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

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Individual submission                                          W. Handte
Internet-Draft                                            Facebook, Inc.
Intended status: Informational                          October 29, 2019
Expires: May 1, 2020

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

Abstract

   Dictionary-based compression enables better performance, but brings
   state into the process of compression, with all the complexities that
   follow.  This document explores the security implications of this
   technique in the context of internet protocols and enumerates known
   risks and mitigations.

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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 1, 2020.

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
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Handte                     Expires May 1, 2020                  [Page 1]
Internet-Draft       Compression Dictionary Security        October 2019

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Compression Environments  . . . . . . . . . . . . . . . .   3
     2.2.  Security Properties . . . . . . . . . . . . . . . . . . .   4
     2.3.  Threat Model  . . . . . . . . . . . . . . . . . . . . . .   4
     2.4.  Existing Attacks  . . . . . . . . . . . . . . . . . . . .   4
   3.  Dictionaries  . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Dictionary Compression  . . . . . . . . . . . . . . . . .   5
     3.2.  Dictionary Contents . . . . . . . . . . . . . . . . . . .   5
       3.2.1.  Unstructured Dictionaries . . . . . . . . . . . . . .   5
       3.2.2.  Structured Dictionaries . . . . . . . . . . . . . . .   6
     3.3.  Using Dictionaries  . . . . . . . . . . . . . . . . . . .   6
       3.3.1.  Generating Dictionaries . . . . . . . . . . . . . . .   6
       3.3.2.  Identifying Dictionaries  . . . . . . . . . . . . . .   7
       3.3.3.  Distributing Dictionaries . . . . . . . . . . . . . .   9
       3.3.4.  Selecting Dictionaries  . . . . . . . . . . . . . . .   9
       3.3.5.  Using Dictionaries  . . . . . . . . . . . . . . . . .  10
       3.3.6.  Deleting Dictionaries . . . . . . . . . . . . . . . .  10
   4.  Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
     4.1.  Revealing Message Content . . . . . . . . . . . . . . . .  11
       4.1.1.  By Observing Which Dictionary is Used . . . . . . . .  11
       4.1.2.  By Observing Message Size . . . . . . . . . . . . . .  12
       4.1.3.  By Observing Timing . . . . . . . . . . . . . . . . .  13
     4.2.  Revealing Dictionary Content  . . . . . . . . . . . . . .  14
       4.2.1.  By Observing Message Size . . . . . . . . . . . . . .  14
       4.2.2.  In Compression  . . . . . . . . . . . . . . . . . . .  14
       4.2.3.  In Decompression  . . . . . . . . . . . . . . . . . .  14
     4.3.  Manipulating Message Content  . . . . . . . . . . . . . .  15
       4.3.1.  By Manipulating Message Content . . . . . . . . . . .  16
       4.3.2.  By Manipulating Dictionary Content  . . . . . . . . .  16
       4.3.3.  By Manipulating Dictionary Identifiers  . . . . . . .  17
     4.4.  Obfuscating Message Content . . . . . . . . . . . . . . .  17
       4.4.1.  From Intermediaries . . . . . . . . . . . . . . . . .  17
       4.4.2.  Multiple Representations  . . . . . . . . . . . . . .  18
     4.5.  Tracking Users  . . . . . . . . . . . . . . . . . . . . .  18
       4.5.1.  Through Dictionary Negotiation  . . . . . . . . . . .  18
       4.5.2.  Through Dictionary Retrieval  . . . . . . . . . . . .  19
     4.6.  Denial of Service . . . . . . . . . . . . . . . . . . . .  19