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<?rfc tocdepth="3"?>
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<?rfc tocappendix="yes"?>
 <!-- updated by KC 05/21/20 -->

<rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std" ipr='trust200902' ipr="trust200902" number="8928" tocInclude="true" obsoletes="" updates="8505" consensus="true" submissionType="IETF" xml:lang="en" version="3" docName="draft-ietf-6lo-ap-nd-23" > symRefs="true" sortRefs="true">

<front>

<title abbrev='Address abbrev="Address Protection ND for LLN'>
    Address Protected LLN">
    Address-Protected Neighbor Discovery for Low-power Low-Power and Lossy Networks
</title>
   <seriesInfo name="RFC" value="8928"/>
    <author initials='P.' surname='Thubert' fullname='Pascal Thubert' role='editor'> initials="P." surname="Thubert" fullname="Pascal Thubert" role="editor">
          <organization abbrev='Cisco'>Cisco abbrev="Cisco">Cisco Systems, Inc</organization> Inc.</organization>
          <address>
             <postal>
                <street>Building D</street>
                <street>45 Allee des Ormes - BP1200 </street>
                <city>MOUGINS - Sophia Antipolis</city>
                <code>06254</code>
                <country>FRANCE</country>
                <country>France</country>
             </postal>
             <phone>+33 497 23 26 34</phone>
             <email>pthubert@cisco.com</email>
          </address>
    </author>
 <author initials='B.' surname='Sarikaya' fullname='Behcet Sarikaya'> initials="B." surname="Sarikaya" fullname="Behcet Sarikaya">
    <organization/>
    <address>
    <postal>
    <street/>
    <street/>
    <city/> <region/> <code/>
       <country/>
    </postal>
    <email>sarikaya@ieee.org</email>
    </address>
    </author>

   <author initials='M.' surname='Sethi' fullname='Mohit Sethi'> initials="M." surname="Sethi" fullname="Mohit Sethi">
    <organization>Ericsson</organization>
    <address>
    <postal>
    <street/>
    <city>Jorvas</city> <region/> <code>02420</code>
    <country>Finland</country>
    </postal>
    <email>mohit@piuha.net</email>
    </address>
    </author>

    <author initials='R.' surname='Struik' fullname='Rene Struik'> initials="R." surname="Struik" fullname="Rene Struik">
    <organization>Struik Security Consultancy</organization>
    <address>
    <postal>
    <street/>
    <city/> <region/> <code/>
    <country/>
    </postal>
    <email>rstruik.ext@gmail.com</email>
    </address>
    </author>

   <date/>
   <date month="October" year="2020" />
   <workgroup>6lo</workgroup>

<!-- [rfced] Please insert any keywords (beyond those that appear in
the title) for use on https://www.rfc-editor.org/search.
-->

   <abstract>
   <t>
	   This document updates the 6LoWPAN IPv6 over Low-Power Wireless
	   Personal Area Network (6LoWPAN) Neighbor Discovery (ND)
	   protocol defined in RFC RFCs 6775 and RFC 8505.  The new extension
	   is called Address Protected Address-Protected Neighbor Discovery (AP-ND) (AP-ND), and
	   it protects the owner of an address against address theft
	   and impersonation attacks in a low-power Low-Power and lossy network Lossy Network
	   (LLN).  Nodes supporting this extension compute a
	   cryptographic identifier (Crypto-ID) (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 proof of ownership is provided, only the owner of
	   that address can modify the registration information,
	   thereby enforcing Source Address Validation.
   </t>
   </abstract>

</front>

<middle>

<section><name>Introduction</name>
    <t>
    	Neighbor Discovery Optimizations optimizations for 6LoWPAN networks <xref target='RFC6775'/> 	(6LoWPAN (aka 6LoWPAN ND) <xref target="RFC6775"/> adapts the original IPv6
    	Neighbor Discovery (IPv6 ND) protocols defined in <xref target='RFC4861'/> target="RFC4861"/> and <xref target='RFC4862'/> target="RFC4862"/> for constrained
    	low-power
    	Low-Power and lossy network (LLN). Lossy Networks (LLNs). 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, LLNs, the 6LBR is the central repository of all the registered addresses in its domain.
    </t>

    <t>
    	The registration mechanism in <xref target='RFC6775'>"Neighbor "Neighbor Discovery Optimization for Low-power and Lossy Networks"</xref> (aka 6LoWPAN ND) IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)" <xref target="RFC6775"></xref> prevents the use of an address if that address
    	is already registered in the subnet (first come come, first serve). served). 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, node and its
    	Registration Ownership Verifier (ROVR).

<!--[rfced] We expanded 'MAC' as 'Medium Access Control (MAC)' per use
in the companion document (draft-ietf-6lo-backbone-router-20).
If that is not correct or you prefer otherwise (perhaps 'Media
Access Control (MAC)'), please let us know.

Original:
   The ROVR is defined in <xref target='RFC8505'>"Registration
   "Registration Extensions for 6LoWPAN Neighbor
        Discovery"</xref> 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).

Updated:
   The ROVR is defined in
   "Registration Extensions for IPv6 over
   Low-Power Wireless Personal Area Network (6LoWPAN) Neighbor Discovery"
   [RFC8505], and it can be derived from the Medium Access Control (MAC)
   address of the device (using the 64-bit Extended Unique Identifier (EUI-64)
   address format specified by IEEE).
-->

 The ROVR is defined in "Registration Extensions for IPv6 over
 Low-Power Wireless Personal Area Network (6LoWPAN) Neighbor Discovery" <xref target="RFC8505"></xref>, and it can be derived from the
    	Medium Access Control (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 spoofed; 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. <xref target='RFC8505'/> target="RFC8505"/> defines an Extended Address Registration
    	Option (EARO) option that transports alternate forms of ROVRs, ROVRs and is a pre-requisite prerequisite for this specification.
    </t>

    <t>
		  In this specification, a 6LN generates a cryptographic ID identifier (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, 6LR and enforced at the 6LR.
                  The 6LR validates ownership of the
		  cryptographic ID
		  Crypto-ID before it creates any new registration state, state or changes existing information.
    </t>

    <t>
		  The protected address registration protocol proposed in this document provides the same conceptual benefit as Source Address Validation Improvement (SAVI) <xref target='RFC7039'/> target="RFC7039"/> in that only the owner of an IPv6 address may source packets with that address.
          As opposed to <xref target='RFC7039'/>, target="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 packet if and only if it has registered the address used as the source of the packet with that 6LR.

          <!--, and a first-hop 6LR that is configured to enforce this rule MUST discard a packet that is not originated from the 6LN that registered

    </t>

    <t>
<!--[rfced] Please confirm the IPv6 source address use of "6lo" here as neither of the packet.
    referenced RFCs use "6lo" by itself.

Original:
  With the 6lo adaptation layer in [RFC4944] and [RFC6282],...
-->
    </t>

    <t>

		  With the 6lo adaptation layer in <xref target='RFC4944'/>
		  target="RFC4944"/> and <xref target='RFC6282'/>, target="RFC6282"/>, a
		  6LN can obtain a better compression for an IPv6
		  address with an Interface ID (IID) that is derived
		  from a Layer-2 Layer 2 (L2) address. As a side note, this is incompatible with Secure "SEcure Neighbor Discovery (SeND) (SEND") <xref target='RFC3971'/> target="RFC3971"/> and Cryptographically "Cryptographically Generated Addresses (CGAs) (CGAs)"
		  <xref target='RFC3972'/>, target="RFC3972"/>, since they derive the IID from cryptographic keys, whereas this specification separates the IID and the key material.
    </t>

</section>

<section><name>Terminology</name>
  <section anchor='bcp'><name>BCP 14</name> anchor="bcp"><name>Requirements Language</name>
        <t>
    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
    "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
    NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
    "<bcp14>MAY</bcp14>", and
    "OPTIONAL" "<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as
    described in BCP 14 BCP&nbsp;14 <xref target='RFC2119'/> target="RFC2119"/> <xref target='RFC8174'/> target="RFC8174"/>
    when, and only when, they appear in all capitals, as shown here.
        </t>
  </section>	<!-- end section "BCP 14" -->

  <section anchor='lo' ><name>Additional anchor="lo"><name>Additional References</name>

    <t>
	The reader may get additional context for this specification from the following references:
	</t><ul spacing='compact'> spacing="normal">

    	<li> <xref target='RFC3971'>"SEcure "SEcure Neighbor Discovery (SEND)"</xref>,</li>
    	<li> (SEND)" <xref target='RFC3972'>"Cryptographically target="RFC3971"></xref>,</li>
    	<li> "Cryptographically Generated Addresses (CGA)"</xref>,</li>
    	<li><xref target='RFC4861'>"Neighbor (CGA)" <xref target="RFC3972"></xref>,</li>
    	<li> "Neighbor Discovery for IP version 6"</xref> 6 (IPv6)" <xref target="RFC4861"></xref> ,</li>
    	<li><xref target='RFC4862'>"IPv6
    	<li> "IPv6 Stateless Address Autoconfiguration"</xref>, Autoconfiguration" <xref target="RFC4862"></xref>, and </li>
    	<li><xref target='RFC4919'>"IPv6
    	<li> "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and Goals "</xref>.</li> Goals" <xref target="RFC4919"></xref>.</li>
	</ul>
  </section>	<!-- Additional References -->

  <section anchor='acronyms'><name>Abbreviations</name> anchor="acronyms"><name>Abbreviations</name>
  <t> This document uses the following abbreviations:
       </t><dl spacing='compact'>
       <dt>6BBR:</dt><dd> 6LoWPAN Backbone Router </dd>
       <dt>6LBR:</dt><dd>

<!--[rfced] We spotted the following abbreviations that are used
    throughout the document but that are not included in the
    "Abbreviations" section.  Should they be added there as well?

DAD
ARO
DAR
DAC
MAC
EUI-64
SAVI
IID
ECC
EDAR
AP-ND
-->

       </t><dl spacing="compact" indent="10">
       <dt>6BBR:</dt><dd> 6LoWPAN Backbone Router </dd>
       <dt>6LBR:</dt><dd> 6LoWPAN Border Router </dd>
       <dt>6LN:</dt><dd> 6LoWPAN Node  </dd>
       <dt>6LR:</dt><dd>6LoWPAN Router </dd>
       <dt>CGA:</dt><dd>Cryptographically Generated Address</dd>
       <dt>EARO:</dt><dd> Extended Address Registration Option</dd>
       <dt>ECDH:</dt><dd> Elliptic curve Diffie–Hellman</dd> Curve Diffie-Hellman</dd>
       <dt>ECDSA:</dt><dd> Elliptic Curve Digital Signature Algorithm</dd>
       <dt>CIPO:</dt><dd>Crypto-ID Parameters Option</dd>
       <dt>LLN:</dt><dd> Low-Power and Lossy Network </dd> Network</dd>
       <dt>JSON:</dt><dd> JavaScript Object Notation</dd>
       <dt>JOSE:</dt><dd> JavaScript Object Signing and Encryption</dd>
       <dt>JWK:</dt><dd> JSON Web Key</dd>
       <dt>JWS:</dt><dd> JSON Web Signature</dd>
       <dt>NA:</dt><dd>  Neighbor Advertisement </dd>
       <dt>ND:</dt><dd>  Neighbor Discovery  </dd>
       <dt>NDP:</dt><dd>  Neighbor Discovery Protocol </dd>
       <dt>NDPSO:</dt><dd> Neighbor Discovery Protocol Signature Option</dd>
       <dt>NS:</dt><dd>  Neighbor Solicitation  </dd>
       <dt>ROVR:</dt><dd> Registration Ownership Verifier </dd>
       <dt>RA:</dt><dd> Router Advertisement  </dd>
       <dt>RS:</dt><dd> Router Solicitation  </dd>
       <dt>RSAO:</dt><dd> RSA Signature Option</dd>
       <dt>SHA:</dt><dd> Secure Hash Algorithm</dd>
       <dt>SLAAC:</dt><dd> Stateless Address Autoconfiguration</dd>
       <dt>TID:</dt><dd> Transaction ID </dd>
       </dl><t>
    </t>
       </dl>

  </section>	<!-- end section "Acronym Definitions" -->
</section>	<!-- end section "Terminology" -->

<section><name>Updating RFC 8505</name>
    <t>
        Section 5.3 of
       <xref target='RFC8505'/> target="RFC8505" sectionFormat="of" section="5.3"/> 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 <bcp14>RECOMMENDED</bcp14> method. <xref target='sec-col'/> target="sec-col"/> discusses collisions when heterogeneous methods to compute the ROVR field coexist inside a same network.
    </t>
    <t>
        This specification introduces a new token called a cryptographic identifier (Crypto-ID) Crypto-ID that is transported in the ROVR field and used to prove indirectly prove the ownership of an address that is being registered by means of <xref target='RFC8505'/>. target="RFC8505"/>. The
        Crypto-ID is derived from a cryptographic public key and additional parameters.
    </t>
    <t>
        The overall mechanism requires the support of Elliptic Curve Cryptography (ECC) and of a hash function as detailed in <xref target='ndpso-generation'/>. target="ndpso-generation"/>. To enable the verification of the proof, the registering node Registering Node needs to supply certain parameters including a nonce and a signature that will demonstrate that the node possesses the private-key private key corresponding to the public-key public key used to build the Crypto-ID.
    </t>

    <t> The elliptic curves and the hash functions listed in <xref target='cryptotypetable'/>
    target="cryptotypetable"/> in <xref target='cryptotypereg'/> target="cryptotypereg"/> can
    be used with this specification; more may be added in the future
    to the corresponding 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 (CIPO) (see <xref target='cryptoidopt'/>) target="cryptoidopt"/>)
        that contains the parameters that are necessary for the proof, a Nonce option (<xref target='RFC3971'/>) Option <xref target="RFC3971"/>, and a an NDP Signature option Option (<xref target='ndpso'/>). target="ndpso"/>).  The NA(EARO) is modified to enable a challenge and transport a Nonce option.
    </t>
        <!--t>
    In order to avoid the need for new ND option types, this specification reuses and extends options defined in SEND <xref target="RFC3971"/> and 6LoWPAN ND <xref target="RFC6775"/> <xref target="RFC8505"/>. This applies 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 <xref target="RFC3971"/>.
    </t-->
    </t>
</section>

<section anchor='cryptoifldg'><name>New anchor="cryptoifldg"><name>New Fields and Options</name>

    <section anchor='cryptoidalg'><name>New anchor="cryptoidalg"><name>New Crypto-ID</name>
    <t>
	The Crypto-ID is transported in the ROVR field of the EARO option and the EDAR message, Extended Duplicate Address Request (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.
    </t><t>
	A node in possession of the necessary cryptographic primitives SHOULD <bcp14>SHOULD</bcp14> 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.
    </t>
<t>

   The Crypto-ID is derived from the public key and a modifier as follows:
</t><ol spacing='compact'> spacing="normal">
   <li>The hash function used internally by the signature scheme and indicated by the Crypto-Type (see also <xref target='cryptotypetable'/> target="cryptotypetable"/> in <xref target='cryptotypereg'/>) target="cryptotypereg"/>)
   is applied to the CIPO. Note that all the reserved and padding bits MUST <bcp14>MUST</bcp14> be set to zero.
   </li>
   <li> The leftmost bits of the resulting hash, up to the desired size, are used as the Crypto-ID.
   </li>
   </ol><t>
   At the time of this writing, a minimal size for the Crypto-ID of 128 bits is RECOMMENDED <bcp14>RECOMMENDED</bcp14> unless backward compatibility is needed <xref target='RFC8505'/>. target="RFC8505"/>. This value is bound to augment in the future.
   </t>
    </section>

    <section anchor='cryptoEARO'><name>Updated anchor="cryptoEARO"><name>Updated EARO</name>
    <t>
	   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:
    </t>
    	<figure anchor='crypto-fig'><name>Enhanced anchor="crypto-fig"><name>Enhanced Address Registration Option</name>
        <artwork>
   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)           ...
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        </artwork>
        </figure>

    <t>
    </t><dl spacing='normal'>

      <dl spacing="normal">
    	<dt>Type:</dt><dd>
	    33
    	</dd>

    	<dt>Length:</dt><dd>
     	Defined in <xref target='RFC8505'/> target="RFC8505"/> and copied in the associated CIPO.
    	</dd>

    	<dt>Status:</dt><dd>
     	Defined in <xref target='RFC8505'/>. target="RFC8505"/>.
       	</dd>

    	<dt>Opaque:</dt><dd>
     	Defined in <xref target='RFC8505'/>. target="RFC8505"/>.
	    </dd>

    	<dt>Rsvd (Reserved):</dt><dd>3-bit unsigned integer.
      	 It MUST <bcp14>MUST</bcp14> be set to zero by the sender and MUST <bcp14>MUST</bcp14> be ignored by the receiver.
	    </dd>

	    <dt>C:</dt><dd>
      	This "C" flag is set to indicate that the ROVR field contains a Crypto-ID and that the 6LN MAY <bcp14>MAY</bcp14> be challenged for ownership as specified in this document.
		</dd>

		<dt>I, R, T:</dt><dd>
	    Defined in <xref target='RFC8505'/>. target="RFC8505"/>.
		</dd>
		<dt>TID:</dt><dd>
	    Defined in <xref target='RFC8505'/>. target="RFC8505"/>.
		</dd>

<!--[rfced] We see that "Registration Lifetime" is not listed in the
    text describing Figure 1.  Please let us know what, if any, text
    should be added.-->

		<dt>Registration Ownership Verifier (ROVR):</dt><dd>
	    When the "C" flag is set, this field contains a Crypto-ID.
		</dd>
	</dl>
    <t>
	This specification uses the Status values "Validation Requested" and
	"Validation Failed", which are defined in <xref target='RFC8505'/>. target="RFC8505"/>.
    </t><t>
	this
	This specification does not define any new Status value. values.
    </t>
    </section>

    <section anchor='cryptoidopt'><name>Crypto-ID anchor="cryptoidopt"><name>Crypto-ID Parameters Option</name>
    <t>
	This specification defines the Crypto-ID Parameters Option (CIPO). CIPO.
    The CIPO carries the parameters used to form a Crypto-ID.    </t> Crypto-ID.</t>

    <t>
    In order to provide cryptographic agility <xref target='RFC7696'/>, target="RFC7696"/>, this specification supports different elliptic-curve based elliptic-curve-based signature schemes,
	indicated by a Crypto-Type field:
        </t>
    <ul>
    <li>
    The ECDSA256 signature scheme, which uses ECDSA with the NIST P-256 curve <xref target='FIPS186-4'/> target="FIPS186-4"/> and the hash function SHA-256 <xref target="RFC6234"></xref> target="RFC6234"/> internally,
	MUST
	<bcp14>MUST</bcp14> be supported by all implementations.
        </li>
    <li>
    The Ed25519 signature scheme, which uses the Pure Edwards-Curve Digital Signature Algorithm (PureEdDSA) <xref target='RFC8032'/> target="RFC8032"/> with the twisted Edwards curve Edwards25519
	<xref target="RFC7748"></xref> target="RFC7748"/> and the hash function SHA-512 <xref target="RFC6234"></xref> target="RFC6234"/> internally, MAY <bcp14>MAY</bcp14> be supported as an alternative.
        </li>
    <li>
    The ECDSA25519 signature scheme, which uses ECDSA <xref target='FIPS186-4'/> target="FIPS186-4"/> with the Weierstrass curve Wei25519 (see <xref target="curves"></xref>) target="curves"/>) and the hash function
	SHA-256 <xref target="RFC6234"></xref> target="RFC6234"/> internally, MAY <bcp14>MAY</bcp14> also be supported.
        </li>
    </ul>
	<t> 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.
    </t>

	<figure anchor='cgapar-fig'><name>Crypto-ID Parameters Option</name> <artwork>

<!--[rfced] FYI: in Figures 2 and 3 (Sections 4.3 and 4.4,
respectively), for consistency with the other figures, we moved
the bit ruler over one space so that it begins over the dash
instead of the plus sign. Please let us know of any concerns.

Updated:

    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  |               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

-->
	<figure anchor="cgapar-fig"><name>Crypto-ID Parameters Option</name> <artwork>
    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                             .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   </artwork>
	</figure>
    <t>
	</t><dl spacing='normal'>
   <dl spacing="normal">
  	<dt>Type:</dt><dd> 8-bit unsigned integer.
  	    to be
  	    IANA has assigned by IANA, value 39; see <xref target='nexndopt'/>. target="nexndopt"/>.
  	</dd>

  	<dt>Length:</dt><dd>
  	    8-bit unsigned integer. The length of the option in units of 8 octets.
  	</dd>

  	<dt>Reserved1:</dt><dd> 5-bit unsigned integer.
      	 It MUST <bcp14>MUST</bcp14> be set to zero by the sender and MUST <bcp14>MUST</bcp14> be ignored by the receiver.
	    </dd>

  	<dt>Public Key Length:</dt><dd>
  	    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 <xref target ="cryptotypetable"/>. target="cryptotypetable"/>.
  	</dd>

  	<dt>Crypto-Type:</dt><dd>8-bit unsigned integer.
      	The type of cryptographic algorithm used in calculation of the Crypto-ID
        indexed by IANA in the "Crypto-Type Subregistry" "Crypto-Types" subregistry in the "Internet Control Message Protocol version 6 (ICMPv6) Parameters" registry
        (see <xref target='cryptotypereg'/>). target="cryptotypereg"/>).

  	</dd>

  	<dt>Modifier:</dt><dd>
  	    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 and, thus, improves the privacy of a constrained node that could not maintain many key-pairs. key pairs.
  	</dd>
   	<dt>EARO Length:</dt><dd> 8-bit unsigned integer.
      The option length of the EARO that contains the Crypto-ID associated with the CIPO.
	    </dd>

  	<dt>Public Key:</dt><dd> A variable-length field, field; the size is indicated in the Public Key Length field.
  	</dd>

  	<dt>Padding:</dt><dd>
        A variable-length field completing that completes the Public Key field to align to the next 8-bytes 8-byte boundary. It MUST <bcp14>MUST</bcp14> be set to zero by the sender and MUST <bcp14>MUST</bcp14> be ignored by the receiver.
  	</dd>
	</dl><t>
    </t>
	</dl>
	<t>
	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 <xref target='RFC6234'/> target="RFC6234"/> for two of the three supported ECC-based signature schemes.
    Some code factorization is also possible for the ECC computation itself.
    </t>
	<t>
	<xref target='I-D.ietf-lwig-curve-representations'/> target="I-D.ietf-lwig-curve-representations"/> provides information
	on how to represent Montgomery curves and (twisted) Edwards curves as curves in short-Weierstrass form form, and it illustrates how this can be used to implement elliptic curve computations using existing implementations that already provide, e.g., ECDSA and ECDH using NIST <xref target='FIPS186-4'/> target="FIPS186-4"/> prime curves. For more details on representation conventions, we refer to
	<xref target='reprconv'/>.</t> target="reprconv"/>.</t>
    </section>

    <section anchor='ndpso'><name>NDP anchor="ndpso"><name>NDP Signature Option</name>

    <t>
	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 <xref target='ndpso-fig'/>. target="ndpso-fig"/>.
    </t>
    <t>
    As opposed to the RSA Signature Option (RSAO) defined in section 5.2. of <xref target='RFC3971'>SEND</xref>, target="RFC3971" sectionFormat="of" section="5.2">SEND</xref>, 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.

    </t>
      <t>
    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, received to be elided, at the expense of the capability to add arbitrary options that would be signed with a an RSAO.
    </t>
    <t>
    An ND message that carries an NDPSO MUST <bcp14>MUST</bcp14> have one and only one EARO. The EARO MUST <bcp14>MUST</bcp14> contain a Crypto-ID in the ROVR field, and the Crypto-ID MUST <bcp14>MUST</bcp14> be associated with the keypair key pair used for the Digital Signature digital signature in the NDPSO.
    </t>
	<t>
    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.
    </t>
	<figure anchor='ndpso-fig'><name>NDP signature anchor="ndpso-fig"><name>NDP Signature Option</name>
        <artwork>
    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                             .
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        </artwork>
	</figure>
    <t>
	</t><dl spacing='normal'>
<dl spacing="normal">
  	<dt>Type:</dt><dd>
  	    to be
  	    IANA has assigned by IANA, value 40; see <xref target='nexndopt'/>. target="nexndopt"/>.
  	</dd>

  	<dt>Length:</dt><dd>
  	    8-bit unsigned integer. The length of the option in units of 8 octets.
  	</dd>

  	<dt>Reserved1:</dt><dd> 5-bit unsigned integer.
      	 It MUST <bcp14>MUST</bcp14> be set to zero by the sender and MUST <bcp14>MUST</bcp14> be ignored by the receiver.
	    </dd>

  	<dt>Digital Signature Length:</dt><dd>
  	    11-bit unsigned integer. The length of the Digital Signature field in bytes.
  	</dd>

   	<dt>Reserved2:</dt><dd> 32-bit unsigned integer.
      	 It MUST <bcp14>MUST</bcp14> be set to zero by the sender and MUST <bcp14>MUST</bcp14> be ignored by the receiver.
	    </dd>
  	<dt>Digital Signature:</dt><dd>
      	A variable-length field containing the digital signature. The length and computation of the digital signature both depend on the Crypto-Type Crypto-Type, which is found in the associated CIPO, CIPO; see <xref target='reprconv'/>. target="reprconv"/>.
        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 <xref target='ndpso-generation'/>. target="ndpso-generation"/>.
  	</dd>

  	<dt>Padding:</dt><dd>
        A variable-length field completing the Digital Signature field to align to the next 8-bytes 8-byte boundary. It MUST <bcp14>MUST</bcp14> be set to zero by the sender and MUST <bcp14>MUST</bcp14> be ignored by the receiver.
  	</dd>
	</dl><t>
    </t>
	</dl>
  </section>

   <section anchor='CIO'> anchor="CIO">
       <name>Extensions to the Capability Indication Option</name>
    <t>
	This specification defines one new capability bits bit in the 6CIO, 6LoWPAN Capability Indication Option (6CIO),
	as defined by <xref target="RFC7400"/> target="RFC7400"/>, for use by the 6LR and 6LBR in IPv6 ND RA messages.

    </t>
    <figure anchor='fig6CIO' anchor="fig6CIO" title="New Capability Bit in the 6CIO">
    <artwork>
    <![CDATA[
    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                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ]]></artwork>
    </artwork>
    </figure>

    <t> New Option Field:</t>
    <dl spacing='normal'> spacing="normal">
	<dt>A:</dt><dd> 1-bit flag. Set to indicate that AP-ND is globally activated in the network.
    </dd>
    </dl>
<t>
    The "A" flag is set by the 6LBR that serves the network and is propagated by the 6LRs.
    It is typically turned on when all 6LRs are migrated to this specification.
</t>
    </section>	<!--New 6LoWPAN Capability Bits in the Capability Indication Option -->
</section>

<section><name>Protocol Scope</name>
    <t>
	     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 border router called a 6LBR per <xref target='RFC6775'/>. target="RFC6775"/>. A 6LBR has sufficient capability to satisfy the needs of duplicate address detection. DAD.
    </t>
    <t>
	     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 autoconfiguration <xref target='RFC4862'/>, target="RFC4862"/>, where there is no guarantee of ownership from the network, and each IPv6 Neighbor Discovery packet must be individually secured <xref target='RFC3971'/>. target="RFC3971"/>.
    </t>
  	<figure anchor='figco'><name>Basic anchor="figco"><name>Basic Configuration</name>
  	<artwork><![CDATA[
  	<artwork>
              ---+-------- ............
                 |      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
           ]]></artwork>
           </artwork>
  	</figure>
    <t>
	     In a mesh network, the 6LR is directly connected to the host device. This specification mandates that the peer-wise layer-2 L2 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.
    </t>
    <t>
       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.
    </t>
</section>

<section><name>Protocol Flows</name>
    <t>
	 The 6LR/6LBR ensures first-come/first-serve first come, first served 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 address, and the address is bound to the ROVR value in the 6LR/6LBR registry.
    </t>
    <t>
    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.

    <!--[rfced] Please review the following text for clarity and let
	us know how we may rephrase.
	We have the following questions: 1) Who is migrating the
	network?
	2) Does one turn on and off the "A" flag to begin and end
	migration?
	3) If not for 2 above, why does one turn the "A" flag back on?
	4) Other mentions of the "A" flag talk about it being set or
	not vs. being turned on or off.  Should this be made consistent?

Original:
The "A" flag enables to migrate a network with the
protection off and then turn it on globally.

-->

    The "A" flag enables to migrate a network with the protection off and then turn it on globally.
    </t>
    <t>
	 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 <bcp14>MUST NOT</bcp14> be altered until the challenge is complete.
    </t>
    <t>
<!--[rfced] Does the following suggested update retain your intended meaning?

Original:
   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,

Perhaps:
   When the "A" flag is on, the 6LR MUST challenge the 6LN 1) when the 6LN
   creates a binding with the "C" flag set in the ROVR, and 2) when a new
   registration attempts to change a parameter of that binding that
   identifies the 6LN, for instance, its Source Link-Layer Address.
-->
     When the "A" flag is on, the 6LR <bcp14>MUST</bcp14> 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.
    </t>
     <t>
     The 6LR MUST <bcp14>MUST</bcp14> also challenge the 6LN if the 6LBR directly signals to do so,
     using an EDAC Message message with a "Validation Requested" status. The EDAR is
     echoed by the 6LR in the NA (EARO) NA(EARO) back to the registering node. Registering Node. The 6LR
     SHOULD
     <bcp14>SHOULD</bcp14> also challenge all its attached 6LNs at the time the 6LBR turns the
     "A" flag on in the 6CIO, 6CIO in orders to detect an issue immediately.
    </t>
    <t>If the 6LR does not support the Crypto-Type, it MUST <bcp14>MUST</bcp14> 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 0, which <bcp14>MUST</bcp14>
    be supported by all 6LRs.
    </t>
    <t>
	    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 <bcp14>MAY</bcp14> use the same Crypto-ID to prove the ownership of multiple IPv6 addresses. The 6LN MAY <bcp14>MAY</bcp14> also derive multiple Crypto-IDs from a same key.
    </t>

    <section anchor='first'><name>First anchor="first"><name>First Exchange with a 6LR</name>
	 <t>
	    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 <xref target='RFC8505'/>. target="RFC8505"/>. The on-link (local) protocol interactions are shown in <xref target='Dynamic-fig'/>. target="Dynamic-fig"/>. 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, NA(EARO, status=Validation Requested) that contains a Nonce Option (shown as NonceLR in <xref target='Dynamic-fig'/>). target="Dynamic-fig"/>).
	</t>

	<figure anchor='Dynamic-fig' suppress-title='false'><name>On-link anchor="Dynamic-fig" suppress-title="false"><name>On-Link Protocol Operation</name>
	<artwork><![CDATA[
	<artwork>
    6LN                                                     6LR
     |                                                       |
     |<-------------------------
     |&lt;------------------------- RA -------------------------|
     |                                                       | ^
     |---------------- NS with EARO (Crypto-ID) ------------>| ------------&gt;| |
     |                                                       | option
     |<-
     |&lt;- NA with EARO(status=Validation Requested), NonceLR  | |
     |                                                       | v
     |------- NS with EARO, CIPO, NonceLN and NDPSO -------->| --------&gt;|
     |                                                       |
     |<-------------------
     |&lt;------------------- NA with EARO ---------------------|
     |                                                       |
                               ...
     |                                                       |
     |--------------- NS with EARO (Crypto-ID) ------------->| -------------&gt;|
     |                                                       |
     |<-------------------
     |&lt;------------------- NA with EARO ---------------------|
     |                                                       |
                               ...
     |                                                       |
     |--------------- NS with EARO (Crypto-ID) ------------->| -------------&gt;|
     |                                                       |
     |<-------------------
     |&lt;------------------- NA with EARO ---------------------|
     |                                                       |
 ]]></artwork>
 </artwork>
	</figure>

    <t>
        The Nonce option 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 the idea from <xref target='RFC3971'/> that simply indicates
	target="RFC3971"/> that the nonce is a random value. Ideally,
	an implementation uses an unpredictable cryptographically
	random value <xref target='RFC4086'/>. target="RFC4086"/>. But that may be
	impractical in some LLN scenarios where in which the devices do not have a guaranteed sense of time and for which computing complex hashes is detrimental to the battery lifetime.
	</t>
	<t> 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 start at a best effort best-effort random value, either value as either the nonce value or as a component to its computation.
	</t>
	<t>
	    The 6LN replies to the challenge with an NS(EARO) that includes a new Nonce option Option (shown as NonceLN in <xref target='Dynamic-fig'/>), target="Dynamic-fig"/>), the CIPO (<xref target='cryptoidopt'/>), target="cryptoidopt"/>), and the NDPSO containing the signature. Both Nonces nonces are included in the signed material.
        This provides a "contributory behavior", so that either party that knows it generates a good quality nonce and knows that the protocol will be secure.
	</t>
	<t>
        The 6LR MUST <bcp14>MUST</bcp14> store the information associated to with 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.

  </t>

	<t>The steps for the registration to the 6LR are as follows:
        </t>
        <t>
            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 an NS(EARO) registration with a new Crypto-ID as a ROVR, and unless the registration is rejected for another reason, it MUST <bcp14>MUST</bcp14> challenge by responding with a an NA(EARO) with a status of "Validation Requested".
        </t>
        <t>
            Upon receiving a first NA(EARO) with a status of "Validation Requested" from a 6LR, the registering node SHOULD Registering Node <bcp14>SHOULD</bcp14> retry its registration with a Crypto-ID Parameters Option (CIPO) CIPO (<xref target='cryptoidopt'/>) target="cryptoidopt"/>) that contains all the necessary material for building the Crypto-ID, the NonceLN that it generated, and the NDP signature Signature Option (<xref target='ndpso'/>) option target="ndpso"/>) 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 <bcp14>MAY</bcp14> 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 <bcp14>SHOULD</bcp14> add the CIPO again.
        </t>
        <t>
            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 NDPSO. At that point point, if the signature in the NDPSO option can be verified, then the validation succeeds. Otherwise Otherwise, the validation fails.
        </t>
        <t>
            If the 6LR fails to validate the signed NS(EARO), it responds with a status of "Validation Failed". After receiving a an NA(EARO) with a status of "Validation Failed",
            the registering node SHOULD Registering Node <bcp14>SHOULD</bcp14> try and an alternate Crypto-Type and if Crypto-Type; even if Crypto-Type 0 fails, it may try to register a different address in the NS message.

	</t>
    </section>

    <section anchor='ndpso-generation'><name>NDPSO generation anchor="ndpso-generation"><name>NDPSO Generation and verification</name> Verification</name>

      <t>
	     The signature generated by the 6LN to provide proof-of-ownership proof of ownership of the
		 private-key
		 private key is carried in the NDP Signature Option (NDPSO). NDPSO.
		 It is generated by the 6LN in a fashion that depends on the Crypto-Type
		 (see <xref target='cryptotypetable'/> target="cryptotypetable"/> in
		 <xref target='cryptotypereg'/>) target="cryptotypereg"/>) chosen by the 6LN as follows:
  	     </t>
         <ul>
         <li><t> Form the message to be signed, by concatenating the following byte-strings in the order listed:</t>

  	     		<ol spacing='compact'> spacing="normal">
  	     		<li>The 128-bit Message Type tag <xref target='RFC3972'/>
			target="RFC3972"/> (in network byte order).
                For this specification specification, the tag is given in <xref target='cgam'/>. target="cgam"/>.
               (The tag value has been generated by the editor of this specification on random.org).</li>
  	     		<li>the CIPO</li>
  	     		<li>the <eref target="https://www.random.org" brackets="angle"/>.)</li>
  	     		<li>The CIPO.</li>
  	     		<li>The 16-byte Target Address (in network byte order) sent in the Neighbor Solicitation (NS) NS message. It is the address which that the 6LN is registering with the 6LR and 6LBR.</li>
  	     		<li>NonceLR
  	     		<li>The NonceLR received from the 6LR (in
			network byte order) in the Neighbor Advertisement (NA) NA message. The
			nonce is at least 6 bytes long as defined in <xref target='RFC3971'/>.</li>
  	     		<li>NonceLN target="RFC3971"/>.</li>
  	     		<li>The NonceLN sent from the 6LN (in network
			byte order). The nonce is at least 6 bytes long as defined in <xref target='RFC3971'/>.</li>
                <li>1-byte Option Length target="RFC3971"/>.</li>
                <li>The 1-byte option length of the EARO containing the Crypto-ID.</li>
  	     		</ol>
          </li>
          <li>
          Apply the signature algorithm specified by the Crypto-Type using the private key.</li>
          </ul>

      <t>
	     The 6LR on
	     Upon receiving the NDPSO and CIPO options options, the 6LR first checks that the EARO Length in the CIPO matches the length of the EARO. If so 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.
       </t>
      <t>
         If
         If, and only if if, the check is successful, it tries to verify
	 the signature in the NDPSO option using the following: following steps:
  	     </t>
        <ul>
         <li><t>Form the message to be verified, by concatenating the following byte-strings in the order listed:</t>
  	     		<ol  spacing='compact'> spacing="normal">
                <li>The 128-bit Message Type tag given in <xref target='cgam'/> target="cgam"/> (in network byte order)</li>
                <li>the CIPO</li>
                <li>the order).</li>
                <li>The CIPO.</li>
                <li>The 16-byte Target Address (in network byte order) received in the Neighbor Solicitation (NS) NS message. It is the address which that the 6LN is registering with the 6LR and 6LBR.</li>
                <li>NonceLR
                <li>The NonceLR sent in the Neighbor Advertisement (NA) NA message. The nonce is
		at least 6 bytes long as defined in <xref target='RFC3971'/>.</li>
                <li>NonceLN received target="RFC3971"/>.</li>
                <li>The NonceLN received from the 6LN (in network byte
		order) in the NS message. The nonce is at least 6 bytes long as defined in <xref target='RFC3971'/>.</li>
                <li>1-byte target="RFC3971"/>.</li>
                <li>The 1-byte EARO Length received in the CIPO.</li>
  	     		</ol>
</li>
          <li>
          Verify the signature on this message with the public-key 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 an EDAR/EDAC flow.
          </li>
          <li>
<!--[rfced] Please review the use of the singular "database" in this
    text:

Original:
...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.

Perhaps:
...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 databases.
-->

          Due to the first-come/first-serve first-come, first-served 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.
  	     </li>

        </ul>

    </section>

    <section anchor='mhopo'><name>Multihop anchor="mhopo"><name>Multi-Hop Operation</name>
     <t>
     A new 6LN that joins the network auto-configures autoconfigures an address and performs an initial registration to a neighboring 6LR with an NS message that carries an Address Registration Option (EARO) EARO <xref target='RFC8505'/>. target="RFC8505"/>.
     </t>
    <t>
     In a multihop multi-hop 6LoWPAN, the registration with Crypto-ID is propagated to 6LBR as shown in <xref target='figReg'/>, target="figReg"/>, which illustrates the
     registration flow all the way to a 6LowPAN Backbone Router (6BBR)
    <xref target='I-D.ietf-6lo-backbone-router'/>. target="RFC8929"/>.
     </t>

	<figure anchor='figReg' suppress-title='false'><name>(Re-)Registration anchor="figReg" suppress-title="false">
       <name>(Re-)Registration Flow</name>
        <artwork><![CDATA[
        <artwork>
     6LN              6LR             6LBR            6BBR
      |                |               |                |
      |   NS(EARO)     |               |                |
      |--------------->|
      |---------------&gt;|               |                |
      |                | Extended DAR  |                |
      |                |-------------->|                |--------------&gt;|                |
      |                |               | proxy NS(EARO) |
      |                |               |--------------->|               |---------------&gt;|
      |                |               |                | NS(DAD)
      |                |               |                | ------> ------&gt;
      |                |               |                |
      |                |               |                | <wait> &lt;wait&gt;
      |                |               |                |
      |                |               | proxy NA(EARO) |
      |                |               |<---------------|               |&lt;---------------|
      |                | Extended DAC  |                |
      |                |<--------------|                |&lt;--------------|                |
      |   NA(EARO)     |               |                |
      |<---------------|
      |&lt;---------------|               |                |
      |                |               |                |
        ]]></artwork>
        </artwork>
	</figure>

     <t>
     The 6LR and the 6LBR communicate using ICMPv6 Extended Duplicate Address Request (EDAR) EDAR and Extended Duplicate Address Confirmation (EDAC) EDAC messages <xref target='RFC8505'/> target="RFC8505"/> as shown in <xref target='figReg'/>. target="figReg"/>.
     This specification extends EDAR/EDAC messages to carry cryptographically generated ROVR.

     </t>
    <t>
     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.
     </t>
    </section>

</section>

<section><name>Security Considerations</name>

  	<section><name>Brown Field</name>
    <t>
    Only 6LRs that are upgraded to this specification are capable to challenge of challenging a registration and repel repelling 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.
    </t>
    </section>

<!--[rfced] Please review the title of Section 7.2.  Might the
    suggested title below be more helpful to the reader?

Original:
Inheriting from RFC 3971

Perhaps:
Threats to the Local Network

-->

    <section><name>Inheriting from RFC 3971</name>
	   <t>
    	   Observations regarding the following threats to the local network in <xref target='RFC3971'/> target="RFC3971"/> also apply to this specification.
         </t>
         <dl spacing='normal'> spacing="normal">
            <dt>Neighbor Solicitation/Advertisement Spoofing:</dt><dd>
		        Threats in section  9.2.1 of RFC3971 <xref target="RFC3971" sectionFormat="of" section="9.2.1"/> apply. AP-ND counters the threats on NS(EARO) messages by requiring that the NDP Signature NDPSO and CIPO options be present in these solicitations.</dd>
            <!--<t hangText="Neighbor Unreachability Detection Failure">
    	      <vspace blankLines="1"/>
		        With RFC6775, a Neighbor Unreadability Detection (NUD) can still be used by the endpoint to assess the liveness of a device. The NUD request may be protected by SEND in which case the provision in section 9.2 of RFC 3972 applies. The response to the NUD may be proxied by a backbone router only if it has a fresh registration state for it. For a registration being protected by this specification, the proxied NUD response provides truthful information on the original owner of the address but it cannot be proven using SEND. If the NUD response is not proxied, the 6LR will pass the lookup to the end device which will respond with a traditional NA. If the 6LR does not have a registration associated for the device, it can issue a NA with EARO (status=Validation Requested) upon the NA from the device, which will trigger a NS that will recreate and revalidate the ND registration.
            </t>-->
            <dt>Duplicate Address Detection DoS Attack:</dt><dd>
		       Inside the LLN, Duplicate Addresses duplicate addresses are sorted out using the ROVR, which differentiates it from a movement. A different ROVR for the same Registered address Address entails a rejection of the second registration <xref target='RFC8505'/>. target="RFC8505"/>.
		       DAD coming from the backbone are is 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, duplication and enables the backbone routers to determine which one has the freshest registration <xref target='RFC8505'/> target="RFC8505"/> and is thus the best candidate to validate the registration for the device attached to it <xref target='I-D.ietf-6lo-backbone-router'/>. target="RFC8929"/>. But this specification does not guarantee that the backbone router claiming an address over the backbone is not an attacker.
            </dd>
           <dt>Router Solicitation and Advertisement Attacks:</dt><dd>
		        This specification does not change the protection of RS and RA RA, which can still be protected by SEND.</dd>
            <dt>Replay Attacks</dt><dd> Attacks:</dt><dd>
		        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).
            </dd>
            <dt>Neighbor Discovery DoS Attack:</dt><dd>
		        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 <bcp14>MUST</bcp14> 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.
	          </dd>
	       </dl>
    </section>

    <section><name>Related to 6LoWPAN ND</name>
    	<t>
    		The threats and mediations discussed in 6LoWPAN ND
		<xref target='RFC6775'/><xref target='RFC8505'/> target="RFC6775"/> <xref target="RFC8505"/> also
		apply here, in particular particular, denial-of-service (DoS) attacks against the registry at the 6LR or 6LBR.

        </t><t>
            Secure ND <xref target='RFC3971'/> target="RFC3971"/> forces the IPv6 address to be cryptographic since it integrates the CGA as the IID in the IPv6 address.

<!--[rfced] We updated 'Kbyte' to be 'KB' in the text below as 'KB' is
used more frequently in RFCs.  If you have any objections, please
let us know.

Original:
   In contrast, this specification saves about 1Kbyte
   in every NS/NA message.

Updated:
   In contrast, this specification saves about 1 KB
   in every NS/NA message.
-->

In contrast, this specification saves about 1 KB 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.
        </t><t>
            With this specification 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, L2 addresses or temporary addresses, e.g., formed pseudo-randomly pseudorandomly and released in relatively short cycles for privacy reasons <xref target='RFC8064'/><xref target='RFC8065'/>, target="RFC8064"/><xref target="RFC8065"/> that cannot be compressed.
        </t><t>
            This specification provides added protection for addresses that are obtained following due procedure <xref target='RFC8505'/> target="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 a DoS attack against the registry at the 6LR or 6LBR, 6LBR or attempt to deplete the pool of available addresses at Layer-2 L2 or Layer-3. L3.

    	</t>
    </section>
	<section><name>Compromised 6LR</name>
    	<t>
        This specification distributes the challenge and its validation at the edge of the network, between the 6LN and its 6LR. This protects against DOS DoS attacks targeted at that central 6LBR. This also saves back and forth back-and-forth exchanges across a potentially large and constrained network.
       </t><t>
        The downside is that the 6LBR needs to trust the 6LR for performing to perform the checking adequately, and the communication between the 6LR and the 6LBR must be protected to avoid tampering with the result of the test.

       </t><t>
       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 it, and has successfully passed the Crpto-ID Crypto-ID validation. The 6LR may then attract and inject traffic at will on behalf of that address address, or let a rogue take ownership of the address.
		</t>
    </section>
    <section anchor='sec-col'><name>ROVR anchor="sec-col"><name>ROVR Collisions</name>
    <t>
<!--[rfced] In the following, would you like to make use of
<sup> for superscript in this document?

Original:
...a collision is 1 - e^{-p^2/(2n)} where n is the
maximum population size (2^64 here, 1.84E19)

-->

    	A collision of Registration Ownership Verifiers (ROVR) ROVRs (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 hash, and, thus,
        random collisions are the only ones possible, the formula (birthday paradox) for calculating the probability of a collision is 1 - e^{-p^2/(2n)} e^{-p^2/(2n)}, where n is the maximum population size (2^64 here, 1.84E19) 1.84E19), and p is the actual population (number of nodes, assuming one Crypto-ID per node).
         </t><t>
        If the Crypto-ID is 64-bits 64 bits (the least possible size allowed), the chance of a collision is 0.01% for a 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 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 <bcp14>RECOMMENDED</bcp14> that nodes do not derive the address being registered from the ROVR.
    	</t>
    </section>
   	<section><name>Implementation Attacks</name>
    	<t> The signature schemes referenced in this specification comply with NIST <xref target='FIPS186-4'/> target="FIPS186-4"/> or Crypto Forum Research Group (CFRG) standards
		<xref target='RFC8032'/> target="RFC8032"/> and offer strong algorithmic security at roughly a 128-bit security level. These signature schemes use elliptic curves that were either
		were specifically designed with exception-free and constant-time arithmetic in mind <xref target='RFC7748'/> target="RFC7748"/> or where one has have extensive implementation experience of resistance
		to timing attacks <xref target='FIPS186-4'/>. target="FIPS186-4"/>.

        </t>
        <t>
        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 <xref target='breaking-ed25519'/>. target="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.
		</t>
    </section>
	<section><name>Cross-Algorithm and Cross-Protocol Attacks</name>
    	<t>
        The keypair key pair used in this specification can be self-generated self-generated, and the public key does not need to be exchanged, e.g., through certificates, with a third party before it is used.

        </t>
        <t>
        New keypairs key pairs can be formed for new registration as the node desires.
        On the other hand, it is safer to allocate a keypair key pair that is used only for the address protection and only for one instantiation of the signature scheme (which includes
		the choice of elliptic curve domain parameters, a used hash function, and applicable representation conventions).
        </t>
        <t>
        The same private key MUST NOT <bcp14>MUST NOT</bcp14> be reused with more than one instantiation of the signature scheme in this specification. The same private key MUST NOT <bcp14>MUST NOT</bcp14> be used for anything other than computing NDPSO signatures per this specification.
		</t>

		<t>
<!--[rfced] Please clarify "MUST NOT reuse these ephemeral private
keys k across signing operations". Is the intended meaning
perhaps "MUST NOT reuse the ephemeral private key k across
signing operations"?

Original:
   ECDSA shall be used strictly as specified in <xref target="FIPS186-4"></xref>. [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.

Perhaps:
   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 the ephemeral
   private key k across signing operations.
-->
		<t> ECDSA shall be used strictly as specified in <xref target="FIPS186-4"/>. In particular, each signing operation of ECDSA <bcp14>MUST</bcp14> use randomly generated
		ephemeral private keys and <bcp14>MUST NOT</bcp14> reuse these ephemeral private keys k across signing operations. This precludes the use of deterministic ECDSA without a random input
		for the determination of k, which is deemed dangerous for the intended applications this document aims to serve.</t>
    </section>

	<section><name>Public Key Validation</name>
	<t>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.
    </t>
    <t>

<!--[rfced] Is Appendix B.1 of [CURVE-REPR] the correct reference in
the sentence below? We do not see mention of "full public key
validation" in this document. Please review and let us know if an
update is needed.

Original:
   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 <xref target='I-D.ietf-lwig-curve-representations'/>); [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 <xref target='I-D.ietf-lwig-curve-representations'/>). </t>
	</section>

	<section><name>Correlating Registrations</name>
    	<t>
          The [CURVE-REPR]).

-->
        For points used with the signature scheme Ed25519, one <bcp14>MUST</bcp14> check
	that this point is not in the small subgroup (see <xref target="I-D.ietf-lwig-curve-representations" sectionFormat="of" section="B.1"/>); for points used with the signature scheme
	ECDSA (i.e., both ECDSA256 and ECDSA25519), one <bcp14>MUST</bcp14> 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 <xref target="I-D.ietf-lwig-curve-representations" sectionFormat="of" section="B.1"/>). </t>
	</section>

	<section><name>Correlating Registrations</name>
    	<t>
          The ROVR field in the EARO introduced in <xref target='RFC8505'/> target="RFC8505"/> extends the EUI-64 field of the ARO defined in <xref target='RFC6775'/>. target="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 <xref target='RFC8505'/> target="RFC8505" sectionFormat="of" section="3"/> indicates that the ROVR and the address being registered are decoupled. A 6LN may use a the same ROVR for multiple registrations or a different ROVR per registration, and the IID must not derive be derived from the ROVR. In theory theory, different 6LNs could use a the same ROVR as long as they do not attempt to register the same address.

    	</t>
    	<t>
          The Modifier modifier used in the computation of the Crypto-ID enables a 6LN to build different Crypto-IDs for different addresses with a same keypair. key pair. Using that facility improves the privacy of the 6LN as at 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 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.
        </t>
    </section>
</section>

<section><name>IANA considerations</name> Considerations</name>

    <section anchor='cgam'><name>CGA anchor="cgam"><name>CGA Message Type</name>
    <t>

<!--[rfced] We noticed the following about the text in Section 8.1
     (CGA Message Type) when compared with the corresponding IANA
     registry at
     https://www.iana.org/assignments/cga-message-types/cga-message-types.xhtml:

a) The corresponding registry with IANA is called "CGA Extension Type
Tags".  The term "Message Type" is not used by IANA in the
subregistry.

b) The IANA registry uses uppercase letters instead of lowercase.

With the above in mind, would the following updates be accurate?  If
not, please let us know any necessary corrections.

Original:

8.1.  CGA Message Type

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

Perhaps:

8.1.  CGA Extension Type

   This document defines a new 128-bit CGA Extension Type Tag under
   the "CGA Extension Type Tags" subregsitry created by [RFC3972]. Tag: 0x8701 55C8 0CCA DD32 6AB7
   E415 F148 84D0.
-->

  	 This document defines a new 128-bit value of a Message Type tag under the CGA Message Type <xref target="RFC3972"/> namespace: 0x8701 55c8 0cca dd32 6ab7 e415 f148 84d0.
    </t>
    </section>

    <section anchor='cryptotypereg'><name>Crypto-Type anchor="cryptotypereg"><name>Crypto-Type Subregistry</name>
    <t>
		IANA is requested to create a new has created the "Crypto-Types" subregistry "Crypto-Type Subregistry" in the "Internet Control Message Protocol version 6 (ICMPv6) Parameters". Parameters" registry.  The registry is indexed by
		an integer in the interval 0..255 and contains an Elliptic Curve, elliptic curve, a Hash Function, hash function, a Signature Algorithm, Representation Conventions,
        Public signature algorithm, representation conventions,
        public key size, and Signature signature size, as shown in
		<xref target='cryptotypetable'/>, target="cryptotypetable"/>, which together specify a signature scheme (and which are fully specified in <xref target="reprconv"></xref>). target="reprconv"/>).
    </t>

<!--[rfced] We had a few questions about the Crypto-Types subregistry
     information captured in Section 8.2.  The registry is viewable at
     https://www.iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml#icmpv6-crypto-types.

a) It is unusual for us to see references in columns other than the
"Reference" column of IANA registries.  Please review if these
references should remain in either or both Table 1 or the IANA
"Crypto-Types" subregistry.

b) The IANA registry uses only the values 0, 1, and 2 in the Cypto-Type
Value column, while this document uses 0 (ECDSA256), 1 (Ed25519), and
2 (ECDSA25519).  Please let us know if/how these should be made
uniform.

c) The IANA registry mentions values 3-255, but with no text
following.  We would generally see something like "Reserved" or
"Unassigned" etc.

d) Related to the point above, in this document we see the following
in the text preceding the figure:

Original:
The registry is indexed by an integer
in the interval 0..255 and contains...

but no mention of values 3-255 in the table itself.  For the ease of
the reader, should those values be added?

-->
    <t>The following Crypto-Type values are defined in this document:
    </t>
        <table anchor="cryptotypetable"><name>Crypto-Types</name>
   <thead>
          <tr>
           <th>Crypto-Type value</th> Value</th>
		   <th align='center'> align="center"> 0 (ECDSA256) </th>
		   <th align='center'> align="center"> 1 (Ed25519) </th>
		   <th align='center'> align="center"> 2 (ECDSA25519) </th>
          </tr>

   </thead><tbody>

			<tr><td>Elliptic curve</td> Curve</td>
    			<td align='center'> align="center"> NIST P-256 <xref target='FIPS186-4'/></td> target="FIPS186-4"/></td>
    			<td align='center'> align="center"> Curve25519 <xref target='RFC7748'/></td> target="RFC7748"/></td>
    			<td align='center'> align="center"> Curve25519 <xref target='RFC7748'/></td> target="RFC7748"/></td>
            </tr>
			<tr><td>Hash function</td> Function</td>
		    	<td align='center'> align="center"> SHA-256 <xref target='RFC6234'/></td> target="RFC6234"/></td>
				<td align='center'> align="center"> SHA-512 <xref target='RFC6234'/></td> target="RFC6234"/></td>
			    <td align='center'> align="center"> SHA-256 <xref target='RFC6234'/></td> target="RFC6234"/></td>
            </tr>
			<tr><td>Signature algorithm</td> Algorithm</td>
				<td align='center'> align="center"> ECDSA <xref target='FIPS186-4'/></td> target="FIPS186-4"/></td>
			    <td align='center'> align="center"> Ed25519 <xref target='RFC8032'/></td> target="RFC8032"/></td>
				<td align='center'> align="center"> ECDSA <xref target='FIPS186-4'/></td> target="FIPS186-4"/></td>
            </tr>
			<tr><td>Representation conventions</td> Conventions</td>
				<td align='center'> align="center"> Weierstrass, (un)compressed, MSB/msb first, <xref target='RFC7518'/> target="RFC7518"/> </td>
			    <td align='center'> align="center"> Edwards, compressed, LSB/lsb first, <xref target='RFC8037'/></td> target="RFC8037"/></td>
			    <td align='center'> align="center"> Weierstrass, (un)compressed, MSB/msb first, <xref target='I-D.ietf-lwig-curve-representations'/></td></tr> target="I-D.ietf-lwig-curve-representations"/></td></tr>
			<tr><td>Public key size</td> Key Size</td>
				<td align='center'> align="center"> 33/65 bytes (compressed/uncompressed)</td>
			    <td align='center'> align="center"> 32 bytes (compressed)</td>
			    <td align='center'> align="center"> 33/65 bytes (compressed/uncompressed) </td></tr>
			<tr><td>Signature size</td> Size</td>
				<td align='center'> align="center"> 64 bytes </td>
			    <td align='center'> align="center"> 64 bytes </td>
			    <td align='center'> align="center"> 64 bytes </td></tr>
			<tr><td>Defining specification</td>
			<tr><td>Reference</td>
			    <td align='center'>This_RFC</td> align="center">RFC 8928</td>
				<td align='center'>This_RFC</td> align="center">RFC 8928</td>
				<td align='center'>This_RFC</td> align="center">RFC 8928</td>
             </tr>
    </tbody>
    </table>
	<t>
	New Crypto-Type values providing similar or better security may be defined in the future.
    </t>
    <t>
    Assignment of new values for new Crypto-Type MUST <bcp14>MUST</bcp14> be done through IANA with
	either "Specification Required" or "IESG Approval" as defined in BCP 26
	<xref target='RFC8126'/>. target="RFC8126">BCP 26</xref>.
    </t>

    </section>

    <section anchor='ndopt'><name>IPv6 anchor="ndopt"><name>IPv6 ND option types </name> Option Types</name>
    <t>
  	 This document registers two new ND option types under the subregistry "IPv6 Neighbor Discovery Option Formats":
    </t>

      <table anchor="nexndopt"><name>New ND options</name> Options</name>
   <thead>

          <tr>
          <th align='center'>Option Name</th> align="left">Description</th>
          <th align='center'>Suggested Value</th> align="center">Type</th>
          <th align='left'>Reference</th> align="left">Reference</th>
          </tr>

   </thead><tbody>
          <tr>
          <td align='center'>NDP Signature align="left">Crypto-ID Parameters Option (NDPSO)</td> (CIPO)</td>
          <td align='center'>38</td> align="center">39</td>
          <td align='left'>This document</td> align="left">RFC 8928</td>
          </tr>
          <tr>
          <td align='center'>Crypto-ID Parameters align="left">NDP Signature Option (CIPO)</td> (NDPSO)</td>
          <td align='center'>39</td> align="center">40</td>
          <td align='left'>This document</td> align="left">RFC 8928</td>
          </tr>

    </tbody>
        </table>
    </section>

    <section title="New 6LoWPAN Capability Bit">
	<t>
	    IANA is requested to make additions has made an addition to the Subregistry subregistry for
	    "6LoWPAN Capability Bits" created for <xref target='RFC7400'/> target="RFC7400"/>
        as follows:
	</t>

        <table anchor="CIOdat"><name>New 6LoWPAN Capability Bit</name>
   <thead>
          <tr>
		   <th align='center'>Capability Bit</th>
		   <th align='left'>Description </th>
		   <th align='left'>Document</th>
          </tr>

   </thead><tbody>

			<tr>
    			<td align='center'>09</td>
    			<td align='left'>AP-ND Enabled (1 bit)</td>
    			<td align='left'>This_RFC</td>
            </tr>

    </tbody>
    </table>

    </section>	<!-- end section "New 6LoWPAN Capability Bits" -->

</section>

<section><name>Acknowledgments</name>
    <t>
     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.
    </t>
          <tr>
		   <th align="center">Bit</th>
		   <th align="left">Description </th>
		   <th align="left">Reference</th>
          </tr>

   </thead><tbody>

			<tr>
    			<td align="center">9</td>
    			<td align="left">AP-ND Enabled (1 bit)</td>
    			<td align="left">RFC 8928</td>
            </tr>

    </tbody>
    </table>

    </section>

</section>

</middle>

<back>

   <displayreference   target="I-D.ietf-6lo-backbone-router"            to="BACKBONE-ROUTER"/>
   <displayreference target="I-D.ietf-lwig-curve-representations" to="CURVE-REPR"/>
   <displayreference target="RFC7696"     to="BCP 201"/> to="BCP201"/>
   <displayreference target="RFC4086"     to="BCP 106"/> to="BCP106"/>
<references><name>References</name>
<references><name>Normative References</name>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml'/>
  	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.3971.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
  	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6234.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.3971.xml"/>
  	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6775.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6234.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7400.xml'/>
  	<!--xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7515.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6775.xml"/>
  	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7517.xml'/--> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7400.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7748.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7748.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8032.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8032.xml"/>
  	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
  	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8505.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8505.xml"/>

  <reference anchor='FIPS186-4'> anchor="FIPS186-4" target="https://nvlpubs.nist.gov/nistpubs/fips/nist.fips.186-4.pdf">
        <front>
            <title> Digital
            <title>Digital Signature Standard (DSS), Federal Information
		    Processing Standards Publication 186-4 </title> (DSS)</title>
        <author>
	   	   <organization>
		     FIPS 186-4
		     </organization>
	     </author>
		<date month='July' year='2013'/>
         </front>
	 <seriesInfo name='US Department of Commerce/National
		     National Institute of Standards and Technology' value=''/>
	</reference>

	<reference anchor='SEC1'>
        <front>
            <title>SEC 1: Elliptic Curve Cryptography, Version 2.0 </title>
        <author>
	   	   <organization>
		     SEC1 Technology
		     </organization>
	     </author>
		<date month='June' year='2009'/> month="July" year="2013"/>
         </front>
          <seriesInfo name='Standards for Efficient Cryptography' value=''/>
	</reference>

</references>

<references><name>Informative references</name>

	   <!--reference anchor="IANA.JOSE.Algorithms">
		<front>
			<title> JSON Web Signature and Encryption Algorithms </title>
			<author>
				<organization>
					IANA
				</organization>
			</author>
			<date year=""></date>
		</front> name="FIPS" value="186-4"/>
	 <seriesInfo name="IANA," value="https://www.iana.org/assignments/jose/jose.xhtml#web-signature-encryption-algorithms"></seriesInfo> name="DOI" value="10.6028/NIST.FIPS.186-4"/>
	</reference>

	<reference anchor="IANA.JOSE.Curves"> anchor="SEC1" target="https://www.secg.org/sec1-v2.pdf">
        <front>
			<title> JSON Web Key
            <title>SEC 1: Elliptic Curve </title> Cryptography</title>
        <author>
	   	   <organization>
					IANA
		    Standards for Efficient Cryptography
		     </organization>
	     </author>
		<date year=""></date> month="May" year="2009"/>
         </front>
		<seriesInfo name="IANA," value="https://www.iana.org/assignments/jose/jose.xhtml#web-key-elliptic-curve"></seriesInfo>
	   </reference-->

	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.3972.xml'/>
	 <refcontent>Version 2</refcontent>

	</reference>

</references>

<references><name>Informative References</name>

	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.4086.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.3972.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.4861.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.4086.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.4862.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.4861.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.4919.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.4862.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.4944.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.4919.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6282.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.4944.xml"/>
  	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7039.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.6282.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7217.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7039.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7518.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7217.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7696.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7518.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8037.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.7696.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8064.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8037.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8065.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8064.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8126.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8065.xml"/>
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.ietf-6lo-backbone-router.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml/reference.RFC.8126.xml"/>

        <!--draft-ietf-6lo-backbone-router-20; in REF - part of
	    C310-->

<reference anchor='RFC8929' target='https://www.rfc-editor.org/info/rfc8929'>
<front>
<title>IPv6 Backbone Router</title>

<author initials='P' surname='Thubert' fullname='Pascal Thubert' role='editor'>
    <organization />
</author>

<author initials='C.E.' surname='Perkins' fullname='Charles Perkins'>
    <organization />
</author>

<author initials='E' surname='Levy-Abegnoli' fullname='Eric Levy-Abegnoli'>
    <organization />
</author>

<date month='October' year='2020' />

</front>

<seriesInfo name='RFC' value='8929' />
<seriesInfo name="DOI" value="10.17487/RFC8929"/>
</reference>

        <!--draft-ietf-lwig-curve-representations-10; Active - AD Evaluation::AD Followup-->
	<xi:include href='https://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.ietf-lwig-curve-representations.xml'/> href="https://xml2rfc.tools.ietf.org/public/rfc/bibxml3/reference.I-D.ietf-lwig-curve-representations.xml"/>

	<reference anchor='breaking-ed25519' target='https://link.springer.com/chapter/10.1007/978-3-319-76953-0_1'> anchor="breaking-ed25519" target="https://link.springer.com/chapter/10.1007/978-3-319-76953-0_1">
        <front>
            <title>Breaking Ed25519 in WolfSSL</title>
        <author initials='N.' surname='Samwel' fullname='Niels Samwel'> initials="N." surname="Samwel" fullname="Niels Samwel">
	   	</author>
        <author initials='L.' surname='Batina' fullname='Leija Batina'> initials="L." surname="Batina" fullname="Leija Batina">
	   	</author>
        <author initials='G.' surname='Bertoni' fullname='Guido Bertoni'> initials="G." surname="Bertoni" fullname="Guido Bertoni">
	   	</author>
        <author initials='J.' surname='Daemen' fullname='Joan Daemen'> initials="J." surname="Daemen" fullname="Joan Daemen">
	   	</author>
        <author initials='R.' surname='Susella' fullname='Ruggero Susella'> initials="R." surname="Susella" fullname="Ruggero Susella">
	   	</author>
		<date year='2018'/> month="March" year="2018"/>
         </front>
	 <seriesInfo name='Cryptographers’ Track at the RSA Conference' value=''/>
	 <refcontent>Topics in Cryptology - CT-RSA, pp. 1-20</refcontent>
	</reference>
</references>
</references>
<section anchor='ps'><name>Requirements anchor="ps"><name>Requirements Addressed in this This Document</name>
    <t>
	     In this section we state section, the requirements of a secure neighbor discovery Neighbor Discovery protocol for low-power and lossy networks. LLNs are stated.
	     </t><ul spacing='compact'> spacing="normal">
	     <li>
	      The protocol MUST <bcp14>MUST</bcp14> be based on the Neighbor Discovery Optimization for Low-power and Lossy Networks the LLN protocol defined in <xref target='RFC6775'/>. RFC6775 target="RFC6775"/>. RFC 6775 utilizes optimizations such as host-initiated interactions for sleeping resource-constrained hosts and the elimination of multicast address resolution.
	     </li>
	     <li>
	       New options to be added to Neighbor Solicitation messages MUST <bcp14>MUST</bcp14> lead to small packet sizes, especially compared with existing protocols such as SEcure Neighbor Discovery (SEND). SEND. Smaller packet sizes facilitate low-power transmission by resource-constrained nodes on lossy links.
	     </li>
	     <li>
	       The support for this registration mechanism SHOULD <bcp14>SHOULD</bcp14> 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 low-power Wi-Fi SHOULD <bcp14>SHOULD</bcp14> be possible.
	     </li>
	     <li>
	       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 <bcp14>SHOULD</bcp14> be unique at least within the LLN connected to a 6LBR.
       </li>
	     <li>

<!--[rfced] Please confirm if 'Unique Interface Identifier' and
'unique identifier' are the same term. If so, may we update the
text to reflect 'unique identifier' for consistency (only 1
instance)?

Original:
*  The Address Registration Option used in the ND registration SHOULD
   be extended to carry the relevant forms of Unique Interface
   Identifier.

Perhaps:
*  The Address Registration Option used in the ND registration SHOULD
   be extended to carry the relevant forms of the unique identifier.
-->
	     <li>
	       The Address Registration Option used in the ND registration <bcp14>SHOULD</bcp14> be extended to carry the relevant forms of the
	       Unique Interface Identifier.
	     </li>
	     <li>
	       The Neighbor Discovery should specify the formation of a site-local address that follows the security recommendations from <xref target='RFC7217'/>. target="RFC7217"/>.
	     </li>
	     </ul><t>
    </t>
	     </ul>
</section>

<section anchor='reprconv'><name>Representation anchor="reprconv"><name>Representation Conventions</name>

	<section><name>Signature Schemes</name>

<!--[rfced] Please confirm if Appendix B of [FIPS186-4] is the correct
     section reference below.  FYI: we see 'curve P-256' discussed in
     Appendix D.2.3.

Original:
   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.
-->

	<t> The signature scheme ECDSA256 corresponding to Crypto-Type 0 is ECDSA, as specified in <xref target='FIPS186-4'/>, target="FIPS186-4"/>, instantiated with the NIST prime curve P-256,
	as specified in Appendix B of <xref target='FIPS186-4'/>, target="FIPS186-4"/>, and the hash function SHA-256, as specified in <xref target='RFC6234'/>, target="RFC6234"/>, where points of this NIST curve are
	represented as points of a short-Weierstrass curve (see <xref target='FIPS186-4'/>) target="FIPS186-4"/>) and are encoded as octet strings in most-significant-bit first (msb) first and
	most-significant-byte first (MSB) first order. The signature itself consists of two integers (r and s), which are each encoded as fixed-size octet strings in most-significant-bit msb
	first and most-significant-byte MSB first order. For details on further details, see <xref target="FIPS186-4"/> for ECDSA, see <xref target='FIPS186-4'/>; target="weirepr"/> for details on the encoding of public keys, and see
        <xref target="weirepr"></xref>; target="bitrepr"/> for details on the signature encoding, see <xref target='bitrepr'/>.</t> encoding.</t>

	<t> The signature scheme Ed25519 corresponding to Crypto-Type 1 is EdDSA, as specified in <xref target='RFC8032'/>, target="RFC8032"/>, instantiated with the Montgomery curve Curve25519, as
	specified in <xref target='RFC7748'/>, target="RFC7748"/>, and the hash function SHA-512, as specified in <xref target='RFC6234'/>, target="RFC6234"/>, where points of this Montgomery curve are
	represented as points of the corresponding twisted Edwards
	curve Edwards25519 (see <xref target='curves'/>) target="curves"/>) and are
	encoded as octet strings in least-significant-bit first (lsb) first
	and least-significant-byte first (LSB) first 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 lsb first and least-significant-byte LSB first order. For details on EdDSA, EdDSA and the encoding of public keys and that of signatures, see the
	specification of pure Ed25519 in <xref target='RFC8032'></xref>.</t> target="RFC8032"/>.</t>

	<t> The signature scheme ECDSA25519 corresponding to Crypto-Type 2 is ECDSA, as specified in <xref target='FIPS186-4'/>, target="FIPS186-4"/>, instantiated with the Montgomery curve
	Curve25519, as specified in <xref target='RFC7748'/>, target="RFC7748"/>, and the hash function SHA-256, as specified in <xref target='RFC6234'/>, target="RFC6234"/>, where points of this Montgomery
	curve are represented as points of the corresponding short-Weierstrass curve Wei25519 (see <xref target='curves'/>) target="curves"/>) and are encoded as octet strings in
	most-significant-bit
	msb first and most-significant-byte MSB 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 msb first and most-significant-byte MSB first order. For details on further details, see <xref target="FIPS186-4"/> for ECDSA, see <xref target='FIPS186-4'/>; target="weirepr"/> for details on the encoding of
	public keys, and see <xref target="weirepr"></xref>; target="bitrepr"/> for details on the signature encoding, see <xref target='bitrepr'/></t> encoding.</t>
	</section>

	<section anchor='bitrepr'><name>Representation anchor="bitrepr"><name>Representation of ECDSA Signatures</name>
	<t> With ECDSA, each signature is an ordered pair (r, s) of integers <xref target='FIPS186-4'/>, target="FIPS186-4"/>, where each integer is represented as a 32-octet string according to the
	Field Element to Octet String
	Field-Element-to-Octet-String conversion rules in <xref target='SEC1'/> target="SEC1"/> and where the ordered pair of integers is represented as the rightconcatenation right concatenation 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 Octet-String-to-Field-Element conversion rules in <xref target='SEC1'/>. target="SEC1"/>.
	</t></section>

	<section anchor='weirepr'><name>Representation anchor="weirepr"><name>Representation of Public Keys Used with ECDSA</name>
	<t> 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 Elliptic-Curve-Point-to-Octet-String
        conversion rules in <xref target='SEC1'/>, target="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 Octet-String-to-Elliptic-Curve-Point conversion rules in <xref target='SEC1'/>, target="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.) </t>
	</section>

<!--[rfced] In Appendix B.4, for the lists of curve parameters, there
     are options for the correct formatting. Please review this file
     and let us know which option you prefer:

     https://www.rfc-editor.org/authors/rfc8928_options.html#section-b.4

where:

Option A: dictionary list (what currently appears in the file)
Option B: sourcecode element (fixed-width font)
Option C: dictionary list (using <tt> for fixed-width font in HTML and
PDF; however, this yields quotation marks in the text output)

If you don't have a preference, we'll go with Option B because it best matches the original.

We sought guidance from Henrik Levkowetz on this formatting, and he
said that <sourcecode> should be used if there is a likelihood of
automated consumption of these lists.  If a new type value such as
<sourcecode type="elliptic-curve-parameters"> would be useful, please
let us know. The current list is here:
https://www.rfc-editor.org/materials/sourcecode-types.txt

For definitions of the elements, please see
https://xml2rfc.tools.ietf.org/xml2rfc-doc.html#name-dl-2
https://xml2rfc.tools.ietf.org/xml2rfc-doc.html#name-sourcecode-2
	-->

	<section anchor='curves'><name>Alternative anchor="curves"><name>Alternative Representations of Curve25519</name>
	<t> The elliptic curve Curve25519, as specified in <xref target='RFC7748'/>, target="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 <xref target='RFC7748'/>; target="RFC7748"/>; the domain parameters of the elliptic curve Wei25519 in
	short-Weierstrass curve form comply with Section 6.1.1 of <xref target='FIPS186-4'/>. target="FIPS186-4"/>. For further details on these curves and on the coordinate transformations referenced above, see
	<xref target='I-D.ietf-lwig-curve-representations'/>. target="I-D.ietf-lwig-curve-representations"/>.  </t>

	<t> General parameters (for all curve models):
		</t><dl spacing='compact'> spacing="compact">
			<dt>p</dt><dd> 2^{255}-19 </dd>
			<dt></dt><dd> 2^{255}-19<br/>
			(=0x7fffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffed) </dd>
			<dt>h</dt><dd> 8 </dd>
			<dt>n</dt><dd> 7237005577332262213973186563042994240857116359379907606001950938285454250989 </dd>
			<dt></dt><dd> <br/>
			(=2^{252} +  0x14def9de a2f79cd6 5812631a 5cf5d3ed) </dd>
		</dl><t> </t>
		</dl>
	<t> Montgomery curve-specific parameters (for Curve25519):
		</t><dl spacing='compact'> spacing="compact">
			<dt>A</dt><dd> 486662 </dd>
			<dt>B</dt><dd> 1 </dd>
			<dt>Gu</dt><dd> 9 (=0x9) </dd>
			<dt>Gv</dt><dd> 14781619447589544791020593568409986887264606134616475288964881837755586237401 </dd>
			<dt></dt><dd> <br/>
			(=0x20ae19a1 b8a086b4 e01edd2c 7748d14c 923d4d7e 6d7c61b2 29e9c5a2 7eced3d9) </dd>
		</dl><t> </t>
		</dl>
	<t> Twisted Edwards curve-specific parameters (for Edwards25519):
		</t><dl spacing='compact'> spacing="compact">
			<dt>a</dt><dd> -1 (-0x01) </dd>
			<dt>d</dt><dd> -121665/121666 </dd>
			<dt></dt><dd> <br/>
			(=37095705934669439343138083508754565189542113879843219016388785533085940283555) </dd>
			<dt></dt><dd> <br/>
			(=0x52036cee 2b6ffe73 8cc74079 7779e898 00700a4d 4141d8ab 75eb4dca 135978a3) </dd>
			<dt>Gx</dt><dd> 15112221349535400772501151409588531511454012693041857206046113283949847762202 </dd>
			<dt></dt><dd> <br/>
			(=0x216936d3 cd6e53fe c0a4e231 fdd6dc5c 692cc760 9525a7b2 c9562d60 8f25d51a) </dd>
			<dt>Gy</dt><dd> 4/5 </dd>
			<dt></dt><dd> <br/>
			(=46316835694926478169428394003475163141307993866256225615783033603165251855960) </dd>
			<dt></dt><dd>(=0x66666666 <br/>
			(=0x66666666 66666666 66666666 66666666 66666666 66666666 66666666 66666658) </dd>
		</dl><t> </t>
		</dl>
	<t> Weierstrass curve-specific parameters (for Wei25519):
		</t><dl spacing='compact'> spacing="compact">
			<dt>a</dt><dd> 19298681539552699237261830834781317975544997444273427339909597334573241639236 </dd>
			<dt></dt><dd> <br/>
			(=0x2aaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaa98 4914a144) </dd>
			<dt>b</dt><dd> 55751746669818908907645289078257140818241103727901012315294400837956729358436 </dd>
			<dt></dt><dd> <br/>
			(=0x7b425ed0 97b425ed 097b425e d097b425 ed097b42 5ed097b4 260b5e9c 7710c864) </dd>
			<dt>GX</dt><dd> 19298681539552699237261830834781317975544997444273427339909597334652188435546 </dd>
			<dt></dt><dd> <br/>
			(=0x2aaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaaaaaaa aaad245a) </dd>
			<dt>GY</dt><dd> 14781619447589544791020593568409986887264606134616475288964881837755586237401 </dd>
			<dt></dt><dd> <br/>
			(=0x20ae19a1 b8a086b4 e01edd2c 7748d14c 923d4d7e 6d7c61b2 29e9c5a2 7eced3d9) </dd>
	</dl><t>
	</dl>
	</section>

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

</section>

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