Using DNSSEC and DNSCrypt in Debian

While there is real progress being made towards eliminating insecure HTTP traffic, DNS is a fundamental Internet service that still usually relies on unauthenticated cleartext. There are however a few efforts to try and fix this problem. Here is the setup I use on my Debian laptop to make use of both DNSSEC and DNSCrypt.

DNSCrypt

DNSCrypt was created to enable end-users to encrypt the traffic between themselves and their chosen DNS resolver.

To switch away from your ISP's default DNS resolver to a DNSCrypt resolver, simply install the dnscrypt-proxy package and then set it as the default resolver either in /etc/resolv.conf:

nameserver 127.0.2.1

if you are using a static network configuration or in /etc/dhcp/dhclient.conf:

supersede domain-name-servers 127.0.2.1;

if you rely on dynamic network configuration via DHCP.

There are two things you might want to keep in mind when choosing your DNSCrypt resolver:

  • whether or not they keep any logs of the DNS traffic
  • whether or not they support DNSSEC

I have personally selected a resolver located in Iceland by setting the following in /etc/default/dnscrypt-proxy:

DNSCRYPT_PROXY_RESOLVER_NAME=ns0.dnscrypt.is

DNSSEC

While DNSCrypt protects the confidentiality of our DNS queries, it doesn't give us any assurance that the results of such queries are the right ones. In order to authenticate results in that way and prevent DNS poisoning, a hierarchical cryptographic system was created: DNSSEC.

In order to enable it, I have setup a local unbound DNSSEC resolver on my machine and pointed /etc/resolv.conf (or /etc/dhcp/dhclient.conf) to my unbound installation at 127.0.0.1.

Then I put the following in /etc/unbound/unbound.conf.d/dnscrypt.conf:

server:
    # Remove localhost from the donotquery list
    do-not-query-localhost: no

forward-zone:
    name: "."
    forward-addr: 127.0.2.1@53

to stop unbound from resolving DNS directly and to instead go through the encrypted DNSCrypt proxy.

Reliability

In my experience, unbound and dnscrypt-proxy are fairly reliable but they eventually get confused (presumably) by network changes and start returning errors.

The ugly but dependable work-around I have found is to create a cronjob at /etc/cron.d/restart-dns.conf that restarts both services once a day:

0 3 * * *    root    /usr/sbin/service dnscrypt-proxy restart
1 3 * * *    root    /usr/sbin/service unbound restart

Captive portals

The one remaining problem I need to solve has to do with captive portals. This can be quite annoying when travelling because it requires me to use the portal's DNS resolver in order to connect to the splash screen that unlocks the wifi connection.

The dnssec-trigger package looked promising but when I tried it on my jessie laptop, it wasn't particularly reliable.

My temporary work-around is to comment out this line in /etc/dhcp/dhclient.conf whenever I need to connect to such annoying wifi networks:

#supersede domain-name-servers 127.0.0.1;

If you've found a better solution to this problem, please leave a comment!