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Versions: 00

Individual submission                                       M. Kucherawy
Internet-Draft                                            Facebook, Inc.
Intended status: Informational                          November 5, 2018
Expires: May 9, 2019


       Security Considerations Regarding Compression Dictionaries
                  draft-kucherawy-httpbis-dict-sec-00

Abstract

   Data compression algorithms benefit from blocks of tuning data called
   "dictionaries".  These can greatly improve data compression speed
   and/or ratios, but their use and application has numerous potential
   security issues of concern to the communities using them.  This
   document enumerates security issues known about compression
   dictionaries at the time of publication so that future proposals for
   use of dictionaries can benefit from this collected material.

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 May 9, 2019.

Copyright Notice

   Copyright (c) 2018 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



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Dictionary Security Concerns  . . . . . . . . . . . . . . . . . 3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 5
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 5
   Appendix B.  Prior Art  . . . . . . . . . . . . . . . . . . . . . . 5




































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1.  Introduction

   Brotli [RFC7932] and Zstandard [RFC8478] are examples of two modern
   data compression algorithms.  While useful in their basic forms, they
   can be made far more effective with specific types of payloads when
   used with an object called a "dictionary".  A dictionary is a map
   that can be applied during compression or uncompression that provides
   an advantage when operating against specific types of content.  One
   might, for example, develop a dictionary that makes the compression
   algorithm more effective when applied to specific types of audio
   data.

   As dictionaries are being developed, some issues have come to light
   that indicate ways that use of dictionaries might introduce
   destructive side effects to the environment in which their use is
   applied.  This document is a collection of those topics, which can be
   consulted as work on dictionaries progresses; later, as RFCs are
   published advancing dictionaries, the content of this document could
   be used as a checklist to ensure that either the algorithms or their
   specification documents have been appropriately evaluated against
   these concerns.

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.

3.  Dictionary Security Concerns

   These subsections each describe an issue that has been raised with
   respect to use of dictionaries as input to compression and
   uncompression.  Where possible and known, acceptable mitigations are
   described.

   [TODO: This is a bullet list for now, but each bullet item will
   gradually be converted into a subsection containing relevant
   discussion.]

   o  Attacks that use dictionary-based compression to recover content
      in the response.

   o  Attacks that use dictionary-based compression to recover content
      in the dictionary.





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   o  Attacks that leverage dictionary-based compression to violate
      CORS/SOP/CSP. [need references and expansions for these]

   o  Attacks that manipulate a response's content by manipulating the
      contents of a dictionary.

   o  Attacks that obfuscate a malicious response's content through the
      use of dictionary-based compression.

   o  Attacks that identify users by fingerprinting their advertisement
      or use of dictionaries.

   o  Attacks that reveal past user behavior or associations through the
      negotiation and use of dictionaries.

   o  Attacks that use dictionaries to achieve denial-of-service /
      resource exhaustion:

      *  against network resources

      *  against storage resources

      *  against computation resources

      *  against the client

      *  against the server

      *  against an intermediary

      *  against a third-party

   o  Inadvertent leakage of private information in the creation of
      dictionaries.

   o  General security risks that follow from complexity of
      implementation.

4.  IANA Considerations

   This document includes no actions for IANA.

   [RFC Editor: Please remove this section before publication.]

5.  Security Considerations

   This document enumerates known security considerations about a space
   that is under development.  The list of issues discussed above may



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   not be exhaustive, but it is hopefully complete enough to ensure
   quality work is produced as a result.

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>.

   [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

   [RFC7932]  Alakuijala, J. and Z. Szabadka, "Brotli Compressed Data
              Format", RFC 7932, DOI 10.17487/RFC7932, July 2016,
              <https://www.rfc-editor.org/info/rfc7932>.

   [RFC8478]  Collet, Y. and M. Kucherawy, Ed., "Zstandard Compression
              and the application/zstd Media Type", RFC 8478,
              DOI 10.17487/RFC8478, October 2018,
              <https://www.rfc-editor.org/info/rfc8478>.

Appendix A.  Acknowledgements

   The author wishes to acknowledge the following for their review and
   constructive criticism of this update: TBD

Appendix B.  Prior Art

   Some prior art worth considering:

   o  draft-lee-sdch-spec, which was implemented in Chrome but then
      withdrawn

   o  draft-vkrasnov-h2-compression-dictionaries

   o  draft-vandevenne-shared-brotli-format

   o  HTTPBIS discussion during IETF 97

   o  Brotli "fetch spec" proposal: https://fetch.spec.whatwg.org/





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   o  various HTTPBIS mailing list threads about dictionaries

Author's Address

   Murray S. Kucherawy
   Facebook, Inc.
   1 Hacker Way
   Menlo Park, CA  94025
   US

   EMail: msk@fb.com








































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