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Versions: (draft-sarikaya-6lo-ap-nd) 00 01 02 03 04 05 06 07 08

6lo                                                      P. Thubert, Ed.
Internet-Draft                                                     Cisco
Updates: 6775 (if approved)                                  B. Sarikaya
Intended status: Standards Track
Expires: April 21, 2019                                         M. Sethi
                                                                Ericsson
                                                               R. Struik
                                             Struik Security Consultancy
                                                        October 18, 2018


 Address Protected Neighbor Discovery for Low-power and Lossy Networks
                        draft-ietf-6lo-ap-nd-08

Abstract

   This document specifies an extension to 6LoWPAN Neighbor Discovery
   (ND) defined in RFC6775 and updated in [I-D.ietf-6lo-rfc6775-update].
   The new extension is called Address Protected Neighbor Discovery (AP-
   ND) and it protects the owner of an address against address theft and
   impersonation attacks in a low-power and lossy network (LLN).  Nodes
   supporting this extension compute a cryptographic identifier (Crypto-
   ID) and use it with one or more of their Registered Addresses.  The
   Crypto-ID identifies the owner of the Registered Address and can be
   used to provide proof of ownership of the Registered Addresses.  Once
   an address is registered with the Crypto-ID and a proof-of-ownership
   is provided, only the owner of that address can modify the
   registration information, thereby enforcing Source Address
   Validation.

Status of This Memo

   This 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 April 21, 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.  References  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  6LoWPAN sub-glossary  . . . . . . . . . . . . . . . . . .   4
   3.  Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . .   5
   4.  New Fields and Options  . . . . . . . . . . . . . . . . . . .   6
     4.1.  New Crypto-ID . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Updated EARO  . . . . . . . . . . . . . . . . . . . . . .   6
     4.3.  Crypto-ID Parameters Option . . . . . . . . . . . . . . .   8
     4.4.  Nonce Option  . . . . . . . . . . . . . . . . . . . . . .   9
     4.5.  NDP Signature Option  . . . . . . . . . . . . . . . . . .   9
   5.  Protocol Scope  . . . . . . . . . . . . . . . . . . . . . . .   9
   6.  Protocol Flows  . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  First Exchange with a 6LR . . . . . . . . . . . . . . . .  11
     6.2.  NDPSO generation and verficiation . . . . . . . . . . . .  13
     6.3.  Multihop Operation  . . . . . . . . . . . . . . . . . . .  14
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
     7.1.  Inheriting from RFC 3971  . . . . . . . . . . . . . . . .  16
     7.2.  Related to 6LoWPAN ND . . . . . . . . . . . . . . . . . .  17
     7.3.  ROVR Collisions . . . . . . . . . . . . . . . . . . . . .  17
   8.  IANA considerations . . . . . . . . . . . . . . . . . . . . .  17
     8.1.  CGA Message Type  . . . . . . . . . . . . . . . . . . . .  17
     8.2.  Crypto-Type Subregistry . . . . . . . . . . . . . . . . .  17
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  18
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     10.2.  Informative references . . . . . . . . . . . . . . . . .  19
   Appendix A.  Requirements Addressed in this Document  . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22





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1.  Introduction

   Neighbor Discovery Optimizations for 6LoWPAN networks [RFC6775]
   (6LoWPAN ND) adapts the original IPv6 neighbor discovery (NDv6)
   protocols defined in [RFC4861] and [RFC4862] for constrained low-
   power and lossy network (LLN).  In particular, 6LoWPAN ND introduces
   a unicast host address registration mechanism that reduces the use of
   multicast. 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 the registered address of a node, and its
   Registration Ownership Verifier (ROVR).  ROVR is defined in
   [I-D.ietf-6lo-rfc6775-update] and it can be derived from the MAC
   address of the device (using the 64-bit Extended Unique Identifier
   EUI-64 address format specified by IEEE).  However, the EUI-64 can be
   spoofed, and therefore, any node connected to the subnet and aware of
   a registered-address-to-ROVR mapping could effectively fake the ROVR.
   This would allow the an attacker to steal the address and redirect
   traffic for that address.  [I-D.ietf-6lo-rfc6775-update] defines an
   Extended Address Registration Option (EARO) option that allows to
   transport alternate forms of ROVRs, and is a pre-requisite for this
   specification.

   In this specification, a 6LN generates a cryptographic ID (Crypto-ID)
   and places it in the ROVR field during the registration of one (or
   more) of its addresses with the 6LR(s).  Proof of ownership of the
   Crypto-ID is passed with the first registration exchange to a new
   6LR, and enforced at the 6LR.  The 6LR validates ownership of the
   cryptographic ID before it creates any new registration state, or
   changes existing information.

   The protected address registration protocol proposed in this document
   enables Source Address Validation (SAVI) [RFC7039].  This ensures
   that only the actual owner uses a registered address in the IPv6
   source address field.  A 6LN can only use a 6LR for forwarding
   packets only if it has previously registered the address used in the
   source field of the IPv6 packet.




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   The 6lo adaptation layer in [RFC4944] and [RFC6282] requires a device
   to form its IPv6 addresses based on its Layer-2 address to enable a
   better compression.  This is incompatible with Secure Neighbor
   Discovery (SeND) [RFC3971] and Cryptographically Generated Addresses
   (CGAs) [RFC3972], since they derive the Interface ID (IID) in IPv6
   addresses with cryptographic keys.

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].

2.1.  References

   Terms and concepts from the following documents are used in this
   specification:

   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]

   o  Neighbor Discovery Optimization for Low-power and Lossy Networks
      [RFC6775]

   o  Terms Used in Routing for Low-Power and Lossy Networks (LLNs)
      [RFC7102]

   o  Terminology for Constrained-Node Networks [RFC7228]

   o  Registration Extensions for 6LoWPAN Neighbor Discovery"
      [I-D.ietf-6lo-rfc6775-update]

2.2.  6LoWPAN sub-glossary

   This document uses the following acronyms:





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   6BBR: 6LoWPAN Backbone Router (proxy for the
         registration)[I-D.ietf-6lo-backbone-router]

   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

   RSAO: RSA Signature Option

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

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 4.1.  A node in possession of the necessary
   cryptographic primitives 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.





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   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 4.3), a
   Nonce option and a variation of the RSA Signature option
   (Section 4.5) 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 this document.  The presence of the EARO option in
   the NS/NA messages indicates that the options are to be processed as
   specified in this document, and not as defined in SEND [RFC3971].

4.1.  New Crypto-ID

   Each 6LN using this specification for address registration MUST
   support Elliptic Curve Crytpograhy (ECC) and a hash function.  The
   choice of elliptic curves and hash function currently defined in this
   specification are listed in Section 8.2.

   The Crypto-ID is computed by a 6LN as follows:

   1.  Depending on the Crypto-Type (see Section 8.2) used by the node,
       the hash function is applied to the JSON Web Key (JWK) [RFC7517]
       encoding of the public-key of the node.

   2.  The leftmost bits of the resulting hash, up to the size of the
       ROVR field, are used as the Crypto-ID.

4.2.  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
                   bytes.

   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
                   receiver.

   C:              This "C" flag is set to indicate that the ROVR field
                   contains a Crypto-ID and that the 6LN MAY be
                   challenged for ownership as specified in this
                   document.

   I:              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 are
   defined.



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4.3.  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 elliptic curves, indicated by
   a Crypto-Type field.  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
                   field.

   Crypto-Type:    The type of cryptographic algorithm used in
                   calculation Crypto-ID.  A value of 0 indicates NIST



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                   P-256, with SHA-256 as the hash algorithm.  A value
                   of 1 is assigned for Ed25519ph, with SHA-512 as the
                   hash algorithm.

   Public Key:     JWK-Encoded Public Key [RFC7517].

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

4.4.  Nonce Option

   This document reuses the Nonce Option defined in section 5.3.2. of
   SEND [RFC3971] without a change.

4.5.  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 corresponding the public-key passed 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 protocol specified here 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 duplicate address
   detection.

   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 other on-path 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
   address.

   A node may use multiple IPv6 addresses at the same time.  The node
   may use a same Crypto-ID, to prove the ownership of multiple IPv6
   addresses.  The separation of the address and the cryptographic
   material avoids the constrained device to compute multiple keys for



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   multiple addresses.  The registration process allows the node to use
   the same Crypto-ID for all of its addresses.

6.1.  First Exchange with a 6LR

   A 6LN registers to a 6LR that is one hop away from it with the "C"
   flag set in the EARO, indicating that the ROVR field contains a
   Crypto-ID.  The Target Address in the NS message indicates the IPv6
   address that the 6LN is trying to register.  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 (shown as NonceLR in Figure 4).  The
   Nonce option MUST contain a random Nonce value that was never used
   with this device.

   The 6LN replies to the challenge with an NS(EARO) that includes a new
   Nonce option (shown as NonceLN in Figure 4), the CIPO (Section 4.3),
   and the NDPSO containing the signature.  The information associated
   to a Crypto-ID stored by the 6LR on the first NS exchange where it
   appears.  The 6LR MUST store the CIPO parameters associated with the
   Crypto-ID so it can be used for more than one address.





























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       6LN                                                     6LR
        |                                                       |
        |<------------------------- RA -------------------------|
        |                                                       | ^
        |---------------- NS with EARO (Crypto-ID) ------------>| |
        |                                                       | option
        |<- NA with EARO (status=Validation Requested), NonceLR-| |
        |                                                       | v
        |------- NS with EARO, CIPO, NonceLN and NDPSO -------->|
        |                                                       |
        |<------------------- NA with EARO ---------------------|
        |                                                       |
                                  ...
        |                                                       |
        |--------------- NS with EARO (Crypto-ID) ------------->|
        |                                                       |
        |<------------------- NA with EARO ---------------------|
        |                                                       |
                                  ...
        |                                                       |
        |--------------- NS with EARO (Crypto-ID) ------------->|
        |                                                       |
        |<------------------- NA with EARO ---------------------|
        |                                                       |

                   Figure 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 will be challenged to
      prove ownership of the Crypto-ID and the Target Address being
      registered in the Neighbor Solicitation message.  The proof is not
      needed again in later registrations for that address.  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".

   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
      6LBR.

   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 4.3) that contains all the



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      necessary material for building the Crypto-ID, the NonceLN that it
      generated, and the NDP signature (Section 4.5) option that proves
      its ownership of the Crypto-ID and intent of registering the
      Target Address.

   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.  It also verifies the signature contained
      in the NDPSO option.  If the Crypto-ID does not match with the
      public-key in the CIPO option, or if the signature in the NDPSO
      option cannot be verified, the validation 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
      to register an alternate target address in the NS message.

6.2.  NDPSO generation and verficiation

   The signature generated by the 6LN to provide proof-of-ownership of
   the private-key is carried in the NDP Signature Option (NDPSO).  It
   is generated by the 6LN as follows:

   o  Concatenate the following in the order listed:

      1.  128-bit type tag (in network byte order)

      2.  JWK-encoded public key

      3.  the 16-byte Target Address (in network byte order) sent in the
          Neighbor Solicitation (NS) message.  It is the address which
          the 6LN is registering with the 6LR and 6LBR.

      4.  NonceLR received from the 6LR (in network byte order) in the
          Neighbor Advertisement (NA) message.  The random nonce is at
          least 6 bytes long as defined in [RFC3971].

      5.  NonceLN sent from the 6LN (in network byte order).  The random
          nonce is at least 6 bytes long as defined in [RFC3971].

      6.  The length of the ROVR field in the NS message cotainting the
          Crypto-ID that was sent.

      7.  1-byte (in network byte order) Crypto-Type value sent in the
          CIPO option.

   o  Depending on the Crypto-Type (see Section 8.2) chosen by the node
      (6LN), apply the hash function on this concatenation.



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   o  Depending on the Crypto-Type (see Section 8.2) chosen by the node
      (6LN), sign the hash output with ECDSA (if curve P-256 is used) or
      sign the hash with EdDSA (if curve EdDSA25519ph).

   The 6LR on receiving the NDPSO and CIPO options first hashes the JWK
   encoded public-key in the CIPO option to make sure that the leftmost
   bits up to the size of the ROVR match.  Only if the check is
   successful, it tries to verify the signature in the NDPSO option
   using the following.

   o  Concatenate the following in the order listed:

      1.  128-bit type tag (in network byte order)

      2.  JWK-encoded public key received in the CIPO option

      3.  the 16-byte Target Address (in network byte order) received in
          the Neighbor Solicitation (NS) message.  It is the address
          which the 6LN is registering with the 6LR and 6LBR.

      4.  NonceLR sent in the Neighbor Advertisement (NA) message.  The
          random nonce is at least 6 bytes long as defined in [RFC3971].

      5.  NonceLN received from the 6LN (in network byte order) in the
          NS message.  The random nonce is at least 6 bytes long as
          defined in [RFC3971].

      6.  The length of the ROVR field in the NS message containing the
          Crypto-ID that was received.

      7.  1-byte (in network byte order) Crypto-Type value received in
          the CIPO option.

   o  Depending on the Crypto-Type (see Section 8.2) indicated by the
      (6LN) in the CIPO, apply the hash function on this concatenation.

   o  Verify the signature with the public-key received and the locally
      computed values.  If the verification succeeds, the 6LR and 6LBR
      add the state information about the Crypto-ID, public-key and
      Target Address being registered to their database.

6.3.  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.




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

   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
   6LR.



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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.

   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

      This specification does not change the protection of RS and RA
      which can still be protected by SEND.

   Replay Attacks

      Nonces (NonceLR and NonceLN) generated by the 6LR and 6LN
      guarantees against replay attacks of the NS(EARO).

   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.



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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 least possible size allowed), 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 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
   document:



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   +--------------+-----------------+---------------+------------------+
   | Crypto-Type  | Signature       | Hash Function | Defining         |
   | value        | Algorithm       |               | Specification    |
   +--------------+-----------------+---------------+------------------+
   | 0            | NIST P-256      | SHA-256       | RFC THIS         |
   |              | [FIPS186-4]     | [RFC6234]     |                  |
   | 1            | Ed25519ph       | SHA-512       | RFC THIS         |
   |              | [RFC8032]       | [RFC6234]     |                  |
   +--------------+-----------------+---------------+------------------+

                           Table 1: Crypto-Types

   As is evident from the table above, although the two curves provide
   similar security, they however rely on different hash functions.
   Supporting multiple hash functions on constrained devices is not
   ideal.  [I-D.struik-lwig-curve-representations] provides 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.  New Crypto-Type values providing
   similar or better security (with less code) can be defined in future.

   Assignment of new values for new Crypto-Type MUST be done through
   IANA with "Specification Required" and "IESG Approval" as defined in
   [RFC8126].

9.  Acknowledgments

   Many thanks to Charlie Perkins for his in-depth review and
   constructive suggestions.  We are also especially grateful to Robert
   Moskowitz for his comments that lead to many improvements.

10.  References

10.1.  Normative References

   [FIPS186-4]
              FIPS 186-4, "Digital Signature Standard (DSS), Federal
              Information Processing Standards Publication 186-4", US
              Department of Commerce/National Institute of Standards and
              Technology Gaithersburg, MD, July 2013.

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



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   [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>.

   [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>.

   [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>.

   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015,
              <https://www.rfc-editor.org/info/rfc7517>.

10.2.  Informative references

   [I-D.ietf-6lo-backbone-router]
              Thubert, P. and C. Perkins, "IPv6 Backbone Router", draft-
              ietf-6lo-backbone-router-07 (work in progress), September
              2018.

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






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   [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>.

   [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>.

   [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,
              <https://www.rfc-editor.org/info/rfc6606>.

   [RFC7039]  Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed.,
              "Source Address Validation Improvement (SAVI) Framework",
              RFC 7039, DOI 10.17487/RFC7039, October 2013,
              <https://www.rfc-editor.org/info/rfc7039>.

   [RFC7102]  Vasseur, JP., "Terms Used in Routing for Low-Power and
              Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
              2014, <https://www.rfc-editor.org/info/rfc7102>.

   [RFC7217]  Gont, F., "A Method for Generating Semantically Opaque
              Interface Identifiers with IPv6 Stateless Address
              Autoconfiguration (SLAAC)", RFC 7217,
              DOI 10.17487/RFC7217, April 2014,
              <https://www.rfc-editor.org/info/rfc7217>.

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,
              <https://www.rfc-editor.org/info/rfc7228>.





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   [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>.

   [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
      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.






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   o  The Neighbour Discovery should specify the formation of a site-
      local address that follows the security recommendations from
      [RFC7217].

Authors' Addresses

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

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


   Behcet Sarikaya
   Plano, TX
   USA

   Email: sarikaya@ieee.org


   Mohit Sethi
   Ericsson
   Jorvas  02420
   Finland

   Email: mohit@piuha.net


   Rene Struik
   Struik Security Consultancy

   Email: rstruik.ext@gmail.com















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