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dprive                                                          H. Zhang
Internet-Draft                                                   P. Aras
Intended status: Standards Track                              Salesforce
Expires: September 12, 2019                                    W. Toorop
                                                              NLnet Labs
                                                            S. Dickinson
                                                              Sinodun IT
                                                               A. Mankin
                                                              Salesforce
                                                          March 11, 2019


                       DNS Zone Transfer over TLS
                   draft-hzpa-dprive-xfr-over-tls-00

Abstract

   DNS zone transfers are transmitted in clear text, which gives
   attackers the opportunity to collect the content of a zone by
   eavesdropping on links.  The DNS Transaction Signature (TSIG) is
   specified to restrict direct zone transfer to authorized clients, but
   it does not add confidentiality.  This document specifies use of TLS
   to prevent zone collection

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.

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



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   (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
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Zone Transfer Confidentiality Overview  . . . . . . . . . . .   3
   4.  Zone Transfer with DOT - Authentication . . . . . . . . . . .   3
   5.  Session Establishment and Closing . . . . . . . . . . . . . .   4
   6.  Performance Considerations  . . . . . . . . . . . . . . . . .   5
   7.  Implementation Considerations . . . . . . . . . . . . . . . .   5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   11. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   5
   12. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     13.1.  Normative References . . . . . . . . . . . . . . . . . .   5
     13.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   DNS has a number of privacy vulnerabilities, as discussed in detail
   in [RFC7626].  Query privacy has received the most attention.  There
   are now standards for three encryption capabilities for queries and
   more work going on to guide deployment [RFC7858] [RFC8484].

   [RFC7626] established that the query transactions are not public and
   needed protection, but on zone transfer it says only: Privacy risks
   for the holder of a zone (the risk that someone gets the data) are
   discussed in [RFC5936] and [RFC5155].

   In what way is exposing the full content of a zone a privacy risk?
   The contents of the zone could include information such as names of
   persons used in names of hosts.  Best practice is not to use personal
   information for domain names, but many such domain names exist.
   There may also be regulatory or other reasons why the zone content in
   full must be treated as private.

   Neither of the RFCs mentioned by RFC7626 contemplates the risk that
   someone gets the data through link eavesdropping.



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   [RFC5155] specifies NSEC3 to prevent zone enumeration, which is when
   queries for the authenticated denial of existences records of DNSSEC
   allow a client to walk through the entire zone.  Note that the need
   for this protection also motivates NSEC5; zone walking is now
   possible with NSEC3 due to crypto-breaking advances, and NSEC5 is a
   response to this problem.

   [RFC5155] does not address data obtained outside zone enumeration
   (nor does NSEC5).  Preventing eavesdropping of zone transfers (this
   draft) is orthogonal to preventing zone enumeration, though they aim
   to protect the same information.

   [RFC5936] specifies using TSIG [RFC2845] for authorization of the
   clients of a zone transfer and for data integrity, but does not
   express any need for confidentiality, and TSIG does not offer
   encryption.  Some operators use SSH tunneling or IPSEC to encrypt the
   transfer data.  Because the AXFR zone transfer is carried out over
   TCP from DNS protocol implementations, encrypting AXFR using DNS over
   TLS [RFC7858], aka DOT, seems like a simple step forward.  This
   document specifies how to use DOT to prevent zone collection from
   zone transfers, including discussion of approaches for IXFR, which
   uses UDP or TCP.

   Next steps: work on questions at DNS table during Hackathon, expand
   this draft, then solicit discussion on the DPRIVE mailing list.

2.  Terminology

   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.

   Privacy terminology is as described in Section 3 of [RFC6973].

   DNS terminology is as described in [RFC8499]:

3.  Zone Transfer Confidentiality Overview

4.  Zone Transfer with DOT - Authentication

   Subsection - TSIG

   Subsection - Mutual TLS






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5.  Session Establishment and Closing

   Subsection - AXFR Sessions

   The connection flow in AXFR is a NOTIFY from the primary server to
   the secondary server, and then an AXFR request from the secondary to
   the primay after which the data flows.

   The connection for AXFR SHOULD be established using port 853, as
   specified in [RFC7858].  If there is no response on port 853, the
   connection MAY be attempted using port 443.

   TODO: diagram of connection flow for AXFR, without and with DOT

   Subsection - IXFR Sessions (?)

   [RFC1995] specifies that Incremental Transfer may use UDP if the
   entire IXFR response can be contained in a single DNS packet,
   otherwise, TCP is used.

   Given this, how should confidentiality of IXFR be provided?  To
   discuss: should IXFR have a mode in which TCP is mandatory?  or
   should there be an approach of starting with DNS over DTLS, and
   switching to DNS over TLS with a TCP switch?  In workloads where
   there are frequent IXFRs, is the persistent mode that TCP-Mode would
   enable (as well as the retries, a benefit?

   Subsection - Policies for Both AXFR and IXFR

   In order to assure the confidentiality of the zone information, all
   the servers (primary and secondary) MUST have a consistent
   confidentiality use.  If any do not, this is a weak link for
   attackers to exploit.  How to do this is TBD.

   The entire group (the primary and all secondaries) MUST have a
   consistent policy on Strict or Non-Strict mode of operation.  How to
   do this is TBD.

   Subsection - Next Steps

   Upcoming open hackathon experiments will feed into this Session
   Establishment and Closing section, as much about this needs
   exploration as well as dicussion on the mailing list.








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6.  Performance Considerations

   The details in [RFC7858] about using persistent connections and TLS
   Session Resume are fully applicable to DNS Transfer over DOT as well.

7.  Implementation Considerations

   TBA

8.  IANA Considerations

   TBD

9.  Security Considerations

   This document specifies a security measure against a DNS risk, the
   risk that an attacker collects entire DNS zones through eavesdropping
   on plaintext DNS zone transfers.  It presents a new Security
   Consideration for DNS.  Some questions to discuss are: should DOT in
   this new case be required to use only TLS1.3 and higher to avoid
   residual exposure?  How should padding be used (if it should)?

10.  Acknowledgements

   Benno, Shumon, Tim

11.  Contributors

   The following contributed significantly to the document:

12.  Changelog

   draft-hzpa-dprive-xfr-over-tls-00

   o  Initial commit

13.  References

13.1.  Normative References

   [I-D.bortzmeyer-dprive-rfc7626-bis]
              Bortzmeyer, S. and S. Dickinson, "DNS Privacy
              Considerations", draft-bortzmeyer-dprive-rfc7626-bis-02
              (work in progress), January 2019.







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   [I-D.dickinson-dprive-bcp-op]
              Dickinson, S., Overeinder, B., Rijswijk-Deij, R., and A.
              Mankin, "Recommendations for DNS Privacy Service
              Operators", draft-dickinson-dprive-bcp-op-01 (work in
              progress), July 2018.

   [RFC1995]  Ohta, M., "Incremental Zone Transfer in DNS", RFC 1995,
              DOI 10.17487/RFC1995, August 1996,
              <https://www.rfc-editor.org/info/rfc1995>.

   [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>.

   [RFC2845]  Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
              Wellington, "Secret Key Transaction Authentication for DNS
              (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,
              <https://www.rfc-editor.org/info/rfc2845>.

   [RFC5077]  Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
              "Transport Layer Security (TLS) Session Resumption without
              Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
              January 2008, <https://www.rfc-editor.org/info/rfc5077>.

   [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
              Security (DNSSEC) Hashed Authenticated Denial of
              Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,
              <https://www.rfc-editor.org/info/rfc5155>.

   [RFC5936]  Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
              (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,
              <https://www.rfc-editor.org/info/rfc5936>.

   [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
              Morris, J., Hansen, M., and R. Smith, "Privacy
              Considerations for Internet Protocols", RFC 6973,
              DOI 10.17487/RFC6973, July 2013,
              <https://www.rfc-editor.org/info/rfc6973>.

   [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, <https://www.rfc-editor.org/info/rfc7525>.






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   [RFC7626]  Bortzmeyer, S., "DNS Privacy Considerations", RFC 7626,
              DOI 10.17487/RFC7626, August 2015,
              <https://www.rfc-editor.org/info/rfc7626>.

   [RFC7766]  Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and
              D. Wessels, "DNS Transport over TCP - Implementation
              Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016,
              <https://www.rfc-editor.org/info/rfc7766>.

   [RFC7830]  Mayrhofer, A., "The EDNS(0) Padding Option", RFC 7830,
              DOI 10.17487/RFC7830, May 2016,
              <https://www.rfc-editor.org/info/rfc7830>.

   [RFC7858]  Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
              and P. Hoffman, "Specification for DNS over Transport
              Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
              2016, <https://www.rfc-editor.org/info/rfc7858>.

   [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>.

   [RFC8310]  Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
              for DNS over TLS and DNS over DTLS", RFC 8310,
              DOI 10.17487/RFC8310, March 2018,
              <https://www.rfc-editor.org/info/rfc8310>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8467]  Mayrhofer, A., "Padding Policies for Extension Mechanisms
              for DNS (EDNS(0))", RFC 8467, DOI 10.17487/RFC8467,
              October 2018, <https://www.rfc-editor.org/info/rfc8467>.

   [RFC8484]  Hoffman, P. and P. McManus, "DNS Queries over HTTPS
              (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
              <https://www.rfc-editor.org/info/rfc8484>.

   [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
              January 2019, <https://www.rfc-editor.org/info/rfc8499>.

13.2.  Informative References







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   [NSEC5Research]
              Goldberg, S., Naor, M., Papadopoulos, D., and L. Reyzin,
              "NSEC5: Provably Preventing DNSSEC Zone Enumeration",
              2015, <https://www.ndss-symposium.org/ndss2015/ndss-2015-
              programme/
              nsec5-provably-preventing-dnssec-zone-enumeration/>.

   [RFC7129]  Gieben, R. and W. Mekking, "Authenticated Denial of
              Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129,
              February 2014, <https://www.rfc-editor.org/info/rfc7129>.

   [RFC7816]  Bortzmeyer, S., "DNS Query Name Minimisation to Improve
              Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
              <https://www.rfc-editor.org/info/rfc7816>.

   [RFC7871]  Contavalli, C., van der Gaast, W., Lawrence, D., and W.
              Kumari, "Client Subnet in DNS Queries", RFC 7871,
              DOI 10.17487/RFC7871, May 2016,
              <https://www.rfc-editor.org/info/rfc7871>.

   [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>.

   [RFC8094]  Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
              Transport Layer Security (DTLS)", RFC 8094,
              DOI 10.17487/RFC8094, February 2017,
              <https://www.rfc-editor.org/info/rfc8094>.

Authors' Addresses

   Han Zhang
   Salesforce
   San Francisco, CA
   United States

   Email: hzhang@salesforce.com


   Pallavi Aras
   Salesforce
   Herndon, VA
   United States

   Email: paras@salesforce.com






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   Willem Toorop
   NLnet Labs
   Science Park 400
   Amsterdam  Amsterdam   1098 XH
   The Netherlands

   Email: willem@nlnetlabs.nl


   Sara Dickinson
   Sinodun IT
   Magdalen Centre
   Oxford Science Park
   Oxford  OX4 4GA
   United Kingdom

   Email: sara@sinodun.com


   Allison Mankin
   Salesforce
   Herndon, VA

   Email: allison.mankin@gmail.com



























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