CGA & SEND maintenance Working S. Krishnan
Group Ericsson
Internet-Draft J. Laganier
Intended status: Experimental QUALCOMM Inc.
Expires: December 2, 2010 M. Bonola
Rome Tor Vergata University
A. Garcia-Martinez
UC3M
May 31, 2010
Secure Proxy ND Support for SEND
draft-ietf-csi-proxy-send-04
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 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 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 secure Proxy ND operation.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 2, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Secure Proxy ND Overview . . . . . . . . . . . . . . . . . . . 6
5. Secure Proxy ND Specification . . . . . . . . . . . . . . . . 8
5.1. Proxy Signature Option . . . . . . . . . . . . . . . . . . 8
5.2. Modified SEND processing rules . . . . . . . . . . . . . . 10
5.2.1. Processing rules for senders . . . . . . . . . . . . . 10
5.2.2. Processing rules for receivers . . . . . . . . . . . . 11
5.3. Proxying Link-Local Addresses . . . . . . . . . . . . . . 12
6. Application Scenarios . . . . . . . . . . . . . . . . . . . . 13
6.1. Scenario 1: Mobile IPv6 . . . . . . . . . . . . . . . . . 13
6.2. Scenario 2: Proxy Mobile IPv6 . . . . . . . . . . . . . . 14
6.3. Scenario 3: RFC 4389 Neighbor Discovery Proxy . . . . . . 17
7. Backward Compatibility with RFC3971 nodes and non-SEND
nodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
7.1. Backward Compatibility with RFC3971 nodes . . . . . . . . 19
7.2. Backward Compatibility with non-SEND nodes . . . . . . . . 19
8. Security Considerations . . . . . . . . . . . . . . . . . . . 22
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
11.1. Normative References . . . . . . . . . . . . . . . . . . . 25
11.2. Informative References . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
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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].
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2. Introduction
Secure Neighbor Discovery (SEND) [RFC3971] specifies a method for
securing Neighbor Discovery (ND) signaling [RFC4861] against specific
threats [RFC3756]. As defined today, SEND assumes that the node
sending a ND message is the owner of the address 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 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".
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3. Terminology
Secure ND Proxy
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 does not belong to the Secure ND Proxy and
for which the Secure ND Proxy is 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 document for Secure Proxy ND support, but uses only the SEND
specification as defined in [RFC3971].
SPND node
An IPv6 node that receives and validates messages according to the
specification defined in this document for Secure Proxy ND
support.
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4. Secure Proxy ND Overview
The original SEND specification [RFC3971] has implicitly assumed that
only the node sending a ND message is the owner of the address from
which the message is sent. This assumption does not allow proxying
of ND 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 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 through
the Authorization Delegation Discovery process defined in
[RFC3971].
o A new Neighbor Discovery option called Proxy Signature (PS)
option. 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 PS option,
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
containing a valid Proxy Signature option is validated, it is
considered as secure.
These extensions are applied in the following way:
o A Secure ND Proxy which proxies ND messages on behalf of a node
can use the PS option to protect the proxied messages. This
Secure ND Proxy 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 be aware of the Secure Proxy ND
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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 these 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] are extended to support the certificate format specified
in [I-D.ietf-csi-send-cert], and are configured with the
appropriate certification path.
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5. Secure Proxy ND Specification
A Secure ND Proxy performs all the operations 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 ND Proxy. The signature of the ND Proxy is
included in a new option called Proxy Signature (PS) option. The
signature is performed over all the NDP options present in the
message and the PS option 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 PS option is described
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 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Key Hash |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Digital Signature .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: PS option layout
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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 16-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.
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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 PS option, i.e. the message was sent by a
Secure ND Proxy.
This specification modifies the sender and receiver processing rules
defined in the SEND specification [RFC3971].
5.2.1. Processing rules for senders
A ICMPv6 message sent by a Secure ND Proxy for a proxied address MUST
contain a PS option and MUST NOT contain either CGA or RSA Signature
options.
A Secure ND Proxy sending a SEND message with the PS option MUST
construct the message as follows:
1. The SEND message is constructed without the PS option as follows:
A. If the Secure ND Proxy is locally generating the SEND message
for a proxied address, the message MUST be constructed as
described in Neighbor Discovery for IP version 6
specification [RFC4861].
B. If the Secure ND Proxy is forwarding a SEND message, first
the authenticity of the intercepted message MUST be 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 intercepted message is finally
modified as described in Section 4 of the ND Proxy
specification [RFC4389].
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C. If the Secure ND Proxy is forwarding a SEND message already
containing a PS option, first the authenticity of the
intercepted message is verified as specified in Section 5.2.2
of this specification. If the SEND message is valid, the
original PS option MUST be removed from the message. The
intercepted message is finally modified as described in
Section 4 of the ND Proxy specification [RFC4389].
2. Timestamp and Nonce options MUST be included according to the
rules specified in SEND [RFC3971]. The value in the Timestamp
option MUST be generated by the proxy. If the proxy is
forwarding a message, the Nonce value in the proxied message MUST
be the same as in the forwarded message, otherwise it is
generated by the proxy.
3. The Proxy Signature option MUST be added as the last option in
the message.
4. The data MUST be 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 Signature option MUST be processed
as specified below:
1. The receiver MUST ignore any RSA and CGA options, as well as any
options that might come after the first PS option. The options
are ignored for both signature verification and NDP processing
purposes.
2. The Key Hash field MUST indicate the use of a known public key.
A valid certification path (see [RFC3971] Section 6.3) between
the receiver's trust anchor and the sender's public key MUST be
known. The Secure Proxy ND's X509v3 certificate MUST contain a
extended key usage extension including the KeyPurposeId value for
the proxy authorization.
3. The Digital Signature field MUST have correct encoding.
4. The Digital Signature verification MUST show that the signature
has been calculated as specified in Section 5.1.
5. The Nonce option MUST be processed as specified in [RFC3971]
Section 5.3.4, except for replacing 'RSA Signature option' by 'PS
option'.
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6. The Timestamp option MUST be processed as specified in [RFC3971]
Section 5.3.4, except for replacing 'RSA Signature option' by 'PS
option'. The receiver SHOULD store the peer-related timing
information specified in [RFC3971] Section 5.3.4.1 and 5.3.4.2
(RDlast, TSlast) separately for each different proxy (which can
be identified by the different Key Hash values of the proxied
message) and separately from the timing information associated to
the IP of node for which the message is proxied. In this way, a
message received for the first time from a proxy (i.e. for which
there is no information stored in the cache) for which the
Timestamp option is checked, SHOULD be checked as messages
received from new peers (as in [RFC3971] section 5.3.4.2).
7. Messages with the Override bit [RFC4861] set MUST override an
existing cache entry regardless if it was created as a result of
a RSA Signature option or a PS option validation. When the
Override bit is not set, the advertisement MUST NOT update a
cached link-layer address created securily by means of RSA
Signature option or PS option validation.
Messages that do not pass all the 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 certain prefix. However,
Neighbor Discovery [RFC4861] states that router does not announce the
Link-Local prefix (fe80::/64). Hence, it is not required for a SEND
certificate to hold a X.509 extension for IP addresses that
authorizes the fe80::/64 prefix. However, some Secure Proxy ND
scenarios ([RFC4389], [RFC5213]) impose providing the proxying
function for the Link-Local address of a node. When Secure ND proxy
functionality for a Link-Local address is required, either a list of
link-local addresses, or the fe80::/64 prefix MUST be explicitly
authorized to be proxied in the corresponding certificate.
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6. Application Scenarios
In this section we describe three different application scenarios for
which Secure Proxy ND support for SEND can be applied. Note that the
particular way in which Secure Proxy ND support is applied (which ND
messages are proxied, in which directions, how the interaction with
non-SEND hosts and RFC3971 hosts is handled, etc.) largely depends on
the 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 message generation is trigged by the
reception of ND messages in other interfaces of the proxy.
6.1. Scenario 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 (MN)
to move from one link to another while maintaining reachability at a
stable address, the so-called MN's Home Address (HoA). When a MN
attaches to a foreign network, all the packets sent to the MN's HoA
by a Correspondent Node (CN) on the home link or a router, are
intercepted by the Home Agent (HA) on that home link, encapsulated
and tunneled to the MN's registered Care-of Address (CoA).
The HA intercepts these packets acting as a ND proxy for this MN.
When a NS is intercepted on the home link, the HA 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) constructed as described in [RFC4861], containing
its own link layer address (HA_LL) as the Target Link Layer Address
Option (TLLAO). Then a timestamp (generated by the proxy) and nonce
(if appropriate, according to [RFC3971]), MUST be included. Finally,
a PS option signing the message MUST be included as the last option
of the message.
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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 | |
| [CGA] | |
| RSA signature | |
|------------------------->| |
| | |
| SRC = HA | |
| DST = N | |
| ICMPv6 NA | |
| TARGET = MN | |
| TLLAO = HA_LL | |
| PS signature | |
|<-------------------------| |
| | |
| traffic | |
| dest= MN HoA | |
|------------------------->| |
| | |
| | tunnelled traffic |
| | dest= MN CoA |
| |------------------------->|
| | |
Figure 2: Proxy ND role of the Home agent in MIPv6
A node receiving the NA containing the PS option (e.g.: the CN in the
home link, or a router) MUST apply the rules defined in
Section 5.2.2. Note that in this case the Override bit of the NA
message is used to control which messages should prevail each case:
the message generated by the proxy once the MN moves from the home
network, or the MN if it comes back to the home link, as defined in
the 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 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
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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 completed (it receives a Proxy Binding Ack - PBA), it
will reply to the 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 still on the same link
and not triggering the IPv6 address reconfiguration (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 | |
| PS | |
|<---------------------| |
| | |
| | |
| | |
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Figure 3: Mobile node's handover in PMIPv6
To avoid potential link-local address collisions between the MAG and
the 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 MN is attached to, to be generated by the LMA when
the 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
of that MN's session.
The approach described above and the current SEND specification are
incompatible since sharing the same link-local address on different
MAGs would require all MAGs of a PMIPv6 domain to construct the CGA
and the RSA Signature option with the same public-private key pair,
which is not acceptable from a security point 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 of the MN
which is contradiction with the way MAG link-local address assignment
occurs in a PMIPv6 domain.
To provide SEND protection, each MAG is configured to act as a proxy
by means of a certificate associated to the PMIPv6 domain,
authorizing each MAG to proxy securely ND messages. In addition, the
certificate must also authorize the MAG to advertise prefixes. Note
that the inclusion of multiple KeyPurposeId values is supported by
[I-D.ietf-csi-send-cert].
When a MAG replies to a RS with a RA, the source address MUST be
equal to the MAG link-local address associated to the MN in this
PMIPv6 domain and its own link layer address as Source link-layer
address. Then a timestamp (generated by the proxy) and nonce (if
appropriate, according to [RFC3971]), MUST be included. Finally, a
PS option signing the message MUST be included as the last option of
the message. This procedure is followed for any other ND message
that could be generated by the MAG to a MN.
A node receiving a message from the MAG containing the PS option MUST
apply the rules defined in Section 5.2.2. Note that unsolicited
messages sent by MAG are validated by the host according to timestamp
values specific to the MAG serving the link, not to any other MAG to
which the host has been connected before in other links.
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6.3. Scenario 3: RFC 4389 Neighbor Discovery Proxy
The description of the problems for deploying SEND in this scenario
can be found in [I-D.ietf-csi-sndp-prob].
Link 1 Link 2
Host A ND Proxy (P) Host B
| | |
| SRC = A | |
| DST = solicited_node(B) | |
| ICMPv6 NS | |
| TARGET = B | |
| 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 | |
|<-------------------------| |
| | |
Figure 4: 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
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ICMPv6 messages: NS, NA, RA, or Redirect. The Secure ND Proxy MUST
verify the authenticity of the received ND message, according to
[RFC3971]. If the SEND message is valid, then it proxies the
original message with the following changes:
1. The message MUST be processed according to [RFC4389]. This
includes changing the source link layer address to the address of
the outgoing interface, maintaining the destination link layer
address as the address in the neighbor entry corresponding to the
destination IPv6 address, etc. In particular any link layer
address within the payload (that is, in a Source Local Link
Address option - SLLAO, or a Target Local Link Address option -
TLLAO) is substituted with the link-layer address of the outgoing
interface.
2. Any CGA or RSA option MUST be removed.
3. If a Nonce option existed in the original message, its value MUST
be preserved in the proxied message. The Timestamp MUST be
generated by the proxy.
4. The PS option MUST be added as the last option in the message,
signing all the information contained so far in the message.
When any other IPv6 unicast packet is received on a proxy interface,
if it is not locally destined then it is forwarded unchanged (other
than using a new link-layer header) to the proxy interface for which
the next hop address appears in the neighbor cache. If no neighbor
cache entry is present, the ND proxy should queue the packet and
initiate a Neighbor Discovery signalling as if the ICMPv6 NS message
were locally generated.
In order to deploy this scenario, nodes in proxied segments MUST know
the certificate authorizing proxy operation. To do so it could be
required to configure at least one device per each proxied segment
(may be the proxy itself) to propagate the required certification
path to authorize proxy operation by means of a CPS/CPA exchange.
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7. Backward Compatibility with RFC3971 nodes and non-SEND nodes
In this section we discuss the interaction of Secure ND Proxies 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 modifications
required in Section 5 cannot interpret correctly a PS option received
in a proxied ND message. These SEND nodes silently discard the PS
option, as specified in [RFC4861] for any unknown option. As a
result, these messages will be treated as unsecured as described in
Section 8 "Transitions Issues" of the SEND specification [RFC3971].
When RFC3971 nodes and SPND nodes exchange ND messages (without proxy
intervention), in either direction, messages are generated according
to the SEND specification [RFC3971], so these nodes interoperate
seamlessly.
In the scenarios in which the 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
Non-SEND nodes receiving NDP packets silently discard PS options, as
specified in [RFC4861] for any unknown option. Therefore, these
nodes interpret messages proxied by a Secure ND Proxy as any other ND
message.
When non-SEND nodes and SPND nodes exchange ND messages (without
proxy intervention), in either direction, the rules specified in
section 8 of [RFC3971] apply.
A Secure ND Proxy 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 unsecured NDP messages. A Secure
ND Proxy 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 by default. In the next
paragraphs we discuss the recommended behavior of the Secure ND Proxy
regarding to the protection level to 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, if the proxied nodes can return to the link in
which the proxy operates, the Secure ND Proxy MUST only generate PS
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options on behalf of nodes with SEND capabilities (i.e. that they
could use SEND to defend their messages if being in the same link
than the proxy, either RFC3971 nodes or SPND nodes). This is
relevant to allow nodes preferring secured information over unsecured
one, and for executing the DAD procedure, as specified in [RFC3971].
Therefore, the Secure ND Proxy MUST generate messages containing the
PS option for SPND and RFC3971 hosts, and MUST NOT generate messages
containing the PS option for non-SEND nodes. Note that ND
advertisements in response to solicitations generated by a Secure ND
Proxy must be secured or not according to the previous considerations
(i.e. to the nature of the proxied node), and not according to the
secure or unsecure nature of the solicitation message.
To apply this rule, we have to consider that depending on the
application scenario the proxy may translate ND messages generated by
a node or synthetise ND messages on behalf of a node that can return
to the link in which the Secure ND Proxy operates.
o For translating ND messages for nodes that can arrive to the link
in which the proxy operates, the rule can be easily applied: only
messages validated in the Secure ND Proxy according to the SEND
specification [RFC3971] MUST be proxied securely by the inclusion
of a PS option. Unsecured ND messages could be proxied if
unsecured operation is enabled in the proxy, but the message
generated by the Secure ND Proxy for the received message MUST NOT
include a PS option.
o For synthesizing ND messages on behalf of remote nodes, different
considerations should be made according to the particular
application scenario.
* For MIPv6, if the MN can return to the home link, it is
required for the proxy to know if the node could use SEND to
defend its address or not. A mismatch between the proxy and
proxied node behavior regarding to SEND operation would result
in unaproppriate operation. A HA including the PS option for
proxying a non-SEND MN would make ND messages sent by the proxy
to be more preferred than ND message of the non-SEND MN when
the MN returns to the home link (even if the proxied messages
have the Override bit set to 1). Not using the PS 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, and MUST use PS option if the MN is a
SPND or RFC3971 host, and MUST NOT use PS option for non-SEND
hosts.
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* For the Proxy Mobile IPv6 scenario, we have to note that a node
moving from a link in which PS option has been used to protect
a link-layer address to a link in which ND messages are not
protected by SEND would prevent the MN from adquiring the new
information until the cached information expires. However, in
this case it is reasonable to consider that all MAGs provide
the same security for protecting ND messages, and that either
all MAGs will behave as Secure ND Proxy, or none, so
configuration could be easier.
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8. Security Considerations
The mechanism described in this document introduces a new Proxy
Signature (PS) Option allowing a Secure ND Proxy to generate or
modify a SEND message for a proxied address. A SPND node will only
accept such a message if it includes a valid PS option generated by
an authorized Secure ND Proxy. Such a message has equivalent
protection to the threats presented in section 9 of [RFC3971] as a
message signed with a RSA Signature option.
The security of proxied ND messages not including a PS option is the
same of an unsecured ND message. The security of a proxied ND
message received by a non-SEND host or RFC3971 host is the same of an
unsecured ND message.
Thanks to the authorization certificate it is provisioned with, a
proxy ND is authorized to issue ND signaling on behalf of nodes on
the subnet. Thus, a compromised proxy is able, like a compromised
router, to siphon off traffic from the host, or mount a man-in-the-
middle attack. However, when two on-link hosts communicate using
their respective link-local addresses, the threats involved with a
compromised router and a compromised proxy ND differs because the
router is not able to siphon off traffic exchanged between the hosts
or mount a man-in-the-middle attack, while the proxy ND can, even if
the hosts use SEND.
The messages for which a Secure ND Proxy performs its function, and
the link for which this function is performed MUST be configured
appropriately for each proxy and scenario. This configuration is
specially relevant if Secure Proxy ND is used for translating ND
messages from one link to another.
Proper configuration of when the PS option must or must not be
included, depending on the proxied nodes being SEND or non-SEND may
result in security considerations which are discussed in Section 7.
Attacks to the timestamp of the secured ND message can be performed
as described in section 7.3 of [I-D.ietf-csi-sndp-prob].
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9. IANA Considerations
IANA is requested to allocate:
A new IPv6 Neighbor Discovery Option type for the PS option, 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.
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10. Acknowledgements
The text has benefited from feedback provided by Jari Arkko, Jean-
Michel Combes, Roque Gagliano, Tony Cheneau and Marcelo Bagnulo.
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11. References
11.1. Normative References
[I-D.ietf-csi-send-cert]
Gagliano, R., Krishnan, S., and A. Kukec, "Certificate
profile and certificate management for SEND",
draft-ietf-csi-send-cert-03 (work in progress),
March 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.
11.2. 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.
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[RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", RFC 3756,
May 2004.
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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
QUALCOMM Incorporated
5775 Morehouse Dr
San Diego, CA 92121
USA
Phone: +1 858 658 3538
Email: 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/
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