Internet DRAFT - draft-ietf-6lo-ap-nd
draft-ietf-6lo-ap-nd
6lo P. Thubert, Ed.
Internet-Draft Cisco
Updates: 8505 (if approved) B. Sarikaya
Intended status: Standards Track
Expires: 1 November 2020 M. Sethi
Ericsson
R. Struik
Struik Security Consultancy
30 April 2020
Address Protected Neighbor Discovery for Low-power and Lossy Networks
draft-ietf-6lo-ap-nd-23
Abstract
This document updates the 6LoWPAN Neighbor Discovery (ND) protocol
defined in RFC 6775 and RFC 8505. 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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 1 November 2020.
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Copyright Notice
Copyright (c) 2020 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
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provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Additional References . . . . . . . . . . . . . . . . . . 4
2.3. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 5
3. Updating RFC 8505 . . . . . . . . . . . . . . . . . . . . . . 5
4. New Fields and Options . . . . . . . . . . . . . . . . . . . 6
4.1. New Crypto-ID . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Updated EARO . . . . . . . . . . . . . . . . . . . . . . 7
4.3. Crypto-ID Parameters Option . . . . . . . . . . . . . . . 8
4.4. NDP Signature Option . . . . . . . . . . . . . . . . . . 10
4.5. Extensions to the Capability Indication Option . . . . . 11
5. Protocol Scope . . . . . . . . . . . . . . . . . . . . . . . 12
6. Protocol Flows . . . . . . . . . . . . . . . . . . . . . . . 13
6.1. First Exchange with a 6LR . . . . . . . . . . . . . . . . 14
6.2. NDPSO generation and verification . . . . . . . . . . . . 16
6.3. Multihop Operation . . . . . . . . . . . . . . . . . . . 17
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
7.1. Brown Field . . . . . . . . . . . . . . . . . . . . . . . 18
7.2. Inheriting from RFC 3971 . . . . . . . . . . . . . . . . 18
7.3. Related to 6LoWPAN ND . . . . . . . . . . . . . . . . . . 19
7.4. Compromised 6LR . . . . . . . . . . . . . . . . . . . . . 20
7.5. ROVR Collisions . . . . . . . . . . . . . . . . . . . . . 20
7.6. Implementation Attacks . . . . . . . . . . . . . . . . . 21
7.7. Cross-Algorithm and Cross-Protocol Attacks . . . . . . . 21
7.8. Public Key Validation . . . . . . . . . . . . . . . . . . 22
7.9. Correlating Registrations . . . . . . . . . . . . . . . . 22
8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 22
8.1. CGA Message Type . . . . . . . . . . . . . . . . . . . . 22
8.2. Crypto-Type Subregistry . . . . . . . . . . . . . . . . . 23
8.3. IPv6 ND option types . . . . . . . . . . . . . . . . . . 24
8.4. New 6LoWPAN Capability Bit . . . . . . . . . . . . . . . 24
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9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24
10. Normative References . . . . . . . . . . . . . . . . . . . . 24
11. Informative references . . . . . . . . . . . . . . . . . . . 26
Appendix A. Requirements Addressed in this Document . . . . . . 28
Appendix B. Representation Conventions . . . . . . . . . . . . . 28
B.1. Signature Schemes . . . . . . . . . . . . . . . . . . . . 28
B.2. Representation of ECDSA Signatures . . . . . . . . . . . 29
B.3. Representation of Public Keys Used with ECDSA . . . . . . 30
B.4. Alternative Representations of Curve25519 . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32
1. Introduction
Neighbor Discovery Optimizations for 6LoWPAN networks [RFC6775]
(6LoWPAN ND) adapts the original IPv6 Neighbor Discovery (IPv6 ND)
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 compared to the Duplicate Address Detection (DAD) mechanism
defined in IPv6 ND. 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 "Neighbor Discovery Optimization for
Low-power and Lossy Networks" [RFC6775] (aka 6LoWPAN ND) 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). The ROVR is defined in
"Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505]
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 an
attacker to steal the address and redirect traffic for that address.
[RFC8505] defines an Extended Address Registration Option (EARO)
option that transports alternate forms of ROVRs, and is a pre-
requisite for this specification.
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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
provides the same conceptual benefit as Source Address Validation
(SAVI) [RFC7039] that only the owner of an IPv6 address may source
packets with that address. As opposed to [RFC7039], which relies on
snooping protocols, the protection is based on a state that is
installed and maintained in the network by the owner of the address.
With this specification, a 6LN may use a 6LR for forwarding an IPv6
packets if and only if it has registered the address used as source
of the packet with that 6LR.
With the 6lo adaptation layer in [RFC4944] and [RFC6282], a 6LN can
obtain a better compression for an IPv6 address with an Interface ID
(IID) that is derived from a Layer-2 address. As a side note, this
is incompatible with Secure Neighbor Discovery (SeND) [RFC3971] and
Cryptographically Generated Addresses (CGAs) [RFC3972], since they
derive the IID from cryptographic keys, whereas this specification
separates the IID and the key material.
2. Terminology
2.1. BCP 14
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.2. Additional References
The reader may get additional context for this specification from the
following references:
* "SEcure Neighbor Discovery (SEND)" [RFC3971],
* "Cryptographically Generated Addresses (CGA)" [RFC3972],
* "Neighbor Discovery for IP version 6" [RFC4861] ,
* "IPv6 Stateless Address Autoconfiguration" [RFC4862], and
* "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals " [RFC4919].
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2.3. Abbreviations
This document uses the following abbreviations:
6BBR: 6LoWPAN Backbone Router
6LBR: 6LoWPAN Border Router
6LN: 6LoWPAN Node
6LR: 6LoWPAN Router
CGA: Cryptographically Generated Address
EARO: Extended Address Registration Option
ECDH: Elliptic curve Diffie-Hellman
ECDSA: Elliptic Curve Digital Signature Algorithm
CIPO: Crypto-ID Parameters Option
LLN: Low-Power and Lossy Network
JSON: JavaScript Object Notation
JOSE: JavaScript Object Signing and Encryption
JWK: JSON Web Key
JWS: JSON Web Signature
NA: Neighbor Advertisement
ND: Neighbor Discovery
NDP: Neighbor Discovery Protocol
NDPSO: Neighbor Discovery Protocol Signature Option
NS: Neighbor Solicitation
ROVR: Registration Ownership Verifier
RA: Router Advertisement
RS: Router Solicitation
RSAO: RSA Signature Option
SHA: Secure Hash Algorithm
SLAAC: Stateless Address Autoconfiguration
TID: Transaction ID
3. Updating RFC 8505
Section 5.3 of [RFC8505] introduces the ROVR that is used to detect
and reject duplicate registrations in the DAD process. The ROVR is a
generic object that is designed for both backward compatibility and
the capability to introduce new computation methods in the future.
Using a Crypto-ID per this specification is the RECOMMENDED method.
Section 7.5 discusses collisions when heterogeneous methods to
compute the ROVR field coexist inside a same network.
This specification introduces a new token called a cryptographic
identifier (Crypto-ID) that is transported in the ROVR field and used
to prove indirectly the ownership of an address that is being
registered by means of [RFC8505]. The Crypto-ID is derived from a
cryptographic public key and additional parameters.
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The overall mechanism requires the support of Elliptic Curve
Cryptography (ECC) and of a hash function as detailed in Section 6.2.
To enable the verification of the proof, the registering node needs
to supply certain parameters including a nonce and a signature that
will demonstrate that the node possesses the private-key
corresponding to the public-key used to build the Crypto-ID.
The elliptic curves and the hash functions listed in Table 1 in
Section 8.2 can be used with this specification; more may be added in
the future to the IANA registry. The signature scheme that specifies
which combination is used (including the curve and the representation
conventions) is signaled by a Crypto-Type in a new IPv6 ND Crypto-ID
Parameters Option (CIPO, see Section 4.3) that contains the
parameters that are necessary for the proof, a Nonce option
([RFC3971]) and a NDP Signature option (Section 4.4). The NA(EARO)
is modified to enable a challenge and transport a Nonce option.
4. New Fields and Options
4.1. New Crypto-ID
The Crypto-ID is transported in the ROVR field of the EARO option and
the EDAR message, and is associated with the Registered Address at
the 6LR and the 6LBR. The ownership of a Crypto-ID can be
demonstrated by cryptographic mechanisms, and by association, the
ownership of the Registered Address can be ascertained.
A node in possession of the necessary cryptographic primitives SHOULD
use Crypto-ID by default as ROVR in its registrations. Whether a
ROVR is a Crypto-ID is indicated by a new "C" flag in the NS(EARO)
message.
The Crypto-ID is derived from the public key and a modifier as
follows:
1. The hash function used internally by the signature scheme
indicated by the Crypto-Type (see also Table 1 in Section 8.2) is
applied to the CIPO. Note that all the reserved and padding bits
MUST be set to zero.
2. The leftmost bits of the resulting hash, up to the desired size,
are used as the Crypto-ID.
At the time of this writing, a minimal size for the Crypto-ID of 128
bits is RECOMMENDED unless backward compatibility is needed
[RFC8505]. This value is bound to augment in the future.
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4.2. Updated EARO
This specification updates the EARO option to enable the use of the
ROVR field to transport the Crypto-ID. The resulting format is as
follows:
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: Defined in [RFC8505] and copied in associated CIPO.
Status: Defined in [RFC8505].
Opaque: Defined in [RFC8505].
Rsvd (Reserved): 3-bit unsigned integer. It MUST be set 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, R, T: Defined in [RFC8505].
TID: Defined in [RFC8505].
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 [RFC8505].
this specification does not define any new Status value.
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4.3. Crypto-ID Parameters Option
This specification defines the Crypto-ID Parameters Option (CIPO).
The CIPO carries the parameters used to form a Crypto-ID.
In order to provide cryptographic agility [BCP 201], this
specification supports different elliptic-curve based signature
schemes, indicated by a Crypto-Type field:
* The ECDSA256 signature scheme, which uses ECDSA with the NIST
P-256 curve [FIPS186-4] and the hash function SHA-256 [RFC6234]
internally, MUST be supported by all implementations.
* The Ed25519 signature scheme, which uses the Pure Edwards-Curve
Digital Signature Algorithm (PureEdDSA) [RFC8032] with the twisted
Edwards curve Edwards25519 [RFC7748] and the hash function SHA-512
[RFC6234] internally, MAY be supported as an alternative.
* The ECDSA25519 signature scheme, which uses ECDSA [FIPS186-4] with
the Weierstrass curve Wei25519 (see Appendix B.4) and the hash
function SHA-256 [RFC6234] internally, MAY also be supported.
This specification uses signature schemes that target similar
cryptographic strength but rely on different curves, hash functions,
signature algorithms, and/or representation conventions. Future
specification may extend this to different cryptographic algorithms
and key sizes, e.g., to provide better security properties or a
simpler implementation.
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 |Reserved1| Public Key Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Crypto-Type | Modifier | EARO Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. Public Key (variable length) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Padding .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Crypto-ID Parameters Option
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Type: 8-bit unsigned integer. to be assigned by IANA, see Table 2.
Length: 8-bit unsigned integer. The length of the option in units
of 8 octets.
Reserved1: 5-bit unsigned integer. It MUST be set to zero by the
sender and MUST be ignored by the receiver.
Public Key Length: 11-bit unsigned integer. The length of the
Public Key field in bytes. The actual length depends on the
Crypto-Type value and on how the public key is represented. The
valid values with this document are provided in Table 1.
Crypto-Type: 8-bit unsigned integer. The type of cryptographic
algorithm used in calculation Crypto-ID indexed by IANA in the
"Crypto-Type Subregistry" in the "Internet Control Message
Protocol version 6 (ICMPv6) Parameters" (see Section 8.2).
Modifier: 8-bit unsigned integer. Set to an arbitrary value by the
creator of the Crypto-ID. The role of the modifier is to enable
the formation of multiple Crypto-IDs from a same key pair, which
reduces the traceability and thus improves the privacy of a
constrained node that could not maintain many key-pairs.
EARO Length: 8-bit unsigned integer. The option length of the EARO
that contains the Crypto-ID associated with the CIPO.
Public Key: A variable-length field, size indicated in the Public
Key Length field.
Padding: A variable-length field completing the Public Key field to
align to the next 8-bytes boundary. It MUST be set to zero by the
sender and MUST be ignored by the receiver.
The implementation of multiple hash functions in a constrained device
may consume excessive amounts of program memory. This specification
enables the use of the same hash function SHA-256 [RFC6234] for two
of the three supported ECC-based signature schemes. Some code
factorization is also possible for the ECC computation itself.
[CURVE-REPR] 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 provide,
e.g., ECDSA and ECDH using NIST [FIPS186-4] prime curves. For more
details on representation conventions, we refer to Appendix B.
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4.4. NDP Signature Option
This specification defines the NDP Signature Option (NDPSO). The
NDPSO carries the signature that proves the ownership of the Crypto-
ID. The format of the NDPSO is illustrated in Figure 3.
As opposed to the RSA Signature Option (RSAO) defined in section 5.2.
of SEND [RFC3971], the NDPSO does not have a key hash field.
Instead, the leftmost 128 bits of the ROVR field in the EARO are used
as hash to retrieve the CIPO that contains the key material used for
signature verification, left-padded if needed.
Another difference is that the NDPSO signs a fixed set of fields as
opposed to all options that appear prior to it in the ND message that
bears the signature. This allows to elide a CIPO that the 6LR
already received, at the expense of the capability to add arbitrary
options that would signed with a RSAO.
An ND message that carries an NDPSO MUST have one and only one EARO.
The EARO MUST contain a Crypto-ID in the ROVR field, and the Crypto-
ID MUST be associated with the keypair used for the Digital Signature
in the NDPSO.
The CIPO may be present in the same message as the NDPSO. If it is
not present, it can be found in an abstract table that was created by
a previous message and indexed by the hash.
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 |Reserved1| Signature Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Digital Signature (variable length) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Padding .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: NDP signature Option
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Type: to be assigned by IANA, see Table 2.
Length: 8-bit unsigned integer. The length of the option in units
of 8 octets.
Reserved1: 5-bit unsigned integer. It MUST be set to zero by the
sender and MUST be ignored by the receiver.
Digital Signature Length: 11-bit unsigned integer. The length of
the Digital Signature field in bytes.
Reserved2: 32-bit unsigned integer. It MUST be set to zero by the
sender and MUST be ignored by the receiver.
Digital Signature: A variable-length field containing the digital
signature. The length and computation of the digital signature
both depend on the Crypto-Type which is found in the associated
CIPO, see Appendix B. For the values of the Crypto-Type defined
in this specification, and for future values of the Crypto-Type
unless specified otherwise, the signature is computed as detailed
in Section 6.2.
Padding: A variable-length field completing the Digital Signature
field to align to the next 8-bytes boundary. It MUST be set to
zero by the sender and MUST be ignored by the receiver.
4.5. Extensions to the Capability Indication Option
This specification defines one new capability bits in the 6CIO,
defined by [RFC7400] for use by the 6LR and 6LBR in IPv6 ND RA
messages.
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 = 1 | Reserved |A|D|L|B|P|E|G|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: New Capability Bit in the 6CIO
New Option Field:
A: 1-bit flag. Set to indicate that AP-ND is globally activated in
the network.
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The "A" flag is set by the 6LBR that serves the network and
propagated by the 6LRs. It is typically turned on when all 6LRs are
migrated to this specification.
5. Protocol Scope
The scope of the protocol specified here is a 6LoWPAN 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
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 o o(6LR)
^
o o | LLN link
o o v
o(6LN)
o
Figure 5: 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 all the LLN links between the 6LR
and the 6LBR are protected so that a packet that was validated by the
first 6LR can be safely routed by other on-path 6LRs to the 6LBR.
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6. Protocol Flows
The 6LR/6LBR ensures first-come/first-serve by storing the ROVR
associated to the address being registered upon the first
registration and rejecting a registration with a different ROVR
value. A 6LN can claim any address as long as it is the first to
make that claim. After a successful registration, the 6LN becomes
the owner of the registered address and the address is bound to the
ROVR value in the 6LR/6LBR registry.
This specification protects the ownership of the address at the first
hop (the edge). Its use in a network is signaled by the "A" flag in
the 6CIO. The flag is set by the 6LBR and propagated unchanged by
the 6LRs. The "A" flag enables to migrate a network with the
protection off and then turn it on globally.
The 6LN places a cryptographic token, the Crypto-ID, in the ROVR that
is associated with the address at the first registration, enabling
the 6LR to later challenge it to verify that it is the original
Registering Node. The challenge may happen at any time at the
discretion of the 6LR and the 6LBR. A valid registration in the 6LR
or the 6LBR MUST NOT be altered until the challenge is complete.
When the "A" flag is on, the 6LR MUST challenge the 6LN when it
creates a binding with the "C" flag set in the ROVR and when a new
registration attempts to change a parameter of that binding that
identifies the 6LN, for instance its Source Link-Layer Address. The
verification protects against a rogue that would steal an address and
attract its traffic, or use it as source address.
The 6LR MUST also challenge the 6LN if the 6LBR directly signals to
do so, using an EDAC Message with a "Validation Requested" status.
The EDAR is echoed by the 6LR in the NA (EARO) back to the
registering node. The 6LR SHOULD also challenge all its attached
6LNs at the time the 6LBR turns the "A" flag on in the 6CIO, to
detect an issue immediately.
If the 6LR does not support the Crypto-Type, it MUST reply with an
EARO Status 10 "Validation Failed" without a challenge. In that
case, the 6LN may try another Crypto-Type until it falls back to
Crypto-Type 0 that MUST be supported by all 6LRs.
A node may use more than one IPv6 address at the same time. The
separation of the address and the cryptographic material avoids the
need for the constrained device to compute multiple keys for multiple
addresses. The 6LN MAY use the same Crypto-ID to prove the ownership
of multiple IPv6 addresses. The 6LN MAY also derive multiple Crypto-
IDs from a same key.
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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 [RFC8505]. The on-link
(local) protocol interactions are shown in Figure 6. 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 6).
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 6: On-link Protocol Operation
The Nonce option contains a nonce value that, to the extent possible
for the implementation, was never employed in association with the
key pair used to generate the Crypto-ID. This specification inherits
from [RFC3971] that simply indicates that the nonce is a random
value. Ideally, an implementation uses an unpredictable
cryptographically random value [BCP 106]. But that may be
impractical in some LLN scenarios where the devices do not have a
guaranteed sense of time and for which computing complex hashes is
detrimental to the battery lifetime.
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Alternatively, the device may use an always-incrementing value saved
in the same stable storage as the key, so they are lost together, and
starting at a best effort random value, either as the nonce value or
as a component to its computation.
The 6LN replies to the challenge with an NS(EARO) that includes a new
Nonce option (shown as NonceLN in Figure 6), the CIPO (Section 4.3),
and the NDPSO containing the signature. Both Nonces are included in
the signed material. This provides a "contributory behavior", so
that either party that knows it generates a good quality nonce knows
that the protocol will be secure.
The 6LR MUST store the information associated to a Crypto-ID on the
first NS exchange where it appears in a fashion that the CIPO
parameters can be retrieved from the Crypto-ID alone.
The steps for the registration to the 6LR are as follows:
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. When a 6LR receives a NS(EARO)
registration with a new Crypto-ID as a ROVR, and unless the
registration is rejected for another reason, it MUST challenge by
responding with a NA(EARO) with a status of "Validation Requested".
Upon receiving a first NA(EARO) with a status of "Validation
Requested" from a 6LR, the registering node SHOULD retry its
registration with a Crypto-ID Parameters Option (CIPO) (Section 4.3)
that contains all the necessary material for building the Crypto-ID,
the NonceLN that it generated, and the NDP signature (Section 4.4)
option that proves its ownership of the Crypto-ID and intent of
registering the Target Address. In subsequent revalidation with the
same 6LR, the 6LN MAY try to omit the CIPO to save bandwidth, with
the expectation that the 6LR saved it. If the validation fails and
it gets challenged again, then it SHOULD add the CIPO again.
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. If the rebuilt Crypto-ID matches the ROVR, the 6LN also
verifies the signature contained in the NDPSO option. If at that
point the signature in the NDPSO option can be verified, then the
validation succeeds. Otherwise the validation fails.
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 and
alternate Crypto-Type and if even Crypto-Type 0 fails, it may try to
register a different address in the NS message.
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6.2. NDPSO generation and verification
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 in a fashion that depends on the Crypto-Type
(see Table 1 in Section 8.2) chosen by the 6LN as follows:
* Form the message to be signed, by concatenating the following
byte-strings in the order listed:
1. The 128-bit Message Type tag [RFC3972] (in network byte
order). For this specification the tag is given in
Section 8.1. (The tag value has been generated by the editor
of this specification on random.org).
2. the CIPO
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 nonce is at least 6
bytes long as defined in [RFC3971].
5. NonceLN sent from the 6LN (in network byte order). The nonce
is at least 6 bytes long as defined in [RFC3971].
6. 1-byte Option Length of the EARO containing the Crypto-ID.
* Apply the signature algorithm specified by the Crypto-Type using
the private key.
The 6LR on receiving the NDPSO and CIPO options first checks that the
EARO Length in the CIPO matches the length of the EARO. If so it
regenerates the Crypto-ID based on the CIPO to make sure that the
leftmost bits up to the size of the ROVR match.
If and only if the check is successful, it tries to verify the
signature in the NDPSO option using the following:
* Form the message to be verified, by concatenating the following
byte-strings in the order listed:
1. The 128-bit Message Type tag given in Section 8.1 (in network
byte order)
2. the CIPO
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
nonce is at least 6 bytes long as defined in [RFC3971].
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5. NonceLN received from the 6LN (in network byte order) in the
NS message. The nonce is at least 6 bytes long as defined in
[RFC3971].
6. 1-byte EARO Length received in the CIPO.
* Verify the signature on this message with the public-key in the
CIPO and the locally computed values using the signature algorithm
specified by the Crypto-Type. If the verification succeeds, the
6LR propagates the information to the 6LBR using a EDAR/EDAC flow.
* Due to the first-come/first-serve nature of the registration, if
the address is not registered to the 6LBR, then flow succeeds and
both the 6LR and 6LBR add the state information about the Crypto-
ID and Target Address being registered to their respective
abstract database.
6.3. Multihop Operation
A new 6LN 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) [RFC8505].
In a multihop 6LoWPAN, the registration with Crypto-ID is propagated
to 6LBR as shown in Figure 7, which illustrates the registration flow
all the way to a 6LowPAN Backbone Router (6BBR) [BACKBONE-ROUTER].
6LN 6LR 6LBR 6BBR
| | | |
| NS(EARO) | | |
|--------------->| | |
| | Extended DAR | |
| |-------------->| |
| | | proxy NS(EARO) |
| | |--------------->|
| | | | NS(DAD)
| | | | ------>
| | | |
| | | | <wait>
| | | |
| | | proxy NA(EARO) |
| | |<---------------|
| | Extended DAC | |
| |<--------------| |
| NA(EARO) | | |
|<---------------| | |
| | | |
Figure 7: (Re-)Registration Flow
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The 6LR and the 6LBR communicate using ICMPv6 Extended Duplicate
Address Request (EDAR) and Extended Duplicate Address Confirmation
(EDAC) messages [RFC8505] as shown in Figure 7. This specification
extends EDAR/EDAC messages to carry cryptographically generated ROVR.
The assumption is that the 6LR and the 6LBR maintain a security
association to authenticate and protect the integrity of the EDAR and
EDAC messages, so there is no need to propagate the proof of
ownership to the 6LBR. The 6LBR implicitly trusts that the 6LR
performs the verification when the 6LBR requires it, and if there is
no further exchange from the 6LR to remove the state, that the
verification succeeded.
7. Security Considerations
7.1. Brown Field
Only 6LRs that are upgraded to this specification are capable to
challenge a registration and repel an attack. In a brown (mixed)
network, an attacker may attach to a legacy 6LR and fool the 6LBR.
So even if the "A" flag could be set at any time to test the protocol
operation, the security will only be effective when all the 6LRs are
upgraded.
7.2. 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. A different ROVR for the same Registered address
entails a rejection of the second registration [RFC8505]. 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 [RFC8505] and is thus the best candidate to validate
the registration for the device attached to it [BACKBONE-ROUTER].
But this specification does not guarantee that the backbone router
claiming an address over the backbone is not an attacker.
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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 A nonce should never repeat for a single key, but
nonces do not need to be unpredictable for secure operation.
Using nonces (NonceLR and NonceLN) generated by both the 6LR and
6LN ensure a contributory behavior that provides an efficient
protection against replay attacks of the challenge/response flow.
The quality of the protection by a random nonce depends on the
random number generator and its parameters (e.g., sense of time).
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.
7.3. Related to 6LoWPAN ND
The threats and mediations discussed in 6LoWPAN ND [RFC6775][RFC8505]
also apply here, in particular denial-of-service attacks against the
registry at the 6LR or 6LBR.
Secure ND [RFC3971] forces the IPv6 address to be cryptographic since
it integrates the CGA as the IID in the IPv6 address. In contrast,
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.
With this specification the 6LN can freely form its IPv6 address(es)
in any fashion, thereby enabling either 6LoWPAN compression for IPv6
addresses that are derived from Layer-2 addresses, or temporary
addresses, e.g., formed pseudo-randomly and released in relatively
short cycles for privacy reasons [RFC8064][RFC8065], that cannot be
compressed.
This specification provides added protection for addresses that are
obtained following due procedure [RFC8505] but does not constrain the
way the addresses are formed or the number of addresses that are used
in parallel by a same entity. A rogue may still perform denial-of-
service attack against the registry at the 6LR or 6LBR, or attempt to
deplete the pool of available addresses at Layer-2 or Layer-3.
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7.4. Compromised 6LR
This specification distributes the challenge and its validation at
the edge of the network, between the 6LN and its 6LR. This protects
against DOS attacks targeted at that central 6LBR. This also saves
back and forth exchanges across a potentially large and constrained
network.
The downside is that the 6LBR needs to trust the 6LR for performing
the checking adequately, and the communication between the 6LR and
the 6LBR must be protected to avoid tampering with the result of the
test.
If a 6LR is compromised, and provided that it knows the ROVR field
used by the real owner of the address, the 6LR may pretend that the
owner has moved, is now attached to it and has successfully passed
the Crpto-ID validation. The 6LR may then attract and inject traffic
at will on behalf of that address or let a rogue take ownership of
the address.
7.5. 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.
Assuming in the calculations/discussion below that the hash used for
calculating the Crypto-ID is a well-behaved cryptographic hash and
thus that random collisions are the only ones possible, the formula
(birthday paradox) for calculating the probability of a collision is
1 - e^{-p^2/(2n)} where n is the maximum population size (2^64 here,
1.84E19) and p is the actual population (number of nodes, assuming
one Crypto-ID per node).
If the Crypto-ID is 64-bits (the least possible size allowed), the
chance of a collision is 0.01% for network of 66 million nodes.
Moreover, the collision is only relevant when this happens within one
stub network (6LBR). In the case of such a collision, a third party
node would be able to claim the registered address of an another
legitimate node, provided that it wishes to use the same address. To
prevent address disclosure and avoid the chances of collision on both
the ROVR and the address, it is RECOMMENDED that nodes do not derive
the address being registered from the ROVR.
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7.6. Implementation Attacks
The signature schemes referenced in this specification comply with
NIST [FIPS186-4] or Crypto Forum Research Group (CFRG) standards
[RFC8032] and offer strong algorithmic security at roughly 128-bit
security level. These signature schemes use elliptic curves that
were either specifically designed with exception-free and constant-
time arithmetic in mind [RFC7748] or where one has extensive
implementation experience of resistance to timing attacks
[FIPS186-4].
However, careless implementations of the signing operations could
nevertheless leak information on private keys. For example, there
are micro-architectural side channel attacks that implementors should
be aware of [breaking-ed25519]. Implementors should be particularly
aware that a secure implementation of Ed25519 requires a protected
implementation of the hash function SHA-512, whereas this is not
required with implementations of the hash function SHA-256 used with
ECDSA256 and ECDSA25519.
7.7. Cross-Algorithm and Cross-Protocol Attacks
The keypair used in this specification can be self-generated and the
public key does not need to be exchanged, e.g., through certificates,
with a third party before it is used.
New keypairs can be formed for new registration as the node desires.
On the other hand, it is safer to allocate a keypair that is used
only for the address protection and only for one instantiation of the
signature scheme (which includes choice of elliptic curve domain
parameters, used hash function, and applicable representation
conventions).
The same private key MUST NOT be reused with more than one
instantiation of the signature scheme in this specification. The
same private key MUST NOT be used for anything other than computing
NDPSO signatures per this specification.
ECDSA shall be used strictly as specified in [FIPS186-4]. In
particular, each signing operation of ECDSA MUST use randomly
generated ephemeral private keys and MUST NOT reuse these ephemeral
private keys k accross signing operations. This precludes the use of
deterministic ECDSA without a random input for determination of k,
which is deemed dangerous for the intended applications this document
aims to serve.
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7.8. Public Key Validation
Public keys contained in the CIPO field (which are used for signature
verification) shall be verified to be correctly formed, by checking
that this public key is indeed a point of the elliptic curve
indicated by the Crypto-Type and that this point does have the proper
order.
For points used with the signature scheme Ed25519, one MUST check
that this point is not a point in the small subgroup (see
Appendix B.1 of [CURVE-REPR]); for points used with the signature
scheme ECDSA (i.e., both ECDSA256 and ECDSA25519), one MUST check
that the point has the same order as the base point of the curve in
question. This is commonly called full public key validation (again,
see Appendix B.1 of [CURVE-REPR]).
7.9. Correlating Registrations
The ROVR field in the EARO introduced in [RFC8505] extends the EUI-64
field of the ARO defined in [RFC6775]. One of the drawbacks of using
an EUI-64 as ROVR is that an attacker that is aware of the
registrations can correlate traffic for a same 6LN across multiple
addresses. Section 3 of [RFC8505] indicates that the ROVR and the
address being registered are decoupled. A 6LN may use a same ROVR
for multiple registrations or a different ROVR per registration, and
the IID must not derive from the ROVR. In theory different 6LNs
could use a same ROVR as long as they do not attempt to register the
same address.
The Modifier used in the computation of the Crypto-ID enables a 6LN
to build different Crypto-IDs for different addresses with a same
keypair. Using that facility improves the privacy of the 6LN as the
expense of storage in the 6LR, which will need to store multiple
CIPOs that contain the same public key. Note that if the attacker is
the 6LR, then the Modifier alone does not provide a protection, and
the 6LN would need to use different keys and MAC addresses in an
attempt to obfuscate its multiple ownership.
8. IANA considerations
8.1. CGA Message Type
This document defines a new 128-bit value of a Message Type tag under
the CGA Message Type [RFC3972] name space: 0x8701 55c8 0cca dd32 6ab7
e415 f148 84d0.
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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 in the
interval 0..255 and contains an Elliptic Curve, a Hash Function, a
Signature Algorithm, Representation Conventions, Public key size, and
Signature size, as shown in Table 1, which together specify a
signature scheme (and which are fully specified in Appendix B).
The following Crypto-Type values are defined in this document:
+----------------+-----------------+--------------+-----------------+
| Crypto-Type | 0 (ECDSA256) | 1 (Ed25519) | 2 (ECDSA25519) |
| value | | | |
+================+=================+==============+=================+
| Elliptic curve | NIST P-256 | Curve25519 | Curve25519 |
| | [FIPS186-4] | [RFC7748] | [RFC7748] |
+----------------+-----------------+--------------+-----------------+
| Hash function |SHA-256 [RFC6234]| SHA-512 |SHA-256 [RFC6234]|
| | | [RFC6234] | |
+----------------+-----------------+--------------+-----------------+
| Signature |ECDSA [FIPS186-4]| Ed25519 |ECDSA [FIPS186-4]|
| algorithm | | [RFC8032] | |
+----------------+-----------------+--------------+-----------------+
| Representation | Weierstrass, | Edwards, | Weierstrass, |
| conventions | (un)compressed, | compressed, | (un)compressed, |
| | MSB/msb first, |LSB/lsb first,| MSB/msb first, |
| | [RFC7518] | [RFC8037] | [CURVE-REPR] |
+----------------+-----------------+--------------+-----------------+
|Public key size | 33/65 bytes | 32 bytes | 33/65 bytes |
| | (compressed/ | (compressed) | (compressed/ |
| | uncompressed) | | uncompressed) |
+----------------+-----------------+--------------+-----------------+
| Signature size | 64 bytes | 64 bytes | 64 bytes |
+----------------+-----------------+--------------+-----------------+
| Defining | This_RFC | This_RFC | This_RFC |
| specification | | | |
+----------------+-----------------+--------------+-----------------+
Table 1: Crypto-Types
New Crypto-Type values providing similar or better security may be
defined in the future.
Assignment of new values for new Crypto-Type MUST be done through
IANA with either "Specification Required" or "IESG Approval" as
defined in BCP 26 [RFC8126].
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8.3. IPv6 ND option types
This document registers two new ND option types under the subregistry
"IPv6 Neighbor Discovery Option Formats":
+------------------------------+-----------------+---------------+
| Option Name | Suggested Value | Reference |
+==============================+=================+===============+
| NDP Signature Option (NDPSO) | 38 | This document |
+------------------------------+-----------------+---------------+
| Crypto-ID Parameters Option | 39 | This document |
| (CIPO) | | |
+------------------------------+-----------------+---------------+
Table 2: New ND options
8.4. New 6LoWPAN Capability Bit
IANA is requested to make additions to the Subregistry for "6LoWPAN
Capability Bits" created for [RFC7400] as follows:
+----------------+-----------------------+----------+
| Capability Bit | Description | Document |
+================+=======================+==========+
| 09 | AP-ND Enabled (1 bit) | This_RFC |
+----------------+-----------------------+----------+
Table 3: New 6LoWPAN Capability Bit
9. Acknowledgments
Many thanks to Charlie Perkins for his in-depth review and
constructive suggestions. The authors are also especially grateful
to Robert Moskowitz and Benjamin Kaduk for their comments and
discussions that led to many improvements. The authors wish to also
thank Shwetha Bhandari for actively shepherding this document and
Roman Danyliw, Alissa Cooper, Mirja Kuhlewind, Eric Vyncke, Vijay
Gurbani, Al Morton, and Adam Montville for their constructive reviews
during the IESG process. Finally Many thanks to our INT area ADs,
Suresh Krishnan and then Erik Kline, who supported us along the whole
process.
10. 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,
<https://www.rfc-editor.org/info/rfc2119>.
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[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>.
[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>.
[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>.
[RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for
IPv6 over Low-Power Wireless Personal Area Networks
(6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November
2014, <https://www.rfc-editor.org/info/rfc7400>.
[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, <https://www.rfc-editor.org/info/rfc7748>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C.
Perkins, "Registration Extensions for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Neighbor
Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018,
<https://www.rfc-editor.org/info/rfc8505>.
[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 , July 2013.
[SEC1] SEC1, "SEC 1: Elliptic Curve Cryptography, Version 2.0",
Standards for Efficient Cryptography , June 2009.
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11. Informative references
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<https://www.rfc-editor.org/info/rfc3972>.
[BCP 106] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005,
<https://www.rfc-editor.org/info/rfc4086>.
[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>.
[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>.
[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>.
[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>.
[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>.
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[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
DOI 10.17487/RFC7518, May 2015,
<https://www.rfc-editor.org/info/rfc7518>.
[BCP 201] 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>.
[RFC8037] Liusvaara, I., "CFRG Elliptic Curve Diffie-Hellman (ECDH)
and Signatures in JSON Object Signing and Encryption
(JOSE)", RFC 8037, DOI 10.17487/RFC8037, January 2017,
<https://www.rfc-editor.org/info/rfc8037>.
[RFC8064] Gont, F., Cooper, A., Thaler, D., and W. Liu,
"Recommendation on Stable IPv6 Interface Identifiers",
RFC 8064, DOI 10.17487/RFC8064, February 2017,
<https://www.rfc-editor.org/info/rfc8064>.
[RFC8065] Thaler, D., "Privacy Considerations for IPv6 Adaptation-
Layer Mechanisms", RFC 8065, DOI 10.17487/RFC8065,
February 2017, <https://www.rfc-editor.org/info/rfc8065>.
[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>.
[BACKBONE-ROUTER]
Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6
Backbone Router", Work in Progress, Internet-Draft, draft-
ietf-6lo-backbone-router-20, 23 March 2020,
<https://tools.ietf.org/html/draft-ietf-6lo-backbone-
router-20>.
[CURVE-REPR]
Struik, R., "Alternative Elliptic Curve Representations",
Work in Progress, Internet-Draft, draft-ietf-lwig-curve-
representations-09, 9 March 2020,
<https://tools.ietf.org/html/draft-ietf-lwig-curve-
representations-09>.
[breaking-ed25519]
Samwel, N., Batina, L., Bertoni, G., Daemen, J., and R.
Susella, "Breaking Ed25519 in WolfSSL", Cryptographers'
Track at the RSA Conference , 2018,
<https://link.springer.com/
chapter/10.1007/978-3-319-76953-0_1>.
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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.
* 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.
* 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.
* 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.
* 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.
* The Address Registration Option used in the ND registration SHOULD
be extended to carry the relevant forms of Unique Interface
Identifier.
* The Neighbor Discovery should specify the formation of a site-
local address that follows the security recommendations from
[RFC7217].
Appendix B. Representation Conventions
B.1. Signature Schemes
The signature scheme ECDSA256 corresponding to Crypto-Type 0 is
ECDSA, as specified in [FIPS186-4], instantiated with the NIST prime
curve P-256, as specified in Appendix B of [FIPS186-4], and the hash
function SHA-256, as specified in [RFC6234], where points of this
NIST curve are represented as points of a short-Weierstrass curve
(see [FIPS186-4]) and are encoded as octet strings in most-
significant-bit first (msb) and most-significant-byte first (MSB)
order. The signature itself consists of two integers (r and s),
which are each encoded as fixed-size octet strings in most-
significant-bit first and most-significant-byte first order. For
details on ECDSA, see [FIPS186-4]; for details on the encoding of
public keys, see Appendix B.3; for details on the signature encoding,
see Appendix B.2.
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The signature scheme Ed25519 corresponding to Crypto-Type 1 is EdDSA,
as specified in [RFC8032], instantiated with the Montgomery curve
Curve25519, as specified in [RFC7748], and the hash function SHA-512,
as specified in [RFC6234], where points of this Montgomery curve are
represented as points of the corresponding twisted Edwards curve
Edwards25519 (see Appendix B.4) and are encoded as octet strings in
least-significant-bit first (lsb) and least-significant-byte first
(LSB) order. The signature itself consists of a bit string that
encodes a point of this twisted Edwards curve, in compressed format,
and an integer encoded in least-significant-bit first and least-
significant-byte first order. For details on EdDSA, the encoding of
public keys and that of signatures, see the specification of pure
Ed25519 in [RFC8032].
The signature scheme ECDSA25519 corresponding to Crypto-Type 2 is
ECDSA, as specified in [FIPS186-4], instantiated with the Montgomery
curve Curve25519, as specified in [RFC7748], and the hash function
SHA-256, as specified in [RFC6234], where points of this Montgomery
curve are represented as points of the corresponding short-
Weierstrass curve Wei25519 (see Appendix B.4) and are encoded as
octet strings in most-significant-bit first and most-significant-byte
first order. The signature itself consists of a bit string that
encodes two integers, each encoded as fixed-size octet strings in
most-significant-bit first and most-significant-byte first order.
For details on ECDSA, see [FIPS186-4]; for details on the encoding of
public keys, see Appendix B.3; for details on the signature encoding,
see Appendix B.2
B.2. Representation of ECDSA Signatures
With ECDSA, each signature is an ordered pair (r, s) of integers
[FIPS186-4], where each integer is represented as a 32-octet string
according to the Field Element to Octet String conversion rules in
[SEC1] and where the ordered pair of integers is represented as the
rightconcatenation of these representation values (thereby resulting
in a 64-octet string). The inverse operation checks that the
signature is a 64-octet string and represents the left-side and
right-side halves of this string (each a 32-octet string) as the
integers r and s, respectively, using the Octet String to Field
Element conversion rules in [SEC1].
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B.3. Representation of Public Keys Used with ECDSA
ECDSA is specified to be used with elliptic curves in short-
Weierstrass form. Each point of such a curve is represented as an
octet string using the Elliptic Curve Point to Octet String
conversion rules in [SEC1], where point compression may be enabled
(which is indicated by the leftmost octet of this representation).
The inverse operation converts an octet string to a point of this
curve using the Octet String to Elliptic Curve Point conversion rules
in [SEC1], whereby the point is rejected if this is the so-called
point at infinity. (This is the case if the input to this inverse
operation is an octet string of length 1.)
B.4. Alternative Representations of Curve25519
The elliptic curve Curve25519, as specified in [RFC7748], is a so-
called Montgomery curve. Each point of this curve can also be
represented as a point of a twisted Edwards curve or as a point of an
elliptic curve in short-Weierstrass form, via a coordinate
transformation (a so-called isomorphic mapping). The parameters of
the Montgomery curve and the corresponding isomorphic curves in
twisted Edwards curve and short-Weierstrass form are as indicated
below. Here, the domain parameters of the Montgomery curve
Curve25519 and of the twisted Edwards curve Edwards25519 are as
specified in [RFC7748]; the domain parameters of the elliptic curve
Wei25519 in short-Weierstrass curve comply with Section 6.1.1 of
[FIPS186-4]. For further details on these curves and on the
coordinate transformations referenced above, see [CURVE-REPR].
General parameters (for all curve models):
p 2^{255}-19
(=0x7fffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff
ffffffed)
h 8
n
723700557733226221397318656304299424085711635937990760600195093828
5454250989
(=2^{252} + 0x14def9de a2f79cd6 5812631a 5cf5d3ed)
Montgomery curve-specific parameters (for Curve25519):
A 486662
B 1
Gu 9 (=0x9)
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Gv
147816194475895447910205935684099868872646061346164752889648818377
55586237401
(=0x20ae19a1 b8a086b4 e01edd2c 7748d14c 923d4d7e 6d7c61b2 29e9c5a2
7eced3d9)
Twisted Edwards curve-specific parameters (for Edwards25519):
a -1 (-0x01)
d -121665/121666
(=3709570593466943934313808350875456518954211387984321901638878553
3085940283555)
(=0x52036cee 2b6ffe73 8cc74079 7779e898 00700a4d 4141d8ab 75eb4dca
135978a3)
Gx
151122213495354007725011514095885315114540126930418572060461132839
49847762202
(=0x216936d3 cd6e53fe c0a4e231 fdd6dc5c 692cc760 9525a7b2 c9562d60
8f25d51a)
Gy 4/5
(=4631683569492647816942839400347516314130799386625622561578303360
3165251855960)
(=0x66666666 66666666 66666666 66666666 66666666 66666666 66666666
66666658)
Weierstrass curve-specific parameters (for Wei25519):
a
192986815395526992372618308347813179755449974442734273399095973345
73241639236
(=0x2aaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaa98
4914a144)
b
557517466698189089076452890782571408182411037279010123152944008379
56729358436
(=0x7b425ed0 97b425ed 097b425e d097b425 ed097b42 5ed097b4 260b5e9c
7710c864)
GX
192986815395526992372618308347813179755449974442734273399095973346
52188435546
(=0x2aaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa
aaad245a)
GY
147816194475895447910205935684099868872646061346164752889648818377
55586237401
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(=0x20ae19a1 b8a086b4 e01edd2c 7748d14c 923d4d7e 6d7c61b2 29e9c5a2
7eced3d9)
Authors' Addresses
Pascal Thubert (editor)
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
06254 MOUGINS - Sophia Antipolis
France
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
Behcet Sarikaya
Email: sarikaya@ieee.org
Mohit Sethi
Ericsson
FI-02420 Jorvas
Finland
Email: mohit@piuha.net
Rene Struik
Struik Security Consultancy
Email: rstruik.ext@gmail.com
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