Address Protected Neighbor Discovery for Low-power and Lossy Networks
draft-ietf-6lo-ap-nd-06
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8928.
Expired & archived
|
|
|---|---|---|---|
| Authors | Pascal Thubert , Behcet Sarikaya , Mohit Sethi | ||
| Last updated | 2018-08-27 (Latest revision 2018-02-23) | ||
| Replaces | draft-sarikaya-6lo-ap-nd | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 8928 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-6lo-ap-nd-06
6lo P. Thubert, Ed.
Internet-Draft Cisco
Updates: 6775 (if approved) B. Sarikaya
Intended status: Standards Track
Expires: August 27, 2018 M. Sethi
Ericsson
February 23, 2018
Address Protected Neighbor Discovery for Low-power and Lossy Networks
draft-ietf-6lo-ap-nd-06
Abstract
This document defines an extension to 6LoWPAN Neighbor Discovery (ND)
[RFC6775][I-D.ietf-6lo-rfc6775-update] called Address Protected ND
(AP-ND); AP-ND protects the owner of an address against address theft
and impersonation inside a low-power and lossy network (LLN). Nodes
supporting this extension compute a cryptographic Owner Unique
Interface ID and associate it with one or more of their Registered
Addresses. The Cryptographic ID uniquely identifies the owner of the
Registered Address and can be used for proof-of-ownership. It is
used in 6LoWPAN ND in place of the EUI-64-based unique ID that is
associated with the registration. Once an address is registered with
a Cryptographic ID, only the owner of that ID can modify the anchor
state information of the Registered Address, and Source Address
Validation can be enforced.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 27, 2018.
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Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . . 5
4. New Fields and Options . . . . . . . . . . . . . . . . . . . 5
4.1. Encoding the Public Key . . . . . . . . . . . . . . . . . 5
4.2. New Crypto-ID . . . . . . . . . . . . . . . . . . . . . . 6
4.3. Updated EARO . . . . . . . . . . . . . . . . . . . . . . 6
4.4. Crypto-ID Parameters Option . . . . . . . . . . . . . . . 8
4.5. Nonce Option . . . . . . . . . . . . . . . . . . . . . . 9
4.6. NDP Signature Option . . . . . . . . . . . . . . . . . . 9
5. Protocol Scope . . . . . . . . . . . . . . . . . . . . . . . 9
6. Protocol Flows . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. First Exchange with a 6LR . . . . . . . . . . . . . . . . 11
6.2. Multihop Operation . . . . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
7.1. Inheriting from RTC 3971 . . . . . . . . . . . . . . . . 15
7.2. Related to 6LoWPAN ND . . . . . . . . . . . . . . . . . . 16
7.3. OUID Collisions . . . . . . . . . . . . . . . . . . . . . 16
8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 17
8.1. CGA Message Type . . . . . . . . . . . . . . . . . . . . 17
8.2. Crypto-Type Subregistry . . . . . . . . . . . . . . . . . 17
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . 18
10.2. Informative references . . . . . . . . . . . . . . . . . 19
Appendix A. Requirements Addressed in this Document . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
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1. Introduction
"Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775]
(6LoWPAN ND) adapts the classical IPv6 ND protocol [RFC4861][RFC4862]
(IPv6 ND) for operations over a constrained low-power and lossy
network (LLN). In particular, 6LoWPAN ND introduces a unicast host
address registration mechanism that contributes to reduce the use of
multicast messages that are present in the classical IPv6 ND
protocol. 6LoWPAN ND defines a new Address Registration Option (ARO)
that is carried in the unicast Neighbor Solicitation (NS) and
Neighbor Advertisement (NA) messages between the 6LoWPAN Node (6LN)
and the 6LoWPAN Router (6LR). Additionally, it also defines the
Duplicate Address Request (DAR) and Duplicate Address Confirmation
(DAC) messages between the 6LR and the 6LoWPAN Border Router (6LBR).
In LLN networks, the 6LBR is the central repository of all the
registered addresses in its domain.
The registration mechanism in 6LoWPAN ND [RFC6775] prevents the use
of an address if that address is already present in the subnet (first
come first serve). In order to validate address ownership, the
registration mechanism enables the 6LR and 6LBR to validate claims
for a registered address with an associated Owner Unique Interface
IDentifier (OUID). 6LoWPAN ND specifies that the OUID is derived from
the MAC address of the device (using the 64-bit Extended Unique
Identifier EUI-64 address format specified by IEEE), which can be
spoofed. Therefore, any node connected to the subnet and aware of a
registered-address-to-OUID mapping could effectively fake the OUID,
steal the address and redirect traffic for that address towards a
different 6LN. The "Update to 6LoWPAN ND"
[I-D.ietf-6lo-rfc6775-update] defines an Extended ARO (EARO) option
that allows to transport alternate forms of OUIDs, and is a
prerequisite for this specification.
According to this specification, a 6LN generates a cryptographic ID
(Crypto-ID) and places it in the OUID field in the registration of
one (or more) of its addresses with the 6LR(s) that the 6LN uses as
default router(s). Proof of ownership of the cryptographic ID
(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 can create a registration state, or a
change the anchor information, that is the Link-Layer Address and
associated parameters, in an existing registration state.
The protected address registration protocol proposed in this document
enables the enforcement of Source Address Validation (SAVI)
[RFC7039], which ensures that only the correct owner uses a
registered address in the source address field in IPv6 packets.
Consequently, a 6LN that sources a packet has to use a 6LR to which
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the source address of the packet is registered to forward the packet.
The 6LR maintains state information for the registered addressed,
including the MAC address, and a link-layer cryptographic key
associated with the 6LN. In SAVI-enforcement mode, the 6LR allows
only packets from a connected Host if the connected Host owns the
registration of the source address of the packet.
The 6lo adaptation layer framework ([RFC4944], [RFC6282]) expects
that a device forms its IPv6 addresses based on Layer-2 address, so
as to enable a better compression. This is incompatible with "Secure
Neighbor Discovery (SeND)" [RFC3971] and "Cryptographically Generated
Addresses (CGAs)" [RFC3972], which derive the Interface ID (IID) in
the IPv6 addresses from cryptographic material. "Privacy
Considerations for IPv6 Address Generation Mechanisms" [RFC7721]
places additional recommendations on the way addresses should be
formed and renewed.
This document specifies that a device may form and register addresses
at will, without a constraint on the way the address is formed or the
number of addresses that are registered in parallel. It enables to
protect multiple addresses with a single cryptographic material and
to send the proof only once to a given 6LR for multiple addresses and
refresher registrations.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Readers are expected to be familiar with all the terms and concepts
that are discussed in [RFC3971], [RFC3972], [RFC4861], [RFC4919],
[RFC6775], and [I-D.ietf-6lo-backbone-router] which proposes an
evolution of [RFC6775] for wider applicability.
This document defines Crypto-ID as an identifier of variable size
which in most cases is 64 bits long. It is generated using
cryptographic means explained later in this document Section 4.2.
"Elliptic Curves for Security" [RFC7748] and "Edwards-Curve Digital
Signature Algorithm (EdDSA)" [RFC8032] provides information on
Elliptic Curve Cryptography (ECC) and a (twisted) Edwards curve,
Ed25519, which can be used with this specification. "Alternative
Elliptic Curve Representations"
[I-D.struik-lwig-curve-representations] provides additional
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
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existing implementations that already implement, e.g., ECDSA and ECDH
using NIST [FIPS-186-4] prime curves.
The document also conforms to the terms and models described in
[RFC5889] and uses the vocabulary and the concepts defined in
[RFC4291] for the IPv6 Architecture. Finally, common terminology
related to Low power And Lossy Networks (LLN) defined in [RFC7102] is
also used.
3. Updating RFC 6775
This specification defines a cryptographic identifier (Crypto-ID)
that can be used as a replacement to the MAC address in the OUID
field of the EARO option; the computation of the Crypto-ID is
detailed in Section 4.2. A node in possession of the necessary
cryptographic material SHOULD use Crypto-ID by default as OUID in its
registration. Whether a OUID is a Crypto-ID is indicated by a new
"C" flag in the NS(EARO) message.
In order to prove its ownership of a Crypto-ID, the registering node
needs to produce the parameters that where used to build it, as well
as a nonce and a signature that will prove that it has the private
key that corresponds to the public key that was used to build the
Crypto-ID. This specification adds the capability to carry new
options in the NS(EARO) and the NBA(EARO). These options are a
variation of the CGA Option Section 4.4, a Nonce option and a
variation of the RSA Signature option Section 4.6 in the NS(EARO) and
a Nonce option in the NA(EARO).
4. New Fields and Options
In order to avoid an inflation of ND option types, this specification
reuses / extends options defined in SEND [RFC3971] and 6LoWPAN ND
[RFC6775][I-D.ietf-6lo-rfc6775-update]. This applies in particular
to the CGA option and the RSA Signature Option. This specification
provides aliases for the specific variations of those options as used
in AP-ND. The presence of the EARO option in the NS/NA messages
indicates that the options are to be understood as specified in this
document. A router that would receive a NS(EARO) and try to process
it as a SEND message will find that the signature does not match and
drop the packet.
4.1. Encoding the Public Key
Public Key is the most important parameter in CGA Parameters (sent by
6LN in an NS message). ECC Public Key could be in uncompressed form
or in compressed form where the first octet of the OCTET STRING is
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0x04 and 0x02 or 0x03, respectively. Point compression can further
reduce the key size by about 32 octets.
4.2. New Crypto-ID
Elliptic Curve Cryptography (ECC) is used to calculate the Crypto-ID.
Each 6LN using a Crypto-ID for registration MUST have a public/
private key pair. The digital signature is constructed by using the
6LN's private key over its EUI-64 (MAC) address. The signature value
is computed using the ECDSA signature algorithm and the hash function
used is SHA-256 [RFC6234].
NIST P-256 [FIPS186-4] that MUST be supported by all implementations.
To support cryptographic algorithm agility [RFC7696], Edwards-Curve
Digital Signature Algorithm (EdDSA) curve Ed25519ph (pre-hashing)
[RFC8032] MAY be supported as an alternate.
The Crypto-ID is computed as follows:
1. An 8-bits modifier is selected, for instance, but not
necessarily, randomly; the modifier enables a device to form
multiple Crypto-IDs with a single key pair. This may be useful
for privacy reasons in order to avoid the correlation of
addresses based on their Crypto-ID;
2. the modifier value and the DER-encoded public key (Section 4.1)
are concatenated from left to right;
3. Digital signature (SHA-256 then either NIST P-256 or EdDSA) is
executed on the concatenation
4. the leftmost bits of the resulting signature are used as the
Crypto-ID;
With this specification, only 64 bits are retained, but it could be
expanded to more bits in the future by increasing the size of the
OUID field.
4.3. Updated EARO
This specification updates the EARO option as follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Status | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved|C|R|T| TID | Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Owner Unique ID (EUI-64 or Crypto-ID) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Enhanced Address Registration Option
Type: 33
Length: 8-bit unsigned integer. The length of the option
(including the type and length fields) in units of 8
bytes.
Status: 8-bit unsigned integer. Indicates the status of a
registration in the NA response. MUST be set to 0 in
NS messages. This specification uses values
introduced in the update to 6LoWPAN ND
[I-D.ietf-6lo-rfc6775-update], such as "Validation
Requested" and "Validation Failed". No additional
value is defined.
Reserved: This field is unused. It MUST be initialized to zero
by the sender and MUST be ignored by the receiver.
C: This "C" flag is set to indicate that the Owner
Unique ID field contains a Crypto-ID and that the 6LN
MAY be challenged for ownership as specified in this
document.
R: Defined in [I-D.ietf-6lo-rfc6775-update].
T and TID: Defined in [I-D.ietf-6lo-rfc6775-update].
Owner Unique ID: When the "C" flag is set, this field contains a
Crypto-ID.
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4.4. Crypto-ID Parameters Option
This specification defines the Crypto-ID Parameters Option (CIPO), as
a variation of the CGA Option that carries the parameters used to
form a Crypto-ID. In order to provide cryptographic agility, AP-ND
supports two possible signature algorithms, indicated by a Crypto-
Type field. A value of 0 indicates that NIST P-256 is used for the
signature operation and SHA-256 as the hash algorithm. NIST P-256
MUST be supported by all implement A value of 1 indicates that
Ed25519ph is used for the signature operation and SHA-256 as the hash
algorithm.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Pad Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Crypto-Type | Modifier | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
. .
. Public Key (variable length) .
. .
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Crypto-ID Parameters Option
Type: 11. This is the same value as the CGA Option, CIPO
is a particular case of the CGA option
Length: 8-bit unsigned integer. The length of the option in
units of 8 octets.
Modifier: 8-bit unsigned integer.
Pad Length: 8-bit unsigned integer. The length of the Padding
field.
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Crypto-Type: The type of cryptographic algorithm used in
calculation Crypto-ID. Default value of all zeros
indicate NIST P-256. A value of 1 is assigned for
Ed25519ph. New values may be defined later.
Public Key: Public Key of 6LN.
Padding: A variable-length field making the option length a
multiple of 8, containing as many octets as specified
in the Pad Length field.
4.5. Nonce Option
This document reuses the Nonce Option defined in section 5.3.2. of
SEND [RFC3971] without a change.
4.6. NDP Signature Option
This document reuses the RSA Signature Option (RSAO) defined in
section 5.2. of SEND [RFC3971]. Admittedly, the name is ill-chosen
since the option is extended for non-RSA Signatures and this
specification defines an alias to avoid the confusion.
The description of the operation on the option detailed in section
5.2. of SEND [RFC3971] apply, but for the following changes:
o The 128-bit CGA Message Type tag [RFC3972] for AP-ND is 0x8701
55c8 0cca dd32 6ab7 e415 f148 84d0. (The tag value has been
generated by the editor of this specification on random.org).
o The signature is computed using the hash algorithm and the digital
signature indicated in the Crypto-Type field of the CIPO option
using the private key associated with the public key in the CIPO.
o The alias NDP Signature Option (NDPSO) can be used to refer to the
RSAO when used as described in this specification.
5. Protocol Scope
The scope of the present work is a 6LoWPAN Low Power Lossy Network
(LLN), typically a stub network connected to a larger IP network via
a Border Router called a 6LBR per [RFC6775].
The 6LBR maintains a registration state for all devices in the
attached LLN, and, in conjunction with the first-hop router (the
6LR), is in a position to validate uniqueness and grant ownership of
an IPv6 address before it can be used in the LLN. This is a
fundamental difference with a classical network that relies on IPv6
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address auto-configuration [RFC4862], where there is no guarantee of
ownership from the network, and any IPv6 Neighbor Discovery packet
must be individually secured [RFC3971].
---+-------- ............
| External Network
|
+-----+
| | 6LBR
+-----+
o o o
o o o o
o o LLN o o o
o o o (6LR)
o (6LN)
Figure 3: Basic Configuration
In a mesh network, the 6LR is directly connected to the host device.
This specification expects that the peer-wise layer-2 security is
deployed so that all the packets from a particular host are securely
identifiable by the 6LR. The 6LR may be multiple hops away from the
6LBR. Packets are routed between the 6LR and the 6LBR via other
6LRs. This specification expects that a chain of trust is
established so that a packet that was validated by the first 6LR can
be safely routed by the next 6LRs to the 6LBR.
6. Protocol Flows
The 6LR/6LBR ensures first-come/first-serve by storing the EARO
information including the Crypto-ID correlated to the node being
registered. The node is free to claim any address it likes as long
as it is the first to make such a claim. After a successful
registration, the node becomes the owner of the registered address
and the address is bound to the Crypto-ID in the 6LR/6LBR registry.
This specification enables to verify the ownership of the binding at
any time assuming that the "C" flag is set. If it is not set, then
the verification methods presented in this specification cannot be
applied. The verification prevents other nodes from stealing the
address and trying to attract traffic for that address or use it as
their source address.
A node may use multiple IPv6 addresses at the same time. The node
may use a same Crypto-ID, or multiple crypto-IDs derived from a same
key pair, to protect multiple IPv6 addresses. The separation of the
address and the cryptographic material avoids the constrained device
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to compute multiple keys for multiple addresses. The registration
process allows the node to bind all of its addresses to the same
Crypto-ID.
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 Owner Unique ID field
contains a Crypto-ID. The on-link (local) protocol interactions are
shown in Figure 4 If the 6LR does not have a state with the 6LN that
is consistent with the NS(EARO), then it replies with a challenge NA
(EARO, status=Validation Requested) that contains a Nonce Option.
The Nonce option MUST contain a Nonce value that was never used with
this device.
The 6LN replies to the challenge with a proof-of-ownership NS(EARO)
that includes the echoed Nonce option, the CIPO with all the
parameters that where used to build EARO with a Crypto-ID, and as the
last option the NDPSO with the signature. The information associated
to a crypto-ID is passed to and stored by the 6LR on the first NS
exchange where it appears. The 6LR SHOULD store the CIPO information
associated with the crypto-ID so it can be used for more than one
address.
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6LN 6LR
| |
|<------------------------- RA -------------------------|
| | ^
|---------------- NS with EARO (Crypto-ID) ------------>| |
| | option
|<- NA with EARO (status=Validation Requested), Nonce --| |
| | v
|-------- NS with EARO, CIPO, Nonce and NDPSO --------->|
| |
|<------------------- NA with EARO ---------------------|
| |
...
| |
|--------------- NS with EARO (Crypto-ID) ------------->|
| |
|<------------------- NA with EARO ---------------------|
| |
...
| |
|--------------- NS with EARO (Crypto-ID) ------------->|
| |
|<------------------- NA with EARO ---------------------|
| |
Figure 4: On-link Protocol Operation
The steps for the registration to the 6LR are as follows:
o Upon the first exchange with a 6LR, a 6LN may be challenged and
have to produce the proof of ownership of the Crypto-ID. However,
it is not expected that the proof is needed again in the periodic
refresher registrations for that address, or when registering
other addresses with the same OUID. When a 6LR receives a
NS(EARO) registration with a new Crypto-ID as a OUID, it SHOULD
challenge by responding with a NA(EARO) with a status of
"Validation Requested". This process of validation MAY be skipped
in networks where there is no mobility.
o The challenge MUST also be triggered in the case of a registration
for which the Source Link-Layer Address is not consistent with a
state that already exists either at the 6LR or the 6LBR. In the
latter case, the 6LBR returns a status of "Validation Requested"
in the DAR/DAC exchange, which is echoed by the 6LR in the NA
(EARO) back to the registering node. This flow should not alter a
preexisting state in the 6LR or the 6LBR.
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o Upon receiving a NA(EARO) with a status of "Validation Requested",
the registering node SHOULD retry its registration with a Crypto-
ID Parameters Option (CIPO) Section 4.4 that contains all the
necessary material for building the Crypto-ID, the Nonce and the
NDP signature Section 4.6 options that prove its ownership of the
Crypto-ID.
o In order to validate the ownership, the 6LR performs the same
steps as the 6LN and rebuilds the Crypto-ID based on the
parameters in the CIPO. If the result is different then the
validation fails. Else, the 6LR checks the signature in the NDPSO
using the public key in the CIPO. If it is correct then the
validation passes, else it fails.
o If the 6LR fails to validate the signed NS(EARO), it responds with
a status of "Validation Failed". After receiving a NA(EARO) with
a status of "Validation Failed", the registering node SHOULD try
an alternate Signature Algorithm and Crypto-ID. In any case, it
MUST NOT use this Crypto-ID for registering with that 6LR again.
6.2. Multihop Operation
In a multihop 6LoWPAN, the registration with Crypto-ID is propagated
to 6LBR as described in Section 6.2. If a chain of trust is present
between the 6LR and the 6LBR, then there is no need to propagate the
proof of ownership to the 6LBR. All the 6LBR needs to know is that
this particular OUID is randomly generated, so as to enforce that any
update via a different 6LR is also random.
A new device that joins the network auto-configures an address and
performs an initial registration to an on-link 6LR with an NS message
that carries an Address Registration Option (EARO) [RFC6775]. The
6LR validates the address with the central 6LBR using a DAR/DAC
exchange, and the 6LR confirms (or denies) the address ownership with
an NA message that also carries an Address Registration Option.
Figure 5 illustrates a registration flow all the way to a 6LowPAN
Backbone Router (6BBR).
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6LN 6LR 6LBR 6BBR
| | | |
| NS(EARO) | | |
|--------------->| | |
| | Extended DAR | |
| |-------------->| |
| | | |
| | | proxy NS(EARO) |
| | |--------------->|
| | | | NS(DAD)
| | | | ------>
| | | |
| | | | <wait>
| | | |
| | | proxy NA(EARO) |
| | |<---------------|
| | Extended DAC | |
| |<--------------| |
| NA(EARO) | | |
|<---------------| | |
| | | |
Figure 5: (Re-)Registration Flow
In a multihop 6LoWPAN, a 6LBR sends RAs with prefixes downstream and
the 6LR receives and relays them to the nodes. 6LR and 6LBR
communicate using ICMPv6 Duplicate Address Request (DAR) and
Duplicate Address Confirmation (DAC) messages. The DAR and DAC use
the same message format as NS and NA, but have different ICMPv6 type
values.
In AP-ND we extend DAR/DAC messages to carry cryptographically
generated OUID. In a multihop 6LoWPAN, the node exchanges the
messages shown in Figure 5. The 6LBR must identify who owns an
address (EUI-64) to defend it, if there is an attacker on another
6LR.
Occasionally, a 6LR might miss the node's OUID (that it received in
ARO). 6LR should be able to ask for it again. This is done by
restarting the exchanges shown in Figure 4. The result enables 6LR
to refresh the information that was lost. The 6LR MUST send DAR
message with ARO to 6LBR. The 6LBR replies with a DAC message with
the information copied from the DAR, and the Status field is set to
zero. With this exchange, the 6LBR can (re)validate and store the
information to make sure that the 6LR is not a fake.
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In some cases, the 6LBR may use a DAC message to solicit a Crypto-ID
from a 6LR and also requests 6LR to verify the EUI-64 6LR received
from 6LN. This may happen when a 6LN node is compromised and a fake
node is sending the Crypto-ID as if it is the node's EUI-64. Note
that the detection in this case can only be done by 6LBR not by 6LR.
7. Security Considerations
7.1. Inheriting from RTC 3971
The observations regarding the threats to the local network in
[RFC3971] also apply to this specification. Considering RFC3971
security section subsection by subsection:
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.
Neighbor Unreachability Detection Failure With RFC6775, a NUD can
still be used by the endpoint to assess the liveliness of a
device. The NUD request may be protected by SEND in which case
the provision in section 92.2. of RFC 3972 applies. The response
to the NUD may be proxied by a backbone router only if it has a
fresh registration state for it. The registration being protected
by this specification, the proxied NUD response provides a
truthful information on the original owner of the address but it
cannot be proven using SEND. If the NUD response is not proxied,
the 6LR will pass the lookup to the end device which will respond
with a traditional NA. If the 6LR does not have a cache entry
associated for the device, it can issue a NA with EARO
(status=Validation Requested) upon the NA from the device, which
will trigger a NS that will recreate and revalidate the ND cache
entry.
Duplicate Address Detection DoS Attack Inside the LLN, Duplicate
Addresses are sorted out using the OUID, which differentiates it
from a movement. DAD coming from the backbone are not forwarded
over the LLN so the LLN is protected by the backbone routers.
Over the backbone, the EARO option is present in NS/NA messages.
This protects against misinterpreting a movement for a
duplication, and enables to decide which backbone router has the
freshest registration and thus most possibly the device attached
to it. But this specification does not guarantee that the
backbone router claiming an address over the backbone is not an
attacker.
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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 given by the 6LR in the NA with EARO
(status=Validation Requested) and echoed in the signed NS
guarantees against replay attacks of the NS(EARO). The NA(EARO)
is not protected and can be forged by a rogue node that is not the
6LR in order to force the 6LN to rebuild a NS(EARO) with the proof
of ownership, but that rogue node must have access to the L2 radio
network next to the 6LN to perform the attack.
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 os 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.
7.2. Related to 6LoWPAN ND
The threats discussed in 6LoWPAN ND [RFC6775] and its update
[I-D.ietf-6lo-rfc6775-update] also apply here. Compared with SeND,
this specification saves about 1Kbyte in every NS/NA message. Also,
this specification separates the cryptographic identifier from the
registered IPv6 address so that a node can have more than one IPv6
address protected by the same cryptographic identifier. SeND forces
the IPv6 address to be cryptographic since it integrates the CGA as
the IID in the IPv6 address. This specification frees the device to
form its addresses in any fashion, so as to enable the classical
6LoWPAN compression which derives IPv6 addresses from Layer-2
addresses, as well as privacy addresses. The threats discussed in
Section 9.2 of [RFC3971] are countered by the protocol described in
this document as well.
7.3. OUID Collisions
Collisions of Owner Unique Interface IDentifier (OUID) (which is the
Crypto-ID in this specification) is a possibility that needs to be
considered. The formula for calculating the probability of a
collision is 1 - e^{-k^2/(2n)} where n is the maximum population size
(2^64 here, 1.84E19) and K is the actual population (number of
nodes). If the Crypto-ID is 64-bit long, then the chance of finding
a collision is 0.01% when the network contains 66 million nodes. It
is important to note that the collision is only relevant when this
happens within one stub network (6LBR). A collision of Crypto-ID is
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a rare event. In the case of a collision, an attacker may be able to
claim the registered address of an another legitimate node. However
for this to happen, the attacker would also need to know the address
which was registered by the legitimate node. This registered address
is however never broadcasted on the network and therefore it provides
an additional entropy of 64-bits that an attacker must correctly
guess. To prevent such a scenario, it is RECOMMENDED that nodes
derive the address being registered independently of the OUID.
8. IANA considerations
8.1. CGA Message Type
This document defines a new 128-bit value under the CGA Message Type
[RFC3972] namespace, 0x8701 55c8 0cca dd32 6ab7 e415 f148 84d0.
8.2. Crypto-Type Subregistry
IANA is requested to create a new subregistry "Crypto-Type
Subregistry" in the "Internet Control Message Protocol version 6
(ICMPv6) Parameters". The registry is indexed by an integer 0..255
and contains a Signature Algorithm and a Hash Function as shown in
Table 1. The following Crypto-Type values are defined in this
document:
+--------------+-----------------+---------------+------------------+
| Crypto-Type | Signature | Hash Function | Defining |
| value | Algorithm | | Specification |
+--------------+-----------------+---------------+------------------+
| 0 | NIST P-256 | SHA-256 | RFC THIS |
| | [FIPS186-4] | [RFC6234] | |
| 1 | Ed25519ph | SHA-256 | RFC THIS |
| | [RFC8032] | [RFC6234] | |
+--------------+-----------------+---------------+------------------+
Table 1: Crypto-Types
Assignment of new values for new Crypto-Type MUST be done through
IANA with "Specification Required" and "IESG Approval" as defined in
[RFC8126].
9. Acknowledgments
Many thanks to Charlie Perkins for his in-depth review and
constructive suggestions. We are also especially grateful to Rene
Struik and Robert Moskowitz for their comments that lead to many
improvements to this document, in particular WRT ECC computation and
references.
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10. References
10.1. Normative References
[FIPS-186-4]
FIPS 186-4, "Digital Signature Standard (DSS), Federal
Information Processing Standards Publication 186-4", US
Department of Commerce/National Institute of Standards and
Technology Gaithersburg, MD, July 2013.
[I-D.ietf-6lo-rfc6775-update]
Thubert, P., Nordmark, E., Chakrabarti, S., and C.
Perkins, "An Update to 6LoWPAN ND", draft-ietf-6lo-
rfc6775-update-13 (work in progress), February 2018.
[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>.
[RFC3279] Bassham, L., Polk, W., and R. Housley, "Algorithms and
Identifiers for the Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 3279, DOI 10.17487/RFC3279, April
2002, <https://www.rfc-editor.org/info/rfc3279>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<https://www.rfc-editor.org/info/rfc3972>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<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>.
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[RFC5758] Dang, Q., Santesson, S., Moriarty, K., Brown, D., and T.
Polk, "Internet X.509 Public Key Infrastructure:
Additional Algorithms and Identifiers for DSA and ECDSA",
RFC 5758, DOI 10.17487/RFC5758, January 2010,
<https://www.rfc-editor.org/info/rfc5758>.
[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>.
10.2. Informative references
[FIPS186-4]
"FIPS Publication 186-4: Digital Signature Standard", July
2013, <http://nvlpubs.nist.gov/nistpubs/FIPS/
NIST.FIPS.186-4.pdf>.
[I-D.ietf-6lo-backbone-router]
Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo-
backbone-router-05 (work in progress), January 2018.
[I-D.struik-lwig-curve-representations]
Struik, R., "Alternative Elliptic Curve Representations",
draft-struik-lwig-curve-representations-00 (work in
progress), November 2017.
[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>.
[RFC5889] Baccelli, E., Ed. and M. Townsley, Ed., "IP Addressing
Model in Ad Hoc Networks", RFC 5889, DOI 10.17487/RFC5889,
September 2010, <https://www.rfc-editor.org/info/rfc5889>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/info/rfc6234>.
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[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>.
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <https://www.rfc-editor.org/info/rfc7102>.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<https://www.rfc-editor.org/info/rfc7217>.
[RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
<https://www.rfc-editor.org/info/rfc7696>.
[RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
Considerations for IPv6 Address Generation Mechanisms",
RFC 7721, DOI 10.17487/RFC7721, March 2016,
<https://www.rfc-editor.org/info/rfc7721>.
[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>.
[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>.
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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.
o The protocol MUST be based on the Neighbor Discovery Optimization
for Low-power and Lossy Networks protocol defined in [RFC6775].
RFC6775 utilizes optimizations such as host-initiated interactions
for sleeping resource-constrained hosts and elimination of
multicast address resolution.
o New options to be added to Neighbor Solicitation messages MUST
lead to small packet sizes, especially compared with existing
protocols such as SEcure Neighbor Discovery (SEND). Smaller
packet sizes facilitate low-power transmission by resource-
constrained nodes on lossy links.
o The support for this registration mechanism SHOULD be extensible
to more LLN links than IEEE 802.15.4 only. Support for at least
the LLN links for which a 6lo "IPv6 over foo" specification
exists, as well as Low-Power Wi-Fi SHOULD be possible.
o As part of this extension, a mechanism to compute a unique
Identifier should be provided with the capability to form a Link
Local Address that SHOULD be unique at least within the LLN
connected to a 6LBR.
o The Address Registration Option used in the ND registration SHOULD
be extended to carry the relevant forms of Unique Interface
IDentifier.
o The Neighbour Discovery should specify the formation of a site-
local address that follows the security recommendations from
[RFC7217].
Authors' Addresses
Pascal Thubert (editor)
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
MOUGINS - Sophia Antipolis 06254
FRANCE
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
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Behcet Sarikaya
Plano, TX
USA
Email: sarikaya@ieee.org
Mohit Sethi
Ericsson
Hirsalantie
Jorvas 02420
Email: mohit@piuha.net
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