The EDNS(0) Padding Option
draft-ietf-dprive-edns0-padding-03

Versions: (draft-mayrhofer-edns0-padding)  00 01         Standards Track
          02 03 rfc7830                                                 
Network Working Group                                       A. Mayrhofer
Internet-Draft                                               nic.at GmbH
Intended status: Standards Track                       November 24, 2015
Expires: May 27, 2016


                       The EDNS(0) Padding Option
                   draft-ietf-dprive-edns0-padding-01

Abstract

   This document specifies the EDNS(0) 'Padding' option, which allows
   DNS clients and servers to pad request and response messages by a
   variable number of octets.

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
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   This Internet-Draft will expire on May 27, 2016.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  The 'Padding' Option  . . . . . . . . . . . . . . . . . . . .   3
   4.  Usage Considerations  . . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   8.  Changes . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     8.1.  draft-ietf-dprive-edns0-padding-01  . . . . . . . . . . .   4
     8.2.  draft-ieft-dprive-edns0-padding-00  . . . . . . . . . . .   5
     8.3.  draft-mayrhofer-edns0-padding-01  . . . . . . . . . . . .   5
     8.4.  draft-mayrhofer-edns0-padding-00  . . . . . . . . . . . .   5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The Domain Name System (DNS) [RFC1035] was specified to transport DNS
   packets in clear text form.  Since this can expose significant
   amounts of information about the internet activities of an end user,
   the IETF has undertaken work to provide confidentiality to DNS
   transactions (see the DPRIVE WG).  Encrypting the DNS transport is
   considered as one of the options to improve the situation.

   However, even if both DNS query and response packets were encrypted,
   meta data of these packets could be used to correlate such packets
   with well known unencrypted packets, hence jeopardizing some of the
   confidentiality gained by encryption.  One such property is the
   message size.

   This document specifies the Extensions Mechanisms for DNS (EDNS(0))
   "Padding" Option, which allows to artificially increase the size of a
   DNS message by a variable number of bytes, significantly hampering
   size-based correlation of the encrypted packet.

2.  Terminology

   The terms "Requestor", "Responder" are to be interpreted as specified
   in [RFC6891].

   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
   [RFC2119].



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3.  The 'Padding' Option

   The EDNS(0) [RFC6891] specifies a mechanism to include new options in
   DNS packets, contained in the RDATA of the OPT meta-RR.  This
   document specifies the 'Padding' option in order to allow clients and
   servers pad DNS packets by a variable number of bytes.  The 'Padding'
   option MUST occur at most once per OPT meta-RR.

   The figure below specifies the structure of the option in the RDATA
   of the OPT RR:

                0                       8                      16
                +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                |                  OPTION-CODE                  |
                +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                |                 OPTION-LENGTH                 |
                +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                |        (PADDING) ...        (PADDING) ...     /
                +-  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -

                                 Figure 1

   The OPTION-CODE for the 'Padding' option is 12.

   The OPTION-LENGTH for the 'Padding' option is the size (in octets) of
   the PADDING.  The minimum number of padding octets is 0.

   The PADDING octets SHOULD be set to 0x00.  Application developers who
   are concerned about misguided lower layer compression MAY instead
   fill the PADDING octets with the output of a cryptographic random
   number generator.  Responders MUST NOT reject messages containing
   non-0x00 PADDING octets.

4.  Usage Considerations

   This document does not specify the actual amount of padding to be
   used, since this depends on the situation in which the option is
   used.  However, padded DNS messages MUST NOT exceed the number of
   octets specified in the Requestor's Payload Size field encoded in The
   RR Class Field (see Section 6.2.3 and 6.2.4 of [RFC6891]).

   Responders MUST pad DNS responses when the respective DNS query
   included the 'Padding' option, unless doing so would violate the
   maximum UDP payload size.

   Responders MAY pad DNS responses when the respective DNS query
   indicated EDNS(0) support of the Requestor.




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   Responders MUST NOT pad DNS responses when the respective DNS query
   did not indicate EDNS(0).

5.  IANA Considerations

   IANA has assigned EDNS Option Code 12 for Padding.

   IANA is requested to update the respective registration record by
   changing the Reference field to [[THISRFC]] and the Status field to
   'Standard'.

6.  Security Considerations

   Padding DNS packets obviously increases their size, and will
   therefore lead to increased traffic, can lead to increased number of
   truncated packets when used over UDP-based transport.

   The use of the EDNS(0) Padding provides only a benefit when DNS
   packets are not transported in clear text.  Implementations therefore
   SHOULD avoid using this option if the DNS transport is not encrypted.

   Padding length might be affected by lower-level compression.
   Therefore (as described in Section 3.3 of [RFC7525]), implementations
   and deployments SHOULD disable TLS-level compression.

   The payload of the 'Padding' option could (like many other fields in
   the DNS protocol) be used as a covert channel.

7.  Acknowledgements

   This document was inspired by a discussion with Daniel Kahn Gillmor
   during IETF93, as an alternative to the proposed padding on the TLS
   layer.  Allison Mankin and Christian Huitema suggested text for this
   document.

8.  Changes

8.1.  draft-ietf-dprive-edns0-padding-01

   Fixed 'octects' typo.  Changed 'covert channel' text to align with
   allowing non-0x00 padding.  changed IANA considerations - assigned
   option code is 12.  Changed field definitions to allow for non-0x00
   padding, removed FORMERR requirement.  referenced rfc7525 in security
   considerations.  added acknowledgements.







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8.2.  draft-ieft-dprive-edns0-padding-00

   Adopted by WG.  Changed text about message size limit based on
   feedback.

8.3.  draft-mayrhofer-edns0-padding-01

   Changed minimum padding size to 0, rewrote Usage Considerations
   section, extended Security considerations section

8.4.  draft-mayrhofer-edns0-padding-00

   Initial version

9.  References

9.1.  Normative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <http://www.rfc-editor.org/info/rfc1035>.

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

   [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
              for DNS (EDNS(0))", STD 75, RFC 6891,
              DOI 10.17487/RFC6891, April 2013,
              <http://www.rfc-editor.org/info/rfc6891>.

9.2.  Informative References

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <http://www.rfc-editor.org/info/rfc7525>.

Author's Address










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Internet-Draft       draft-ietf-dprive-edns0-padding       November 2015


   Alexander Mayrhofer
   nic.at GmbH
   Karlsplatz 1/2/9
   Vienna  1010
   Austria

   Email: alex.mayrhofer.ietf@gmail.com












































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