wdiff draft-ietf-6lo-ap-nd-01.txt draft-ietf-6lo-ap-nd-02.txt

6lo B. Sarikaya, Ed. Sarikaya
Internet-Draft Huawei USA
Updates: 6775 (if approved) P. Thubert
Intended status: Standards Track Cisco
Expires: November 16, 25, 2017 M. Sethi, Ed. Sethi
Ericsson
May 15, 24, 2017

Address Protected Neighbor Discovery for Low-power and Lossy Networks
draft-ietf-6lo-ap-nd-01
draft-ietf-6lo-ap-nd-02

Abstract

This document defines an extension to 6LoWPAN Neighbor Discovery.
This extension is designed for low-power and lossy network
environments and it supports multi-hop operation. Discovery, RFC
6775. Nodes supporting this extension compute a Cryptographically cryptographic Owner
Unique Interface ID and associate it with one or more of their
Registered Addresses. The
Cryptographic ID (Crypto-ID) uniquely identifies the owner of the
Registered Address. It is used in place of the EUI-64 address that
is specified in RFC 6775. Once an address is registered with a
Cryptographic ID, only the owner of that ID can modify the anchor
state information of the Registered Address in the 6LR Address, and 6LBR. Source Address
Validation can be enforced.

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
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This Internet-Draft will expire on November 16, 25, 2017.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Requirements . . Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . . 4
4. Protocol Interactions . New Fields and Options . . . . . . . . . . . . . . . . . . . 5
4.1. Overview . . New Crypto-ID . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Updating RFC 6775 Updated EARO . . . . . . . . . . . . . . . . . . . . 7
4.2.1. . . 6
4.3. New Crypto-ID Calculation Parameters Option . . . . . . . . . . . . . 7
5. Protocol Overview . . . . . 10
4.3. . . . . . . . . . . . . . . . . . 8
5.1. Protocol Scope . . . . . . . . . . . . . . . . . . . . . 8
5.2. Protocol Flows . . . . . . . . . . . . . . . . . . . . . 9
5.3. Multihop Operation . . . . . . . . . . . . . . . . . . . 13
5. 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. 12
7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 14
7. 13
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
8. 13
9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 14
9. 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1. 13
10.1. Normative References . . . . . . . . . . . . . . . . . . 15
9.2. 13
10.2. Informative references . . . . . . . . . . . . . . . . . 14
Appendix A. Requirements Addressed in this Document . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17

1. Introduction

Neighbor discovery for IPv6 [RFC4861] and stateless address
autoconfiguration [RFC4862] and their extensions are together collectively
referred to as neighbor
discovery protocols (NDP). They are defined for regular hosts that
have sufficient memory and computation capabilities. These protocols
are however not suitable for resource-constrained devices.
Therefore, they require adaptation the IPv6 Neighbor Discovery Protocol (IPv6 NDP). In
order to work on resource-constrained
hosts operating enable IPv6 NDP operations over a constrained low-power and
lossy network (LLN). Neighbor (LLN), "Neighbor Discovery optimizations for 6LoWPAN networks include simple
optimizations such as
networks" [RFC6775] (6LoWPAN ND), reduces the use of multicast in the
original protocol and introduces a unicast host address registration feature. This
feature uses the address
technique. The registration option mechanism leverages a new Address
Registration Option (ARO) which that is sent carried in the unicast Neighbor
Solicitation (NS) and Neighbor Advertisement (NA) messages [RFC6775].

With 6LoWPAN ND [RFC6775], between
the ARO option includes a EUI-64 interface
ID to uniquely identify 6LoWPAN Node (6LN) and the interface of 6LoWPAN Router (6LR), as well as the Registered
Duplicate Address on
the registering device, so as to correlate further registrations for Request (DAR) and Duplicate Address Confirmation
(DAC) messages between the same address 6LR and avoid address duplication. The EUI-64 interface
ID the 6LoWPAN Border Router (6LBR),
which is not secure and its ownership cannot be verified. Consequently,
any device claiming the same EUI-64 interface ID may take over an
existing registration and attract central repository of all the traffic for that address. registered addresses in
its domain.

The
address registration mechanism in 6LoWPAN ND [RFC6775] is limited was created for
the original purpose of Duplicate Address Detection (DAD), whereby
use of an address would be granted as it does long as the address is not
require
already present in the subnet (first come first serve). In order to
validate address ownership, the registration mechanism enables the
6LR and 6LBR to correlate further claims for a node registered address
from the device to prove its ownership which it is granted with a Owner Unique Interface
IDentifier (OUID). With 6LoWPAN ND, the OUID is derived from the MAC
address of the EUI-64 Interface ID. device (EUI-64), which can be spoofed. Therefore, any
node connected to the subnet and aware of the
registered address to EUI-64 interface ID a registered-address-to-
OUID mapping may effectively fake the same interface ID and OUID, steal an address.

In this document, we extend 6LoWPAN ND to protect the address
ownership with cryptographic material, but as opposed to Secure
Neighbor Discovery (SEND) [RFC3971] and Cryptographically Generated
Addresses (CGAs) [RFC3972], the cryptographic material generated is
not embedded in the Interface ID (IID) as an IPv6 address. Instead,
the generated cryptographic ID is used as a correlator associated
with the registration of the IP address. This approach is made
possible with 6LoWPAN ND [RFC6775], where the 6LR and
attract the 6LBR
maintain state information traffic for each Registered Address. If that address towards a
cryptographic ID is associated with the first 6LoWPAN ND
registration, then it can be used to validate any future updates to
the registration. different Node. In
order to achieve this ownership verification, in this extension
specification, allow a more secured registration mechanism, the EUI-64 interface ID used in "Update to
6LoWPAN ND is replaced
with cryptographic material whose ownership can be verified. The
extension also provides new means for ND" [I-D.ietf-6lo-rfc6775-update] opens the 6LR to validate ownership semantics of the registration,
ARO option and thus, the ownership allows to transport alternate forms of registered address.
The resulting protocol is called Protected Address Registration
protocol (ND-PAR).

In ND-PAR, OUIDs.

With this specification, a node typically 6LN generates one 64-bit a cryptographic ID
(Crypto-ID) (Crypto-
ID) and uses places it as Unique Interface ID in the OUID field in the registration of one (or
more) of its addresses with the 6LR, which 6LR(s) that it attaches to and uses as default router.
router(s). Proof of ownership of the cryptographic ID (Crypto-ID) is
passed with the first registration to a given 6LR, and enforced at
the 6LR, in a new Crypto-ID Parameters Option (CIPO). The 6LR
validates ownership of the cryptographic ID typically upon the creation or update of a
registration state, for instance following an apparent movement from one point or a change in the anchor information, such as
Link-Layer Address and associated Layer-2 cryptographic material.

The protected address registration protocol proposed in this document
enables the enforcement of
attachment Source Address Validation (SAVI)
[RFC7039], which ensures that only the correct owner uses a
registered address in the source address field in IPv6 packets. With
this specification, a 6LN that sources a packet has to another. The ARO option use a 6LR to
which the source address of the packet is modified registered to carry forward the
Unique Interface ID, and through
packet. The 6LR maintains state information for the DAR/DAC exchange.

Compared registered
addressed along with SeND, this specification saves ~1Kbyte in every NS/NA
message. Also SeND requires one cryptographic address per IPv6
address. This specification separates the MAC address, and link-layer cryptographic identifier
key associated with that node. In SAVI-enforcement mode, the 6LR
allows only packets from a connected Host if the IPv6 connected Host owns
the registration of the source address so of the packet.

The 6lo adaptation layer framework ([RFC4944], [RFC6282]) expects
that a node can have more than one IPv6
address protected by the same cryptographic identifier. SeND forces
the device forms its IPv6 address addresses based on Layer-2 address, so
as to be cryptographic since it integrates enable a better compression. This is incompatible with "Secure
Neighbor Discovery (SEND)" [RFC3971] and "Cryptographically Generated
Addresses (CGAs)" [RFC3972], which derive the CGA as
an IID. 6LoWPAN derives Interface ID (IID) in
the IPv6 address addresses from other things like cryptographic material. "Privacy
Considerations for IPv6 Address Generation Mechanisms"
[I-D.ietf-6man-ipv6-address-generation-privacy] places additional
recommendations on the way addresses should be formed and renewed.

This specification allows a
short device to form and register addresses at
will, without a constraint on the way the address is formed or the
number of addresses that are registered in 802.15.4 parallel. It enables to enable
protect multiple addresses with a better compression. single cryptographic material and
to send the proof only once to a given 6LR for multiple addresses and
refresher registrations.

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].

Readers are expected to be familiar with all the terms and concepts
that are discussed in [RFC3971], [RFC3972], [RFC4861], [RFC4919],
[RFC6775], and [I-D.ietf-6lo-backbone-router] which proposes an
evolution of [RFC6775] for wider applicability.

This document defines Crypto-ID as an identifier of variable size
which in most cases is 64 bits long. It is generated using
cryptographic means explained later in this document.

The document also conforms to the terms and models described in
[RFC5889] and uses the vocabulary and the concepts defined in
[RFC4291] for the IPv6 Architecture.

This document uses [RFC7102] for Terminology in Low power And Lossy
Networks.

3. Requirements

In Updating RFC 6775

With this section we state requirements of specification, 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 node SHOULD be extensible
to more LLN links than IEEE 802.15.4 only. Support for at least
the LLN links for which use a 6lo "IPv6 over foo" specification
exists, as well cryptographic identifier
(Crypto-ID) 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 OUID in its registration; the ND registration SHOULD
be extended to carry the relevant forms of Unique Interface
IDentifier.

o The Neighbour Discovery should specify the formation of a site-
local address that follows the security recommendations from
[RFC7217].

4. Protocol Interactions

Protected address and registration neighbor discovery protocol (ND-
PAR) modifies Neighbor Discovery Optimization for Low-power and Lossy
Networks [RFC6775] Crypto-ID is calculated
as explained described in this section. Section 4.1. Overview The scope of the present work is a 6LoWPAN Low Power Lossy Network
(LLN), typically a stub network connected to a larger IP network via
a Border Router called fact that a 6LBR per [RFC6775].

Figure 1: Basic Configuration

The 6LBR maintains OUID is a registration state for all devices in the
attached LLN, and, in conjunction with the first-hop router (the
6LR), Crypto-ID is
indicated in a position to validate uniqueness and grant ownership of
an IPv6 address before it can be used new 'C' flag in the LLN. This is a
fundamental difference with a classical network that relies on IPv6
address auto-configuration [RFC4862], where there is no guarantee of
ownership from the network, and any IPv6 Neighbor Discovery packet
must be individually secured [RFC3971].

In a mesh network, the 6LR is directly connected to the host device. NS(ARO) message.

This specification expects that the peer-wise layer-2 security is
deployed so that all the packets from also introduces 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 new option, the 6LBR via other
6LRs. This specification expects CIPO, that a chain of trust is
established so that a packet that was validated by the first 6LR can
be safely routed by the next 6LRs to the 6LBR.

[I-D.ietf-6tisch-architecture] suggests
used to use prove ownership of RPL [RFC6550] as
the routing protocol between the 6LRs and the 6LBR, and leveraging a
backbone router [I-D.ietf-6lo-backbone-router] to extend the LLN in a
larger multilink subnet [RFC4903]. In that model, a registration
flow happens as shown in Figure 2. Note that network beyond the 6LBR
is out of scope for this document.

6LoWPAN Node 6LR 6LBR
(RPL leaf) (router) (root)
| | |
| 6LoWPAN ND |6LoWPAN ND+RPL | Efficient ND
| LLN link |Route-Over mesh| IPv6 link
| | |
| NS(ARO) | |
|-------------->| |
| 6LoWPAN ND | DAR (then DAO)|
| |-------------->|
| | |
| | |
| | |
| | |
| | |
| | |
| | |
| | DAC |
| |<--------------|
| NA(ARO) | |
|<--------------| |

Figure 2: (Re-)Registration Flow over Multi-Link Subnet Crypto-ID. A new device node that joins registers for
the network auto-configures an address and
performs an initial registration first time to an on-link 6LR with an NS message
that carries a new Address Registration Option (ARO) [RFC6775]. The 6LR validates the address with the central 6LBR using SHOULD place a DAR/DAC
exchange, and the 6LR confirms (or denies) the address ownership with
an NA message that also carries an Address Registration Option.

The CIPO option to its
registration mechanism in [RFC6775] was created for the original
purpose of Duplicate Address Detection (DAD), whereby use of an
address would be granted as long as the address but is not already
present in the subnet. But [RFC6775] does not require that the 6LR
use the registration for source address validation (SAVI) [RFC7039].

Protected address registration protocol proposed in this document
enforces SAVI. With this we ensure that only the correct owner uses expected to place the registered address option in the source address field. Therefore a
destination node can trust that the source is the real owner without
using SeND. All packets destined next
periodic refresher registrations for a node go through the 6LR to
which it is attached. The 6LR maintains state information that address, or for the
registered addressed along
registration of other addresses with the MAC address, and link-layer
cryptographic key associated with that node. The same OUID. When a 6LR therefore only
delivers packets to the real owner based on its state information.

In order to validate address ownership, the
receives a NS(ARO) registration mechanism
(that goes all the way to the 6LBR with the DAR/DAC) enables the 6LBR
to correlate further claims for a registered address from the device
to which new Crypto-ID as a OUID, then
it is granted, based on SHOULD challenge by responding with a Unique Interface IDentifier (UID). NA(ARO) with a status of
"Proof requested". This UID whole process MAY be skipped in networks
where there is derived from the MAC address no or ultra low expectations of mobility.

The challenge will also be triggered in the device (EUI-64).

This document uses case of a randomly generated value as an alternate UID registration
for which the registration. Proof of ownership of the UID Source Link-Layer Address is passed not consistent with the
first registration to a given 6LR, and enforced
state that already exists either at the 6LR, which
validates the proof. With this new operation, the 6LR allows only
packets from a connected host if the connected host owns the
registration of the source address of or the packet. 6LBR. In a multihop 6LoWPAN, the registration with Crypto-ID is propagated
to
latter case, the 6LBR as described in Section 4.3. If returns a chain status of trust is present
between the 6LR and "Proof requested" in the 6LBR, then there
DAR/DAC exchange, which is no need to propagate the
proof of ownership to the 6LBR. All echoed by the 6LBR needs to know is that
this particular UID is randomly generated, so as to enforce that any
update via a different 6LR is also random.

4.2. Updating RFC 6775

Protocol interactions are as defined in Figure 2. The Crypto-ID is
calculated as described in Section 4.2.1.

The Target Address field in NS message is set to the prefix
concatenated with NA (ARO) back to
the node's address. registering node. This address does flow should not need
duplicate address detection as Crypto-ID is globally unique. So a
host cannot steal an address that is already registered unless it has
the key used for generating the Crypto-ID. The same Crypto-ID can
thus be used to protect multiple addresses e.g. when the node
receives alter a different prefix.

Local or on-link protocol interactions are shown in Figure 3.
Crypto-ID and ARO are passed to and stored by the 6LR/6LBR on the
first NS and not sent again preexisting state
in the next NS. The operation starts
with 6LR sending a Router Advertisement (RA) message to 6LN.

Upon a claim. The node becomes owner of that address and the address
is bound to the Crypto-ID in the 6LR/6LBR registry. This procedure
avoids the constrained device to compute multiple keys for multiple
addresses. The registration process allows the node to tie all the
addresses to the same Crypto-ID and have the 6LR/6LBR enforce first-
come first-serve after that.

A condition where NA(ARO) with a 6LN uses multiple IPv6 addresses may happen when status of "Proof requested", the registering
node moves at a different place and receives SHOULD retry its registration with a different prefix.
In this scenario, CIPO option that proves its
ownership of the node uses Crypto-ID.

If the same Crypto-ID to protect its new
IPv6 address. This prevents other nodes from stealing 6LR cannot validate the address
and trying to use proof, it as their source address.

Note that if the device that moves always forms new MAC and IP
address [RFC6775], then this new address can be used for
registration. In case responds with a status of
"Incorrect Proof". Upon a collision NA(ARO) with a status of "Incorrect
Proof", the new MAC and therefore IP
address, the registering node can easily form a new IPv6 address. This is one
case where the SHOULD NOT use of Crypto-ID would not be needed. this Crypto-ID or
ND-PAR should be activated when the IP address is claimed at another
place, or for a different MAC address at the same place, e.g. for MAC
address privacy [I-D.ietf-6man-ipv6-address-generation-privacy].

6LN 6LR
| |
|<------------------- RA --------------------------|
| |
|----------- NS with ARO and Crypto-ID ----------->|
| |
|<---------- NA with ARO (status=req-proof) -------|
| |
|----------- NS with ARO and Crypto-ID ----------->|
| |
|<---------------- NA with ARO --------------------|
| |
... ...
| |
|------------ NS with ARO and Crypto-ID ---------->|
| |
| |
|<---------------- NA with ARO --------------------|
... ...
| |
|----------- NS
registering with ARO that 6LR anymore.

4. New Fields and Options

4.1. New Crypto-ID ----------->|
| |
| |
|<---------------- NA with ARO --------------------|

Figure 3: On-link Protocol Operation

Elliptic Curve Cryptography (ECC) is used in the calculation of
cryptographic identifier (Crypto-ID). the
Crypto-ID. The digital signature is constructed by using the 6LN's
private key over its EUI-64 (MAC) address. The signature value is
computed using the ECDSA signature algorithm and the hash function
used is SHA-256 [RFC6234]. Public Key is the most important
parameter in CGA Parameters (sent by 6LN in an NS message). ECC
Public Key could be in uncompressed form or in compressed form where
the first octet of the OCTET STRING is 0x04 and 0x02 or 0x03,
respectively. Point compression can further reduce the key size by
about 32 octets.

After calculating its Crypto-ID, a 6LN sends it along with the CGA
parameters in the first NS message, see Figure 3. In order to send
Crypto-ID, a modified address registration option called Enhanced
Address Registration Option (EARO) is defined in Figure 4. As
defined in the figure this ID is variable length, varying between 64
to 128 bits. This ID is 128 bits long only if it is used as IPv6
address. This may happen when some application uses one IP address
of the device as device ID. It would make sense in that case to
build a real CGA IPv6 address. The prefix of the address would be
obtained from prefix information option (PIO in RA) [RFC4861].

6LN also sends some other parameters to enable 6LR or 6LBR to verify
the Crypto-ID. The option shown in Figure 5 can be used. In the
figure, CGA Parameters field contains the public key, prefix and some
other values. It is a simplified form of CGA Option defined in
[RFC3971].

4.2.1. Crypto-ID Calculation

First, the modifier is set to a random or pseudo-random 128-bit
value. Next, concatenate from left to right the modifier, 9 zero
octets and the ECC public key. SHA-256 algorithm is applied on the
concatenation. The 112 leftmost bits of the hash value is taken.
Concatenate from left to right the modifier value, the subnet prefix
and the encoded public key. NIST P-256 is executed on the
concatenation. The leftmost bits of the result is used as the
Crypto-ID. The length is normally With this specification, the last 64 bits, however bits are retained,
but it could be 128
bits. expanded to more bits in the future by increasing the
size of the OUID field.

In respecting the cryptographical cryptographic algorithm agility [RFC7696], Curve
25519 [RFC7748] can also be used instead of NIST P-256. This is
indicated by 6LN by setting the Crypto Type field in CGA Parameters
Option the CIPO option
to a value of 1. If 6LBR does not support Curve 25519, it will set
Crypto Type field to zero. This means that the default algorithm
(NIST P-256) will be used.

4.2. Updated EARO

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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |C|T| TID | Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Owner Unique ID (EUI-64 or equivalent) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: 1: Enhanced Address Registration Option

Type:

TBA1

Length:

8-bit unsigned integer. The length of the option (including the
type and length fields) in units of 8 bytes. The value 0 is
invalid. A value of 3 with the C flag set indicates a Crypto-ID
of 128 bits.

Status:

8-bit unsigned integer. Indicates the status of a registration in
the NA response. MUST be set to 0 in NS messages. See below. This
specification leverages values introduced in the Update to 6LoWPAN
ND [I-D.ietf-6lo-rfc6775-update], such as 5: Proof Requested, and
does not require additional values to be defined.

Reserved:

This field is unused. It MUST be initialized to zero by the
sender and MUST be ignored by the receiver.

This specification introduces a C bit when set bit, which is used set to indicate
that the Owner Unique ID fields field contains a Crypto-ID.

T and TID:

Defined in [I-D.ietf-6lo-backbone-router]. [I-D.ietf-6lo-rfc6775-update].

Owner Unique ID:

When using this specification, this field contains Crypto-ID, a variable
length field to carry the Crypto-ID.

4.3. New Crypto-ID or random UID. Parameters Option

This field is
normally 64 bits long. It could be 128 bits long if IPv6 address
is used as specification introduces a new option, the Crypto-ID. Crypto-ID Parameters
Option (CIPO), that carries the proof of ownership of a crypto-ID.

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 | Crypto Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Modifier (16 octets) +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Subnet Prefix (8 octets) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
+ Public Key (variable length) +
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 5: CGA 2: Crypto-ID Parameters Option

Type:

TBA2

CIPO, to be assigned by IANA.

Length:

The length of the option in units of 8 octets.

Pad Length:

The length of the Padding field.

Crypto Type:

The type of cryptographic algorithm used in calculation Crypto-ID.
Default value of all zeros indicate NIST P-256. A value of 1 is
assigned for Curve 25519. New values may be defined later.

Modifier:

128 bit random value.

Subnet Prefix:

64 bit subnet prefix.

Public Key:

ECC public key of 6LN.

Padding:

A variable-length field making the option length a multiple of 8,
containing as many octets as specified in the Pad Length field.

4.3.

5. Protocol Overview

5.1. Protocol Scope

The scope of the present work 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].

The 6LBR maintains a registration state for all devices in the
attached LLN, and, in conjunction with the first-hop router (the
6LR), is in a position to validate uniqueness and grant ownership of
an IPv6 address before it can be used in the LLN. This is a
fundamental difference with a classical network that relies on IPv6
address auto-configuration [RFC4862], where there is no guarantee of
ownership from the network, and any 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 expects 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 expects that a chain of trust is
established so that a packet that was validated by the first 6LR can
be safely routed by the next 6LRs to the 6LBR.

5.2. Protocol Flows

The 6TiSCH Architecture [I-D.ietf-6tisch-architecture] suggests to
use of RPL [RFC6550] as the routing protocol between the 6LRs and the
6LBR. In that model, a registration flow happens as shown in
Figure 4.

6LoWPAN Node 6LR 6LBR
(RPL leaf) (router) (RPL root)
| | |
| 6LoWPAN ND | 6LoWPAN ND |
| | |
| | |
| NS(ARO) | |
|-------------->| |
| 6LoWPAN ND | DAR |
| |-------------->|
| |(then RPL DAO) |
| | |
| | DAC |
| |<--------------|
| NA(ARO) | |
|<--------------| |
| | |
| | |

Figure 4: (Re-)Registration Flow

A new device that joins the network auto-configures an address and
performs an initial registration to an on-link 6LR with an NS message
that carries an Address Registration Option (ARO) [RFC6775]. The 6LR
validates the address with the central 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.

In a multihop 6LoWPAN, the registration with Crypto-ID is propagated
to 6LBR as described in Section 5.3. If a chain of trust is present
between the 6LR and the 6LBR, then there is no need to propagate the
proof of ownership to the 6LBR. All the 6LBR needs to know is that
this particular OUID is randomly generated, so as to enforce that any
update via a different 6LR is also random.

Local or on-link protocol interactions are shown in Figure 5.
Crypto-ID and ARO are passed to and stored by the 6LR/6LBR on the
first NS and not sent again in the next NS. The operation starts
with 6LR sending a Router Advertisement (RA) message to 6LN.

The 6LR/6LBR ensures first-come/first-serve by storing the ARO and
the Crypto-ID correlated to the node being registered. The node is
free to claim any address it likes 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 binding can be verified
later, which 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 uses multiple IPv6 addresses at any time. This condition
may happen for privacy reasons
[I-D.ietf-6man-ipv6-address-generation-privacy], or when the node
moves at a different place and auto-configures an new address from a
different prefix. In those situations, the node may use the same
Crypto-ID to protect multiple IPv6 addresses. The separation of the
address and the Crypto-ID avoids the constrained device to compute
multiple keys for multiple addresses. The registration process
allows the node to tie all of its addresses to the same Crypto-ID and
have the 6LR/6LBR enforce first-come first-serve after that.

6LN 6LR
| |
|<------------------- RA --------------------------|
| |
|----------- NS with ARO and Crypto-ID ----------->|
| |
|<---------- NA with ARO (status=proof requested) -|
| |
|----------- NS with ARO and Crypto-ID ----------->|
| |
|<---------------- NA with ARO --------------------|
| |
... ...
| |
|------------ NS with ARO and Crypto-ID ---------->|
| |
| |
|<---------------- NA with ARO --------------------|
... ...
| |
|----------- NS with ARO and Crypto-ID ----------->|
| |
| |
|<---------------- NA with ARO --------------------|

Figure 5: On-link Protocol Operation

5.3. Multihop Operation

In multihop 6LoWPAN, 6LBR sends RAs with prefixes downstream and it
is the 6LR that receives and relays them to the nodes. 6LR and 6LBR
communicate with the ICMPv6 Duplicate Address Request (DAR) and the
Duplicate Address Confirmation (DAC) messages. The DAR and DAC use
the same message format as NS and NA with different ICMPv6 type
values.

In ND-PAR we extend DAR/DAC messages to carry cryptographically
generated UID. OUID. In a multihop 6LoWPAN, the node exchanges the
messages shown in Figure 2. 4. The 6LBR must be aware of who owns an
address (EUI-64) to defend the first node if there is an attacker on
another 6LR. Because of this the content that the source signs and
the signature needs to be propagated to the 6LBR in DAR message. For
this purpose the DAR message sent by 6LR to 6LBR MUST contain CGA
Parameters and Digital Signature Option carrying the CGA that the
node calculates and its public key.
CIPO option. DAR message also contains ARO.

It is possible that occasionally, a 6LR may miss the node's UID OUID
(that it received in ARO). 6LR should be able to ask for it again.
This is done by restarting the exchanges shown in Figure 3. 5. The
result enables 6LR to refresh the information that was lost. 6LR MUST
send DAR message with ARO to 6LBR. 6LBR as a reply forms a DAC
message with the information copied from the DAR and the Status field
is set to zero. With this exchange, the 6LBR can (re)validate and
store the information to make sure that the 6LR is not a fake.

In some cases 6LBR may use DAC message to signal to 6LR that it
expects Crypto-ID from 6LR also asks 6LR to verify the EUI-64 6LR
received from 6LN. This may happen when a 6LN node is compromised
and a fake node is sending the Crypto-ID as if it is the node's EUI-
64. Note that the detection in this case can only be done by 6LBR
not by 6LR.

6. Security Considerations

The same considerations observations regarding the threats to the Local Link Network covered in
[RFC3971] apply. also apply to this specification.

This document inherits threats discussed in 6LoWPAN ND [RFC6775] and
its update [I-D.ietf-6lo-rfc6775-update] and addresses the potential
attacks related to address stealing and spoofing within a LLN.
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,
so as to enable the classical 6LoWPAN compression which derives IPv6
addresses from Layer-2 addresses, as well as privacy addresses.

The threats discussed in Section 9.2 of [RFC3971] are countered by
the protocol described in this document as well.

Collisions of Crypto-ID is a possibility that needs to be considered.
The formula for calculating probability of a collision is 1 -
e^{-k^2/(2n)}. If the Crypto-ID is 64-bit long, then the chance of
finding a collision is 0.01% when the network contains 66 million
nodes. It is important to note that the collision is only relevant
when this happens within one stub network (6LBR). A collision of ID
in ND-PAR is a rare event. However, when such a collision does
happen, the protocol operation is not affected, although it opens a
window for a node to hijack an address from another. The link-layer
security ensures that the nodes would normally not be aware of a
collision on the subnet. If a malicious node is able to gain
knowledge of a collision through other means, the only thing that it
could do is to steal addresses from the other honest node. This
would be no different from what is already possible in a 6lo network
today.

7. IANA considerations

IANA is requested to assign two new option type values, TBA1 and TBA2 values for the CIPO
under the subregistry "IPv6 Neighbor Discovery Option Formats".

8. Acknowledgements

We are grateful to Rene Struik and Robert Moskowitz for their
comments that lead to many improvements to this document.

9. Change Log

o submitted version -00 as a working group draft after adoption, and
corrected the order of authors

o submitted version -01 with no changes

o submitted version -02 with these changes: Moved Requirements to
Appendix A, Section 4.2 moved to Section 3, New section 4 on New
Fields and Options, Section 4 changed to Protocol Overview as
Section 5 with Protocol Scope and Flows subsections.

10. References

9.1.

10.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://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,
<http://www.rfc-editor.org/info/rfc3971>.

[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<http://www.rfc-editor.org/info/rfc3972>.

[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <http://www.rfc-editor.org/info/rfc4291>.

[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,
<http://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,
<http://www.rfc-editor.org/info/rfc4862>.

[RFC4903] Thaler, D., "Multi-Link Subnet Issues",

[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 4903, 6775, DOI 10.17487/RFC4903, June 10.17487/RFC6775, November 2012,
<http://www.rfc-editor.org/info/rfc6775>.

[I-D.ietf-6lo-rfc6775-update]
Thubert, P., Nordmark, E., and S. Chakrabarti, "An Update
to 6LoWPAN ND", draft-ietf-6lo-rfc6775-update-05 (work in
progress), May 2017.

10.2. Informative references

[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<http://www.rfc-editor.org/info/rfc3971>.

[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<http://www.rfc-editor.org/info/rfc3972>.

[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,
<http://www.rfc-editor.org/info/rfc4903>.
<http://www.rfc-editor.org/info/rfc4944>.

[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,
<http://www.rfc-editor.org/info/rfc6282>.

[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,
<http://www.rfc-editor.org/info/rfc4919>.

[RFC5889] Baccelli, E., Ed. and M. Townsley, Ed., "IP Addressing
Model in Ad Hoc Networks", RFC 5889, DOI 10.17487/RFC5889,
September 2010, <http://www.rfc-editor.org/info/rfc5889>.

[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,
<http://www.rfc-editor.org/info/rfc6234>.

[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<http://www.rfc-editor.org/info/rfc6550>.

[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,
<http://www.rfc-editor.org/info/rfc6775>.

[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <http://www.rfc-editor.org/info/rfc7102>.

[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,
<http://www.rfc-editor.org/info/rfc7039>.

[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,
<http://www.rfc-editor.org/info/rfc7217>.

[RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
<http://www.rfc-editor.org/info/rfc7696>.

[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, <http://www.rfc-editor.org/info/rfc7748>.

9.2. Informative references

[I-D.ietf-6lo-backbone-router]
Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo-
backbone-router-03 (work in progress), January 2017.

[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-11 (work
in progress), January 2017.

[I-D.ietf-6man-ipv6-address-generation-privacy]
Cooper, A., Gont, F., and D. Thaler, "Privacy
Considerations for IPv6 Address Generation Mechanisms",
draft-ietf-6man-ipv6-address-generation-privacy-08 (work
in progress), September 2015.

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 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 The Address Registration Option used in the ND registration SHOULD
be extended to carry the relevant forms of Unique Interface
IDentifier.

o The Neighbour Discovery should specify the formation of a site-
local address that follows the security recommendations from
[RFC7217].

Authors' Addresses

Behcet Sarikaya (editor)
Huawei USA
5340 Legacy Dr. Building 3
Plano, TX 75024

Email: sarikaya@ieee.org

Pascal Thubert
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

Mohit Sethi (editor)
Ericsson
Hirsalantie
Jorvas 02420

Email: mohit@piuha.net