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Dynamic Host Configuration H. Tschofenig
Internet-Draft Nokia Siemens Networks
Intended status: Standards Track A. Yegin
Expires: January 15, 2009 Samsung
D. Forsberg
Nokia
July 14, 2008
Bootstrapping RFC3118 Delayed DHCP Authentication Using EAP-based
Network Access Authentication
draft-yegin-eap-boot-rfc3118-03.txt
Status of this Memo
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This Internet-Draft will expire on January 15, 2009.
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Abstract
The DHCP authentication extension (RFC 3118) cannot be widely
deployed due to lack of a key agreement protocol. This document
outlines how EAP-based network access authentication mechanisms can
be used to establish bootstrap keying material that can be used to
subsequently use RFC 3118 security.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview and Building Blocks . . . . . . . . . . . . . . . . . 6
4. Buliding DHCP SA . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. 802.1X . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2. PPP . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.3. PANA . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.4. Computing DHCP SA . . . . . . . . . . . . . . . . . . . . 11
5. Delivering DHCP SA . . . . . . . . . . . . . . . . . . . . . . 13
6. Using DHCP SA . . . . . . . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
9. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 23
10. Acknowledegments . . . . . . . . . . . . . . . . . . . . . . . 24
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
11.1. Normative References . . . . . . . . . . . . . . . . . . . 25
11.2. Informative References . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
Intellectual Property and Copyright Statements . . . . . . . . . . 28
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1. Introduction
The Extensible Authentication Protocol (EAP) [RFC3748] provides a
network access authentication framework by carrying authentication
process between the hosts and the access networks. The combination
of EAP with a AAA architecture allows authentication and
authorization of a roaming user to an access network. A successful
authentication between a client and the network produces a
dynamically created trust relation between the two. Almost all EAP
methods (e.g., EAP-TLS, EAP-SIM) are capable of generating
cryptographic keys between the EAP peer and the EAP server. Using
key transport via the AAA infrastructure the EAP server makes the
EAP-provided keying material available to the Authenticator (e.g.,
Network Access Server; NAS) after a successful authentication
attempt. These keys are commonly used in conjunction with per-packet
security mechanisms (e.g., link-layer ciphering). This procedure is
described in [I-D.ietf-eap-keying].
DHCP [RFC2131] is a protocol which provides a host with configuration
parameters. The base DHCP does not include any security mechanism,
hence it is vulnerable to a number of security threats. The security
considerations section of RFC 2131 [RFC2131] identifies it as "quite
insecure" and lists various security threats.
RFC 3118 [RFC3118] is the DHCP authentication protocol that defines
how to authenticate various DHCP messages. It does not support
roaming clients and assumes out-of-band or manual key establishment.
These limitations have been inhibiting widespread deployment of this
security mechanism as noted in a DHCPv4 threat analysis
[I-D.ietf-dhc-v4-threat-analysis].
It is possible to use the authentication and key exchange procedure
executed during the network access authentication to bootstrap a
security association for DHCP. The access authentication procedure
can be utilized to dynamically provide the keying material to RFC
3118 based security protection for DHCP. This document defines how
to use the EAP-based access authentication procedure to bootstrap RFC
3118 security.
The general framework of the mechanism described in this I-D can be
outlined as follows:
1. The client gains network access by utilizing an EAP method that
generates session keys. As part of the network access process,
the client and the authentication agent (NAS) communicate their
intention to create a DHCP security association and exchange the
required parameters (e.g., nonce, key ID, etc.) The required
information exchange is handled by the EAP lower-layer which also
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carries EAP.
2. Although the newly generated DHCP SA is already available to the
DHCP client, in case the NAS (acting as a DHCP relay) and the
DHCP server are not co-located, the SA parameters need to be
communicated to the DHCP server. This requires a protocol
exchange, which can be piggybacked with the DHCP signaling.
3. The DHCP signaling that immediately follows the network access
authentication process utilizes RFC 3118 to secure the protocol
exchange. Both the client and the server rely on the DHCP SA to
compute and verify the authentication codes.
This framework requires extensions to the EAP lower-layers (PPP
[RFC1661], IEEE 802.1X , PANA [RFC5191]) to carry the supplemental
parameters required for the generation of the DHCP SA. Another
extension is required to carry the DHCP SA parameters from a DHCP
relay to a DHCP server. RFC 3118 can be used without any
modifications or extensions.
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2. Terminology
In this document, the key words "MAY", "MUST, "MUST NOT",
OPTIONAL","RECOMMENDED "SHOULD", and "SHOULD NOT", are to be
interpreted as described in [RFC2119].
This document uses the following terms:
DHCP Security Association:
To secure DHCP messages a number of parameters including the key
that is shared between the client (DHCP client) and the DHCP
server have to be established. These parameters are collectively
referred to as DHCP security association (or in short DHCP SA).
DHCP SA can be considered as a group security association. The
DHCP SA parameters are provided to the DHCP server as soon as the
client chooses the server to carry out DHCP. The same DHCP SA can
be used by any one of the DHCP servers that are available to the
client.
DHCP Key:
This term refers to the fresh and unique session key dynamically
established between the DHCP client and the DHCP server. This key
is used to protect DHCP messages as described in [RFC3118].
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3. Overview and Building Blocks
The bootstrapping mechanism requires protocol interaction between the
client host (which acts as a DHCP client), the NAS and the DHCP
server. A security association will be established between the DHCP
server and the DHCP client to protect the DHCP messages.
A DHCP SA is generated based on the EAP method derived key after a
successful EAP method protocol run. Both the client and the NAS
should agree on the generation of a DHCP SA after the EAP SA is
created. This involves a handshake between the two and exchange of
additional parameters (such as nonce, key ID, etc.). These
additional information needs to be carried over the EAP lower-layer
that also carries the EAP payloads.
The DHCP SA is ultimately needed by the DHCP client and the DHCP
server. On the network side, the DHCP SA information needs to be
transferred from the NAS (where it is generated) to the DHCP server
(where it will be used). On the client host side, it is transferred
from the network access authentication client to the DHCP client.
NAS is always located one IP hop away from the client. If the DHCP
server is on the same link, it can be co-located with the NAS. When
the NAS and the DHCP server are co-located, an internal mechanism,
such as an API, is sufficient for transferring the SA information.
If the DHCP server is multiple hops away from the DHCP client, then
there must be a DHCP relay on the same link as the client. In that
case, the NAS should be co-located with the DHCP relay
[RFC4014] enables transmission of AAA-related RADIUS attributes from
a DHCP relay to a DHCP server in the form of relay agent information
options. DHCP SA is generated at the end of the AAA process, and
therefore it can be provided to the DHCP server in a sub-option
carried along with other AAA-related information. Confidentiality,
replay, and integrity protection of this exchange MUST be provided.
[I-D.ietf-dhc-relay-agent-ipsec] proposes IPsec protection of the
DHCP messages exchanged between the DHCP relay and the DHCP server.
DHCP objects (protected with IPsec) can therefore be used to
communicate the necessary parameters.
Two different deployment scenarios are illustrated in Figure 1.
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+---------+ +------------------+
|EAP Peer/| |EAP Authenticator/|
| DHCP |<============>| DHCP server |
| client | EAP and DHCP | |
+---------+ +------------------+
Client Host NAS
+---------+ +------------------+ +-----------+
|EAP Peer/| |EAP Authenticator/| | |
| DHCP |<============>| DHCP relay |<========>|DHCP server|
| client | EAP and DHCP | | DHCP | |
+---------+ +------------------+ +-----------+
Client Host NAS
Figure 1: Protocols and end points.
When the DHCP SA information is received by the DHCP server and
client, it can be used along with RFC 3118 to protect DHCP messages
against various security threats. This draft provides the guidelines
regarding how the RFC 3118 protocol fields should be filled in based
on the DHCP SA.
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4. Buliding DHCP SA
DHCP SA is created at the end of the EAP-based access authentication
process. This section describes extensions to the EAP lower-layers
for exchanging the additional information, and the process of
generating the DHCP SA.
4.1. 802.1X
This work needs to be done in the IEEE and hence this section is
intentionally left blank.
4.2. PPP
A new IPCP configuration option is defined in order to bootstrap DHCP
SA between the PPP peers. Each end of the link must separately
request this option for mutual establishment of DHCP SA. Only one
side sending the option will not produce any state.
The detailed DHCP-SA Configuration Option is presented below.
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 | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Secret ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Nonce Data ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: DHCP SA Configuration Option
Type
o TBD
Length
o >=24
Reserved
o A 16-bit value reserved for future use. It MUST be initialized to
zero by the sender, and ignored by the receiver.
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Secret ID
o 32 bit value that identifies the DHCP Key produced as a result of
the bootstrapping process. This value is determined by the NAS
and sent to the client. The NAS determines this value by randomly
picking a number from the available secret ID pool. If the client
does not request DHCP-SA configuration option, this value is
returned to the available identifiers pool. Otherwise, it is
allocated to the client until the DHCP SA expires. The client
MUST set this field to all 0s in its own request.
Nonce Data (variable length)
o Contains the random data generated by the transmitting entity.
This field contains the Nonce_client value when the option is sent
by client, and the Nonce_NAS value when the option is sent by NAS.
Nonce value MUST be randomly chosen and MUST be at least 128 bits
in size. Nonce values MUST NOT be reused.
4.3. PANA
A new PANA AVP is defined in order to bootstrap DHCP SA. The DHCP-
AVP is included in the PANA-Bind-Request message if PAA (NAS) is
offering DHCP SA bootstrapping service. If the PaC wants to proceed
with creating DHCP SA at the end of the PANA authentication, it MUST
include DHCP-AVP in its PANA-Bind-Answer message.
Absence of this AVP in the PANA-Bind-Request message sent by the PAA
indicates unavailability of this additional service. In that case,
PaC MUST NOT include DHCP-AVP in its response, and PAA MUST ignore
received DHCP-AVP. When this AVP is received by the PaC, it may or
may not include the AVP in its response depending on its desire to
create a DHCP SA. A DHCP SA can be created as soon as each entity
has received and sent one DHCP-AVP.
The detailed DHCP-AVP format is presented below:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AVP Flags | AVP Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Secret ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Nonce Data ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: DHCP AVP Format
AVP Code
o TBD
AVP Flags
o The AVP Flags field is eight bits. The following bits are
assigned:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|V M r r r r r r|
+-+-+-+-+-+-+-+-+
Figure 4: DHCP AVP Flags
M(andatory)
o The 'M' Bit, known as the Mandatory bit, indicates whether support
of the AVP is required. This bit is not set in DHCP-AVP.
V(endor)
o The 'V' bit, known as the Vendor-Specific bit, indicates whether
the optional Vendor-Id field is present in the AVP header. This
bit is not set in DHCP-AVP.
r(eserved)
o These flag bits are reserved for future use, and MUST be set to
zero, and ignored by the receiver.
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AVP Length
o The AVP Length field is three octets, and indicates the number of
octets in this AVP including the AVP Code, AVP Length, AVP Flags,
and AVP data.
Secret ID
o A 32-bit value that identifies the DHCP Key produced as a result
of the bootstrapping process. This value is determined by the PAA
and sent to the PaC. The PAA determines this value by randomly
picking a number from the available secret ID pool. If PaC's
response does not contain DHCP-AVP then this value is returned to
the available identifiers pool. Otherwise, it is allocated to the
PaC until the DHCP SA expires. The PaC MUST set this field to all
0s in its response.
Nonce Data (variable length)
o Contains the random data generated by the transmitting entity.
This field contains the Nonce_client value when the AVP is sent by
PaC, and the Nonce_NAS value when the AVP is sent by PAA. Nonce
value MUST be randomly chosen and MUST be at least 128 bits in
size. Nonce values MUST NOT be reused.
4.4. Computing DHCP SA
The key derivation procedure is reused from IKE [RFC2409]. The
character '|' denotes concatenation.
DHCP Key = HMAC-SHA1(MSK, const | Secret ID | Nonce_client |
Nonce_NAS)
The values have the following meaning:
MSK:
A key derived by the EAP peer and EAP (authentication) server at
the end of the successful network access AAA.
const:
This is a string constant. The value of the const parameter is
set to "EAP RFC 3118 Bootstrapping".
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Secret ID:
The unique identifier of the DHCP key as carried by the EAP lower-
layer protocol extension.
Nonce Client:
This random number is provided by the client and carried by the
EAP lower-layer protocol extension.
Nonce NAS:
This random number is provided by the NAS and carried by the EAP
lower-layer protocol.
DHCP Key:
This session key is 128-bit in length and used as the session key
for securing DHCP messages. Figure 1 of [EAP-Key] refers to this
derived key as a Transient Session Key (TSK).
The lifetime of the DHCP security association has to be limited to
prevent the DHCP server from storing state information indefinitely.
The lifetime of the DHCP SA SHOULD be set equal to the lifetime of
the network access service. The client host, NAS, and the DHCP
server SHOULD be (directly or indirectly) aware of this lifetime at
the end of a network access AAA.
The PaC can at any time trigger a new bootstrapping protocol run to
establish a new security association with the DHCP server. The IP
address lease time SHOULD be limited by the DHCP SA lifetime
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5. Delivering DHCP SA
When the NAS and the DHCP server are not co-located, the DHCP SA
information is carried from the NAS (DHCP relay) to the DHCP server
in a DHCP relay agent info option. This sub-option can be included
along with the RADIUS attributes sub-option that is carried after the
network access authentication.
The format of the DHCP SA sub-option is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SubOpt Code | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Secret ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ DHCP Key +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: DHCP SA Suboption
subopt code:
TBD
Length:
This value is set to 26.
Reserved:
A 16-bit value reserved for future use. It MUST be initialized to
zero by the sender, and ignored by the receiver.
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Secret ID:
This is the 32-bit value assigned by the NAS and used to identify
the DHCP key.
DHCP Key:
128-bit DHCP key computed by the NAS is carried in this field.
Lifetime:
The lifetime of the DHCP SA. This Unsigned32 value contains the
number of seconds remaining before the DHCP SA is considered
expired.
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6. Using DHCP SA
Once the DHCP SA is in place, it is used along with RFC 3118 to
secure the DHCP protocol exchange.
RFC 3118 [RFC3118] defines two security protocols with a newly
defined authentication option:
o Configuration token
o Delayed authentication
The generic format of the authentication option is defined in Section
2 of RFC 3118 [RFC3118] and contains the following fields:
o Code
o Delayed authentication
The value for the Code field of this authentication option is 90.
o Length
The Length field indicates the length of the authentication option
payload.
o Protocol
RFC 3118 [RFC3118] defines two values for the Protocol field - zero
and one. A value of zero indicates the usage of the configuration
token authentication option.
As described in Section 4 of RFC 3118 [RFC3118] the configuration
token only provides weak entity authentication. Hence its usage is
not recommended. This authentication option will not be considered
for the purpose of bootstrapping.
A value of one in the Protocol field in the authentication option
indicates the delayed authentication. The usage of this option is
subsequently assumed in this document.
Since the value for this field is known in advance it does not need
to be negotiated between the DHCP client and DHCP server.
o Algorithm
RFC 3118 [RFC3118] only defines the usage of HMAC-MD5 (value 1 in the
Algorithm field). This document assumes that HMAC-MD5 is used to
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protect DHCP messages.
Since the value for this field is known in advance it does not need
to be negotiated. [Editor's Note: Based on crypto agility
requirements it seems reasonable to consider future algorithm support
as well.]
o Replay Detection Method (RDM)
The value of zero for the RDM name space is assigned to use a
monotonically increasing value.
Since the value for this field is known in advance it does not need
to be negotiated.
o Replay Detection
This field contains the value that is used for replay protection.
This value MUST be monotonically increasing according to the provided
replay detection method. An initial value must, however, be set. In
case of bootstrapping with EAP an initial value of zero is used. The
length of 64 bits (and a start-value of zero) ensures that a sequence
number rollover is very unlikely to occur.
Since the value for this field is known in advance it does not need
to be negotiated.
o Authentication Information
The content of this field depends on the type of message where the
authentication option is used. Section 5.2 of RFC 3118 [RFC3118]
does not provide content for the DHCPDISCOVER and the DHCPINFORM
message. Hence for these messages no additional considerations need
to be specified in this document.
Since the value for this field is known in advance it does not need
to be negotiated.
For a DHCPOFFER, DHCPREQUEST or DHCPACK message the content of the
Authentication Information field is given as:
o Secret ID (32 bits)
o HMAC-MD5 (128 bits)
The Secret ID is chosen by the NAS to prevent collisions. [NOTE: If
there are multiple NASes per DHCP server, this identifier space might
need to be pre-partitioned among the NASes.]
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HMAC-MD5 is the output of the key message digest computation. Note
that not all fields of the DHCP message are protected as described in
RFC 3118 [RFC3118].
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7. Security Considerations
This document describes a mechanism for dynamically establishing a
security association to protect DHCP signaling messages.
If the NAS and the DHCP server are co-located then the session keys
and the security parameters are transferred locally (via an API
call). Some security protocols already exercise similar methodology
to separate functionality.
If the NAS and the DHCP server are not co-located then there is some
similarity to the requirements and issues discussed with the EAP
Keying Framework (see [I-D.ietf-eap-keying]). The DHCP key is a
Transient Session Key (TEK) from [I-D.ietf-eap-keying]. The key is
generated by both the DHCP client and the DHCP relay, and transported
from the DHCP relay to the DHCP server. The DHCP protocol exchange
between the DHCP client and DHCP server is protected using this key.
EAP peer (DHCP client) +-----------------------+ DHCP server
/\ /
/ \ Protocol: EAP /
/ \ lower-layer; /
/ \ Auth: Mutual; /
/ \ Unique key: /
Protocol: EAP; / \ DHCP key /
Auth: Mutual; / \ / Protocol: DHCP, or API;
Unique keys:MSK, / \ / Auth: Mutual;
EMSK / \ / Unique key: DHCP key
/ \ /
/ \ /
Auth. server +----------------------+ Authenticator
Protocol: AAA; (NAS, DHCP relay)
Auth: Mutual;
Unique key:
AAA session key
Figure 6: Keying Architecture
Figure 6 describes the participating entities and the protocols
executed among them. It must be ensured that the derived session key
between the DHCP client and the DHCP server is fresh and unique.
The key transport mechanism, which is used to carry the session key
between the NAS and DHCP server, must provide the following
functionality:
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o Confidentiality protection
o Replay protection
o Integrity protection
Furthermore, it is necessary that the two parties (DHCP server and
the NAS) authorize the establishment of the DHCP security
association.
Below we provide a list of security properties of the suggested
mechanism:
Algorithm independence:
This proposal bootstraps a DHCP security association for RFC 3118
where only a single integrity algorithm (namely HMAC-MD5) is
proposed which is mandatory to implement.
Establish strong, fresh session keys (maintain algorithm
independence):
This scheme relies on EAP methods to provide strong and fresh
session keys for each initial authentication and key exchange
protocol run. Furthermore the key derivation function provided in
Section 4.4 contains random numbers provided by the client and the
NAS which additionally add randomness to the generated key.
Replay protection:
Replay protection is provided at different places. The EAP method
executed between the EAP peer and the EAP server MUST provide a
replay protection mechanism. Additionally random numbers and the
secret ID are included in the key derivation procedure which aim
to provide a fresh and unique session key between the DHCP client
and the DHCP server. Furthermore, the key transport mechanism
between the NAS and the DHCP server must also provide replay
protection (in addition to confidentiality protection). Finally,
the security mechanisms provided in RFC 3118, for which this draft
bootstraps the security association, also provides replay
protection.
Authenticate all parties:
Authentication between the EAP peer and the EAP server is based on
the used EAP method. After a successful authentication and
protocol run, the host and the NAS in the network provide MSK
confirmation either based on the 4-way handshake in IEEE 802.11i
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or based on the protected PANA exchange. DHCP key confirmation
between the DHCP client and server is provided with the first
protected DHCP message exchange.
Perform authorization:
Authorization for network access is provided during the EAP
exchange. The authorization procedure for DHCP bootstrapping is
executed by the NAS before this service is offered to the client.
The NAS might choose not to include DHCP-AVP or DHCP SA
Configuration Option during network access authorization based on
the authorization policies.
Maintain confidentiality of session keys:
The DHCP session keys are only known to the intended parties
(i.e., to the DHCP client, relay, and server). The EAP protocol
itself does not transport keys. The exchanged random numbers
which are incorporated into the key derivation function do not
need to be kept confidential. DHCP relay agent information MUST
be protected using [RFC4014] with non-null IPsec encryption.
Confirm selection of 'best' cipher-suite:
This proposal does not provide confidentiality protection of DHCP
signaling messages. Only a single algorithm is offered for
integrity protection. Hence no algorithm negotiation and
therefore no confirmation of the selection occur.
Uniquely name session keys:
The DHCP SA is uniquely identified using a Secret ID (described in
[RFC3118] and reused in this document).
Compromised NAS and DHCP server:
A compromised NAS may leak the DHCP session key and the EAP
derived session key (e.g., MSK). It will furthermore allow
corruption of the DHCP protocol executed between the hosts and the
DHCP server since NAS either acts as a DHCP relay or a DHCP
server. A compromised NAS may also allow creation of further DHCP
SAs or other known attacks on the DHCP protocol (e.g., address
depletion). A compromised NAS will not be able to modify, replay,
inject DHCP messages which use security associations established
without the EAP-based bootstrapping mechanism (e.g., manually
configured DHCP SAs). On the other hand, a compromised DHCP
server may only leak the DHCP key information. MSK will not be
compromised in this case.
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Bind key to appropriate context:
The key derivation function described in Section 4.4 includes
parameters (such as the secret ID and a constant) which prevents
reuse of the established session key for other purposes.
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8. IANA Considerations
[Editor's Note: A future version of this draft will provide IANA
considerations.]
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9. Open Issues
This document describes a bootstrapping procedure for DHCPv4. The
same procedure could be applied for DHCPv6 but is not described in
this document.
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10. Acknowledegments
We would like to thank Yoshihiro Ohba and Mohan Parthasarathy for
their feedback to this document. Additionally, we would to thank
Ralph Droms, Allison Mankin and Barr Hibbs for their support to
continue this work.
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11. References
11.1. Normative References
[RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
RFC 1661, July 1994.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP
Messages", RFC 3118, June 2001.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)",
RFC 3748, June 2004.
[RFC4014] Droms, R. and J. Schnizlein, "Remote Authentication
Dial-In User Service (RADIUS) Attributes Suboption for the
Dynamic Host Configuration Protocol (DHCP) Relay Agent
Information Option", RFC 4014, February 2005.
11.2. Informative References
[I-D.ietf-dhc-relay-agent-ipsec]
Droms, R., "Authentication of DHCP Relay Agent Options
Using IPsec", draft-ietf-dhc-relay-agent-ipsec-02 (work in
progress), May 2005.
[I-D.ietf-dhc-v4-threat-analysis]
Hibbs, R., "Dynamic Host Configuration Protocol for IPv4
(DHCPv4) Threat Analysis",
draft-ietf-dhc-v4-threat-analysis-03 (work in progress),
June 2006.
[I-D.ietf-eap-keying]
Aboba, B., Simon, D., and P. Eronen, "Extensible
Authentication Protocol (EAP) Key Management Framework",
draft-ietf-eap-keying-22 (work in progress),
November 2007.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.
[RFC5191] Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A.
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Yegin, "Protocol for Carrying Authentication for Network
Access (PANA)", RFC 5191, May 2008.
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Authors' Addresses
Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland
Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
Alper E. Yegin
Samsung
Istanbul,
Turkey
Phone:
Email: a.yegin@partner.samsung.com
Dan Forsberg
Nokia Research Center
P.O. Box 407
FIN-00045
Finland
Phone: +358 50 4839470
Email: dan.forsberg@nokia.com
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