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IETF RFC 8928
Last modified on Monday, November 23rd, 2020
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Internet Engineering Task Force (IETF) P. Thubert, Ed.
Request for Comments: 8928 Cisco
Updates: 8505 B. Sarikaya
Category: Standards Track
ISSN: 2070-1721 M. Sethi
Ericsson
R. Struik
Struik Security Consultancy
November 2020
Address-Protected Neighbor Discovery for Low-Power and Lossy Networks
 Abstract
This document updates the IPv6 over Low-Power Wireless Personal Area
Network (6LoWPAN) Neighbor Discovery (ND) protocol defined in RFCs
6775 and 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 is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/RFC 8928.
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 and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction
2. Terminology
2.1. Requirements Language
2.2. Background
2.3. Abbreviations
3. Updating RFC 8505
4. New Fields and Options
4.1. New Crypto-ID
4.2. Updated EARO
4.3. Crypto-ID Parameters Option
4.4. NDP Signature Option
4.5. Extensions to the Capability Indication Option
5. Protocol Scope
6. Protocol Flows
6.1. First Exchange with a 6LR
6.2. NDPSO Generation and Verification
6.3. Multi-Hop Operation
7. Security Considerations
7.1. Brown Field
7.2. Threats Identified in RFC 3971
7.3. Related to 6LoWPAN ND
7.4. Compromised 6LR
7.5. ROVR Collisions
7.6. Implementation Attacks
7.7. Cross-Algorithm and Cross-Protocol Attacks
7.8. Public Key Validation
7.9. Correlating Registrations
8. IANA Considerations
8.1. CGA Message Type
8.2. Crypto-Type Subregistry
8.3. IPv6 ND Option Types
8.4. New 6LoWPAN Capability Bit
9. References
9.1. Normative References
9.2. Informative References
Appendix A. Requirements Addressed in This Document
Appendix B. Representation Conventions
B.1. Signature Schemes
B.2. Representation of ECDSA Signatures
B.3. Representation of Public Keys Used with ECDSA
B.4. Alternative Representations of Curve25519
Acknowledgments
Authors' Addresses
1. Introduction
Neighbor Discovery optimizations for 6LoWPAN networks (aka 6LoWPAN
ND) [RFC 6775] adapts the original IPv6 Neighbor Discovery protocols
defined in [RFC 4861] and [RFC 4862] for constrained Low-Power and
Lossy Networks (LLNs). 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 LLNs, the 6LBR is the central repository of all the Registered
Addresses in its domain.
The registration mechanism in "Neighbor Discovery Optimization for
IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)"
[RFC 6775] prevents the use of an address if that address is already
registered in the subnet (first come, first served). In order to
validate address ownership, "Registration Extensions for IPv6 over
Low-Power Wireless Personal Area Network (6LoWPAN) Neighbor
Discovery" [RFC 8505] defines a Registration Ownership Verifier (ROVR)
field. [RFC 8505] enables a 6LR and 6LBR to validate the association
between the Registered Address of a node and its ROVR. The ROVR can
be derived from the link-layer 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; 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.
[RFC 8505] defines an Extended Address Registration Option (EARO) that
transports alternate forms of ROVRs and is a prerequisite for this
specification.
In this specification, a 6LN generates a cryptographic identifier
(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 Crypto-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
Improvement (SAVI) [RFC 7039] in that only the owner of an IPv6
address may source packets with that address. As opposed to
[RFC 7039], which relies on snooping protocols, the protection
provided by this document 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 packet if
and only if it has registered the address used as the source of the
packet with that 6LR.
With the 6LoWPAN adaptation layer in [RFC 4944] and [RFC 6282], a 6LN
can obtain better compression for an IPv6 address with an Interface
ID (IID) that is derived from a Layer 2 (L2) address. Such
compression is incompatible with "SEcure Neighbor Discovery (SEND")
[RFC 3971] and "Cryptographically Generated Addresses (CGAs)"
[RFC 3972], since they derive the IID from cryptographic keys. This
specification, on the other hand, separates the IID generation from
cryptographic computations and can enable better compression.
2. Terminology
2.1. Requirements Language
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 [RFC 2119] [RFC 8174] when, and only when, they appear in all
capitals, as shown here.
2.2. Background
The reader may get additional context for this specification from the
following references:
* "SEcure Neighbor Discovery (SEND)" [RFC 3971],
* "Cryptographically Generated Addresses (CGA)" [RFC 3972],
* "Neighbor Discovery for IP version 6 (IPv6)" [RFC 4861] ,
* "IPv6 Stateless Address Autoconfiguration" [RFC 4862], and
* "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals" [RFC 4919].
2.3. Abbreviations
This document uses the following abbreviations:
6BBR: 6LoWPAN Backbone Router
6LBR: 6LoWPAN Border Router
6LN: 6LoWPAN Node
6LR: 6LoWPAN Router
AP-ND: Address-Protected Neighbor Discovery
CGA: Cryptographically Generated Address
DAD: Duplicate Address Detection
EARO: Extended Address Registration Option
ECC: Elliptic Curve Cryptography
ECDH: Elliptic Curve Diffie-Hellman
ECDSA: Elliptic Curve Digital Signature Algorithm
EDAC: Extended Duplicate Address Confirmation
EDAR: Extended Duplicate Address Request
CIPO: Crypto-ID Parameters Option
LLN: Low-Power and Lossy Network
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 [RFC 8505] 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 network.
This specification introduces a new identifier called a Crypto-ID
that is transported in the ROVR field and used to indirectly prove
the ownership of an address that is being registered by means of
[RFC 8505]. The Crypto-ID is derived from a cryptographic public key
and additional parameters.
The overall mechanism requires the support of Elliptic Curve
Cryptography (ECC) and 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 corresponding IANA registry. The cryptographic
algorithms used (including the curve and the representation
conventions) are signaled by the Crypto-Type field in a new IPv6 ND
Crypto-ID Parameters Option (CIPO) (see Section 4.3) that contains
the parameters that are necessary for address validation. A new NDP
Signature Option (Section 4.4) is also specified in this document to
carry the resulting signature. A Nonce Option [RFC 3971] is added in
the NA(EARO) that is used to request the validation, and all three
options are needed in the NS(EARO) that provides the validation.
4. New Fields and Options
4.1. New Crypto-ID
The Crypto-ID is transported in the ROVR field of the EARO and the
Extended Duplicate Address Request (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 EARO of 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 and
indicated by the Crypto-Type (see 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 [RFC 8505]
(in which case it is at least 64 bits). The size of the Crypto-ID is
likely to increase in the future.
4.2. Updated EARO
This specification updates the EARO 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 [RFC 8505] and copied in the "EARO Length" field
in the associated CIPO.
Status: Defined in [RFC 8505].
Opaque: Defined in [RFC 8505].
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 [RFC 8505].
TID and Registration Lifetime: Defined in [RFC 8505].
Registration Ownership Verifier (ROVR): When the "C" flag is set,
this field contains a Crypto-ID.
This specification uses the status codes "Validation Requested" and
"Validation Failed", which are defined in [RFC 8505].
This specification does not define any new status codes.
4.3. Crypto-ID Parameters Option
This specification defines the CIPO. The CIPO carries the parameters
used to form a Crypto-ID.
In order to provide cryptographic agility [BCP201], 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 [RFC 6234]
internally, MUST be supported by all implementations.
* The Ed25519 signature scheme, which uses the Pure Edwards-Curve
Digital Signature Algorithm (PureEdDSA) [RFC 8032] with the twisted
Edwards curve Edwards25519 [RFC 7748] and the hash function SHA-512
[RFC 6234] 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 [RFC 6234] 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
Type: 8-bit unsigned integer. IANA has assigned value 39; 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 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 of the Crypto-ID indexed by IANA in
the "Crypto-Types" subregistry in the "Internet Control Message
Protocol version 6 (ICMPv6) Parameters" registry (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 the same key pair. This
reduces the traceability and, thus, improves the privacy of a
constrained node without requiring 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; the size is indicated in the
Public Key Length field.
Padding: A variable-length field that completes the Public Key field
to align to the next 8-byte 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 [RFC 6234] 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 it 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, refer to Appendix B.
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 and validates the address being registered. 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 [RFC 3971], 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 a CIPO that the 6LR already
received to be omitted, at the expense of the capability to add
arbitrary options that would be signed with an 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 key pair 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
Type: IANA has assigned value 40; 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-byte 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 bit in the 6LoWPAN
Capability Indication Option (6CIO), as defined by [RFC 7400], 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.
The "A" flag is set by the 6LBR that serves the network and is
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 [RFC 6775]. A 6LBR has sufficient capability to
satisfy the needs of DAD.
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 autoconfiguration [RFC 4862], where there is no
guarantee of ownership from the network, and each IPv6 Neighbor
Discovery packet must be individually secured [RFC 3971].
---+-------- ............
| 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 L2 security is
deployed so that all the packets from a particular host are
protected. 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.
6. Protocol Flows
The 6LR/6LBR ensures first come, first served 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. Once every node in the network is upgraded to support this
specification, the "A" flag can be set to turn the protection on
globally.
The 6LN places a cryptographic identifier, 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 in a subnet is set, the 6LR MUST challenge the 6LN
before it creates a Binding with the "C" flag set in the EARO. The
6LR MUST also challenge the 6LN when a new registration attempts to
change a parameter of an already validated Binding for that 6LN, for
instance, its Source link-layer address. Such verification protects
against an attacker that attempts to steal the address of an honest
node.
The 6LR MUST indicate to the 6LBR that it performed a successful
validation by setting a status code of 5 ("Validation Requested") in
the EDAR. Upon a subsequent EDAR from a new 6LR with a status code
that is not 5 for a validated Binding, the 6LBR MUST indicate to the
new 6LR that it needs to challenge the 6LN using a status code of 5
in the Extended Duplicate Address Confirmation (EDAC).
The 6LR MUST challenge the 6LN when the 6LBR signals to do so, which
is done with an EDAC message with a status code of 5. The EDAC 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 in orders to detect an issue
immediately.
If the 6LR does not support the Crypto-Type, it MUST reply with an
EARO status code of 10 "Validation Failed" without a challenge. In
that case, the 6LN may try another Crypto-Type until it falls back to
Crypto-Type 0, which 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 the same key pair by changing the modifier.
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 [RFC 8505]. 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 used before. This specification
inherits the idea from [RFC 3971] that the nonce is a random value.
Ideally, an implementation uses an unpredictable cryptographically
random value [BCP106]. But that may be impractical in some LLN
scenarios with resource-constrained devices.
Alternatively, the device may use an always-incrementing value saved
in the same stable storage as the key, so they are lost together, and
start at a best-effort random value as either the nonce value or a
component to its computation.
The 6LN replies to the challenge with an NS(EARO) that includes the
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" that
results in better security even when the nonces of one party are not
generated as specified.
The 6LR MUST store the information associated with 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 an 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 an NA(EARO) with a status code of "Validation
Requested".
Upon receiving a first NA(EARO) with a status code of "Validation
Requested" from a 6LR, the Registering Node SHOULD retry its
registration with a CIPO (Section 4.3) that contains all the
necessary material for building the Crypto-ID, the NonceLN that it
generated, and the NDP Signature Option (Section 4.4) 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. At that point, if the
signature in the NDPSO 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 code of "Validation Failed". After receiving an NA(EARO) with
a status code of "Validation Failed", the Registering Node SHOULD try
an alternate Crypto-Type; even if Crypto-Type 0 fails, it may try to
register a different address in the NS message.
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 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 [RFC 3972] (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 <https://www.random.org>.)
2. The CIPO.
3. The 16-byte Target Address (in network byte order) sent in the
NS message. It is the address that the 6LN is registering
with the 6LR and 6LBR.
4. The NonceLR received from the 6LR (in network byte order) in
the NA message. The nonce is at least 6 bytes long as defined
in [RFC 3971].
5. The NonceLN sent from the 6LN (in network byte order). The
nonce is at least 6 bytes long as defined in [RFC 3971].
6. The 1-byte option length of the EARO containing the Crypto-ID.
* Apply the signature algorithm specified by the Crypto-Type using
the private key.
Upon receiving the NDPSO and CIPO options, the 6LR 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 using the following steps:
* 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 NS message. It is the address that the 6LN is registering
with the 6LR and 6LBR.
4. The NonceLR sent in the NA message. The nonce is at least 6
bytes long as defined in [RFC 3971].
5. The NonceLN received from the 6LN (in network byte order) in
the NS message. The nonce is at least 6 bytes long as defined
in [RFC 3971].
6. The 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 an EDAR/EDAC
flow.
* Due to the first-come, first-served 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 databases.
6.3. Multi-Hop Operation
A new 6LN that joins the network autoconfigures an address and
performs an initial registration to a neighboring 6LR with an NS
message that carries an EARO [RFC 8505].
In a multi-hop 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) [RFC 8929].
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
The 6LR and the 6LBR communicate using ICMPv6 EDAR and EDAC messages
[RFC 8505] 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, the
verification succeeded.
7. Security Considerations
7.1. Brown Field
Only 6LRs that are upgraded to this specification are capable of
challenging a registration and avoiding 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. Threats Identified in RFC 3971
Observations regarding the following threats to the local network in
[RFC 3971] also apply to this specification.
Neighbor Solicitation/Advertisement Spoofing: Threats in
Section 9.2.1 of [RFC 3971] apply. AP-ND counters the threats on
NS(EARO) messages by requiring that the NDPSO and CIPO be present
in these solicitations.
Duplicate Address Detection DoS Attack: Inside the LLN, duplicate
addresses are sorted out using the ROVR. A different ROVR for the
same Registered Address entails a rejection of the second
registration [RFC 8505]. DADs coming from the backbone network are
not forwarded over the LLN to provide some protection against DoS
attacks inside the resource-constrained part of the network.
However, the EARO is present in the NS/NA messages exchanged over
the backbone network. This protects against misinterpreting node
movement as a duplication and enables the Backbone Routers to
determine which subnet has the most recent registration [RFC 8505]
and is thus the best candidate to validate the registration
[RFC 8929].
Router Solicitation and Advertisement Attacks: This specification
does not change the protection of RS and RA, which can still be
protected by SEND.
Replay Attacks: Nonces should never repeat but they do not need to
be unpredictable for secure operation. Using nonces (NonceLR and
NonceLN) generated by both the 6LR and 6LN ensures 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.
Neighbor Discovery DoS Attack: A rogue node that can 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 code of 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 attacker.
7.3. Related to 6LoWPAN ND
The threats and mitigations discussed in 6LoWPAN ND [RFC 6775]
[RFC 8505] also apply here, in particular, denial-of-service (DoS)
attacks against the registry at the 6LR or 6LBR.
Secure ND [RFC 3971] 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 1 KB 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 L2 addresses or temporary addresses
that cannot be compressed, e.g., formed pseudorandomly and released
in relatively short cycles for privacy reasons [RFC 8064][RFC 8065].
This specification provides added protection for addresses that are
obtained following due procedure [RFC 8505] but does not constrain the
way the addresses are formed or the number of addresses that are used
in parallel by a same entity. An attacker may still perform a DoS
attack against the registry at the 6LR or 6LBR or attempt to deplete
the pool of available addresses at L2 or L3.
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 to perform the
checking adequately, and the communication between the 6LR and the
6LBR must be protected to avoid tampering with the result of the
validation.
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 Crypto-ID validation. The 6LR may then attract and inject
traffic at will on behalf of that address, or let an attacker take
ownership of the address.
7.5. ROVR Collisions
A collision of ROVRs (i.e., the Crypto-ID in this specification) is
possible, but it is a rare event. Assuming that the hash used for
calculating the Crypto-ID is a well-behaved cryptographic hash, and,
thus, random collisions are the only ones possible, if n = 2^(k) is
the maximum number of hash values (i.e., a k-bit hash) and p is the
number of nodes, then (assuming one Crypto-ID per node) the formula 1
- e^(-p^(2)/(2n)) provides an approximation of the probability that
there is at least one collision (birthday paradox).
If the Crypto-ID is 64 bits (the least possible size allowed), the
chance of a collision is 0.01% for a 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, an honest node
might accidentally claim the Registered Address of another legitimate
node (with the same Crypto-ID). To prevent such rare events, it is
RECOMMENDED that nodes do not derive the address being registered
from the ROVR.
7.6. Implementation Attacks
The signature schemes referenced in this specification comply with
NIST [FIPS186-4] or Crypto Forum Research Group (CFRG) standards
[RFC 8032] and offer strong algorithmic security at roughly a 128-bit
security level. These signature schemes use elliptic curves that
either were specifically designed with exception-free and constant-
time arithmetic in mind [RFC 7748] or have 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 key pair 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 key pairs can be formed for new registrations if the node
desires. However, the same private key MUST NOT be reused with more
than one instantiation of the signature scheme in this specification.
Also, 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 the ephemeral
private key k across signing operations. This precludes the use of
deterministic ECDSA without a random input for the determination of
k, which is deemed dangerous for the intended applications this
document aims to serve.
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 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 [RFC 8505] extends the EUI-64
field of the ARO defined in [RFC 6775]. 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 the same 6LN across multiple
addresses. Section 3 of [RFC 8505] indicates that the ROVR and the
address being registered are decoupled. A 6LN may use the same ROVR
for multiple registrations or a different ROVR per registration, and
the IID must not be derived from the ROVR. In theory, different 6LNs
could use the 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 the same
key pair. Using that facility improves the privacy of the 6LN at the
expense of storage in the 6LR, which will need to store multiple
CIPOs that contain the same public key. Note that if an attacker
gains access to the 6LR, then the modifier alone does not provide
protection, and the 6LN would need to generate different key pairs
and link-layer addresses in an attempt to obfuscate its multiple
ownership.
8. IANA Considerations
8.1. CGA Message Type
This document defines a new 128-bit CGA Extension Type Tag under the
"CGA Extension Type Tags" subregistry of the Cryptographically
Generated Addresses (CGA) Message Type Name Space created by
[RFC 3972].
Tag: 0x8701 55c8 0cca dd32 6ab7 e415 f148 84d0.
8.2. Crypto-Type Subregistry
IANA has created the "Crypto-Types" subregistry in the "Internet
Control Message Protocol version 6 (ICMPv6) Parameters" registry.
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.
Detailed explanations are provided 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] | [RFC 7748] | [RFC 7748] |
+----------------+-----------------+--------------+-----------------+
|Hash Function |SHA-256 [RFC 6234]| SHA-512 |SHA-256 [RFC 6234]|
| | | [RFC 6234] | |
+----------------+-----------------+--------------+-----------------+
|Signature |ECDSA [FIPS186-4]| Ed25519 |ECDSA [FIPS186-4]|
|Algorithm | | [RFC 8032] | |
+----------------+-----------------+--------------+-----------------+
|Representation | Weierstrass, | Edwards, | Weierstrass, |
|Conventions | (un)compressed, | compressed, | (un)compressed, |
| | MSB/msb-order, |LSB/lsb-order,| MSB/msb-order, |
| | [SEC1] | [RFC 8032] | [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 |
+----------------+-----------------+--------------+-----------------+
|Reference | RFC 8928 | RFC 8928 | RFC 8928 |
+----------------+-----------------+--------------+-----------------+
Table 1: Crypto-Types
New Crypto-Type values providing similar or better security may be
defined in the future.
Assignment of values for new Crypto-Type MUST be done through IANA
with either "Specification Required" or "IESG Approval" as defined in
BCP 26 [RFC 8126].
8.3. IPv6 ND Option Types
This document registers two new ND option types under the subregistry
"IPv6 Neighbor Discovery Option Formats":
+====================================+======+===========+
| Description | Type | Reference |
+====================================+======+===========+
| Crypto-ID Parameters Option (CIPO) | 39 | RFC 8928 |
+------------------------------------+------+-----------+
| NDP Signature Option (NDPSO) | 40 | RFC 8928 |
+------------------------------------+------+-----------+
Table 2: New ND Options
8.4. New 6LoWPAN Capability Bit
IANA has made an addition to the subregistry for "6LoWPAN Capability
Bits" created for [RFC 7400] as follows:
+=====+=======================+===========+
| Bit | Description | Reference |
+=====+=======================+===========+
| 9 | AP-ND Enabled (1 bit) | RFC 8928 |
+-----+-----------------------+-----------+
Table 3: New 6LoWPAN Capability Bit
9. References
9.1. Normative References
[FIPS186-4]
National Institute of Standards and Technology, "Digital
Signature Standard (DSS)", FIPS 186-4,
DOI 10.6028/NIST.FIPS.186-4, July 2013,
<https://nvlpubs.nist.gov/nistpubs/fips/
nist.fips.186-4.pdf>.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC 2119, March 1997,
<https://www.rfc-editor.org/info/RFC 2119>.
[RFC 3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC 3971, March 2005,
<https://www.rfc-editor.org/info/RFC 3971>.
[RFC 6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC 6234, May 2011,
<https://www.rfc-editor.org/info/RFC 6234>.
[RFC 6775] 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/RFC 6775, November 2012,
<https://www.rfc-editor.org/info/RFC 6775>.
[RFC 7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for
IPv6 over Low-Power Wireless Personal Area Networks
(6LoWPANs)", RFC 7400, DOI 10.17487/RFC 7400, November
2014, <https://www.rfc-editor.org/info/RFC 7400>.
[RFC 7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC 7748, January
2016, <https://www.rfc-editor.org/info/RFC 7748>.
[RFC 8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC 8032, January 2017,
<https://www.rfc-editor.org/info/RFC 8032>.
[RFC 8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC 8174,
May 2017, <https://www.rfc-editor.org/info/RFC 8174>.
[RFC 8505] 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/RFC 8505, November 2018,
<https://www.rfc-editor.org/info/RFC 8505>.
[SEC1] Standards for Efficient Cryptography, "SEC 1: Elliptic
Curve Cryptography", Version 2, May 2009,
<https://www.secg.org/sec1-v2.pdf>.
9.2. Informative References
[BCP106] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC 4086, June 2005,
<https://www.rfc-editor.org/info/RFC 4086>.
[BCP201] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, DOI 10.17487/RFC 7696, November 2015,
<https://www.rfc-editor.org/info/RFC 7696>.
[breaking-ed25519]
Samwel, N., Batina, L., Bertoni, G., Daemen, J., and R.
Susella, "Breaking Ed25519 in WolfSSL", Topics in
Cryptology - CT-RSA, pp. 1-20, March 2018,
<https://link.springer.com/
chapter/10.1007/978-3-319-76953-0_1>.
[CURVE-REPR]
Struik, R., "Alternative Elliptic Curve Representations",
Work in Progress, Internet-Draft, draft-ietf-lwig-curve-
representations-14, 15 November 2020,
<https://tools.ietf.org/html/draft-ietf-lwig-curve-
representations-14>.
[RFC 3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC 3972, March 2005,
<https://www.rfc-editor.org/info/RFC 3972>.
[RFC 4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC 4861, September 2007,
<https://www.rfc-editor.org/info/RFC 4861>.
[RFC 4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC 4862, September 2007,
<https://www.rfc-editor.org/info/RFC 4862>.
[RFC 4919] 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/RFC 4919, August 2007,
<https://www.rfc-editor.org/info/RFC 4919>.
[RFC 4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC 4944, September 2007,
<https://www.rfc-editor.org/info/RFC 4944>.
[RFC 6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC 6282, September 2011,
<https://www.rfc-editor.org/info/RFC 6282>.
[RFC 7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed.,
"Source Address Validation Improvement (SAVI) Framework",
RFC 7039, DOI 10.17487/RFC 7039, October 2013,
<https://www.rfc-editor.org/info/RFC 7039>.
[RFC 7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC 7217, April 2014,
<https://www.rfc-editor.org/info/RFC 7217>.
[RFC 8064] Gont, F., Cooper, A., Thaler, D., and W. Liu,
"Recommendation on Stable IPv6 Interface Identifiers",
RFC 8064, DOI 10.17487/RFC 8064, February 2017,
<https://www.rfc-editor.org/info/RFC 8064>.
[RFC 8065] Thaler, D., "Privacy Considerations for IPv6 Adaptation-
Layer Mechanisms", RFC 8065, DOI 10.17487/RFC 8065,
February 2017, <https://www.rfc-editor.org/info/RFC 8065>.
[RFC 8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC 8126, June 2017,
<https://www.rfc-editor.org/info/RFC 8126>.
[RFC 8929] Thubert, P., Ed., Perkins, C.E., and E. Levy-Abegnoli,
"IPv6 Backbone Router", RFC 8929, DOI 10.17487/RFC 8929,
November 2020, <https://www.rfc-editor.org/info/RFC 8929>.
Appendix A. Requirements Addressed in This Document
In this section, the requirements of a secure Neighbor Discovery
protocol for LLNs are stated.
* The protocol MUST be based on the Neighbor Discovery Optimization
for the LLN protocol defined in [RFC 6775]. RFC 6775 utilizes
optimizations such as host-initiated interactions for sleeping
resource-constrained hosts and the 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 SEND. Smaller packet sizes facilitate low-power
transmission by resource-constrained nodes on lossy links.
* The registration mechanism SHOULD be extensible to other LLN links
and not be limited to IEEE 802.15.4 only. LLN links for which a
6lo "IPv6 over foo" specification exist, as well as low-power Wi-
Fi, SHOULD be supported.
* As part of this protocol, 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 the unique identifier.
* The Neighbor Discovery should specify the formation of a site-
local address that follows the security recommendations from
[RFC 7217].
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 D.1.2 of [FIPS186-4], and the
hash function SHA-256, as specified in [RFC 6234], 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 MSB and msb
order. For further details, see [FIPS186-4] for ECDSA, see
Appendix B.3 for the encoding of public keys, and see Appendix B.2
for signature encoding.
The signature scheme Ed25519 corresponding to Crypto-Type 1 is EdDSA,
as specified in [RFC 8032], instantiated with the Montgomery curve
Curve25519, as specified in [RFC 7748], and the hash function SHA-512,
as specified in [RFC 6234], 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 LSB and lsb order. For details on EdDSA
and the encoding of public keys and signatures, see the specification
of pure Ed25519 in [RFC 8032].
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 [RFC 7748], and the hash function
SHA-256, as specified in [RFC 6234], 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 MSB and msb order. The signature itself consists of
a bit string that encodes two integers (r and s), which are each
encoded as fixed-size octet strings in MSB and msb order. For
further details, see [FIPS186-4] for ECDSA, see Appendix B.3 for the
encoding of public keys, and see Appendix B.2 for signature encoding.
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 FieldElement-to-OctetString conversion rules in
[SEC1] and where the ordered pair of integers is represented as the
right concatenation 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 OctetString-to-FieldElement
conversion rules in [SEC1]. In both cases, the field with these
conversion rules is the set of integers modulo n, where n is the
(prime) order of the base point of the curve in question. (For
elliptic curve nomenclature, see Appendix B.1 of [CURVE-REPR].)
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 [RFC 7748], 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 [RFC 7748]; the domain parameters of the elliptic curve
Wei25519 in short-Weierstrass form 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)
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
(=0x20ae19a1 b8a086b4 e01edd2c 7748d14c 923d4d7e 6d7c61b2 29e9c5a2
7eced3d9)
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 Kühlewind, Éric 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 Erik Kline, who supported us along the whole
process.
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
RFC TOTAL SIZE: 72143 bytes
PUBLICATION DATE: Monday, November 23rd, 2020
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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