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DoHoT: making practical use of DNS over HTTPS over Tor
https://github.com/alecmuffett/dohot

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DoHoT: making practical use of DNS over HTTPS over Tor

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# DoHoT: making practical use of DNS over HTTPS over Tor



This is the first document for a new project called `DoHoT` DNS, which I

hope will grow to help people recoup some privacy in places where they

have previously not considered it lacking.



## News/Updates



### 2020/11/02



Measuring 1.26 million requests to my DoHoT server since July 14th,

with a [revised configuration](dnscrypt-proxy.toml)

per this repository; practical client-side latency analysis is as follows:



* min: 0

* max: 10726

* count: 1261084

* mean: 466.60

* median: 268

* median_low: 268

* median_high: 268

* median_grouped: 267.57

* mode: 0

* stdev: 752.24

* variance: 565862.02

* pstdev: 752.24

* pvariance: 565861.57

* p1: 0

* p10: 0

* p20: 0

* p25: 0

* p30: 0

* p33: 125

* p40: 183

* p50: 268

* p60: 408

* p66: 474

* p70: 519

* p75: 587

* p80: 683

* p90: 1112

* p95: 1531

* P99: 3686



#### Highlights



* 30% of requests are served from cache

* 50% of requests are served in less than 270ms

* 68% of requests are served in less than 500ms (not shown)

* 90% of requests are served in less than 1200ms

* 99% of requests are served in less than 3700ms

* the configuration enforces a timeout of 10000ms; this is rarely reached



### 2020/07/14



I have updated the repo to cite DNSCrypt-Proxy (DNSCP) version

`2.0.44` by default, and to use the standard configuration files for

all DoH servers. Also there has been some general configuration

cleanup - mostly to use DNSCP defaults for timeouts and keepalives -

and better documentation.



## TL;DR



I set up a DNS stub resolver using *DNS over HTTPS over Tor* at home.

For four months - during the UK COVID-19 lockdown / shelter-in-place -

my partner and I have lived with it exclusively.  It has worked so

well that we haven't noticed any practical change in our internet

service experience.



## Goals



What I seek with this project is to explain, to encourage, and to

simplify adoption of DNS over HTTPS over Tor.



## Disclaimers



* Likely none of this is new.

* I probably describe nothing that is novel.

* Other people will have done this before, and are probably doing it

  now, although arguably from a base of less experience than myself

  regarding Tor and performance tuning.

* None of the software I describe has been written by me, but instead

  has been written by people cleverer and more dedicated than I.

* DNS experts will almost certainly describe the latency figures that

  I publish here as "excessively slow", "impractical", or

  "unusable". I firmly disagree, at least for the domestic or

  individual user, and I present several months' worth of both numbers

  and "24x7 lived experience" to back up my perspective.



## The Experiment



For more than four months my home - excluding a small

[extranet](https://en.wikipedia.org/wiki/Extranet) - has gone utterly

"DNS Dark", so that absolutely no `Do53` traditional UDP or TCP DNS

traffic has come from my house.



This has been during the period of the COVID-19 "lockdown" so my

domestic network use has greatly increased in this time: streaming

Netflix & Amazon Prime, work videoconferencing over Microsoft Teams

and Google Meet, home banking, shopping, family video over Facebook

Portal, etc; desktops, laptops, mobile devices, tablets, IoT... the

internet has been a critical resource for life, and yet no traditional

DNS traffic has left my home since February.



To fulfil the actual need for IP address resolution, I set up a

Raspberry Pi as a home DNS server - in much the same manner that I

have previously operated a [Pi-Hole Ad-Blocker](https://pi-hole.net) -

except on this occasion:



* I configured a `dnscrypt-proxy` resolver listening to port 53

* set the resolver to exclusively use `DoH` for upstream resolution

* configured `DoH` to use only the SOCKS5 interface provided by a local `tor` daemon

* advertised that resolver using DHCP on my home network, and finally...

* set my firewall to block all network egress to ports 53 & 853, TCP & UDP

  * except for permitting the resolver itself to have just enough port 53 access to bootstrap



## Experiment Results Summary



Almost all of the documentation that I have read - including some

amongst the `dnscrypt-proxy` source code - has told me that `DoHoT`

would be laggy, unlivably slow, and a bad idea.  I cannot

agree. Although DNS-query latency figures have been somewhat inflated,

my actual experience of internet usage has been "business as usual".



It's helpful that every four hours `dnscrypt-proxy` prints a summary

of upstream request latency amongst the loadbalanced pool of resolvers

that it is using, and I shall present the statistics for the entirety

of June 2020, plus a little bit of May and July.



The headline stats are:



![196 lowest-latency DoHoT fetches from 3 DoH providers, June 2020](img/june-2020.png)



* a pool of 3 `DoH` providers for the initial experiment: A, B, and C

* 196 data points from May 31st to July 2nd

* p50 / median request lowest-latency: 193ms

* p90 request lowest-latency: 372ms

* p95 request lowest-latency: 425ms

* max request lowest-latency: 815ms



![sorted distribution of DoHoT fetches from 3 DoH providers, June 2020](img/lowest-latency.png)



Manual spot-testing from my extranet suggests that resolution of

`.com` names that are not in my ISP's upstream resolver cache will

take 140 to 170ms to be resolved via `Do53`, and that resolution of a

domain in `.cn` can take 670ms.  These numbers are ad-hoc, but I find

it reassuring that the best-case times for `DoHoT` are in the same

ballpark as survivable normal/worst-case times for `Do53`.



## Why DoHoT?



The DNS protocol is more than 40 years old, was never designed for

privacy, and is broadly instrumented - i.e.: logged, sold, spied-upon,

and interfered-with - by:



1. Cafes, Hotels, Aircraft, and other "captive portals"

2. Internet Service Providers (ISPs)

3. The upstream peers and bearer-providers for ISPs

4. Partner-companies to the above, which monetise the ability to

   control, manipulate and track DNS results

5. Nation-state Governments which want to exert control upon peoples'

   access to information



As I have written

[elsewhere](https://medium.com/@alecmuffett/why-every-privacy-activist-should-embrace-dns-over-https-a361e727657f)

the launch of the `DoH` protocol presents a marvellous opportunity;

the protocol itself has been represented as rather

[contentious](https://www.theregister.co.uk/2019/09/24/mozilla_backtracks_doh_for_uk_users/)

but a careful reading of some of the more

[critical](https://www.eset.com/blog/business/the-battle-for-dns-and-data/)

[coverage](https://www.theregister.co.uk/2018/10/23/paul_vixie_slaps_doh_as_dns_privacy_feature_becomes_a_standard/)

suggests that the criticisms tend to come from people or organisations

in categories 2 through 5 above, perhaps concerned that

increased DNS privacy may impact their business models, revenue,

income, or their quiet "obligations" to nation-state security

services.  as if people being enabled with privacy would somehow be

"their fault".



### DoH as an Opportunity



Some critics ignore the "first mile" transport-security benefits of

`DoH` and instead [frame the concerns](https://www.zdnet.com/article/dns-over-https-causes-more-problems-than-it-solves-experts-say/)

by complaining about problems that `DoH` doesn't actually address; for

instance:



[ZDnet article](https://www.zdnet.com/article/dns-over-https-causes-more-problems-than-it-solves-experts-say/):

> The response to DoH's anointment as a major privacy-preserving

> solution has been downright acid, in some cases. Critics have taken

> a jab at the protocol on different plains, which we'll try to

> organize and categorize below:

>

> * DoH doesn't actually prevent ISPs user tracking

> * DoH creates havoc in the enterprise sector

> * DoH weakens cyber-security

> * DoH helps criminals

> * DoH shouldn't be recommended to dissidents

> * DoH centralizes DNS traffic at a few DoH resolvers



The cited criticisms are not reasonable because the concerns that are

raised are generally not for `DoH` to fix:



#### "DoH doesn't actually prevent ISPs user tracking"



`DoH` was never meant as a wholesale "cure" for ISP user-tracking;

it's meant to reduce DNS observation, tampering, and interference.



#### "DoH creates havoc in the enterprise sector"



I have worked in the "enterprise sector" since 1992; I am sorry to be

glib but this equally glib claim is nonsense.



#### "DoH weakens cyber-security"



Again this is a vague concern - DoH weakens what aspects of security,

how, for whom, and to what compensating benefits, to whom? - but also

it should be noted that the prime weaknesses in cybersecurity are

"users" and "software" yet we are somehow content to have more of both

of those?



#### "DoH helps criminals"



Helps criminals? So does "the internet" in general - it would not be

able to have cybercrime without computers.



#### "DoH shouldn't be recommended to dissidents"



So far as I am aware, nobody is recommending `DoH` for "dissidents";

`DoH` is being recommended more broadly to *people who want more privacy*.



#### "DoH centralizes DNS traffic at a few DoH resolvers"



Aha! This latter concern has some substance, and it is worth

consideration; generally there are three aspects to this concern:



1. "DNS is a 'distributed' protocol, and `DoH` is antithetical to 'distribution'!".

  * I deal with this matter extensively in a separate

    [blogpost](https://medium.com/@alecmuffett/why-every-privacy-activist-should-embrace-dns-over-https-a361e727657f)

2. "There are not enough `DoH` providers and users may be deanonymised via analysis of huge data sets!"

  * Mozilla has sought to address this concern with their

    [Trusted Recursive Resolver](https://wiki.mozilla.org/Trusted_Recursive_Resolver) program;

    but simplistically it seems logical that the proper solution to "too

    few" `DoH` providers is to encourage *more* of them, not *fewer*.

3. "A small number of *Big Data Companies* will get all the tracking information, instead of us!"

  * This is an actionable concern, and one where we can make an improvement well beyond `DoH` let alone `Do53`.



The fear that "Big Data Companies" will mine `DoH` request data for

profit is valid and is one which the likes of (e.g.)  Mozilla are

already working on

([see point 2, here](https://blog.mozilla.org/netpolicy/2020/02/25/the-facts-mozillas-dns-over-https-doh/)) -

but it's one where the internet is also already equipped with a well-tested solution:

[Tor](https://www.torproject.org).



### Why Tor, and why use DoH over Tor?



One of the goals of the Tor project is to provide anonymity of clients

from servers; there are *other* benefits to Tor and Tor "Onion

Networking", but this is the most popular rationale for Tor's use.



It's also a rationale which meshes insanely well, with `DoH`.



Tor does not support UDP and therefore cannot provide anonymity for

`Do53` traffic, but because `DoH` is normal HTTPS it can be carried

efficiently over Tor connections.



Therefore:



* if the individual provides and controls a local `Do53` resolver,

  not least for normal, "legacy" use - being offered by DHCP, etc.

* and that resolver is configured to resolve upstream, using `DoH`

* and that resolver is configured to strip linkable identifiers from `DoH` requests

* and that resolver connects to various major `DoH` providers over Tor

* then the provider will not know who is making the request, nor from where it came, nor will be able to "link" requests



This architecture follows Tor's

["anonymity loves company"](https://www.freehaven.net/doc/wupss04/usability.pdf)

model for privacy, and **offers far better privacy, integrity,

unblockability and untrackability than anything** offered by `Do53`,

`DoT` (DNS over TLS on port 853), raw `DoH` or indeed any other DNS

lookup-service.



And the technology already exists, is free, and my data and experience is that it

works really well for home users, perhaps more.



## How do I build a DoHoT server?



[See here](INSTALL.md); this project is project evolving and I will be updating it.



## Surely there have been some issues?



There are a few patterns or weird experiences that I have noted:



### The Ubiquity WiFi dashboard will complain about "latency", indefinitely



![clip of dashboard](img/unifi-complaints.png)



My WiFi router dashboard perpetually complains about "High DNS

Latency", which only goes to show that expectations of "low latency"

in modern DNS are lower than what humans are actually okay with.



### Chromecast honours DHCP's DoHoT DNS server, but also tries to use 8.8.8.8



Approximately every 20 seconds my Chromecast attempts to send a

request to 8.8.8.8, which my firewall drops and logs. I find this

interesting, but it's not really a DoHoT problem so much as a matter

of my choice to block any non-DoHoT DNS requests.



The Chromecast - including upgrades - still works fine, so I am

ignoring this matter.



### "Human Error" is surprisingly common



Every so often I visit somewhere that causes me to temporarily

hardcode my laptop or phone DNS server to 1.1.1.1 or 8.8.8.8; then I

come home and the device stops working until I remember to reset the

DNS to be the automatic DHCP default.



Again I consider this to be due to my choice to block any non-DoHoT DNS requests, but it's probably

also good discipline from a privacy perspective.  I actually used to believe that my privacy self-discipline was better than this, but I was wrong.



This situation is interesting to compare to criticism from DoH

critics who argue that it is they - your service provider, your

ISP - rather than you, who should be limiting access to alternative

sources of DNS resolution.



### Absolutely nothing at home is using Port 853



`DoT` / DNS-over-TLS on port 853 is touted by DNS experts as the "proper" solution

for DNS privacy and security, but I have not yet seen any devices or

applications actually using it.



## Footnotes and FAQs



### Why are you only publishing 4 weeks' worth of graphs?



I set this up in early February, and then COVID-19 happened, and I

basically forgot about it; however my server *does* retain slightly

more than 4 weeks worth of logs.  I will try to do better in future.



### Why are you not annotating the DoH providers?



To do so would not seem relevant; after some advanced technical

experimentation with DoH and

[EOTK](https://github.com/alecmuffett/eotk) I simply picked three

ordinary DoH providers and set them up as resolvers in

DNSCrypt-Proxy.



Since the whole point of using Tor is to divorce the server from the

client, I believe that - especially given the automatic load-balancing

of DNSCrypt-Proxy - so long as the results appear consistent it

doesn't really matter who won the race to give the first response; so

why risk being seen to pick favourites?



### Did the latency drop significantly around June 6th?



Looking at the graph above, I noticed that "cliff edge" too. I'm not

sure, but after checking with some members of the Tor project, some

newer, faster Tor infrastructure may have become more prevalent around

that time. Another member of the Tor community reminded me that it may

be that my Tor instance changed "guard" to a faster one.