The use of social media by terrorists and their sympathisers is a serious problem. But it has attracted some poorly thought through solutions. Of course we need better intelligence about the terrorists’ plans and whereabouts. That has been demonstrated by the way that the Paris plotters were able to hatch and carry out their plans without, it seems, the security services having any clue beforehand. Of course, also, we need to do more to disrupt and discredit the propaganda that the violent jihadis use to recruit the susceptible. sAnd of course it would be nice if there were a single simple measure that would accomplish these things. But there is not. More to the point, granting even wider powers to the security services to attack encrypted communications wouldn’t help.

There are two reasons for this, one technical and the other operational. The technical one is simple: done properly, modern encryption is just about unbreakable, and the tools to do it have been available on the internet for 20 years at least. The strength of the encryption derives from the underlying mathematics. It’s not something governments can wish away or make illegal any more than parliament can repeal the law of gravity. You must be motivated to use encryption, but few people could be more motivated than a terrorist in hostile territory.

Then there is the operational point that out of the billions of messages exchanged every day around the world, only a tiny fraction ought to interest the security services. They are looking for needles in a very large haystack. Increasing their surveillance powers would add more hay without making the needles any more visible. The French security services had all the powers of surveillance that the British could possibly demand and still could not detect the attacks until too late. There is no single simple solution to the problem.

There are, however, some complicated and pedestrian measures which will make things better. More watchers and listeners could help, though there will never be enough of them to keep tabs on everyone who might be a terrorist. Beyond that, there are some small sacrifices of privacy which are actually worthwhile, in ways that tampering with encryption could not be. The coordinated use of passenger registration on airlines will make it easier to track travel around Europe, and that’s something which is going to be necessary for political as well as security reasons. The various police databases used internationally against terrorism do need to be better coordinated. At the same time they will need to be better secured. One of the strongest arguments against governments collecting larger quantities of information about their citizens is that this never stays secure: corrupt insiders and hackers from the outside can often gain access to really damaging dossiers. This is a risk which we must do more to diminish.

Basic IT hygiene of this kind operates below the level of headlines about encryption or cybersecurity, which are sure signs of politicians who have realised that something must be done but have no idea what, nor even what it should be done about. Neither perfect security nor perfect privacy is attainable. Neither of them should be fetishised. What’s needed here is a careful and well-informed judgment about the ways in which any particular measure can be expected to make us actually safer.