Alternative DNS Resolver

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Introduction[edit]

By Whonix ™ default, Tor is used for DNS resolution. If you suspect a Tor exit relay to tamper with DNS, you can get a second opinion from another non-Tor DNS server. This may also be useful, in special cases if you want to resolve types of DNS over Tor, which are unsupported by Tor itself, such as MX [1], SRV or DNSSEC. [2]

It is recommended against to use non-Tor DNS resolvers for an extended amount of time. Although it is technically possible to completely replace DNS resolution (not using Tor for DNS resolution anymore), it is recommended against. That would add too much power to a single DNS server. Using a permanent DNS server is recommended against just as using a permanent Tor exit relay is recommended against.

Note, that even if you correctly set up all settings, it might happen that this won't work. Sometimes Tor or the DNS server causes a timeout. This gets even worse, when you additionally tunnel the DNS request through an additional proxy (for example: Tor → JonDonym → DNS server).

Read first: Stream Isolation.

Required knowledge:

  • Difference between encryption and authentication.
  • All traffic originating from Whonix-Workstation ™ and Whonix-Gateway ™ is routed over Tor. [3] [4] [5] [6] [7] [8] [9] (<-- read the footnotes)

Ambox warning pn.svg.png Note that most applications, such as Tor Browser, will not automatically profit from setting up an alternative DNS resolver.

  • This is because applications in Whonix ™ are configured to use SocksPort instead of Trans- or DnsPort, see Stream Isolation for details.
  • Another reason is, that many applications do not yet make use of authenticated DNS (DNSSEC).

However, you could use alternative DNS revolvers with these applications when deconfiguring socks proxy settings.

For example, Tor Browser would be unaffected by these changes alone. In theory, a user that intended to change Tor Browser DNS settings would have to enable transparent proxying in Tor Browser which however is discouraged as this changes the web fingerprint.

Advanced users only!

Recursive Authenticated DNSSEC over Tor[edit]

Introduction[edit]

DNSSEC aware, DNSSEC validating, recursive DNS resolution over TCP, over Tor using Unbound. Unencypted, because Root name servers do not support encryption yet, there is a DNS Security Optimization Problem.

These instructions completely replace Tor's DNS resolver the whole Whonix-Workstation ™. Not recommended for a longer amount of time, see warning above.

Installation[edit]

Everything inside Whonix-Workstation ™.

1. Create folder /etc/unbound/unbound.conf.d.

mkdir --parents /etc/unbound/unbound.conf.d

2. Unbound configuration.

Open file /etc/unbound/unbound.conf.d/50_user.conf in an editor with administrative (root) write permissions.

This box uses sudoedit for better security. This is an example and other tools can also achieve the same goal. If this example does not work for you or if you are not using Whonix ™, please refer to this link.

sudoedit /etc/unbound/unbound.conf.d/50_user.conf

3. Paste the following lines.

server: hide-identity: yes hide-version: yes interface: 127.0.0.1 do-ip6: no tcp-upstream: yes ## TODO: onion resolution over Tor-only does not work yet. ## Please use search engines, see unbound documentation, ## find out how to fix this and improve this documentation! ## ## Optional to leave resolving onion to Tor. ## Feel free to comment the following 4 lines out, ## but this would break onion resolving since unbound ## cannot resolve '.onion' domains. #forward-zone: # name: "onion" # forward-addr: 10.152.152.10@9050 # forward-no-cache: yes

4. Save.

5. Install dnssec-trigger, which automatically installs and configures the unbound DNS resolver.

Install package(s) dnssec-trigger.

A. Update the package lists and upgrade the system.

sudo apt update && sudo apt full-upgrade

B. Install the dnssec-trigger package(s).

Using apt command line parameter --no-install-recommends is in most cases optional.

sudo apt install --no-install-recommends dnssec-trigger

C. Done.

The procedure of installing package(s) dnssec-trigger is complete.

6. Done.

7. Testing DNSSEC

DNSCrypt[edit]

Introduction[edit]

DNSCrypt supports encryption, DNSSEC but DNSCrypt does not validate DNSSEC signatures yet. [10]

These instructions completely replace Tor's DNS resolver with a dnscrypt-enabled resolver for all users and the whole Whonix-Workstation ™. Not recommended for a longer amount of time, see warning above.

Installation[edit]

Apply all instructions inside your Whonix-Workstation ™.

1) Install the dnscrypt-proxy package.

Install package(s) dnscrypt-proxy.

A. Update the package lists and upgrade the system.

sudo apt update && sudo apt full-upgrade

B. Install the dnscrypt-proxy package(s).

Using apt command line parameter --no-install-recommends is in most cases optional.

sudo apt install --no-install-recommends dnscrypt-proxy

C. Done.

The procedure of installing package(s) dnscrypt-proxy is complete.

2) Open file /etc/dnscrypt-proxy/dnscrypt-proxy.toml in an editor with administrative (root) write permissions.

This box uses sudoedit for better security. This is an example and other tools can also achieve the same goal. If this example does not work for you or if you are not using Whonix ™, please refer to this link.

sudoedit /etc/dnscrypt-proxy/dnscrypt-proxy.toml

Add the following text at the very top of the file. Note: The default server did not work for the author of this page. Therefore the following instructions advice to comment that server out and add a random alternative server was chosen which worked. [11] This is not an endorsement or non-endorsement of any server. Pick your own server. DNSCrypt publishes a list of servers here.

force_tcp = true #proxy = "socks5://127.0.0.1:9050" server_names = ['arvind-io']

Comment out:

server_names = ['cloudflare']

In other words, rewrite server_names = ['cloudflare'] to #server_names = ['cloudflare'] by adding a hash # in front of it. So it would look like this.

#server_names = ['cloudflare']

Save.

Restart dnscrypt-proxy.service.

sudo systemctl restart dnscrypt-proxy.service

Restart dnscrypt-proxy.socket.

sudo systemctl restart dnscrypt-proxy.socket

3) Open file /etc/resolv.conf in an editor with administrative (root) write permissions.

This box uses sudoedit for better security. This is an example and other tools can also achieve the same goal. If this example does not work for you or if you are not using Whonix ™, please refer to this link.

sudoedit /etc/resolv.conf

4) Comment out everything and add [12] (It is not 127.0.0.1. It really is 127.0.2.1.):

options use-vc nameserver 127.0.2.1

Save.

Testing[edit]

DNSCrypt In Use[edit]

Stop dnscrypt-proxy systemd socket.

sudo systemctl stop dnscrypt-proxy.socket

Test again. Now it is expected to fail.

Restart dnscrypt-proxy systemd socket.

sudo systemctl restart dnscrypt-proxy.socket

Test again. Now it is expected to work.

FAQ[edit]

Why not Use DNSCrypt by Default in Whonix ™?[edit]

DNSCrypt may have good use cases for clearnet activities. However, it is not useful in Whonix ™ and therefore should not be installed and activated by default for everyone. Although some users may have high expectations, DNSCrypt does not magically solve all DNS-related security issues, nor does it implement end-to-end DNS encryption to the destination server. [13] Most important of all, the server will still see all DNS requests in cleartext. [14]

There are several other reasons why DNSCrypt is not activated by default. Firstly, Tor distributes trust because the DNS server changes as circuits are rotated. For pre-installed applications, circuits are also stream-isolated and change every ten minutes by default. Notably, in early 2018 there are 78 open resolvers that support the protocol.

Public resolvers supporting DNSCrypt have not yet acted in a way to cause mistrust. However, even if the operators were absolutely trustworthy, complete confidence is also needed in their servers - it is unwise to let the DNS security for all Whonix ™ users depend on a few servers. Another consideration is load balancing. If Whonix ™ relied upon a DNSCrypt supporting server by default, DNS would break for all users if that server ever decided to forbid connections from the Tor network [15] or if the servers went down for maintenance.

Would result in a unique web fingerprint, i.e. visited websites can distinguish Whonix ™ users using DNSCrypt from other Tor users using Tor to resolve DNS.

For more detailed information about DNSCrypt, refer to these related forum posts.

Can I Use DNSCrypt on the Host or Router for Clearnet?[edit]

This configuration is possible; read the next section before proceeding.

Does DNSCrypt on the Host or Router Harm Anonymity when Using Tor / Whonix ™?[edit]

The short answer to this question is no. The longer answer is DNSCrypt on the host or in the router only affects clearnet activities. Tor assumes in advance that a user's local network and ISP are completely unsafe and untrustworthy. Tor and Whonix ™ are unaffected by DNS settings that are made on the host or in the router.

It is debatable whether DNSCrypt is useful or not for clearnet activities since there are various pros and cons. It is useful when using foreign or untrusted Wi-Fi networks that are shared with others, since DNS requests could potentially be modified or read. That said, trust is just shifted from the ISP to a DNSCrypt-supporting DNS server, such as OpenDNS. If the DNS server supporting DNSCrypt leaks a user's network address and/or logs queries as part of their business model, then it might actually be worse than using the ISP! It is hard to mount an argument for which party is more trustworthy, the ISP or a third party provider.

Footnotes[edit]

  1. Required for some Mixmaster servers over Tor.
  2. Since Whonix ™ version 0.2.1 Whonix-Gateway ™ traffic is also routed over Tor. In this way, use of Whonix ™ is hidden from persons or systems observing the network.
  3. To preserve the anonymity of a user's Whonix-Workstation ™ activities, it is not necessary to torify Whonix-Gateway ™ own traffic.
  4. For reader interest: If DNS settings on Whonix-Gateway ™ are changed in /etc/resolv.conf, this only affects Whonix-Gateway ™ own DNS requests issued by applications using the system's default DNS resolver. By default, no applications issuing network traffic on Whonix-Gateway ™ use the system's default DNS resolver. All applications installed by default on Whonix-Gateway ™ that issue network traffic (apt, systemcheck, sdwdate) are explicitly configured, or forced by uwt wrappers, to use their own Tor SocksPort (see Stream Isolation).
  5. Whonix-Workstation ™ default applications are configured to use separate Tor SocksPorts (see Stream Isolation), thereby not using the system's default DNS resolver. Any applications in Whonix-Workstation ™ that are not configured for stream isolation - for example nslookup - will use the default DNS server configured in Whonix-Workstation ™ (via /etc/network/interfaces), which is the Whonix-Gateway ™. Those DNS requests are redirected to Tor's DnsPort by Whonix-Gateway ™ firewall. Whonix-Gateway ™ /etc/resolv.conf does not affect Whonix-Workstation ™ DNS requests.
  6. Traffic generated by the Tor process itself which runs by Debian default under user debian-tor originating from Whonix-Gateway ™ can use the internet normally. This is because user debian-tor is exempted in Whonix-Gateway ™ Firewall, allowed to use the "normal" internet.
  7. The Tor software (as of 0.4.5.6) (and no changed were announced at time of writing) almost exclusively uses TCP traffic. See also Tor wiki page, chapter UDP. For DNS, see next footnote.
  8. Tor does not require, use functional (system) DNS for most functionality. IP addresses of Tor directory authorities are hardcoded in the Tor software as per Tor upstream default. Exceptions include:
    • proxy settings using proxies with host names rather than IP addresses
    • the Tor pluggable transport meek lite to resolve domains used in setting url=, front= to IP addresses.
  9. Quote https://github.com/DNSCrypt/dnscrypt-proxy/issues/167#issuecomment-367689381

    dnscrypt-proxy doesn't validate dnssec signatures yet :)

  10. Test was done using:
    dig +dnssec google.com
  11. options use-vc is optional as in it also works without it.
  12. Conceptually, end-end DNS encryption is illogical. If the IP address of the destination server was known in advance, then DNS would not be required in the first place.
  13. https://security.stackexchange.com/questions/162601/what-are-the-privacy-advantages-of-a-dns-encryption-service-such-as-dnscrypt
  14. Due to the Tor network abuse such as DDOS attacks on their servers.