CGA & SEND maintenance Working S. Krishnan
Group Ericsson
Internet-Draft J. Laganier
Intended status: Experimental QUALCOMM Inc.
Expires: April 1, 2011 M. Bonola
Rome Tor Vergata University
A. Garcia-Martinez
UC3M
September 28, 2010
Secure Proxy ND Support for SEND
draft-ietf-csi-proxy-send-05
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 and/or posses a
key which authorizes the node to act as a router, so that it is in
possession of the private key or keys used to generate the digital
signature on each message. This means that the Proxy ND signaling
performed by nodes that do not possess knowledge of the address
owner's private key and/or knowledge of a router's 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 April 1, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
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document authors. All rights reserved.
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
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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 . . . . . . . . . . . . . . 13
6. Application Scenarios . . . . . . . . . . . . . . . . . . . . 14
6.1. Scenario 1: Mobile IPv6 . . . . . . . . . . . . . . . . . 14
6.2. Scenario 2: Proxy Mobile IPv6 . . . . . . . . . . . . . . 15
6.3. Scenario 3: RFC 4389 Neighbor Discovery Proxy . . . . . . 18
7. Backward Compatibility with RFC3971 nodes and non-SEND
nodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.1. Backward Compatibility with RFC3971 nodes . . . . . . . . 20
7.2. Backward Compatibility with non-SEND nodes . . . . . . . . 20
8. Security Considerations . . . . . . . . . . . . . . . . . . . 23
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
11.1. Normative References . . . . . . . . . . . . . . . . . . . 27
11.2. Informative References . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
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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 and/or posses a key which authorizes the node to act
as a router, so that it is in possession of the private key or keys
used to generate the digital signature on each message. This means
that the Proxy ND signaling performed by nodes that do not possess
knowledge of the address owner's private key and/or knowledge of a
router's 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 secure a Neighbor Discovery Protocol (NDP)
message without knowing the private key related to the source
address of the node, or the key related to the router
authorization, for which the node acts on behalf.
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 the ND protocol defined in [RFC4861] and
[RFC4862], without additional security.
RFC3971 node
An IPv6 node that does not implement the specification defined in
this document for Secure Proxy ND support, but uses 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.
Translated NDP message
A NDP message issued by a Secure ND Proxy as a result of a
received NDP message originated by the owner of the address or
originated by another node acting on behalf of the owner of the
address.
Synthetic NDP message
A NDP message issued by a Secure ND Proxy that is not the result
of a received NDP message.
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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, Secure Proxy ND certificates
include one or more KeyPurposeId values which can be used for
authorizing proxies to sign RA and Redirect messages, or to sign
NA, NS or RS messages on behalf or other nodes. The inclusion of
this 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 or RSA Signature options. This option
MUST be appended to any NDP message (NA, NS, RS, RA and Redirect)
to secure it.
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 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.
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o In order to allow nodes to successfully validate secured proxied
messages, the nodes MUST be aware of 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 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] when they send 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 identify an authorized proxy
generating a translated or synthetic SEND message for a proxied
address.
This is accomplished by signing the message with a private 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 Neighbor Discovery Protocol (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
This specification modifies the sender and receiver processing rules
defined in the SEND specification [RFC3971].
5.2.1. Processing rules for senders
A Secure ND Proxy MUST NOT use a key to sign NDP message types which
do not correspond to the authorization granted to the considered key.
NA, NS and RS messages MUST be signed with a key corresponding to a
Secure Proxy ND certificate with a KeyPurposeId value
[I-D.ietf-csi-send-cert] of id-kp-sendProxiedOwner, and the source
addresses of the messages MUST be encompassed in the prefix
associated to the certificate. RA and Redirect messages MUST be
signed with a key corresponding to a Secure Proxy ND certificate with
a KeyPurposeId value of id-kp-sendProxiedRouter. The prefix included
in the RA message for on-link determination and/or stateless address
autoconfiguration, and the Target Address of the Redirect message,
MUST be encompassed in the prefix associated to that certificate.
A secured NDP 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. Section 7 discusses in which cases a NDP message
has to be secured in an scenario including non-SEND nodes.
A Secure ND Proxy sending a secured message on behalf of other node
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 generating a synthetic SEND message
for a proxied address, the message MUST be constructed as
described in Neighbor Discovery for IP version 6
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specification [RFC4861].
B. If the Secure ND Proxy is generating a translated 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].
C. If the Secure ND Proxy is translating 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
translating a message which includes a Nonce, the Nonce value in
the proxied message MUST be the same as in the intercepted
message. If the proxy is synthesizing a solicitation message,
the Nonce value MUST be generated by the proxy. If the proxy is
synthesizing an advertisement message, the Nonce value MUST
correspond to the solicitation message to which the proxy is
responding.
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.
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2. The Key Hash field MUST indicate the use of a known public key.
A valid certification path (see [I-D.ietf-csi-send-cert] Section
9) between the receiver's trust anchor and the sender's public
key MUST be known. The Secure Proxy ND's X509v3 certificate MUST
contain an extended key usage extension including the appropriate
KeyPurposeId value and prefix for the message to validate:
* For RA messages, a KeyPurposeId value of id-kp-
sendProxiedRouter MUST exist for the certificate, and the
prefix included in the RA message for on-link determination
and/or stateless address autoconfiguration MUST be encompassed
in the prefix associated to that certificate.
* For Redirect messages, a KeyPurposeId value of id-kp-
sendProxiedRouter MUST exist for the certificate, and the
prefix included in the Target Address of the Redirect message
MUST be encompassed in the prefix associated to that
certificate.
* For NA, NS and RS messages, a KeyPurposeId value of id-kp-
sendProxiedOwner MUST exist for the certificate, and the
source addresses of the messages MUST be encompassed in the
prefix associated to the certificate.
If any of these tests fails, the verification fails.
3. The Digital Signature field MUST have correct encoding, otherwise
the verification of the message including the PS option fails.
4. The Digital Signature verification MUST show that the signature
has been calculated as specified in Section 5.1, otherwise the
verification of the message including the PS option fails.
5. The Nonce option MUST be processed as specified in [RFC3971]
Section 5.3.4, except for replacing 'RSA Signature option' by 'PS
option'; if these tests fail, the verification of the message
including the PS option fails.
6. The Timestamp option MUST be processed as specified in [RFC3971]
Section 5.3.4, except for replacing 'RSA Signature option' by 'PS
option'. If these tests fail, the verification of the message
including the PS option fails. 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 could be identified by the different Key
Hash values of the proxied message) and separately from the
timing information associated to the IP address of a node for
which the message is proxied. In this way, a message received
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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 a message received from a new
peer (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 securely by means of RSA
Signature option or PS option validation.
Messages for which the verification fails MUST be silently discarded
if the node has been configured to accept only secured ND messages.
The messages MAY be accepted if the host has been configured to
accept both secured and unsecured messages but MUST be treated as an
unsecured message.
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 routers do 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 direction, 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 messages are translated from the
messages received in other interfaces of the proxy.
6.1. Scenario 1: Mobile IPv6
The description of the problems for deploying SEND in this scenario
is presented 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).
To deploy Secure Proxy ND in this scenario, i.e. to secure the HA
operation, a Secure Proxy ND certificate with a KeyPurposeId value of
id-kp-sendProxiedOwner for the prefix of the home link is required.
The Secure ND Proxy is configured with the private key associated to
this certificate. When a NS is intercepted by the HA 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 | |
|------------------------->| |
| | |
| | tunneled 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 on each
case: the message generated by the proxy when 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 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 it is performed by two functional entities: the Local
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Mobility Anchor (LMA) and the Mobile Access Gateway (MAG).
When the MN connects to a new access link, it sends a muliticast
Router Solicitation (RS). The MAG on the new access link, upon
detecting the MN's attachment, signals the LMA requesting an update
of the binding state of the MN (by means of a Proxy Binding Update -
PBU). Once the signaling is completed (it receives a Proxy Binding
Ack - PBA), the MAG replies to the MN with a 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, so the IPv6 address reconfiguration procedure is not triggered
(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 on the link to
which the MN is attached to be generated by the LMA when the MN first
attaches 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 an acceptable security policy.
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 would change after each handoff of
the MN, which is in contradiction with the way MAG link-local address
assignment occurs in a PMIPv6 domain.
To provide SEND protection, each MAG MUST be configured to act as a
proxy by means of a certificate associated to the PMIPv6 domain,
authorizing each MAG to proxy securely NA and RS messages by means of
a KeyPurposeId value of id-kp-sendProxiedOwner. In addition, the
certificate MUST also authorize the MAG to advertise prefixes by
associating to the same certificate a KeyPurposeId value of id-kp-
sendProxiedRouter. 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, with 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 the MN.
A node receiving a message from the MAG containing the PS option MUST
apply the processing rules defined in Section 5.2.2. Note that
unsolicited messages sent by the MAG should be 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, according to processing step number 6 of Section 5.2.2.
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6.3. Scenario 3: RFC 4389 Neighbor Discovery Proxy
The description of the problems for deploying SEND in this scenario
is presented 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: RFC 4389 Neighbor Discovery Proxy operation
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 MUST parse any IPv6 packet it receives on a proxy
interface to check whether it contains one of the following NDP
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messages: NS, NA, RS, 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. To
be able to sign any NS, NA, RS, RA o Redirect message, the key
used must correspond to a certificate with KeyPurposeId values of
id-kp-sendProxiedOwner and id-kp-sendProxiedRouter.
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 Secure ND Proxy SHOULD queue the packet
and initiate a Neighbor Discovery signaling as if the 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. As stated in
[RFC3971], network operators may want to run a mixture of nodes
accepting secured and unsecured NDP messages at the same time.
Secure ND Proxies and SPND nodes SHOULD support the use of secured
and unsecured NDP messages at the same time.
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 (note that the
difference between RFC3971 nodes and SPND nodes only affect to the
ability to process received NDP messages containing a PS option, not
in the way they generate messages secured by SEND).
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 proxying 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 security is provided by default. In the next
paragraphs we discuss the recommended behavior of the Secure ND Proxy
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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
options on behalf of nodes with SEND capabilities (i.e. that they
could use SEND to defend their messages if present on the same link
as the proxy, i.e. being either RFC3971 nodes or SPND nodes). This
is relevant to allow nodes to prefer secured information over
unsecured one, and to properly execute the DAD procedure, as
specified in [RFC3971]. Therefore, in this case the Secure ND Proxy
MUST synthesize/translate messages containing the PS option for SPND
and RFC3971 hosts, and MUST NOT synthesize/translate 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.
In order to apply this rule, the Secure ND Proxy needs to know the
security capabilities of the proxied node. The way this information
is acquired depends on the application scenario, and it is discussed
next:
o For scenarios in which ND messages are translated for nodes that
can arrive to the link in which the proxy operates, the rule can
be easily applied: only for messages validated in the Secure ND
Proxy according to the SEND specification [RFC3971], or according
to Section 5.2.2 of this specification for messages containing a
PS option (which means that another proxy previously checked that
the original message was secured), the message 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 scenarios in which ND messages are synthesized 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 HA including the PS option for
proxying a non-SEND MN would make ND messages sent by the proxy
to be more preferred than a ND message of the non-SEND MN when
the MN returns to the home link (even if the proxied messages
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have the Override bit set to 1). Not using the PS option for a
RFC3971 or SPND MN would make the address in the home link more
vulnerable when the MN is away than when it is in the home
link, defeating the purpose of the Secure Proxy ND mechanism.
Therefore, in this case the HA MUST know the SEND capabilities
of the MN, MUST use the PS option if the MN is a SPND or
RFC3971 host, and MUST NOT use PS option for non-SEND hosts.
* For the Proxy Mobile IPv6 scenario, 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 is
expected to 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 synthesize or
translate a SEND message for a proxied address, to Redirect traffic
for given target addresses or to advertise prefix information by
means of RA messages. A SPND node only accepts such a message if it
includes a valid PS option generated by a properly authorized Secure
ND Proxy (with a certificate containing a KeyPurposeId with value id-
kp-sendProxiedOwner for protecting NA, NS and RS messages, or
containing a KeyPurposeId value of id-kp-sendProxiedRouter for
protecting RA and Redirect messages). Such a message has equivalent
protection against 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 as an unsecured ND message. The security of a proxied ND
message received by a non-SEND host or RFC3971 host is the same as an
unsecured ND message.
When a message including a PS option is received by a SPND node, any
CGA or RSA options also included in the message are removed and the
remaining message further processed. Altough properly formed proxied
messages MUST NOT include at the same time PS and CGA/RSA options,
discarding them if they appear does not affect to the security. If
the PS option is validated, then the information included in the
message has been validly generated by a proxy, and should be honored
(remember that anti-replay protection is provided by means of nonce
and timestamp options). If the PS option is not validated, then it
is treated as an unsecured message. In any case, there is no gain
for an attacker from appending false or old CGA/RSA information to a
message secured by a Secure ND Proxy.
A compromised Secure ND Proxy provisioned with an authorization
certificate with a KeyPurposeId value of id-kp-sendProxiedRouter is
able, like a compromised router to siphon off traffic from the host,
or mount a man-in-the-middle attack, for hosts communicating to off-
link hosts. A compromised Secure ND Proxy provisioned with an
authorization certificate with a KeyPurposeId value of id-kp-
sendProxiedOwner can siphon off traffic or mount a man-in-the-middle
attack for communication between on-link hosts, even if the hosts use
SEND. Note that different application scenarios may require one type
of authorization, the other, or both. To minimize security risks,
authorization capabilities SHOULD NOT exceed the ones strictly
required by the application scenario to be deployed.
The messages for which a Secure ND Proxy performs its function and
the link for which this function is performed MUST be configured
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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.
Section 7 discusses the security considerations resulting from the
decision of appending or omitting the PS option depending on the
SEND-awareness of the proxied nodes.
Protection against replay attacks from unsolicited messages such as
NA, RA, and Redirects is provided by means of the Timestamp option.
When Secure ND Proxy is used, each proxy and the host for which a
proxy acts on behalf are considered to be different peers in terms of
Timestamp verification. Since the information provided by the host
and a proxy maybe different, including different link-layer
addresses, a replay attack could affect the operation of a third
node: replaying messages issued by a host that is no longer in the
link can prevent the use of a proxy, and replaying messages of a
proxy when the host is back in the link can prevent communication
with the host. This kind of attacks can be performed until the
timestamp of the peer (either the host or a proxy) is no longer valid
for the receiver. The window of vulnerability is in general larger
for the first message received from a new peer than for subsequent
messages received from the same peer (see [RFC3971]). A more
detailed analysis of the possible attacks related with the Timestamp
option is 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, Marcelo Bagnulo, Alexey
Melnikov and Sandra Murphy.
The work of Alberto Garcia-Martinez was supported in part by T2C2
project (TIN2008-06739-C04-01, granted by the Spanish Science and
Innovation Ministry).
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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-07 (work in progress),
September 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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