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Versions: (draft-sarikaya-6lo-ap-nd) 00 01 02 03 04

6lo                                                          B. Sarikaya
Internet-Draft
Updates: 6775 (if approved)                                   P. Thubert
Intended status: Standards Track                                   Cisco
Expires: May 18, 2018                                           M. Sethi
                                                                Ericsson
                                                       November 14, 2017


 Address Protected Neighbor Discovery for Low-power and Lossy Networks
                        draft-ietf-6lo-ap-nd-04

Abstract

   This document defines an extension to 6LoWPAN Neighbor Discovery RFC
   6775.  Nodes supporting this extension compute a cryptographic Owner
   Unique Interface ID and associate it with one or more of their
   Registered Addresses.  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 May 18, 2018.

Copyright Notice

   Copyright (c) 2017 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



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

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



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   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 (EUI-64), 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 to a given 6LR, and
   enforced at the 6LR, in a new Crypto-ID Parameters Option (CIPO).
   The 6LR validates ownership of the cryptographic ID upon the creation
   of a registration state, or a change in the anchor information, such
   as Link-Layer Address and associated Layer-2 cryptographic material.

   The protected address registration protocol proposed in this document
   enables the enforcement of 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
   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



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   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 4.1.
   "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-lwip-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 [FIPS186-4] 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 4.1.  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.

   This specification introduces a new option, the CIPO, that is used to
   prove ownership of the Crypto-ID.  A node that registers for the



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   first time to a 6LR SHOULD place a CIPO option in its registration.
   However, it is not expected to place the option in the periodic
   refresher registrations for that address, or to register 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.

   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.

   Upon receiving a NA(EARO) with a status of "Validation Requested",
   the registering node SHOULD retry its registration with a CIPO option
   that proves its ownership of the Crypto-ID.

   If the 6LR cannot validate the CIPO, it responds with a status of
   "Validation Failed".  After receiving a NA(EARO) with a status of
   "Validation Failed", the registering node MUST NOT use this Crypto-ID
   for registering with that 6LR.

4.  New Fields and Options

4.1.  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].  Public Key is the most important
   parameter in CGA Parameters (sent by 6LN in an NS message).  ECC
   Public Key could be in uncompressed form or in compressed form where
   the first octet of the OCTET STRING is 0x04 and 0x02 or 0x03,
   respectively.  Point compression can further reduce the key size by
   about 32 octets.

   To support cryptographic algorithm agility [RFC7696], Edwards-Curve
   Digital Signature Algorithm (EdDSA) curve Ed25519ph (pre-hashing)
   [RFC8032] can also be used as an alternate to the default NIST P-256
   [FIPS186-4].  This is indicated by 6LN using the Crypto Type field in
   the CIPO option.  The document currently only defines two possible
   values for the Crypto Type field.  A value of 0 indicates that NIST



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   P-256 is used for the signature operation and SHA-256 as the hash
   algorithm.  A value of 1 indicates that Ed25519ph is used for the
   signature operation and SHA-256 as the hash algorithm.  New values
   for the Crypto Type maybe defined in the future for new curves.

   The Crypto-ID is computed as follows:

   1.  the modifier is set to a random or pseudo-random 128-bit value

   2.  the modifier, 9 zero octets and the ECC public key are
       concatenated from left to right.

   3.  the SHA-256 algorithm is applied on the concatenation

   4.  the 112 leftmost bits of the hash value are retained

   5.  the modifier value, the EUI-64 transformation of the device Link
       Layer Address and the encoded public key are concatenated from
       left to right

   6.  Digital signature (NIST P-256 or EdDSA) is executed on the
       concatenation

   7.  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.

4.2.  Updated EARO

   This specification updates the EARO option 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     |    Reserved   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Reserved  |C|T|     TID       |     Registration Lifetime     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +          Owner Unique ID (EUI-64 or equivalent)               +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


              Figure 1: Enhanced Address Registration Option



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   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.

   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.

4.3.  New Crypto-ID Parameters Option

   This specification introduces a new option, the Crypto-ID Parameters
   Option (CIPO), that carries the proof of ownership of a crypto-ID.






















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


                   Figure 2: Crypto-ID Parameters Option

   Type:           CIPO, to be assigned by IANA.

   Length:         The length of the option in units of 8 octets.

   Pad Length:     The length of the Padding field.

   Crypto Type:    The type of cryptographic algorithm used in
                   calculation Crypto-ID.  Default value of all zeros
                   indicate NIST P-256.  A value of 1 is assigned for
                   Ed25519ph.  New values may be defined later.

   Modifier:       128 bit random value.

   Subnet Prefix:  64 bit subnet prefix.




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   Public Key:     ECC public key of 6LN.

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

5.  Protocol Overview

5.1.  Protocol Scope

   The scope of the present work is a 6LoWPAN Low Power Lossy Network
   (LLN), typically a stub network connected to a larger IP network via
   a Border Router called a 6LBR per [RFC6775].

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

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


                       Figure 3: Basic Configuration

   In a mesh network, the 6LR is directly connected to the host device.
   This specification expects that the peer-wise layer-2 security is
   deployed so that all the packets from a particular host are securely
   identifiable by the 6LR.  The 6LR may be multiple hops away from the
   6LBR.  Packets are routed between the 6LR and the 6LBR via other
   6LRs.  This specification expects that a chain of trust is
   established so that a packet that was validated by the first 6LR can
   be safely routed by the next 6LRs to the 6LBR.





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5.2.  Protocol Flows

   Figure 4 illustrates a registration flow all the way to a 6LowPAN
   Backbone Router (6BBR).

   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.

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


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


                     Figure 4: (Re-)Registration Flow

   On-link (local) protocol interactions are shown in Figure 5.  Crypto-
   ID and ARO are passed to and stored by the 6LR on the first NS and




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   not sent again in the next NS.  The operation starts with 6LR sending
   a Router Advertisement (RA) message to 6LN.

   The 6LR/6LBR ensures first-come/first-serve by storing the ARO and
   the Crypto-ID correlated to the node being registered.  The node is
   free to claim any address it likes as long as it is the first to make
   such a claim.  After a successful registration, the node becomes the
   owner of the registered address and the address is bound to the
   Crypto-ID in the 6LR/6LBR registry.  This binding can be verified
   later, which prevents other nodes from stealing the address and
   trying to attract traffic for that address or use it as their source
   address.

   A node may use multiple IPv6 addresses at the same time.  The node
   may use the same Crypto-ID to protect multiple IPv6 addresses.  The
   separation of the address and the Crypto-ID avoids the constrained
   device to compute multiple keys for multiple addresses.  The
   registration process allows the node to bind all of its addresses to
   the same Crypto-ID.

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

                   Figure 5: On-link Protocol Operation





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5.3.  Multihop Operation

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

   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 5.  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.

   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.

6.  Security Considerations

   The observations regarding the threats to the local network in
   [RFC3971] also apply to this specification.

   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



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

   Collisions of 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
   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.

7.  IANA considerations

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

7.1.  Crypto Type Registry

   The following Crypto Type values are defined in this document:

    +-------------------+--------------------------------------------+
    | Crypto Type value | Algorithms                                 |
    +-------------------+--------------------------------------------+
    | 0                 | NIST P-256 [FIPS186-4] , SHA-256 [RFC6234] |
    | 1                 | Ed25519ph [RFC8032], SHA-256 [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].








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8.  Acknowledgements

   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.

9.  References

9.1.  Normative References

   [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-10 (work in progress), October 2017.

   [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>.

   [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>.

   [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>.

9.2.  Informative references

   [FIPS186-4]
              "FIPS Publication 186-4: Digital Signature Standard", July
              2013, <http://nvlpubs.nist.gov/nistpubs/FIPS/
              NIST.FIPS.186-4.pdf>.



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   [I-D.ietf-6lo-backbone-router]
              Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo-
              backbone-router-04 (work in progress), July 2017.

   [I-D.struik-lwip-curve-representations]
              Struik, R., "Alternative Elliptic Curve Representations",
              draft-struik-lwip-curve-representations-00 (work in
              progress), October 2017.

   [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>.

   [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>.

   [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>.




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   [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>.

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



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      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

   Behcet Sarikaya
   Plano, TX
   USA

   Email: sarikaya@ieee.org


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

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


   Mohit Sethi
   Ericsson
   Hirsalantie
   Jorvas  02420

   Email: mohit@piuha.net




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