September 14, 2016 | Jim Killock

GCHQ should not push ISPs to interfere with DNS results

GCHQ have a dual and rather contradictory mandate: they are asked to get around security measures, break into systems and snoop on citizens. They are also asked to protect the UK from cyber attacks by improving security protections.


While these two goals are not automatically in conflict, they are certainly in tension, which will also raise questions of trust. Is GCHQ’s strategy intended to secure our systems, or in fact to keep them vulnerable?

Today’s announcement that GCHQ’s National Cyber Security Centre wish ISPs to manipulate DNS results to prevent access to phishing sites smacks of exactly this conflict. (The Domain Name System (DNS) is what resolves an ordinary web address like openrightsgroup.org to a unique number (IP address) that gets your web browser to the correct web server.)

Their Director General, Ciaran Martin, explained in a speech that:

The great majority of cyber attacks are not terribly sophisticated. They can be defended against. And if they get through their impact can be contained. But far too many of these basic attacks are getting through. And they are doing a lot of damage

we're exploring a flagship project on scaling up DNS filtering: what better way of providing automated defences at scale than by the major private providers effectively blocking their customers from coming into contact with known malware and bad addresses?

Now it's crucial that all of these economy-wide initiatives are private sector led. The Government does not own or operate the Internet. Consumers use have a choice. Any DNS filtering would have to be opt out based. So addressing privacy concerns and citizen choice is hardwired into our programme.

There are a number of problems with this approach. Privacy and logging are one; but so is the collateral damage that comes from DNS blocking. Phishing tends to abuse URLs rather than whole sites, so the impact of blocking entire sites can sometimes be huge. And there are alternatives targeting specific known problems, such as Chrome’s “safer browsing” product.

Having ISPs able to serve up “spoof” DNS results for whole websites is, perhaps coincidentally, tremendously useful when implementing censorship.

The DNS blocking approach, even if “voluntary” and a matter of choice, would potentially run up against industry initiatives to improve security of customers through preventing the manipulation of DNS results, such as DNSSEC (among others). The aim of these projects is to prevent “spoof” DNS results, which allow intermediaries to interfere with web pages, replace adverts, or serve fake pages based on users mis-spelling domains. It would have made it impossible for the Phorm model of interception of user web traffic to work, for instance. 

Even if we trust ISPs and governments not to abuse their extending powers of censorship, we ought to be worried that GCHQ are proposing at least one security measure which undermines international efforts to improve the integrity of the Internet, and thereby also, its security. Perhaps this reveals some of the weaknesses of a state-led approach to Internet security. It would also likely be redundant if clients switched to encrypted resolvers run by other parties.

For instance, GCHQ seems to be more keen on working with a handful of big players, who can make ‘major’ interventions to ‘protect’ the public. Rather than expecting the market, the endpoints, and helping users themselves to do better, GCHQ no doubt find it easier to work with people who can deliver change ‘at scale’.

Or to look at it another way, GCHQ’s proposed solution may not be mandatory, but could impose a certain kind of stasis on technical innovation in the UK, by retarding the adoption of better DNS security. Does GCHQ really know better than the technical bodies, such as the Internet Engineering Taskforce (IETF) and their commercial participants, who are promoting changes to DNS?

There is no doubt that GCHQ have information which would be useful for people’s security. However, precisely what their motivations are, and what their role should be, are much more open to question. For this reason, we have called for their cyber security role to be divorced from their surveillance capabilities and placed under independent management.

That aside, GCHQ’s idea to promote the tampering of DNS results may be superficially attractive in the short term, but would be a medium term mistake.