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DNS Privacy Considerations

Overview#

DNS Privacy Considerations Privacy Considerations associated with the use of the Domain Name System (DNS).

RFC 7626 describes the Privacy Considerations associated with the use of the DNS by Internet users.

Some of the issues in simple terms:

  • Almost every activity on the Internet starts with a DNS query (and often several). A key function of the DNS is to map human readable names (e.g. example.com DNS Domain) to IP Address that computers need in order to connect to each other.
  • Those queries can reveal not only what websites an individual visits but also metadata about other services such as the domains of email contacts or chat services.
  • Whilst the data in the DNS is public, individual transactions made by an End-User should not be public.
  • DNS queries are sent in Cleartext (using UDP or TCP) which means passive eavesdroppers can observe all the DNS lookups performed.
  • Domain Name System is a globally distributed system that crosses international boundaries and often uses servers in many different countries in order to provide resilience.
  • It is well known that the NSA used the MORECOWBELL and QUANTUMDNS tools to perform covert monitoring, mass surveillance and hijacking of Domain Name System traffic.
  • Some Service Providers (Internet Service Providers) log DNS queries at the resolver and share this information with third-parties in ways not known or obvious to end users.
  • Some ISPs embed user information (e.g. a UserId or MAC Address) within DNS queries that go to the ISPs resolver in order to provide services such as Parental Filtering. This allows for fingerprinting of individual users.
  • Some CDNs embed user information (client subnets) in queries from resolvers to authoritative servers (to geo-locate end users). This allows for correlations of queries to particular subnets.
  • some VPNs will still leak your DNS queries by sending them unencrypted to your ISP. Use the nice tool from anonymyster.com to check is this is happening with your VPN!

Possible Solutions for DNS Privacy Considerations#

DNS over TLS (DoT)#

RFC 7858 specified DNS over TLS as a Standards Track protocol in May . There is active work in this area.

There are now multiple implementations (including Stubby a local DNS Privacy stub resolver) and a number of experimental servers deployed.

DNS over DTLS#

RFC 8094 specified DNS over DTLS as an Experimental Standard in Feb 2017. To our knowledge that are no implementations of DNS-over-DTLS planned or in progress.

One issue with DNS-over-DTLS is that it must still truncate DNS responses if the response size it too large (just as UDP does) and so it cannot be a standalone solution for privacy without a fallback mechanism (such as DNS-over-TLS) also being available.

DNS over HTTPS (DoH)#

The IETF created a new DoH working group in Sept 2017 to look at how DNS messages could be sent over an existing HTTP/2 connection. As of Sept 2018 the draft https://datatracker.ietf.org/doc/draft-ietf-doh-dns-over-https/ is in in the RFC editor queue and there are several experimental implementations and deployments. Note that with DoH it is possible to intermingle DNS and HTTP traffic on the same connection and make blocking of encrypted DNS harder. It should be noted that this draft addresses almost purely protocol issues and a follow up document on discovery and operational usage is expected.

DNSCrypt#

DNSCrypt is a method of authenticating communications between a DNS client and a DNS resolver that has been around since 2011.
  • DNSCrypt prevents DNS spoofing.
  • DNSCrypt uses cryptographic signatures to verify that responses originate from the chosen DNS resolver and haven't been tampered with (the messages are still sent over UDP). As a side effect DNSCrypt provides increased privacy because the DNS message content is encrypted.
  • DNSCrypt is an open specification but it has not been standardized by the IETF. There are multiple implementations and a set of DNSCrypt servers available.
  • OpenDNS offers DNSCrypt
Also check out an in depth comparison from Tenta.

DNS over HTTPS (proxied)#

There are implementations available (e.g. from BII) of proxies that will tunnel DNS over HTTPS.

Google offers a proprietary DNS-over-HTTPS service using a JSON format for DNS queries.

A new working group was formed in Sept 2017 by the IETF: DNS-over-HTTPS (DOH)

DNS over QUIC#

A draft was submitted in April 2017 to the IETF QUIC Working group on DNS over QUIC

DNSCurve#

DNSCurve was developed in 2010 with encrypting the resolver to authoritative communications in mind. It was not standardized by the IETF.

More Information#

There might be more information for this subject on one of the following: