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Versions: (draft-jiang-dhc-sedhcpv6) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21

DHC Working Group                                               S. Jiang
Internet-Draft                              Huawei Technologies Co., Ltd
Intended status: Standards Track                                   L. Li
Expires: June 12, 2016                                            Y. Cui
                                                     Tsinghua University
                                                               T. Jinmei
                                                           Infoblox Inc.
                                                                T. Lemon
                                                           Nominum, Inc.
                                                                D. Zhang
                                                       December 10, 2015


                             Secure DHCPv6
                       draft-ietf-dhc-sedhcpv6-10

Abstract

   The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) enables
   DHCPv6 servers to pass configuration parameters.  It offers
   configuration flexibility.  If not being secured, DHCPv6 is
   vulnerable to various attacks.  This document analyzes the security
   issues of DHCPv6 and specifies a secure DHCPv6 mechanism for the
   authentication and encryption between DHCPv6 client and DHCPv6
   server.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 12, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language and Terminology . . . . . . . . . . . .   3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Issues of DHCPv6 . . . . . . . . . . . . . . . . . .   4
   5.  secure DHCPv6 overview  . . . . . . . . . . . . . . . . . . .   5
     5.1.  Solution Overview . . . . . . . . . . . . . . . . . . . .   5
     5.2.  New Components  . . . . . . . . . . . . . . . . . . . . .   7
     5.3.  Support for Algorithm Agility . . . . . . . . . . . . . .   7
     5.4.  Imposed Additional Constraints  . . . . . . . . . . . . .   8
     5.5.  Applicability . . . . . . . . . . . . . . . . . . . . . .   8
   6.  DHCPv6 Client Behavior  . . . . . . . . . . . . . . . . . . .   9
   7.  DHCPv6 Server Behavior  . . . . . . . . . . . . . . . . . . .  11
   8.  Relay Agent Behavior  . . . . . . . . . . . . . . . . . . . .  13
   9.  Processing Rules  . . . . . . . . . . . . . . . . . . . . . .  14
     9.1.  Timestamp Check . . . . . . . . . . . . . . . . . . . . .  14
   10. Extensions for Secure DHCPv6  . . . . . . . . . . . . . . . .  15
     10.1.  New DHCPv6 Options . . . . . . . . . . . . . . . . . . .  15
       10.1.1.  Certificate Option . . . . . . . . . . . . . . . . .  15
       10.1.2.  Signature Option . . . . . . . . . . . . . . . . . .  16
       10.1.3.  Timestamp Option . . . . . . . . . . . . . . . . . .  17
       10.1.4.  Encrypted-message Option . . . . . . . . . . . . . .  18
     10.2.  New DHCPv6 Messages  . . . . . . . . . . . . . . . . . .  19
       10.2.1.  Encrypted-Query Message  . . . . . . . . . . . . . .  19
       10.2.2.  Encrypted-Response Message . . . . . . . . . . . . .  19
     10.3.  Status Codes . . . . . . . . . . . . . . . . . . . . . .  20
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  20
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  22
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  23
     14.2.  Informative References . . . . . . . . . . . . . . . . .  24
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24







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1.  Introduction

   The Dynamic Host Configuration Protocol for IPv6 (DHCPv6, [RFC3315])
   enables DHCPv6 servers to pass configuration parameters and offers
   configuration flexibility.  If not being secured, DHCPv6 is
   vulnerable to various attacks.

   This document analyzes the security issues of DHCPv6 in details and
   provides the following mechanisms for improving the security of
   DHCPv6 between client and server:

   o  the authentication of the DHCPv6 client and the DHCPv6 server to
      defend against active attack, such as spoofing attack.

   o  the encryption between the DHCPv6 client and the DHCPv6 server in
      order to protect the DHCPv6 from passive attack, such as pervasive
      monitoring.

   o  the integrity check of DHCPv6 messages by the recipient of the
      message based on signature.

   o  anti-replay protection based on timestamps.

   Note: this secure mechanism in this document does not protect outer
   options in Relay-Forward and Relay-Reply messages, either added by a
   relay agent toward a server or added by a server toward a relay
   agent, because they are only transported within operator networks and
   considered less vulnerable.  Communication between a server and a
   relay agent, and communications between relay agents, may be secured
   through the use of IPsec, as described in section 21.1 in [RFC3315].

   The security mechanisms specified in this document achieves the
   DHCPv6 authentication and encryption based on the sender's public key
   certificate.  We introduce two new DHCPv6 messages: Encrypted-Query
   message and Encrypted-Response message and four new DHCPv6 options:
   certificate option, signature option, timestamp option and encrypted-
   message option for the DHCPv6 authentication and encryption.  The
   certificate option is used for the DHCPv6 authentication.  It also
   integrates signature option for the integrity check and timestamps
   option for anti-replay protection.  The Encryption-Query message,
   Encryption-Response message, and encrypted-message option are used
   for the DHCPv6 encryption.

2.  Requirements Language and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119] when they



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   appear in ALL CAPS.  When these words are not in ALL CAPS (such as
   "should" or "Should"), they have their usual English meanings, and
   are not to be interpreted as [RFC2119] key words.

3.  Terminology

   This section defines terminology specific to secure DHCPv6 used in
   this document.

   secure DHCPv6 client:  A node that initiates the DHCPv6 request on a
                   link to obtain the DHCPv6 configuration parameters
                   from one or more DHCPv6 servers.  The configuration
                   process is authenticated and encrypted using the
                   defined mechanisms in this document.

   secure DHCPv6 server:  A node that responds to requests from clients
                   using the authentication and encryption mechanism
                   defined in this document.

4.  Security Issues of DHCPv6

   DHCPv6 is a client/server protocol that provides managed
   configuration of devices.  It enables a DHCPv6 server to
   automatically configure relevant network parameters on clients.  The
   basic DHCPv6 specification [RFC3315] defines security mechanisms, but
   they have significant flaws and can be improved

   The basic DHCPv6 specifications can optionally authenticate the
   origin of message and validate the integrity of messages using an
   authentication option with a symmetric key pair.  [RFC3315] relies on
   pre-established secret keys.  For any kind of meaningful security,
   each DHCPv6 client would need to be configured with its own secret
   key; [RFC3315] provides no mechanism for doing this.

   For the out of band approach, operators can set up a key database for
   both servers and clients from which the client obtains a key before
   running DHCPv6.  Manual key distribution runs counter to the goal of
   minimizing the configuration data needed at each host.

   [RFC3315] provides an additional mechanism for preventing off-network
   timing attacks using the Reconfigure message: the Reconfigure Key
   authentication method.  However, this method provides little message
   integrity or source integrity check, and it protects only the
   Reconfigure message.  This key is transmitted in plaintext.

   In addition, the current DHCPv6 messages are still transmitted in
   clear text and the privacy information within the DHCPv6 message is
   not protected from passive attack, such as pervasive monitoring.  The



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   IETF has expressed strong agreement that PM is an attack that needs
   to be mitigated where possible in [RFC7258].

   In comparison, the security mechanism defined in this document
   provides the authentication and encryption mechanism based on the
   public key certificates on the client or server.  The DHCPv6
   authentication can protect DHCPv6 from active attack, such as
   spoofing attack.  And the DHCPv6 encryption defends against passive
   attack, such as pervasive monitoring attack.

5.  secure DHCPv6 overview

5.1.  Solution Overview

   This solution provides the authentication and encryption mechanisms
   based on the public certificates of the DHCPv6 client and server.
   Before the standard DHCPv6 configuration process, the Information-
   request and Reply messages are exchanged to select one authenticated
   DHCPv6 server.  The following DHCPv6 configuration process is
   encrypted to avoid the privacy disclosure.  We introduce two new
   DHCPv6 messages: Encrypted-Query message, Encrypted-Response message
   and four new DHCPv6 options: encrypted-message option, certificate
   option, signature option, timestamp option.  Based on the new defined
   messages and options, the corresponding authentication and encryption
   mechanisms are proposed.

   The following figure illustrates the secure DHCPv6 procedure.  The
   DHCPv6 client first sends an Information-request message to the
   standard multicast address to all DHCPv6 servers.  The Information-
   request message is used to request the servers for server
   authentication information, without going through any address, prefix
   or non-security option assignment process.  The information-request
   is sent without client's privacy information, such as client
   identifier option to minimize information leak and increase client's
   privacy.  When receiving the Information-request message, the server
   sends the Reply message that contains the server's certificate
   option, signature option, timestamp option, and server identifier
   option.  Upon the receipt of the Reply message, the DHCPv6 client
   verifies the server's identity according to the contained server
   authentication information in Reply message.  If there are multiple
   authenticated DHCPv6 servers, the client selects one authenticated
   DHCPv6 server for the following DHCPv6 configuration process.  If
   there are no authenticated DHCPv6 servers or existing servers failed
   authentication, the client behavior is policy specific.  Depending on
   its policy, it can choose to connect repeat the server discovery
   process after certain delay or attempt to connect to a different
   network.




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   After the server's authentication, the first DHCPv6 message sent from
   client to server, such as Solicit message, contains the client's
   certificate option, signature option and timestamp option for client
   authentication.  The DHCPv6 message sent from client to server is
   encrypted with the server's public key and encapsulated into the
   encrypted-message option.  The DHCPv6 client sends the Encrypted-
   Query message to server, which carries the server identifier option
   and the encrypted-message option.  When the DHCPv6 server receives
   the Encrypted-Query message, it decrypts the message using its
   private key.  If the decrypted message contains the client's
   certificate option, signature option, timestamp option, the DHCPv6
   server verifies the client's identity according to the contained
   client authentication information.  After the client's
   authentication, the server sends the Encrypted-Response message to
   the client, which contains the encrypted-message option.  The
   encrypted-message option contains the encrypted DHCPv6 message sent
   from server to client, which is encrypted using the client's public
   key.  The message that fails client authentication, MUST be dropped.
   And the server sends the corresponding error status code to client.

           +-------------+                           +-------------+
           |DHCPv6 Client|                           |DHCPv6 Server|
           +-------------+                           +-------------+
                  |            Information-request           |
                  |----------------------------------------->|
                  |           Option Request option          |
                  |                                          |
                  |                    Reply                 |
                  |<-----------------------------------------|
                  |             certificate option           |
                  |              signature option            |
                  |              timestamp option            |
                  |         server identifier option         |
                  |                                          |
                  |            Encryption-Query              |
                  |----------------------------------------->|
                  |          encrypted-message option        |
                  |          server identifier option        |
                  |                                          |
                  |            Encryption-Response           |
                  |<-----------------------------------------|
                  |          encrypted-message option        |
                  |                                          |

                          Secure DHCPv6 Procedure

   It is worth noticing that the signature on a Secure DHCPv6 message
   can be expected to significantly increase the size of the message.



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   One example is normal DHCPv6 message length plus a 1 KB for a X.509
   certificate and signature and 256 Byte for a signature.  IPv6
   fragments [RFC2460] are highly possible.  In practise, the total
   length would be various in a large range.  Hence, deployment of
   Secure DHCPv6 should also consider the issues of IP fragment, PMTU,
   etc.  Also, if there are firewalls between secure DHCPv6 clients and
   secure DHCPv6 servers, it is RECOMMENDED that the firewalls are
   configured to pass ICMP Packet Too Big messages [RFC4443].

5.2.  New Components

   The new components of the solution specified in this document are as
   follows:

   o  Servers and clients that use certificates first generate a public/
      private key pair and then obtain a public key certificate from a
      Certificate Authority that signs the public key.  One option is
      defined to carry the certificate.

   o  A signature generated using the private key which is used by the
      receiver to verify the integrity of the DHCPv6 messages and then
      the authentication of the client/server.  Another option is
      defined to carry the signature.

   o  A timestamp that can be used to detect replayed packet.  The
      secure DHCPv6 client/server need to meet some accuracy
      requirements and be synced to global time, while the timestamp
      checking mechanism allows a configurable time value for clock
      drift.  The real time provision is out of scope of this document.
      Another option is defined to carry the current time of the client/
      server.

   o  An encrypted-message option that contains the encrypted DHCPv6
      message.

   o  An Encrypted-Query message that sent from client to server.  The
      Encrypted-Query message contains the encrypted-message option and
      server identifier option.

   o  An Encrypted-Response message that sent from server to client.
      The Encrypted-Response message contains the encrypted-message
      option.

5.3.  Support for Algorithm Agility

   Hash functions are used to provide message integrity checks.  In
   order to provide a means of addressing problems that may emerge in
   the future with existing hash algorithms, as recommended in



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   [RFC4270], this document provides a mechanism for negotiating the use
   of more secure hashes in the future.

   In addition to hash algorithm agility, this document also provides a
   mechanism for signature algorithm agility.

   The support for algorithm agility in this document is mainly a
   unilateral notification mechanism from sender to recipient.  A
   recipient MAY support various algorithms simultaneously among
   different senders, and the different senders in the same
   administrative domain may be allowed to use various algorithms
   simultaneously.  It is NOT RECOMMENDED that the same sender and
   recipient use various algorithms in a single communication session.

   If the recipient does not support the algorithm used by the sender,
   it cannot authenticate the message.  In the client-to-server case,
   the server SHOULD reply with an AlgorithmNotSupported status code
   (defined in Section 10.3).  Upon receiving this status code, the
   client MAY resend the message protected with the mandatory algorithm
   (defined in Section 10.1.2).

5.4.  Imposed Additional Constraints

   The client/server that supports the identity verification MAY impose
   additional constraints for the verification.  For example, it may
   impose limits on minimum and maximum key lengths.

   Minbits  The minimum acceptable key length for public keys.  An upper
      limit MAY also be set for the amount of computation needed when
      verifying packets that use these security associations.  The
      appropriate lengths SHOULD be set according to the signature
      algorithm and also following prudent cryptographic practice.  For
      example, minimum length 1024 and upper limit 2048 may be used for
      RSA [RSA].

5.5.  Applicability

   Secure DHCPv6 is applicable in environments where physical security
   on the link is not assured and attacks on DHCPv6 are a concern, such
   as enterprise network.  In enterprise network, the security policy is
   strict and the clients are stable terminals.  The PKI model is used
   for the secure DHCPv6 deployment.  The deployment of PKI is out of
   the scope of this document.  The server is always considered to have
   connectivity to authorized CA and verify the clients' certificates.
   The client performs the server authentication locally.  The trusted
   servers' certificates or trusted CAs' certificates, which form a
   certification path [RFC5280], is deployed in the client to achieve
   the server authentication.  The DHCPv6 client obtains the trusted



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   certificates through the pre-configuration method or out of band,
   such as QR code.  After the mutual authentication, the DHCPv6 message
   is encrypted with the recipient's public key, which is contained in
   the certificate.

6.  DHCPv6 Client Behavior

   For the security DHCPv6 client, it must have a public certificate.
   The client may be pre-configured with a public key certificate, which
   is signed by a CA trusted by the server, and its corresponding
   private key.

   The DHCPv6 client multicasts the Information-request message to the
   DHCPv6 servers.  The Information-request message MUST NOT include any
   option which may reveal the private information of the client, such
   as the client identifier option.  The information-request message is
   used by the DHCPv6 client to request the server's identity
   verification information without having addresses, prefixes or any
   non-security options assigned to it.  The Option Request option in
   the Information-request message MUST contain the option code of
   certificate option, signature option, timestamp option, and server
   identifier option.

   When receiving the Reply messages from DHCPv6 servers, a secure
   DHCPv6 client SHOULD discard any DHCPv6 messages that meet any of the
   following conditions:

   o  the signature option is missing,

   o  multiple signature options are present,

   o  the certificate option is missing.

   And then the client SHOULD first check the support of the hash and
   signature algorithms that the server used.  If the check fails, the
   Reply message SHOULD be dropped.  If both hash and signature
   algorithms are supported, the client then checks the authority of
   this server.  The client SHOULD also use the same algorithms in the
   return messages.

   The client SHOULD validate the certificate according to the rules
   defined in [RFC5280].  An implementation may create a local trust
   certificate record for verified certificates in order to avoid
   repeated verification procedure in the future.  A certificate that
   finds a match in the local trust certificate list is treated as
   verified.  At this point, the client has either recognized the
   authentication of the server, or decided to drop the message.




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   The client MUST now authenticate the server by verifying the
   signature and checking timestamp (see details in Section 9.1), if
   there is a timestamp option.  The order of two procedures is left as
   an implementation decision.  It is RECOMMENDED to check timestamp
   first, because signature verification is much more computationally
   expensive.

   The signature field verification MUST show that the signature has
   been calculated as specified in Section 10.1.2.  Only the messages
   that get through both the signature verification and timestamp check
   (if there is a timestamp option) are accepted.  Reply message that
   does not pass the above tests MUST be discarded.

   If there are multiple authenticated DHCPv6 servers, the client
   selects one DHCPv6 server for the following network parameters
   configuration.  If there are no authenticated DHCPv6 servers or
   existing servers failed authentication, the client behavior is policy
   specific.  Depending on its policy, it can choose to connect using
   plain, unencrypted DHCPv6, repeat the server discovery process after
   certain delay or attempt to connect to a different network.  The
   client MUST NOT conduct the server discovery process immediately to
   avoid the packet storm.

   Once the server has been authenticated, the DHCPv6 client sends the
   Encrypted-Query message to the DHCPv6 server.  The Encrypted-Query
   message is constructed with the encrypted-message option, which MUST
   be constructed as explained in Section 10.1.4, and server identifier
   option.  The encrypted-message option contains the DHCPv6 message
   that is encrypted using the selected server's public key.  The server
   identifier option is externally visible to avoid extra of decryption
   cost by those unselected servers.

   The information for client authentication is contained in the
   Solicit/Information-request message, which is encrypted and then
   encapsulated into the Encrypted-Query message to avoid client privacy
   disclosure.  The Solicit/Information-request message MUST contain the
   certificate option, which MUST be constructed as explained in
   Section 10.1.1.  In addition, one and only one signature option MUST
   be contained, which MUST be constructed as explained in
   Section 10.1.2.  It protects the message header and all DHCPv6
   options except for the Authentication Option.  One and only one
   Timestamp option, which MUST be constructed as explained in
   Section 10.1.3.  The Timestamp field SHOULD be set to the current
   time, according to sender's real time clock.

   For the received Encrypted-Response message, the client extracts the
   encrypted-message option and decrypts it using its private key to
   obtain the original DHCPv6 message.  Then it handles the message as



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   per [RFC3315].  If the client fails to get the proper parameters from
   the chosen server, it sends the Encrypted-Query message to another
   authenticated server for parameters configuration until the client
   obtains the proper parameters.

   When the client receives a Reply message with an error status code,
   the error status code indicates the failure reason on the server
   side.  According to the received status code, the client MAY take
   follow-up action:

   o  Upon receiving an AlgorithmNotSupported error status code, the
      client SHOULD resend the message protected with one of the
      mandatory algorithms.

   o  Upon receiving an AuthenticationFail error status code, the client
      is not able to build up the secure communication with the
      recipient.  However, there may be other DHCPv6 servers available
      that successfully complete authentication.  The client MAY use the
      AuthenticationFail as a hint and switch to other public key
      certificate if it has another one; but otherwise treat the message
      containing the status code as if it had not been received.  But it
      SHOULD NOT retry with the same certificate.  However, if the
      client decides to retransmit using the same certificate after
      receiving AuthenticationFail, it MUST NOT retransmit immediately
      and MUST follow normal retransmission routines defined in
      [RFC3315].

   o  Upon receiving a TimestampFail error status code, the client MAY
      resend the message with an adjusted timestamp according to the
      returned clock from the DHCPv6 server.  The client SHOULD NOT
      change its own clock, but only compute an offset for the
      communication session.

   o  Upon receiving a SignatureFail error status code, the client MAY
      resend the message following normal retransmission routines
      defined in [RFC3315].

7.  DHCPv6 Server Behavior

   For the secure DHCPv6 server, it also MUST have a public certificate.
   The server may be pre-configured a public key certificate, which is
   signed by a CA trusted by the server, and its corresponding private
   key.

   When the DHCPv6 server receives the Information-request message and
   the contained Option Request option informs the request for the
   server authentication information, it replies the Reply message to
   the client.  The reply message MUST contain the requested certificate



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   option, which MUST be constructed as explained in Section 10.1.1.  In
   addition, the Reply message MUST contain one and only one Signature
   option, which MUST be constructed as explained in Section 10.1.2.  It
   protects the message header and all DHCPv6 options except for the
   Authentication Option.  Besides, the Reply message SHOULD contain one
   and only one Timestamp option, which MUST be constructed as explained
   in Section 10.1.3.  The Timestamp field SHOULD be set to the current
   time, according to server's real time clock.

   Upon the receipt of Encrypted-Query message, the server checks the
   server identifier option.  It decrypts the encrypted-message option
   using its private key if it is the target server.  The DHCPv6 server
   drops the message that is not for it, thus not paying cost to decrypt
   the message.

   If the decrypted message is Solicit/Information-request message, the
   secure DHCPv6 server SHOULD discard the received message that meet
   any of the following conditions:

   o  the signature option is missing,

   o  multiple signature options are present,

   o  the certificate option is missing.

   In such failure, the server SHOULD reply an UnspecFail (value 1,
   [RFC3315]) error status code.

   The server SHOULD first check the support of the hash and signature
   algorithms that the client used.  If the check fails, the server
   SHOULD reply with an AlgorithmNotSupported error status code, defined
   in Section 10.3, back to the client.  If both hash and signature
   algorithms are supported, the server then checks the authority of
   this client.

   If a certificate option is provided, the server SHOULD validate the
   certificate according to the rules defined in [RFC5280].  An
   implementation may create a local trust certificate record for
   verified certificates in order to avoid repeated verification
   procedure in the future.  A certificate that finds a match in the
   local trust certificate list is treated as verified.

   The message that fails certificate validation, MUST be dropped.  In
   such failure, the DHCPv6 server SHOULD reply an AuthenticationFail
   error status code, defined in Section 10.3, back to the client.  At
   this point, the server has either recognized the authentication of
   the client, or decided to drop the message.




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   If the server does not send the timestamp option, the client ignores
   the timestamp check and verifies the signature.  If there is a
   timestamp option, the server MUST now authenticate the client by
   verifying the signature and checking timestamp (see details in
   Section 9.1).  The order of two procedures is left as an
   implementation decision.  It is RECOMMENDED to check timestamp first,
   because signature verification is much more computationally
   expensive.  Depending on server's local policy, the message without a
   Timestamp option MAY be acceptable or rejected.  If the server
   rejects such a message, a TimestampFail error status code, defined in
   Section 10.3, should be sent back to the client.  The reply message
   that carries the TimestampFail error status code SHOULD carry a
   timestamp option, which indicates the server's clock for the client
   to use.

   The signature field verification MUST show that the signature has
   been calculated as specified in Section 10.1.2.  Only the clients
   that get through both the signature verification and timestamp check
   (if there is a Timestamp option) are accepted as authenticated
   clients and continue to be handled their message as defined in
   [RFC3315].  Clients that do not pass the above tests MUST be treated
   as unauthenticated clients.  The DHCPv6 server SHOULD reply a
   SignatureFail error status code, defined in Section 10.3, for the
   signature verification failure; or a TimestampFail error status code,
   defined in Section 10.3, for the timestamp check failure, back to the
   client.

   Once the client has been authenticated, the DHCPv6 server sends the
   Encrypted-response message to the DHCPv6 client.  The Encrypted-
   response message contains the encrypted-message option, which MUST be
   constructed as explained in Section 10.1.4.  The encrypted-message
   option contains the encrypted DHCPv6 message that is encrypted using
   the authenticated client's public key.

8.  Relay Agent Behavior

   When a DHCPv6 relay agent receives an Encrypted-query or Encrypted-
   response message, it may not recognize this message.  The unknown
   messages MUST be forwarded as describes in [RFC7283].

   When a DHCPv6 relay agent recognizes the Encrypted-query and
   Encrypted-response messages, it forwards the message according to
   section 20 of [RFC3315].  There is nothing more the relay agents have
   to do, it neither needs to verify the messages from client or server,
   nor add any secure DHCPv6 options.  Actually, by definition in this
   document, relay agents SHOULD NOT add any secure DHCPv6 options.





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   Relay-forward and Relay-reply messages MUST NOT contain any
   additional certificate option or signature Option or timestamp
   Option, aside from those present in the innermost encapsulated
   messages from the client or server.

9.  Processing Rules

9.1.  Timestamp Check

   In order to check the Timestamp option, defined in Section 10.1.3,
   recipients SHOULD be configured with an allowed timestamp Delta
   value, a "fuzz factor" for comparisons, and an allowed clock drift
   parameter.  The recommended default value for the allowed Delta is
   300 seconds (5 minutes); for fuzz factor 1 second; and for clock
   drift, 0.01 second.

   Note: the Timestamp mechanism is based on the assumption that
   communication peers have roughly synchronized clocks, with certain
   allowed clock drift.  So, accurate clock is not necessary.  If one
   has a clock too far from the current time, the timestamp mechanism
   would not work.

   To facilitate timestamp checking, each recipient SHOULD store the
   following information for each sender, from which at least one
   accepted secure DHCPv6 message is successfully verified (for both
   timestamp check and signature verification):

   o  The receive time of the last received and accepted DHCPv6 message.
      This is called RDlast.

   o  The timestamp in the last received and accepted DHCPv6 message.
      This is called TSlast.

   A verified (for both timestamp check and signature verification)
   secure DHCPv6 message initiates the update of the above variables in
   the recipient's record.

   Recipients MUST check the Timestamp field as follows:

   o  When a message is received from a new peer (i.e., one that is not
      stored in the cache), the received timestamp, TSnew, is checked,
      and the message is accepted if the timestamp is recent enough to
      the reception time of the packet, RDnew:

         -Delta < (RDnew - TSnew) < +Delta

      After the signature verification also succeeds, the RDnew and
      TSnew values SHOULD be stored in the cache as RDlast and TSlast.



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   o  When a message is received from a known peer (i.e., one that
      already has an entry in the cache), the timestamp is checked
      against the previously received Secure DHCPv6 message:

         TSnew + fuzz > TSlast + (RDnew - RDlast) x (1 - drift) - fuzz

      If this inequality does not hold or RDnew < RDlast, the recipient
      SHOULD silently discard the message.  If, on the other hand, the
      inequality holds, the recipient SHOULD process the message.

      Moreover, if the above inequality holds and TSnew > TSlast, the
      recipient SHOULD update RDlast and TSlast after the signature
      verification also successes.  Otherwise, the recipient MUST NOT
      update RDlast or TSlast.

   An implementation MAY use some mechanism such as a timestamp cache to
   strengthen resistance to replay attacks.  When there is a very large
   number of nodes on the same link, or when a cache filling attack is
   in progress, it is possible that the cache holding the most recent
   timestamp per sender will become full.  In this case, the node MUST
   remove some entries from the cache or refuse some new requested
   entries.  The specific policy as to which entries are preferred over
   others is left as an implementation decision.

   An implementation MAY statefully record the latest timestamps from
   senders.  In such implementation, the timestamps MUST be strictly
   monotonously increasing.  This is reasonable given that DHCPv6
   messages are rarely misordered.

10.  Extensions for Secure DHCPv6

   This section describes the extensions to DHCPv6.  Five new DHCPv6
   options, two new DHCPv6 messages and five status codes are defined.

10.1.  New DHCPv6 Options

10.1.1.  Certificate Option

   The certificate option carries the public key certificate of the
   client/server.  The format of the certificate option is described as
   follows:










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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      OPTION_CERTIFICATE       |         option-len            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   .                    Certificate (variable length)              .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   option-code    OPTION_CERTIFICATE (TBA1).

   option-len     Length of certificate in octets.

   Certificate    A variable-length field containing certificate. The
                  encoding of certificate and certificate data MUST
                  be in format as defined in Section 3.6, [RFC7296].
                  The support of X.509 certificate - Signature (4)
                  is mandatory.

10.1.2.  Signature Option

   The signature option allows a signature that is signed by the private
   key to be attached to a DHCPv6 message.  The signature option could
   be any place within the DHCPv6 message while it is logically created
   after the entire DHCPv6 header and options, except for the
   Authentication Option.  It protects the entire DHCPv6 header and
   options, including itself, except for the Authentication Option.  The
   format of the Signature option is described as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     OPTION_SIGNATURE          |        option-len             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     HA-id     |     SA-id     |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                                                               |
   .                    Signature (variable length)                .
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   option-code    OPTION_SIGNATURE (TBA2).

   option-len     2 + Length of Signature field in octets.

   HA-id          Hash Algorithm id. The hash algorithm is used for
                  computing the signature result. This design is



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                  adopted in order to provide hash algorithm agility.
                  The value is from the Hash Algorithm for Secure
                  DHCPv6 registry in IANA. The support of SHA-256 is
                  mandatory. A registry of the initial assigned values
                  is defined in Section 8.

   SA-id          Signature Algorithm id. The signature algorithm is
                  used for computing the signature result. This
                  design is adopted in order to provide signature
                  algorithm agility. The value is from the Signature
                  Algorithm for Secure DHCPv6 registry in IANA. The
                  support of RSASSA-PKCS1-v1_5 is mandatory. A
                  registry of the initial assigned values is defined
                  in Section 8.

   Signature      A variable-length field containing a digital
                  signature. The signature value is computed with
                  the hash algorithm and the signature algorithm,
                  as described in HA-id and SA-id. The signature
                  constructed by using the sender's private key
                  protects the following sequence of octets:

                  1. The DHCPv6 message header.

                  2. All DHCPv6 options including the Signature
                  option (fill the signature field with zeroes)
                  except for the Authentication Option.

                  The signature field MUST be padded, with all 0, to
                  the next octet boundary if its size is not a
                  multiple of 8 bits. The padding length depends on
                  the signature algorithm, which is indicated in the
                  SA-id field.

   Note: if both signature and authentication option are present,
   signature option does not protect the Authentication Option.  It
   allows the Authentication Option be created after signature has been
   calculated and filled with the valid signature.  It is because both
   options need to apply hash algorithm to whole message, so there must
   be a clear order and there could be only one last-created option.
   changing auth option, the authors chose not include authentication
   option in the signature.

10.1.3.  Timestamp Option

   The Timestamp option carries the current time on the sender.  It adds
   the anti-replay protection to the DHCPv6 messages.  It is optional.




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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     OPTION_TIMESTAMP          |        option-len             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                     Timestamp (64-bit)                        |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   option-code    OPTION_TIMESTAMP (TBA3).

   option-len     8, in octets.

   Timestamp      The current time of day (SeND-format timestamp
                  in UTC (Coordinated Universal Time). It can reduce
                  the danger of replay attacks.

10.1.4.  Encrypted-message Option

   The encrypted-message option carries the encrypted DHCPv6 message
   with the recipient's public key.

   The format of the encrypted-message option is:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          option-code          |           option-len          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                  encrypted DHCPv6 message                     .
     .                       (variable)                              .
     .                                                               .
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 1: encrypted-message Option Format

   option-code  OPTION_ENCRYPTED_MSG (TBA4).

   option-len  Length of the encrypted DHCPv6 message.

   encrypted DHCPv6 message  A variable length field containing the
      encrypted DHCPv6 message sent by the client or the server.  In
      Encrypted-Query message, it contains encrypted DHCPv6 message sent
      by a client.  In Encrypted-response message, it contains encrypted
      DHCPv6 message sent by a server.



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10.2.  New DHCPv6 Messages

10.2.1.  Encrypted-Query Message

   The Encrypted-Query message is sent from DHCPv6 client to DHCPv6
   server, which contains the server identifier option and encrypted-
   message option.

   The format of the Encrypted-Query message is:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    msg-type   |               transaction-id                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     .                             DUID                              .
     |                           (variable)                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                      encrypted-message option                 .
     .                           (variable)                          .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 2: The format of Encrypted-Query Message

   msg-type        ENCRYPTED-QUERY (TBA5)

   transaction-id  The transaction ID for this message exchange.

   DUID            The DUID for the server.

   encrypted-message option  The encrypted DHCPv6 message.

10.2.2.  Encrypted-Response Message

   The Encrypted-Response message is sent from DHCPv6 server to DHCPv6
   client, which contains the encrypted-message option.

   The format of the Encrypted-Response message is:











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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    msg-type   |               transaction-id                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     .                      encrypted-message option                 .
     .                           (variable)                          .
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 3: The format of Encrypted-Response Message

   msg-type        ENCRYPTED-RESPONSE (TBA6).

   transaction-id  The transaction ID for this message exchange.

   encrypted-message option  The encrypted DHCPv6 message.

10.3.  Status Codes

   The following new status codes, see Section 5.4 of [RFC3315] are
   defined.

   o  AlgorithmNotSupported (TBD7): indicates that the DHCPv6 server
      does not support algorithms that sender used.

   o  AuthenticationFail (TBD8): indicates that the DHCPv6 client fails
      authentication check.

   o  TimestampFail (TBD9): indicates the message from DHCPv6 client
      fails the timestamp check.

   o  SignatureFail (TBD10): indicates the message from DHCPv6 client
      fails the signature check.

11.  Security Considerations

   This document provides the authentication and encryption mechanisms
   for DHCPv6.

   [RFC6273] has analyzed possible threats to the hash algorithms used
   in SEND.  Since the Secure DHCPv6 defined in this document uses the
   same hash algorithms in similar way to SEND, analysis results could
   be applied as well: current attacks on hash functions do not
   constitute any practical threat to the digital signatures used in the
   signature algorithm in the Secure DHCPv6.




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   A server, whose local policy accepts messages without a Timestamp
   option, may have to face the risk of replay attacks.

   A window of vulnerability for replay attacks exists until the
   timestamp expires.  Secure DHCPv6 nodes are protected against replay
   attacks as long as they cache the state created by the message
   containing the timestamp.  The cached state allows the node to
   protect itself against replayed messages.  However, once the node
   flushes the state for whatever reason, an attacker can re-create the
   state by replaying an old message while the timestamp is still valid.
   In addition, the effectiveness of timestamps is largely dependent
   upon the accuracy of synchronization between communicating nodes.
   However, how the two communicating nodes can be synchronized is out
   of scope of this work.

   Attacks against time synchronization protocols such as NTP [RFC5905]
   may cause Secure DHCPv6 nodes to have an incorrect timestamp value.
   This can be used to launch replay attacks, even outside the normal
   window of vulnerability.  To protect against these attacks, it is
   recommended that Secure DHCPv6 nodes keep independently maintained
   clocks or apply suitable security measures for the time
   synchronization protocols.

12.  IANA Considerations

   This document defines five new DHCPv6 [RFC3315] options.  The IANA is
   requested to assign values for these five options from the DHCPv6
   Option Codes table of the DHCPv6 Parameters registry maintained in
   http://www.iana.org/assignments/dhcpv6-parameters.  The five options
   are:

      The Certificate Option (TBA1), described in Section 10.1.1.

      The Signature Option (TBA2), described in Section 10.1.2.

      The Timestamp Option (TBA3),described in Section 10.1.3.

      The Encrypted-message Option (TBA4), described in Section 10.1.4.

   The IANA is also requested to assign value for these two messages
   from the DHCPv6 Message Types table of the DHCPv6 Parameters registry
   maintained in http://www.iana.org/assignments/dhcpv6-parameters.  The
   two messages are:

      The Encrypted-Query Message (TBA5), described in Section 10.2.1.

      The Encrypted-Response Message (TBA6), described in
      Section 10.2.2.



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   The IANA is also requested to add two new registry tables to the
   DHCPv6 Parameters registry maintained in
   http://www.iana.org/assignments/dhcpv6-parameters.  The two tables
   are the Hash Algorithm for Secure DHCPv6 table and the Signature
   Algorithm for Secure DHCPv6 table.

   Initial values for these registries are given below.  Future
   assignments are to be made through Standards Action [RFC5226].
   Assignments for each registry consist of a name, a value and a RFC
   number where the registry is defined.

   Hash Algorithm for Secure DHCPv6.  The values in this table are 8-bit
   unsigned integers.  The following initial values are assigned for
   Hash Algorithm for Secure DHCPv6 in this document:

             Name        |  Value  |  RFCs
      -------------------+---------+--------------
            SHA-256      |   0x01  | this document
            SHA-512      |   0x02  | this document

   Signature Algorithm for Secure DHCPv6.  The values in this table are
   8-bit unsigned integers.  The following initial values are assigned
   for Signature Algorithm for Secure DHCPv6 in this document:

             Name        |  Value  |  RFCs
      -------------------+---------+--------------
       RSASSA-PKCS1-v1_5 |   0x01  | this document

   IANA is requested to assign the following new DHCPv6 Status Codes,
   defined in Section 10.3, in the DHCPv6 Parameters registry maintained
   in http://www.iana.org/assignments/dhcpv6-parameters:

         Code  |           Name        |   Reference
      ---------+-----------------------+--------------
         TBD7  | AlgorithmNotSupported | this document
         TBD8  |   AuthenticationFail  | this document
         TBD9  |     TimestampFail     | this document
         TBD10 |     SignatureFail     | this document

13.  Acknowledgements

   The authors would like to thank Tomek Mrugalski, Bernie Volz, Randy
   Bush, Yiu Lee, Jianping Wu, Sean Shen, Ralph Droms, Jari Arkko, Sean
   Turner, Stephen Farrell, Christian Huitema, Stephen Kent, Thomas
   Huth, David Schumacher, Francis Dupont, Gang Chen, Suresh Krishnan,
   Fred Templin, Robert Elz, Nico Williams, Erik Kline, Alan DeKok,
   Bernard Aboba, Sam Hartman, Qi Sun, Zilong Liu, and other members of
   the IETF DHC working group for their valuable comments.



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   This document was produced using the xml2rfc tool [RFC2629].

14.  References

14.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <http://www.rfc-editor.org/info/rfc2460>.

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <http://www.rfc-editor.org/info/rfc3315>.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", RFC 4443,
              DOI 10.17487/RFC4443, March 2006,
              <http://www.rfc-editor.org/info/rfc4443>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <http://www.rfc-editor.org/info/rfc5280>.

   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
              <http://www.rfc-editor.org/info/rfc5905>.

   [RFC7283]  Cui, Y., Sun, Q., and T. Lemon, "Handling Unknown DHCPv6
              Messages", RFC 7283, DOI 10.17487/RFC7283, July 2014,
              <http://www.rfc-editor.org/info/rfc7283>.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
              2014, <http://www.rfc-editor.org/info/rfc7296>.






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14.2.  Informative References

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              DOI 10.17487/RFC2629, June 1999,
              <http://www.rfc-editor.org/info/rfc2629>.

   [RFC4270]  Hoffman, P. and B. Schneier, "Attacks on Cryptographic
              Hashes in Internet Protocols", RFC 4270,
              DOI 10.17487/RFC4270, November 2005,
              <http://www.rfc-editor.org/info/rfc4270>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC6273]  Kukec, A., Krishnan, S., and S. Jiang, "The Secure
              Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273,
              DOI 10.17487/RFC6273, June 2011,
              <http://www.rfc-editor.org/info/rfc6273>.

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <http://www.rfc-editor.org/info/rfc7258>.

   [RSA]      RSA Laboratories, "RSA Encryption Standard, Version 2.1,
              PKCS 1", November 2002.

Authors' Addresses

   Sheng Jiang
   Huawei Technologies Co., Ltd
   Q14, Huawei Campus, No.156 Beiqing Road
   Hai-Dian District, Beijing, 100095
   CN

   Email: jiangsheng@huawei.com


   Lishan Li
   Tsinghua University
   Beijing  100084
   P.R.China

   Phone: +86-15201441862
   Email: lilishan9248@126.com





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   Yong Cui
   Tsinghua University
   Beijing  100084
   P.R.China

   Phone: +86-10-6260-3059
   Email: yong@csnet1.cs.tsinghua.edu.cn


   Tatuya Jinmei
   Infoblox Inc.
   3111 Coronado Drive
   Santa Clara, CA
   US

   Email: jinmei@wide.ad.jp


   Ted Lemon
   Nominum, Inc.
   2000 Seaport Blvd
   Redwood City, CA  94063
   USA

   Phone: +1-650-381-6000
   Email: Ted.Lemon@nominum.com


   Dacheng Zhang
   Beijing
   CN

   Email: dacheng.zhang@gmail.com


















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