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DNS Extensions                                                 H. Rafiee
INTERNET-DRAFT
Updates RFC 2845 (if approved)                                 C. Meinel
Intended Status: Standards Track                Hasso Plattner Institute
Expires: November 8, 2015                                    May 8, 2015


CGA-TSIG/e: Algorithms for Secure DNS Authentication and Optional DNS
Confidentiality
                 <draft-rafiee-intarea-cga-tsig-12.txt>

Abstract

   This document describes a new mechanism for secure DNS authentication
   and a possible mechanism for DNS data confidentiality in various
   scenarios especially DNS resolvers. It also focuses on reducing human
   interaction during secure authentication and DNS message encryption.
   This document supports both IPv4 and IPv6 enabled networks.



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 November 8, 2015.





Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors. All rights reserved. This document is subject to
   BCP 78 and the IETF Trust's Legal Provisions Relating to IETF
   Documents (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


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   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.  Changes to this document [only for authors/editors]  . . . . .  4
   2.  Introduction   . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Functional description of CGA-TSIG/e Mechanisms  . . . . .  5
   3.  Conventions Used In This Document  . . . . . . . . . . . . . .  7
   4.  Algorithm Overview   . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  CGA-TSIG   . . . . . . . . . . . . . . . . . . . . . . . .  8
       4.1.1.  The CGA-TSIG DATA Structure    . . . . . . . . . . . .  8
       4.1.2.  CGA-TSIG DATA    . . . . . . . . . . . . . . . . . . .  9
         4.1.2.1.  IPv6 Specific Data   . . . . . . . . . . . . . . . 10
         4.1.2.2.  IPv4 Specific Data   . . . . . . . . . . . . . . . 10
       4.1.3.  Generation of CGA-TSIG DATA    . . . . . . . . . . . . 10
   5.  General Verification Steps   . . . . . . . . . . . . . . . . . 11
   6.  CGA-TSIG/CGA-TSIGe Use Case Scenarios  . . . . . . . . . . . . 13
     6.1.  DNS Resolving Scenario (stub to recursive)   . . . . . . . 13
       6.1.1.  Client Verification Process (CGA-TSIGe only)   . . . . 14
       6.1.2.  Resolver Verification Process  . . . . . . . . . . . . 14
     6.2.  DNS Resolving Scenario (Authoritative NS to Recursive NS)  15
   7.  SeND Is Not Supported (IPv6 only)  . . . . . . . . . . . . . . 16
   8.  CGA-TSIG/e Attack Protections  . . . . . . . . . . . . . . . . 16
     8.1.  IP Spoofing    . . . . . . . . . . . . . . . . . . . . . . 16
     8.2.  Resolver Configuration Attack  . . . . . . . . . . . . . . 17
     8.3.  Exposing A Shared Secret   . . . . . . . . . . . . . . . . 17
     8.4.  Replay Attack    . . . . . . . . . . . . . . . . . . . . . 17
     8.5.  Data Confidentiality   . . . . . . . . . . . . . . . . . . 17
   9.  Update to TSIG Specification   . . . . . . . . . . . . . . . . 17
   10.  Security Considerations . . . . . . . . . . . . . . . . . . . 18
   11.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
   12.  Appendix  . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     12.1.  A Sample Key Storage For CGA-TSIG   . . . . . . . . . . . 19
     12.2.  Stored parameters in the node   . . . . . . . . . . . . . 19
     12.3.  CGA Generation Script   . . . . . . . . . . . . . . . . . 20
     12.4.  CGA-TSIGe (DNS privacy)   . . . . . . . . . . . . . . . . 21
       12.4.1.  The CGA-TSIGe DATA Structure    . . . . . . . . . . . 21
         12.4.1.1.  Public Key Request  . . . . . . . . . . . . . . . 22
         12.4.1.2.  Public Key Response   . . . . . . . . . . . . . . 22
       12.4.2.  Generation of CGA-TSIGe DATA    . . . . . . . . . . . 23
         12.4.2.1.  IPv6 Specifics  . . . . . . . . . . . . . . . . . 23
           12.4.2.1.1.  Generation of Query Request Message   . . . . 23
           12.4.2.1.2.  Generation of Query Response Message  . . . . 26
         12.4.2.2.  IPv4 Scenario   . . . . . . . . . . . . . . . . . 26
           12.4.2.2.1.  Generation of Query Request Message   . . . . 27
           12.4.2.2.2.  Generation of Query Response Message  . . . . 27
       12.4.3.  Process of Public Key Response Message  . . . . . . . 27
         12.4.3.1.  IPv6 only Scenarios   . . . . . . . . . . . . . . 27


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         12.4.3.2.  IPv4 only Scenarios   . . . . . . . . . . . . . . 28
       12.4.4.  Process of Encrypted Query Request Message  . . . . . 28
       12.4.5.  Process of Encrypted Query Response Message   . . . . 28
     12.5.  Other Optional Use case scenarios   . . . . . . . . . . . 28
       12.5.1.  The FQDN Or PTR Update (IPv6 only)  . . . . . . . . . 29
         12.5.1.1.  Verification Process  . . . . . . . . . . . . . . 29
       12.5.2.  DNS Zone Transfer   . . . . . . . . . . . . . . . . . 30
         12.5.2.1.  Verification Process  . . . . . . . . . . . . . . 31
   13.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 31
   14.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 31
     14.1.  Normative . . . . . . . . . . . . . . . . . . . . . . . . 31
     14.2.  Informative . . . . . . . . . . . . . . . . . . . . . . . 32
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34










































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1.  Changes to this document [only for authors/editors]

   This section should be removed before any publication.

   - Introduction section: added explanation about secure authentication
   and the exact focus of this document. updated explanation to DNS
   privacy problems and added a reference to DNS privacy problem
   statement document, removed problem statement section since it is
   already mentioned in introduction. Removed terminology and added
   reference to existing DNS terminology draft

   - Overview of CGA-TSIG algorithm section: explained different
   operations via questions and answers to keep the readers focus on the
   main functions.

   - Appendix section: moved DNS privacy to appendix section. moved FQDN
   and PTR scenario to appendix section in other supported scenario.

   - CGA-TSIG section: removed IP tag, old signature and old public key.
   Removed the text about DNS update

   - CGA-TSIGe section: removed IP tag, old signature and old public
   key.


2.  Introduction

   Authentication is a key feature that protects both DNS server and
   client from several attacks ? identity spoofing, unauthorized update
   of DNS records, phishing, etc. This is especially critical in
   different DNS scenarios. This draft only focuses on three DNS
   scenarios that are during Dynamic DNS (DDNS) [RFC2136] of updating
   PTR and Fully Qualified Domain Name (FQDN) resource records (RRs) and
   any other values on DNS Servers , DNS zone update ([AI]XFR) for
   multiple DNS servers (authenticating two DNS servers), and during
   authentication of recursive DNS servers on clients.

   TSIG [RFC2845] is based on MAC authentication. It uses one way
   hashing and a shared secret for the authentication of DNS messages
   especially during DDNS. In this mechanism there need to be a shared
   secret shared among all clients and DNS servers that want to process
   DDNS. The configuration and sharing this shared secret among all
   these nodes are manual. If the shared secret is known to attacker,
   then the manual step for sharing this shared secret should be
   repeated. TSIG is also unable to protect a node against some
   well-known DNS attacks. One example is DNS amplification attack.

   To address the above problems and securing the last miles of the
   internet where DNSSEC might not be able to protect it easily, this
   document introduces CGA-TSIG algorithm. The purpose of CGA-TSIG is
   automation (minimizing human interaction) and secure authentication.



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   Besides, DNS messages might contain important data which might allow
   an attacker to analyze the behavior of users in a network or pursue
   further attacks. These data might be confidential and need
   protection. There are recently a lot of concerns about DNS privacy
   and hiding the data exchanges between stub resolvers' and DNS server
   from prying eyes (either in active or passive attacks).

   In appendix of this document, the small changes that needed in
   CGA-TSIG algorithm to also consider DNS privacy is introduced and
   call this new algorithm as CGA-TSIGe. CGA-TSIGe protects a node
   against DNS privacy attacks explained in [dns-privacy]. It does this
   by providing a node with a mechanism to securely verify the DNS
   resolver (to avoid spoofed DNS messages) and encrypt the whole DNS
   message. It uses the current available Resource Records (RRs) to
   carry any parameters requires for this process. After encryption
   process, this encrypted message is encapsulated in a new DNS message
   (new DNS header is added to it) and the required parameters are added
   in the additional section of this new DNS message for decryption
   purposes in the receiver node. CGA-TSIGe uses both asymmetric and
   symmetric cryptography. Asymmetric cryptography is used for
   encrypting the 16 byte secret key. This secret key then can be used
   as a key for the symmetric encryption algorithm in order to encrypt
   the whole DNS message. This process will increase the DNS performance
   by avoiding the encryption of a large DNS message using a public key
   cryptography. Both CGA-TSIG and CGA-TSIGe support both IPv4 and IPv6
   enabled network and considered as new algorithms in the TSIG Resource
   Record (RR).


2.1.  Functional description of CGA-TSIG/e Mechanisms

   - Purpose

   1-secure authentication, 2-minimize human interaction and 3- provide
   data confidentiality required to accomplish a shared secret or key
   exchange. If only number 1 and 2 is the purpose, then the algorithm
   is called CGA-TSIG. When 1,2, and 3 all together is the purpose, then
   the algorithm is called CGA-TSIGe (it is explained in Appendix).

   Since this protocol is added to "Other Data" section of TSIG RR, when
   a DNS client or server does not support CGA-TSIG, it easily ignores
   CGA-TSIG option without returning any error and returns back to
   compatibility mode, i.e., using DNS server without encryption.



   - How client and server receives the IP address/hash of public key of
   DNS server?

   There are two possibilities: 1- From a DNS option in router
   advertisement message [RFC6106] 2- From a DHCP/v6 server protected
   via SAVI approaches [savi-dhcp] or any monitoring node



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   - What if the network is not trusted (e.g. untrusted DHCP server,
   untrusted router, untrusted DNS server)

   This is only applicable for resolver scenario. User can easily
   introduce the IP address of trusted resolver (or select home resolver
   from the list of trusted resolvers in its computer). For automation
   purpose, the implementation SHOULD provide a possibility to store a
   short list of trusted resolvers so that the client can pick one of
   them.



   - How CGA-TSIG/e Prevents Spoofing and authenticate DNS servers or
   clients (depends on scenario)

   In the IPv6 scenario, the algorithms use Cryptographically Generated
   Addresses (CGA) [RFC3972] or Secure Simple Addressing Scheme for IPv6
   Autoconfiguration (SSAS) [4, 5]. Both CGA and SSAS provide the nodes
   with the necessary proof of IP address ownership by providing a
   cryptographic binding between a host's public key and its IP address
   without the need for the introduction of infrastructure. In other
   word, by receiving any message from a DNS resolver, client can verify
   its signature and since the key is bound to the IP address, the
   client can make sure that the value is from the same resolver as it
   already received the IP address from DHCP server or an option in
   router advertisement message.

   In IPv4 scenarios, the algorithms use the hash of public key as an
   authentication approach. For example, in resolver scenario, the
   client receives the DNS resolver?s hash of (IPv4 + public key) from a
   DHCPv4 server that is protected by SAVI approaches or other
   monitoring approaches. When the client receives the key from DNS
   server it calculates the hash of (IPv4 + public key) and compare this
   value with what it received from DHCP server. If it matches, then the
   client can trust any value received from the DNS server.



   - How Client and server do key exchange in DNS privacy scenario
   (Appendix)

   Client sends an empty message and adding TSIG in additional part and
   set the algorithm to CGA-TSIGe. This message then can be sent to DNS
   server. DNS server then knows it should submit its key to client,
   sign it with its own private key.



   - In CGA-TSIGe, if the whole message is encrypted, How the DNS server
   knows how to decrypt the message



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   After a client receives the public key of DNS server in a secure
   manner (as explained in prior paragraphs), it generates a random
   number and call this number a secret key (it is similar to session
   key in TLS or SSL). It, then, encrypts the whole DNS message and
   encapsulates it in a new DNS message (that is adding new header and
   additional section). In additional section of this new DNS message,
   it includes CGA-TSIGe and all its required parameters. In other word,
   the whole encrypted messages is like a query section in new DNS
   message. Then the secret key is encrypted using the public key of DNS
   server and this message is submitted to the DNS server.

   When the DNS server receives this message, if the additional section
   includes CGA-TSIGe, then it first decrypts the secret key using
   public key cryptography and then decrypts the whole DNS message using
   this secret key and a symmetric algorithm such as AES.




3.  Conventions Used In This Document

   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 RFC 2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC 2119 significance.

   => This sign in the document should be interpreted as "change to".

   IPv6 only: this indicates that the explained approach can be used
   only in IPv6 scenario

   IPv4 only: this indicates that the explained approach can be used
   only in IPv4 scenario

   IPv4 and IPv6: This indicates that the explained approach can be used
   in both IPv4 and IPv6 scenario and there are no differences.

   | This sign in this document should be interpreted as
   ?concatenation?.

   Note: This document uses the names CGA-TSIG and CGA-TSIGe. But it
   does not mean that the algorithm in use in this document is only CGA.
   The "CGA" name was taken from the first versions of this draft and
   continued to be appeared in the latest versions of this draft. This
   draft also uses TSIG as a carrier protocol to avoid changing the
   current DNS protocol.

   The terms used in this documents are defined in [dns-terms].




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4.  Algorithm Overview

   The following section explain the CGA-TSIG (secure authentication)
   data structure in IPv4 and IPv6 scenarios. A CGA-TSIG data structure
   is an option to the TSIG Resource Record (RR).


4.1.  CGA-TSIG


4.1.1.  The CGA-TSIG DATA Structure

   The CGA-TSIG data structure SHOULD be added to the Other DATA section
   of the RDATA field in the TSIG Resource Record (RR) (see figures 1
   and 2). The DNS RRTYPE MUST be set to TSIG [RFC2845]. The RDATA
   Algorithm Name MUST be set to CGA-TSIG. The CGA-TSIG name is used
   when there is no need for DNS data confidentiality. The CGA-TSIGe
   (Please refer to Appendix) is used when all parts of a DNS message
   should be encrypted to provide data confidentiality. The Name MUST be
   set to root (.). This is the smallest possible value that can be
   used. The MAC Size MUST be set to 0 when the Algorithm Name is
   CGA-TSIG.

   A detailed explanation of the standard RDATA fields can be found in
   section 2.3 [RFC2845]. This document focuses only on the new
   structure added to the Other DATA section. These new fields are
   CGA-TSIG Len and CGA-TSIG DATA. The TSIG RR is added to an additional
   section of the DNS message.

   +---------------------------------------+
   |              Algorithm Name           |
   |               (CGA-TSIG)              |
   +---------------------------------------+
   |              Time Signed              |
   |                                       |
   +---------------------------------------+
   |                  Fudge                |
   |                                       |
   +---------------------------------------+
   |                 MAC Size              |
   |                                       |
   +---------------------------------------+
   |                   MAC                 |
   |                                       |
   +---------------------------------------+
   |               Original ID             |
   |                                       |
   +---------------------------------------+
   |                   Error               |
   |                                       |
   +---------------------------------------+
   |                Other Len              |
   |                                       |


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   +---------------------------------------+
   |               Other Data              |
   |                                       |
   +---------------------------------------+
   Figure 1:   Modified TSIG RDATA
   The CGA-TSIG DATA Field and the CGA-TSIG Len will occupy the first
   two slots of Other DATA. Figure 2 shows the layout. Any extra
   options/data should be placed after CGA-TSIG field. CGA-TSIG Len is
   the length of CGA-TSIG DATA in byte.

   +---------------------------------------+
   |             CGA-TSIG Len              |
   |              (2 bytes)                |
   +---------------------------------------+
   |             CGA-TSIG DATA             |
   |                                       |
   +---------------------------------------+
   |             Other Options             |
   |                                       |
   +---------------------------------------+
   Figure 2: Other DATA section of RDATA field

4.1.2.  CGA-TSIG DATA

   Figure 3 explains detail structure of CGA-TSIG DATA section. Fields
   that are marked (*) are different depending on IPv6 or IPv4.

   +---------------------------------------+
   |             AsyAlgorithm              |
   |              (15 bytes)               |
   +---------------------------------------+
   |                  Type *               |
   |                (u_int16_t)            |
   +---------------------------------------+
   |              Parameters Len           |
   |                (1 byte)               |
   +---------------------------------------+
   |                Parameters *           |
   |                (variable)             |
   +---------------------------------------+
   |             Signature Len             |
   |               (1 bytes)               |
   +---------------------------------------+
   |                Signature              |
   |               (variable)              |
   +---------------------------------------+
   Figure 3: structure of CGA-TSIG DATA section
   - AsyAlgorithm: Asymmetric algorithm. IANA numeric value for RSA
   algorithm 1.2.840.113549.1.1.1[RFC4055]. For ECC, IANA needs to
   define a new number.

   - Type: Name of algorithm



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   - Parameters Len: Length of parameters

   - Signature Len: Length of public key cryptography signature

   - Signature: Please refer to section 4.1.3 of this document




4.1.2.1.  IPv6 Specific Data

   For IPv6, the Type field indicates the Interface ID generation
   algorithm that is used in SeND (An Interface ID is the 64 rightmost
   bits of an IPv6 address). The field allows for future development.
   The default value for CGA is 1 and for SSAS is 2.


4.1.2.2.  IPv4 Specific Data

   For IPv4, the Type field indicates the hashing function used to
   generate the hash of (public key + IPv4). By default, it is SHA256.
   This value SHOULD be set to 1 for SHA256 and other numeric
   incremental value for other hashing algorithms. This allows for
   future hashing functions.


4.1.3.  Generation of CGA-TSIG DATA

   In order to use CGA-TSIG as an authentication approach, some of the
   parameters need to be cached during IP address generation. If no
   parameters are available in the cache, please see section 7.

   1. Obtain Require Parameters From Cache.

   For IPv6, if the Type Field above is CGA, then the parameters that
   SHOULD be cached are the modifier, algorithm type, location of the
   public/private keys and the IP addresses of the host. For IPv4, the
   location to the key pairs needs to be cached in order to generate the
   signature.

   Note: If the node is a DNS server (resolver or Authoritative Name
   Server) that does not support SeND but wants to use the CGA-TSIG
   algorithm, a script can be used to generate the CGA parameters.
   (Please refer to the section 12.2. appendix)

   2. Generate Signature

   The signature is generated by concatenation of the following values
   where Type is the 128-bit Message Type tag value. This value for CGA
   (SeND) is 0x086F CA5E 10B2 00C9 9C8C E001 6427 7C08.

   Plain text= Type | Entire DNS message (Please refer to figure 4 and
   figure 5)


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   Then the node uses its own private key obtained from the cache as
   explained in last step to sign the plain text. This signature MUST be
   added to the signature field of the CGA-TSIG DATA record. The Time
   Signed field uses the same timestamp in RDATA. This will prevent
   replay attacks by changing the signature each time a Node sends a DNS
   message. The format of DNS messages is explained in section 4.1.3
   [RFC1035].

   +-----+------+--------+
   |Type |Length|Reserved|
   |1byte|1 byte| 1 byte |
   +---------------------+
   |        Header       |
   |       12 bytes      |
   +---------------------+
   |     Zone section    |
   |   variable length   |
   +---------------------+
   |    prerequisite     |
   |   variable length   |
   +---------------------+
   |    Update section   |
   |   variable length   |
   +---------------------+
   |   Additional Data   |
   |   variable length   |
   +---------------------+
   Figure 4 DNS update message

   +-----+------+--------+
   |Type |Length|Reserved|
   |1byte|1 byte| 1 byte |
   +---------------------+
   |        Header       |
   |       12 bytes      |
   +---------------------+
   |       Question      |
   |   variable length   |
   +---------------------+
   |       Answer        |
   |   variable length   |
   +---------------------+
   |       Authority     |
   |   variable length   |
   +---------------------+
   |   Additional Data   |
   |   variable length   |
   +---------------------+
   Figure 5 DNS Query message (section 4.)

5.  General Verification Steps



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   This section explains general verification steps and can be used as a
   reference for verification in different scenarios. The modification
   of these steps is possible according the use case scenarios (next
   section).

   Sender authentication is necessary in order to prevent attackers from
   making unauthorized modifications to DNS servers through the use of
   spoofed DNS messages. The verification process uses the following
   steps:

   1. Verify The Signature (IPv4 and IPv6)

   The Signature contained in CGA-TSIG DATA should be verified. This can
   be done by retrieving the public key and signature from CGA-TSIG DATA
   and using this public key to verify the signature. If the
   verification process is successful, then execute step 2. Otherwise,
   the message should be discarded.

   2. Check The Time Signed (IPv4 and IPv6)

   The Time Signed value is obtained from TSIG RDATA and is called t(1).
   The current system time is then obtained and converted to UTC time
   and is called t(2). Fudge time is obtained from TSIG RDATA and is
   called t(fudge). If t(1) is in the range of t(2) and t(2) minus/plus
   t(fudge) (see formula 1), then step 3 will be executed. Otherwise,
   the message will be considered spoofed and discarded. The range is
   used in consideration of the delays that can occur during its
   transmission over TCP or UDP. Both times must use UTC time in order
   to avoid differences in time based on different geographical
   locations.

   (t(1) - t(fudge)) <= t(2) <=(t(1) + t(fudge))

   Formula: (1)

   3. Execute The CGA Verification (IPv6 only)

   These steps are in section 5 of [RFC3972]. If the sender of the DNS
   message uses another algorithm, instead of CGA, then this step
   becomes the verification step for that algorithm. If the verification
   process is successful, then step 6 will be executed. Otherwise the
   message will be discarded without further action.

   4. Generate The Hash of (public key | IP address) (IPv4 only)

   The DNS server retrieves the hashing Algorithm Type from the
   CGA-TSIGe DATA structure. It then uses the following concatenations.

   Digest = hash(public key | IP address of the update requester)

   Where hash is SHA256 algorithm (by default) or another algorithm
   identified in Type section of CGA-TSIG DATA structure. It then
   compares digest with the hash value available in the DNS


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   configuration. If they are the same, the Update Message should be
   processed, otherwise, go to step 5.

   5. Verify The Source IP Address (IPv6 only)

   The source IP Address of the Update requester MUST be checked against
   the one contained in the DNS configuration. If they are the same, the
   Update Message should be processed, otherwise, proceed to step 7.

   6. Verify The Public Key (IPv6 only)

   The DNS server checks whether or not the public key retrieved from
   CGA-TSIG DATA is the same as what is available in the cache where the
   public keys and IP addresses are saved. If this Public Key is not
   found in the cache, then the update will be rejected. Otherwise, when
   the Old Public Key Length is not zero go to step 8.


6.  CGA-TSIG/CGA-TSIGe Use Case Scenarios


6.1.  DNS Resolving Scenario (stub to recursive)

   A DNS query request sent by a host, such as a client or a mail
   server, does not need to generate CGA-TSIG DATA because the resolver
   responds to anonymous queries. The Resolver's response SHOULD contain
   the CGA-TSIG DATA field in order to verify him. However, the client
   needs to include the TSIG RDATA and set the Algorithm Type to
   CGA-TSIG, and it MUST set the CGA-TSIG Len to zero (0). This allows
   the resolver to include CGA-TSIG in the client.

   If the Node needs to deploy DNS data confidentiality (please refer to
   section 12.4.), then it needs to set the Algorithm Type to CGA-TSIGe
   and follows the step explained in section 12.4.2. In this particular
   scenario, the Node MUST set Message Hash in CGA-TSIGe. This allows
   the DNS server to ensure data integrity without going to the process
   of message decryption.

   In the generation of the CGA-TSIG/CGA-TSIGe for a Resolver, there is
   no need to include the IP Tag. This is because the Resolvers do not
   usually have several IP addresses so the client does not need to keep
   several IP addresses for the same resolver.

   +----------------+                        +----------------+
   |  DNS Resolver  |                        |   DNS client   |
   |                |  Ask for public key    |                |
   |                |   <------------------- |                |
   |                |      Here you are      |                |
   |                |   -------------------> |                |
   |                |                        | Verification   |
   |                |                        | explained in   |
   |                |                        | section 12.4.3  |
   |                |                        |                |


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   |                |                        | Generation of  |
   |                |                        | Query request  |
   |                |                        |set message hash|
   |                |                        |explained in    |
   |                |                        |section 12.4.2   |
   |                |   Encrypted DNS message|                |
   |                |   <------------------- |                |
   |   Verification |                        |                |
   |   explained in |                        |                |
   |   section 6.1.1|                        |                |
   |                |                        |                |
   |   DNS message  |                        |                |
   |   decryption   |                        |                |
   |   explained in |                        |                |
   |   section 12.4.4|                        |                |
   |   Encrypt Query|                        |                |
   |   response     |                        |                |
   |   explained in |                        |                |
   |   section 12.4.2|                        |                |
   |                |Encrypted Query response|                |
   |                |   -------------------> |                |
   |                |                        | Verification   |
   |                |                        | explained in   |
   |                |                        | section 6.1.2  |
   |                |                        |                |
   |                |                        | DNS message    |
   |                |                        | decryption     |
   |                |                        | explained in   |
   |                |                        | section 12.4.5  |
   +----------------+                        +----------------+
   Figure 11. DNS resolving scenario using CGA-TSIGe
   (Data confidentiality and secure authentication)

6.1.1.  Client Verification Process (CGA-TSIGe only)

   1. Retrieves Hashing Algorithm From CGA-TSIGe

   The resolver retrieves the hashing algorithm from CGA-TSIGe Type
   field.

   2. Executes Hashing Algorithm on DNS Message

   The Resolver computes the SHA algorithm on the whole DNS message. It
   compares this with the value obtained from Message Hash of CGA-TSIGe.
   If they are the same, it decrypts the message using the shared secret
   obtained from the digest_secret_key section of the Other DATA section
   of TSIG RRType.


6.1.2.  Resolver Verification Process

   When a Resolver responds to the client's query request for the first
   time, the client saves its Public Key in a file. This allows the


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   client to verify this Resolver when it changes its IP Address due to
   privacy or security concerns. The steps 2 and 3 of the verification
   process are the same as those steps explained in section 5. These
   steps are as follows:

   1. Verify The Hash of Public Key (IPv4 only)

   The client retrieves the SHA Algorithm Type from the Type section of
   CGA-TSIG/CGA-TSIGe, concatenates the following values:

   digest= hash(Resolver's Public Key | the Resolver's IP address)

   Where hash is a hash function (by default; SHA256). The client
   compares the digest with the value in its cache (received securely
   from a DHCP server or manually set by client). If they are the same,
   it stores its Public Key in its cache, and continues onto the next
   step. Otherwise the message will be discarded.

   2. Verify The Signature (IPv4 and IPv6)

   The Signature contained in CGA-TSIG/CGA-TSIGe DATA can be verified by
   retrieving the Public Key and Signature from the CGA-TSIG/CGA-TSIGe
   DATA. If the verification process is successful, continue onto step
   3, otherwise the message will be discarded.

   3. Check The Time Signed (IPv4 and IPv6)

   4. Execute The CGA Verification (IPv6 only)

   5. Verify The Source IP Address (IPv6 only)

   If the Resolver's source IP address is the same as that which is
   known for the host or the length of Old Public Key is not zero (0),
   then step 6 will be executed. Otherwise the message SHOULD be
   discarded without further action.

   6. Verify The Public Key (IPv6 only)

   The client checks whether or not the Public Key retrieved from
   CGA-TSIG/CGA-TSIGe DATA matches any Public Key that was previously
   saved in the storage where the Public Key and IP addresses of
   Resolvers are saved. If there is a match, then the message is
   processed. If not, then step 7 will be executed.


6.2.  DNS Resolving Scenario (Authoritative NS to Recursive NS)

   This verification step of Authoritative Name Server to Recursive Name
   Server is the same as that explained in section 5. In this case the
   Recursive Name Server does not need to generate CGA-TSIG DATA, but
   the Root Name Server does need to include it in order to enable the
   Recursive Name Server to verify it. The Recursive Name Server needs
   to include the TSIG RDATA and set the Algorithm Type to CGA-TSIG. It


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   MUST set the CGA-TSIG Len to zero (0). This allows the Root Name
   Server to know when to include CGA-TSIG for verification process in
   client.

   In case the node needs to use DNS data confidentiality, then it needs
   to set the Algorithm Type to CGA-TSIGe and follows the step explained
   in section 12.4.2. In this particular scenario, the Node MUST set the
   Message Hash in CGA-TSIGe. This allows the DNS server to ensure the
   data integrity of this message without going to the process of
   message decryption.


7.  SeND Is Not Supported (IPv6 only)

   In the case where there are no cache parameters available during the
   IP Address generation, there are then three scenarios that come into
   play here. In the first scenario there is the case where the sender
   of a DNS message needs to generate a key pair and generate the
   CGA-TSIG or CGA-TSIGe data structure as explained in section 4.1 or
   section 12.4. The Node SHOULD skip the first section of the
   verification processes explained in section 5, section 6.1.1, and
   section 6.1.2.

   In the second scenario, as explained in section 4.1.3 (step 1), it is
   not necessary for the server to support the SeND or CGA algorithm.
   The DNS administrator can make a one-time use of a CGA script to
   generate the CGA parameters and then manually configure the IP
   address of the DNS server. Later, the DNS server can use those values
   as a means for authenticating other Nodes. The verifier Nodes also do
   not necessarily need to support SeND. They only need to support
   CGA-TSIG.

   In the third scenario, as explained in section 12.4.2.2., the Node
   can use the same approach used for IPv4 and retrieve the hash of
   (Public Key + IPv6 Address) from the DHCPv6 server.


8.  CGA-TSIG/e Attack Protections

   There are several types of attacks that CGA-TSIG/CGA-TSIGe can
   prevent. The use of CGA-TSIG will reduce the number of messages
   needed between a client and a server in order to establish a secure
   channel. To exchange the shared secret between a DNS Resolver and a
   client, when TSIG is used, a minimum of four (4) messages are
   required. By modifying [RFC2845] to use CGA-TSIG, this will decrease
   the number of messages needed . The messages used in [RFC2930] (TKEY
   RR) are not needed when CGA-TSIG is used.


8.1.  IP Spoofing

   This prevents the attack by finding a binding between the IP address
   and the Public Key for both IPv4 and IPv6 , with different


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   approaches.


8.2.  Resolver Configuration Attack

   When using CGA-TSIG/CGA-TSIGe, the DNS server (or client), would not
   need further configuration. This reduces the possibility of human
   errors being introduced into the DNS configurations. Since this type
   of attack is predicated on human error, the chances of it occurring
   are minimized.


8.3.  Exposing A Shared Secret

   Using CGA-TSIG/CGA-TSIGe will decrease the number of manual steps
   required in generating the new shared secret and in exchanging it
   among the hosts to update the old shared secret. This manual step is
   required after a shared secret is leaked.


8.4.  Replay Attack

   Using the Time Signed value in the Signature modifies the content of
   the Signature each time the Node generates and sends it to the DNS
   server. If the attacker attempts to spoof the timestamp, the DNS
   server will check this message by verifying the signature. In this
   case, the verification process will fail preventing the replay
   attack.


8.5.  Data Confidentiality

   Encrypting the whole DNS message will deny the attacker from knowing
   the content of DNS messages. This will avoid zone walking and many
   other attacks on DNS RRs.


9.  Update to TSIG Specification

   To support CGA-TSIG/e as a new algorithm in TSIG, updates needs to be
   made in the following sections of TSIG specification. In case any
   node does not support CGA-TSIG/e, it only ignores these new
   algorithms.

   - Section 4.2: The server MUST not generate a signed response to an
   unsigned request => The server MUST not generate a signed response to
   an unsigned request, unless the Algorithm Name filed contains
   CGA-TSIG or CGA-TSIGe.

   - Section 4.5.2: It MUST include the client's current time in the
   time signed field, the server's current time (a u_int48_t) in the
   other data field, and 6 in the other data length field => It MUST
   include the client's current time in the time signed field, the


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   server's current time (a u_int48_t) in the other data field, and if
   the Algorithm Name is CGA-TSIG or CGA-TSIGe, then add the length of
   this client's current time to the total length of Other DATA field.
   The client's current time in this case will be placed after the
   CGA-TSIG/CGA-TSIGe Data.

10.  Security Considerations

   The approach explained in this draft, CGA-TSIG, is a solution for
   securing DNS messages from spoofing type attacks like those explained
   in section 1.1.

   A problem that may arise here concerns attacks against the CGA
   algorithm. In this section we will explain the possibility of such
   attacks against CGA [5] and explain the available solutions that we
   considered in this draft.

   a) Discover an Alternative Key Pair Hashing of the Victim's Node
   Address

   In this case an attacker would have to find an alternate key pair
   hashing of the victim's address. The probability for success of this
   type of attack will rely on the security properties of the underlying
   hash function, i.e., an attacker will need to break the second
   pre-image resistance of that hash function. The attacker will perform
   a second pre-image attack on a specific address in order to match
   other CGA parameters using Hash1 and Hash2. The cost of doing this is
   (2^59+1) * 2^(16*1). If the user uses a sufficient security level, it
   will be not feasible for an attacker to carry out this type of attack
   due to the cost involved. Changing the IP address frequently will
   also decrease the chance for this type of attack succeeding.

   b) DoS to Kill a CGA Node

   Sending a valid or invalid CGA signed message with high frequency
   across the network can keep the destination node(s) busy with the
   verification process. This type of DoS attack is not specific to CGA,
   but it can be applied to any request-response protocol. One possible
   solution ,to mitigate this attack, is to add a controller to the
   verifier side of the process to determine how many messages a node
   has received over a certain period of time from a specific node. If a
   determined threshold rate is exceeded, then the node will stop
   further receipt of incoming messages from that node.

   c) CGA Privacy Implication

   Due to the high computational complexity necessary for the creation
   of a CGA, it is likely that once a node generates an acceptable CGA
   it will continue its use at that subnet. The result is that nodes
   using CGAs are still susceptible to privacy related attacks. One
   solution to these types of attacks is setting a lifetime for the
   address as explained in RFC 4941.



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11.  IANA Considerations

   The IANA has allowed for choosing new algorithm(s) for use in the
   TSIG Algorithm name. Algorithm name refers to the algorithm described
   in this document. The requirement to have this name registered with
   IANA is specified.

   In section 5.1, Type should allow for the use of future optional
   algorithms with regard to SeND. The default value is CGA. For this
   algorithm and other algorithms, (such as SSAS [4, 5], there needs to
   be a new number sequentially.

   IANA also needs to define a numeric algorithm number for ECC. The
   similar way that is defined for RSA.




12.  Appendix


12.1.  A Sample Key Storage For CGA-TSIG

   create table cgatsigkeys (
   id           INT auto_increment,
   pubkey       VARCHAR(300),
   primary key(id)
   );
   create table cgatsigips (
   id           INT auto_increment,
   idkey        INT,
   IP           VARCHAR(20),
   FOREIGN KEY (idkey) REFERENCES cgatsigkeys(id)
   primary key(id)
   );
   CGA-TSIG tables on mysql backend database

12.2.  Stored parameters in the node

   Here is a sample format of stored parameters in the node. For
   example, the modifier is stored as bytes and each byte might be
   separated by a comma (for example : 284,25,14,...). Algorithmtype is
   the algorithm used in signing the message. Zero is the default
   algorithm for RSA. Secval is the CGA Sec value that is, by default,
   one. GIP is the global IP address of this node (for example:
   2001:abc:def:1234:567:89a). oGIP is the old IP address of this node,
   before the generation of the new IP address. Keys contains the path
   where the CGA-TSIG algorithm can find the PEM format used for the
   public/private keys (for example: /home/myuser/keys.pem ).

   <?xml version="1.0" encoding="UTF-8"?>


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   <Details>
   <CGATSIG>
   <modifier value=""/>
   <algorithmtype value="1.2.840.113549.1.1.1"/>
   <secval value="1"/>
   <GIP value=""/>
   <oGIP value=""/>
   <Keys value=""/>
   </CGATSIG>
   </Details>
   XML file contains the cached DATA

12.3.  CGA Generation Script

   Here introduces a sample CGA generation script for the nodes that
   does not support SeND.

   byte[] modifier;
   typedef int bool;
   #define true 1
   #define false 0
   //  length_of_digest : 8 leftmost bytes of digest.
   //this function sets sec value on the first byte of digest
   //since interface ID is only 8 bytes, it returns only 8 leftmost bytes of digest
   byte[] set_secvalue(byte[] digest,int length_of_digest);
   //this function compares the 16 by cga_sec_value bits of digest to zero
   bool compare(byte[] digest, int cga_sec_value);
   //this function executes hashing function on cga_parameters
   byte[] sha1(byte[] cga_parameters);
   //this function reads public key from a file
   byte[] read_public_key(char[] public_key_path);
   //this function increments the modifier by one
   increment(byte[] modifier);
   //this function concatenates the input values.
   byte[] concat(byte[], byte[],....);
   //Write in a file
   CacheCGAparameters(byte[] ipv6_address, byte[] modifier, char[]
   public_key_path, int cga_sec_value, byte[] public_key_algorithm);
   //--------------main function ------------------------
   int main(char[] interface_name)
   {
   byte[] cga=cgagen("\\xxx\key.pub",prefix);
   byte[] ipv6_address=concat(prefix,cga);
   //set the CGA address on a desired interface
   setIP(ipv6_address,"eth0\0");
   CacheCGAparameters(ipv6_address,modifier,public_key_path, cga_sec_value,
   '1.2.840.113549.1.1.1');
   }
   //------------------sample function for CGA Generation--------------
   byte[] cgagen(char[] public_key_path, byte[] prefix, int cga_sec_value)
   {
   bool flag=true;
   byte[] cga;


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   byte[] public_key=read_public_key(public_key_path);
   modifier= randomnumber(16);
   while(flag)
   {
   //concatinate all values
   byte[] cgaparameters=concat(modifier,prefix,0,public_key);
   byte[] digest=sha1(cgaparameters);
   if(compare(digest,cga_sec_value)==false)
   increment(modifier);
   else
   flag=false;
   }
   cga=set_secvalue(digest,8);
   return cga;
   }
   //-------------Sample function for random number generator----
   //random generator explained in ra_privacy draft
   byte[] randomnumber(int length_byte)
   {
   byte[] num=new byte[length_byte];
   srand(time(NULL));
   for(int i=0;i<length_byte;i++)
   num[i]=rand() %254;
   }


12.4.  CGA-TSIGe (DNS privacy)

   One possible solution to provide the encryption for DNS messages is
   the use of a symmetric algorithm. The following sections explain this
   process. CGA-TSIGe do this encryption step similar to TLS protocol.
   The difference is that it encapsulate the whole DNS message and add a
   new header while in TLS after a secure channel is established, all
   data is sent via this secure channel.


12.4.1.  The CGA-TSIGe DATA Structure

   The node MUST set the Algorithm Type in TSIG RDATA to CGA-TSIGe.
   Other sections of CGA-TSIGe DATA are similar to CGA-TSIG DATA
   (explained in section 4.1). This section only explains the
   differences between CGA-TSIG and CGA-TSIGe. Figure 6 shows CGA-TSIGe
   DATA structure.

   - Message Hash = 3-bit hashing algorithm identifier | hash (whole DNS
   message)

   The value of Message Hash is the concatenation of the 3 bits hashing
   algorithm identifier with the hash of the whole DNS message (see
   figure 4 and 5 for the whole DNS message). This is used for data
   integrity of the packet. For SHA256, the value of hashing algorithm
   SHOULD set to 1. For other hashing algorithms, this 3 bits SHOULD set
   to sequential value after one. The field Message Hash Len is the


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   length of Message Hash.

   - digest_secret_key len: Length of digest_secret_key (encrypted
   secret key)

   - digest_secret_key = encryption of a 16 byte random number using DNS
   server?s public key

   +---------------------------------------+
   |             AsyAlgorithm              |
   |                                       |
   +---------------------------------------+
   |                Type                   |
   |                                       |
   +---------------------------------------+
   |             Parameter Len             |
   |              (1 byte)                 |
   +---------------------------------------+
   |             Parameters                |
   |             (variable)                |
   +---------------------------------------+
   |            Signature Len              |
   |               (1 byte)                |
   +---------------------------------------+
   |              Signature                |
   |              (variable)               |
   +---------------------------------------+
   |          Message Hash Len             |
   |              (1 byte)                 |
   +---------------------------------------+
   |            Message Hash               |
   |             (variable)                |
   +---------------------------------------+
   |          digest_secret_key Len        |
   |              (1 byte)                 |
   +---------------------------------------+
   |           digest_secret_key           |
   |             (variable)                |
   +---------------------------------------+
   Figure 6 CGA-TSIGe DATA Field

12.4.1.1.  Public Key Request

   In the TSIG RDATA section, the Algorithm Name MUST be set to
   'CGA-TSIGe', and the CGA-TSIGe Len field MUST be set to zero. This
   alerts the DNS server that the other Node needs its public key for
   encryption purposes. This format is used if a Node does not want to
   use DNSKEY RR [RFC3757] to retrieve the public key of the DNS server.


12.4.1.2.  Public Key Response

   The DATA structure is similar to CGA-TSIG. There is only a flag field


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   which indicates that it is a response to the public key request
   message.

   +---------------------------------------+
   |             AsyAlgorithm              |
   |                                       |
   +---------------------------------------+
   |                Type                   |
   |                                       |
   +---------------------------------------+
   |             Parameter Len             |
   |              (1 byte)                 |
   +---------------------------------------+
   |             Parameters                |
   |             (variable)                |
   +---------------------------------------+
   |              Signature                |
   |              (variable)               |
   +---------------------------------------+
   |            Signature Len              |
   |               (1 byte)                |
   +---------------------------------------+
   |              Signature                |
   |              (variable)               |
   +---------------------------------------+
   |               Flag                    |
   |             (1 bit)                   |
   +---------------------------------------+
   Figure 7 CGA-TSIGe DATA Field (public key response)

12.4.2.  Generation of CGA-TSIGe DATA


12.4.2.1.  IPv6 Specifics

   Nodes can securely obtain the IP address of DNS resolvers from the
   DHCPv6 server (use SAVI-DHCP [savi-dhcp]); or from a DNS option of
   Router Advertisement message [RFC6106] after authenticating with the
   router via a trusted authority. The IP addresses can be generated
   using CGA, SSAS or other mechanisms.

   This is the same approach that a node can use for obtaining a DNS
   server IP address during a Dynamic DNS update.

   In case this approach is used for zone transfer, to avoid any
   malicious update to DNS server, it is RECOMMENDED that this IP
   address is set manually on the DNS server for the first time or cache
   the IP address of trusted resolvers in a trusted list and randomly
   select them in a insecure network.


12.4.2.1.1.  Generation of Query Request Message



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   1. Retrieve Public Key of DNS Server

   To encrypt the DNS message using a symmetric algorithm for
   performance purposes, first, a Node needs to retrieve the public key
   of the DNS server. It is possible to use the current DNSKEY RR
   [RFC3757] to send the public key of the DNS server. When the client
   wants to update any records on the DNS server, it first sends a DNS
   message asking for the public key of the DNS Server. The DNS Server
   then answers this query and includes the public key contained in the
   DNSKEY RR with the SEP flag set to zero (0). This indicates that it
   is not the zone key. It is also possible to use the RR format
   explained in sections 12.4.1.1 and 12.4.1.2 of this document. The DNS
   server SHOULD include CGA-TSIGe DATA so that the client can verify
   its IP address. In this case, there will be a binding between a DNS
   Server's public key and its IP address. If the Node can verify the
   DNS Server public key (explained below), it goes to step 2. Otherwise
   it discards the DNS message without further action.

   2. Obtain Required Parameters From Cache.

   This step is the same as what is explained in section .1.3.

   3. Generation of Secret Key

   After a successful verification, the Node generates a 16 byte random
   number called a secret key. The Node can use any algorithm explained
   in [RFC4086] to generate a good randomized value. It encrypts the
   secret key using the DNS Server?s public key. Then, the Node sets the
   digest_secret_key in CGA-TSIGe DATA structure to this encrypted
   secret key and set the digest_secret_key len to the length of this
   encrypted value. Similar to CGA-TSIG, MAC Size in TSIG RDATA MUST set
   to 0. The DNS Server knows what to do with MAC field from the
   Algorithm Type in TSIG.

   4. Encryption of DNS message

   The Node uses the secret key generated in the previous step to
   encrypt the header, zone section, prerequisite, and update section
   for the DNS update message (see figure 8) or encrypt header,
   question, answer, authority of a DNS Query (see figure 9). It then
   calculates the length of a digest as a number of bytes in multiples
   of 8. For example, if the digest is 242 bytes then 242 = (30 * 8) +
   2. Therefore, 6 bytes are added as padding, and then 31 is placed at
   the beginning of digest (see figure 10). If there is no padding for
   the digest then one zero-filled byte will be added at the end of
   digest. This allows the DNS Server to interpret this digest as a long
   string.

   +-----+------+--------+
   |Type |Length|Reserved|
   |1byte|1 byte| 1 byte |
   +---------------------+
   |        Header       |


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   |       12 bytes      |
   +---------------------+
   |  Encrypted sections |
   |   variable length   |
   +---------------------+
   |   Additional Data   |
   |   variable length   |
   +---------------------+
   Figure 8 Encrypted DNS update message

   +-----+------+--------+
   |Type |Length|Reserved|
   |1byte|1 byte| 1 byte |
   +---------------------+
   |        Header       |
   |       12 bytes      |
   +---------------------+
   |  Encrypted sections |
   |   variable length   |
   +---------------------+
   |   Additional Data   |
   |   variable length   |
   +---------------------+
   Figure 9 Encrypted DNS Query message

   +---------------------+
   |    Len of digest    |
   |     (1 byte)        |
   +---------------------+
   |        digest       |
   |   variable length   |
   +---------------------+
   Figure 10 Digest format in DNS question section

   The Node then adds a new header with the following data. This will
   allow the DNS Server to process this message. CGA-TSIGe actually uses
   the whole encrypted section as one single question followed by
   additional data.

   Field Sub-field Value Intrepretation
   -------------------------------------------------------
   ID             0xdb42  Response should have ID 0xdb42
   Flags           0x0100
   QR       0     It's a query
   OPCODE    0     Standard query
   TC       0     Not truncated
   RD       1     Recursion requested
   RA       0     Not meaningful for query
   Z        0     Reserved
   RCODE      0     Not meaningful for query
   QDCOUNT           0x0001 One question follows
   ANCOUNT           0x0000 No answers follow
   NSCOUNT           0x0000 No records follow


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   ARCOUNT           0x0001 No additional records follow
   The digest will be interpreted like the following table.

   Data       Intrepretation
   ------------------------------------------
   0x1f       String of length 248 follows
   0x777777.. String is xxxxxx
   0x00       End of this string
   5. Generation of Message Hash

   In a case where a DNS Server responds to anonymous queries, as in a
   DNS Resolver scenario, the Node executes SHA256 by default on the
   whole DNS message. This includes the additional section and the TSIG
   RR as a part of additional section of DNS message. It then computes
   the Message Hash Len. In this case the message does not need to be
   signed by the Node (stub resolver) using its private key. This is
   because the DNS Server does not expect to verify the Node and it only
   checks for the message integrity and confidentiality. In the case a
   message contains Message Hash, the Node MUST set the Parameters Len ,
   Signature Len, Old Pubkey Len and Old Signature Len to zero (0) and
   it SHOULD skips steps 6 and 7.


12.4.2.1.2.  Generation of Query Response Message

   This is similar to generation of query request message as explained
   in section 12.4.2.1.1. of this document. However, steps 1, 3 and 5
   should be skipped.

   1. Obtain Required Parameters From Cache.

   2. Encryption of DNS message

   Query response needs to be encrypted using a shared secret obtain
   from the Query Request message explained in section 12.4.4.

   3. Generation of Signature

   This step is the same as what is explained in section 4.1.3.


12.4.2.2.  IPv4 Scenario

   The key pairs needs to be cached in order to generate a signature. If
   this Node changes its IP address, it also needs to cache the old IP
   address. Similar to the IPv6 scenario, the Node can obtain the hash
   of (public key + IPv4) and the IPv4 address of the DNS server from a
   DHCPv4 server. It can use [savi-dhcp]. If this Node is in unsecured
   environment, it can manually add the hash of (public key + IPv4
   address) of its trusted DNS server. This is especially true in the
   Resolver scenario. The implementers SHOULD define a possibility for
   users to change the default value for CGA-TSIGe.



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12.4.2.2.1.  Generation of Query Request Message

   1. Retrieves Public Key of DNS server

   This is similar to IPv6 scenario.

   2. Obtain Required Parameters From Cache.

   This step is the same as what is explained in section 4.1.3.

   3. Generation of Secret Key

   4. Encryption of DNS Message

   5. Generation of Message Hash

   All Three are similar to IPv6 scenario.

   6. Generation of Signature

   This step is the same as what is explained in section 4.1.3.


12.4.2.2.2.  Generation of Query Response Message

   This is similar to IPv6 scenario.

   2. Obtain Required Parameters From Cache.

   This step is the same as what is explained in section 4.1.3.

   1. Obtain Required Parameters From Cache.

   2. Encryption of DNS message

   Query response needs to be encrypted using a shared secret obtain
   from the Query Request message explained in section 12.4.4.

   3. Generation of Signature

   This step is the same as what is explained in section 4.1.3.


12.4.3.  Process of Public Key Response Message

   This section explains the verification needed for the process of
   public key response (The format of this message was explained in
   section 12.4.1.2)


12.4.3.1.  IPv6 only Scenarios



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   Depends on the algorithm used by the DNS server, CGA or SSAS
   verification process MUST be executed.


12.4.3.2.  IPv4 only Scenarios

   The verifier node MUST execute hashing function on (public key + IPv4
   address) and compare this value with the value exists on its cache or
   the value retrieved from a DNS server in a secure manner.


12.4.4.  Process of Encrypted Query Request Message

   When the DNS server receives the message from any node with TSIG
   RDATA Algorithm type set to CGA-TSIGe, it executes the following
   steps:

   1- Retrieves The Secret Key

   The DNS server retrieves the secret key from digest_secret_key field.
   Secret key is a random value generated by the node (such as a stub
   resolver) and encrypted using the public key of this DNS server
   (section 12.4.2.1.1 explains the steps to generate and encrypt this
   value). DNS server then decrypts this secret key using its own
   private key.

   2- Decrypts the DNS Message

   The DNS server decrypts the DNS server message using this secret key
   and the symmetric algorithm, which by default is AES. The DNS server
   can then start the verification process explained in the next
   section.


12.4.5.  Process of Encrypted Query Response Message

   When the node (like a client) receives a query response message from
   any node with TSIG RDATA Algorithm type set to CGA-TSIGe, it executes
   the following steps:

   1- Retrieves The Secret Key

   This node, itself, generated this secret key. It fetches this secret
   key from its memory.

   2- Decrypts the DNS Message

   The node decrypts the query response message using this secret key
   and the symmetric algorithm, which by default is AES. The node can
   then start the verification process explained in the next sections.


12.5.  Other Optional Use case scenarios


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   Besides DNS privacy, secure authentication mechanism introduced in
   this document can be used in other DNS scenario for the purpose of
   reducing human interaction and secure Dynamic DNS updates. Minimizing
   the amount of human interaction reduces the vulnerability to attacks
   introduced by human errors. This is because secure authentication
   (and prevent IP spoofing) can be seen as a base to prevent many
   different DNS attacks such as DNS spoofing, DNS amplification,
   Unauthorized DNS Update (DDNS), etc. For example, protecting DNS
   servers from unauthorized update during dynamic DNS update (DDNS) is
   an example scenario that requires human interactions for the
   configuration of each node for a secure authentication. Manual
   configuration of each node to enable them securely update their PTR
   or FQDN only increases overheads on domain administrators. This is
   because nodes might join and leave the networks or might frequently
   change their IP addresses. Therefore, they want to update their PTR
   or FQDN records on DNS servers accordingly. If the Dynamic Host
   Configuration Protocol (DHCP) is in use, then the DHCP server can do
   this update on behalf of the nodes in this network on a DNS server.
   When Neighbor Discovery Protocol (NDP) is in use, there is no feature
   available that allows the host process a secure update for its own
   FQDN or PTR. Using a shared secret which is shared between many nodes
   for secure authentication during DDNS process, similar to TSIG
   mechanism requires the exchange of this shared secret manually
   between these nodes. This results in repeating the key exchange
   between many nodes (This process involves human interaction) where
   one of these nodes are compromised due to virus or other problems.


12.5.1.  The FQDN Or PTR Update (IPv6 only)

   Normally the DHCPv6 server will update the client's RRs on their
   behalf in the scenario where SeND is used as a secure NDP, the Nodes
   will need to do this process unless a stateless DHCPv6 server is
   available. CGA-TSIG/CGA-TSIGe can be used to give Nodes the ability
   of doing this process themselves. In this case the clients need to
   include the CGA-TSIG/CGA-TSIGe option to allow the DNS server to
   verify them. The verification process is as following.


12.5.1.1.  Verification Process

   The verification steps are the same as those is explained in section
   5, but removing step 4 and modifying step 5.

   1. Verify The Signature

   2. Check The Time Signed

   3. Execute The CGA Verification

   4. Verify The Public Key



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   The DNS server checks if the public key retrieved from
   CGA-TSIG/CGA-TSIGe DATA is the same as what was available in cache.
   If no entry is found for this public key, and the FQDN or PTR is also
   not available in the DNS server, then the DNS server will store the
   public key of this Node and add this Node's PTR and FQDN.


12.5.2.  DNS Zone Transfer

   This section discusses the use of CGA-TSIGe for the secure
   authentication and encryption of DNS messages exchanged between a
   Master Server and a Slave Server. In the case of processing a DNS
   zone update ([AI]XFR) for multiple DNS servers (authenticating two
   DNS servers), there are three possible scenarios with regard to the
   authentication process which differs from that of the authentication
   of a Node (client) with one DNS server. This is needed for human
   intervention. Since the zone contains important information, both DNS
   servers MUST use CGA-TSIGe and encrypt the values. The only exception
   is when CGA-TSIG is required for secure authentication and the data
   encryption is handled by other protocols.

   a. Add The DNS servers' IP address To A Slave Server Configuration
   (IPv6 only)

   A DNS server administrator should only manually add the IP address of
   the Master Server to the configuration file of the Slave Server. When
   the DNS update message is processed, the Slave Server can
   authenticate the Master Server based on the source IP address and
   then, prove the ownership of this address by use of the CGA-TSIGe
   option from the TSIG RR. This scenario will be valid until the IP
   address in any of these DNS servers, changes.

   To automate this process, the sender's public key of the DNS Update
   message must be saved on the other DNS server, after the source IP
   address has been successfully verified for the first time. In this
   case, when the sender generates a new IP address by executing the CGA
   algorithm using the same public key, the other DNS server can still
   verify it and add its new IP address to the DNS configuration file
   automatically.

   b. Retrieve Public/Private Keys From A Third Party Trusted Authority
   (TA) (IPv6 only)

   The message exchange option of SeND [RFC3971] may be used for the
   retrieval of third party certificates. This may be done automatically
   from the TA by using the Certificate Path Solicitation and
   Certificate Path Advertisement messages. Like in section 4.2, the
   certificate should be saved on the DNS server for later use. Whenever
   any of those servers want to generate a new IP address, the DNS
   update process can be accomplished without human intervention.

   c. Store The Hash of (public key + IPv4 address) to DNS configuration
   file (IPv4 and IPv6)


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   An administrator needs to manually generate the hash of the
   concatenation of public key with the IPv4 address of the authorized
   node the DNS configuration file. Whenever a node wants to change its
   IP address or public key, the DNS server can generates this value
   automatically and compare with the old value it has and then after a
   successful verification steps (it will be explain in next section),
   it will replace the old hash value with the new one.


12.5.2.1.  Verification Process

   The verification steps are similar to section 5 of this document.

13.  Acknowledgements

   The continual improvement of this document is as a result of the
   helps and assistance of its supporters.

   The authors would like to thank all those people who directly helped
   in improving this draft and all supporters of this draft, especially
   Ralph Droms, Andrew Sullivan, Ted Lemon, Brian Haberman, Erik
   Nordmark, Brian Dickson, Dan Wing. The authors would like also to
   special acknowledge the supports of NLnet Labs director and
   researchers; Olaf Kolkman, Matthijs Mekking and their master student
   Marc Buijsman.

   The authors would like to express their special appreciation and
   thanks to Tim Wicinski and Joel Halpern who spent a lot of time to
   review, revise and improve this draft.



14.  References

14.1.  Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to
             Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.

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

   [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander,
             "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.

   [RFC2119] Bradner, S., "Key words for use in RFCs to
             Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2930] Eastlake 3rd, D., "Secret Key Establishment for
             DNS (TKEY RR)", RFC 2930, September 2000.

   [RFC1035] Mockapetris, P., "Domain Names - Implementation


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             And Specification", RFC 1035, November 1987.

   [RFC4941] Narten, T., Draves, R., Krishnan, S., "Privacy
             Extensions for Stateless Address Autoconfiguration in
             IPv6", RFC 4941, September 2007.

   [RFC2136] Vixie, P. (Editor), Thomson, S., Rekhter, Y.,
             Bound, J., "Dynamic Updates in the Domain Name System (DNS
             UPDATE)", RFC 2136, April 1997.

   [RFC2845] Vixie, P., Gudmundsson, O. , Eastlake 3rd, D.,
             Wellington, B., " Secret Key Transaction Authentication for
             DNS (TSIG)", RFC 2845, May 2000.

   [RFC6106] Jeong, J., Park, S., Beloeil, L., Madanapalli,
             S.,"IPv6 Router Advertisement Options for DNS
             Configuration",RFC 6106, November 2010.

   [RFC4086] Eastlake, D., Schiller, J., and Crocker, D.,
             "Randomness Requirements for Security", BCP 106, RFC
             4086,June 2005.

   [RFC4055] Schaad, J., Kaliski, B., and Housley, R.,
             "Additional Algorithms and Identifiers for RSA Cryptography
             for use in the Internet X.509 Public Key infrastructure
             Certificate and Certificate Revocation List (CRL) Profile",
             RFC 4055,June 2005.

   [RFC6840] Weiler, S. and Blacka, D., "Clarifications and
             Implementation Notes for DNS Security (DNSSEC)", RFC
             6840,February 2013.

   [RFC3757] Kolkman, O., Schlyter, J., and Lewis, E., "Domain
             Name System KEY (DNSKEY) Resource Record (RR) Secure Entry
             Point (SEP) Flag",RFC 3757,April 2004.

14.2.  Informative References

   [1] Aura, T., "Cryptographically Generated Addresses (CGA)",
       Lecture Notes in Computer Science, Springer, vol. 2851/2003, pp.
       29-43, 2003.

   [2] Montenegro, G. and Castelluccia, C., "Statistically Unique
       and Cryptographically Verifiable (SUCV) Identifiers and
       Addresses," ISOC Symposium on Network and Distributed System
       Security (NDSS 2002), the Internet Society, 2002.

   [3] AlSa'deh, A., Rafiee, H., Meinel, C., "IPv6 Stateless Address
       Autoconfiguration: Balancing Between Security, Privacy and
       Usability". Lecture Notes in Computer Science, Springer(5th
       International Symposium on Foundations & Practice of Security
       (FPS). October 25 - 26, 2012 Montreal, QC, Canada), 2012.



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   [4] Rafiee, H., Meinel, C., "A Simple Secure Addressing
       Generation Scheme for IPv6 AutoConfiguration (SSAS)". Work in
       progress, http://tools.ietf.org/html/draft-rafiee-6man-ssas,
       2013.

   [5] Rafiee, H., Meinel, C., "A Simple Secure Addressing Scheme
       for IPv6 AutoConfiguration (SSAS)", 11th International conference
       on Privacy, Security and Trust (IEEE PST), 2013.

   [6] AlSa'deh, A., Rafiee, H., Meinel, C., "Cryptographically
       Generated Addresses (CGAs): Possible Attacks and Proposed
       Mitigation Approaches," in proceedings of 12th IEEE International
       Conference on Computer and Information Technology (IEEE CIT'12),
       pp.332-339, 2012.

   [7] Rafiee, H., Meinel, C., "A Secure, Flexible Framework for DNS
       Authentication in IPv6 Autoconfiguration" in proceedings of The
       12th IEEE International Symposium on Network Computing and
       Applications (IEEE NCA13), 2013.

   [savi-dhcp] Bi, J., Wu, J., Yao, G, Baker, F.,"SAVI
               Solution for DHCP",
               http://tools.ietf.org/html/draft-ietf-savi-dhcp-23, April
               2014

   [dns-privacy] Bortzmeyer, S., " DNS privacy
                 considerations",
                 https://tools.ietf.org/html/draft-ietf-dprive-problem-statement-02,
                 August 2015

   [dns-terms] Hoffman, P., Sullivan, A., Fujiwara, K., "DNS
               Terminology",
               https://tools.ietf.org/html/draft-hoffman-dns-terminology-01,
               July 2015





















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Authors' Addresses

      Hosnieh Rafiee
      http://www.rozanak.com
      Munich, Germany
      Phone: +49 (0)162 204 74 58
      E-mail: ietf@rozanak.com


      Christoph Meinel
      Hasso-Plattner-Institute
      Prof.-Dr.-Helmert-Str. 2-3
      Potsdam, Germany
      Email: meinel@hpi.uni-potsdam.de







































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