"It is one that will be the subject of some very frank discussions. Turnbull has been at pains to emphasise the government does not want a "so called" backdoor to access devices and messages. But that is not how the technologists frame this debate. Credit:AAP "We are in a position now where increasingly police and security agencies can intercept telecommunications, but they cannot read them." US tech companies have been loath to decode any of their systems for intelligence and police agencies, even in counter-terrorism cases. Apple refused to "unlock" one of its phones used by a terrorist in the San Bernadino shootings that killed 14 people in 2015.

Mr Turnbull said that he'd use the first, closed-door session of the G20 summit in the German city of Hamburg to deliver "my message – we need to have much greater co-operation because the terrorist threat is absolutely global". US tech companies have been loath to decode any of their systems for intelligence and police agencies. Credit:Bloomberg He named three popular encrypted messaging services: "The point is, what are the responsibilities that a WhatsApp or a Telegram or a Signal, what are the responsibilities they owe to public safety? "You have got a very real global threat where terrorist organisations, Islamist terrorist organisations, are using these digital platforms to do us harm." After the test, US President Donald Trump also called on China to act . Credit:AP

On another aspect of the counter-terrorism campaign, many governments have demanded that social media companies block Islamic State and other terrorist groups from using their services. Islamic State has used Facebook and Twitter as main channels for spreading propaganda and recruiting terrorists. Mr Turnbull said in the interview that the social media companies seemed to be ready to co-operate: "My sense is there is plenty of goodwill there. But on the issue of encryption, that is a much more complex problem." The head of the US Studies Centre at Sydney University, Simon Jackman, agreed that the social media companies "will give governments something" in voluntarily blocking terrorists on their platforms, "and countries can call it a win, but encryption is a much harder one". The Prime Minister foreshadowed tough US resistance: "There are a variety of views about this. You have the imperative of law enforcement and public safety.

"But on the other hand, particularly in the US, you have a very strong libertarian tradition both on the left and the right. "You saw an example of that – which most Australians would have found inconceivable – with Apple refusing to assist in unlocking a mobile phone that had belonged to one of the San Bernardino terrorists." Apple refused a court order in that case. At the time, Donald Trump said that "I agree 100 per cent with the courts" and said it was a matter of common sense. But Professor Jackman said that "whatever Trump's personal views, he's just not in a position to deliver on encryption. Any attempt at compelling them [US tech companies] to do something by way of a legislative or executive order will hit a brick wall because of the First Amendment of the US constitution", guaranteeing free speech. Mr Turnbull said that although he had not spoken to the US President on the matter, there had been much pre-G20 discussion between leaders.

British Prime Minister Theresa May and German Chancellor Angela Merkel, the summit's host, share his position, Mr Turnbull said. "We are going to have to hear from different countries and in particular from the US – because this is where most of these platforms are hosted, of course, [though] Telegram is hosted in Germany," he said. "Are they prepared to take the steps, and do they believe they have the legal ability to take the steps, to ensure that, subject to appropriate legal authorisation and warrants, that they must make available in a decrypted form communications between people who are under investigation, for example, terrorist activities?"