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DNS over TLS. Secure the DNS!
Posted on 04-22-2017 21:59:17 UTC | Updated on 04-22-2017 22:08:25 UTC
Section: /software/unbound/ | Permanent Link

Secure the Web

A while back we had the "secure the web" initiative, where everyone was inspired to enable encryption (https) on their websites. This was so we could thwart things like eavesdropping and content hijacking. In 2016 about about half of website visits where https. This is great and things seem to be only getting better. ISP's can not see the content in https traffic. Not seeing your traffic content anymore makes them sad. What makes them happy? They can still see all of your DNS requests.

Your ISP can see the websites you visit

Every ISP assigns you some of their DNS servers for you to use when you connect to them for your internet connection. Every time you type in a website name in your browser bar, this request goes to their DNS servers to look up an number called an IP address. After this happens an IP address is returned to your computer, and the connection to the website is made. Your ISP now has a log of the website you requested attached to the rest of the information they have about you. Then they build profiles about you, and sell that info to 3rd parties to target advertising to you in many different ways. Think you'll be slick and switch out their DNS servers with someone else's like Google's free DNS servers (8.8.8.8)? Think again. Any request through your ISP to any DNS server on the internet is unencrypted. Your ISP can slurp up all same requests and get the same info they did just like when you were using their DNS servers. Just like when they could see all of your content with http before https. This also means that your DNS traffic could possibly be intercepted and hijacked by other people or entities. TLS prevents this.

Securing the DNS

The thing that secures https is Transport Layer Security (TLS). It is a set of cryptographic protocols that provides communications security over a computer network. Now that we are beginning to secure the websites I think it is high time we secure the DNS. Others seem to agree. In 2016 rfc7858 and rfc8094 was submitted to Internet Engineering Task Force (IETF) which describes the use of DNS over TLS and DNS over DTLS. Hopefully these will eventually become a standard and all DNS traffic will be more secure in transit. Can you have DNS over TLS today? Yes you can!

Trying DNS over TLS now

DNS over TLS is in its infancy currently, but there are ways to try it out now. You could try using Stubby, a program that acts as a local DNS Privacy stub resolver (using DNS-over-TLS). You will have compile Stubby on Linux or OS X to use it. You could also setup your own DNS server at home and point it to some upstream forwarders that support DNS over TLS. This is what I have done to start testing this. I use Unbound as my local DNS server on my lan for all of my client machines. I used the configuration settings provided by our friends over at Calomel.org to setup my Ubound server to use DNS over TLS. Here is a list of other open source DNS software that can use DNS over TLS. With my Unbound setup, all of my DNS traffic is secured from interception and modification. So how is my testing going?

The early days

Since this is not a IETF standard yet, there are not a lot of providers of DNS over TLS resolvers. I have had to rearrange my list of DNS over TLS providers a few times when some of the servers were just not resolving hostnames. The latency is also higher than using your local ISP's DNS servers or using someones like Googles DNS servers. This is not very noticeable since my local DNS server caches the lookups. I have a feeling the generous providers of these DNS over TLS services are being overwhelmed and can not handle the load of the requests. This is where bigger companies come into play.

Places like Google or OpenDNS do not support DNS over TLS yet, but I'm hoping that they will get on board with this. Google especially since they have been big proponents of making all websites https. They also have the infrastructure to pull this off. Even if someone like Google turned this on, that means they get your DNS traffic instead of your ISP. Will this ever end?

Uggh, people can still see my traffic

Let's face it, if your connected to the internet, at some point someone gets to see where your going. You just have to choose who you want/trust to give this information to. If you point your DNS servers to Google they get to see your DNS requests. If I point my DNS at these test DNS over TLS servers then they get to see my DNS traffic. It seems like the lesser of 2 evils to send your DNS to 2nd party DNS servers then to your ISP. If you use your ISP's DNS servers they know the exact name attached to the IP address they assigned you and the customer that is making the query. I have been holding off telling you the bad news. https SNI will still give up the domain names you visit.

Through all of this even if you point your DNS traffic to a DNS over TLS server your ISP can still see many of the sites you go to. This is thanks to something in https called Server Name Indication (SNI). When you make a connection to an https enabled website there is a process called a handshake. This is the exchange of information before the encryption starts. During this unencrypted handshake (ClientHello) one of the things that is sent by you is a remote host name. This allows the server on the other end to choose appropriate certificate based on the requested host name. This happens when multiple virtual hosts reside on the same server, and this a very common setup. Unfortunately, your ISP can see this, slurp it up, and log this to your account/profile. So now what?

Would a VPN help? Yes, but remember now your DNS queries go to your VPN provider. What is nice is your ISP will not see any of your traffic anymore. That pesky SNI issue mentioned above goes away when using a VPN. But now your trusted endpoint is your VPN provider. They now can log all the sites you go to. So choose wisely when picking a VPN provider. Read their policy on saving logs, choose one that will allow you to pay with Bitcoin so you will be anonymous as possible. With a VPN provider you also have to be careful about DNS leaking. If your VPN client is not configured right, or you forget to turn it on or, any other myriad of ways a VPN can fail, your traffic will go right back to your ISP.

Even VPN's don't make you anonymous

So you have encrypted your DNS and web traffic with TLS and your using a VPN. Good for you, now your privacy is a bit better, but not anonymity. Your still being tracked. This time it is AD networks and services you use. I'm not going to go into this as many other people have written on this topic. Just know that your being tracked one way or another.

I know this all seems hopeless, but securing the web's infrasturcture bit by bit helps improve privacy just a little more. DNS like http is unencrypted. There was a big push to get websites to encrypt their data, now there needs to be the same attention given to DNS.

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