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Versions: 00 01 02 draft-ietf-trans-gossip

TRANS                                                        L. Nordberg
Internet-Draft                                                  NORDUnet
Intended status: Experimental                           October 27, 2014
Expires: April 30, 2015


                            Gossiping in CT
                     draft-linus-trans-gossip-ct-00

Abstract

   This document describes gossiping in Certificate Transparency
   [RFC6962].

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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   This Internet-Draft will expire on April 30, 2015.

Copyright Notice

   Copyright (c) 2014 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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   (http://trustee.ietf.org/license-info) in effect on the date of
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.






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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Problem . . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Who should gossip . . . . . . . . . . . . . . . . . . . . . .   3
   4.  What kind of data to gossip about . . . . . . . . . . . . . .   3
     4.1.  Signed Tree Heads . . . . . . . . . . . . . . . . . . . .   3
       4.1.1.  Web browsers  . . . . . . . . . . . . . . . . . . . .   3
       4.1.2.  CT monitors . . . . . . . . . . . . . . . . . . . . .   4
       4.1.3.  MTA:s . . . . . . . . . . . . . . . . . . . . . . . .   4
       4.1.4.  MUA:s . . . . . . . . . . . . . . . . . . . . . . . .   4
       4.1.5.  XMPP clients  . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Illegitimate Signed Certificate Timestamps  . . . . . . .   4
   5.  Security considerations . . . . . . . . . . . . . . . . . . .   5
   6.  Open questions  . . . . . . . . . . . . . . . . . . . . . . .   5
   7.  IANA considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   5
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Gossiping in Certificate Transparency (CT) can be split up in three
   pieces:

   o  A general gossip protocol.  This document uses
      [draft-linus-trans-gossip] for a general gossip protocol.

   o  Gossip strategy and policy - what data to gossip and how to deal
      with incoming gossip information.

   o  Gossiping rules, i.e. what type of data and with whom to gossip.

   The scope for this document is the last point, the gossiping rules.

2.  Problem

   Gossiping about what's known about CT logs helps solving the problem
   of detecting malicious logs showing different views to different
   clients, a.k.a. the partitioning attack.

   The separate problem of how to disseminate information about a log
   misbehaving in other ways may be helped by gossiping but poses a
   potential threat to the privacy of end users.  Gossiping about log
   data linkable to a specific log entry and through that to a specific
   site has to be constrained to using the gossiping message format and
   gossiping transports for sending sensitive data only to particular
   recipients.



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3.  Who should gossip

   o  TLS clients using PKIX (i.e. web browsers, MTA:s, MUA:s, XMPP
      clients)

   o  CT auditors and CT monitors

4.  What kind of data to gossip about

   This section describes what type of log data to gossip.

4.1.  Signed Tree Heads

   All CT clients SHOULD gossip about Signed Tree Heads (STH's) with as
   many other CT clients as possible.

   Gossiping about STH's enables detection of logs presenting more than
   one view of the log.

   An STH contains: - the size of the tree being signed - a timestamp
   indicating the time when the tree was signed - the merkle tree hash
   of the tree being signed - a signature made by the log

   An STH received from a client may indicate the following about that
   client: - gossiping - using CT, as late as the timestamp and tree
   size indicate - talking, indirectly, to the log indicated by the tree
   hash - software being used and software version

   Which STH's to send and how often is part of gossiping strategy and
   out of scope for this document.

   [TBD gossip about inclusion proofs and consistency proofs too?]

   STH's are sent to a preconfigured gossip service in a
   [draft-linus-trans-gossip] GOSSIP-MSG message with 'gossip-data' as a
   JSON object [RFC7159] with the following content:

   o  sths: array of [RFC6962] Signed Tree Head's

4.1.1.  Web browsers

   Web browsers SHOULD send STH's to web servers using Transparency
   Gossiping [draft-linus-trans-gossip] by sending GOSSIP-MSG messages
   to a gossip service.  Web browsers SHOULD use the
   [draft-linus-trans-gossip-transport-https] transport and MAY use
   other transports as well.





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   Which web servers STH's will be sent to depends on which web servers
   the chosen transports are connected to and those web servers
   capability and willingness to convey gossip.  This is handled by the
   gossip transports.

   Web browsers MAY register as a gossip transport themselves and
   perform the sending and receiving of gossip messages using
   connections already in use.

4.1.2.  CT monitors

   CT monitors SHOULD send STH's to web servers using Transparency
   Gossiping [draft-linus-trans-gossip] by sending GOSSIP-MSG messages
   to a gossip service.

   CT monitors SHOULD use as many transports as possible.

4.1.3.  MTA:s

   TBD

4.1.4.  MUA:s

   TBD

4.1.5.  XMPP clients

   TBD

4.2.  Illegitimate Signed Certificate Timestamps

   If a TLS client detects misbehaviour of a log related to a given
   Signed Certificate Timestamp (SCT) it MAY send that SCT to the web
   server it got the SCT from.  A corresponding X.509 certificate chain
   MAY be sent along with the SCT.  The
   [draft-linus-trans-gossip-transport-https] messaging format SHOULD be
   used for this.

   SCT's and corresponding X.509 certificates are sent to a
   preconfigured gossip service in a [draft-linus-trans-gossip] GOSSIP-
   MSG message with 'gossip-data' as a JSON object [RFC4627] with the
   following content:

   o  entry: An array of objects consisting of

      *  sct: An [RFC6962] Signed Certificate Timestamp





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      *  x509_chain: An array of base64-encoded X.509 certificates.  The
         first element is the end-entity certificate, the second chains
         to the first and so on.

   The 'x509_chain' element can be empty or include as many certificates
   part of the same chain as available.

   Note that 'gossip-data' is base64-encoded.

5.  Security considerations

   o  TODO expand on why gossiping STH's is ok

   o  TODO expand on why gossiping SCT's is bad for privacy in the
      general case

6.  Open questions

   o  TODO active vs. passive participants

7.  IANA considerations

   TBD

8.  Contributors

   TBD

9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, July 2006.

   [RFC6962]  Laurie, B., Langley, A., and E. Kasper, "Certificate
              Transparency", RFC 6962, June 2013.

   [RFC7159]  Bray, T., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, March 2014.

   [draft-linus-trans-gossip]
              "Transparency Gossip", n.d..

   [draft-linus-trans-gossip-transport-https]
              "Transparency Gossip HTTPS transport", n.d..




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Author's Address

   Linus Nordberg
   NORDUnet

   Email: linus@nordu.net













































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