Title : Port of the week: dnscrypt-proxy
Author: Solène
Date  : 19 October 2016
Tags  : unix security portoftheweek

### 2020 Update

Now, unwind on OpenBSD and unbound can support DNS over TLS or DNS
over HTTPS, dnscrypt lost a bit of relevance but it's still usable
and a good alternative.


### Dnscrypt

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.