Address Protected Neighbor Discovery for Low-power and Lossy Networks
draft-ietf-6lo-ap-nd-08
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8928.
|
|
|---|---|---|---|
| Authors | Pascal Thubert , Behcet Sarikaya , Mohit Sethi , Rene Struik | ||
| Last updated | 2018-10-18 | ||
| Replaces | draft-sarikaya-6lo-ap-nd | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 8928 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-6lo-ap-nd-08
6lo P. Thubert, Ed.
Internet-Draft Cisco
Updates: 6775 (if approved) B. Sarikaya
Intended status: Standards Track
Expires: April 21, 2019 M. Sethi
Ericsson
R. Struik
Struik Security Consultancy
October 18, 2018
Address Protected Neighbor Discovery for Low-power and Lossy Networks
draft-ietf-6lo-ap-nd-08
Abstract
This document specifies an extension to 6LoWPAN Neighbor Discovery
(ND) defined in RFC6775 and updated in [I-D.ietf-6lo-rfc6775-update].
The new extension is called Address Protected Neighbor Discovery (AP-
ND) and it protects the owner of an address against address theft and
impersonation attacks in a low-power and lossy network (LLN). Nodes
supporting this extension compute a cryptographic identifier (Crypto-
ID) and use it with one or more of their Registered Addresses. The
Crypto-ID identifies the owner of the Registered Address and can be
used to provide proof of ownership of the Registered Addresses. Once
an address is registered with the Crypto-ID and a proof-of-ownership
is provided, only the owner of that address can modify the
registration information, thereby enforcing Source Address
Validation.
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 https://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 21, 2019.
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Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://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. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. References . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. 6LoWPAN sub-glossary . . . . . . . . . . . . . . . . . . 4
3. Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . . 5
4. New Fields and Options . . . . . . . . . . . . . . . . . . . 6
4.1. New Crypto-ID . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Updated EARO . . . . . . . . . . . . . . . . . . . . . . 6
4.3. Crypto-ID Parameters Option . . . . . . . . . . . . . . . 8
4.4. Nonce Option . . . . . . . . . . . . . . . . . . . . . . 9
4.5. NDP Signature Option . . . . . . . . . . . . . . . . . . 9
5. Protocol Scope . . . . . . . . . . . . . . . . . . . . . . . 9
6. Protocol Flows . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. First Exchange with a 6LR . . . . . . . . . . . . . . . . 11
6.2. NDPSO generation and verficiation . . . . . . . . . . . . 13
6.3. Multihop Operation . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7.1. Inheriting from RFC 3971 . . . . . . . . . . . . . . . . 16
7.2. Related to 6LoWPAN ND . . . . . . . . . . . . . . . . . . 17
7.3. ROVR Collisions . . . . . . . . . . . . . . . . . . . . . 17
8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 17
8.1. CGA Message Type . . . . . . . . . . . . . . . . . . . . 17
8.2. Crypto-Type Subregistry . . . . . . . . . . . . . . . . . 17
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . 18
10.2. Informative references . . . . . . . . . . . . . . . . . 19
Appendix A. Requirements Addressed in this Document . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
Neighbor Discovery Optimizations for 6LoWPAN networks [RFC6775]
(6LoWPAN ND) adapts the original IPv6 neighbor discovery (NDv6)
protocols defined in [RFC4861] and [RFC4862] for constrained low-
power and lossy network (LLN). In particular, 6LoWPAN ND introduces
a unicast host address registration mechanism that reduces the use of
multicast. 6LoWPAN ND defines a new Address Registration Option (ARO)
that is carried in the unicast Neighbor Solicitation (NS) and
Neighbor Advertisement (NA) messages exchanged between a 6LoWPAN Node
(6LN) and a 6LoWPAN Router (6LR). It also defines the Duplicate
Address Request (DAR) and Duplicate Address Confirmation (DAC)
messages between the 6LR and the 6LoWPAN Border Router (6LBR). In
LLN networks, the 6LBR is the central repository of all the
registered addresses in its domain.
The registration mechanism in 6LoWPAN ND [RFC6775] prevents the use
of an address if that address is already registered in the subnet
(first come first serve). In order to validate address ownership,
the registration mechanism enables the 6LR and 6LBR to validate the
association between the registered address of a node, and its
Registration Ownership Verifier (ROVR). ROVR is defined in
[I-D.ietf-6lo-rfc6775-update] and it can be derived from the MAC
address of the device (using the 64-bit Extended Unique Identifier
EUI-64 address format specified by IEEE). However, the EUI-64 can be
spoofed, and therefore, any node connected to the subnet and aware of
a registered-address-to-ROVR mapping could effectively fake the ROVR.
This would allow the an attacker to steal the address and redirect
traffic for that address. [I-D.ietf-6lo-rfc6775-update] defines an
Extended Address Registration Option (EARO) option that allows to
transport alternate forms of ROVRs, and is a pre-requisite for this
specification.
In this specification, a 6LN generates a cryptographic ID (Crypto-ID)
and places it in the ROVR field during the registration of one (or
more) of its addresses with the 6LR(s). Proof of ownership of the
Crypto-ID is passed with the first registration exchange to a new
6LR, and enforced at the 6LR. The 6LR validates ownership of the
cryptographic ID before it creates any new registration state, or
changes existing information.
The protected address registration protocol proposed in this document
enables Source Address Validation (SAVI) [RFC7039]. This ensures
that only the actual owner uses a registered address in the IPv6
source address field. A 6LN can only use a 6LR for forwarding
packets only if it has previously registered the address used in the
source field of the IPv6 packet.
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The 6lo adaptation layer in [RFC4944] and [RFC6282] requires a device
to form its IPv6 addresses based on its Layer-2 address to enable a
better compression. This is incompatible with Secure Neighbor
Discovery (SeND) [RFC3971] and Cryptographically Generated Addresses
(CGAs) [RFC3972], since they derive the Interface ID (IID) in IPv6
addresses with cryptographic keys.
2. Terminology
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].
2.1. References
Terms and concepts from the following documents are used in this
specification:
o SEcure Neighbor Discovery (SEND) [RFC3971]
o Cryptographically Generated Addresses (CGA) [RFC3972]
o Neighbor Discovery for IP version 6 [RFC4861]
o IPv6 Stateless Address Autoconfiguration[RFC4862],
o Problem Statement and Requirements for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Routing [RFC6606]
o IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals [RFC4919]
o Neighbor Discovery Optimization for Low-power and Lossy Networks
[RFC6775]
o Terms Used in Routing for Low-Power and Lossy Networks (LLNs)
[RFC7102]
o Terminology for Constrained-Node Networks [RFC7228]
o Registration Extensions for 6LoWPAN Neighbor Discovery"
[I-D.ietf-6lo-rfc6775-update]
2.2. 6LoWPAN sub-glossary
This document uses the following acronyms:
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6BBR: 6LoWPAN Backbone Router (proxy for the
registration)[I-D.ietf-6lo-backbone-router]
6LBR: 6LoWPAN Border Router
6LN: 6LoWPAN Node
6LR: 6LoWPAN Router (relay to the registration process)
CIPO: Crypto-ID Parameters Option
(E)ARO: (Extended) Address Registration Option
DAD: Duplicate Address Detection
LLN: Low-Power and Lossy Network (a typical IoT network)
NA: Neighbor Advertisement
ND: Neighbor Discovery
NDP: Neighbor Discovery Protocol
NDPSO: NDP Signature Option
NS: Neighbor Solicitation
ROVR: Registration Ownership Verifier (pronounced rover)
RA: Router Advertisement
RS: Router Solicitation
RSAO: RSA Signature Option
TID: Transaction ID (a sequence counter in the EARO)
3. Updating RFC 6775
This specification defines a cryptographic identifier (Crypto-ID)
that can be used as a replacement to the MAC address in the ROVR
field of the EARO option; the computation of the Crypto-ID is
detailed in Section 4.1. A node in possession of the necessary
cryptographic primitives SHOULD use Crypto-ID by default as ROVR in
its registration. Whether a ROVR is a Crypto-ID is indicated by a
new "C" flag in the NS(EARO) message.
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In order to prove its ownership of a Crypto-ID, the registering node
needs to supply certain parameters including a nonce and a signature
that will prove that the node has the private-key corresponding to
the public-key used to build the Crypto-ID. This specification adds
the capability to carry new options in the NS(EARO) and the NA(EARO).
The NS(EARO) carries a variation of the CGA Option (Section 4.3), a
Nonce option and a variation of the RSA Signature option
(Section 4.5) in the NS(EARO). The NA(EARO) carries a Nonce option.
4. New Fields and Options
In order to avoid the need for new ND option types, this
specification reuses/ extends options defined in SEND [RFC3971] and
6LoWPAN ND [RFC6775] [I-D.ietf-6lo-rfc6775-update]. This applies in
particular to the CGA option and the RSA Signature Option. This
specification provides aliases for the specific variations of those
options as used in this document. The presence of the EARO option in
the NS/NA messages indicates that the options are to be processed as
specified in this document, and not as defined in SEND [RFC3971].
4.1. New Crypto-ID
Each 6LN using this specification for address registration MUST
support Elliptic Curve Crytpograhy (ECC) and a hash function. The
choice of elliptic curves and hash function currently defined in this
specification are listed in Section 8.2.
The Crypto-ID is computed by a 6LN as follows:
1. Depending on the Crypto-Type (see Section 8.2) used by the node,
the hash function is applied to the JSON Web Key (JWK) [RFC7517]
encoding of the public-key of the node.
2. The leftmost bits of the resulting hash, up to the size of the
ROVR field, are used as the Crypto-ID.
4.2. Updated EARO
This specification updates the EARO option as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Status | Opaque |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Rsvd |C| I |R|T| TID | Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
... Registration Ownership Verifier (ROVR) ...
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Enhanced Address Registration Option
Type: 33
Length: 8-bit unsigned integer. The length of the option
(including the type and length fields) in units of 8
bytes.
Status: 8-bit unsigned integer. Indicates the status of a
registration in the NA response. MUST be set to 0 in
NS messages.
Opaque: Defined in [I-D.ietf-6lo-rfc6775-update].
Rsvd (Reserved): This field is unused. It MUST be initialized to
zero by the sender and MUST be ignored by the
receiver.
C: This "C" flag is set to indicate that the ROVR field
contains a Crypto-ID and that the 6LN MAY be
challenged for ownership as specified in this
document.
I: Defined in [I-D.ietf-6lo-rfc6775-update].
R: Defined in [I-D.ietf-6lo-rfc6775-update].
T and TID: Defined in [I-D.ietf-6lo-rfc6775-update].
Registration Ownership Verifier (ROVR): When the "C" flag is set,
this field contains a Crypto-ID.
This specification uses Status values "Validation Requested" and
"Validation Failed", which are defined in 6LoWPAN ND
[I-D.ietf-6lo-rfc6775-update]. No other new Status values are
defined.
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4.3. Crypto-ID Parameters Option
This specification defines the Crypto-ID Parameters Option (CIPO), as
a variation of the CGA Option that carries the parameters used to
form a Crypto-ID. In order to provide cryptographic agility
[RFC7696], AP-ND supports two possible elliptic curves, indicated by
a Crypto-Type field. NIST P-256 [FIPS186-4] MUST be supported by all
implementations. The Edwards-Curve Digital Signature Algorithm
(EdDSA) curve Ed25519ph (pre-hashing) [RFC8032] MAY be supported as
an alternate.
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 | Pad Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Crypto-Type | Modifier | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
. .
. Public Key (variable length) .
. .
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Crypto-ID Parameters Option
Type: 11. This is the same value as the CGA Option, CIPO
is a particular case of the CGA option
Length: 8-bit unsigned integer. The length of the option in
units of 8 octets.
Modifier: 8-bit unsigned integer.
Pad Length: 8-bit unsigned integer. The length of the Padding
field.
Crypto-Type: The type of cryptographic algorithm used in
calculation Crypto-ID. A value of 0 indicates NIST
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P-256, with SHA-256 as the hash algorithm. A value
of 1 is assigned for Ed25519ph, with SHA-512 as the
hash algorithm.
Public Key: JWK-Encoded Public Key [RFC7517].
Padding: A variable-length field making the option length a
multiple of 8, containing as many octets as specified
in the Pad Length field.
4.4. Nonce Option
This document reuses the Nonce Option defined in section 5.3.2. of
SEND [RFC3971] without a change.
4.5. NDP Signature Option
This document reuses the RSA Signature Option (RSAO) defined in
section 5.2. of SEND [RFC3971]. Admittedly, the name is ill-chosen
since the option is extended for non-RSA Signatures and this
specification defines an alias to avoid the confusion.
The description of the operation on the option detailed in section
5.2. of SEND [RFC3971] apply, but for the following changes:
o The 128-bit CGA Message Type tag [RFC3972] for AP-ND is 0x8701
55c8 0cca dd32 6ab7 e415 f148 84d0. (The tag value has been
generated by the editor of this specification on random.org).
o The signature is computed using the hash algorithm and the digital
signature indicated in the Crypto-Type field of the CIPO option
using the private-key corresponding the public-key passed in the
CIPO.
o The alias NDP Signature Option (NDPSO) can be used to refer to the
RSAO when used as described in this specification.
5. Protocol Scope
The scope of the protocol specified here is a 6LoWPAN Low Power Lossy
Network (LLN), typically a stub network connected to a larger IP
network via a Border Router called a 6LBR per [RFC6775]. A 6LBR has
sufficient capability to satisfy the needs of duplicate address
detection.
The 6LBR maintains registration state for all devices in its attached
LLN. Together with the first-hop router (the 6LR), the 6LBR assures
uniqueness and grants ownership of an IPv6 address before it can be
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used in the LLN. This is in contrast to a traditional network that
relies on IPv6 address auto-configuration [RFC4862], where there is
no guarantee of ownership from the network, and each IPv6 Neighbor
Discovery packet must be individually secured [RFC3971].
---+-------- ............
| External Network
|
+-----+
| | 6LBR
+-----+
o o o
o o o o
o o LLN o o o
o o o (6LR)
o (6LN)
Figure 3: Basic Configuration
In a mesh network, the 6LR is directly connected to the host device.
This specification mandates that the peer-wise layer-2 security is
deployed so that all the packets from a particular host are securely
identifiable by the 6LR. The 6LR may be multiple hops away from the
6LBR. Packets are routed between the 6LR and the 6LBR via other
6LRs. This specification mandates that a chain of trust is
established so that a packet that was validated by the first 6LR can
be safely routed by other on-path 6LRs to the 6LBR.
6. Protocol Flows
The 6LR/6LBR ensures first-come/first-serve by storing the EARO
information including the Crypto-ID associated to the node being
registered. The node can claim any address as long as it is the
first to make such a claim. After a successful registration, the
node becomes the owner of the registered address and the address is
bound to the Crypto-ID in the 6LR/6LBR registry.
This specification enables the 6LR to verify the ownership of the
binding at any time assuming that the "C" flag is set. The
verification prevents other nodes from stealing the address and
trying to attract traffic for that address or use it as their source
address.
A node may use multiple IPv6 addresses at the same time. The node
may use a same Crypto-ID, to prove the ownership of multiple IPv6
addresses. The separation of the address and the cryptographic
material avoids the constrained device to compute multiple keys for
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multiple addresses. The registration process allows the node to use
the same Crypto-ID for all of its addresses.
6.1. First Exchange with a 6LR
A 6LN registers to a 6LR that is one hop away from it with the "C"
flag set in the EARO, indicating that the ROVR field contains a
Crypto-ID. The Target Address in the NS message indicates the IPv6
address that the 6LN is trying to register. The on-link (local)
protocol interactions are shown in Figure 4. If the 6LR does not
have a state with the 6LN that is consistent with the NS(EARO), then
it replies with a challenge NA (EARO, status=Validation Requested)
that contains a Nonce Option (shown as NonceLR in Figure 4). The
Nonce option MUST contain a random Nonce value that was never used
with this device.
The 6LN replies to the challenge with an NS(EARO) that includes a new
Nonce option (shown as NonceLN in Figure 4), the CIPO (Section 4.3),
and the NDPSO containing the signature. The information associated
to a Crypto-ID stored by the 6LR on the first NS exchange where it
appears. The 6LR MUST store the CIPO parameters associated with the
Crypto-ID so it can be used for more than one address.
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6LN 6LR
| |
|<------------------------- RA -------------------------|
| | ^
|---------------- NS with EARO (Crypto-ID) ------------>| |
| | option
|<- NA with EARO (status=Validation Requested), NonceLR-| |
| | v
|------- NS with EARO, CIPO, NonceLN and NDPSO -------->|
| |
|<------------------- NA with EARO ---------------------|
| |
...
| |
|--------------- NS with EARO (Crypto-ID) ------------->|
| |
|<------------------- NA with EARO ---------------------|
| |
...
| |
|--------------- NS with EARO (Crypto-ID) ------------->|
| |
|<------------------- NA with EARO ---------------------|
| |
Figure 4: On-link Protocol Operation
The steps for the registration to the 6LR are as follows:
o Upon the first exchange with a 6LR, a 6LN will be challenged to
prove ownership of the Crypto-ID and the Target Address being
registered in the Neighbor Solicitation message. The proof is not
needed again in later registrations for that address. When a 6LR
receives a NS(EARO) registration with a new Crypto-ID as a ROVR,
it SHOULD challenge by responding with a NA(EARO) with a status of
"Validation Requested".
o The challenge is triggered when the registration for a Source
Link-Layer Address is not verifiable either at the 6LR or the
6LBR. In the latter case, the 6LBR returns a status of
"Validation Requested" in the DAR/DAC exchange, which is echoed by
the 6LR in the NA (EARO) back to the registering node. The
challenge MUST NOT alter a valid registration in the 6LR or the
6LBR.
o Upon receiving a NA(EARO) with a status of "Validation Requested",
the registering node SHOULD retry its registration with a Crypto-
ID Parameters Option (CIPO) (Section 4.3) that contains all the
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necessary material for building the Crypto-ID, the NonceLN that it
generated, and the NDP signature (Section 4.5) option that proves
its ownership of the Crypto-ID and intent of registering the
Target Address.
o In order to validate the ownership, the 6LR performs the same
steps as the 6LN and rebuilds the Crypto-ID based on the
parameters in the CIPO. It also verifies the signature contained
in the NDPSO option. If the Crypto-ID does not match with the
public-key in the CIPO option, or if the signature in the NDPSO
option cannot be verified, the validation fails.
o If the 6LR fails to validate the signed NS(EARO), it responds with
a status of "Validation Failed". After receiving a NA(EARO) with
a status of "Validation Failed", the registering node SHOULD try
to register an alternate target address in the NS message.
6.2. NDPSO generation and verficiation
The signature generated by the 6LN to provide proof-of-ownership of
the private-key is carried in the NDP Signature Option (NDPSO). It
is generated by the 6LN as follows:
o Concatenate the following in the order listed:
1. 128-bit type tag (in network byte order)
2. JWK-encoded public key
3. the 16-byte Target Address (in network byte order) sent in the
Neighbor Solicitation (NS) message. It is the address which
the 6LN is registering with the 6LR and 6LBR.
4. NonceLR received from the 6LR (in network byte order) in the
Neighbor Advertisement (NA) message. The random nonce is at
least 6 bytes long as defined in [RFC3971].
5. NonceLN sent from the 6LN (in network byte order). The random
nonce is at least 6 bytes long as defined in [RFC3971].
6. The length of the ROVR field in the NS message cotainting the
Crypto-ID that was sent.
7. 1-byte (in network byte order) Crypto-Type value sent in the
CIPO option.
o Depending on the Crypto-Type (see Section 8.2) chosen by the node
(6LN), apply the hash function on this concatenation.
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o Depending on the Crypto-Type (see Section 8.2) chosen by the node
(6LN), sign the hash output with ECDSA (if curve P-256 is used) or
sign the hash with EdDSA (if curve EdDSA25519ph).
The 6LR on receiving the NDPSO and CIPO options first hashes the JWK
encoded public-key in the CIPO option to make sure that the leftmost
bits up to the size of the ROVR match. Only if the check is
successful, it tries to verify the signature in the NDPSO option
using the following.
o Concatenate the following in the order listed:
1. 128-bit type tag (in network byte order)
2. JWK-encoded public key received in the CIPO option
3. the 16-byte Target Address (in network byte order) received in
the Neighbor Solicitation (NS) message. It is the address
which the 6LN is registering with the 6LR and 6LBR.
4. NonceLR sent in the Neighbor Advertisement (NA) message. The
random nonce is at least 6 bytes long as defined in [RFC3971].
5. NonceLN received from the 6LN (in network byte order) in the
NS message. The random nonce is at least 6 bytes long as
defined in [RFC3971].
6. The length of the ROVR field in the NS message containing the
Crypto-ID that was received.
7. 1-byte (in network byte order) Crypto-Type value received in
the CIPO option.
o Depending on the Crypto-Type (see Section 8.2) indicated by the
(6LN) in the CIPO, apply the hash function on this concatenation.
o Verify the signature with the public-key received and the locally
computed values. If the verification succeeds, the 6LR and 6LBR
add the state information about the Crypto-ID, public-key and
Target Address being registered to their database.
6.3. Multihop Operation
In a multihop 6LoWPAN, the registration with Crypto-ID is propagated
to 6LBR as described in this section. If the 6LR and the 6LBR
maintain a security association, then there is no need to propagate
the proof of ownership to the 6LBR.
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A new device that joins the network auto-configures an address and
performs an initial registration to a neighboring 6LR with an NS
message that carries an Address Registration Option (EARO) [RFC6775].
The 6LR validates the address with an 6LBR using a DAR/DAC exchange,
and the 6LR confirms (or denies) the address ownership with an NA
message that also carries an Address Registration Option.
Figure 5 illustrates a registration flow all the way to a 6LowPAN
Backbone Router (6BBR).
6LN 6LR 6LBR 6BBR
| | | |
| NS(EARO) | | |
|--------------->| | |
| | Extended DAR | |
| |-------------->| |
| | | |
| | | proxy NS(EARO) |
| | |--------------->|
| | | | NS(DAD)
| | | | ------>
| | | |
| | | | <wait>
| | | |
| | | proxy NA(EARO) |
| | |<---------------|
| | Extended DAC | |
| |<--------------| |
| NA(EARO) | | |
|<---------------| | |
| | | |
Figure 5: (Re-)Registration Flow
In a multihop 6LoWPAN, a 6LBR sends RAs with prefixes downstream and
the 6LR receives and relays them to the nodes. 6LR and 6LBR
communicate using ICMPv6 Duplicate Address Request (DAR) and
Duplicate Address Confirmation (DAC) messages. The DAR and DAC use
the same message format as NS and NA, but have different ICMPv6 type
values.
In AP-ND we extend DAR/DAC messages to carry cryptographically
generated ROVR. In a multihop 6LoWPAN, the node exchanges the
messages shown in Figure 5. The 6LBR must identify who owns an
address (EUI-64) to defend it, if there is an attacker on another
6LR.
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7. Security Considerations
7.1. Inheriting from RFC 3971
Observations regarding the following threats to the local network in
[RFC3971] also apply to this specification.
Neighbor Solicitation/Advertisement Spoofing
Threats in section 9.2.1 of RFC3971 apply. AP-ND counters the
threats on NS(EARO) messages by requiring that the NDP Signature
and CIPO options be present in these solicitations.
Duplicate Address Detection DoS Attack
Inside the LLN, Duplicate Addresses are sorted out using the ROVR,
which differentiates it from a movement. DAD coming from the
backbone are not forwarded over the LLN, which provides some
protection against DoS attacks inside the resource-constrained
part of the network. Over the backbone, the EARO option is
present in NS/NA messages. This protects against misinterpreting
a movement for a duplication, and enables the backbone routers to
determine which one has the freshest registration and is thus the
best candidate to validate the registration for the device
attached to it. But this specification does not guarantee that
the backbone router claiming an address over the backbone is not
an attacker.
Router Solicitation and Advertisement Attacks
This specification does not change the protection of RS and RA
which can still be protected by SEND.
Replay Attacks
Nonces (NonceLR and NonceLN) generated by the 6LR and 6LN
guarantees against replay attacks of the NS(EARO).
Neighbor Discovery DoS Attack
A rogue node that managed to access the L2 network may form many
addresses and register them using AP-ND. The perimeter of the
attack is all the 6LRs in range of the attacker. The 6LR must
protect itself against overflows and reject excessive registration
with a status 2 "Neighbor Cache Full". This effectively blocks
another (honest) 6LN from registering to the same 6LR, but the 6LN
may register to other 6LRs that are in its range but not in that
of the rogue.
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7.2. Related to 6LoWPAN ND
The threats discussed in 6LoWPAN ND [RFC6775] and its update
[I-D.ietf-6lo-rfc6775-update] also apply here. Compared with SeND,
this specification saves about 1Kbyte in every NS/NA message. Also,
this specification separates the cryptographic identifier from the
registered IPv6 address so that a node can have more than one IPv6
address protected by the same cryptographic identifier. SeND forces
the IPv6 address to be cryptographic since it integrates the CGA as
the IID in the IPv6 address. This specification frees the device to
form its addresses in any fashion, thereby enabling not only 6LoWPAN
compression which derives IPv6 addresses from Layer-2 addresses but
also privacy addresses.
7.3. ROVR Collisions
A collision of Registration Ownership Verifiers (ROVR) (i.e., the
Crypto-ID in this specification) is possible, but it is a rare event.
The formula for calculating the probability of a collision is 1 -
e^{-k^2/(2n)} where n is the maximum population size (2^64 here,
1.84E19) and K is the actual population (number of nodes). If the
Crypto-ID is 64-bits (the least possible size allowed), the chance of
a collision is 0.01% when the network contains 66 million nodes.
Moreover, the collision is only relevant when this happens within one
stub network (6LBR). In the case of such a collision, an attacker
may be able to claim the registered address of an another legitimate
node. However for this to happen, the attacker would also need to
know the address which was registered by the legitimate node. This
registered address is never broadcasted on the network and therefore
providing an additional 64-bits that an attacker must correctly
guess. To prevent address disclosure, it is RECOMMENDED that nodes
derive the address being registered independently of the ROVR.
8. IANA considerations
8.1. CGA Message Type
This document defines a new 128-bit value under the CGA Message Type
[RFC3972] namespace, 0x8701 55c8 0cca dd32 6ab7 e415 f148 84d0.
8.2. Crypto-Type Subregistry
IANA is requested to create a new subregistry "Crypto-Type
Subregistry" in the "Internet Control Message Protocol version 6
(ICMPv6) Parameters". The registry is indexed by an integer 0..255
and contains a Signature Algorithm and a Hash Function as shown in
Table 1. The following Crypto-Type values are defined in this
document:
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+--------------+-----------------+---------------+------------------+
| Crypto-Type | Signature | Hash Function | Defining |
| value | Algorithm | | Specification |
+--------------+-----------------+---------------+------------------+
| 0 | NIST P-256 | SHA-256 | RFC THIS |
| | [FIPS186-4] | [RFC6234] | |
| 1 | Ed25519ph | SHA-512 | RFC THIS |
| | [RFC8032] | [RFC6234] | |
+--------------+-----------------+---------------+------------------+
Table 1: Crypto-Types
As is evident from the table above, although the two curves provide
similar security, they however rely on different hash functions.
Supporting multiple hash functions on constrained devices is not
ideal. [I-D.struik-lwig-curve-representations] provides information
on how to represent Montgomery curves and (twisted) Edwards curves as
curves in short-Weierstrass form and illustrates how this can be used
to implement elliptic curve computations using existing
implementations that already implement, e.g., ECDSA and ECDH using
NIST [FIPS186-4] prime curves. New Crypto-Type values providing
similar or better security (with less code) can be defined in future.
Assignment of new values for new Crypto-Type MUST be done through
IANA with "Specification Required" and "IESG Approval" as defined in
[RFC8126].
9. Acknowledgments
Many thanks to Charlie Perkins for his in-depth review and
constructive suggestions. We are also especially grateful to Robert
Moskowitz for his comments that lead to many improvements.
10. References
10.1. Normative References
[FIPS186-4]
FIPS 186-4, "Digital Signature Standard (DSS), Federal
Information Processing Standards Publication 186-4", US
Department of Commerce/National Institute of Standards and
Technology Gaithersburg, MD, July 2013.
[I-D.ietf-6lo-rfc6775-update]
Thubert, P., Nordmark, E., Chakrabarti, S., and C.
Perkins, "Registration Extensions for 6LoWPAN Neighbor
Discovery", draft-ietf-6lo-rfc6775-update-21 (work in
progress), June 2018.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<https://www.rfc-editor.org/info/rfc3972>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 6775, DOI 10.17487/RFC6775, November 2012,
<https://www.rfc-editor.org/info/rfc6775>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
<https://www.rfc-editor.org/info/rfc7517>.
10.2. Informative references
[I-D.ietf-6lo-backbone-router]
Thubert, P. and C. Perkins, "IPv6 Backbone Router", draft-
ietf-6lo-backbone-router-07 (work in progress), September
2018.
[I-D.struik-lwig-curve-representations]
Struik, R., "Alternative Elliptic Curve Representations",
draft-struik-lwig-curve-representations-02 (work in
progress), July 2018.
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[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals",
RFC 4919, DOI 10.17487/RFC4919, August 2007,
<https://www.rfc-editor.org/info/rfc4919>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<https://www.rfc-editor.org/info/rfc4944>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/info/rfc6234>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>.
[RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem
Statement and Requirements for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Routing",
RFC 6606, DOI 10.17487/RFC6606, May 2012,
<https://www.rfc-editor.org/info/rfc6606>.
[RFC7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed.,
"Source Address Validation Improvement (SAVI) Framework",
RFC 7039, DOI 10.17487/RFC7039, October 2013,
<https://www.rfc-editor.org/info/rfc7039>.
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <https://www.rfc-editor.org/info/rfc7102>.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<https://www.rfc-editor.org/info/rfc7217>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>.
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[RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
<https://www.rfc-editor.org/info/rfc7696>.
[RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC8032, January 2017,
<https://www.rfc-editor.org/info/rfc8032>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
Appendix A. Requirements Addressed in this Document
In this section we state requirements of a secure neighbor discovery
protocol for low-power and lossy networks.
o The protocol MUST be based on the Neighbor Discovery Optimization
for Low-power and Lossy Networks protocol defined in [RFC6775].
RFC6775 utilizes optimizations such as host-initiated interactions
for sleeping resource-constrained hosts and elimination of
multicast address resolution.
o New options to be added to Neighbor Solicitation messages MUST
lead to small packet sizes, especially compared with existing
protocols such as SEcure Neighbor Discovery (SEND). Smaller
packet sizes facilitate low-power transmission by resource-
constrained nodes on lossy links.
o The support for this registration mechanism SHOULD be extensible
to more LLN links than IEEE 802.15.4 only. Support for at least
the LLN links for which a 6lo "IPv6 over foo" specification
exists, as well as Low-Power Wi-Fi SHOULD be possible.
o As part of this extension, a mechanism to compute a unique
Identifier should be provided with the capability to form a Link
Local Address that SHOULD be unique at least within the LLN
connected to a 6LBR.
o The Address Registration Option used in the ND registration SHOULD
be extended to carry the relevant forms of Unique Interface
IDentifier.
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o The Neighbour Discovery should specify the formation of a site-
local address that follows the security recommendations from
[RFC7217].
Authors' Addresses
Pascal Thubert (editor)
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
MOUGINS - Sophia Antipolis 06254
FRANCE
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
Behcet Sarikaya
Plano, TX
USA
Email: sarikaya@ieee.org
Mohit Sethi
Ericsson
Jorvas 02420
Finland
Email: mohit@piuha.net
Rene Struik
Struik Security Consultancy
Email: rstruik.ext@gmail.com
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