Days after President Donald Trump met with North Korean dictator Kim Jong Un[1] in Singapore, the president touted the strength of the two leaders' relationship. "I can now call him," he told reporters at the White House on Friday. "I gave him a very direct number. He can now call me if he has any difficulty. We have communication."
The US and North Korea have an extremely complicated and thorny diplomatic relationship—it wasn't long ago that Trump casually threatened a nuclear strike[2]—and any gesture of goodwill between the two nations potentially helps better it. But Trump's claim concerned security experts Friday, who noted that if the president really did give his personal number to Kim Jong Un, he would also have created a major national security exposure in the process.
"Absolutely that is a problem," says Karsten Nohl, chief scientist at the German firm Security Research Labs, who researches cell network attacks. Hackers can abuse flaws in the way cellphone networks interoperate[3] to listen in on someone's phone calls, intercept their text messages, and track their location. If Trump wasn't careful, he may have given Kim Jong Un an easy and expansive tool for spying on the top tier of the US government. The White House did not return a request for comment.
"If he were well-advised and listened to that advice, he would probably give out a random phone number that forwards to his phone number, versus a phone number that is really off of the SIM card in his phone," Nohl says. "As president of the US, he could probably have a list of 1,000 phone numbers, all of which reach his phone."
That's how things are supposed to work. But Trump has a poor track record for