6lo                                                      P. Thubert, Ed.
Internet-Draft                                                     Cisco
Updates: 6775 (if approved)                                  B. Sarikaya
Intended status: Standards Track
Expires: August 27, 2018                                        M. Sethi
                                                       February 23, 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 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",
   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

   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

   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

   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

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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

       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.  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

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

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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

   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

   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

   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

   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

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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

   | 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, "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,

   [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,

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

   [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,

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

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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,

   [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,

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-05 (work in progress), January 2018.

              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,

   [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,

   [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,

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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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