Facebook Encryption Eyed in Fight Against Online Child Sex Abuse

“A secure messenger should provide the same amount of privacy as you have in your living room,” said Erica Portnoy, a technologist at the Electronic Frontier Foundation, a digital rights group. “And the D.O.J. is saying it would be worth putting a camera in every living room to catch a few child predators.”

But Mr. Raman, the associate deputy attorney general, said platforms like Facebook provided opportunities for child predators that were not readily available in the real world, creating a need for more scrutiny.

“It’s a unique platform,” he said. “You have a combination of open profiles, which almost creates a menu of options if you’re a child predator, and also will provide — if they implement their plans — the sort of mechanisms for drilling down and contacting children” with encryption.

Criminals have become adept at using encryption and the so-called dark web to cloak themselves, requiring greater effort by law enforcement to identify them. Even so, mainstream technology companies, like Apple, have come to embrace encryption technologies, particularly after disclosures about large-scale data collection by the National Security Agency.

“There are really good reasons to have end-to-end encryption, but we have to acknowledge it comes with trade-offs,” said Hany Farid, a professor at the University of California, Berkeley, who helped develop technology in 2009 for detecting online child abuse imagery.

Gavin Portnoy, a spokesman for the clearinghouse of abuse material, the National Center for Missing and Exploited Children, said officials there opposed the widespread adoption of encryption. “The rape and sexual exploitation of children that we see in millions of reports to the cyber tip line will continue to circulate online, but will be invisible to tech companies,” he said.

The Times reported on Saturday that tech companies flagged 45 million photos and videos as child sex abuse material last year. Those images were contained in 18.4 million reports, nearly 12 million of which came from Facebook Messenger. It was unclear whether photos and videos of abuse were actually more prevalent on Facebook or were just being detected at a high rate.