DNSCrypt and Dnsmasq

Your ISP provides name to IP address resolution for any domain that is not resolvable within your local network. These unsecured requests can be spoofed by an attacker which could lead to a man-in-the-middle attack. Your ISP may also be able to monitor your traffic. Fortunately there is a simple solution to ensure data integrity while also protecting your privacy.

DNSCrypt encrypts and authenticates DNS traffic between your computer and a DNS resolver.  This ensures the IP addresses being returned to you have not been manipulated while also maintaining data confidentiality. In the following example we are going to demonstrate how to install DNSCrypt on a system running Linux and then cache those requests using Dnsmasq.

The distribution we will be working with today is Arch Linux. Let’s start out by installing the necessary packages

sudo pacman -S dnscrypt-proxy dnsmasq

Next enable the service

sudo systemctl enable dnscrypt-proxy.socket

Modify the nameserver entry within the /etc/resolv.conf file to point to the localhost

sudo vi /etc/resolv.conf
nameserver 127.0.0.1

Certain processes such as NetworkManager can overwrite the resolv.conf file following a reboot. To fix this refer to the following link and select the process which applies to your system.

As configured all DNS requests will now be sent to the default resolver which is dnscrypt.eu-nl. It is recommended that you select the server closest to you for faster name resolution.

Pick a server from the following list

sudo localc /usr/share/dnscrypt-proxy/dnscrypt-resolvers.csv

Replace the server with the one you selected within the dnscrypt-proxy.service file

sudo systemctl edit dnscrypt-proxy.service --full

Restart the service

sudo systemctl restart dnscrypt-proxy.service

Check that the service is running and that there are no certificate errors reported with the DNS resolver

sudo systemctl status dnscrypt-proxy.service
● dnscrypt-proxy.service - DNSCrypt client proxy
 Loaded: loaded (/etc/systemd/system/dnscrypt-proxy.service; enabled; vendor preset: disabled)
 Active: active (running) since Thu 2015-08-27 18:59:31 EDT; 2h 46min ago
 Main PID: 578 (dnscrypt-proxy)
 CGroup: /system.slice/dnscrypt-proxy.service
 └─578 /usr/bin/dnscrypt-proxy -R okturtles

Aug 27 20:01:14 arch dnscrypt-proxy[578]: [INFO] Refetching server certificates
Aug 27 20:01:14 arch dnscrypt-proxy[578]: [INFO] Server certificate #808464433 received
Aug 27 20:01:14 arch dnscrypt-proxy[578]: [INFO] This certificate looks valid
Aug 27 20:01:14 arch dnscrypt-proxy[578]: [INFO] Chosen certificate #808464433 is valid from [2015-02-04] to [2016-02-04]
Aug 27 20:01:14 arch dnscrypt-proxy[578]: [INFO] Server key fingerprint is CB51:0B61:7A1F:FCEB:27CE:26B5:8934:978A:04FF:D9E7:42A4:6A6B:0960:0F0F:F084:595C

Confirm the socket is running

sudo systemctl status dnscrypt-proxy.socket
● dnscrypt-proxy.socket - dnscrypt-proxy listening socket
 Loaded: loaded (/etc/systemd/system/dnscrypt-proxy.socket; enabled; vendor preset: disabled)
 Active: active (running) since Thu 2015-08-27 18:59:31 EDT; 2h 46min ago
 Listen: 127.0.0.1:40 (Stream)
 127.0.0.1:40 (Datagram)

Next we will setup a local DNS cache using Dnsmasq and configure DNSCrypt to forward to it. This will speed up name resolution and avoid sending repeat requests to the DNS resolver.

sudo systemctl edit dnscrypt-proxy.socket --full

Since the DNS cache needs to listen on port 53 we will configure DNScrypt to listen on an alternate port. In this example we will use port 40

[Unit]
Description=dnscrypt-proxy listening socket
#After=network.target

[Socket]
ListenStream=127.0.0.1:40
ListenDatagram=127.0.0.1:40

[Install]
WantedBy=sockets.target

Next restart dnscrypt-proxy.socket so that the changes can take effect

sudo systemctl restart dnscrypt-proxy.socket

Configure Dnsmasq strictly as a local cache

vi /etc/dnsmasq.conf
no-resolv
server=127.0.0.1#40
listen-address=127.0.0.1

Next enable the Dnsmasq service

sudo systemctl enable dnsmasq

And finally start the Dnsmasq service

sudo systemctl start dnsmasq

For a quick test try looking up a domain on the Internet using dig

dig google.com

; <<>> DiG 9.10.2-P3 <<>> google.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<

If Dnsmasq is working correctly then a subsequent request will resolve the domain almost instantly. The line to use for comparison is the “Query time”

[red@arch ~]$ dig google.com
; <<>> DiG 9.10.2-P3 <<>> google.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<

References
DNSCrypt
Dnsmasq


2 Comments

  1. when changing the port 40, automatically cease to have internet connection. Why can it be?

    • np

      January 6, 2016 at 2:12 pm

      Hi, were you able to restart the dnscrypt-proxy.socket after changing the port? (sudo systemctl restart dnscrypt-proxy.socket) If all else fails you can try selecting a different DNS resolver from localc /usr/share/dnscrypt-proxy/dnscrypt-resolvers.csv, ideally it should be the one closest to your geographical location. Curious, does everything work without the DNS cache configured?

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