Re: [tsvwg] [saag] 3rd WGLC (limited-scope): draft-ietf-tsvwg-transport-encrypt-15, closes 29 June 2020

Eric Rescorla <> Tue, 30 June 2020 01:00 UTC

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From: Eric Rescorla <>
Date: Mon, 29 Jun 2020 17:59:38 -0700
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To: "Black, David" <>
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Subject: Re: [tsvwg] [saag] 3rd WGLC (limited-scope): draft-ietf-tsvwg-transport-encrypt-15, closes 29 June 2020
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> This 3rd WGLC is limited to the following two topics:
>     Whether or not to proceed with a request for RFC publication
> of the draft.   The decision on whether or not to proceed will
> be based on rough consensus of the WG, see RFC 7282.
> During the 2nd WGLC, Eric Rescorla and David Schinazi expressed
> strong views that this draft should not be published –  those
> concerns have not been resolved and are carried forward to
> this WGLC.  This email message was an attempt to summarize
> those concerns:
> Further explanation from both Eric Rescorla and David Schinazi
> is welcome and encouraged to ensure that their concerns are
> clearly understood.

Well, I'll try again, but I'm not sure that I can do better than
I have before.

For reasons that are laid out in RFC 7258, the trend in protocol
design in IETF is towards encrypting more and more. The last two
transport protocols that were designed and widely deployed (SCTP over
DTLS and QUIC) both encrypt the vast majority of the protocol
metadata. This document advertises itself as "considerations"
for design of such protocols:

   The transport protocols developed for the Internet are used across a
   wide range of paths across network segments with many different
   regulatory, commercial, and engineering considerations.  This
   document considers some of the costs and changes to network
   management and research that are implied by widespread use of
   transport protocols that encrypt their transport header information.
   It reviews the implications of developing transport protocols that
   use end-to-end encryption to provide confidentiality of their
   transport layer headers, and considers the effect of such changes on
   transport protocol design, transport protocol evolution, and network
   operations.  It also considers some anticipated implications on
   application evolution.  This provides considerations relating to the
   design of transport protocols and features where the transport
   protocol encrypts some or all of their header information.

However, as I said above, the new transport protocols that are
actually being designed already feature metadata encryption and as far
as I can tell, there is no prospective protocol new transport protocol
design project for which these issues might be live. In that context,
it's hard not to read this document with its long litany of practices
which are impacted by metadata encryption as a critique of the
decisions by SCTP/DTLS and QUIC to encrypt most of the metadata.

This impression is reinforced by the description of the actual
practices themselves, which focuses almost entirely on practices
which appear to be benignly motivated (e.g., performance monitoring,
troubleshooting, etc.) However, we also know that metadata is widely
used for practices in which the network operator is adversarial
to the user, for instance:

- Blocking traffic based on TCP port, IP address, SNI, etc.

- Performance-based traffic class discrimination

- Monitoring the user's behavior via indicia like the ones above
  or via traffic analysis (see [0])

Yes, I understand that the authors explicitly disclaim judgement on
these practices, and the document does briefly touch on the general
idea, though the "concerns...have been voiced" tends to minimize those
concerns [1] but the selection of practices to focus on is extremely
telling. Focusing on the downsides of encryption for (at least
arguably well-meaning) network players while mostly ignoring the large
class of non-benign behaviors which encryption is intended to protect
against has the effect of overemphasizing the costs of encryption to
those players and minimizing the benefits to the endpoints whom it is
intended to protect.

To be maximally clear: I don't object to this document existing
and I don't think that the opinions implicit in it are ones that
should not be expressed. I merely don't think that it should be
published as an IETF Consensus document.


[1]    Another motivation stems from increased concerns about privacy and
      surveillance.  Users value the ability to protect their identity
      and location, and defend against analysis of the traffic.
      Revelations about the use of pervasive surveillance [RFC7624]
      have, to some extent, eroded trust in the service offered by
      network operators and have led to an increased use of encryption
      to avoid unwanted eavesdropping on communications.  Concerns have
      also been voiced about the addition of information to packets by
      third parties to provide analytics, customisation, advertising,
      cross-site tracking of users, to bill the customer, or to
      selectively allow or block content.  Whatever the reasons, the
      IETF is designing protocols that include transport header
      encryption (e.g., QUIC [I-D.ietf-quic-transport]) to supplement
      the already widespread payload encryption, and to further limit
      exposure of transport metadata to the network.