Widespread digital encryption presents a massive challenge to law enforcement, FBI Director James Comey told lawmakers on Wednesday, urging Silicon Valley to come up with a solution.
"Our job is to look at a haystack the size of this country to find needles that are increasingly invisible to us because of end-to-end encryption," Comey told the U.S. Senate Committee on the Judiciary.
The U.S. government has been criticized by privacy advocates and tech firms for requesting a "back door" to access private user data on encrypted systems — a measure that could leave that same technology open to hackers.
More from NBC News:
U.S. intelligence agencies go back to old-fashioned paper after massive hacks
France prosecutor says Salhi doesn't remember beheading, sending photos
Donald Trump: I didn't expect backlash 'this severe'
Comey warned that criminals could use encrypted communications to avoid surveillance and that ISIL was using the technology to recruit members.
"This is not your grandfather's al-Qaeda," Comey said.
Silicon Valley companies have mostly been opposed to giving law enforcement this kind of access. Comey warned that fully encrypted communications — which only allow the sender and recipient of a message to read it — left criminal investigators in the dark.
"People watch TV and think the FBI has a way to break that encryption," Comey said. "We do not."
Comey and Sally Yates, deputy attorney general for the Department of Justice, both disputed the idea that the government wants a "back door" to encrypted data.
"We're not seeking a front door, back door, or any other kind of door," Yates said.
Instead, she said, federal law enforcement wants tech companies to somehow retain data that might be accessed later during investigations.
"Even when we have the authority to search digital communications, we can't get the information that we need," Yates said, arguing that user data is becoming "warrant-proof."
Comey acknowledged the risk that hackers might steal consumer information using access given to the government. He didn't offer any technical solutions, but instead stressed how important it was for tech companies to find a way to keep data both secure and available to the government.
"Maybe this is too hard," he said. "But given the stakes, we need to give it a shot."