DNS message checksums
draft-muks-dnsop-dns-message-checksums-00

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Last updated 2015-09-28
Replaces draft-muks-dns-message-checksums
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Internet Engineering Task Force                             M. Sivaraman
Internet-Draft                               Internet Systems Consortium
Intended status: Experimental                         September 28, 2015
Expires: March 31, 2016

                         DNS message checksums
               draft-muks-dnsop-dns-message-checksums-00

Abstract

   This document describes a method for a client to be able to verify
   that IP-layer PDU fragments of a UDP DNS message have not been
   spoofed by an off-path attacker.

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 March 31, 2016.

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
   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.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  DNS message checksum method . . . . . . . . . . . . . . . . .   3
   3.  The CHECKSUM EDNS(0) option . . . . . . . . . . . . . . . . .   4
     3.1.  Wire format . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Option fields . . . . . . . . . . . . . . . . . . . . . .   4
       3.2.1.  NONCE . . . . . . . . . . . . . . . . . . . . . . . .   4
       3.2.2.  ALGORITHM . . . . . . . . . . . . . . . . . . . . . .   4
       3.2.3.  DIGEST  . . . . . . . . . . . . . . . . . . . . . . .   4
     3.3.  Presentation format . . . . . . . . . . . . . . . . . . .   5
   4.  Checksum computation  . . . . . . . . . . . . . . . . . . . .   5
   5.  Security considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative references  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative references  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Checksum algorithms  . . . . . . . . . . . . . . . .   7
   Appendix B.  Change History (to be removed before publication)  .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   [RFC1035] describes how DNS messages are to be transmitted over UDP.
   A DNS query message is transmitted using one UDP datagram from client
   to server, and a corresponding DNS reply message is transmitted using
   one UDP datagram from server to client.

   As a UDP datagram is transmitted in a single IP PDU, in theory the
   size of a UDP datagram (including various lower internet layer
   headers) can be as large as 64 KiB.  But practically, if the datagram
   size exceeds the path MTU, then the datagram will either be
   fragmented at the IP layer, or dropped by a forwarder.  In the case
   of IPv4, DNS datagrams may be fragmented by a sender or a forwarder.
   In the case of IPv6, DNS datagrams are fragmented by the sender only.

   IP-layer fragmentation for large DNS response datagrams introduce
   risk of cache poisoning by off-path attackers [Fragment-Poisonous] in
   which an attacker can circumvent some defense mechanisms like port,
   IP, and query randomization [RFC5452].

   This memo introduces the concept of a DNS message checksum which may
   be used to stop the effects of such off-path attacks.

   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].

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