Mobile IP Working Group Charles E. Perkins
INTERNET DRAFT Nokia Research Center
26 February 2002 Pat R. Calhoun
Black Storm Systems
AAA Registration Keys for Mobile IP
draft-ietf-mobileip-aaa-key-09.txt
Status of This Memo
This document is a submission by the mobile-ip Working Group of the
Internet Engineering Task Force (IETF). Comments should be submitted
to the mobile-ip@sunroof.eng.sun.com mailing list.
Distribution of this memo is unlimited.
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are working
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Abstract
AAA servers, such as RADIUS and DIAMETER, are in use within the
Internet today to provide authentication and authorization services
for dial-up computers. Mobile IP requires strong authentication
between the mobile node and its home agent. When the mobile node
shares a security association with its home AAA server, however, it
is possible to use that security association to create derivative
security associations between the mobile node and its home agent,
and again between the mobile node and the foreign agent currently
offering connectivity to the mobile node. This document specifies
extensions to the Mobile IP Registration Reply packet that can be
used to create such security information at the mobile node.
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1. Introduction
AAA servers, such as RADIUS [13] and DIAMETER [4], are in use within
the Internet today to provide authentication and authorization
services for dial-up computers. Such services are likely to be
equally valuable for mobile nodes using Mobile IP [12] when the
nodes are attempting to connect to foreign domains with AAA servers.
Requirements for interactions between AAA and Mobile IP are outlined
in RFC 2977 [6]; that document describes an infrastructure which
enables AAA servers to authenticate and authorize network access
requests from mobile nodes. See also appendix B. The Mobile IP
Registration Request is considered to be a request for network
access. It is then possible to augment the functionality of
the Mobile IP mobility agents so that they can translate between
Mobile IP registration messages and the messages used within the
AAA infrastructure architected in RFC 2977. Mobility agents and
AAA servers that conform to the requirements of RFC 2977 can be
considered as appropriate network entities to support the message
types specified in this document. Please consult RFC 2977 for
further details.
Mobile IP requires strong authentication between the mobile node and
its home agent. When the mobile node shares a security association
with its home AAA server, however, it is possible to use that
security association to create derivative security associations
between the mobile node and its home agent, and again between the
mobile node and the foreign agent currently offering connectivity to
the mobile node. This document specifies extensions to the Mobile
IP Registration messages that can be used to create those security
associations at the mobile node.
AAA servers typically use the Network Access Identifier (NAI) [1]
to uniquely identify the mobile node; the mobile node's home
address is not always necessary to provide that function. Thus,
it is possible for a mobile node to authenticate itself, and be
authorized for connection to the foreign domain, without having any
home address. However, for Mobile IP to work, the mobile node is
required to have a security association with its home agent. When
the Mobile IP Registration Reply packet is authenticated by the
MN-AAA Authentication Extension [3], the mobile node can verify that
the keys contained in the extensions were produced by the AAA server,
and thus may be reliably used to create security associations with
the home agent, or alternatively with the foreign agent.
It is also assumed that the AAA entities involved (i.e., the AAAH,
AAAL, and the AAA interface features of the foreign agents and home
agents) all have means outside of the scope of this document for
exchanging keys. The extensions within this document are intended to
work with any AAA protocol suite that allows for such key exchange.
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2. Terminology
security association
The information shared by two network nodes that
enables them to carry out the operations needed for
some security protocol that the nodes intend to
operate. For the purposes of this document, all
security associations will contain the following
information:
key a number, kept secret. Only nodes in
possession of the key have any hope of
using the security algorithm to obtain
correct results.
SPI Security Parameters Index. This number
enables selection of one security
association in case that several exist
between the two nodes operaing a security
procedure.
Also for the purposes of this document, a mobile
node is allowed to have a security association with
another node even though it does not necessarily
know the IP address of that node. It is only
required that the mobile node use the security
association for purpose in accordance with the
expectations of the other node.
security algorithm
A set of rules for using input data and a secret key
for producing data for use in security protocols.
For example, HMAC-MD5 [8] is the security algorithm
that all nodes using Mobile IP must implement
for the purposes of producing and verifying
authentication data.
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 [2].
Other terminology is used as defined in the base Mobile IP
specification [12].
Furthermore, in order to simplify the discussion, we have used the
word "Extension" instead of "Subtype of the Generalized Extension"
in many cases. So, for instance, instead of using the phrase "The
Unsolicited MN-FA Key Material From AAA Subtype of the Generalized
MN-FA Key Reply Extension", we would instead use the phrase "The
Unsolicited MN-FA Key Material From AAA Extension".
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3. Overview of Operations with Key Extensions
When a mobile node depends on an AAA infrastructure to obtain
authorization for network connectivity and Mobile IP registration,
it may not have any pre-existing security relationships with either
its home agent, or the foreign agent controlling the access to the
foreign network. The extensions defined in this document allow a AAA
agent to supply key material to mobile nodes to be used as the basis
of its security association with mobile agents (foreign agents and
home agents). The AAA agent that will act on these extensions is
part of the AAA infrastructure, and is typically identified within
the foreign domain by methods outside the scope of this specification
(see appendix B).
The key material is requested by the mobile node in new extensions to
Mobile IP Registration Request messages, and supplied to the mobile
node in extensions to the Mobile IP Registration Reply messages.
The method by which key material is supplied to the mobility agents
themselves is out of scope for this document, and would depend on the
particular details of the security architecture for the AAA servers
in the foreign and home domains (see RFC 2977 and appendix B). For
the purposes of this document, we assume that there is a suitable AAA
infrastructure available to the foreign agents, and that the mobile
node does have a security association with at least one AAA server in
its home domain.
The protocol and messages in this document are intended to facilitate
the following operations which may occur between the mobile node, AAA
server, home agent, and foreign agent. However, the only message
flows specified in this document are the Registration Request between
the mobile node and the foreign agent, and Registration Reply between
the foreign agent and the mobile node.
1. When a mobile node travels away from home, it may not have a
security association with its home agent, perhaps because it does
not yet have a home address.
2. If the mobile node does not have a Mobility Security Association
with the foreign agent, it SHOULD include an MN-FA Key Request
extension (see Section 10) as part of its Registration Request
that it sends to the Foreign Agent.
3. Similarly, if the mobile node does not have a Mobility Security
Association with the home agent, it MUST add an MN-HA Key Request
extension (see Section 11) as part of its Registration Request
that it sends to the Foreign Agent.
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4. If one or more Key Request extensions were added, the mobile
node adds the MN-AAA Authentication extension is added to its
Registration Request.
5. By action of the foreign agent, which is presumed to be also
a participant in some AAA protocol, the mobile node's key
requests and authentication data are transferred, typically after
reformatting to fit into the appropriate AAA messages, which are
out of scope for this document.
6. At the time the information within the MN-AAA Authentication
extension is verified by the AAA server, the AAA server also
generates Key Material, if it has been requested by the mobile
node.
7. The respective AAA keys are distributed to the Home and Foreign
Agent via the AAA protocol.
8. The mobile node first generates the key using the Key Material
provided, according to its security association with the AAA.
Using that key, the mobile node authenticates the Reply message.
If the Reply passes authentication and contains the Unsolicited
MN-HA Key Material From AAA extension (see section 9), the
generated key is then used to establish the mobile node's
security association with its home agent, and is used to
authenticate the MN-HA authentication extension.
9. Similarly, if the Reply passes authentication and contains
the Unsolicited MN-FA Key Material From AAA extension (see
section 8), the mobile node generates the key using the Key
Material provided, according to its security association with the
AAA. The resulting key is used to establish the mobile node's
security association with its new foreign agent, and is used
to compute the authentication data used in the Mobile-Foreign
authentication extension.
Any registration reply containing the Unsolicited MN-HA Key Material
From AAA extension MUST also contain a subsequent Mobile Home
Authentication Extension, created using the generated MN-HA key.
Similarly, a reply containing the Unsolicited MN-FA Key Material
From AAA extension MUST also contain a subsequent Mobile Foreign
Authentication Extension, created using the the MN-FA key.
4. Mobility Security Associations
Mobility Security Associations between Mobile IP entities
(mobile nodes, home agents, foreign agents) contain both the
necessary cryptographic key information, and a way to identify
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the cryptographic algorithm which uses the key to produce the
authentication information typically included in the Mobile Home
Authentication extension or the Mobile Foreign Authentication
extension. In order for the mobile node to make use of key material
created by the AAA server, the mobile node also has to be able to
identify and select the appropriate cryptographic algorithm that uses
the key to produce the authentication.
The algorithm identifiers are tabulated in the list of Authentication
Algorithms allowable as values for the "Attribute Type" (5)
(i.e., "Authentication Algorithm"), one of the classifications
in the tabulated Attribute Types for "IPSEC Security Association
Attributes". See http://www.iana.org/assignments/isakmp-registry
for the full listing of all Attribute Types and other Attributes for
IPSEC Security Associations.
Mobility Security Associations shared between mobile nodes and home
agents also require a replay protection method. The following table
contains the supported replay methods.
Replay Method Name Reference
-------------- ------------ --------------
1 None RFC 3220 [12]
2 Timestamps RFC 3220 [12]
3 Nonces RFC 3220 [12]
5. Key Material Creation and Derivation
This section contains the procedures followed in the creation of the
Key Material by AAA servers, and the key derivation procedures used
by mobile nodes. Note that the AAA servers will also make use of the
derivation procedures to deliver the keys via the AAA protocol. AAA
servers that follow these procedures will produce results that can
be understood by mobile nodes. Mobility agents (home agent, foreign
agent) will faithfully transcribe the results into the appropriate
Mobile IP extensions.
The example that follows makes use of HMAC-MD5 [7]. All mobile nodes
and mobility agents implementing Mobile IP, and implementing the
extensions specified in this document, MUST implement HMAC-MD5 [12].
Other cryptographic functions MAY also be used.
The following steps are performed on the AAA server:
1. The AAA server identifies the mobile node. If the Home Address
field of the Registration Request is either zero (0), or all ones
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(1), then the Mobile Node's NAI is used instead of the mobile
node's home address.
2. The AAA server generates a random [5] value of at least 64 bits
to be used as the Key Material.
3. The AAA server provides the random value for later insertion into
the Key extension, in the ``Key Material'' field.
The following steps are performed on the mobile node:
1. The mobile node calculates
key = HMAC-MD5 (Key Material | home address)
2. The mobile node creates the security association, using the key
and the other relevant information in the Key Extension.
The secret key used within the HMAC-MD5 computation is the AAA-key
pointed to by the AAA SPI, which has been previously configured as
the basis for a security assocation between the mobile node and the
AAA server creating the key.
6. Generalized Key Request/Reply Extensions
The extensions in this section are Generalized Extensions, and have
subtypes as specified in section 7.
6.1. Generalized MN-FA Key Request Extension
Figure 1 illustrates the Generalized MN-FA Key Request Extension.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Subtype | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mobile Node SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MN-FA Key Request Subtype Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: The Generalized Mobile IP MN-FA Key Request Extension
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Type TBD (not skippable) (see [12] and section 13)
Subtype a number assigned to identify the way in
which the Key Request Data is to be used when
generating the registration key
Length The 16-bit Length field indicates the length of
the extension. It is equal to the number of
bytes in the MN-FA Key Request Subtype Data plus
4 (for the Mobile Node SPI field), and SHOULD be
at least 20.
Mobile Node SPI The Security Parameters Index that the mobile
node will assign for the security association
created for use with the registration key.
MN-FA Key Request Subtype Data
Data needed to carry out the creation of the
registration key on behalf of the mobile node.
The Generalized MN-FA Key Request Extension defines a set of
extensions, identified by subtype, which may be used by a mobile node
in a Mobile IP Registration Request message to request that some
other entity create a key for use by the mobile node with the mobile
node's new foreign agent.
6.2. Generalized MN-FA Key Reply Extension
The Generalized MN-FA Key Reply extension supplies a registration key
requested by using one of the subtypes of the Generalized MN-FA Key
Request extension. Figure 2 illustrates the format Generalized MN-FA
Key Reply Extension.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Subtype | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MN-FA Key Reply Subtype Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The Generalized Mobile IP MN-FA Key Reply Extension
Type TBD (not skippable) (see [12] and section 13)
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Subtype a number assigned to identify the way in which the
MN-FA Key Reply Subtype Data is to be decrypted to
obtain the registration key
Length The 16-bit Length field is equal to the number of bytes
in the MN-FA Key Reply Subtype Data.
MN-FA Key Reply Subtype Data
An encoded copy of the key to be used between the
mobile node and the foreign agent, along with any other
information needed by the recipient to create the
designated Mobility Security Association.
For each subtype, the format of the MN-FA Key Reply Subtype Data has
to be separately defined according to the particular method required
to set up the security association.
In some cases, the MN-FA Key supplied in the data for a subtype of
this extension comes by a request which was sent using a subtype of
the Generalized MN-FA Key Request Extension. In that case, the SPI
to be used when employing the security association defined by the
registration key is the same as given in the original request.
6.3. Generalized MN-HA Key Request Extension
Figure 3 illustrates the Generalized MN-HA Key Request Extension.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Subtype | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mobile Node SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MN-HA Key Request Subtype Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: The Generalized Mobile IP MN-HA Key Request Extension
Type TBD (not skippable) (see [12] and section 13)
Subtype a number assigned to identify the way in
which the Key Request Data is to be used when
generating the registration key
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Length The 16-bit Length field indicates the length of
the extension. It is equal to the number of
bytes in the MN-HA Key Request Subtype Data plus
4 (for the Mobile Node SPI field), and SHOULD be
at least 20.
Mobile Node SPI The Security Parameters Index that the mobile
node will assign for the security association
created for use with the registration key.
MN-HA Key Request Subtype Data
Data needed to carry out the creation of the
registration key on behalf of the mobile node.
The Generalized MN-HA Key Request Extension defines a set of
extensions, identified by subtype, which may be used by a mobile node
in a Mobile IP Registration Request message to request that some
other entity create a key for use by the mobile node with the mobile
node's new home agent.
6.4. Generalized MN-HA Key Reply Extension
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Subtype | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MN-HA Key Reply Subtype Data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: The Generalized Mobile IP MN-HA Key Reply Extension
Type TBD (not skippable) (see [12] and section 13)
Subtype a number assigned to identify the way in which the
MN-HA Key Reply Subtype Data is to be decrypted to
obtain the registration key
Length The 16-bit Length field indicates the length of the
extension. It is equal to the number of bytes in the
MN-HA Key Reply Subtype Data plus 4 (for the Lifetime
field).
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Lifetime This field indicates the duration of time (in seconds)
for which the MN-HA key is valid.
MN-HA Key Reply Subtype Data
An encrypted copy of the key to be used between the
mobile node and its home agent, along with any other
information needed by the mobile node to create the
designated Mobility Security Association with the home
agent.
For each subtype, the format of the MN-HA Key Reply Subtype Data has
to be separately defined according to the particular method required
to set up the security association.
7. Key Request/Reply Subtypes
The extension subtypes in this section are subtypes of the
Generalized Extensions specified in section 6.
8. Unsolicited MN-FA Key Material From AAA Subtype
The Unsolicited MN-FA Key Material From AAA extension, shown in
figure 5, uses subtype 7 of the Generalized MN-FA Key Reply Extension
(see section 6.2).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AAA SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FA SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm Identifier | Key Material ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: The Unsolicited MN-FA Key Material From AAA
Subtype-Specific Data
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lifetime This field indicates the duration of time (in seconds)
for which the MN-FA key is valid.
AAA SPI A 32-bit opaque value, indicating the SPI that the
mobile node must use to determine the algorithm to use
for establishing the FA security information.
FA SPI The SPI for the Security Association to the FA that the
MN creates as a result of processing this extension
Algorithm Identifier
This field indicates the algorithm to be used (selected
from among the values in the "Authentication Algorithm"
table cited in section 4). for future computations of
the Mobile-Foreign Authentication Extension.
Key Material
A random [5] value of at least 64 bits.
The Key Material is added by the AAA server for use by the mobile
node in creating the MN-FA key, which is used to secure future Mobile
IP registrations with the same foreign agent. The Unsolicited MN-FA
Key Material From AAA extension MUST appear in the Registration Reply
before the Mobile-Foreign Authentication extension.
Once the mobile node creates the FA Security Information, by using
the algorithm indexed by the AAA SPI, it stores the FA Security
Information indexed by the FA SPI in its list of Mobile Security
Associations.
If the foreign agent receives a Registration Reply that has no
Unsolicited MN-FA Key Material From AAA extension, and thus cannot
establish a Mobility Security Association with the mobile node, the
foreign agent MAY change the Code value of the Registration Reply to
MISSING_MN_FA (see section 12), effectively causing the registration
to fail.
9. Unsolicited MN-HA Key Material From AAA Subtype
The Unsolicited MN-HA Key Material From AAA is subtype 1 of the
Generalized MN-HA Key Reply Extension (see section 6.4).
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AAA SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HA SPI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm Identifier | Replay Method |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key Material ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: The Unsolicited MN-HA Key Material From AAA
Subtype-Specific Data
AAA SPI A 32-bit opaque value, indicating the SPI that the
mobile node must use to determine the algorithm to use
for establishing the HA security information.
HA SPI The SPI for the Security Association to the HA that the
MN creates as a result of processing this extension
Algorithm Identifier
This field indicates the algorithm to be used for
future computations of the MN-HA Authentication
Extension (see section 4)
Replay Method
This field contains the replay method to be used for
future Registration messages (see section 4).
Key Material
A random [5] value of at least 64 bits.
The Unsolicited MN-HA Material Key From AAA subtype-specific data is
shown in figure 6. The Mobile Node creates the MN-HA key using the
Key Material that has previously been configured for securing all
such communication requirements with the AAA server which will be
contacted within the AAA infrastructure (see appendix B). The key
is intended for use by the mobile node to secure future Mobile IP
registrations with its home agent. The MN-HA Key Reply MUST appear
in the Registration Reply before the MN-HA Authentication extension.
Once the mobile node creates the MN-HA Key, by using the algorithm
specified in the AAA SPI, it stores the HA Security Information
indexed by the HA SPI in its list of Mobile Security Associations.
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The mobile node uses the Identification field data from the
Registration Request as its initial synchronization data with the
home agent.
10. MN-FA Key Request From AAA Subtype
The MN-FA Key Request From AAA subtype data uses subtype 7 of the
Generalized MN-FA Key Request Extension (see section 6.1). The
MN-FA Key Request From AAA extension MUST appear in the Registration
Request before the MN-AAA Authentication extension. The subtype data
field is zero in length.
11. MN-HA Key Request From AAA Subtype
The MN-HA Key Request From AAA subtype data uses subtype 7 of the
Generalized MN-HA Key Request Extension (see section 6.3). The
MN-HA Key Request From AAA extension MUST appear in the Registration
Request before the MN-AAA Authentication extension. The subtype data
field is zero in length.
12. Error Values
Each entry in the following table contains the name of Code [12] to
be returned in a Registration Reply, the value for the Code, and the
section in which the error is first mentioned in this specification.
Error Name Value Section
---------------------- ----- ---------
MISSING_MN_FA 107 8
13. IANA Considerations
The numbers for the Generalized Extensions in section 6 are
taken from the numbering space defined for Mobile IP registration
extensions defined in RFC 3220 [12] as extended in RFC 2356 [10].
The numbers suggested in this section are already in use by
implementations which have been tested for interoperability.
The number 7, assigned to the Unsolicited MN-HA Key Material From AAA
Subtype extension, was taken from the numbering space defined for the
Generalized MN-HA Key Reply Extension (see section 6.4).
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The number 7, assigned to the MN-FA Key Request From AAA Subtype
extension, was taken from the numbering space defined for the
Generalized MN-FA Key Request Extension (see section 6.1).
The number 1, assigned to the Unsolicited MN-FA Key Material From AAA
Subtype extension, was taken from the numbering space defined for the
Generalized MN-FA Key Reply Extension (see section 6.2).
The number 7, assigned to the MN-HA Key Request From AAA Subtype
extension, was taken from the numbering space defined for the
Generalized MN-HA Key Request Extension (see section 6.3).
The Code values specified for errors, listed in section 12, MUST NOT
conflict with any other code values listed in RFC 3220, RFC 3024 [9],
or RFC 2356 [10]. They are to be taken from the space of error
values conventionally associated with rejection by the foreign agent
(i.e., 64-127).
Section 4 introduces the Algorithm Identifier namespace that requires
IANA management. This specification makes use of 1-3; all other
values other than zero (0) are available for assignment, pending
review and approval by a Designated Expert [11].
Section 4 introduces the Replay Method Identifier namespace that
requires IANA management. This specification makes use of 1-3;
all other values other than zero (0) are available for assignment,
pending review and approval by a Designated Expert [11].
14. Security Considerations
The extensions in this document are intended to provide the
appropriate level of security for Mobile IP entities (mobile node,
foreign agent, and home agent) to operate Mobile IP registration
protocol. The security associations resulting from use of these
extensions do not offer any higher level of security than what is
already implicit in use of the security association between the
mobile node and the AAA.
Since the extensions defined in this specification only carries Key
Material, which is used to derive keys, it does not expose any data
that could be used in an attack aimed at recovering the key shared
between the mobile node and the AAA. The authors do not believe this
specification introduces new security risks.
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15. Acknowledgements
Thanks to Fredrik Johansson and the members of the IESG for their
useful comments on this document.
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[8] D. Kristol and L. Montulli. HTTP State Management Mechanism.
Request for Comments (Proposed Standard) 2109, Internet
Engineering Task Force, February 1997.
[9] Editor G. Montenegro. Reverse Tunneling for Mobile IP, revised.
Request for Comments (Proposed Standard) 3024, Internet
Engineering Task Force, January 2001.
[10] G. Montenegro and V. Gupta. Sun's SKIP Firewall Traversal for
Mobile IP. Request for Comments (Informational) 2356, Internet
Engineering Task Force, June 1998.
[11] T. Narten and H. Alvestrand. Guidelines for Writing an IANA
Considerations Section in RFCs. Request for Comments (Best
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Internet Draft AAA Keys for Mobile IP 26 February 2002
Current Practice) 2434, Internet Engineering Task Force, October
1998.
[12] C. Perkins. IP Mobility Support. Request for Comments
(Proposed Standard) 3220, Internet Engineering Task Force,
December 2001.
[13] C. Rigney, A. Rubens, W. Simpson, and S. Willens. Remote
Authentication Dial In User Service (RADIUS). Request for
Comments (Proposed Standard) 2865, Internet Engineering Task
Force, June 2000.
A. Changes Since Previous Revision
In this revision of the document, there have been several major
changes as a result of suggestions received during Last Call.
- Generalized Key Extensions previously specified in another
document have been instead specified in this document in order
that this document can be self-contained and not dependent on the
standardization status of the other document.
- Additional explanation has been included for the purposes of
clarifying the problem space and solution approach.
- An appendix has been added to describe the expected AAA
infrastructure that will produce the keys that are to be
distributed within the extensions specified in this document.
- Ladder diagrams have been included to illustrate the expected
message flows containing the extensions defined in this document.
- HMAC-MD5 has been mandated for implementation by the mobile node,
for compatibility with RFC 3220 [12]. The example text has been
modified accordingly (see section 5).
- A table of Algorithm Identifiers has been identified as the
numbering space for algorithm selection when establishing
the security association using the keys distributed with the
extensions in this document. See section 4.
- A terminology section has been added.
- This appendix has been added.
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B. AAA Infrastructure
In this appendix, we attempt to capture the main features of a basic
model for operation of AAA servers that is assumed for understanding
of the use of the Mobile IP registration extensions described in this
document. This information has been adapted from the discussion in
RFC 2977 [6].
Within the Internet, a mobile node belonging to one administrative
domain (called the home domain) often needs to use resources provided
by another administrative domain (called the foreign domain).
An foreign agent that handles the mobile node's Registration
Request is likely to require that the mobile node provide some
credentials that can be authenticated before access to the resources
is permitted. These credentials may be provided as part of the
Mobile-AAA Authentication extension [3], relying on the existence
of an AAA infrastructure such as is described in this section, and
also described in RFC 2977 and RFC 3012 [3]. Such credentials are
typically managed by entities within the mobile node's home domain.
They may be also used for setting up secure communications with the
mobile node.
Local Domain Home Domain
+--------------+ +----------------------+
| +------+ | | +------+ |
| | | | | | | |
| | AAAL | | | | AAAH | |
| | +-------------------+ | |
| +---+--+ | | +------+ |
| | | | |
| | | +----------------------+
+------+ | +---+--+ |
| | | | | | MN = mobile node
| MN |- -|- -| FA | | FA = foreign agent
| | | | | | AAAL = local authority
+------+ | +------+ | AAAH = home authority
| |
+--------------+
Figure 7: AAA Servers in Home and Local Domains
The foreign agent often does not have direct access to the data
needed to verify the credentials. Instead, the foreign agent is
expected to consult an authority (typically in the same foreign
domain) in order to request proof that the mobile node has acceptable
credentials. Since the foreign agent and the local authority (AAAL)
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are part of the same administrative domain, they are expected to have
established, or be able to establish for the necessary lifetime, a
secure channel for the purposes of exchanging sensitive (access)
information, and keeping it private from (at least) the visiting
mobile node.
The local authority (AAAL) itself may not have enough information
stored locally to carry out the verification for the credentials
of the mobile node. In contrast to the foreign agent, however,
the AAAL is expected to be configured with enough information to
negotiate the verification of mobile node credentials with its home
domain. The home and foreign domains should be configured with
sufficient security relationships and access controls so that they
can negotiate the authorization, and also enable the mobile node to
acquire security associations with the foreign domain. requested
resources. For the purposes of the key exchanges specified within
this document, the authorization is expected to depend only upon
secure authentication of the mobile node's credentials.
Once the authorization has been obtained by the local authority, and
the authority has notified the foreign agent about the successful
negotiation, the foreign agent can deliver the Registration Reply to
the mobile node along with the desired key material.
In figure 7, there might be many mobile nodes from many different
Home Domains. Each Home Domain provides a AAAH that can check
credentials originating from mobile nodes administered by that Home
Domain. There is a security model implicit in figure 7, and it is
crucial to identify the specific security associations assumed in
the security model. These security associations are illustrated in
figure 8, and are considered to be relatively long-lived security
associations.
First, it is natural to assume that the mobile node has a security
association with the AAAH, since that is roughly what it means for
the mobile node to belong to the home domain.
Second, from the model illustrated in figure 7 it is clear that AAAL
and AAAH have to share a security association, because otherwise
they could not rely on the authentication results, authorizations,
nor even the accounting data which might be transacted between them.
Requiring such bilateral security relationships is, however, in the
end not scalable; the AAA framework MUST provide for more scalable
mechanisms, but the methods by which such a broker model is to be
created are out of scope for this document. See RFC 2977 for more
details.
Finally, from figure 7, it is clear that the foreign agent can
naturally share a security association with the AAAL. This is
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necessary in order for the model to work because the foreign agent
has to have a way to find out that it is permissible to allocate
the local resources to the mobile node, and further to transmit any
successful Registration Reply to the mobile node.
Figure 8 illustrates the natural security associations we understand
from our proposed model. Note that there may be, by mutual agreement
between AAAL and AAAH, a third party inserted between AAAL and
AAAH to help them arbitrate secure transactions in a more scalable
fashion. The broker model which has been designed to enable such
third-party processing should not have any effect on the Mobile IP
extensions specified in this document, and so no description is
provided here; see RFC 2977 [6] for more details.
+------+ +------+
| | | |
| AAAL +--------------+ AAAH |
| | | |
+---+--+ +--+---+
| |
| |
+---+--+ +--+---+
MN = mobile node | | | |
FA = foreign agent | FA | | MN |
AAAL = local authority | | | |
AAAH = home authority +------+ +------+
Figure 8: Security Associations
Nodes in two separate administrative domains (for instance, AAAH
and AAAL) often must take additional steps to verify the identity
of their communication partners, or alternatively to guarantee
the privacy of the data making up the communication. While these
considerations lead to important security requirements, as mentioned
above in the context of security between servers, we consider the
exact choice of security associations between the AAA servers to
be beyond the scope of this document. The choices are unlikely
to depend upon Mobile IP, or any specific features of the general
model illustrated in figure 7. On the other hand, the security
associations needed between Mobile IP entities are of central
importance in the design of the key exchange extensions in this
document.
One further detail deserves mention. The key associations to be
established between the mobile node and the foreign agent have
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to be communicated to the foreign agent as well as to the mobile
node. The way that the key is distributed to the foreign agent
is not relevant to any material in this document, and is expected
to be handled as part of the AAA protocol processing between the
AAAH and AAAL, and the further AAA protocol processing between the
AAAL and the foreign agent. Any method by which the key can be
securely transmitted to the AAAL and then relayed (possibly with
re-encryption) to the foreign agent, is expected to be outside the
jurisdiction of any Mobile IP specification, and thus compatible ( by
reason of non-interference) with the protocol extensions specified in
this document.
C. Message Flow for Requesting and Receiving Registration Keys
In this section, we show message flows for requesting and receiving
a reqistration key from the AAA infrastructure, described in
section B. Challenge values, as specified in [3], might be added to
the Advertisement and Registration messages for additional replay
protection, but are not illustrated here.
Diagram 9 illustrates the message flow for the case when the mobile
node explicitly requests a registration key.
MN FA AAA Infrastructure
| | |
|<--- Advertisement-----| |
| (if needed) | |
| | |
|-- RReq+AAA Key Req.-->| |
| |--- RReq + AAA Key Req.--->|
| | |
| |<--- RRep + AAA Key Rep.---|
|<-- RRep+AAA Key Rep.--| |
| | |
Figure 9: Message Flows for Requesting and
Receiving Registration Keys
In diagram 9, the following message flow is illustrated:
1. The foreign agent disseminates an Agent Advertisement. This
advertisement MAY have been produced after receiving an Agent
Solicitation from the mobile node (not shown in the diagram).
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2. The mobile node creates a Registration Request including the
MN-HA Key Request and/ore MN-FA Key Request, as needed, along
with an authorization-enabling authentication extension as
required by Mobile IP [12].
3. The foreign agent relays the Registration Request either to its
locally configured AAA Infrastructure (see appendix B), according
to local policy.
4. The foreign agent receives a Registration Reply with the
appropriate indications for authorizing connectvity for the
mobile node, which also includes the necessary AAA Key Reply
extensions. Along with this Registration Reply, the foreign
agent may also receive key material by some other secure method
appropriate for communications between it and its local AAA
infrastructure.
5. The foreign agent relays the Registration Reply to the mobile
node, along with the new Key Reply extensions to be used by the
mobile node to establish security associations with the relevant
mobility agents (foreign agent and/or home agent).
Diagram 10 illustrates the message flow for the case when the
mobile node receives an unsolicited registration key from the AAA
Infrastructure.
MN FA AAA Infrastructure
| | |
|<--- Advertisement-----| |
| (if needed) | |
| | |
| ------ RReq --------->| |
| |------- RReq ------------->|
| | |
| |<--- RRep + AAA Key Rep.---|
|<-- RRep+AAA Key Rep.--| |
| | |
Figure 10: Message Flow for Receiving
Unsolicited Registration Keys
In diagram 10, the following message flow is illustrated:
1. The foreign agent disseminates an Agent Advertisement. This
advertisement MAY have been produced after receiving an Agent
Solicitation from the mobile node (not shown in the diagram).
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2. The mobile node creates a Registration Request including an
authorization-enabling authentication extension as required by
Mobile IP [12].
3. The foreign agent relays the Registration Request either to its
locally configured AAA Infrastructure (see appendix B), according
to local policy.
4. The foreign agent receives a Registration Reply with the
appropriate indications for authorizing connectvity for the
mobile node, which also includes the necessary AAA Key Reply
extensions. Along with this Registration Reply, the foreign
agent may also receive key material by some other secure method
appropriate for communications between it and its local AAA
infrastructure.
5. The foreign agent relays the Registration Reply to the mobile
node, along with the new Key Reply extensions to be used by the
mobile node to establish security associations with the relevant
mobility agents (foreign agent and/or home agent).
Addresses
The working group can be contacted via the current chairs:
Basavaraj Patil Phil Roberts
Nokia Megisto Corp.
6000 Connection Dr. Suite 120
20251 Century Blvd
Irving, TX. 75039 Germantown MD 20874
USA USA
Phone: +1 972-894-6709 Phone: +1 847-202-9314
Email: Basavaraj.Patil@nokia.com Email: PRoberts@MEGISTO.com
Questions about this memo can also be directed to the authors:
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Charles E. Perkins Pat R. Calhoun
Communications Systems Lab
Nokia Research Center Black Storm Networks
313 Fairchild Drive 250 Cambridge Avenue, Suite 200
Mountain View, California 94043 Palo Alto, California, 94306
USA USA
Phone: +1-650 625-2986 Phone: +1 650-617-2932
EMail: charliep@iprg.nokia.com Email: pcalhoun@diameter.org
Fax: +1 650 625-2502 Fax: +1 650-786-6445
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