The Wire Image of a Network Protocol

Document Type Active Internet-Draft
Last updated 2019-03-04 (latest revision 2018-11-05)
Replaces draft-trammell-wire-image
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RFC Editor RFC Editor state AUTH48
Network Working Group                                        B. Trammell
Internet-Draft                                             M. Kuehlewind
Intended status: Informational                                ETH Zurich
Expires: May 9, 2019                                   November 05, 2018

                  The Wire Image of a Network Protocol


   This document defines the wire image, an abstraction of the
   information available to an on-path non-participant in a networking
   protocol.  This abstraction is intended to shed light on the
   implications on increased encryption has for network functions that
   use the wire image.

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Trammell & Kuehlewind      Expires May 9, 2019                  [Page 1]
Internet-Draft                 Wire Image                  November 2018

1.  Introduction

   A protocol specification defines a set of behaviors for each
   participant in the protocol: which lower-layer protocols are used for
   which services, how messages are formatted and protected, which
   participant sends which message when, how each participant should
   respond to each message, and so on.

   Implicit in a protocol specification is the information the protocol
   radiates toward nonparticipant observers of the messages sent among
   participants, often including participants in lower layer protocols.
   Any information that has a clear definition in the protocol's message
   format(s), or is implied by that definition, and is not
   cryptographically confidentiality-protected can be unambiguously
   interpreted by those observers.  This information comprises the
   protocol's wire image, which we define and discuss in this document.

   It is the wire image, not the protocol's specification, that
   determines how third parties on the network paths among protocol
   participants will interact with that protocol.

   The increasing deployment of transport-layer security [RFC8226] to
   protect application-layer headers and payload, as well as the
   definition and deployment of QUIC [QUIC], a transport protocol which
   encrypts most of its own control information, bring new relevance to
   this question.  QUIC is, in effect, the first IETF-defined transport
   protocol to take care of the minimization of its own wire image, to
   prevent ossification and improve end-to-end privacy by reducing
   information radiation.

   The flipside of this trend is the impact of a less visible wire image
   on various functions driven by third-party observation of the wire
   image.  In contrast to ongoing discussions about this tussle, this
   draft treats the wire image as a pure abstraction, with the hope that
   it can shed some light on these discussions.

2.  Definition

   The wire image of the set of protocols in use for a given
   communication is the view of that set of protocols as observed by an
   entity not participating in the communication.  It is the sequence of
   packets sent by each participant in the communication, including the
   content of those packets and metadata about the observation itself:
   the time at which each packet is observed, and the vantage point of
   the observer.

Trammell & Kuehlewind      Expires May 9, 2019                  [Page 2]
Internet-Draft                 Wire Image                  November 2018

3.  Discussion

   This definition illustrates some important properties of the wire

   Key is that the wire image is not limited to merely "the unencrypted
   bits in the header".  In particular, the metadata, such as sequences
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