McCaul: Encrypted communications "the biggest threat"

House Homeland Security Chairman Michael McCaul said that encrypted communications and the dark web are the "biggest threat today" because they give terrorists the opportunity to communicate in a space the government cannot monitor.

"I think the biggest threat today is the idea that terrorists can communicate in dark space, dark platforms, and we can't see what they're saying," he said Sunday on CBS' "Face the Nation." He said the "only rational explanation" he has for the Paris attacks "is that they were using these dark platforms in dark space to communicate that, even if we have a court order, we can't see."

There has been no conclusive evidence that the attackers used encrypted messaging services to plan the attack, and at least part of it was conducted over unencrypted SMS messaging. Asked about evidence that they used encryption technology, McCaul said "there are strong indicators that they did" and "in my judgment, they were talking in the dark space and that's how they pulled it off without detection."

In a separate interview on "Face the Nation," Sen. Dianne Feinstein, the top Democrat on the Senate Intelligence Committee, called encryption technology the "Achilles heel" of the internet.

McCaul also defended his bill that was recently passed by the House of Representatives to pause the U.S. plan to take in 10,000 refugees fleeing the war in Syria.

"I take ISIS at its word when it says we want to exploit the refugee program to infiltrate the West," McCaul said. "Our top national security officials, whether it be the FBI director or secretary of Homeland Security, both privately and publicly in testimony before my committee expressed their concerns and warnings about this program. So, I take that seriously. And we introduced this legislation to put a hold on it until we have assurances that we can properly vet, do background checks, and then have them certify, so they're responsible and accountable that there's no terrorists coming into the country."

In response to suggestion by Republican presidential candidate Donald Trump that the U.S. should be monitoring certain mosques, McCaul said the U.S. should "be involved in the Muslim community with outreach programs to identify the signs of radicalization so we can stop them."