6lo                                                      P. Thubert, Ed.
Internet-Draft                                                     Cisco
Updates: 6775 (if approved)                                  B. Sarikaya
Intended status: Standards Track
Expires: March 7, 2019                                          M. Sethi
                                                       September 3, 2018

 Address Protected Neighbor Discovery for Low-power and Lossy Networks


   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 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
   registration 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 March 7, 2019.

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Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  BCP 14  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  References  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  6LoWPAN sub-glossary  . . . . . . . . . . . . . . . . . .   5
     2.4.  Crypto-ID . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . .   6
   4.  New Fields and Options  . . . . . . . . . . . . . . . . . . .   6
     4.1.  Encoding the Public Key . . . . . . . . . . . . . . . . .   7
     4.2.  New Crypto-ID . . . . . . . . . . . . . . . . . . . . . .   7
     4.3.  Updated EARO  . . . . . . . . . . . . . . . . . . . . . .   7
     4.4.  Crypto-ID Parameters Option . . . . . . . . . . . . . . .   9
     4.5.  Nonce Option  . . . . . . . . . . . . . . . . . . . . . .  10
     4.6.  NDP Signature Option  . . . . . . . . . . . . . . . . . .  10
   5.  Protocol Scope  . . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Protocol Flows  . . . . . . . . . . . . . . . . . . . . . . .  11
     6.1.  First Exchange with a 6LR . . . . . . . . . . . . . . . .  12
     6.2.  Multihop Operation  . . . . . . . . . . . . . . . . . . .  13
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
     7.1.  Inheriting from RFC 3971  . . . . . . . . . . . . . . . .  15
     7.2.  Related to 6LoWPAN ND . . . . . . . . . . . . . . . . . .  16
     7.3.  ROVR 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 IPv6 ND (NDv6) 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 reduces the use of multicast
   messages that are present in the NDv6 protocol.  6LoWPAN ND defines a
   new Address Registration Option (ARO) that is carried in the unicast
   Neighbor Solicitation (NS) and Neighbor Advertisement (NA) messages
   exchanged between a 6LoWPAN Node (6LN) and a 6LoWPAN Router (6LR).
   It also defines the Duplicate Address Request (DAR) and Duplicate
   Address Confirmation (DAC) messages between the 6LR and the 6LoWPAN
   Border Router (6LBR).  In LLN networks, the 6LBR is the central
   repository of all the registered addresses in its domain.

   The registration mechanism in 6LoWPAN ND [RFC6775] prevents the use
   of an address if that address is already registered in the subnet
   (first come first serve).  In order to validate address ownership,
   the registration mechanism enables the 6LR and 6LBR to validate the
   association between a registered address and a Registration Ownership
   Verifier (ROVR).  6LoWPAN ND specifies that the ROVR 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-ROVR mapping could effectively fake the ROVR,
   steal the address and redirect traffic for that address towards a
   different 6LN.  The "Registration Extensions for 6LoWPAN Neighbor
   Discovery" [I-D.ietf-6lo-rfc6775-update] defines an Extended ARO
   (EARO) option that allows to transport alternate forms of ROVRs, and
   is a prerequisite for this specification.

   According to this specification, a 6LN generates a cryptographic ID
   (Crypto-ID) and places it in the ROVR 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, or a change the
   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 Source Address Validation (SAVI) [RFC7039], which ensures
   that only the 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 the source address of the packet is registered
   to forward the packet.  The 6LR maintains state information for the

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   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]) specifies
   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 key 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, Multiple
   addresses with a single ROVR, which only needs to be sent once to a
   given 6LR for multiple addresses and registration updates.

2.  Terminology

2.1.  BCP 14

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.2.  References

   In this document, readers will encounter terms and concepts that are
   discussed in the following documents:

   o  "SEcure Neighbor Discovery (SEND)" [RFC3971],

   o  "Cryptographically Generated Addresses (CGA)" [RFC3972],

   o  "Neighbor Discovery for IP version 6" [RFC4861],

   o  "IPv6 Stateless Address Autoconfiguration" [RFC4862],

   o  "Problem Statement and Requirements for IPv6 over Low-Power
      Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606],

   o  "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
      Overview, Assumptions, Problem Statement, and Goals" [RFC4919],

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   o  "Neighbor Discovery Optimization for Low-power and Lossy Networks"

   o  "Terms Used in Routing for Low-Power and Lossy Networks (LLNs)"

   o  "Terminology for Constrained-Node Networks" [RFC7228], and

   o  "Registration Extensions for 6LoWPAN Neighbor Discovery"

2.3.  6LoWPAN sub-glossary

   This document often uses the following acronyms:

   6BBR: 6LoWPAN Backbone Router (proxy for the registration)

   6LBR: 6LoWPAN Border Router

   6LN:  6LoWPAN Node

   6LR:  6LoWPAN Router (relay to the registration process)

   CIPO: Crypto-ID Parameters Option

   (E)ARO:  (Extended) Address Registration Option

   DAD:  Duplicate Address Detection

   LLN:  Low-Power and Lossy Network (a typical IoT network)

   NA:   Neighbor Advertisement

   ND:   Neighbor Discovery

   NDP:  Neighbor Discovery Protocol

   NDPSO:  NDP Signature Option

   NS:   Neighbor Solicitation

   ROVR: Registration Ownership Verifier (pronounced rover)

   RA:   Router Advertisement

   RS:   Router Solicitation

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   RSAO: RSA Signature Option

   TID:  Transaction ID (a sequence counter in the EARO)

2.4.  Crypto-ID

   This document defines a new Crypto-ID as an identifier of variable
   size which is 64 to 256 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
   existing implementations that already implement, e.g., ECDSA and ECDH
   using NIST [FIPS-186-4] prime curves.

3.  Updating RFC 6775

   This specification defines a cryptographic identifier (Crypto-ID)
   that can be used as a replacement to the MAC address in the ROVR
   field of the EARO option; the computation of the Crypto-ID is
   detailed in Section 4.2.  A node in possession of the necessary
   cryptographic material SHOULD use Crypto-ID by default as ROVR in its
   registration.  Whether a ROVR is a Crypto-ID is indicated by a new
   "C" flag in the NS(EARO) message.

   In order to prove its ownership of a Crypto-ID, the registering node
   needs to supply certain parameters including a nonce and a signature
   that will prove that the node has the private key corresponding to
   the public key used to build the Crypto-ID.  This specification adds
   the capability to carry new options in the NS(EARO) and the NA(EARO).
   The NS(EARO) carries a variation of the CGA Option (Section 4.4), a
   Nonce option and a variation of the RSA Signature option
   (Section 4.6) in the NS(EARO).  The NA(EARO) carries a Nonce option.

4.  New Fields and Options

   In order to avoid the need for new ND option types, this
   specification reuses / extends options defined in SEND [RFC3971] and
   6LoWPAN ND [RFC6775] [I-D.ietf-6lo-rfc6775-update].  This applies in
   particular to the CGA option and the RSA Signature Option.  This
   specification provides aliases for the specific variations of those
   options as used in AP-ND.  The presence of the EARO option in the NS/

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   NA messages indicates that the crypto options are to be processed as
   specified in this document, not as a SEND message.

4.1.  Encoding the Public Key

   A 6LN provides its public key in an NS message.  The public key could
   be in uncompressed form or in compressed form where the first octet
   of the OCTET STRING is 0x04 and 0x02 or 0x03, respectively.  Point
   compression can further reduce the key size by about 32 octets.

4.2.  New Crypto-ID

   Each 6LN using a Crypto-ID for registration MUST have a public/
   private key pair.

   The Crypto-ID is computed as follows:

   1.  An 8-bit modifier is selected, enabling a device to form multiple
       Crypto-IDs with a single key pair.  This is 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.  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].

   4.  the leftmost bits of the resulting hash are used as the Crypto-
       ID, up to the size of the ROVR 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     |    Opaque     |
     |Rsvd |C| I |R|T|     TID       |     Registration Lifetime     |
     |                                                               |
    ...            Registration Ownership Verifier (ROVR)           ...
     |                                                               |

              Figure 1: Enhanced Address Registration Option

   Type:           33

   Length:         8-bit unsigned integer.  The length of the option
                   (including the type and length fields) in units of 8

   Status:         8-bit unsigned integer.  Indicates the status of a
                   registration in the NA response.  MUST be set to 0 in
                   NS messages.

   Opaque:         Defined in [I-D.ietf-6lo-rfc6775-update].

   Rsvd (Reserved):  This field is unused.  It MUST be initialized to
                   zero by the sender and MUST be ignored by the

   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

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

   R:              Defined in [I-D.ietf-6lo-rfc6775-update].

   T and TID:      Defined in [I-D.ietf-6lo-rfc6775-update].

   Registration Ownership Verifier (ROVR):  When the "C" flag is set,
                   this field contains a Crypto-ID.

   This specification uses Status values "Validation Requested" and
   "Validation Failed", which are defined in 6LoWPAN ND
   [I-D.ietf-6lo-rfc6775-update].  No other new Status values is

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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
   [RFC7696], AP-ND supports two possible signature algorithms,
   indicated by a Crypto-Type field.  Elliptic Curve Cryptography (ECC)
   is used to calculate the Crypto-ID.  NIST P-256 [FIPS186-4] MUST be
   supported by all implementations.  The Edwards-Curve Digital
   Signature Algorithm (EdDSA) curve Ed25519ph (pre-hashing) [RFC8032]
   MAY be supported as an alternate.

       0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      |     Type      |    Length     |  Pad Length   |   Reserved    |
      |  Crypto-Type  | Modifier      |       Reserved                |
      |                                                               |
      |                                                               |
      .                                                               .
      .                  Public Key (variable length)                 .
      .                                                               .
      |                                                               |
      |                                                               |
      |                                                               |
      .                                                               .
      .                           Padding                             .
      .                                                               .
      |                                                               |

                   Figure 2: Crypto-ID Parameters Option

   Type:           11.  This is the same value as the CGA Option, CIPO
                   is a particular case of the CGA option

   Length:         8-bit unsigned integer.  The length of the option in
                   units of 8 octets.

   Modifier:       8-bit unsigned integer.

   Pad Length:     8-bit unsigned integer.  The length of the Padding

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   Crypto-Type:    The type of cryptographic algorithm used in
                   calculation Crypto-ID.  A value of 0 indicates NIST
                   P-256, with SHA-256 as the hash algorithm.  A value
                   of 1 is assigned for Ed25519ph, with SHA-256 as the
                   hash algorithm.

   Public Key:     DER-Encoded Public Key.

   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].  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

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   used in the LLN.  This is in contrast to a traditional network that
   relies on IPv6 address auto-configuration [RFC4862], where there is
   no guarantee of ownership from the network, and each IPv6 Neighbor
   Discovery packet must be individually secured [RFC3971].

               ---+-------- ............
                  |      External Network
               |     | 6LBR
             o    o   o
      o     o   o     o
         o   o LLN   o    o     o
            o   o   o       (6LR)
                    o         (6LN)

                       Figure 3: Basic Configuration

   In a mesh network, the 6LR is directly connected to the host device.
   This specification mandates that the peer-wise layer-2 security is
   deployed so that all the packets from a particular host are securely
   identifiable by the 6LR.  The 6LR may be multiple hops away from the
   6LBR.  Packets are routed between the 6LR and the 6LBR via other
   6LRs.  This specification mandates that a chain of trust is
   established so that a packet that was validated by the first 6LR can
   be safely routed by 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 associated to the node being
   registered.  The node can claim any address as long as it is the
   first to make such a claim.  After a successful registration, the
   node becomes the owner of the registered address and the address is
   bound to the Crypto-ID in the 6LR/6LBR registry.

   This specification enables the 6LR to verify the ownership of the
   binding at any time assuming that the "C" flag is set.  The
   verification prevents other nodes from stealing the address and
   trying to attract traffic for that address or use it as their source

   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 use the same Crypto-ID for all of its

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 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 an NS(EARO) that includes the
   echoed Nonce option, the CIPO Section 4.4, and the NDPSO with the
   signature.  The information associated to a crypto-ID stored by the
   6LR on the first NS exchange where it appears.  The 6LR SHOULD store
   the CIPO parameters associated with the crypto-ID so it can be used
   for more than one address.

       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

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   The steps for the registration to the 6LR are as follows:

   o  Upon the first exchange with a 6LR, a 6LN may be challenged to
      prove ownership of the Crypto-ID.  The proof is not needed again
      in later registrations for that address, or when registering other
      addresses with the same ROVR.  When a 6LR receives a NS(EARO)
      registration with a new Crypto-ID as a ROVR, it SHOULD challenge
      by responding with a NA(EARO) with a status of "Validation
      Requested".  This process of validation MAY be skipped in networks
      where there is no mobility.

   o  The challenge is triggered when the registration for a Source
      Link-Layer Address is not verifiable either at the 6LR or the
      6LBR.  In the latter case, the 6LBR returns a status of
      "Validation Requested" in the DAR/DAC exchange, which is echoed by
      the 6LR in the NA (EARO) back to the registering node.  The
      challenge MUST NOT alter a valid registration in the 6LR or the

   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 Crypto-ID.  The registering node MUST NOT use the
      same Crypto-ID for subsequent registration attempts.

6.2.  Multihop Operation

   In a multihop 6LoWPAN, the registration with Crypto-ID is propagated
   to 6LBR as described in this section.  If the 6LR and the 6LBR
   maintain a security association, then there is no need to propagate
   the proof of ownership to the 6LBR.

   A new device that joins the network auto-configures an address and
   performs an initial registration to a neighboring 6LR with an NS

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   message that carries an Address Registration Option (EARO) [RFC6775].
   The 6LR validates the address with an 6LBR using a DAR/DAC exchange,
   and the 6LR confirms (or denies) the address ownership with an NA
   message that also carries an Address Registration Option.

   Figure 5 illustrates a registration flow all the way to a 6LowPAN
   Backbone Router (6BBR).

        6LN              6LR             6LBR            6BBR
         |                |               |                |
         |   NS(EARO)     |               |                |
         |--------------->|               |                |
         |                | Extended DAR  |                |
         |                |-------------->|                |
         |                |               |                |
         |                |               | proxy NS(EARO) |
         |                |               |--------------->|
         |                |               |                | NS(DAD)
         |                |               |                | ------>
         |                |               |                |
         |                |               |                | <wait>
         |                |               |                |
         |                |               | proxy NA(EARO) |
         |                |               |<---------------|
         |                | Extended DAC  |                |
         |                |<--------------|                |
         |   NA(EARO)     |               |                |
         |<---------------|               |                |
         |                |               |                |

                     Figure 5: (Re-)Registration Flow

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

   In AP-ND we extend DAR/DAC messages to carry cryptographically
   generated ROVR.  In a multihop 6LoWPAN, the node exchanges the
   messages shown in Figure 5.  The 6LBR must identify who owns an
   address (EUI-64) to defend it, if there is an attacker on another

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7.  Security Considerations

7.1.  Inheriting from RFC 3971

   Observations regarding the following threats to the local network in
   [RFC3971] also apply to this specification.

   Neighbor Solicitation/Advertisement Spoofing

      Threats in section 9.2.1 of RFC3971 apply.  AP-ND counters the
      threats on NS(EARO) messages by requiring that the NDP Signature
      and CIPO options be present in these solicitations.

   Neighbor Unreachability Detection Failure

      With RFC6775, a NUD can still be used by the endpoint to assess
      the liveness of a device.  The NUD request may be protected by
      SEND in which case the provision in section 9.2 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.  For a
      registration being protected by this specification, the proxied
      NUD response provides 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 registration 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 registration.

   Duplicate Address Detection DoS Attack

      Inside the LLN, Duplicate Addresses are sorted out using the ROVR,
      which differentiates it from a movement.  DAD coming from the
      backbone are not forwarded over the LLN, which provides some
      protection against DoS attacks inside the resource-constrained
      part of the network.  Over the backbone, the EARO option is
      present in NS/NA messages.  This protects against misinterpreting
      a movement for a duplication, and enables the backbone routers to
      determine which one has the freshest registration and is thus the
      best candidate to validate the registration for the device
      attached to it.  But this specification does not guarantee that
      the backbone router claiming an address over the backbone is not
      an attacker.

   Router Solicitation and Advertisement Attacks

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      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 is all the 6LRs in range of the attacker.  The 6LR must
      protect itself against overflows and reject excessive registration
      with a status 2 "Neighbor Cache Full".  This effectively blocks
      another (honest) 6LN from registering to the same 6LR, but the 6LN
      may register to other 6LRs that are in its range but not in that
      of the rogue.

7.2.  Related to 6LoWPAN ND

   The threats discussed in 6LoWPAN ND [RFC6775] and its update
   [I-D.ietf-6lo-rfc6775-update] also apply here.  Compared with SeND,
   this specification saves about 1Kbyte in every NS/NA message.  Also,
   this specification separates the cryptographic identifier from the
   registered IPv6 address so that a node can have more than one IPv6
   address protected by the same cryptographic identifier.  SeND forces
   the IPv6 address to be cryptographic since it integrates the CGA as
   the IID in the IPv6 address.  This specification frees the device to
   form its addresses in any fashion, thereby enabling not only 6LoWPAN
   compression which derives IPv6 addresses from Layer-2 addresses but
   also privacy addresses.

7.3.  ROVR Collisions

   A collision of Registration Ownership Verifiers (ROVR) (i.e., the
   Crypto-ID in this specification) is possible, but it is a rare event.
   The formula for calculating the probability of a collision is 1 -
   e^{-k^2/(2n)} where n is the maximum population size (2^64 here,
   1.84E19) and K is the actual population (number of nodes).  If the
   Crypto-ID is 64-bits, the chance of a collision is 0.01% when the
   network contains 66 million nodes.  Moreover, the collision is only
   relevant when this happens within one stub network (6LBR).  In the

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   case of such a collision, an attacker may be able to claim the
   registered address of an another legitimate node.  However for this
   to happen, the attacker would also need to know the address which was
   registered by the legitimate node.  This registered address is never
   broadcasted on the network and therefore providing an additional
   64-bits that an attacker must correctly guess.  To prevent address
   disclosure, it is RECOMMENDED that nodes derive the address being
   registered independently of the ROVR.

8.  IANA considerations

8.1.  CGA Message Type

   This document defines a new 128-bit value under the CGA Message Type
   [RFC3972] namespace, 0x8701 55c8 0cca dd32 6ab7 e415 f148 84d0.

8.2.  Crypto-Type Subregistry

   IANA is requested to create a new subregistry "Crypto-Type
   Subregistry" in the "Internet Control Message Protocol version 6
   (ICMPv6) Parameters".  The registry is indexed by an integer 0..255
   and contains a Signature Algorithm and a Hash Function as shown in
   Table 1.  The following Crypto-Type values are defined in this

   | 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

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

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10.  References

10.1.  Normative References

              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.

              Thubert, P., Nordmark, E., Chakrabarti, S., and C.
              Perkins, "Registration Extensions for 6LoWPAN Neighbor
              Discovery", draft-ietf-6lo-rfc6775-update-21 (work in
              progress), June 2018.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
              "SEcure Neighbor Discovery (SEND)", RFC 3971,
              DOI 10.17487/RFC3971, March 2005,

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, DOI 10.17487/RFC3972, March 2005,

   [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,

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,

   [RFC6606]  Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem
              Statement and Requirements for IPv6 over Low-Power
              Wireless Personal Area Network (6LoWPAN) Routing",
              RFC 6606, DOI 10.17487/RFC6606, May 2012,

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   [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,

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

10.2.  Informative references

              "FIPS Publication 186-4: Digital Signature Standard", July
              2013, <http://nvlpubs.nist.gov/nistpubs/FIPS/

              Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo-
              backbone-router-06 (work in progress), February 2018.

              Struik, R., "Alternative Elliptic Curve Representations",
              draft-struik-lwig-curve-representations-02 (work in
              progress), July 2018.

   [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,

   [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,

   [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,

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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,

   [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,

   [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,

   [RFC7696]  Housley, R., "Guidelines for Cryptographic Algorithm
              Agility and Selecting Mandatory-to-Implement Algorithms",
              BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,

   [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,

   [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,

   [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,

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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

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

Authors' Addresses

   Pascal Thubert (editor)
   Cisco Systems, Inc
   Building D
   45 Allee des Ormes - BP1200
   MOUGINS - Sophia Antipolis  06254

   Phone: +33 497 23 26 34
   Email: pthubert@cisco.com

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   Behcet Sarikaya
   Plano, TX

   Email: sarikaya@ieee.org

   Mohit Sethi
   Jorvas  02420

   Email: mohit@piuha.net

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