The Wire Image of a Network Protocol

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Last updated 2018-10-10
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Network Working Group                                        B. Trammell
Internet-Draft                                             M. Kuehlewind
Intended status: Informational                                ETH Zurich
Expires: April 13, 2019                                 October 10, 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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   This Internet-Draft will expire on April 13, 2019.

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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

   The increasing deployment of transport-layer security [RFC8226] to
   protect application-layer headers and payload, as well as the
   definition and deployment of QUIC [I-D.ietf-quic-transport], 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.  [RFC8404] examines this issue from a network operator's
   viewpoint, and [I-D.ietf-tsvwg-transport-encrypt] focuses on
   transport-layer implications of increasing encryption.
   [I-D.ietf-quic-manageability] is, in part, a third-party user's guide
   to the QUIC wire image.  In contrast to those documents, this draft
   treats the wire image as a pure abstraction, with the hope that it
   can shed some light on these discussions.

2.  Definition

   More formally, the wire image of the set of protocols in use for a
   communication observed at a given point in the network consists of
   the sequence of packets sent by each participant in the
   communication, each expressed as a sequence of bits with the
   associated arbitrary-precision time at which the packet was observed.

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3.  Discussion

   This definition appears at first glance to be so impractically formal
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