Illustration: David Rowe. So what should voters make of the Abbott government's new national security bill? It seems the three most significant elements are a new power to allow spies to plant software on targeted computers, new penalties for intelligence whistleblowing, and a prohibition on anybody releasing any information about "special intelligence operations". But it isn't clear what the practical implications of these powers are. Are there any boundaries on what constitutes a special intelligence operation? Could journalists be prosecuted for reporting on national security leaks? Getting details out of the government is like pulling fingernails. National security is a unique area of public policy. It's one of the most important functions of government. Yet citizens have very little idea of what the government does under the guise of protecting them.

So the debate over national security powers is always held under a veil of ignorance. Usually serious public policy discussion requires evidence. But when we're talking about security those evidentiary standards go out the window. The best we get is hand-waving about terrorism and, now, Australian residents fighting in Syria. We're told to take the government on trust. Given that a basic principle of democracy is that governments must justify themselves to the citizenry, this is a problem. Terrorism is a real threat. But it is not a blank cheque for legislative change. The democratic accountability problem is enhanced even further by the fact that – as the Edward Snowden leaks have demonstrated – Western governments have repeatedly lied about their national security actions and have kept hidden evidence of their own wrongdoing. In his recent book, Secrets and Leaks: the Dilemma of State Secrecy, Princeton academic Rahul Sagar argues there are no easy ways to impose democratic accountability on the national security state. Blind trust isn't an option. Democracies cannot rely on blind trust. Unfortunately radical openness isn't an option either. We don't want the bad guys to know everything about ongoing enforcement operations.

Institutional accountability mechanisms – like parliamentary committees and independent watchdogs – are good, but they tend to be captured by the agencies they are overseeing. Sagars conclusion is that the best we can hope is that whistleblowers expose wrongdoings. When America's mass surveillance program was first revealed by Snowden last year, the Obama administration instinctively responded the program was necessary to prevent terrorism. Yet in December, 2013 the administration's own advisory panel concluded that bulk mass surveillance "was not essential to preventing attacks" and traditional, targeted surveillance methods was sufficient. This panel was no naive civil libertarian whitewash. One member was even a former CIA deputy director. A study by the New America Foundation – a bipartisan thinktank partly funded by the US government – concluded mass surveillance "has had no discernible impact on preventing acts of terrorism".

Australia is one of the members of America's Five Eyes surveillance coalition, alongside Canada, the United Kingdom and New Zealand. Unfortunately our governments have been no more honest than American administrations about the need for new security powers. For instance, the government claims its national security bill is mostly just a long-overdue update of 1970s-era telecommunications interception law. But this argument would be more plausible if the Telecommunications (Interception and Access) Act 1979 had not been updated more than 50 separate times in the past two decades. The bill is apparently the first of a series. Attorney-General George Brandis said last week a second tranche of reform will make it easier to prosecute Australians fighting overseas, and make it illegal to "promote" terrorism. OK. But it's already illegal to "incite" terrorism. Is that not enough? Will the government explain, specifically, why changes are needed? Don't hold your breath. A third tranche is likely to introduce mandatory data retention. That policy would require internet service providers to record almost everything every Australian does on the internet, just in case law enforcement agencies – from anti-terror spies to competition regulators – decide, in the future, to have a look. Mandatory data retention is both expensive and repressive. There will probably be a fourth tranche. Tony Abbott wants to be a tough-on-terror prime minister.

The Snowden revelations should teach us one thing. Now, more than ever, the burden of proof rests on those who say we must trade off our liberty and privacy for security. That burden has not been met. Chris Berg is policy director at the Institute of Public Affairs. Twitter: @chrisberg