wdiff draft-ietf-csi-proxy-send-01.txt draft-ietf-csi-proxy-send-02.txt

Network
CGA & SEND maintenance Working Group S. Krishnan
Internet-Draft
Group Ericsson
Internet-Draft J. Laganier
Intended status: Standards Track J. Laganier QUALCOMM Inc.
Expires: January 14, September 4, 2010 DoCoMo Euro-Labs M. Bonola
Rome Tor Vergata University
July 13, 2009
A. Garcia-Martinez
UC3M
March 3, 2010

Secure Proxy ND Support for SEND
draft-ietf-csi-proxy-send-01
draft-ietf-csi-proxy-send-02

Abstract

Secure Neighbor Discovery (SEND) specifies a method for securing
Neighbor Discovery (ND) signaling against specific threats. As
defined today, SEND assumes that the node sending a ND message is the
owner of the address from which the message is send, so that it is in
possession of the private key used to generate the digital signature
on the message. This means that the Proxy ND signaling performed by
nodes that do not possess knowledge of the address owner's private
key cannot be secured using SEND. This document extends the current
SEND specification in order to support Proxy ND operation.

Status of this Memo

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Abstract

Secure Neighbor Discovery (SEND) specifies a method for securing
Neighbor Discovery (ND) signaling against specific threats. As
specified today, SEND assumes that the node advertising an address is
the owner Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the address Trust Legal Provisions and is are provided without warranty as
described in possession of the private key used
to generate the digital signature on the message. This means that
the Proxy ND signaling initiated by nodes that do not possess
knowledge of the address owner's private key cannot be secured using
SEND. This document extends the current SEND specification with
support for Proxy ND, the Secure Proxy ND Support for SEND. BSD License.

Table of Contents

1. Requirements notation . . . . . . . . . . . . . . . . . . . . 4 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 5
4. Application Scenarios . Secure Proxy ND Overview . . . . . . . . . . . . . . . . . . . 7
4.1. Scenario 1: RFC 4389 Neighbor Discovery 6
5. Secure Proxy ND Specification . . . . . . . . . . 7
4.2. Scenario 2: Mobile IPv6 . . . . . . 8
5.1. Proxy Signature Option . . . . . . . . . . . . . . . . . . 8
4.3. Scenario 3: Proxy Mobile IPv6
5.2. Modified SEND processing rules . . . . . . . . . . . . . . 10
5. Secure Proxy ND Overview
5.2.1. Processing rules for senders . . . . . . . . . . . . . 10
5.2.2. Processing rules for receivers . . . . . . . . . . . . 11
5.3. Proxying Link-Local Addresses . . . . . . . . . . . . . . 12
6. Secure Proxy ND Specification Application Scenarios . . . . . . . . . . . . . . . . . . . 14
6.1. Proxy Signature Option . 13
6.1. Scenario 1: Mobile IPv6 . . . . . . . . . . . . . . . . . 14 13
6.2. Modified SEND processing rules Scenario 2: Proxy Mobile IPv6 . . . . . . . . . . . . . . 16
6.2.1. Processing rules for senders 15
6.3. Scenario 3: RFC 4389 Neighbor Discovery Proxy . . . . . . 17
7. Backward Compatibility with RFC3971 nodes and non-SEND
nodes . . . . . . . . . . 16
6.2.2. Processing rules for receivers . . . . . . . . . . . . 17
7. . . . . . . 20
7.1. Backward Compatibility with legacy SEND RFC3971 nodes . . . . . . . . 20
7.2. Backward Compatibility with non-SEND nodes . . . . . . . . 18 20
8. Security Considerations . . . . . . . . . . . . . . . . . . . 19 23
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 24
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
10.1. Normative References . . . . . . . . . . . . . . . . . . . 25
10.2. Informative References . . 21
Authors' Addresses . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . 22

1. Requirements notation

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", . . . . . . . . . . . . . . . . 26

1. Requirements notation

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 [RFC2119].

2. Introduction

Secure Neighbor Discovery (SEND) [RFC3971] specifies a method for
securing
neighbor discovery Neighbor Discovery (ND) signaling [RFC4861] against specific
threats. As
specified defined today, SEND assumes that the node advertising an address sending a ND
message is the owner of the address and from which the message is sent,
so that it is in possession of the private key used to generate the
digital signature on the message. This means that the Proxy ND
signaling initiated performed by nodes that do not possess knowledge of the
address owner's private key cannot be secured using SEND.

This document extends the current SEND specification with support for
Proxy ND. From this point on we refer to such extension as "Secure
Proxy ND Support for SEND".

3. Terminology

Secure Proxy ND

A node authorized to either modify or generate a SEND message
without knowing the private key related to the source address of
the ICMPv6 ND message.

Proxied IPv6 address

An IPv6 address that doesn't does not belong to the Secure Proxy ND and
for which the Secure Proxy ND is advertising.

4. Application Scenarios

In performing advertisements.

Non-SEND node

An IPv6 node that does not implement the SEND [RFC3971]
specification but uses only the ND protocol defined in [RFC4861]
and [RFC4862], without security.

RFC3971 node

An IPv6 node that does not implement the specification defined in
this section we provide three different application scenarios document for
which Secure Proxy ND support, but uses only the ICMPv6 Neighbor Discovery signaling cannot be secured by
using SEND
specification as defined in [RFC3971].

SPND node

An IPv6 node that implements the current specification defined in this
document for Secure Proxy ND support.

4. Secure Proxy ND Overview

The original SEND specification.

Either specification [RFC3971] has implicitly assumed that
only the node sending a ND message is the owner of the entities described in address from
which the following three scenarios,
(i.e.: message is sent. This assumption does not allow proxying
of ND Proxy, MIPv6 Home Agent, PMIPv6 Mobile Access Gateway) can
be consider as messages since the advertiser is required to generate a valid
RSA Signature option, which in turns requires possession of the
public-private key pair that was used to generate a CGA, or that was
associated to a router certificate.

To be able to separate the roles of ownership and advertiser the
following extensions to the SEND protocol are defined:

o A Secure Proxy ND.

4.1. Scenario 1: RFC 4389 Neighbor Discovery Proxy

Link 1 Link 2

Host A ND Proxy (P) Host B
| | |
| SRC = certificate, which is a certificate authorizing
an entity to act as an ND proxy. It is a X509v3 certificate in
which the purpose for which the certificate is issued has been
specified explicitly as described in a companion document
[I-D.ietf-csi-send-cert]. Briefly, a KeyPurposeID value is
defined for authorizing proxies. The inclusion of the proxy
authorization value allows the certificate owner to perform
proxying of SEND messages for a range of addresses indicated in
the same certificate. This certificate can be exchanged as a
result of the Authorization Delegation Discovery process defined
in [RFC3971].

o A | |
| DST = solicited_node(B) | |
| ICMPv6 NS | |
| TARGET = B | |
| SLLAO = B_LL | |
|------------------------->| |
| | SRC = new Neighbor Discovery option called Proxy Signature option
(PSO). This option contains the hash value of the public key of
the proxy, and the digital signature of the SEND message computed
with the private key of the proxy. The hash of the public key of
the proxy is computed over the public key contained in the Secure
Proxy ND's certificate. When a ND message contains a PSO, it MUST
NOT contain CGA and RSA Signature options. This option can be
appended to any ND message: NA, NS, RS, RA and Redirect.

o A modification of the SEND processing rules for all ND messages:
NA, NS, RS, RA, and Redirect. When any of these messages is
received with a valid Proxy Signature option, it is considered as
secure.

These extensions are applied in the following way:

o A Secure Proxy ND which proxies ND messages on behalf of a node
can use the PSO option to protect the proxied messages. This
Secure Proxy ND becomes part of the trusted infrastructure just
like a SEND router.

o In order to allow nodes to successfully validate secured proxied
messages, the nodes must know the Secure Proxy ND certificate (in
the format described in [I-D.ietf-csi-send-cert]) and must apply
the modified processing rules specified in this document. We call
this nodes 'SPND nodes'. Note that the rules for generating ND
messages in SPND nodes do not change, so these nodes behave as
defined in [RFC3971] for sending ND messages.

o To allow SPND nodes to know the certificate path required to
validate the public key of the proxy, devices responding to CPS
(Certification Path Solicitation) messages with CPA (Certification
Path Advertisements) as defined in Section 6 of SEND specification
[RFC3971] must handle the certificate format specified in
[I-D.ietf-csi-send-cert], and must be configured with the
appropriate certification path.

The proposed approach resolves the incompatibilities between the
current SEND specification and the application scenarios described in
Section 6.

5. Secure Proxy ND Specification

A Secure Proxy ND performs all the operation described in the SEND
specification [RFC3971] with the addition of new processing rules to
ensure that the receiving node can differentiate between an
authorized proxy generating or forwarding a SEND message for a
proxied address, and a malicious node doing the same.

This is accomplished by signing the message with the public key of
the authorized Secure Proxy ND. The signature of the ND Proxy is
included in a new option called Proxy Signature option (PSO). The
signature is performed over all the NDP options present in the
message and the PSO is appended as the last option in the message.

5.1. Proxy Signature Option

The Proxy Signature option allows public key-based signatures to be
attached to NDP messages. The format of the PSO is described in the
following diagram:

Figure 1: PSO layout

Type

TBA

Length

The length of the option (including the Type, Length, Reserved,
Key Hash, Digital Signature, and Padding fields) in units of 8
octets.

Reserved

A 11-bit field reserved for future use. The value MUST be
initialized to zero by the sender, and MUST be ignored by the
receiver.

Key Hash

A 128-bit field containing the most significant (leftmost) 128
bits of a SHA-1 [SHA1] hash of the public key used for
constructing the signature. Its purpose is to associate the
signature to a particular key known by the receiver. Such a key
MUST be the same one within the corresponding Secure Proxy ND's
certificate.

Digital Signature

A variable-length field containing a PKCS#1 v1.5 signature,
constructed by using the sender's private key over the following
sequence of octets:

1. The 128-bit CGA Message Type tag [RFC3972] value for Secure
Proxy ND, 0x09F5 2BE5 3B62 4C76 CB96 4E7F CDC9 2804 (The tag
value has been generated randomly by the editor of this
specification).

2. The 128-bit Source Address field from the IP header.

3. The 128-bit Destination Address field from the IP header.

4. The 8-bit Type, 8-bit Code, and 16-bit Checksum fields from
the ICMP header.

5. The NDP message header, starting from the octet after the ICMP
Checksum field and continuing up to but not including NDP
options.

6. All NDP options preceding the Proxy Signature option.

The signature value is computed with the RSASSA-PKCS1-v1_5
algorithm and SHA-1 hash, as defined in [RSA].

This field starts after the Key Hash field. The length of the
Digital Signature field is determined by the ASN.1 BER coding of
the PKCS#1 v1.5 signature.

Padding

This variable-length field contains padding. The length of the
padding field is determined by the length of the Proxy Signature
Option minus the length of the other fields.

5.2. Modified SEND processing rules

The modifications described in the following section applies when a
SEND message contains the Proxy Signature option (PSO), i.e. the
message was sent by a Secure Proxy ND.

This specification modifies the sender and receiver processing rules
for the CGA and RSA options defined in the SEND specification
[RFC3971].

5.2.1. Processing rules for senders

A |
| | ICMPv6 NA |
| | TARGET = B |
| | TLLAO = B_LL |
| |<-------------------------|
| SRC = B | |
| DST = message sent by a Secure Proxy ND for a proxied address MUST
contain a Proxy Signature option (PSO) and MUST NOT contain CGA and
RSA Signature options.

A | |
| ICMPv6 NA | |
| TARGET = B | |
| TLLAO = B_LL | |
|<-------------------------| |
| | |

Figure 1: Secure Proxy ND operations sending a SEND message with the PSO Signature
option MUST construct the message as follows:

1. The SEND message is constructed without the PSO as follows:

A. If the Secure Proxy ND is locally generating the SEND message
for a proxied address, the message is constructed as
described in Neighbor Discovery for IP version 6
specification [RFC4861].

B. If the Secure Proxy ND is forwarding a SEND message, first
the authenticity of the intercepted message is verified as
specified in SEND specification [RFC3971], Section 5. If the
SEND message is valid, any CGA or RSA option MUST be removed
from the message. The Neighbor Discovery (ND) intercepted message is finally
modified as described in Section 4 of the ND Proxy
specification [RFC4389] provides [RFC4389].

C. If the Secure Proxy ND is forwarding a
method by which multiple link layer segments are bridged into SEND message already
containing a
single segment and specifies PSO, first the authenticity of the intercepted
message is verified as specified in Section 6.2.2 of this
draft. If the SEND message is valid, the original PSO MUST
be removed from the message. The intercepted message is
finally modified as described in Section 4 of the IP-layer support that enables
bridging under these circumstances.

A ND Proxy shall parse any IPv6 packet it receives on a proxy
interface
specification[RFC4389].

2. Timestamp and Nonce options are included according to check whether it contains one of the following ICMPv6
messages: Neighbor Solicitation (NS), Neighbor Advertisement (NA),
Router Advertisement, or Redirect. Since each of these messages
contains rules
specified in SEND [RFC3971]. The value in the Timestamp option
MUST be generated by the Proxy. If the proxy is forwarding a link-layer address which might not
message, the Nonce value in the proxied message MUST be valid on another
segment, the ND same
as in the forwarded message.

3. The Proxy Signature option is added as the last option in the
message.

4. The data is signed as explained in Section 5.1.

5.2.2. Processing rules for receivers

Any SEND message without a Proxy Signature option MUST be treated as
specified in the SEND specification [RFC3971].

A SEND message including a Proxy proxies these packets Signature option MUST be processed
as follows, specified below:

1. The receiver MUST ignore any RSA and CGA options, as
illustrated in Figure 1:

1. well as any
options that might come after the first PSO. The source link layer address will be options are
ignored for both signature verification and NDP processing
purposes.

2. The Key Hash field MUST indicate the address use of a known public key.
A valid certification path (see [RFC3971] Section 6.3) between
the outgoing
interface.

2. The destination link layer address will be receiver's trust anchor and the address in sender's public key MUST be
known. The Secure Proxy ND's X509v3 certificate MUST contain a
extended key usage extension including the
neighbor entry corresponding to KeyPurposeId value for
the destination IPv6 address. proxy authorization.

3. A link layer address within The Digital Signature field MUST have correct encoding.

4. The Digital Signature verification MUST show that the payload (that is, signature
has been calculated as specified in Section 5.1.

5. Timestamp and Nonce options MUST be processed as specified in
[RFC3971] Section 5.3.4, except for replacing 'RSA Signature
option' by 'PSO option'.

6. Messages with the Override bit [RFC4861] set should override an
existing cache entry regardless if it was created as a Source
Local Link Address result of
a RSA Signature option - SLLAO, or a Target Local Link Address PSO option - TLLAO) validation. When it is substituted with
not set the advertisement will not update a cached link-layer
address created securily by means of RSA Signature option or PSO
option validation.

Messages that do not pass all the
outgoing interface.

Moreover, when any other IPv6 unicast packet is received above tests MUST be silently
discarded if the host has been configured to accept only secured ND
messages.

5.3. Proxying Link-Local Addresses

Secure Neighbor Discovery [RFC3971] relies on certificates to prove
that routers are authorized to announce a proxy
interface, if it is certain prefix. However,
Neighbor Discovery [RFC4861] states that router does not locally destined then announce the
Link-Local prefix (fe80::/64). Hence, it is forwarded
unchanged (other than using not required for a new link-layer header) SEND
certificate to the proxy
interface for which the next hop hold a X.509 IP address appears in extensions that authorizes the neighbor
cache. If no neighbor cache entry is present,
fe80::/64 prefix. Some scenarios ([RFC4389], [RFC5213]) impose that
the Secure ND proxy should
queue provides proxying function for the packet and initiate Link-Local
address of a Neighbor Discovery signalling as if
the ICMPv6 NS message were locally generated.

A node. When Secure ND proxy cannot protect proxied ND messages since protection functionality on a Link-
Local address is required, either a list of an
ND message as per link-local addresses, or
the current SEND specification requires knowledge
of fe80::/64 prefix MUST be explicitly authorized to be proxied in
the private key of each node corresponding certificate.

6. Application Scenarios

In this section we describe three different application scenarios for
which it Secure Proxy ND Support for SEND can be applied. Note that the
particular way in which Secure Proxy ND support is generating or
forwarding a applied (which ND message
messages are proxied, in which directions, how the interaction with
non-SEND hosts and RFC3971 hosts is handled, etc.) largely depends on
the bridged link layer segments.

4.2. particular scenario considered. In the first two scenarios
presented below, ND messages are synthesized on behalf of off-link
nodes. In the third one, ND messages are generated in reaction to ND
messages being received by other interfaces of the proxied node.

6.1. Scenario 2: 1: Mobile IPv6

The description of the problems for deploying SEND in this scenario
can be found in [I-D.ietf-csi-sndp-prob].

The Mobile IPv6 protocol (MIPv6) [RFC3775] allows a mobile node Mobile Node (MN)
to move from one link to another while maintaining reachability at a
stable address, the so-called MN's home address (HoA.) Home Address (HoA). When a mobile node MN
attaches to a foreign network, all the packets sent to the MN's HoA
and forwarded on the home link
by a correspondent node Correspondent Node (CN) on the home link, or a
router router, are
intercepted by the home agent Home Agent (HA) on that home link, encapsulated
and tunneled to the mobile node's MN's registered care-of
address (CoA.) Care-of Address (CoA).

The HA intercepts these packets by being acting as a Neighbor Discovery ND proxy for this MN.
Lets assume that the nodes in the home link use SEND. When a Neighbor Solicitation (NS) secured
NS is intercepted on the home link, the home agent HA checks the validity of the
received message according to the rules stated in [RFC3971]. If the
message is valid, it checks if the Target address within the NS
matches with any of the MN's Home Address in the Binding Cache and if
so, it replies with a Neighbor Advertisement (NA) containing constructed as
described in [RFC4861], so it contains its own link layer address
(HA_LL) as the Target Link Layer Address Option (TLLAO), as illustrated in Figure 2.

Node (N) Home Agent (HA) Mobile Node (MN)
on Home Link on Home Link on Foreign Link
| | |
| SRC = N | |
| DST = solicited_node(MN) | |
| ICMPv6 NS | |
| TARGET = MN | |
| SLLAO = N_LL | |
|------------------------->| |
| | |
| SRC = MN | |
| DST = N | |
| ICMPv6 NA | |
| TARGET = MN | |
| TLLAO = HA_LL | |
|<-------------------------| |
| | |
| traffic | |
| dest= MN HoA | |
|------------------------->| |
| | |
| | tunnelled traffic |
| | dest= MN CoA |
| |------------------------->|
| | |

Figure 2: Proxy ND role of the Home agent in MIPv6

It is not possible to apply the current SEND specification to protect
the NA message issued by the HA. To generate an ICMPv6 NA with a
valid CGA PSO
option and signing the corresponding RSA Signature option, message, added as the HA
needs knowledge last option of the private key related to the MN's
Cryptographically Generated Address (CGA.) Any ICMPv6 NA without a
valid CGA and RSA signature option is to be treated as insecure by a
SEND receiver.

4.3. Scenario 3: Proxy Mobile IPv6

MN new MAG LMA
| | |
MN Attached message.

Node (N) Home Agent (HA) Mobile Node (MN)
on Home Link on Home Link on Foreign Link
| | |
| SRC = N | | MN Attached Event from MN/Network
| DST = solicited_node(MN) | |
|
|--- ICMPv6 RS ------->| |
| | |
| |--- PBU ------------->|
| | |
| | Accept PBU
| | |
| |<------------- PBA ---|
| | | NS | Accept PBA |
| TARGET = MN | |
| |==== Bi-Dir Tunnel ===| SLLAO = N_LL | |
|
|<------ ICMPv6 RA ----| [CGA] | |
| RSA signature | |
|------------------------->| |
| | |
|

Figure 3: Mobile node's handover in PMIPv6

Proxy Mobile IPv6 [I-D.ietf-netlmm-proxymip6] is a network-based
mobility management protocol that provides an IP mobility management
support for MNs without requiring MNs being involved in the mobility
related signaling. The IP mobility management is totally hidden to
the MN in a Proxy Mobile IPv6 domain and is performed by two
functional entities: the Local Mobility Anchor (LMA) and the Mobile
Access Gateway (MAG.)

When the MN connects to a new access link it will send a multicast
ICMPv6 Router Solicitation (RS.) The MAG on the new access link,
upon detecting the MN's attachment, will signal the LMA for updating
the binding state of the MN (Proxy Binding Update - PBU) and once the
signaling is complete (Proxy Binding Ack - PBA - received), it will
reply to the MN with a ICMPv6 Router Advertisement (RA) containing
its home network prefix(es) that were assigned to that mobility
session, making the MN believe it is still on the same link and not
triggering the IPv6 address reconfiguration (figure Figure 3.)
To avoid potential link-local address collisions between the MAG and
the SRC = HA | |
| DST = N | |
| ICMPv6 NA | |
| TARGET = MN after a handoff to a new link, the Proxy Mobile IPv6
specification requires the MAG's link-local address configured on the
link to which the | |
| TLLAO = HA_LL | |
| PSO signature | |
|<-------------------------| |
| | |
| traffic | |
| dest= MN is attached to be generated once by the LMA when
the HoA | |
|------------------------->| |
| | |
| | tunnelled traffic |
| | dest= MN first attach to a PMIPv6 domain, and to be provided to the new
MN's serving MAG after each handoff. Thus, from the MN's point of
view, the MAG's link-local address remains constant for the duration CoA |
| |------------------------->|
| | |

Figure 2: Proxy ND role of that MN's session.

The approach described above and the current SEND specification are
incompatible since:

Sharing Home agent in MIPv6

A node receiving the same link-local address on different MAGs would
require all MAGs of a PMIPv6 domain to construct NA containing the CGA and PSO (e.g.: the
RSA Signature option with CN in the same public-private key pair, which
is not acceptable from home
link, or a security point router) must have a certificate of view.

Using different public-private key pairs on different MAGs would
mean different MAGs use different CGAs as link-local address.
Thus the serving MAG's link-local address changes after each
handoff public key of the MN which is contradiction with the way MAG link-
local address assignment occurs in
HA acting as a PMIPv6 domain.

5. Secure Proxy ND Overview

The original SEND specification [RFC3971] has implicitly assumed that
the owner of the address was ND. To do so, a certificate for the one who was advertising HA
could be made available through the prefix.
This assumption does not allow proxying of a CGA based address as Authorization Delegation
Discovery process [RFC3971] performed at the
receiver requires home link, i.e. the advertiser
devices responding to generate a valid CGA and RSA
Signature option, which CPS messages should be configured to include in turns requires possession
CPA messages information about the HA certificate.

The Override bit of the public-
private key pair that was NA message is used to generate the CGA.

This specification explicitly separates control which messages
should prevail each case: the roles of ownership and
advertiser message generated by extending the SEND protocol as follows:

o A certificate authorizing an entity proxy once the
MN moves from the home network, or the MN if it come back to act the home
link, as an ND proxy is
introduced. This is achieved via specifying explicitly defined in the
X509v3 certificate the purpose MIPv6 specification [RFC3775]

6.2. Scenario 2: Proxy Mobile IPv6

Proxy Mobile IPv6 [RFC5213] is a network-based mobility management
protocol that provides an IP mobility management support for which MNs
without requiring MNs being involved in the certificate mobility related
signaling. The IP mobility management is
issued, as described totally hidden to the MN in
a companion document
[I-D.krishnan-cgaext-send-cert-eku]. Briefly, Proxy Mobile IPv6 domain and is performed by two KeyPurposeID
values are defined: one for authorizing routers, functional
entities: the Local Mobility Anchor (LMA) and one for
authorizing proxies. The inclusion of the proxy authorization
value allows Mobile Access
Gateway (MAG).

When the certificate owner MN connects to perform proxying of SEND
messages for a set of prefixes indicated in new access link it will send a multicast
ICMPv6 Router Solicitation (RS). The MAG on the same certificate.

o A new option called Proxy Signature option (PSO) is defined. This
option contains access link,
upon detecting the MN's attachment, will signal the LMA for updating
the key hash value binding state of the Secure Proxy ND's public
key MN (Proxy Binding Update - PBU) and once the digital signature computed over
signaling is complete (it receives a Proxy Binding Ack - PBA), it
will reply to the SEND message. The
key has value MN with a ICMPv6 Router Advertisement (RA)
containing the home network prefix(es) that were assigned to that
mobility session, making the MN believe it is computed over still on the public key within same link
and not triggering the Secure
Proxy ND's certificate.

o The SEND processing rules are modified for all Neighbor Discovery
messages: NA, NS, RS, RA, IPv6 address reconfiguration (figure
Figure 3).

MN new MAG LMA
| | |
MN Attached | |
| | |
| MN Attached Event from MN/Network |
| | |
| SRC = MN | |
| DST = all-routers | |
| ICMPv6 RS | |
| [CGA] | |
| RSA signature | |
|--------------------->| |
| | |
| |--- PBU ------------->|
| | |
| | Accept PBU
| | |
| |<------------- PBA ---|
| | |
| Accept PBA |
| | |
| |==== Bi-Dir Tunnel ===|
| | |
| SRC = MAG4MN | |
| DST = MN | |
| ICMPv6 RA | |
| SLL = MAG_LL | |
| PSO | |
|<---------------------| |
| | |
| | |
| | |

Figure 3: Mobile node's handover in PMIPv6

To avoid potential link-local address collisions between the MAG and Redirect. When any of these
messages is received with
the MN after a handoff to a valid new link, the Proxy Signature option, it Mobile IPv6
specification requires the MAG's link-local address configured on the
link to which the MN is
considered as secure even if it doesn't contain attached to, to be generated once by the LMA
when the MN first attach to a CGA option.

The Secure Proxy ND becomes part PMIPv6 domain, and to be provided to
the new MN's serving MAG after each handoff. Thus, from the MN's
point of view, the trusted infrastructure just
like a SEND router. The Secure Proxy ND is MAG's link-local address remains constant for the
duration of that MN's session.

Each MAG can be granted a certificate per each link-local address
expected by any MN that specifies the range of addresses for which it is allowed could attach to
perform proxying the link. However, the use
of SEND messages. Hosts Secure Proxy ND can use greatly reduce the same process number of certificates
needed. In this case, each MAG is configured to
discover the certification path between act as a proxy and one by
means of the host's a certification path from a trust anchors as anchor associated to the one defined for routers in Section 6 of SEND
specification [RFC3971].

The proposed approach resolves
PMIPv6 domain, authorizing each MAG to proxy securely ND messages.

When a secured RS message is issued by the incompatibilities between MN, the
current SEND specification and MAG checks its
validity according to the application scenarios described rules stated in
Section 4. Since SEND messages containing [RFC3971]. If the message
is valid, it replies with a Proxy Signature option
are not required RA with source address equal to carry a CGA option, the IPv6 source MAG
link-local address is no
longer cryptographically bound associated to the signature, and MN in this PMIPv6 domain and its
own link layer address as Source link-layer address, with the PSO
option signing the message, added as the sender last option of the message.

When the MN receives this message, it may issue a
Neighbor Discovery CPS message is not required in
order to be the owner of the
claimed address. Thus, obtain the Secure Proxy ND is able certification path associated to either forward
and generate SEND messages for a proxied address within the set public key
of
prefixes for which it is authorized.

6. Secure Proxy ND Specification

A Secure ND Proxy performs all the operation described in the SEND
specification [RFC3971] PSO (or may have this certification path already available).
The MN node must be configured with a trust anchor related with the addition of new processing rules
MAG's certificate. The MAG (or other device) could be configured to
ensure that the receiving node can differentiate between an
authorized proxy generating or forwarding
provide its certification path in a SEND CPS message for as a
proxied address, and response to a malicious node doing the same.

This is accomplished by signing the
CPA message with issued by the public key of MN. With this information, the authorized Secure Proxy ND. The signature of MN can
validate the neighbor
discovery proxy is included in a new option called Proxy Signature
option (PSO.) The signature is performed over all RS information, and use the NDP options
present in same link-local address to
access to the message MAG.

The MAG will intercept secured NS messages and reply with NA messages
containing its own link layer address as the Target Link Layer
Address Option (TLLAO), with a PSO is appended option signing the message, added
as the last option in of the message.

6.1. Proxy Signature Option The Proxy Signature option allows public key-based signatures to be
attached to NDP same applies for Redirect
messages.

6.3. Scenario 3: RFC 4389 Neighbor Discovery Proxy

The format description of the PSO is described problems for deploying SEND in this scenario
can be found in the
following diagram:

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 [I-D.ietf-csi-sndp-prob].

Link 1 Link 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Host A ND Proxy (P) Host B
| Type | Length | Reserved
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ SRC = A | |
| Key Hash DST = solicited_node(B) | |
| ICMPv6 NS | |
| TARGET = B |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
|
. .
. Digital Signature .
. . SLLAO = A_LL | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|------------------------->| |
| | SRC = A |
| | DST = solicited_node(B) |
| | ICMPv6 NS |
| | TARGET = B |
| | SLLAO = P_LL |
| |------------------------->|
| | |
| | SRC = B |
| | DST = A |
| | ICMPv6 NA |
| | TARGET = B |
| | TLLAO = B_LL |
| |<-------------------------|
| SRC = B | |
| DST = A | |
| ICMPv6 NA | |
| TARGET = B | |
| TLLAO = P_LL | |
|<-------------------------| |
|
. .
. Padding .
. . | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: PSO layout

Type

TBA

Length Proxy ND operations

The Neighbor Discovery (ND) Proxy specification [RFC4389] provides a
method by which multiple link layer segments are bridged into a
single segment and specifies the IP-layer support that enables
bridging under these circumstances.

A Secure ND Proxy shall parse any IPv6 packet it receives on a proxy
interface to check whether it contains one of the following secured
ICMPv6 messages: NS, NA, RA, or Redirect. The length Secure ND Proxy MUST
verify the authenticity of the option (including received ND message, according to
[RFC3971]. If the Type, Length, Reserved,
Key Hash, Digital Signature, and Padding fields) in units of 8
octets.

Reserved

A 16-bit field reserved for future use. SEND message is valid, then it proxied the
original message with the following changes:

1. The value MUST be
initialized message is processed according to zero by [RFC4389]. This includes
changing the sender, and MUST source link layer address will be ignored by the
receiver.

Key Hash

A 128-bit field containing the most significant (leftmost) 128
bits of a SHA-1 [SHA1] hash address of the public key used for
constructing
outgoing interface, maintaining the signature. Its purpose is to associate destination link layer
address as the
signature to a particular key known by address in the receiver. Such a key
MUST be neighbor entry corresponding to the same one
destination IPv6 address, etc. In particular any link layer
address within the Secure Proxy ND's certificate.

Digital Signature

A variable-length field containing payload (that is, in a PKCS#1 v1.5 signature,
constructed by using the sender's private key over Source Local Link
Address option - SLLAO, or a Target Local Link Address option -
TLLAO) is substituted with the following
sequence link-layer address of octets:

1. The 128-bit CGA Message Type tag [RFC3972] value for Secure
Proxy ND, 0x09F5 2BE5 3B62 4C76 CB96 4E7F CDC9 2804 (The tag
value has been generated randomly by the editor of this
specification.) outgoing
interface.

2. The 128-bit Source Address field from the IP header. Any CGA or RSA option is removed.

3. If a Nonce option existed in the original message, its value is
preserved in the proxied message. The 128-bit Destination Address field from Timestamp is generated by
the IP header. proxy.

4. The 8-bit Type, 8-bit Code, and 16-bit Checksum fields from PSO option is added as the ICMP header.

5. The NDP message header, starting from last option in the octet after message,
signing all the ICMP
Checksum field and continuing up to but information contained so far in the message.

Moreover, when any other IPv6 unicast packet is received on a proxy
interface, if it is not including NDP
options.

6. All NDP options preceding locally destined then it is forwarded
unchanged (other than using a new link-layer header) to the Proxy Signature option.

The signature value proxy
interface for which the next hop address appears in the neighbor
cache. If no neighbor cache entry is computed with present, the RSASSA-PKCS1-v1_5
algorithm ND proxy should
queue the packet and SHA-1 hash, initiate a Neighbor Discovery signalling as defined if
the ICMPv6 NS message were locally generated.

In order to deploy this scenario, nodes in [RSA].

This field starts after proxied segments MUST know
the Key Hash field. The length of certificate authorizing proxy operation. To do so it could be
required to configure at least one device per each proxied segment
(may be the
Digital Signature field is determined by proxy itself) to propagate the length required certification
path to authorize proxy operation by means of a CPS/CPA exchange.

While more robust mechanisms could be developed for securing the RSA
Signature option minus
scenario described in [RFC4389], if hosts have been upgraded to apply
the length rules stated in Section 5.2.2, for example, to benefit from
secure support for other scenarios, the application of this mechanism
is straighforward.

7. Backward Compatibility with RFC3971 nodes and non-SEND nodes

In this section we discuss the interaction of Secure Proxy ND nodes
and SPND nodes with RFC3971 nodes and non-SEND nodes.

7.1. Backward Compatibility with RFC3971 nodes

RFC3971 nodes, i.e. SEND nodes not compliant with the other fields (including modifications
required in Section 5 cannot interpret correctly a PSO option
received in a proxied ND message. These SEND nodes silently discard
the variable length Pad field.)

Padding

This variable-length field contains padding, PSO option, as specified in [RFC4861] for any unknown option. As
a result, these messages will be treated as many bytes long unsecured as
remain after the end described in
Section 8 "Transitions Issues" of the signature.

6.2. Modified SEND processing rules

The modifications described specification [RFC3971].

When RFC3971 nodes and SPND nodes exchange ND messages (without proxy
intervention), in either direction, messages are generated according
to the following section applies when a SEND message contains specification [RFC3971], so these nodes interoperate
seamlessly.

In the Proxy Signature option (PSO), i.e. scenarios in which the
message was sent proxy translates ND messages, the
messages to translate can either be originated in a RFC3971 node or
in an SPND node, without interoperability issues.

7.2. Backward Compatibility with non-SEND nodes

Plain ND nodes receiving NDP packets silently discard PSO options, as
specified in [RFC4861] for any unknown option. Therefore, these node
interpret messages proxied by a Secure Proxy ND.

This specification modifies the sender ND as any other ND
message.

When non-SEND nodes and receiver processing rules
for the following options defined SPND nodes exchange ND messages (without
proxy intervention), in either direction, the SEND specification
[RFC3971]: CGA option, RSA option.

6.2.1. Processing rules specified in
section 8 of [RFC3971] apply.

A secure Proxy ND SHOULD support the use of secured and unsecured NDP
messages at the same time, although it MAY have a configuration that
causes not to perform proxing for senders unsecured NDP messages. A ICMPv6 message sent secure
Proxy ND MAY also have a configuration option whereby it disables
secure ND proxying completely. This configuration SHOULD be switched
off by default, that is SEND is used. In the next paragraphs we
discuss the recommended behavior of the Secure Proxy ND regarding to
which protection level provide to proxied messages in a mixed
scenario involving SPND/RFC3971 nodes and non-SEND nodes. In
particular, two different situations occur depending on if the
proxied nodes are RFC3971 or SPND, or if they are non-SEND nodes.

As a rule of thumb, the Secure Proxy ND should only generate PSO
options for a proxied address MUST
contain a Proxy Signature option (PSO) and MUST NOT contain CGA and
RSA Signature options.

A Secure Proxy ND sending a nodes which have SEND message with capabilities (i.e. that they could
use SEND to defend their messages if being in the PSO Signature
option MUST construct same link than the message as follows:

1. The SEND message
proxy, either RFC3971 nodes or SPND nodes). This is constructed without relevant to
allow nodes preferring secured information over unsecured one, and
for executing the PSO DAD procedure, as follow:

A. If specified in [RFC3971].
Therefore, the Secure Proxy ND is locally generating SHOULD generate messages containing
the SEND message PSO option for a proxied address, SPND and RFC3971 hosts, and SHOULD NOT generate
messages containing the message is constructed as
described in Neighbor Discovery PSO option for IP version 6
specification [RFC4861].

B. If the non-SEND nodes. Note that ND
advertisements in response to solicitations generated by a Secure
Proxy ND is forwarding a SEND message, first must be secured or not according to the authenticity previous
considerations (i.e. to the nature of the intercepted message is verified as
specified in SEND specification [RFC3971] Section 5. If proxied node), and not
according to the
SEND message is valid, any CGA secure or RSA option MUST be removed
from unsecure nature of the solicitation
message. The intercepted message is finally
modified as described in Section 4 of

To apply this rule, we have to consider that depending on the
application scenario the proxy may translate ND Proxy
specification [RFC4389].

2. The Proxy Signature option is added as messages generated by
a node or synthetise ND messages on behalf of a node.

o For ND translated messages, the last option rule can be easily applied: only
messages validated in the
message.

3. The data is signed as explained in Section 6.1.

6.2.2. Processing rules for receivers

Any SEND message without a Secure Proxy Signature option ND according to the SEND
specification [RFC3971] MUST be treated as
specified proxied securely by the inclusion
of a PSO option. Unsecured ND messages could be proxied if
unsecured operation is enabled in the SEND specification [RFC3971].

A SEND proxy, but the message including a
generated by the Secure Proxy Signature option ND for the received message MUST NOT
include a PSO option.

o For ND messages synthesised on behalf of remote nodes, different
considerations should be processed
as specified below:

1. The receiver MUST ignore any RSA and CGA options, as well as any
options that might come after made according to the first PSO. The options are
ignored particular
application scenario.

* For MIPv6, if the MN can return to the home link, it is
required for both signature verification and NDP processing
purposes.

2. The Key Hash field MUST indicate the proxy to know if the node could use of a known public key. SEND to
defend its address or not. A valid certification path (see [RFC3971] Section 6.3) mismatch between the receiver's trust anchor proxy and the sender's public key MUST be
known. The Secure Proxy ND's X509v3 certificate MUST contain a
extended key usage extension
proxied node behavior regarding to SEND operation would result
in unaproppriate operation. A HA including the KeyPurposeId value PSO option for
proxying a non-SEND MN would make ND messages sent by the proxy authorization.

3. The Digital Signature field MUST
to be more preferred than ND message of the non-SEND MN if the
MN returns to the home link (even if the proxied messages have correct encoding and MUST
NOT exceed
the length of Override bit set to 1). Not using the PSO option for a
RFC3971 or SPND MN would make more vulnerable the address in
the home link when the MN is away than when it is in the home
link (and would defeat the purpose of the Secure Proxy ND
mechanism). Therefore, in this case the HA must know the SEND
capabilities of the MN.

* We can state the same for the Proxy Signature option minus Mobile IPv6 scenario as for
the
Padding.

4. The Digital Signature verification MUST show MIPv6 scenario. Note that the signature a node moving from a link in
which PSO has been calculated as specified used to protect a link-layer address to a
link in Section 6.1.

Messages that do which ND messages are not pass all SEND-enabled would prevent
the above tests MUST be silently
discarded if node from adquiring the host has been configured new information until the
corresponding cache expires. However, in this case it is
reasonable to accept only secured consider that all MAGs provide the same security
for protecting ND
messages.

7. Backward Compatibility with legacy SEND nodes messages, and that either all MAGs will
behave as Secure Proxy ND, or none, so configuration could be
easier.

8. Security Considerations

The PSO added by mechanism described in this document introduces a new Proxy
Signature Option (PSO) allowing a Secure Proxy ND will be ignored by nodes
implementing the original to generate or
modify a SEND specification and hence message for a proxied address. An SPND node will not cause
any interoperability problems. Since the only
accept such a message if it includes a valid PSO generated by an
authorized Secure Proxy ND also
removes ND. Such a message has equivalent protection
to the original threats presented in section 9 of [RFC3971] as a message
signed with a RSA option, these Signature option.

The security of proxied ND messages will be treated as
"unsecured" not including a PSO option is the
same of an unsecured ND message. The security of a proxied ND
message as described in Section 8 "Transitions Issues" received by a non-SEND host or RFC3971 host is the same of an
unsecured ND message.

Thanks to the SEND specification [RFC3971]. Thus, this specification does not
introduce any new transition issue compared authorization certificate it is provisioned with, a
proxy ND is authorized to issue ND signaling on behalf of nodes on
the original SEND
specification.

8. Security Considerations

The mechanism described in this document introduce subnet. Thus, a new Proxy
Signature Option (PSO) allowing compromised proxy is able, like a Secure Proxy ND compromised
router, to generate siphon off traffic from the host, or
modify a SEND message for mount a proxied address. A node will only accept
such man-in-the-
middle attack. However, when two on-link hosts communicate using
their respective link-local addresses, the threats involved with a message if it includes
compromised router and a valid PSO generated by an authorized
Secure Proxy ND.

If, on compromised proxy ND differs because the other hand, a message does
router is not include able to siphon off traffic exchanged between the hosts
or mount a PSO, then man-in-the-middle attack, while the proxy ND can, even if
the hosts use SEND.

The messages for which a Secure Proxy ND support doens't introduce any further security issues
since this specification does not modify perform its function, and
the SEND processing rules link for which this function is performed MUST be configured
appropriately for each proxy and scenario. This configuration is
specially relevant if
an ICMPv6 Secure Proxy ND message does is used for translating ND
messages from one link to another.

Proper configuration of when the PSO option must or must not contain a PSO. Thus, be
included, depending on the same security
considerations than that of proxied node being SEND applies (cf. or non-SEND may
result in security considerations, as discussed in Section 9 7.

Attacks to the timestamp of the SEND
specification [RFC3971].) secured ND message can be performed
as describe in section 7.3 of [I-D.ietf-csi-sndp-prob].

9. IANA Considerations

IANA is requested to allocate:

A new IPv6 Neighbor Discovery Option types type for the PSO, as TBA.
The value need to be allocated from the namespace specified in the
IANA registry IPv6 NEIGHBOR DISCOVERY OPTION FORMATS located at
http://www.iana.org/assignments/icmpv6-parameters.

A new 128-bit value under the CGA Message Type [RFC3972]
namespace, 0x09F5 2BE5 3B62 4C76 CB96 4E7F CDC9 2804.

10. References

10.1. Normative References

[I-D.ietf-netlmm-proxymip6]
Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6",
draft-ietf-netlmm-proxymip6-18 (work in progress),
May 2008.

[I-D.krishnan-cgaext-send-cert-eku]

[I-D.ietf-csi-send-cert]
Gagliano, R., Krishnan, S., Kukec, A., and K. Ahmed, A. Kukec, "Certificate
profile and certificate management for SEND",
draft-krishnan-cgaext-send-cert-eku-03
draft-ietf-csi-send-cert-02 (work in progress),
March 2009.
February 2010.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.

[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.

[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.

[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, April 2006.

[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.

[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.

[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.

[RSA] RSA Laboratories, "RSA Encryption Standard, Version 2.1",
PKCS 1 , November 2002.

[SHA1] National Institute of Standards and Technology, "Secure
Hash Standard", FIPS PUB 180-1 , April 1995.

10.2. Informative References

[I-D.ietf-csi-sndp-prob]
Combes, J., Krishnan, S., and G. Daley, "Securing Neighbor
Discovery Proxy: Problem Statement",
draft-ietf-csi-sndp-prob-04 (work in progress),
January 2010.

Authors' Addresses

Suresh Krishnan
Ericsson
8400 Decarie Blvd.
Town of Mount Royal, QC
Canada

Phone: +1 514 345 7900 x42871
Email: suresh.krishnan@ericsson.com

Julien Laganier
DoCoMo Communications Laboratories Europe GmbH
Landsberger Strasse 312
Munich D-80687
Germany
QUALCOMM Incorporated
5775 Morehouse Dr
San Diego, CA 92121
USA

Phone: +49 89 56824 231 +1 858 658 3538
Email: julien.ietf@laposte.net
URI: http://www.docomolab-euro.com/ julienl@qualcomm.com

Marco Bonola
Rome Tor Vergata University
Via del Politecnico, 1
Rome I-00133
Italy

Phone:
Email: marco.bonola@gmail.com

Alberto Garcia-Martinez
U. Carlos III de Madrid
Av. Universidad 30
Leganes, Madrid 28911
Spain

Phone: +34 91 6248782
Email: alberto@it.uc3m.es
URI: http://www.it.uc3m.es/