Certificate Transparency: Domain Label Redaction
draft-strad-trans-redaction-01

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Last updated 2017-01-17
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TRANS (Public Notary Transparency)                          R. Stradling
Internet-Draft                                           Comodo CA, Ltd.
Intended status: Experimental                                 E. Messeri
Expires: July 21, 2017                                    Google UK Ltd.
                                                        January 17, 2017

            Certificate Transparency: Domain Label Redaction
                     draft-strad-trans-redaction-01

Abstract

   This document defines mechanisms to allow DNS domain name labels that
   are considered to be private to not appear in public Certificate
   Transparency (CT) logs, while still retaining most of the security
   benefits that accrue from using Certificate Transparency.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on July 21, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Stradling & Messeri       Expires July 21, 2017                 [Page 1]
Internet-Draft          CT Domain Label Redaction           January 2017

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Redaction Mechanisms  . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Using Wildcard Certificates . . . . . . . . . . . . . . .   3
     3.2.  Using a Name-Constrained Intermediate CA  . . . . . . . .   4
       3.2.1.  Presenting SCTs, Inclusion Proofs and STHs  . . . . .   5
       3.2.2.  Matching an SCT to the Correct Certificate  . . . . .   6
     3.3.  Redacting Labels in Precertificates . . . . . . . . . . .   6
       3.3.1.  redactedSubjectAltName Certificate Extension  . . . .   7
       3.3.2.  Verifying the redactedSubjectAltName extension  . . .   8
       3.3.3.  Reconstructing the TBSCertificate . . . . . . . . . .   8
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
     4.1.  Avoiding Overly Redacted Domain Names . . . . . . . . . .   8
   5.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   9
     5.1.  Ensuring Effective Redaction  . . . . . . . . . . . . . .   9
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Some domain owners regard certain DNS domain name labels within their
   registered domain space as private and security sensitive.  Even
   though these domains are often only accessible within the domain
   owner's private network, it's common for them to be secured using
   publicly trusted Transport Layer Security (TLS) server certificates.

   Certificate Transparency v1 [RFC6962] and v2
   [I-D.ietf-trans-rfc6962-bis] describe protocols for publicly logging
   the existence of TLS server certificates as they are issued or
   observed.  Since each TLS server certificate lists the domain names
   that it is intended to secure, private domain name labels within
   registered domain space could end up appearing in CT logs, especially
   as TLS clients develop policies that mandate CT compliance.  This
   seems like an unfortunate and potentially unnecessary privacy leak,
   because it's the registered domain names in each certificate that are
   of primary interest when using CT to look for suspect certificates.
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