Abuse-Resistant OpenPGP Keystores
draft-dkg-openpgp-abuse-resistant-keystore-04

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openpgp                                                       D. Gillmor
Internet-Draft                                                      ACLU
Intended status: Informational                           August 22, 2019
Expires: February 23, 2020

                   Abuse-Resistant OpenPGP Keystores
             draft-dkg-openpgp-abuse-resistant-keystore-04

Abstract

   OpenPGP transferable public keys are composite certificates, made up
   of primary keys, direct key signatures, user IDs, identity
   certifications ("signature packets"), subkeys, and so on.  They are
   often assembled by merging multiple certificates that all share the
   same primary key, and are distributed in public keystores.

   Unfortunately, since many keystores permit any third-party to add a
   certification with any content to any OpenPGP certificate, the
   assembled/merged form of a certificate can become unwieldy or
   undistributable.  Furthermore, keystores that are searched by user ID
   or fingerprint can be made unusable for specific searches by public
   submission of bogus certificates.  And finally, keystores open to
   public submission can also face simple resource exhaustion from
   flooding with bogus submissions, or legal or other risks from uploads
   of toxic data.

   This draft documents techniques that an archive of OpenPGP
   certificates can use to mitigate the impact of these various attacks,
   and the implications of these concerns and mitigations for the rest
   of the OpenPGP ecosystem.

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

   This Internet-Draft will expire on February 23, 2020.

Gillmor                 Expires February 23, 2020               [Page 1]
Internet-Draft      Abuse-Resistant OpenPGP Keystores        August 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
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   5
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   7
     2.1.  Certificate Flooding  . . . . . . . . . . . . . . . . . .   7
     2.2.  User ID Flooding  . . . . . . . . . . . . . . . . . . . .   8
     2.3.  Fingerprint Flooding  . . . . . . . . . . . . . . . . . .   8
     2.4.  Keystore Flooding . . . . . . . . . . . . . . . . . . . .   9
     2.5.  Toxic Data  . . . . . . . . . . . . . . . . . . . . . . .   9
   3.  Keystore Interfaces . . . . . . . . . . . . . . . . . . . . .   9
     3.1.  Certificate Refresh . . . . . . . . . . . . . . . . . . .  10
     3.2.  Certificate Discovery . . . . . . . . . . . . . . . . . .  10
     3.3.  Certificate Lookup  . . . . . . . . . . . . . . . . . . .  11
       3.3.1.  Full User ID Lookup . . . . . . . . . . . . . . . . .  11
       3.3.2.  E-mail Address Lookup . . . . . . . . . . . . . . . .  12
       3.3.3.  Other Lookup Mechanisms . . . . . . . . . . . . . . .  12
     3.4.  Certificate Validation  . . . . . . . . . . . . . . . . .  12
     3.5.  Certificate Submission  . . . . . . . . . . . . . . . . .  14
   4.  Simple Mitigations  . . . . . . . . . . . . . . . . . . . . .  14
     4.1.  Decline Large Packets . . . . . . . . . . . . . . . . . .  14
     4.2.  Enforce Strict User IDs . . . . . . . . . . . . . . . . .  15
     4.3.  Scoped User IDs . . . . . . . . . . . . . . . . . . . . .  15
     4.4.  Strip or Standardize Unhashed Subpackets  . . . . . . . .  15
       4.4.1.  Issuer Fingerprint  . . . . . . . . . . . . . . . . .  15
       4.4.2.  Cross-sigs  . . . . . . . . . . . . . . . . . . . . .  15
       4.4.3.  First-party Attestations  . . . . . . . . . . . . . .  16
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