In the ongoing debate between law enforcement and the technology community over encryption, the threat of terrorism in the homeland has long been the ace in the FBI's hand.
FBI Director James Comey has in recent months repeatedly asked tech companies to create products that allow law enforcement to access encrypted communications if they obtain a warrant, warning that strong encryption allows terror suspects to plot "in the dark."
Speaking before the Senate Homeland Security Committee on Thursday, Comey said the threat of homegrown terrorism has brought the tech industry to the table to talk about ways to cooperate with law enforcement over encryption.
"I think, in part, the ISIL threat focused everybody's minds," Comey said, and convinced opponents that "we're really not just making this up."
The Justice Department has in the past demurred when asked to approximate the scale of what officials often call the "going dark problem." But pressed by committee chairman Ron Johnson on how many terror suspects his agents have actually lost track of because of encryption, Comey on Thursday gave the closest thing to a statistic that the department has publicly shared.
"Probably the best number I can give in an open setting is dozens," Comey said.
Johnson seemed taken aback at the response and moved on to ask another question. Later, he returned to the FBI director's answer.
"I'm a little concerned about numbers, but I will say, I'm surprised if it is only a couple dozen people who have been inspired by social media and then moved into encrypted accounts," Johnson said.
Previously, the Justice Department's Kiran Raj expressed a need for better public data about the number of cases affected by strong encryption.
"We need to do a better job explaining how many cases are affected by this," Raj, the senior counsel to the deputy attorney general, said at a panel discussion last month hosted by Georgetown University and Just Security.
Pressure has increased in recent weeks against the FBI's push for access to encrypted messages.
This month, two former NSA directors—Michael McConnell and Michael Hayden—said they support strong encryption, and pushed law enforcement to find another way to do its job. And the tech community has ramped up calls for the White House to come out against "back doors" that would allow the FBI to read encrypted communications.
Meanwhile, Comey is carrying on his charm offensive. Even as he asked if the tech community has "really tried" to solve the problem at a hearing last month, he maintained that law enforcement and tech companies share common goals.
To prove the point, Comey likes to repeat that his agency is not "an alien force imposed on the American people."
"The conversations are ongoing and they've gotten healthier," he said Thursday. "People have stripped out a lot of the venom. Folks aren't questioning as much as they used to each other's motives. Because we're in a place where we recognize we care about the same stuff."