The Wire Image of a Network Protocol
draft-trammell-wire-image-04

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Last updated 2018-09-05 (latest revision 2018-04-10)
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Network Working Group                                        B. Trammell
Internet-Draft                                             M. Kuehlewind
Intended status: Informational                                ETH Zurich
Expires: October 12, 2018                                 April 10, 2018

                  The Wire Image of a Network Protocol
                      draft-trammell-wire-image-04

Abstract

   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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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.

   Several documents currently under discussion in IETF working groups
   and the IETF in general, for example [QUIC-MANAGEABILITY],
   [EFFECT-ENCRYPT], and [TRANSPORT-ENCRYPT], discuss in part impacts on
   the third-party use of wire images caused by a migration from
   protocols whose wire images are largely not confidentiality protected
   (e.g.  HTTP over TCP) to protocols whose wire images are
   confidentiality protected (e.g.  H2 over QUIC).

   This document presents the wire image abstraction with the hope that
   it can shed some light on these discussions.

2.  Definition

   More formally, the wire image of a protocol consists of the sequence
   of messages sent by each participant in the protocol, each expressed
   as a sequence of bits with an associated arbitrary-precision time at
   which it was sent.

3.  Discussion

   This definition is so vague as to be difficult to apply to protocol
   analysis, but it does illustrate some important properties of the
   wire image.

   Key is that the wire image is not limited to merely "the unencrypted
   bits in the header".  In particular, interpacket timing, packet size,

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   and message sequence information can be used to infer other
   parameters of the behavior of the protocol, or to fingerprint
   protocols and/or specific implementations of the protocol; see
   Section 3.1.

   An important implication of this property is that a protocol which
   uses confidentiality protection for the headers it needs to operate
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