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6lo                                                      P. Thubert, Ed.
Internet-Draft                                                     Cisco
Updates: 8505 (if approved)                                  B. Sarikaya
Intended status: Standards Track
Expires: 1 November 2020                                        M. Sethi
                                                                Ericsson
                                                               R. Struik
                                             Struik Security Consultancy
                                                           30 April 2020


 Address Protected Neighbor Discovery for Low-power and Lossy Networks
                        draft-ietf-6lo-ap-nd-23

Abstract

   This document updates the 6LoWPAN Neighbor Discovery (ND) protocol
   defined in RFC 6775 and RFC 8505.  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 1 November 2020.






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Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  BCP 14  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Additional References . . . . . . . . . . . . . . . . . .   4
     2.3.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Updating RFC 8505 . . . . . . . . . . . . . . . . . . . . . .   5
   4.  New Fields and Options  . . . . . . . . . . . . . . . . . . .   6
     4.1.  New Crypto-ID . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Updated EARO  . . . . . . . . . . . . . . . . . . . . . .   7
     4.3.  Crypto-ID Parameters Option . . . . . . . . . . . . . . .   8
     4.4.  NDP Signature Option  . . . . . . . . . . . . . . . . . .  10
     4.5.  Extensions to the Capability Indication Option  . . . . .  11
   5.  Protocol Scope  . . . . . . . . . . . . . . . . . . . . . . .  12
   6.  Protocol Flows  . . . . . . . . . . . . . . . . . . . . . . .  13
     6.1.  First Exchange with a 6LR . . . . . . . . . . . . . . . .  14
     6.2.  NDPSO generation and verification . . . . . . . . . . . .  16
     6.3.  Multihop Operation  . . . . . . . . . . . . . . . . . . .  17
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
     7.1.  Brown Field . . . . . . . . . . . . . . . . . . . . . . .  18
     7.2.  Inheriting from RFC 3971  . . . . . . . . . . . . . . . .  18
     7.3.  Related to 6LoWPAN ND . . . . . . . . . . . . . . . . . .  19
     7.4.  Compromised 6LR . . . . . . . . . . . . . . . . . . . . .  20
     7.5.  ROVR Collisions . . . . . . . . . . . . . . . . . . . . .  20
     7.6.  Implementation Attacks  . . . . . . . . . . . . . . . . .  21
     7.7.  Cross-Algorithm and Cross-Protocol Attacks  . . . . . . .  21
     7.8.  Public Key Validation . . . . . . . . . . . . . . . . . .  22
     7.9.  Correlating Registrations . . . . . . . . . . . . . . . .  22
   8.  IANA considerations . . . . . . . . . . . . . . . . . . . . .  22
     8.1.  CGA Message Type  . . . . . . . . . . . . . . . . . . . .  22
     8.2.  Crypto-Type Subregistry . . . . . . . . . . . . . . . . .  23
     8.3.  IPv6 ND option types  . . . . . . . . . . . . . . . . . .  24
     8.4.  New 6LoWPAN Capability Bit  . . . . . . . . . . . . . . .  24



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   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  24
   10. Normative References  . . . . . . . . . . . . . . . . . . . .  24
   11. Informative references  . . . . . . . . . . . . . . . . . . .  26
   Appendix A.  Requirements Addressed in this Document  . . . . . .  28
   Appendix B.  Representation Conventions . . . . . . . . . . . . .  28
     B.1.  Signature Schemes . . . . . . . . . . . . . . . . . . . .  28
     B.2.  Representation of ECDSA Signatures  . . . . . . . . . . .  29
     B.3.  Representation of Public Keys Used with ECDSA . . . . . .  30
     B.4.  Alternative Representations of Curve25519 . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32

1.  Introduction

   Neighbor Discovery Optimizations for 6LoWPAN networks [RFC6775]
   (6LoWPAN ND) adapts the original IPv6 Neighbor Discovery (IPv6 ND)
   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 compared to the Duplicate Address Detection (DAD) mechanism
   defined in IPv6 ND.  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 "Neighbor Discovery Optimization for
   Low-power and Lossy Networks" [RFC6775] (aka 6LoWPAN ND) 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).  The ROVR is defined in
   "Registration Extensions for 6LoWPAN Neighbor Discovery" [RFC8505]
   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 an
   attacker to steal the address and redirect traffic for that address.
   [RFC8505] defines an Extended Address Registration Option (EARO)
   option that transports alternate forms of ROVRs, and is a pre-
   requisite for this specification.






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   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
   provides the same conceptual benefit as Source Address Validation
   (SAVI) [RFC7039] that only the owner of an IPv6 address may source
   packets with that address.  As opposed to [RFC7039], which relies on
   snooping protocols, the protection is based on a state that is
   installed and maintained in the network by the owner of the address.
   With this specification, a 6LN may use a 6LR for forwarding an IPv6
   packets if and only if it has registered the address used as source
   of the packet with that 6LR.

   With the 6lo adaptation layer in [RFC4944] and [RFC6282], a 6LN can
   obtain a better compression for an IPv6 address with an Interface ID
   (IID) that is derived from a Layer-2 address.  As a side note, this
   is incompatible with Secure Neighbor Discovery (SeND) [RFC3971] and
   Cryptographically Generated Addresses (CGAs) [RFC3972], since they
   derive the IID from cryptographic keys, whereas this specification
   separates the IID and the key material.

2.  Terminology

2.1.  BCP 14

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

2.2.  Additional References

   The reader may get additional context for this specification from the
   following references:

   *  "SEcure Neighbor Discovery (SEND)" [RFC3971],
   *  "Cryptographically Generated Addresses (CGA)" [RFC3972],
   *  "Neighbor Discovery for IP version 6" [RFC4861] ,
   *  "IPv6 Stateless Address Autoconfiguration" [RFC4862], and
   *  "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
      Overview, Assumptions, Problem Statement, and Goals " [RFC4919].




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2.3.  Abbreviations

   This document uses the following abbreviations:

   6BBR:  6LoWPAN Backbone Router
   6LBR:  6LoWPAN Border Router
   6LN:  6LoWPAN Node
   6LR:  6LoWPAN Router
   CGA:  Cryptographically Generated Address
   EARO:  Extended Address Registration Option
   ECDH:  Elliptic curve Diffie-Hellman
   ECDSA:  Elliptic Curve Digital Signature Algorithm
   CIPO:  Crypto-ID Parameters Option
   LLN:  Low-Power and Lossy Network
   JSON:  JavaScript Object Notation
   JOSE:  JavaScript Object Signing and Encryption
   JWK:  JSON Web Key
   JWS:  JSON Web Signature
   NA:  Neighbor Advertisement
   ND:  Neighbor Discovery
   NDP:  Neighbor Discovery Protocol
   NDPSO:  Neighbor Discovery Protocol Signature Option
   NS:  Neighbor Solicitation
   ROVR:  Registration Ownership Verifier
   RA:  Router Advertisement
   RS:  Router Solicitation
   RSAO:  RSA Signature Option
   SHA:  Secure Hash Algorithm
   SLAAC:  Stateless Address Autoconfiguration
   TID:  Transaction ID


3.  Updating RFC 8505

   Section 5.3 of [RFC8505] introduces the ROVR that is used to detect
   and reject duplicate registrations in the DAD process.  The ROVR is a
   generic object that is designed for both backward compatibility and
   the capability to introduce new computation methods in the future.
   Using a Crypto-ID per this specification is the RECOMMENDED method.
   Section 7.5 discusses collisions when heterogeneous methods to
   compute the ROVR field coexist inside a same network.

   This specification introduces a new token called a cryptographic
   identifier (Crypto-ID) that is transported in the ROVR field and used
   to prove indirectly the ownership of an address that is being
   registered by means of [RFC8505].  The Crypto-ID is derived from a
   cryptographic public key and additional parameters.




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   The overall mechanism requires the support of Elliptic Curve
   Cryptography (ECC) and of a hash function as detailed in Section 6.2.
   To enable the verification of the proof, the registering node needs
   to supply certain parameters including a nonce and a signature that
   will demonstrate that the node possesses the private-key
   corresponding to the public-key used to build the Crypto-ID.

   The elliptic curves and the hash functions listed in Table 1 in
   Section 8.2 can be used with this specification; more may be added in
   the future to the IANA registry.  The signature scheme that specifies
   which combination is used (including the curve and the representation
   conventions) is signaled by a Crypto-Type in a new IPv6 ND Crypto-ID
   Parameters Option (CIPO, see Section 4.3) that contains the
   parameters that are necessary for the proof, a Nonce option
   ([RFC3971]) and a NDP Signature option (Section 4.4).  The NA(EARO)
   is modified to enable a challenge and transport a Nonce option.

4.  New Fields and Options

4.1.  New Crypto-ID

   The Crypto-ID is transported in the ROVR field of the EARO option and
   the EDAR message, and is associated with the Registered Address at
   the 6LR and the 6LBR.  The ownership of a Crypto-ID can be
   demonstrated by cryptographic mechanisms, and by association, the
   ownership of the Registered Address can be ascertained.

   A node in possession of the necessary cryptographic primitives SHOULD
   use Crypto-ID by default as ROVR in its registrations.  Whether a
   ROVR is a Crypto-ID is indicated by a new "C" flag in the NS(EARO)
   message.

   The Crypto-ID is derived from the public key and a modifier as
   follows:

   1.  The hash function used internally by the signature scheme
       indicated by the Crypto-Type (see also Table 1 in Section 8.2) is
       applied to the CIPO.  Note that all the reserved and padding bits
       MUST be set to zero.
   2.  The leftmost bits of the resulting hash, up to the desired size,
       are used as the Crypto-ID.

   At the time of this writing, a minimal size for the Crypto-ID of 128
   bits is RECOMMENDED unless backward compatibility is needed
   [RFC8505].  This value is bound to augment in the future.






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4.2.  Updated EARO

   This specification updates the EARO option to enable the use of the
   ROVR field to transport the Crypto-ID.  The resulting format is as
   follows:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      |     Length    |    Status     |    Opaque     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Rsvd |C| I |R|T|     TID       |     Registration Lifetime     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
    ...            Registration Ownership Verifier (ROVR)           ...
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


               Figure 1: Enhanced Address Registration Option


   Type:  33

   Length:  Defined in [RFC8505] and copied in associated CIPO.

   Status:  Defined in [RFC8505].

   Opaque:  Defined in [RFC8505].

   Rsvd (Reserved):  3-bit unsigned integer.  It MUST be set 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, R, T:  Defined in [RFC8505].

   TID:  Defined in [RFC8505].

   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 [RFC8505].

   this specification does not define any new Status value.



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4.3.  Crypto-ID Parameters Option

   This specification defines the Crypto-ID Parameters Option (CIPO).
   The CIPO carries the parameters used to form a Crypto-ID.

   In order to provide cryptographic agility [BCP 201], this
   specification supports different elliptic-curve based signature
   schemes, indicated by a Crypto-Type field:

   *  The ECDSA256 signature scheme, which uses ECDSA with the NIST
      P-256 curve [FIPS186-4] and the hash function SHA-256 [RFC6234]
      internally, MUST be supported by all implementations.

   *  The Ed25519 signature scheme, which uses the Pure Edwards-Curve
      Digital Signature Algorithm (PureEdDSA) [RFC8032] with the twisted
      Edwards curve Edwards25519 [RFC7748] and the hash function SHA-512
      [RFC6234] internally, MAY be supported as an alternative.

   *  The ECDSA25519 signature scheme, which uses ECDSA [FIPS186-4] with
      the Weierstrass curve Wei25519 (see Appendix B.4) and the hash
      function SHA-256 [RFC6234] internally, MAY also be supported.

   This specification uses signature schemes that target similar
   cryptographic strength but rely on different curves, hash functions,
   signature algorithms, and/or representation conventions.  Future
   specification may extend this to different cryptographic algorithms
   and key sizes, e.g., to provide better security properties or a
   simpler implementation.

        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     |Reserved1|  Public Key Length  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Crypto-Type  | Modifier      |  EARO Length  |               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +
      |                                                               |
      .                                                               .
      .                  Public Key (variable length)                 .
      .                                                               .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                           Padding                             .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 2: Crypto-ID Parameters Option



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   Type:  8-bit unsigned integer.  to be assigned by IANA, see Table 2.

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

   Reserved1:  5-bit unsigned integer.  It MUST be set to zero by the
      sender and MUST be ignored by the receiver.

   Public Key Length:  11-bit unsigned integer.  The length of the
      Public Key field in bytes.  The actual length depends on the
      Crypto-Type value and on how the public key is represented.  The
      valid values with this document are provided in Table 1.

   Crypto-Type:  8-bit unsigned integer.  The type of cryptographic
      algorithm used in calculation Crypto-ID indexed by IANA in the
      "Crypto-Type Subregistry" in the "Internet Control Message
      Protocol version 6 (ICMPv6) Parameters" (see Section 8.2).

   Modifier:  8-bit unsigned integer.  Set to an arbitrary value by the
      creator of the Crypto-ID.  The role of the modifier is to enable
      the formation of multiple Crypto-IDs from a same key pair, which
      reduces the traceability and thus improves the privacy of a
      constrained node that could not maintain many key-pairs.

   EARO Length:  8-bit unsigned integer.  The option length of the EARO
      that contains the Crypto-ID associated with the CIPO.

   Public Key:  A variable-length field, size indicated in the Public
      Key Length field.

   Padding:  A variable-length field completing the Public Key field to
      align to the next 8-bytes boundary.  It MUST be set to zero by the
      sender and MUST be ignored by the receiver.


   The implementation of multiple hash functions in a constrained device
   may consume excessive amounts of program memory.  This specification
   enables the use of the same hash function SHA-256 [RFC6234] for two
   of the three supported ECC-based signature schemes.  Some code
   factorization is also possible for the ECC computation itself.

   [CURVE-REPR] 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 provide,
   e.g., ECDSA and ECDH using NIST [FIPS186-4] prime curves.  For more
   details on representation conventions, we refer to Appendix B.




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4.4.  NDP Signature Option

   This specification defines the NDP Signature Option (NDPSO).  The
   NDPSO carries the signature that proves the ownership of the Crypto-
   ID.  The format of the NDPSO is illustrated in Figure 3.

   As opposed to the RSA Signature Option (RSAO) defined in section 5.2.
   of SEND [RFC3971], the NDPSO does not have a key hash field.
   Instead, the leftmost 128 bits of the ROVR field in the EARO are used
   as hash to retrieve the CIPO that contains the key material used for
   signature verification, left-padded if needed.

   Another difference is that the NDPSO signs a fixed set of fields as
   opposed to all options that appear prior to it in the ND message that
   bears the signature.  This allows to elide a CIPO that the 6LR
   already received, at the expense of the capability to add arbitrary
   options that would signed with a RSAO.

   An ND message that carries an NDPSO MUST have one and only one EARO.
   The EARO MUST contain a Crypto-ID in the ROVR field, and the Crypto-
   ID MUST be associated with the keypair used for the Digital Signature
   in the NDPSO.

   The CIPO may be present in the same message as the NDPSO.  If it is
   not present, it can be found in an abstract table that was created by
   a previous message and indexed by 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     |Reserved1|  Signature Length   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            Reserved2                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                                                               .
      .          Digital Signature  (variable length)                 .
      .                                                               .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      .                           Padding                             .
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 3: NDP signature Option





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   Type:  to be assigned by IANA, see Table 2.

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

   Reserved1:  5-bit unsigned integer.  It MUST be set to zero by the
      sender and MUST be ignored by the receiver.

   Digital Signature Length:  11-bit unsigned integer.  The length of
      the Digital Signature field in bytes.

   Reserved2:  32-bit unsigned integer.  It MUST be set to zero by the
      sender and MUST be ignored by the receiver.

   Digital Signature:  A variable-length field containing the digital
      signature.  The length and computation of the digital signature
      both depend on the Crypto-Type which is found in the associated
      CIPO, see Appendix B.  For the values of the Crypto-Type defined
      in this specification, and for future values of the Crypto-Type
      unless specified otherwise, the signature is computed as detailed
      in Section 6.2.

   Padding:  A variable-length field completing the Digital Signature
      field to align to the next 8-bytes boundary.  It MUST be set to
      zero by the sender and MUST be ignored by the receiver.


4.5.  Extensions to the Capability Indication Option

   This specification defines one new capability bits in the 6CIO,
   defined by [RFC7400] for use by the 6LR and 6LBR in IPv6 ND RA
   messages.


       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 = 1  |   Reserved      |A|D|L|B|P|E|G|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Reserved                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 4: New Capability Bit in the 6CIO

   New Option Field:

   A:  1-bit flag.  Set to indicate that AP-ND is globally activated in
      the network.



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   The "A" flag is set by the 6LBR that serves the network and
   propagated by the 6LRs.  It is typically turned on when all 6LRs are
   migrated to this specification.

5.  Protocol Scope

   The scope of the protocol specified here is a 6LoWPAN 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
   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       o    o(6LR)
                      ^
       o      o       | LLN link
            o     o   v
                      o(6LN)
              o

                       Figure 5: 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 all the LLN links between the 6LR
   and the 6LBR are protected so that a packet that was validated by the
   first 6LR can be safely routed by other on-path 6LRs to the 6LBR.



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6.  Protocol Flows

   The 6LR/6LBR ensures first-come/first-serve by storing the ROVR
   associated to the address being registered upon the first
   registration and rejecting a registration with a different ROVR
   value.  A 6LN can claim any address as long as it is the first to
   make that claim.  After a successful registration, the 6LN becomes
   the owner of the registered address and the address is bound to the
   ROVR value in the 6LR/6LBR registry.

   This specification protects the ownership of the address at the first
   hop (the edge).  Its use in a network is signaled by the "A" flag in
   the 6CIO.  The flag is set by the 6LBR and propagated unchanged by
   the 6LRs.  The "A" flag enables to migrate a network with the
   protection off and then turn it on globally.

   The 6LN places a cryptographic token, the Crypto-ID, in the ROVR that
   is associated with the address at the first registration, enabling
   the 6LR to later challenge it to verify that it is the original
   Registering Node.  The challenge may happen at any time at the
   discretion of the 6LR and the 6LBR.  A valid registration in the 6LR
   or the 6LBR MUST NOT be altered until the challenge is complete.

   When the "A" flag is on, the 6LR MUST challenge the 6LN when it
   creates a binding with the "C" flag set in the ROVR and when a new
   registration attempts to change a parameter of that binding that
   identifies the 6LN, for instance its Source Link-Layer Address.  The
   verification protects against a rogue that would steal an address and
   attract its traffic, or use it as source address.

   The 6LR MUST also challenge the 6LN if the 6LBR directly signals to
   do so, using an EDAC Message with a "Validation Requested" status.
   The EDAR is echoed by the 6LR in the NA (EARO) back to the
   registering node.  The 6LR SHOULD also challenge all its attached
   6LNs at the time the 6LBR turns the "A" flag on in the 6CIO, to
   detect an issue immediately.

   If the 6LR does not support the Crypto-Type, it MUST reply with an
   EARO Status 10 "Validation Failed" without a challenge.  In that
   case, the 6LN may try another Crypto-Type until it falls back to
   Crypto-Type 0 that MUST be supported by all 6LRs.

   A node may use more than one IPv6 address at the same time.  The
   separation of the address and the cryptographic material avoids the
   need for the constrained device to compute multiple keys for multiple
   addresses.  The 6LN MAY use the same Crypto-ID to prove the ownership
   of multiple IPv6 addresses.  The 6LN MAY also derive multiple Crypto-
   IDs from a same key.



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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 [RFC8505].  The on-link
   (local) protocol interactions are shown in Figure 6.  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 6).

       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 6: On-link Protocol Operation

   The Nonce option contains a nonce value that, to the extent possible
   for the implementation, was never employed in association with the
   key pair used to generate the Crypto-ID.  This specification inherits
   from [RFC3971] that simply indicates that the nonce is a random
   value.  Ideally, an implementation uses an unpredictable
   cryptographically random value [BCP 106].  But that may be
   impractical in some LLN scenarios where the devices do not have a
   guaranteed sense of time and for which computing complex hashes is
   detrimental to the battery lifetime.



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   Alternatively, the device may use an always-incrementing value saved
   in the same stable storage as the key, so they are lost together, and
   starting at a best effort random value, either as the nonce value or
   as a component to its computation.

   The 6LN replies to the challenge with an NS(EARO) that includes a new
   Nonce option (shown as NonceLN in Figure 6), the CIPO (Section 4.3),
   and the NDPSO containing the signature.  Both Nonces are included in
   the signed material.  This provides a "contributory behavior", so
   that either party that knows it generates a good quality nonce knows
   that the protocol will be secure.

   The 6LR MUST store the information associated to a Crypto-ID on the
   first NS exchange where it appears in a fashion that the CIPO
   parameters can be retrieved from the Crypto-ID alone.

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

   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.  When a 6LR receives a NS(EARO)
   registration with a new Crypto-ID as a ROVR, and unless the
   registration is rejected for another reason, it MUST challenge by
   responding with a NA(EARO) with a status of "Validation Requested".

   Upon receiving a first NA(EARO) with a status of "Validation
   Requested" from a 6LR, the registering node SHOULD retry its
   registration with a Crypto-ID Parameters Option (CIPO) (Section 4.3)
   that contains all the necessary material for building the Crypto-ID,
   the NonceLN that it generated, and the NDP signature (Section 4.4)
   option that proves its ownership of the Crypto-ID and intent of
   registering the Target Address.  In subsequent revalidation with the
   same 6LR, the 6LN MAY try to omit the CIPO to save bandwidth, with
   the expectation that the 6LR saved it.  If the validation fails and
   it gets challenged again, then it SHOULD add the CIPO again.

   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 rebuilt Crypto-ID matches the ROVR, the 6LN also
   verifies the signature contained in the NDPSO option.  If at that
   point the signature in the NDPSO option can be verified, then the
   validation succeeds.  Otherwise the validation fails.

   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 and
   alternate Crypto-Type and if even Crypto-Type 0 fails, it may try to
   register a different address in the NS message.



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6.2.  NDPSO generation and verification

   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 in a fashion that depends on the Crypto-Type
   (see Table 1 in Section 8.2) chosen by the 6LN as follows:

   *  Form the message to be signed, by concatenating the following
      byte-strings in the order listed:

      1.  The 128-bit Message Type tag [RFC3972] (in network byte
          order).  For this specification the tag is given in
          Section 8.1.  (The tag value has been generated by the editor
          of this specification on random.org).
      2.  the CIPO
      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 nonce is at least 6
          bytes long as defined in [RFC3971].
      5.  NonceLN sent from the 6LN (in network byte order).  The nonce
          is at least 6 bytes long as defined in [RFC3971].
      6.  1-byte Option Length of the EARO containing the Crypto-ID.

   *  Apply the signature algorithm specified by the Crypto-Type using
      the private key.

   The 6LR on receiving the NDPSO and CIPO options first checks that the
   EARO Length in the CIPO matches the length of the EARO.  If so it
   regenerates the Crypto-ID based on the CIPO to make sure that the
   leftmost bits up to the size of the ROVR match.

   If and only if the check is successful, it tries to verify the
   signature in the NDPSO option using the following:

   *  Form the message to be verified, by concatenating the following
      byte-strings in the order listed:

      1.  The 128-bit Message Type tag given in Section 8.1 (in network
          byte order)
      2.  the CIPO
      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
          nonce is at least 6 bytes long as defined in [RFC3971].




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      5.  NonceLN received from the 6LN (in network byte order) in the
          NS message.  The nonce is at least 6 bytes long as defined in
          [RFC3971].
      6.  1-byte EARO Length received in the CIPO.

   *  Verify the signature on this message with the public-key in the
      CIPO and the locally computed values using the signature algorithm
      specified by the Crypto-Type.  If the verification succeeds, the
      6LR propagates the information to the 6LBR using a EDAR/EDAC flow.

   *  Due to the first-come/first-serve nature of the registration, if
      the address is not registered to the 6LBR, then flow succeeds and
      both the 6LR and 6LBR add the state information about the Crypto-
      ID and Target Address being registered to their respective
      abstract database.

6.3.  Multihop Operation

   A new 6LN 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) [RFC8505].

   In a multihop 6LoWPAN, the registration with Crypto-ID is propagated
   to 6LBR as shown in Figure 7, which illustrates the registration flow
   all the way to a 6LowPAN Backbone Router (6BBR) [BACKBONE-ROUTER].

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

                      Figure 7: (Re-)Registration Flow



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   The 6LR and the 6LBR communicate using ICMPv6 Extended Duplicate
   Address Request (EDAR) and Extended Duplicate Address Confirmation
   (EDAC) messages [RFC8505] as shown in Figure 7.  This specification
   extends EDAR/EDAC messages to carry cryptographically generated ROVR.

   The assumption is that the 6LR and the 6LBR maintain a security
   association to authenticate and protect the integrity of the EDAR and
   EDAC messages, so there is no need to propagate the proof of
   ownership to the 6LBR.  The 6LBR implicitly trusts that the 6LR
   performs the verification when the 6LBR requires it, and if there is
   no further exchange from the 6LR to remove the state, that the
   verification succeeded.

7.  Security Considerations

7.1.  Brown Field

   Only 6LRs that are upgraded to this specification are capable to
   challenge a registration and repel an attack.  In a brown (mixed)
   network, an attacker may attach to a legacy 6LR and fool the 6LBR.
   So even if the "A" flag could be set at any time to test the protocol
   operation, the security will only be effective when all the 6LRs are
   upgraded.

7.2.  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.  A different ROVR for the same Registered address
      entails a rejection of the second registration [RFC8505].  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 [RFC8505] and is thus the best candidate to validate
      the registration for the device attached to it [BACKBONE-ROUTER].
      But this specification does not guarantee that the backbone router
      claiming an address over the backbone is not an attacker.



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   Router Solicitation and Advertisement Attacks:  This specification
      does not change the protection of RS and RA which can still be
      protected by SEND.

   Replay Attacks  A nonce should never repeat for a single key, but
      nonces do not need to be unpredictable for secure operation.
      Using nonces (NonceLR and NonceLN) generated by both the 6LR and
      6LN ensure a contributory behavior that provides an efficient
      protection against replay attacks of the challenge/response flow.
      The quality of the protection by a random nonce depends on the
      random number generator and its parameters (e.g., sense of time).

   Neighbor Discovery DoS Attack:  A rogue node that managed to access
      the L2 network may form many addresses and register them using AP-
      ND.  The perimeter of the attack is all the 6LRs in range of the
      attacker.  The 6LR MUST protect itself against overflows and
      reject excessive registration with a status 2 "Neighbor Cache
      Full".  This effectively blocks another (honest) 6LN from
      registering to the same 6LR, but the 6LN may register to other
      6LRs that are in its range but not in that of the rogue.

7.3.  Related to 6LoWPAN ND

   The threats and mediations discussed in 6LoWPAN ND [RFC6775][RFC8505]
   also apply here, in particular denial-of-service attacks against the
   registry at the 6LR or 6LBR.

   Secure ND [RFC3971] forces the IPv6 address to be cryptographic since
   it integrates the CGA as the IID in the IPv6 address.  In contrast,
   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.

   With this specification the 6LN can freely form its IPv6 address(es)
   in any fashion, thereby enabling either 6LoWPAN compression for IPv6
   addresses that are derived from Layer-2 addresses, or temporary
   addresses, e.g., formed pseudo-randomly and released in relatively
   short cycles for privacy reasons [RFC8064][RFC8065], that cannot be
   compressed.

   This specification provides added protection for addresses that are
   obtained following due procedure [RFC8505] but does not constrain the
   way the addresses are formed or the number of addresses that are used
   in parallel by a same entity.  A rogue may still perform denial-of-
   service attack against the registry at the 6LR or 6LBR, or attempt to
   deplete the pool of available addresses at Layer-2 or Layer-3.




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7.4.  Compromised 6LR

   This specification distributes the challenge and its validation at
   the edge of the network, between the 6LN and its 6LR.  This protects
   against DOS attacks targeted at that central 6LBR.  This also saves
   back and forth exchanges across a potentially large and constrained
   network.

   The downside is that the 6LBR needs to trust the 6LR for performing
   the checking adequately, and the communication between the 6LR and
   the 6LBR must be protected to avoid tampering with the result of the
   test.

   If a 6LR is compromised, and provided that it knows the ROVR field
   used by the real owner of the address, the 6LR may pretend that the
   owner has moved, is now attached to it and has successfully passed
   the Crpto-ID validation.  The 6LR may then attract and inject traffic
   at will on behalf of that address or let a rogue take ownership of
   the address.

7.5.  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.
   Assuming in the calculations/discussion below that the hash used for
   calculating the Crypto-ID is a well-behaved cryptographic hash and
   thus that random collisions are the only ones possible, the formula
   (birthday paradox) for calculating the probability of a collision is
   1 - e^{-p^2/(2n)} where n is the maximum population size (2^64 here,
   1.84E19) and p is the actual population (number of nodes, assuming
   one Crypto-ID per node).

   If the Crypto-ID is 64-bits (the least possible size allowed), the
   chance of a collision is 0.01% for network of 66 million nodes.
   Moreover, the collision is only relevant when this happens within one
   stub network (6LBR).  In the case of such a collision, a third party
   node would be able to claim the registered address of an another
   legitimate node, provided that it wishes to use the same address.  To
   prevent address disclosure and avoid the chances of collision on both
   the ROVR and the address, it is RECOMMENDED that nodes do not derive
   the address being registered from the ROVR.










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7.6.  Implementation Attacks

   The signature schemes referenced in this specification comply with
   NIST [FIPS186-4] or Crypto Forum Research Group (CFRG) standards
   [RFC8032] and offer strong algorithmic security at roughly 128-bit
   security level.  These signature schemes use elliptic curves that
   were either specifically designed with exception-free and constant-
   time arithmetic in mind [RFC7748] or where one has extensive
   implementation experience of resistance to timing attacks
   [FIPS186-4].

   However, careless implementations of the signing operations could
   nevertheless leak information on private keys.  For example, there
   are micro-architectural side channel attacks that implementors should
   be aware of [breaking-ed25519].  Implementors should be particularly
   aware that a secure implementation of Ed25519 requires a protected
   implementation of the hash function SHA-512, whereas this is not
   required with implementations of the hash function SHA-256 used with
   ECDSA256 and ECDSA25519.

7.7.  Cross-Algorithm and Cross-Protocol Attacks

   The keypair used in this specification can be self-generated and the
   public key does not need to be exchanged, e.g., through certificates,
   with a third party before it is used.

   New keypairs can be formed for new registration as the node desires.
   On the other hand, it is safer to allocate a keypair that is used
   only for the address protection and only for one instantiation of the
   signature scheme (which includes choice of elliptic curve domain
   parameters, used hash function, and applicable representation
   conventions).

   The same private key MUST NOT be reused with more than one
   instantiation of the signature scheme in this specification.  The
   same private key MUST NOT be used for anything other than computing
   NDPSO signatures per this specification.

   ECDSA shall be used strictly as specified in [FIPS186-4].  In
   particular, each signing operation of ECDSA MUST use randomly
   generated ephemeral private keys and MUST NOT reuse these ephemeral
   private keys k accross signing operations.  This precludes the use of
   deterministic ECDSA without a random input for determination of k,
   which is deemed dangerous for the intended applications this document
   aims to serve.






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7.8.  Public Key Validation

   Public keys contained in the CIPO field (which are used for signature
   verification) shall be verified to be correctly formed, by checking
   that this public key is indeed a point of the elliptic curve
   indicated by the Crypto-Type and that this point does have the proper
   order.

   For points used with the signature scheme Ed25519, one MUST check
   that this point is not a point in the small subgroup (see
   Appendix B.1 of [CURVE-REPR]); for points used with the signature
   scheme ECDSA (i.e., both ECDSA256 and ECDSA25519), one MUST check
   that the point has the same order as the base point of the curve in
   question.  This is commonly called full public key validation (again,
   see Appendix B.1 of [CURVE-REPR]).

7.9.  Correlating Registrations

   The ROVR field in the EARO introduced in [RFC8505] extends the EUI-64
   field of the ARO defined in [RFC6775].  One of the drawbacks of using
   an EUI-64 as ROVR is that an attacker that is aware of the
   registrations can correlate traffic for a same 6LN across multiple
   addresses.  Section 3 of [RFC8505] indicates that the ROVR and the
   address being registered are decoupled.  A 6LN may use a same ROVR
   for multiple registrations or a different ROVR per registration, and
   the IID must not derive from the ROVR.  In theory different 6LNs
   could use a same ROVR as long as they do not attempt to register the
   same address.

   The Modifier used in the computation of the Crypto-ID enables a 6LN
   to build different Crypto-IDs for different addresses with a same
   keypair.  Using that facility improves the privacy of the 6LN as the
   expense of storage in the 6LR, which will need to store multiple
   CIPOs that contain the same public key.  Note that if the attacker is
   the 6LR, then the Modifier alone does not provide a protection, and
   the 6LN would need to use different keys and MAC addresses in an
   attempt to obfuscate its multiple ownership.

8.  IANA considerations

8.1.  CGA Message Type

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






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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 in the
   interval 0..255 and contains an Elliptic Curve, a Hash Function, a
   Signature Algorithm, Representation Conventions, Public key size, and
   Signature size, as shown in Table 1, which together specify a
   signature scheme (and which are fully specified in Appendix B).

   The following Crypto-Type values are defined in this document:

   +----------------+-----------------+--------------+-----------------+
   | Crypto-Type    |   0 (ECDSA256)  | 1 (Ed25519)  |  2 (ECDSA25519) |
   | value          |                 |              |                 |
   +================+=================+==============+=================+
   | Elliptic curve |    NIST P-256   |  Curve25519  |    Curve25519   |
   |                |   [FIPS186-4]   |  [RFC7748]   |    [RFC7748]    |
   +----------------+-----------------+--------------+-----------------+
   | Hash function  |SHA-256 [RFC6234]|   SHA-512    |SHA-256 [RFC6234]|
   |                |                 |  [RFC6234]   |                 |
   +----------------+-----------------+--------------+-----------------+
   | Signature      |ECDSA [FIPS186-4]|   Ed25519    |ECDSA [FIPS186-4]|
   | algorithm      |                 |  [RFC8032]   |                 |
   +----------------+-----------------+--------------+-----------------+
   | Representation |   Weierstrass,  |   Edwards,   |   Weierstrass,  |
   | conventions    | (un)compressed, | compressed,  | (un)compressed, |
   |                |  MSB/msb first, |LSB/lsb first,|  MSB/msb first, |
   |                |    [RFC7518]    |  [RFC8037]   |   [CURVE-REPR]  |
   +----------------+-----------------+--------------+-----------------+
   |Public key size |   33/65 bytes   |   32 bytes   |   33/65 bytes   |
   |                |   (compressed/  | (compressed) |   (compressed/  |
   |                |  uncompressed)  |              |  uncompressed)  |
   +----------------+-----------------+--------------+-----------------+
   | Signature size |     64 bytes    |   64 bytes   |     64 bytes    |
   +----------------+-----------------+--------------+-----------------+
   | Defining       |     This_RFC    |   This_RFC   |     This_RFC    |
   | specification  |                 |              |                 |
   +----------------+-----------------+--------------+-----------------+

                           Table 1: Crypto-Types

   New Crypto-Type values providing similar or better security may be
   defined in the future.

   Assignment of new values for new Crypto-Type MUST be done through
   IANA with either "Specification Required" or "IESG Approval" as
   defined in BCP 26 [RFC8126].



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8.3.  IPv6 ND option types

   This document registers two new ND option types under the subregistry
   "IPv6 Neighbor Discovery Option Formats":

    +------------------------------+-----------------+---------------+
    |         Option Name          | Suggested Value | Reference     |
    +==============================+=================+===============+
    | NDP Signature Option (NDPSO) |        38       | This document |
    +------------------------------+-----------------+---------------+
    | Crypto-ID Parameters Option  |        39       | This document |
    |            (CIPO)            |                 |               |
    +------------------------------+-----------------+---------------+

                         Table 2: New ND options

8.4.  New 6LoWPAN Capability Bit

   IANA is requested to make additions to the Subregistry for "6LoWPAN
   Capability Bits" created for [RFC7400] as follows:

           +----------------+-----------------------+----------+
           | Capability Bit | Description           | Document |
           +================+=======================+==========+
           |       09       | AP-ND Enabled (1 bit) | This_RFC |
           +----------------+-----------------------+----------+

                    Table 3: New 6LoWPAN Capability Bit

9.  Acknowledgments

   Many thanks to Charlie Perkins for his in-depth review and
   constructive suggestions.  The authors are also especially grateful
   to Robert Moskowitz and Benjamin Kaduk for their comments and
   discussions that led to many improvements.  The authors wish to also
   thank Shwetha Bhandari for actively shepherding this document and
   Roman Danyliw, Alissa Cooper, Mirja Kuhlewind, Eric Vyncke, Vijay
   Gurbani, Al Morton, and Adam Montville for their constructive reviews
   during the IESG process.  Finally Many thanks to our INT area ADs,
   Suresh Krishnan and then Erik Kline, who supported us along the whole
   process.

10.  Normative References

   [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>.



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   [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>.

   [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>.

   [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>.

   [RFC7400]  Bormann, C., "6LoWPAN-GHC: Generic Header Compression for
              IPv6 over Low-Power Wireless Personal Area Networks
              (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November
              2014, <https://www.rfc-editor.org/info/rfc7400>.

   [RFC7748]  Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
              for Security", RFC 7748, DOI 10.17487/RFC7748, January
              2016, <https://www.rfc-editor.org/info/rfc7748>.

   [RFC8032]  Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
              Signature Algorithm (EdDSA)", RFC 8032,
              DOI 10.17487/RFC8032, January 2017,
              <https://www.rfc-editor.org/info/rfc8032>.

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

   [RFC8505]  Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C.
              Perkins, "Registration Extensions for IPv6 over Low-Power
              Wireless Personal Area Network (6LoWPAN) Neighbor
              Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018,
              <https://www.rfc-editor.org/info/rfc8505>.

   [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 , July 2013.

   [SEC1]     SEC1, "SEC 1: Elliptic Curve Cryptography, Version 2.0",
              Standards for Efficient Cryptography , June 2009.



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11.  Informative references

   [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
              RFC 3972, DOI 10.17487/RFC3972, March 2005,
              <https://www.rfc-editor.org/info/rfc3972>.

   [BCP 106]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              DOI 10.17487/RFC4086, June 2005,
              <https://www.rfc-editor.org/info/rfc4086>.

   [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>.

   [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>.

   [RFC6282]  Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
              Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
              DOI 10.17487/RFC6282, September 2011,
              <https://www.rfc-editor.org/info/rfc6282>.

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

   [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>.




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   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <https://www.rfc-editor.org/info/rfc7518>.

   [BCP 201]  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>.

   [RFC8037]  Liusvaara, I., "CFRG Elliptic Curve Diffie-Hellman (ECDH)
              and Signatures in JSON Object Signing and Encryption
              (JOSE)", RFC 8037, DOI 10.17487/RFC8037, January 2017,
              <https://www.rfc-editor.org/info/rfc8037>.

   [RFC8064]  Gont, F., Cooper, A., Thaler, D., and W. Liu,
              "Recommendation on Stable IPv6 Interface Identifiers",
              RFC 8064, DOI 10.17487/RFC8064, February 2017,
              <https://www.rfc-editor.org/info/rfc8064>.

   [RFC8065]  Thaler, D., "Privacy Considerations for IPv6 Adaptation-
              Layer Mechanisms", RFC 8065, DOI 10.17487/RFC8065,
              February 2017, <https://www.rfc-editor.org/info/rfc8065>.

   [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>.

   [BACKBONE-ROUTER]
              Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6
              Backbone Router", Work in Progress, Internet-Draft, draft-
              ietf-6lo-backbone-router-20, 23 March 2020,
              <https://tools.ietf.org/html/draft-ietf-6lo-backbone-
              router-20>.

   [CURVE-REPR]
              Struik, R., "Alternative Elliptic Curve Representations",
              Work in Progress, Internet-Draft, draft-ietf-lwig-curve-
              representations-09, 9 March 2020,
              <https://tools.ietf.org/html/draft-ietf-lwig-curve-
              representations-09>.

   [breaking-ed25519]
              Samwel, N., Batina, L., Bertoni, G., Daemen, J., and R.
              Susella, "Breaking Ed25519 in WolfSSL", Cryptographers'
              Track at the RSA Conference , 2018,
              <https://link.springer.com/
              chapter/10.1007/978-3-319-76953-0_1>.



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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.

   *  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.
   *  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.
   *  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.
   *  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.
   *  The Address Registration Option used in the ND registration SHOULD
      be extended to carry the relevant forms of Unique Interface
      Identifier.
   *  The Neighbor Discovery should specify the formation of a site-
      local address that follows the security recommendations from
      [RFC7217].


Appendix B.  Representation Conventions

B.1.  Signature Schemes

   The signature scheme ECDSA256 corresponding to Crypto-Type 0 is
   ECDSA, as specified in [FIPS186-4], instantiated with the NIST prime
   curve P-256, as specified in Appendix B of [FIPS186-4], and the hash
   function SHA-256, as specified in [RFC6234], where points of this
   NIST curve are represented as points of a short-Weierstrass curve
   (see [FIPS186-4]) and are encoded as octet strings in most-
   significant-bit first (msb) and most-significant-byte first (MSB)
   order.  The signature itself consists of two integers (r and s),
   which are each encoded as fixed-size octet strings in most-
   significant-bit first and most-significant-byte first order.  For
   details on ECDSA, see [FIPS186-4]; for details on the encoding of
   public keys, see Appendix B.3; for details on the signature encoding,
   see Appendix B.2.



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   The signature scheme Ed25519 corresponding to Crypto-Type 1 is EdDSA,
   as specified in [RFC8032], instantiated with the Montgomery curve
   Curve25519, as specified in [RFC7748], and the hash function SHA-512,
   as specified in [RFC6234], where points of this Montgomery curve are
   represented as points of the corresponding twisted Edwards curve
   Edwards25519 (see Appendix B.4) and are encoded as octet strings in
   least-significant-bit first (lsb) and least-significant-byte first
   (LSB) order.  The signature itself consists of a bit string that
   encodes a point of this twisted Edwards curve, in compressed format,
   and an integer encoded in least-significant-bit first and least-
   significant-byte first order.  For details on EdDSA, the encoding of
   public keys and that of signatures, see the specification of pure
   Ed25519 in [RFC8032].

   The signature scheme ECDSA25519 corresponding to Crypto-Type 2 is
   ECDSA, as specified in [FIPS186-4], instantiated with the Montgomery
   curve Curve25519, as specified in [RFC7748], and the hash function
   SHA-256, as specified in [RFC6234], where points of this Montgomery
   curve are represented as points of the corresponding short-
   Weierstrass curve Wei25519 (see Appendix B.4) and are encoded as
   octet strings in most-significant-bit first and most-significant-byte
   first order.  The signature itself consists of a bit string that
   encodes two integers, each encoded as fixed-size octet strings in
   most-significant-bit first and most-significant-byte first order.
   For details on ECDSA, see [FIPS186-4]; for details on the encoding of
   public keys, see Appendix B.3; for details on the signature encoding,
   see Appendix B.2

B.2.  Representation of ECDSA Signatures

   With ECDSA, each signature is an ordered pair (r, s) of integers
   [FIPS186-4], where each integer is represented as a 32-octet string
   according to the Field Element to Octet String conversion rules in
   [SEC1] and where the ordered pair of integers is represented as the
   rightconcatenation of these representation values (thereby resulting
   in a 64-octet string).  The inverse operation checks that the
   signature is a 64-octet string and represents the left-side and
   right-side halves of this string (each a 32-octet string) as the
   integers r and s, respectively, using the Octet String to Field
   Element conversion rules in [SEC1].











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B.3.  Representation of Public Keys Used with ECDSA

   ECDSA is specified to be used with elliptic curves in short-
   Weierstrass form.  Each point of such a curve is represented as an
   octet string using the Elliptic Curve Point to Octet String
   conversion rules in [SEC1], where point compression may be enabled
   (which is indicated by the leftmost octet of this representation).
   The inverse operation converts an octet string to a point of this
   curve using the Octet String to Elliptic Curve Point conversion rules
   in [SEC1], whereby the point is rejected if this is the so-called
   point at infinity.  (This is the case if the input to this inverse
   operation is an octet string of length 1.)

B.4.  Alternative Representations of Curve25519

   The elliptic curve Curve25519, as specified in [RFC7748], is a so-
   called Montgomery curve.  Each point of this curve can also be
   represented as a point of a twisted Edwards curve or as a point of an
   elliptic curve in short-Weierstrass form, via a coordinate
   transformation (a so-called isomorphic mapping).  The parameters of
   the Montgomery curve and the corresponding isomorphic curves in
   twisted Edwards curve and short-Weierstrass form are as indicated
   below.  Here, the domain parameters of the Montgomery curve
   Curve25519 and of the twisted Edwards curve Edwards25519 are as
   specified in [RFC7748]; the domain parameters of the elliptic curve
   Wei25519 in short-Weierstrass curve comply with Section 6.1.1 of
   [FIPS186-4].  For further details on these curves and on the
   coordinate transformations referenced above, see [CURVE-REPR].

   General parameters (for all curve models):

   p  2^{255}-19
      (=0x7fffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff
      ffffffed)
   h  8
   n
      723700557733226221397318656304299424085711635937990760600195093828
      5454250989
      (=2^{252} + 0x14def9de a2f79cd6 5812631a 5cf5d3ed)


   Montgomery curve-specific parameters (for Curve25519):

   A  486662
   B  1
   Gu  9 (=0x9)





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   Gv
      147816194475895447910205935684099868872646061346164752889648818377
      55586237401
      (=0x20ae19a1 b8a086b4 e01edd2c 7748d14c 923d4d7e 6d7c61b2 29e9c5a2
      7eced3d9)


   Twisted Edwards curve-specific parameters (for Edwards25519):

   a  -1 (-0x01)
   d  -121665/121666
      (=3709570593466943934313808350875456518954211387984321901638878553
      3085940283555)
      (=0x52036cee 2b6ffe73 8cc74079 7779e898 00700a4d 4141d8ab 75eb4dca
      135978a3)
   Gx
      151122213495354007725011514095885315114540126930418572060461132839
      49847762202
      (=0x216936d3 cd6e53fe c0a4e231 fdd6dc5c 692cc760 9525a7b2 c9562d60
      8f25d51a)
   Gy  4/5
      (=4631683569492647816942839400347516314130799386625622561578303360
      3165251855960)
      (=0x66666666 66666666 66666666 66666666 66666666 66666666 66666666
      66666658)


   Weierstrass curve-specific parameters (for Wei25519):

   a
      192986815395526992372618308347813179755449974442734273399095973345
      73241639236
      (=0x2aaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaa98
      4914a144)
   b
      557517466698189089076452890782571408182411037279010123152944008379
      56729358436
      (=0x7b425ed0 97b425ed 097b425e d097b425 ed097b42 5ed097b4 260b5e9c
      7710c864)
   GX
      192986815395526992372618308347813179755449974442734273399095973346
      52188435546
      (=0x2aaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa
      aaad245a)
   GY
      147816194475895447910205935684099868872646061346164752889648818377
      55586237401




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      (=0x20ae19a1 b8a086b4 e01edd2c 7748d14c 923d4d7e 6d7c61b2 29e9c5a2
      7eced3d9)


Authors' Addresses

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

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


   Behcet Sarikaya

   Email: sarikaya@ieee.org


   Mohit Sethi
   Ericsson
   FI-02420 Jorvas
   Finland

   Email: mohit@piuha.net


   Rene Struik
   Struik Security Consultancy

   Email: rstruik.ext@gmail.com

















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