The Associated Press took a scolding tone, suggesting that the president is endangering national security by having sensitive conversations over a mobile device. Former Pentagon adviser Derek Chollet ominously told the AP: "If you are speaking on an open line, then it's an open line, meaning those who have the ability to monitor those conversations are doing so."
But is talking to foreign leaders on a cellphone really such a security risk? Experts from Rice University and Security Research Labs told me it wasn't so obvious.
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The security of a smartphone depends on how it's configured and how it's used. And while Trump himself is hardly a security expert, the US government employs some of the world's most sophisticated security professionals. And they have likely taken elaborate precautions to maximize the security of the president's wireless communications.
We don't know exactly what security precautions might have been taken, but one clue comes from a recent reports that Trump has swapped his ancient Android phone for an iPhone. According to Axios's Mike Allen, Trump's new iPhone has just one third-party app: Twitter.
It's probably an updated version of the locked-down iPhone President Obama described last year. In an interview with Jimmy Fallon, the former president complained about the phone's limited functionality.
"I imagine they locked down the phone in a variety of ways beyond removing apps," says Dan Wallach, a security expert at Rice University, by email.
An obvious change, Wallach says, would be to replace the default phone app — which makes calls over the insecure conventional cell phone network — with an app that routes phone calls through an encrypted link to NSA headquarters in Fort Meade, MD.
"That's a pretty good solution," says Karsten Nohl, a security expert at Security Research Labs who has done groundbreaking research on the security of cellular networks. Indeed, he says, making calls using an encrypted smartphone app could be "as safe as what you'd be using from a landline phone in the White House."
Of course, no communications system is perfect. Nohl says one big issue is that different countries have developed their own proprietary encrypted networks for internal communications. These systems aren't compatible with each other, so when world leaders call each other, they're sometimes forced to use unencrypted lines. But Nohl says countries face this challenge whether their leaders are making calls with a cellphone or a landline phone.
It's also possible that despite the National Security Agency's precautions, foreign governments could hack into Trump's cellphone itself. But in that case, it wouldn't matter that much whether Trump took calls on his cellphone or via a nearby landline — so long as the smartphone was in the room, the hackers would be able to hear every word Trump said.
Indeed, it's likely that when Trump makes calls using his cellphone, the biggest security threats come from things other than his own cellphone. For example, we can assume foreign intelligence agencies are trying to hack the personal cellphones of Trump's aides, family members, and others who spend time with the president. They may also try to plant listening devices in locations — like Trump's Mar-a-Lago resort — where Trump might have sensitive conversations. This is why presidents normally have sensitive conversations in Sensitive Compartmented Information Facilities — essentially high-tech tents that ensure no listening devices are within earshot.
But there doesn't seem to be anything inherently insecure about a president taking calls from foreign leaders on a cellphone that has been suitably locked down by US intelligence agencies. Modern cryptography is extremely robust, and it allows cellphones to make calls that are essentially impervious to eavesdropping.