Apple battles FBI over iPhone "backdoor"

Dan Guido, an expert in hacking operating systems, said that to unlock the phone, the FBI would need to install an update to Apple's iOS operating system so that investigators could circumvent the security protections, including one that wipes data if an incorrect password is entered too many times.

He said that only Apple can provide that software because the phones will only install updates that are digitally signed with a secret cryptographic key.

"That key is one of the most valuable pieces of data the entire company owns," he said. "Someone with that key can change all the data on all the iPhones.”

The notion of opening that key is anathema to the Electronic Frontier Foundation, an online rights group. "Once this master key is created, governments around the world will surely demand that Apple undermine the security of their citizens as well," the foundation said in a statement.

American Civil Liberties Union staff attorney Alex Abdo said the government's request risked a "dangerous" precedent. “The Constitution does not permit the government to force companies to hack into their customers' devices," he said.

The ruling was a topic of discussion on the presidential campaign trail on Wednesday US time.

Donald Trump, the front-runner for the Republican Party's nomination to run in the 8 November election, appearing on Fox News Channel’s "Fox & Friends," said, "I agree 100 percent with the courts - in that case, we should open it (the iPhone) up. ... We have to use common sense."

Another Republican candidate, US Senator Marco Rubio of Florida, called it a “tough issue” that would require government to work closely with the tech industry to find a solution. Rubio said he hoped Apple would voluntarily comply with the court order.

Lance James, an expert in forensics who is chief scientist with cyber intelligence firm Flashpoint, said Apple could respond to the order without providing crypto keys or specialised tools that could be used to unlock other phones.

Apple technicians could create software that would unlock the phone, allowing the company to create a backup file with all of its contents that they could provide to law enforcement, James said.

Asked about the issue in an interview with CNBC TV, the CEO of mobile carrier T-Mobile, John Legere, said he understood both sides of the issue.

Legere called the request "unheralded" and "groundbreaking" but said, "I really don't know how to balance" customer privacy and national security issues.

Additional reporting by Megan Cassella, Doina Chiacu and Susan Heavey in Washington, Steve Holland and Joseph Menn in San Francisco; Writing by Grant McCool; Editing by Jonathan Oatis