US, Apple ratchet up encryption rhetoric

The US Department of Justice has filed a motion seeking to compel Apple Inc to comply with a judge's order to unlock the encrypted iPhone belonging to one of the San Bernardino shooters, portraying the tech giant's refusal as a "marketing strategy".

In response, a senior Apple executive, speaking on condition of anonymity, characterised the Justice Department's filing as an effort to argue its case in the media before the company has a chance to respond.

The back and forth escalated a showdown between the Obama administration and Silicon Valley over security and privacy.

The Federal Bureau of Investigation is seeking the tech company's help to access shooter Syed Rizwan Farook's phone by disabling some of its passcode protections. The company has pushed back and on Thursday won three extra days to respond to the order.

Another senior Apple executive said congress was the right place for a debate over encryption, not a courtroom.

Apple was stunned that such a legal request had come from the US government rather than a country with weaker traditions of protecting privacy and civil liberties.

The motion to compel Apple to comply did not carry specific penalties, and the Justice Department declined to comment on what recourse it was willing to seek.

In the order, prosecutors acknowledged that the latest filing was "not legally necessary" since Apple had not yet responded to the initial order.

A federal court hearing in California has been scheduled for March 22 in the case, according to Thom Mrozek, a spokesman for the US Attorney's Office for the Central District of California.

The Justice Department said its Friday motion was a response to Apple CEO Tim Cook's public statement on Wednesday, which included a refusal to "hack our own users and undermine decades of security advancements that protect our customers".

"Rather than assist the effort to fully investigate a deadly terrorist attack ... Apple has responded by publicly repudiating that order," prosecutors wrote in the Friday filing.

"Apple's current refusal to comply with the court's order, despite the technical feasibility of doing so, instead appears to be based on its concern for its business model and public brand marketing strategy."

The two senior Apple executives said the company had worked hard to help investigators and tried multiple avenues including sending engineers with FBI agents to a WiFi network that would recognise the phone and begin an automatic backup if that had been enabled.

Some technology experts and privacy advocates backing Apple suggest Farook's work phone likely contains little data of value. They have accused the Justice Department of choreographing the case to achieve a broader goal of gaining support for legislation or a legal precedent that would force companies to crack their encryption for investigators.