[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Nits]

Versions: 00

DNSOP Working Group                                              O. Sury
Internet-Draft                               Internet Systems Consortium
Updates: 7873 (if approved)                                    W. Toorop
Intended status: Standards Track                              NLnet Labs
Expires: September 12, 2019                               March 11, 2019


      Algorithms for Domain Name System (DNS) Cookies construction
              draft-sury-toorop-dns-cookies-algorithms-00

Abstract

   [RFC7873] left the construction of Server Cookies to the discretion
   of the DNS Server (implementer) which has resulted in a gallimaufry
   of different implementations.  As a result, DNS Cookies are
   impractical to deploy on multi-vendor anycast networks, because the
   Server Cookie constructed by one implementation cannot be validated
   by another.

   This document provides precise directions for creating Server Cookies
   to address this issue.  Furthermore, [FNV] is obsoleted as a suitable
   Hash function for calculating DNS Cookies.  [SipHash-2.4] is
   introduced as a new REQUIRED Hash function for calculating DNS
   Cookies.

   This document updates [RFC7873]

Status of This Memo

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

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

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

   This Internet-Draft will expire on September 12, 2019.








Sury & Toorop          Expires September 12, 2019               [Page 1]


Internet-Draft           dns-cookies-algorithms               March 2019


Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Contents of this document . . . . . . . . . . . . . . . .   3
     1.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Constructing a Client Cookie  . . . . . . . . . . . . . . . .   3
   3.  Constructing a Server Cookie  . . . . . . . . . . . . . . . .   3
     3.1.  The Version Sub-Field . . . . . . . . . . . . . . . . . .   4
     3.2.  The Cookie algo Sub-Field . . . . . . . . . . . . . . . .   4
     3.3.  The Reserved Sub-Field  . . . . . . . . . . . . . . . . .   4
     3.4.  The Timestamp Sub-Field . . . . . . . . . . . . . . . . .   4
     3.5.  The Hash Sub-Field  . . . . . . . . . . . . . . . . . . .   5
   4.  Cookie Algorithms . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   In [RFC7873] in Section 6 it is "RECOMMENDED for simplicity that the
   Same Server Secret be used by each DNS server in a set of anycast
   servers."  However, how precisely a Server Cookie is calculated from
   this Server Secret, is left to the implementation.

   This guidance has let to DNS Cookie implementations, calculating the
   Server Cookie in different ways.  This causes problems with anycast
   deployments with DNS Software from multiple vendors, because even
   when all DNS Software would share the same secret, as RECOMMENDED in
   Section 6.  of [RFC7873], they all produce different Server Cookies
   based on that secret and (at least) the Client Cookie and Client IP
   Address.



Sury & Toorop          Expires September 12, 2019               [Page 2]


Internet-Draft           dns-cookies-algorithms               March 2019


1.1.  Contents of this document

   In Section Section 2 instructions for constructing a Client Cookie
   are given

   In Section Section 3 instructions for constructing a Server Cookie
   are given

   In Section Section 4 the different hash functions usable for DNS
   Cookie construction are listed.  [FNV] and HMAC-SHA-256-64 [RFC6234]
   are obsoleted and AES [RFC5649] and [SipHash-2.4] are introduced as a
   REQUIRED hash function for DNS Cookie implementations.

1.2.  Definitions

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

2.  Constructing a Client Cookie

   The Client Cookie is a nonce and should be treated as such.  For
   simplicity, it can be calculated from Client IP Address, Server IP
   Address and a secret known only to the Client.  The Client Cookie
   SHOULD have at least 64-bits of entropy.  If a secure pseudorandom
   function (like SipHash24) is used there's no need to change Client
   secret periodically and change the Client secret only if it has been
   compromised.

   It's recommended but not required that a pseudorandom function is
   used to construct the Client Cookie:

        Client-Cookie = MAC_Algorithm(
            Client IP Address | Server IP Address, Client Secret )

   where "|" indicates concatenation.

3.  Constructing a Server Cookie

   The Server Cookie is effectively message authentication code (MAC)
   and should be treated as such.

   The Server Cookie is not required to be changed periodically if a
   secure pseudorandom function is used.





Sury & Toorop          Expires September 12, 2019               [Page 3]


Internet-Draft           dns-cookies-algorithms               March 2019


   The 128-bit Server Cookie consists of Sub-Fields: a 1 octet Version
   Sub-Field, a 1 octet Cookie Algorithm Sub-Field, a 2 octet Reserved
   Sub-Field, a 4 octet Timestamp Sub-Field and a 8 octet Hash Sub-
   Field.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Version    |  Cookie Algo  |           Reserved            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                           Timestamp                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             Hash                              |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.1.  The Version Sub-Field

   The Version Sub-Field prescribes the structure and Hash calculation
   formula.  This document defines Version 1 to be the structure and way
   to calculate the Hash Sub-Field as defined in this Section.

3.2.  The Cookie algo Sub-Field

   The Cookie Algo value defines what algorithm function to use for
   calculating the Hash Sub-Field as described in Section 3.5.  The
   values are described in Section 4.

3.3.  The Reserved Sub-Field

   The value of the Reserved Sub-Field is reserved for future versions
   of Server Side Cookie construction.  Even though the value has no
   specific meaning in this Version, note that it *is* used in
   determining the Hash value as described in Section 3.5.

3.4.  The Timestamp Sub-Field

   The Timestamp value prevents Replay Attacks and MUST be checked by
   the server to be within a defined period of time.  The DNS Server
   SHOULD allow Cookies within 1 hour period in the past and 5 minutes
   into the future to allow operation of low volume clients and certain
   time skew between the DNS servers in the anycast.

   The DNS Server SHOULD generate new Server Cookie at least if the
   received Server Cookie from the Client is older than half an hour.






Sury & Toorop          Expires September 12, 2019               [Page 4]


Internet-Draft           dns-cookies-algorithms               March 2019


3.5.  The Hash Sub-Field

   It's important that all the DNS servers use the same algorithm for
   computing the Server Cookie.  This document defines the Version 1 of
   the Server Side algorithm to be:

     Hash = Cookie_Algorithm(
         Client Cookie | Version | Cookie Algo | Reserved | TimeStamp,
         Server Secret )

4.  Cookie Algorithms

   Implementation recommendations for Cookie Algorithms [DNSCOOKIE-
   IANA]:

       +--------+-----------------+---------------+---------------+
       | Number | Mnemonics       | Client Cookie | Server Cookie |
       +--------+-----------------+---------------+---------------+
       | 1      | FNV             | MUST NOT      | MUST NOT      |
       | 2      | HMAC-SHA-256-64 | MUST NOT      | MUST NOT      |
       | 3      | AES             | MAY           | MAY           |
       | 4      | SIPHASH24       | MUST          | MUST          |
       +--------+-----------------+---------------+---------------+

   [FNV] is a Non-Cryptographic Hash Algorithm and this document
   obsoletes the usage of FNV in DNS Cookies.

   HMAC-SHA-256-64 is an HMAC-SHA-256 [RFC6234] algorithm reduced to
   64-bit.  This particular algorithm was implemented in BIND, but it
   was never the default algorithm and the computational costs makes it
   unsuitable to be used in DNS Cookies.  Therefore this document
   obsoletes the usage of HMAC-SHA-256 algorithm in the DNS Cookies.

   The AES algorithm [RFC5649] has been the default DNS Cookies
   algorithm in BIND until version x.y.z, and other implementations MAY
   implement AES algorithm as implemented in BIND for backwards
   compatibility.  However it's recommended that new implementations
   implement only a pseudorandom functions for DNS Cookies, in this
   document that would be SipHash24.

   [SipHash-2.4] is a pseudorandom function suitable as message
   authentication code, and this document REQUIRES compliant DNS Server
   to use SipHash24 as a mandatory and default algorithm for DNS Cookies
   to ensure interoperability between the DNS Implementations.







Sury & Toorop          Expires September 12, 2019               [Page 5]


Internet-Draft           dns-cookies-algorithms               March 2019


5.  IANA Considerations

   IANA is requested to create and maintain a sub-registry (the "DNS
   Cookie Algorithm" registry) of the "Domain Name System (DNS)
   Parameters" registry.  The initial values for this registry are
   described in Section 4.

6.  References

6.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5649]  Housley, R. and M. Dworkin, "Advanced Encryption Standard
              (AES) Key Wrap with Padding Algorithm", RFC 5649,
              DOI 10.17487/RFC5649, September 2009,
              <https://www.rfc-editor.org/info/rfc5649>.

   [RFC6234]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and SHA-based HMAC and HKDF)", RFC 6234,
              DOI 10.17487/RFC6234, May 2011,
              <https://www.rfc-editor.org/info/rfc6234>.

   [RFC7873]  Eastlake 3rd, D. and M. Andrews, "Domain Name System (DNS)
              Cookies", RFC 7873, DOI 10.17487/RFC7873, May 2016,
              <https://www.rfc-editor.org/info/rfc7873>.

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

6.2.  Informative References

   [FNV]      Fowler, G., Noll, L., Vo, K., Eastlake, D., and T. Hansen,
              "The FNV Non-Cryptographic Hash Algorithm",
              <https://datatracker.ietf.org/doc/draft-eastlake-fnv>.

   [SipHash-2.4]
              Aumasson, J. and D. Bernstein, "SipHash: a fast short-
              input PRF", 2012, <https://131002.net/siphash/>.








Sury & Toorop          Expires September 12, 2019               [Page 6]


Internet-Draft           dns-cookies-algorithms               March 2019


Authors' Addresses

   Ondrej Sury
   Internet Systems Consortium
   CZ

   Email: ondrej@isc.org


   Willem Toorop
   NLnet Labs
   Science Park 400
   Amsterdam  1098 XH
   Netherlands

   Email: willem@nlnetlabs.nl



































Sury & Toorop          Expires September 12, 2019               [Page 7]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/