Review of draft-mm-wg-effect-encrypt-09

Martin Thomson <martin.thomson@gmail.com> Fri, 07 April 2017 03:25 UTC

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From: Martin Thomson <martin.thomson@gmail.com>
Date: Fri, 7 Apr 2017 13:24:59 +1000
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Subject: Review of draft-mm-wg-effect-encrypt-09
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Draft: draft-mm-wg-effect-encrypt-09
Date: 2017-04-07

Overall

This document is unfocused and unclear in its intent.  It is filled with
unsubstantiated claims, misleading statements, bias, and implied recommendations
for bad practices.  I would oppose its publication in the current form.
Furthermore, I don't believe that small scale or editorial changes would be
sufficient to correct these problems.


Aside from weakening its utility and/or arguments, the lack of focus will allow
this document to be abused in various ways.  For instance, it might imply IETF
endorsement of the practices described in the document.  Given that the IETF has
published positions that in some cases reject these practices, this document
needs to be very precise with its claims.  In its current form, it is not nearly
careful enough.

If this document is going to be published as an RFC, then it needs to be very
clear about its intent and its position - or lack thereof - toward these
practices.  It might be possible to say that these practices were employed in
networks in the past and that encryption is reducing the viability of those
practices.  A value-neutral statement like that might be acceptable as long as
it were framed carefully.

What is problematic is the implicit argument that is presented.  This document
could easily be construed as the IETF legitimizing these practices.  This
includes things on which the IETF has published statements (see for example RFC
2804).

This steps firmly into to sticky mess that is the politics of encryption policy.
If the IETF is going to make a political statement with this document, then that
statement needs to be a lot better than this.

Furthermore, any statement needs to be consistent with previous statements,
where in this case that primarily means RFC 7258.  Right now it reads as an
attempt to dilute RFC 7258.

If this document were more clearly formulated as an even-handed treatment of
what happens today - without judgment - then it could be useful.  Here the model
of RFC 7754 is a good one.  It describes the different facets of a use case,
then the different practices that might be employed to achieve that goal.  For
each practice the pros, cons, and technical limitations are covered with an eye
to all involved parties.


The Real Purpose of this Document

I think that this is the real question that this document wants to ask is:

   In a world where we are forced to defend against pervasive monitoring by
   motivated and malicious actors, can we find a role for less pervasive
   monitoring by well-intentioned entities?

There is an interesting discussion to be had here, but I'm convinced after my
review that this document is the wrong vehicle for that discussion.  I'm also
inclined to suggest that this is the wrong question to ask in the first place.

To the extent that we have the tools necessary to protect against pervasive
monitoring, we have to accept that more-legitimate uses of monitoring are
collateral.  Mostly, that's just a function of the limitations of the imperfect
tools we have.

The value in this document is in the rather comprehensive collection of use
cases.  Sure, some we might not attribute much weight to, like wiretapping.
Others are frankly frightening and not just in the Orwellian sense.

The problems that are implied by the current practices of network operators is a
large vein of unexplored work for the community.  Spending effort on finding
better solutions to legitimate problems is worthwhile.

In other words, the right question might be:

   For each of these practices that we see today, are the use cases that
   motivate them legitimate and how might be implement alternative techniques
   that properly respect privacy and security?


Two- and Three- Party Interactions

A great many sections of the document are unclear about the relationships
between different actors.  It seems like many of the activities describe, which
are presented here as being beneficial, are performed by a third party without
the consent or involvement of the two communicating peers.  After all, those are
the cases where encryption most often interferes.

The assertion that some benefit is accrued to communicating peers as a result of
these actions is the constant subject of the text.  I observe that in most of
the cases listed in this document, the benefit is accrued primarily to the third
party.

Clarity around the arguments that the document makes with respect to benefits to
each of the involved parties is sorely lacking.

In addition to this, where benefits truly do accrue to communicating peers,
technical options that don't rely on privacy-invasive techniques are routinely
dismissed in an offhand fashion.  In this way, any moral imprimatur attributed
to the use case is used to justify the privacy-invasive method.


Document Structure

This document is very hard to read (and review).  Probably my biggest complaint
is that the sections are haphazardly organized.  They contain a mixture of use
cases (what does SP X want to do) and techniques (how do they do these things).
Material is duplicated between sections.  Sections cover 10 different use cases
while talking about techniques, then other sections talk about different
techniques whiles talking about a scenario.  This leads to a lot of repetition.

There are three axes that this document contemplates:

 - the techniques that are currently used in networks
 - the use cases that motivate these techniques
 - the deployment scenarios in which these use cases manifest

It would appear that the document attemps to start from the deployment
scenarios.  However, this causes use cases and techniques to be mixed.
Judicious use of cross-referencing might have made this arrangement tractable,
but there are virtually no cross references.


Section 1

I find the introduction of this document difficult to parse.  I think that what
it wants to say is pretty straightforward, but it manages this in quite an
obtuse way.  Here's what I think that it is trying to say:

1. The IETF (and the larger community) has reacted to revelations of pervasive
   monitoring by increasing the use of encryption.
2. That has been somewhat successful.
3. More encryption has an impact on some practices that network operators have
   become accustomed to employing.

Expressed in this way, you can see how you could make a value-neutral
statement.

On the first, you can definitely make an argument based on the documents that
the IETF have published.  However, it is a mistake here in assuming that the
IETF - or the revelations of global-scale surveillance - is directly responsible
for the uptick in adoption of cryptographic protection for Internet traffic.
This is something that the community as a whole has been working towards for
many years; these trends predate the actions this draft focuses on.  This is
particularly true for the hosted provider cases in Section 3, where business
motivations for protection are far stronger than any concerns over government
surveillance.  Yeah, that's a subjective view, but I'm just reviewing, I don't
have to write a statement that will be labelled as having IETF consensus.

The immediate focus on opportunistic security is highly misleading, especially
in the web case.  The amount of opportunistically secured web traffic is
miniscule by global standards.  Since Firefox is the only browser to support OS
for the web, so adjust the following by market share: <https://mzl.la/2oc46ch>;.

I understand that mail is more often opportunistically secured, and you will
hear the virtues of OS sung from the rooftops, but all evidence suggests that
this is just a transitory state.  Instant messaging is closer to the web case,
with the trend toward strong protections that include authentication.  Of
course, I don't believe that mail or instant messaging represent any significant
traffic volume, so you need to be very careful about the nature of the claims
that are being made.  It has to be that the volume of mail has to be a rounding
error when it comes to capacity planning for networks.

On the second point, when making claims about prevalence of encryption, I would
advise caution when citing statistics.  Here's the graph for the Mozilla figures
that I think are being cited <https://mzl.la/2obZjrb>;. Here's a different graph
with a different number <https://mzl.la/2oc263J>;.  This highlights the point
that statistics need to be carefully cited, because bare claims are difficult to
assess.  Methodology matters when it comes to these sorts of claims - are we
talking proportions of packets, requests, flows, or something else?
Furthermore, the citations in the document are made more difficult to assess by
being measured at very different times (where the two I cite here were made at
roughly the same point in time).

The statistics do support the notion that there is a significant amount of
encryption in use, but it would appear that the claim is that the amount of
encryption is *increasing*.  This is not an extraordinary claim, but no evidence
is offered in support of the claim.  It isn't a certain thing either.  From the
statistics that I have access to, there was a definite uptick in October of
2015, but the rate appears to be stable since then.

It appears that the remainder of the document is intended to address the third
of my points in some detail.  That's a good structure in theory, but see above.

I don't think that the "service provider" taxonomy works for this document.
Based solely on the structure of the document, the only service provider that
this document concerns itself with is the one who forwards the packets.  That
application service providers are involved as one of the endpoints is relevant
in some cases, but not all.  For that reason, I prefer "network operator" and to
use specific terms like "mail host" or "web server" as appropriate to the
context.


Section 2 (top section)

I like that the attacks on SMTP by network operators is highlighted here.

There's an implicit argument here that runs counter to established IETF
consensus.

   Some methods used by service providers are impacted by the use of encryption
   where middle boxes were in use to perform functions that range from load
   balancing techniques to monitoring for attacks or enabling "lawful
   intercept", such that described in [ETSI101331] and [CALEA] in the US.

This fails to remain neutral.  This implicitly makes a value-judgment about
relative morality/acceptability/value of certain practices.  What is
particularly insidious about this particular form is that it invites
interpretation that is subjectively coloured.  For instance, as a non-EU and
non-US citizen, I might consider the use of the particular lawful intercept
techniques offensive; thus I might interpret this as a spectrum between
inoffensive to offensive.  An employee of the US government might view this
somewhat differently and interpret this as a scale between low-value to
high-value.  I'm guessing here, but this is really just to highlight my point
about care.

A more serious concern is this statement:

   The loss of access to these fields may prompt undesirable security practices
   in order to gain access to the fields in unencrypted data flows.

I've read this argument before (see https://queue.acm.org/detail.cfm?id=2508864
for the long form), and it might even have an element of truth to it.  However,
it's not a statement that I personally attribute any real credibility to, and
nor do I think that it needs to be credited with any amount of seriousness.  I
certainly disagree with the IETF making any such statement.  It says that we are
collectively willing to bow in response to (anticipated) threats of violence.

Section 2.1

This is one of the few sections that talk about what it means to operate a
service as opposed to operate a network.

Overall, this section doesn't work particularly well.  The distinction between
integrated and standalone load balancing is an interesting division, but it
doesn't leverage this distinction well.  What causes a standalone load-balancer
to be necessary?  Is this something a network operator uses?  I see text on NFV
later, but it's far removed from the original text and it seems aspirational
rather than concrete.  On the other hand, many of the concerns in this document
simply don't apply to an integrated load balancer.

The amount of text on QUIC here is surprising.  Given how much of QUIC is
changing right now, we shouldn't publish a document that attempts to make claims
about what QUIC is or how it is operated.  This attempts to dive into the
details of QUIC connection migration in a way that presumes much about the
outcome of issues that the QUIC working group is still struggling with.

I would strongly recommend removing QUIC-specific language from this section and
the document as a whole.  We have an operational document in the QUIC working
group that would be a good venue to discuss some of these concerns.

Is this an oblique reference to (the much-loved) RFC 7974?

   Current protocols, such as TCP, allow the development of stateless integrated
   load balancers by availing such load balancers of additional plain text
   information in client-to-server packets.

Otherwise, I don't know what it means.

BTW, I like this parenthetical:

   (That said, care must be exercised to make sure that the information encoded
   by the endpoints is not sufficient to identify unique flows and facilitate
   Persistent Surveillance attack vector.)

I'm going to take this to the QUIC working group, because QUIC certainly doesn't
meet that bar right now.  It fully facilitates Persistent Surveillance in its
current form (proper noun?  I haven't really seen that term before, even though
it draws a neat parallel with Pervasive Surveillance).

Editorial:
* "pop" is a term of art that needs explanation.
* "QUIC?s", "network?s" - avoid smart quotes, and - more generally - the
  possessive form for the inanimate.
* "QUIC's server-generated flow IDs" -> "QUIC's connection IDs".

Section 2.2

I think that this sums the situation up reasonably well.  It fails the
value-neutral test in a few ways though.  As I understand the situation,
surveying operates at many levels.  For accurate planning, models of endpoint
behaviour are used to determine things like whether loss or congestion is
affecting throughput.  Really good models require knowledge of what users are
attempting to do and the applications they are using (as mentioned, things like
browser version matter in these models).  For instance, it isn't enough to
understand that the user is trying to receive 720p video, you also have to know
that a 4k stream for the same content is available.

The degree to which these models are privacy-invasive is not even acknowledged.

Nit: Did you realize that "well-intentioned" is a euphemism?  I'd expect that
subtlety to be lost on many readers though.

Section 2.3.1

I find this sad, even if I can recognize the truth of it:

   A monitoring system could easily identify a specific browser,
   and by correlating other information, identify a specific user.

As a browser vendor, we don't consider this to be a feature, it's a bug.

Section 2.3.2.1

This is a strange section under which to put caching.  Caching is a use case
akin to compression.  I don't see it as belonging to the class of things that
rely on DPI.  You just intermediate the cleartext HTTP in the way that RFC 7230
recognizes.  Note that RFC 7230 explicitly does not endorse the practice of
transparent proxying for a range of reasons, not the least of which is the
complete lack of transparency (yep).

Section 2.3.2.2

Again, it's strange to see differential treatment under DPI.  I was fairly sure
that fingerprinting was used here as well.

Section 2.4

This section doesn't even attempt to recognize that applications are much better
now at scaling content to suit the device on which that content is intended to
be consumed.  It should.

This section should not represent compression as an unmitigated good.  I'm told
that significant damage can be done to video streams by "well-intentioned"
compression middleboxes.

Yet again I see a call back to the implicit threat of violence in "they will
adopt undesirable security practices".  Statements in that form have no place in
IETF RFCs.

Section 2.5

This mentions RFC 7754 then blithely ignores its primary conclusion. Generally,
The treatment in RFC 7754 of this subject is more even-handed.

The use of particular examples (betting, gambling, dating) shows cultural bias.

Jargon warning: "core network", "the mobile network" ("the"?)

Section 2.5.2

   This type of granular filtering could occur at the endpoint, however the
   ability to efficiently provide this as a service without new efficient
   management solutions for end point solutions impacts providers.

The initial premise here (up to the first comma) is the conclusion of RFC 7754.
I disagree with the conclusion, and I suspect so does RFC 7754.  In scenarios
where this matters, endpoints are routinely managed centrally.  The range of
options for this sort of management are plentiful and diverse.

Section 2.5.3

This describes a captive portal, which in the case where the service provider
has a relationship with their customers, seems like a poor solution.  See the
CAPPORT working group for ways in which people are actually working on a
solution to this problem.

Section 2.6

The capitalization of section headings is inconsistent here (and throughout).

Section 2.6.1

Isn't this a duplicate of Section 2.1?

Section 2.6.2

I can't parse this statement:

   Approved access to a network is a prerequisite to requests for Internet
   traffic - hence network access, including any authentication and
   authorization, is not impacted by encryption.

And then we get into zero rating, which is a hot-button topic.  No
acknowledgment given to the sensitivities on the subject, or even a superficial
exploration of the technical options that are available.

This text references a non-existent Appendix.

Section 2.6.5

This paragraph is strange.  It starts by describing what appears to be use cases
(are those scare quotes?).  It finishes by implying that these are attacks on
privacy (which they are).

What is "Non-Customer Proprietary Network Information"?  I hope that this isn't
an attempt to somehow privilege the information so that it seems less than
privacy-invasive.

Section 2.7

This is one of the areas that is most legitimately affected by increased
adoption of encryption.  I have no doubt that having detailed information about
the application and its use makes the process of troubleshooting easier.

This is the first mention in the document of network-based optimization.  Was
the section describing that cut from an earlier draft?

The use of websockets as a primary example is an odd one.  It's just not that
common.  For reference, we see >20% failure rates on encrypted websockets and
>50% failures in the clear; no one in their right mind would rely on websockets.
If the point is that HTTP is carrying more traffic (see
http://conferences.sigcomm.org/hotnets/2010/papers/a6-popa.pdf) saying just that
would be more effective.

Section 3

It would help if "hosted environments" was defined before diving in.

Section 3.1

The paragraph on DLP is ironically amusing.  Encryption exists to prevent
private information leakage, but the assertion here is that encryption is
hampering DLP attempts.

It's true that protection of intellectual property is an important business
goal, but this handling suggests an architecture that I'm fairly sure is counter
to established wisdom (see "SSL added and removed here :-)":
https://www.washingtonpost.com/rf/image_404h/2010-2019/WashingtonPost/2013/10/30/Local/Images/GOOGLE-CLOUD-EXPLOITATION1383148810.jpg).
Worse, this casually dismisses a model that is actually more likely to work.
Malware encrypts too (https://arxiv.org/abs/1607.01639).

Section 3.1.1

Who is the customer here?

Why does the hosting provider need to monitor access?  They have the ability to
limit accesses, but this is suggesting that what happens within the envelope of
what they permit is important for them to know.  I'd be surprised if you could
show that this is true.  Hosting providers - in my experience - value their
ongoing business and would not jeapardize it by snooping on their customers.
It's different if the customer opts in to a security service, but that
demonstrates a cooperative situation, where the rest of this document is largely
concerned with adversarial uses of encryption.

Section 3.1.2

This is another example where the organization of the document could
be improved.

Again with the "SSL added and removed here :-)" recommendation.  PCI don't
permit that for good reason.

Section 3.2.1

I don't believe that monitoring of these types of application require cleartext
access.  There are two parties involved: the provider of the application and the
user of it.  The provider has most of the power here and can theoretically
design the system to allow whatever level of access they require.  To the extent
that the user needs protection from the application provider, that is a matter
of negotiation between them.

I don't see how the adversarial three-party situation presented in the rest of
the document applies in this situation.

Section 3.2.2

No real mention of the effect of encryption here, or is this just saying that
there is no issue here?

I don't see the point of the PGP/Dark Mail paragraph.  I'd be leery of the IETF
saying things like "PGP may be a front runner" though.

Section 3.3

There's certainly a lot of detail here, but I had a really hard time extracting
value from this section.  I can't see how data storage is fundamentally
different to the general case of an application provider.

Section 4.1.1

I appreciate the recognition that endpoint-based techniques work.  The
implication that this isn't the obvious solution, much less so.

Section 4.1.2

I'm confused about the purpose of this section.  This seems to be talking about
the sort of network-based methodologies an application provider might employ to
ensure that their application is working as intended.  Why would the application
provider not have access to detailed logging and usage metrics?

As an aside, I skimmed through ietf-ippm-6man-pdm-option, since it is cited no
fewer than three times in the same paragraph.  It makes some fairly bold claims
about its effect on privacy that I don't believe will hold up to analysis.

Section 4.1.3.1

This section correctly identifies the issue as one of shortcomings in logging,
not increased use of encryption.

I would have stopped there, but the section persists and ultimately references
RFC 7974, which is widely recognized as a monstrously bad idea (the IESG note is
fairly clear on this point).

Section 4.1.3.2

"HTTP/2", not "HTTP2".

I don't see how this section belongs in this document.  The 1:1 correlation
between actions and flows in HTTP was a mistake of the 1980s that we've spent a
lot of time on correcting (sometimes unsuccessfully, see pipelining).

Section 4.1.3.3

It's not a "service call" it's just a request.

Section 4.2

If the inclusion of a reference to RFC 7457 is to support a claim that TLS is
attacked, that's sailing far too close to an endorsement of attacks than I am
comfortable with.  However, I don't believe that any of the listed attacks
remain viable in modern applications.  What is most often the case is that a
trust anchor is installed on enterprise users' machines and new certificates are
minted as needed.  In other words, the host that is accessing the HTTPS site is
owned by the enterprise and modified so that it can comply with its policies.

When you recommend attack like this (to be clear, I would oppose publication of
text that does this), you need to acknowledge the downsides.  For example, MitM
devices routinely break connections, they hide the true security status of
communications from endpoints and users, they frequently implement weaker
versions of protocols, they often don't include the same degree of rigor in
things like certificate validation, and probably many more things that I can't
casually list off the cuff.

The discussion of caching here warrants a new section.

Section 5.1

s/effect/affect

No complaint here, just an advertisement for technical solutions that aren't
affected by increases in encryption.  Good, though I'm not sure if the section
meets the document's criteria for inclusion.

Section 5.3

No cititation for APWG.  Not an IETF working group from what I can see.

There's a presumption here that administrators need to perform these tasks.  Why
can't endpoints do this?  It would certainly be a whole lot less invasive that
way.  Take a look at how browsers implement checks for "bad" sites (which
include phishing sites).  These methods have some fairly significant privacy
safeguards without compromising on performance.

Section 5.5

See my comment about about endpoint-based methods.

Section 5.6

I believe that the spoofed source address problem is not relevant to this
document.  It's a fairly well understood problem.  That said, if we could wave a
magic wand and get BCP 38 deployed, that might be nice.

Section 6.1

As this says, it's fairly well understood that - for HTTP - SNI is used.  The
point that it is optional is interesting, but doesn't deserve the amount of
attention this section devotes to it.  The clients that don't include SNI are in
a diminishing minority.

That said, this doesn't pay any attention to another feature in HTTP/2:
connection coalescing.

Section 6.2

ALPN will be encrypted in TLS 1.3.

Section 6.3

This reads as a invitation to perform traffic analysis (a statement that I
oppose).  Note that we have added padding to most recent protocols (HTTP/2 and
TLS 1.3 in particular) to give endpoints the ability to resist this sort of
attack.

Note that block ciphers can add ~240 octets of discretionary padding per record.
That can be pretty effective if you are careful.

Section 7

This section is duplicative of much of the rest of the document.  I realize that
editing is hard, but see my earlier comments about structure.

It's obvious that this section is about QUIC.  That shows in several ways.  It's
nice how it doesn't say so out loud, but it leaks through in several confusing
ways.  See below.

Section 7.1

This section is purportedly about encrypted ACKs, which won't happen until we
get to QUIC.  But the points regarding proxies (b, c, d) are not prevented by
encrypted ACKs, they are prevented by encryption more generally.  Point e is
defeated by integrity protection of ACKs, not confidentiality protection.

I hope that the IETF never publishes draft-dolson-plus-middlebox-benefits; it
makes claims about the benefits of specific solutions for different use cases
with the goal of justifying those solutions.  At the same time, it fails to
recognize the existence of alternative, often superior, solutions for those use
cases.  In other words, it has many of the same issues as this document.

FWIW, also be OK if draft-thomson-http-bc never went anywhere as well; I don't
know how to close the gap between the privacy assurances I wish it had and the
privacy weaknesses it has.

The phrase "trusted proxies" is a dangerously misleading phrase.  The concept of
trust is - particularly in this context - frequently abused.

Sections 7.2 and 7.3

I'd be interested in learning about the justification for these features (again,
go back to my comment about to whom the benefit accrues, and I'd advise caution
not to make the trickle-down economics mistake of using second-order effects).
Personally, I'm not that sad that they are going to be negatively affected.

Section 7.2, Point d seems to be saying something about a multiplexed protocol,
not one that has an encrypted transport header (see above regarding QUIC).

All these points equally apply to HTTPS, which suggest that encrypted transport
headers is not the issue (unless by transport we mean HTTP).

Section 7.4

s/GPSR/GPRS/ ?

Section 8

I generally agree with the first statement here, but after having read the
document, I could take away some very different views on what the "problems at
hand" actually are.  I suspect that different people will have very different
takeaways.

The conclusion section of a document is not the right place to start introducing
new information, particularly information relevant to RFC 2804.

Not sure where this is going:

   Terrorists and criminals have been using encryption for many years.

Because it's disconnected from the remainder of the paragraph.  If you are going
to invoke the T-word, you had better have a strong argument to make.  On the
final sentence of that paragraph, the subject ("This") is unclear.