Today we unveil a major report on whether law enforcement and intelligence agencies should have exceptional access to cryptographic keys and to our computer and communications data generally. David Cameron has called for this, as have US law enforcement leaders such as FBI Director James Comey.

This policy repeats a mistake of the 1990s. The Clinton administration tried for years to seize control of civilian cryptography, first with the Clipper Chip, and then with various proposals for ‘key escrow’ or ‘trusted third party encryption’. Back then, a group of experts on cryptography and computer security got together to explain why this was a bad idea. We have now reconvened in response to the attempt by Cameron and Comey to resuscitate the old dead horse of the 1990s.

Our report, Keys Under Doormats: Mandating insecurity by requiring government access to all data and communications, is timed to set the stage for a Wednesday hearing of the Senate Judiciary Committee at which Mr Comey will present his proposals. The reply to Comey will come from Peter Swire, who was on the other side twenty years ago (he was a Clinton staffer) and has written a briefing on the first crypto war here. Peter was recently on President Obama’s NSA review group. He argues that the real way to fix the problems complained of is to fix the mutual legal assistance process – which is also my own view.

Our report is also highly relevant to the new ‘Snoopers’ Charter’ that Home Secretary Teresa May has promised to put before parliament this fall. Mrs May has made clear she wants access to everything.

However this is both wrong in principle, and unworkable in practice. Building back doors into all computer and communication systems is against most of the principles of security engineering, and it also against the principles of human rights. Our right to privacy, set out in section 8 of the European Convention on Human Rights, can only be overridden by mechanisms that meet three tests. First, they must be set out in law, with sufficient clarity for their effects to be foreseeable; second, they must be proportionate; third, they must be necessary in a democratic society. As our report makes clear, universal exceptional access will fail all these tests by a mile.

For more, see the New York Times.