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My name is Solène Rapenne. I like learning and sharing experiences about IT stuff. Hobbies: '(BSD OpenBSD h+ Lisp cmdline gaming internet-stuff Crossbow). I love % and lambda characters. OpenBSD developer solene@.

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Port of the week: dnscrypt-proxy

Written by Solène, on 19 October 2016.
Tags: #unix #security #portoftheweek

Today I will talk about net/dnscrypt-proxy. This let you encrypt your DNS traffic between your resolver and the remote DNS recursive server. More and more countries and internet provider use DNS to block some websites, and now they tend to do “man in the middle” with DNS answers, so you can’t just use a remote DNS you find on the internet. While a remote dnscrypt DNS server can still be affected by such “man in the middle” hijack, there is a very little chance DNS traffic is altered in datacenters / dedicated server hosting.

The article also deal with unbound as a dns cache because dnscrypt is a bit slow and asking multiple time the same domain in a few minutes is a waste of cpu/network/time for everyone. So I recommend setting up a DNS cache on your side (which can also permit to use it on a LAN).

At the time I write this article, their is a very good explanation about “how to install it” is named dnscrypt-proxy–1.9.5p3 in the folder /usr/local/share/doc/pkg-readmes/. The following article is made from this file. (Article updated at the time of OpenBSD 6.3)

While I write for OpenBSD this can be easily adapted to anthing else Unix-like.

Install dnscrypt

# pkg_add dnscrypt-proxy

Resolv.conf

Modify your resolv.conf file to this

/etc/resolv.conf :

nameserver 127.0.0.1
lookup file bind
options edns0

When using dhcp client

If you use dhcp to get an address, you can use the following line to force having 127.0.0.1 as nameserver by modifying dhclient config file. Beware, if you use it, when upgrading the system from bsd.rd, you will get 127.0.0.1 as your DNS server but no service running.

/etc/dhclient.conf :

supersede domain-name-servers 127.0.0.1;

Unbound

Now, we need to modify unbound config to tell him to ask DNS at 127.0.0.1 port 40. Please adapt your config, I will just add what is mandatory. Unbound configuration file isn’t in /etc because it’s chrooted

/var/unbound/etc/unbound.conf:

server:
    # this line is MANDATORY
    do-not-query-localhost: no

forward-zone:
    name: "."
    forward-addr: 127.0.0.1@40
    # address dnscrypt listen on

If you want to allow other to resolv through your unbound daemon, please see parameters interface and access-control. You will need to tell unbound to bind on external interfaces and allow requests on it.

Dnscrypt-proxy

Now we need to configure dnscrypt, pick a server in the following LIST /usr/local/share/dnscrypt-proxy/dnscrypt-resolvers.csv, the name is the first column.

As root type the following (or use doas/sudo), in the example we choose dnscrypt.eu-nl as a DNS provider

# rcctl enable dnscrypt_proxy
# rcctl set dnscrypt_proxy flags -E -m1 -R dnscrypt.eu-nl -a 127.0.0.1:40
# rcctl start dnscrypt_proxy

Conclusion

You should be able to resolv address through dnscrypt now. You can use tcpdump on your external interface to see if you see something on udp port 53, you should not see traffic there.

If you want to use dig hostname -p 40 @127.0.0.1 to make DNS request to dnscrypt without unbound, you will need net/isc-bind which will provide /usr/local/bin/dig. OpenBSD base dig can’t use a port different than 53.