. Note that, whenever the
stored challenge value is no longer in the CHALLENGE_WINDOW, it can
be deleted from the foreign agent's records, perhaps along with all
other registration information for the mobile node if it is no longer
registered.
It is presumed that the foreign agent keeps an array of advertised
Challenges, a record of the last advertised challenge used by a
mobile node, and also a record of the last challenge provided to a
mobile node in a Registration Reply or unicast Agent Advertisement.
To meet the security obligations outlined in Section 12, the foreign
agent SHOULD use one of the already stored, previously unused
challenges when responding to an unauthenticated Registration Request
or Agent Solicitation. If none of the already stored challenges are
previously unused, the foreign agent SHOULD generate a new challenge,
include it in the response, and store it in the per-Mobile data
structure.
3.3. Foreign Agent Processing of Registration Replies
The foreign agent SHOULD include a new Mobile-Foreign Challenge The foreign agent SHOULD include a new Mobile-Foreign Challenge
Extension in any Registration Reply, successful or not. If the Extension in any Registration Reply, successful or not. If the
foreign agent includes this extension in a successful Registration foreign agent includes this extension in a successful Registration
Reply, the extension SHOULD precede a Mobile-Foreign authentication Reply, the extension SHOULD precede a Mobile-Foreign authentication
extension if present. Suppose the Registration Reply includes a extension if present. Suppose the Registration Reply includes a
Challenge extension from the home agent, and the foreign agent wishes Challenge extension from the home agent, and the foreign agent wishes
to include another Challenge extension with the Registration Reply to include another Challenge extension with the Registration Reply
for use by the mobile node. In that case, the foreign agent MUST for use by the mobile node. In that case, the foreign agent MUST
delete the Challenge extension from the home agent from the delete the Challenge extension from the home agent from the
Registration Reply, along with any Foreign-Home authentication Registration Reply, along with any Foreign-Home authentication
extension, before appending the new Challenge extension to the extension, before appending the new Challenge extension to the
Registration Reply. Registration Reply.
One example of a situation where the foreign agent MAY omit the One example of a situation where the foreign agent MAY omit the
inclusion of a Mobile-Foreign Challenge Extension in the Registration inclusion of a Mobile-Foreign Challenge extension in the Registration
Reply would be when a new challenge has been multicast recently. Reply would be when a new challenge has been multicast recently.
If a foreign agent has conditions in which it omits the inclusion of If a foreign agent has conditions in which it omits the inclusion of
a Mobile-Foreign Challenge Extension in the Registration Reply, it a Mobile-Foreign Challenge extension in the Registration Reply, it
still MUST respond with an agent advertisement containing a still MUST respond with an agent advertisement containing a
previously unused challenge in response to a subsequent agent previously unused challenge in response to a subsequent agent
solicitation from the same mobile node. Otherwise (when the said solicitation from the same mobile node. Otherwise (when the said
conditions are not met) the foreign agent MUST include a previously conditions are not met) the foreign agent MUST include a previously
unused challenge in any Registration Reply, successful or not. unused challenge in any Registration Reply, successful or not.
If the foreign agent does not remove the Challenge extension from the
Registration Request received from the mobile node then the foreign
agent SHOULD store the Challenge value as part of the pending
registration request list [RFC3344]. Also, if the Registration Reply
coming from the home agent does not include the Challenge extension,
the foreign agent SHOULD NOT reject the Registration Request message.
If the Challenge Extension is present in the Registration Reply, it
MUST be the same Challenge value that was included in the
Registration Request. If the Challenge value differs in the
Registration Reply received from the home agent, the foreign agent
MUST insert an FA Error extension with Status value
HA_WRONG_CHALLENGE in the Registration Reply sent to the mobile node
(see Section 10).
A mobile node MUST be prepared to use a challenge from a unicast or A mobile node MUST be prepared to use a challenge from a unicast or
multicast Agent Advertisement in lieu of one returned in a multicast Agent Advertisement in lieu of one returned in a
Registration Reply, and MUST solicit for one if it has not already Registration Reply, and MUST solicit for one if it has not already
received one in a Registration Reply. received one in a Registration Reply.
If the foreign agent receives a Registration Reply with the Code If the foreign agent receives a Registration Reply with the Code
value HA_BAD_AAA_AUTH, it MUST be relayed to the mobile node. value HA_BAD_AAA_AUTH, the Registration Reply with this Code value
MUST be relayed to the mobile node. In this document, whenever the
foreign agent is required to reject a Registration Request, it MUST
put the given code in the usual Code field of the Registration Reply,
unless the Registration Reply has already been received from the home
agent. In this case the foreign agent MUST preserve the value of the
Code field set by the home agent and MUST put its own rejection code
in the Status field of the FA Error extension (defined in [FAERR]).
3.4 Home Agent Processing for the Challenge Extensions 3.4. Home Agent Processing of Challenge Extensions
If the home agent receives a Registration Request with the Mobile- If the home agent receives a Registration Request with the Mobile-
Foreign Challenge extension, and recognizes the extension, the home Foreign Challenge extension, and recognizes the extension, the home
agent MUST include the Challenge extension in the Registration Reply. agent MUST include the Challenge extension in the Registration Reply.
The Challenge Extension MUST be placed after the Mobile-Home The Challenge extension MUST be placed after the Mobile-Home
authentication extension, and the extension SHOULD be authenticated authentication extension, and the extension SHOULD be authenticated
by a Foreign-Home Authentication extension. by a Foreign-Home Authentication extension.
The home agent MAY receive a Registration Request with the Mobile-AAA The home agent may receive a Registration Request with the Mobile-AAA
Authentication extension. If the Mobile-AAA Authentication extension Authentication extension. If the Mobile-AAA Authentication extension
is used by the home agent as an authorization-enabling extension and is used by the home agent as an authorization-enabling extension and
the verification fails due to incorrect authenticator, the home agent the verification fails due to incorrect authenticator, the home agent
MAY reject the Registration Reply with the error code MAY reject the Registration Reply with the error code
HA_BAD_AAA_AUTH. HA_BAD_AAA_AUTH.
Since the extension type for the Challenge extension is within the Since the extension type for the Challenge extension is within the
range 128-255, the home agent MUST process such a Registration range 128-255, the home agent MUST process such a Registration
Request even if it does not recognize the Challenge extension Request even if it does not recognize the Challenge extension
[RFC3344]. In this case, the home agent will send a Registration [RFC3344]. In this case, the home agent will send a Registration
Reply to the foreign agent that does not include the Challenge Reply to the foreign agent that does not include the Challenge
extension. extension.
3.5 Mobile Node Processing for Registration Replies 3.5. Mobile Node Processing of Registration Replies
A mobile node might receive the following error codes in the
Registration Reply from the foreign agent as a response to the
Registration Request. The error codes are defined in Section 10.
UNKNOWN_CHALLENGE: This error code is received by the mobile node in
the case where the mobile node has moved to a new foreign agent that
cannot validate the challenge provided in the Registration Request.
In such instances, the mobile node MUST use a new Challenge value in
any new registration, obtained either from an Agent Advertisement, or
from a Challenge extension to the Registration Reply containing the
error.
MISSING_CHALLENGE: A mobile node that does not include a Challenge
when the Mobile-Foreign Authentication extension is present may
receive a MISSING_CHALLENGE error. In this case, the mobile node
SHOULD send a Challenge extension containing an unused challenge in
the next Registration Request.
BAD_AUTHENTICATION: This error is sent by the foreign agent if the
Registration Request contains a Mobile-Foreign Authentication
extension with an incorrect authenticator that fails verification. A
mobile node that receives a BAD_AUTHENTICATION Code value SHOULD
include the Mobile-AAA Authentication Extension in the next
Registration Request. This will make it possible for the Foreign
Agent to use its AAA infrastructure in order to authenticate the
mobile node. In this case, the mobile node MUST use a new Challenge
value in any new registration, obtained either from an Agent
Advertisement, or from a Challenge extension to the Registration
Reply containing the error.
FA_BAD_AAA_AUTH: This error is sent by the foreign agent if the
Registration Request contains a Mobile-AAA Authentication extension
with an incorrect authenticator that fails verification. A mobile
node that receives a FA_BAD_AAA_AUTH MUST use a new Challenge value
in any new registration, obtained either from an Agent Advertisement,
or from a Challenge extension to the Registration Reply containing
the error.
HA_BAD_AAA_AUTH: This error is sent by the home agent if the A mobile node might receive the error code in the Registration Reply
Registration Request contains a Mobile-AAA Authentication extension from the foreign agent as a response to the Registration Request.
with an incorrect authenticator that fails verification. A mobile The error codes are defined in Section 10.
node that receives a HA_BAD_AAA_AUTH MUST use a new Challenge value
in any new registration, obtained either from an Agent Advertisement,
or from a Challenge extension to the Registration Reply containing
the error.
STALE_CHALLENGE: If the foreign agent receives a Registration Request In any case, if the mobile node attempts to register again after such
with a Challenge extension containing a Challenge value previously an error, it MUST use a new Challenge value in such a registration,
used by that mobile node, the mobile node MAY receive a Registration obtained either from an Agent Advertisement, or from a Challenge
Reply to the mobile node containing the Code value STALE_CHALLENGE. extension to the Registration Reply containing the error.
In such instances, the mobile node MUST use a new Challenge value in
next Registration Request, obtained either from an Agent
Advertisement, or from a Challenge extension to the Registration
Reply containing the error.
HA_WRONG_CHALLENGE: This error is sent by the foreign agent if the In the co-located care-of address mode, the mobile node receives a
Registration Reply from the home agent contains a different Challenge Registration Reply without the Challenge extension and processes the
value from the one included in the Registration Request. Registration Reply as specified in [RFC3344]. In this case, the
Challenge value 0 is recommended for the authenticator computation
mentioned in Section 8.
4. Mobile-Foreign Challenge Extension 4. Mobile-Foreign Challenge Extension
This section specifies a new Mobile IP Registration extension that is This section specifies a new Mobile IP Registration extension that is
used to satisfy a Challenge in an Agent Advertisement. The Challenge used to satisfy a Challenge in an Agent Advertisement. The Challenge
extension to the Registration Request message is used to indicate the extension to the Registration Request message is used to indicate the
challenge that the mobile node is attempting to satisfy. challenge that the mobile node is attempting to satisfy.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
skipping to change at page 15, line 31 skipping to change at page 14, line 31
132 (skippable) (see [RFC3344]) 132 (skippable) (see [RFC3344])
Length: Length:
Length of the Challenge value Length of the Challenge value
Challenge: Challenge:
The Challenge field is copied from the Challenge field found in The Challenge field is copied from the Challenge field found in
the Agent Advertisement Challenge extension (see section 2). the received Challenge extension.
Suppose the mobile node has successfully registered using one of the Suppose the mobile node has successfully registered using one of the
Challenge Values within the CHALLENGE_WINDOW values advertised by the Challenge Values within the CHALLENGE_WINDOW values advertised by the
foreign agent. In that case, in any new Registration Request the foreign agent. In that case, in any new Registration Request the
mobile node MUST NOT use any Challenge Value which was advertised by mobile node MUST NOT use any Challenge Value which was advertised by
the foreign agent before the Challenge Value in the mobile node's the foreign agent before the Challenge Value in the mobile node's
last Registration Request. last Registration Request.
5. Generalized Mobile IP Authentication Extension 5. Generalized Mobile IP Authentication Extension
Several new authentication extensions have been designed for various Several new authentication extensions have been designed for various
control messages proposed for extensions to Mobile IP. A new control messages proposed for extensions to Mobile IP. A new
authentication extension is required for a mobile node to present its authentication extension is required for a mobile node to present its
credentials to any other entity other than the ones already defined; credentials to any other entity other than the ones already defined;
the only entities defined in the base Mobile IP specification the only entities defined in the base Mobile IP specification
[RFC3344] are the home agent and the foreign agent. It is the [RFC3344] are the home agent and the foreign agent. The purpose of
purpose of the generalized authentication extension defined here to the generalized authentication extension defined here is to collect
collect together data for all such new authentication applications together data for all such new authentication applications into a
into a single extension type with subtypes. single extension type with subtypes.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Subtype | Length | | Type | Subtype | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPI | | SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authenticator ... | Authenticator ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 18, line 12 skipping to change at page 17, line 12
1 Mobile-AAA Authentication subtype (see Section 6) 1 Mobile-AAA Authentication subtype (see Section 6)
6. Mobile-AAA Authentication subtype 6. Mobile-AAA Authentication subtype
The Generalized Authentication extension with subtype 1 will be The Generalized Authentication extension with subtype 1 will be
referred to as a Mobile-AAA Authentication extension. The mobile referred to as a Mobile-AAA Authentication extension. The mobile
node MAY include a Mobile-AAA Authentication extension in any node MAY include a Mobile-AAA Authentication extension in any
Registration Request. This extension MAY co-exist in the same Registration Request. This extension MAY co-exist in the same
Registration Request with Authentication extensions defined for Registration Request with Authentication extensions defined for
Mobile IP Registration by [RFC3344]. If the mobile node does not Mobile IP Registration ([RFC3344]). If the mobile node does not
include a Mobile-Foreign Authentication [RFC3344] extension, then it include a Mobile-Foreign Authentication extension, then it MUST
MUST include the Mobile-AAA Authentication extension whenever the include the Mobile-AAA Authentication extension whenever the
Challenge extension is present. If both are present, the Mobile-AAA Challenge extension is present. If both are present, the Mobile-AAA
Authentication extension MUST precede the Mobile-Foreign Authentication extension MUST precede the Mobile-Foreign
Authentication extension. Authentication extension.
If the Mobile-AAA Authentication extension is present, then the If the Mobile-AAA Authentication extension is present, the Mobile-
Registration Message sent by the mobile node MUST contain the Mobile-
Home Authentication extension [RFC3344] if it shares a security
association with the home agent. If both are present, the Mobile-
Home Authentication Extension MUST appear prior to the Mobile-AAA Home Authentication Extension MUST appear prior to the Mobile-AAA
Authentication extension. The corresponding response MUST include Authentication extension. The corresponding response MUST include
the Mobile-Home Authentication Extension, and MUST NOT include the the Mobile-Home Authentication Extension, and MUST NOT include the
Mobile-AAA Authentication Extension. Mobile-AAA Authentication Extension.
The default algorithm for computation of the authenticator is HMAC- The default algorithm for computation of the authenticator is HMAC-
MD5 [RFC2104] computed on the following data, in the order shown: MD5 [RFC2104] computed on the following data, in the order shown:
Preceding Mobile IP data || Type, Subtype, Length, SPI Preceding Mobile IP data || Type, Subtype, Length, SPI
where the Type, Length, Subtype, and SPI are as shown in Section 5. where the Type, Length, Subtype, and SPI are as shown in Section 5.
The resulting function call, as described in [RFC2104], would be: The Preceding Mobile IP data refers to the UDP payload (the
Registration Request or Registration Reply data) and all prior
Extensions in their entirely. The resulting function call, as
described in [RFC2104], would be:
hmac_md5(data, datalen, Key, KeyLength, authenticator); hmac_md5(data, datalen, Key, KeyLength, authenticator);
Each mobile node MUST support the ability to produce the Each mobile node MUST support the ability to produce the
authenticator by using HMAC-MD5 as shown. Just as with Mobile IP, it authenticator by using HMAC-MD5 as shown. Just as with Mobile IP, it
must be possible to configure the use of any arbitrary 32-bit SPI must be possible to configure the use of any arbitrary 32-bit SPI
outside of the SPIs in the reserved range 0-255 for selection of this outside of the SPIs in the reserved range 0-255 for selection of this
default algorithm. default algorithm.
7. Reserved SPIs for Mobile IP 7. Reserved SPIs for Mobile IP
skipping to change at page 20, line 32 skipping to change at page 19, line 32
MD5(Preceding Mobile IP data || MD5(Preceding Mobile IP data ||
Type, Subtype (if present), Length, SPI) || Type, Subtype (if present), Length, SPI) ||
Least-order 237 bytes from Challenge Least-order 237 bytes from Challenge
where the Type, Length, SPI, and possibly Subtype, are the fields of where the Type, Length, SPI, and possibly Subtype, are the fields of
the authentication extension in use. For instance, all four of these the authentication extension in use. For instance, all four of these
fields would be in use when SPI == CHAP_SPI is used with the fields would be in use when SPI == CHAP_SPI is used with the
Generalized Authentication extension. Since the RADIUS protocol Generalized Authentication extension. Also, in case of co-located
cannot carry attributes of length greater than 253, the preceding care-of address, the Challenge value 0 is used (refer Section
Mobile IP data, type, subtype (if present), length and SPI are hashed Section 3.5). Since the RADIUS protocol cannot carry attributes of
using MD5. Finally, the least significant 237 bytes of the challenge length greater than 253, the preceding Mobile IP data, type, subtype
are concatenated. If the challenge has fewer than 238 bytes, this (if present), length and SPI are hashed using MD5. Finally, the
algorithm includes the high-order byte in the computation twice, but least significant 237 bytes of the challenge are concatenated. If
ensures that the challenge is used exactly as is. Additional padding the challenge has fewer than 238 bytes, this algorithm includes the
is never used to increase the length of the challenge; the input data high-order byte in the computation twice, but ensures that the
is allowed to be shorter than 237 bytes long. challenge is used exactly as is. Additional padding is never used to
increase the length of the challenge; the input data is allowed to be
shorter than 237 bytes long.
9. Configurable Parameters 9. Configurable Parameters
Every Mobile IP agent supporting the extensions defined in this Every Mobile IP agent supporting the extensions defined in this
document SHOULD be able to configure each parameter in the following document SHOULD be able to configure each parameter in the following
table. Each table entry contains the name of the parameter, the table. Each table entry contains the name of the parameter, the
default value, and the section of the document in which the parameter default value, and the section of the document in which the parameter
first appears. first appears.
+------------------+---------------+---------------------+ +------------------+---------------+---------------------+
skipping to change at page 22, line 9 skipping to change at page 21, line 9
Table 1: Configurable Parameters Table 1: Configurable Parameters
Note that CHALLENGE_WINDOW SHOULD be at least 2. This makes it far Note that CHALLENGE_WINDOW SHOULD be at least 2. This makes it far
less likely that mobile nodes will register using a Challenge value less likely that mobile nodes will register using a Challenge value
that is outside the set of values allowable by the foreign agent. that is outside the set of values allowable by the foreign agent.
10. Error Values 10. Error Values
Each entry in the following table contains the name of the Code Each entry in the following table contains the name of the Code
[RFC3344] to be returned in a Registration Reply, the value for the [RFC3344] to be returned in a Registration Reply, the value for the
Code, and the section in which the error is first mentioned in this Code, and the section in which the error is mentioned in this
specification. specification.
+--------------------+-------+--------------------------+ +--------------------+-------+--------------------------+
| Error Name | Value | Section of Document | | Error Name | Value | Section of Document |
+--------------------+-------+--------------------------+ +--------------------+-------+--------------------------+
| UNKNOWN_CHALLENGE | 104 | 3.2 | | UNKNOWN_CHALLENGE | 104 | 3.2 |
| | | | | | | |
| BAD_AUTHENTICATION | 67 | 3.2 - also see [RFC3344] | | BAD_AUTHENTICATION | 67 | 3.2 - also see [RFC3344] |
| | | | | | | |
| MISSING_CHALLENGE | 105 | 3.1, 3.2 | | MISSING_CHALLENGE | 105 | 3.1, 3.2 |
skipping to change at page 23, line 7 skipping to change at page 22, line 7
| | | | | | | |
| HA_BAD_AAA_AUTH | TBD | 3.4 | | HA_BAD_AAA_AUTH | TBD | 3.4 |
| | | | | | | |
| HA_WRONG_CHALLENGE | TBD | 3.2 | | HA_WRONG_CHALLENGE | TBD | 3.2 |
+--------------------+-------+--------------------------+ +--------------------+-------+--------------------------+
Table 2: Error Values Table 2: Error Values
11. IANA Considerations 11. IANA Considerations
All protocol values in this specification are to be the same as The following are currently assigned by IANA for RFC 3012 ([RFC3012])
defined in RFC 3012 [RFC3012]. Additionaly, new error codes which are applicable to this document. IANA should record these
FA_BAD_AAA_AUTH, HA_BAD_AAA_AUTH, and HA_WRONG_CHALLENGE are defined values as part of this document.
by this document. Among these, HA_WRONG_CHALLENGE may appear in the
Status code of the FA Error extension defined in [FAERR]. The Generalized Mobile IP Authentication extension defined in
Section Section 5 is a Mobile IP registration extension. IANA has
assigned a value of 36 for this extension.
A new number space is to be created for enumerating subtypes of
the Generalized Authentication extension (see section Section 5).
New subtypes of the Generalized Authentication extension, other
than the number (1) for the MN-AAA authentication extension
specified in section Section 6, must be specified and approved by
a designated expert.
The MN-FA Challenge extension defined in Section Section 4 is a
router advertisement extension as defined in RFC 1256 [[RFC1256]]
and extended in RFC 3344 [[RFC3344]]. IANA should assign a value
of 132 for this purpose.
The Code values defined in section Section 10 are error codes as
defined in RFC 3344 ([RFC3344]). They correspond to error values
conventionally associated with rejection by the foreign agent
(i.e., values from the range 64-127). The Code value 67 is a pre-
existing value which is to be used in some cases with the
extension defined in this specification. IANA should record the
values as defined in section Section 10.
A new section for enumerating algorithms identified by specific
SPIs within the range 0-255 is added by IANA. The CHAP_SPI number
(2) discussed in section Section 8 is assigned from this range of
reserved SPI numbers. New assignments from this reserved range
must be specified and approved by the Mobile IP working group.
SPI number 1 should not be assigned unless in the future the
Mobile IP working group decides that SKIP is not important for
enumeration in the list of reserved numbers. SPI number 0 should
not be assigned.
Additionally, new error codes FA_BAD_AAA_AUTH, HA_BAD_AAA_AUTH, and
HA_WRONG_CHALLENGE are defined by this document. Among these,
HA_WRONG_CHALLENGE may appear in the Status code of the FA Error
extension defined in [FAERR].
12. Security Considerations 12. Security Considerations
In the event that a malicious mobile node attempts to replay the In the event that a malicious mobile node attempts to replay the
authenticator for an old Mobile-Foreign Challenge, the foreign agent authenticator for an old Mobile-Foreign Challenge, the foreign agent
would detect it since the agent always checks whether it has recently would detect it since the agent always checks whether it has recently
advertised the Challenge (see Section 3.2). Allowing mobile nodes advertised the Challenge (see Section 3.2). Allowing mobile nodes
with different IP addresses or NAIs to use the same Challenge value with different IP addresses or NAIs to use the same Challenge value
does not represent a security vulnerability, because the does not represent a security vulnerability, because the
authentication data provided by the mobile node will be computed over authentication data provided by the mobile node will be computed over
data that is different (at least by the bytes of the mobile nodes' IP data that is different (at least the mobile nodes' IP address will
addresses). vary).
If the foreign agent chooses a Challenge value (see Section 2) with If the foreign agent chooses a Challenge value (see Section 2) with
fewer than 4 bytes, the foreign agent SHOULD include the value of the fewer than 4 bytes, the foreign agent SHOULD include the value of the
Identification field in the records it maintains for the mobile node. Identification field in the records it maintains for the mobile node.
The foreign agent can then determine whether the Registration The foreign agent can then determine whether the Registration
messages using the short Challenge value are in fact unique, and thus messages using the short Challenge value are in fact unique, and thus
assuredly not replayed from any earlier registration. assuredly not replayed from any earlier registration.
Section 8 (SPI For RADIUS AAA Servers) defines a method of computing Section 8 (SPI For RADIUS AAA Servers) defines a method of computing
the Generalized Mobile IP Authentication Extension's authenticator the Generalized Mobile IP Authentication Extension's authenticator
field using MD5 in a manner that is consistent with RADIUS [RFC2138]. field using MD5 in a manner that is consistent with RADIUS [RFC2138].
The use of MD5 in the method described in Section 8 is less secure The use of MD5 in the method described in Section 8 is less secure
than HMAC-MD5 [RFC2104], and should be avoided whenever possible. than HMAC-MD5 [RFC2104], and MUST be avoided whenever possible.
Note that an active attacker may try to prevent successful Note that an active attacker may try to prevent successful
registrations by sending a large number of Agent Solicitations or registrations by sending a large number of Agent Solicitations or
bogus Registration Requests, each of which could cause the foreign bogus Registration Requests, each of which could cause the foreign
agent to respond with a fresh challenge, invalidating the challenge agent to respond with a fresh challenge, invalidating the challenge
that the MN is currently trying to use. To prevent such attacks, the that the MN is currently trying to use. To prevent such attacks, the
foreign agent MUST NOT invalidate previously unused challenges when foreign agent MUST NOT invalidate previously unused challenges when
responding to unauthenticated Registration Requests or Agent responding to unauthenticated Registration Requests or Agent
Solicitations. In addition, the foreign agent MUST NOT allocate new Solicitations. In addition, the foreign agent MUST NOT allocate new
storage when responding to such messages, because this would also storage when responding to such messages, because this would also
create the possibility of denial of service. create the possibility of denial of service.
The Challenge extension specified in this document need not be used
for co-located care-of address mode. In this case, replay protection
is provided by the Identification field in the Registration Request
message [RFC3344].
13. Acknowledgments 13. Acknowledgments
The authors would like to thank Tom Hiller, Mark Munson, the TIA The authors would like to thank Pete McCann, Ahmad Muhanna, Henrik
TR45-6 WG, Gabriel Montenegro, Vipul Gupta, Pete McCann, Robert Levkowetz, Kent Leung, Alpesh Patel, Madjid Nakhjiri, Gabriel
Marks, Ahmad Muhanna, and Luca Salgarelli for their useful Montenegro, Jari Arkko and other MIP4 WG participants for their
discussions. A recent draft by Mohamed Khalil, Raja Narayanan, Emad useful discussions.
Qaddoura, and Haseeb Akhtar has also suggested the definition of a
generalized authentication extension similar to the specification
contained in Section 5.
14. Normative References 14. Normative References
[FAERR] Perkins, C., "Foreign Agent Error Extension for Mobile [FAERR] Perkins, C., "Foreign Agent Error Extension for Mobile
IPv4", draft-perkins-mip4-faerr-00.txt (work in progress), IPv4", draft-perkins-mip4-faerr-02.txt (work in progress),
January 2004. January 2004.
[RFC1256] Deering, S., "ICMP Router Discovery Messages", RFC 1256, [RFC1256] Deering, S., "ICMP Router Discovery Messages", RFC 1256,
September 1991. September 1991.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992. April 1992.
[RFC1750] Eastlake, D., Crocker, S., and J. Schiller, "Randomness [RFC1750] Eastlake, D., Crocker, S., and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994. Recommendations for Security", RFC 1750, December 1994.
skipping to change at page 26, line 5 skipping to change at page 25, line 5
[RFC2794] Calhoun, P. and C. Perkins, "Mobile IP Network Access [RFC2794] Calhoun, P. and C. Perkins, "Mobile IP Network Access
Identifier Extension for IPv4", RFC 2794, March 2000. Identifier Extension for IPv4", RFC 2794, March 2000.
[RFC3012] Perkins, C. and P. Calhoun, "Mobile IPv4 Challenge/ [RFC3012] Perkins, C. and P. Calhoun, "Mobile IPv4 Challenge/
Response Extensions", RFC 3012, November 2000. Response Extensions", RFC 3012, November 2000.
[RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344, [RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
August 2002. August 2002.
Authors' Addresses
Charles E. Perkins
Nokia Research Center
Communications Systems Lab
313 Fairchild Drive
Mountain View, California 94043
Fax: +1 650 625-2502
Email: charles.perkins@nokia.com
Pat R. Calhoun
Black Storm Networks
110 Nortech Parkway
San Jose, CA 95134
Fax: +1 720-293-7501
Email: pcalhoun@diameter.org
Jayshree Bharatia
Nortel Networks
2221, Lakeside Blvd
Richardson, TX 75082
Fax: +1 972-684-3775
Email: jayshree@nortelnetworks.com
Appendix A. Change History Appendix A. Change History
List of the changes for draft-ietf-mobileip-rfc3012bis-03: The following is the list of changes from RFC 3012 ([RFC3012]):
o Foreign agent recommended to include a Challenge in every o Foreign agent recommended to include a Challenge in every
Registration Reply, so that mobile node can re-register without Registration Reply, so that mobile node can re-register without
waiting for an Advertisement. waiting for an Advertisement.
o Foreign agent MUST record applicable challenge values used by each o Foreign agent MUST record applicable challenge values used by each
mobile node. mobile node.
o Mobile node forbidden to use Challenge values which were o Mobile node forbidden to use Challenge values which were
advertised previous to the last Challenge value which it had used advertised previous to the last Challenge value which it had used
for a registration. for a registration.
o Terminology for stale challenge vs. unused challenge clarified. o Challenge definitions are cleaned up.
o Terminology for "valid" challenge deleted in favor of "unused
challenge".
o Programming suggestion added as an appendix. o Programming suggestion added as an appendix.
List of the changes for draft-ietf-mobileip-rfc3012bis-04:
o The definition of "previously used challenge" is merged with
"stale challenge" definition in section 1.1.
o Reference 7 is updated from RFC 3320 to RFC 3344 and reference 9
is updated from RFC 2138 to RFC 2865 in "Reference" section.
o Reference to RFC 3344 is added in section 3.
o HMAC_CHAP_SPI option is added for Generalized Mobile IP o HMAC_CHAP_SPI option is added for Generalized Mobile IP
Authentication extension. Upon receipt of HMAC_CHAP_SPI, HMAC-MD5 Authentication extension. Upon receipt of HMAC_CHAP_SPI, HMAC-MD5
is used instead of MD5 for computing the authenticator. is used instead of MD5 for computing the authenticator.
o Clarified processing of error messages at the mobile node (section o Added FA_BAD_AAA_AUTH and HA_BAD_AAA_AUTH error codes to report
3.1).
o Modified text of section 2.1 and 3.2 for further clarity.
List of the changes for draft-ietf-mobileip-rfc3012bis-05:
o Added BAD_AAA_AUTHENTICATION_SET_BY_FA and
BAD_AAA_AUTHENTICATION_SET_BY_HA error codes to report
authentication errors caused while processing Mobile-AAA authentication errors caused while processing Mobile-AAA
Authentication extension. Authentication extension. Also, added the error code
HA_WRONG_CHALLENGE to indicate that Challenge value differs in the
Registration Reply received from the home agent compare to the one
sent to the home agent in the Registration Request.
o Processing of the Mobile-AAA Authentication extension is clarified o Processing of the Mobile-AAA Authentication extension is clarified
for the foreign agent and the home agent. for the foreign agent and the home agent.
o Co-existence of the Mobile-AAA Authentication extension in the o Co-existence of the Mobile-AAA Authentication extension in the
same Registration Request is made explicit. same Registration Request is made explicit.
o The situation in which the foreign agent sets MISSING_CHALLENGE is o The situation in which the foreign agent sets MISSING_CHALLENGE is
clarified further. clarified further.
o The use of Mobile-AAA Authentication Extension is allowed by the o The use of Mobile-AAA Authentication Extension is allowed by the
mobile node with co-located care-of-address. mobile node with co-located care-of address.
List of the changes for draft-ietf-mip4-rfc3012bis-00:
o Minor editorial changes are made through out the document.
o Added definition of "previously used challenge" and removed
definition of "stale challenge" from section 1.1.
o Renamed BAD_AAA_AUTHENTICATION_SET_BY_FA to FA_BAD_AAA_AUTH and
BAD_AAA_AUTHENTICATION_SET_BY_HA to HA_BAD_AAA_AUTH.
o Defined an order of the Mobile-AAA Authentication extension
received with the authentication extension(s) defined in RFC 3344
[RFC3344].
o Added protection against bogus Registration Reply and Agent o Added protection against bogus Registration Reply and Agent
Advertisement. Also, the processing of the Challenge is clarified Advertisement. Also, the processing of the Challenge is clarified
if it is received in the multicast/unicast Agent Advertisement. if it is received in the multicast/unicast Agent Advertisement.
List of the changes for draft-ietf-mip4-rfc3012bis-01:
o Minor editorial changes are made through out the document.
o Added reference of FA Error extension in the References section o Added reference of FA Error extension in the References section
and also updated relevant text in section 3.2 and section 11. and also updated relevant text in section 3.2 and section 11.
List of the changes for draft-ietf-mip4-rfc3012bis-02:
o Minor editorial changes are made in Appendix C and Appendix D.
o Updated Boilerplate.
List of the changes for draft-ietf-mip4-rfc3012bis-03:
o Removed HMAC_MD5_SPI support from section 3.1, 8 and 9.
o Corrected figure titles 1 and 3.
List of the changes for draft-ietf-mip4-rfc3012bis-04:
o Clarified use of FA Error extension in section 3.2. Also,
editorial changes are made in 1, 1.1, 3.1 and 3.2 sections.
o Introduced HA_WRONG_CHALLENGE error code.
Appendix B. Verification Infrastructure Appendix B. Verification Infrastructure
The Challenge extensions in this protocol specification are expected The Challenge extensions in this protocol specification are expected
to be useful to help the foreign agent manage connectivity for to be useful to help the foreign agent manage connectivity for
visiting mobile nodes, even in situations where the foreign agent visiting mobile nodes, even in situations where the foreign agent
does not have any security association with the mobile node or the does not have any security association with the mobile node or the
mobile node's home agent. In order to carry out the necessary mobile node's home agent. In order to carry out the necessary
authentication, it is expected that the foreign agent will need the authentication, it is expected that the foreign agent will need the
assistance of external administrative systems, which have come to be assistance of external administrative systems, which have come to be
called AAA systems. For the purposes of this document, we call the called AAA systems. For the purposes of this document, we call the
external administrative support the "verification infrastructure". external administrative support the "verification infrastructure".
The verification infrastructure is described to motivate the design The verification infrastructure is described to motivate the design
of the protocol elements defined in this document, and is not of the protocol elements defined in this document, and is not
strictly needed for the protocol to work. The foreign agent is free strictly needed for the protocol to work. The foreign agent is free
to use any means at its disposal to verify the credentials of the to use any means at its disposal to verify the credentials of the
mobile node. This could, for instance, rely on a separate protocol mobile node. This could, for instance, rely on a separate protocol
between the foreign agent and the Mobile IP home agent, and still be between the foreign agent and the Mobile IP home agent, and still be
completely invisible to the mobile node. completely invisible to the mobile node.
In order to verify the credentials of the mobile node, we imagine In order to verify the credentials of the mobile node, we assume that
that the foreign agent has access to a verification infrastructure the foreign agent has access to a verification infrastructure that
that can return a secure notification to the foreign agent that the can return a secure notification to the foreign agent that the
authentication has been performed, along with the results of that authentication has been performed, along with the results of that
authentication. This infrastructure may be visualized as shown in authentication. This infrastructure may be visualized as shown in
Figure 4. Figure 4.
+----------------------------------------------------+ +----------------------------------------------------+
| | | |
| Verification and Key Management Infrastructure | | Verification and Key Management Infrastructure |
| | | |
+----------------------------------------------------+ +----------------------------------------------------+
^ | ^ | ^ | ^ |
skipping to change at page 32, line 31 skipping to change at page 28, line 31
| | Authorization, incl. | | | | Authorization, incl. | |
| |<-- RRep + Auth.Ext.-----| | | |<-- RRep + Auth.Ext.-----| |
| | | | | | | |
|<-- RRep+Auth.Ext--| | | |<-- RRep+Auth.Ext--| | |
| + New Challenge | | | | + New Challenge | | |
Figure 5: Message Flows for FA Challenge Messaging Figure 5: Message Flows for FA Challenge Messaging
In Figure 5, the following informational message flow is illustrated: In Figure 5, the following informational message flow is illustrated:
1. The foreign agent disseminates a Challenge Value in an Agent 1. The foreign agent includes a Challenge Value in a unicast Agent
Advertisement if needed. This advertisement MAY have been Advertisement if needed. This advertisement MAY have been
produced after receiving an Agent Solicitation from the mobile produced after receiving an Agent Solicitation from the mobile
node (not shown in the diagram). node (not shown in the diagram).
2. The mobile node creates a Registration Request including the 2. The mobile node creates a Registration Request including the
advertised Challenge Value in the Challenge Extension, along with advertised Challenge Value in the Challenge extension, along with
an Mobile-AAA authentication extension. an Mobile-AAA authentication extension.
3. The foreign agent relays the Registration Request either to the 3. The foreign agent relays the Registration Request either to the
home agent specified by the mobile node, or else to its locally home agent specified by the mobile node, or else to its locally
configured Verification Infrastructure (see Appendix B), configured Verification Infrastructure (see Appendix B),
according to local policy. according to local policy.
4. The foreign agent receives a Registration Reply with the 4. The foreign agent receives a Registration Reply with the
appropriate indications for authorizing connectivity for the appropriate indications for authorizing connectivity for the
mobile node. mobile node.
skipping to change at page 34, line 34 skipping to change at page 30, line 34
Authentication Authentication
In Figure 6, the following informational message flow is illustrated: In Figure 6, the following informational message flow is illustrated:
1. The foreign agent disseminates a Challenge Value in an Agent 1. The foreign agent disseminates a Challenge Value in an Agent
Advertisement if needed. This advertisement MAY have been Advertisement if needed. This advertisement MAY have been
produced after receiving an Agent Solicitation from the mobile produced after receiving an Agent Solicitation from the mobile
node (not shown in the diagram). node (not shown in the diagram).
2. The mobile node creates a Registration Request including the 2. The mobile node creates a Registration Request including the
advertised Challenge Value in the Challenge Extension, along with advertised Challenge Value in the Challenge extension, along with
an Mobile-Foreign Authentication extension. an Mobile-Foreign Authentication extension.
3. The foreign agent relays the Registration Request to the home 3. The foreign agent relays the Registration Request to the home
agent specified by the mobile node. agent specified by the mobile node.
4. The foreign agent receives a Registration Reply with the 4. The foreign agent receives a Registration Reply with the
appropriate indications for authorizing connectivity for the appropriate indications for authorizing connectivity for the
mobile node. mobile node.
5. The foreign agent relays the Registration Reply to the mobile 5. The foreign agent relays the Registration Reply to the mobile
node, possibly along with a new Challenge Value to be used by the node, possibly along with a new Challenge Value to be used by the
mobile node in its next Registration Request message. If the mobile node in its next Registration Request message. If the
Reply contains the Code value HA_BAD_AAA_AUTH (see Section 10), Reply contains the Code value HA_BAD_AAA_AUTH (see Section 10),
the foreign agent takes actions indicated for rejected the foreign agent takes actions indicated for rejected
registrations. registrations.
Appendix E. Foreign Agent Algorithm for Tracking Used Challenges Appendix E. Example Pseudo-Code for Tracking Used Challenges
If the foreign agent maintains a large CHALLENGE_WINDOW, it becomes
more important for scalability purposes to efficiently compare
incoming challenges against the set of Challenge values which have
been advertised recently. This can be done by keeping the Challenge
values in order of advertisement, and by making use of the mandated
behavior that mobile nodes MUST NOT use Challenge values which were
advertised before the last advertised Challenge value that the mobile
node has attempted to use. The following stylized programmatic
algorithm accomplishes this objective. The maximum amount of total
storage required by this algorithm is equal to Size*(CHALLENGE_WINDOW
+ (2*N)), where N is the current number of mobile nodes for which the
foreign agent is storing challenge values. Note that, whenever the
stored challenge value is no longer in the CHALLENGE_WINDOW, it can
be deleted from the foreign agent's records, perhaps along with all
other registration information for the mobile node if it is no longer
registered.
In the program fragment, it is presumed that the foreign agent keeps
an array of advertised Challenges ("VALID_ADV_CHALLENGES"), a record
of the last advertised challenge used by a mobile node, and also a
record of the last challenge provided to a mobile node in a
Registration Reply or unicast Agent Advertisement.
To meet the security obligations outlined in Section 12, the foreign
agent SHOULD use one of the already stored, previously unused
challenges when responding to an unauthenticated Registration Request
or Agent Solicitation. If none of the already stored challenges are
previously unused, the foreign agent SHOULD generate a new challenge,
include it in the response, and store it in the per-Mobile data
structure.
current_chal := RegistrationRequest.challenge_extension_value current_chal := RegistrationRequest.challenge_extension_value
last_chal := mobile_node_record.last_used_adv_chal last_chal := mobile_node_record.last_used_adv_chal
if (current_chal == mobile_node_record.RegReply_challenge) { if (current_chal == mobile_node_record.RegReply_challenge) {
update (mobile_node_record, current_chal) update (mobile_node_record, current_chal)
return (OK) return (OK)
} }
else if (current_chal "among" VALID_ADV_CHALLENGES[]{ else if (current_chal "among" VALID_ADV_CHALLENGES[]{
if (last_chal "among" VALID_ADV_CHALLENGES[]) { if (last_chal "among" VALID_ADV_CHALLENGES[]) {
skipping to change at page 37, line 5 skipping to change at page 32, line 5
} }
else { else {
update (mobile_node_record, current_chal) update (mobile_node_record, current_chal)
return (OK) return (OK)
} }
} }
else { else {
send_error(UNKNOWN_CHALLENGE); send_error(UNKNOWN_CHALLENGE);
} }
Authors' Addresses
Charles E. Perkins
Nokia Research Center
Communications Systems Lab
313 Fairchild Drive
Mountain View, California 94043
Phone: +1 650 625-2986
Email: charles.perkins@nokia.com
Pat R. Calhoun
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
Phone: +1 408-853-5269
Email: pcalhoun@cisco.com
Jayshree Bharatia
Nortel Networks
2221, Lakeside Blvd
Richardson, TX 75082
Phone: +1 972-684-5767
Email: jayshree@nortel.com
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on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
skipping to change at page 37, line 41 skipping to change at page 33, line 41
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
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to the rights, licenses and restrictions contained in BCP 78, and to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
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