WASHINGTON — The Justice Department has renewed its fight for access to encrypted communications, arguing that it is a vital crime-fighting tool even as technology companies and advocates have countered that it will threaten individual privacy.
Attorney General William P. Barr took aim at Facebook’s plan to make WhatsApp and its other messaging services more secure, pressing its chief executive, Mark Zuckerberg, to create a loophole to that goal of full encryption. The Justice Department said that investigators needed lawful access to encrypted communications to fight terrorism, organized crime and child pornography.
“Companies should not deliberately design their systems to preclude any form of access to content even for preventing or investigating the most serious crimes,” Mr. Barr, joined by his British and Australian counterparts, wrote in a letter to Mr. Zuckerberg that was reviewed by The New York Times and dated Friday. BuzzFeed News first reported on the letter.
Mr. Barr’s request was the latest salvo in a yearslong fight by law enforcement officials for access to popular communications platforms that have become increasingly secure. The conflict last came to a head in 2016, when a federal judge ordered Apple to help the F.B.I. unlock an iPhone recovered after the 2015 mass shooting in San Bernardino, Calif. The F.B.I. ultimately cracked it without Apple’s help, easing tensions for a time with the tech companies.
The letter also showed that the Justice Department was trying a coordinated approach with close allies to prod technology companies to change their position.
At issue are end-to-end encryption, which would ensure that only the sender and recipient can read messages sent using a particular messaging service, and so-called back doors, which would give the authorities access to such data.
Tech company officials have said that strong encryption is necessary to protect legitimate users of their platforms all over the world, including journalists and government critics. Facebook respects the role of law enforcement but believes people have a right to communicate privately online, said Andy Stone, a company spokesman.
“End-to-end encryption already protects the messages of over a billion people every day,” Mr. Stone said. “We strongly oppose government attempts to build back doors because they would undermine the privacy and security of people everywhere.”
With 1.5 billion users, Facebook’s WhatsApp is perhaps the world’s most commonly used encrypted communications platform. Privacy experts and tech company officials said that creating a back door would effectively destroy the secrecy of such platforms.
“We are being spied upon by everybody and everywhere,” said Susan Landau, a Tufts University computer security professor. “It is very easy to listen in on communications. Securing data is a clear national security interest.”
The Justice Department and its counterparts in Australia and Britain have long pushed for back doors to other tech platforms but are focusing on Facebook because of Mr. Zuckerberg’s plan to add end-to-end encryption to all of the company’s platforms, a government official said in a background briefing for reporters on Thursday.
Mr. Barr and Britain’s home secretary, Priti Patel, signed a pact late Thursday that eases the legal barriers for American and British law enforcement agencies to request electronic data from tech companies in both countries for investigations into terrorism, child sexual abuse and other crimes. Under the current system, such requests can take up to two years to process.
Facebook has also become a focus of law enforcement’s push against encryption because of the role it could play in the spread of online child sexual abuse images if it were extended to its Messenger platform, The Times reported on Wednesday.
Facebook’s dominant position and huge user base across its platforms make it a tempting target for the Trump administration as it begins a renewed push against end-to-end encryption.
In Washington and around the world, there has been an aggressive antitrust push against the big tech companies. President Trump has repeatedly railed against Facebook, Twitter and other companies, claiming that they have inhibited conservatives’ speech.
In recent weeks, Facebook has taken steps to mend fences in Washington. Mr. Zuckerberg and Sheryl Sandberg, the company’s chief operating officer, have made trips to Capitol Hill, and Mr. Zuckerberg met Mr. Trump for the first time last month, even pausing for a photograph in the Oval Office.
Other tech executives, like Tim Cook of Apple, enjoy a more cordial relationship with Mr. Trump. The two meet regularly.
Still, Trump administration officials have weighed whether to seek legislation that would effectively ban end-to-end and other forms of encryption.
Mr. Barr, who took office in February, has embraced the push. In a speech in July, he called on tech companies to stop using advanced encryption that keeps out law enforcement officials.
He was to deliver remarks on Friday at a Justice Department summit on how encryption has stymied the government’s ability to gain access to information, a problem that local and federal law enforcement agencies have coined “going dark.”
The summit, which Facebook representatives will also attend, will focus on the effect of encryption on child exploitation cases.
An explosion in reports of online photos and videos of children being sexually abused — a record 45 million were reported last year — can be traced to failings by technology companies, the Justice Department, Congress and others to give law enforcement agencies the tools and resources they need, The Times reported on Saturday.
Mr. Barr’s letter highlighted an instance when a man was imprisoned on a conviction of sexually abusing a child starting at age 11 because prosecutors presented as evidence message logs between the man and the child that Facebook had provided.
Facebook and others have devised methods to detect and remove child exploitative imagery, including one that relies on photo-matching technology. Facebook and WhatsApp are working with other major tech companies to share both information and photo-matching technology, relying on machine learning to ban groups suspected of trafficking in child pornography.
WhatsApp also regularly submits information to law enforcement officials when necessary and bans accounts suspected of or associated with illicit material.
But even with such measures, Facebook can hardly monitor the billions of pieces of content flowing through its encrypted systems every day, which is by design. Mr. Zuckerberg has predicted that such systems will grow increasingly popular as the internet evolves.
“The future of communication will increasingly shift to private, encrypted services where people can be confident what they say to each other stays secure and their messages and content won’t stick around forever,” Mr. Zuckerberg said in a statement this year announcing the changes. “This is the future I hope we will help bring about.”
Still, at a town hall-style meeting on Thursday with employees at Facebook’s headquarters in Menlo Park, Calif., Mr. Zuckerberg acknowledged some of the trade-offs the company must deal with regarding encryption.
“These are some of the hardest decisions we have to make,” he said.
In their letter, Mr. Barr and the British and Australian officials said law enforcement must be able to unlock encryption systems to retrieve information to “safeguard the public, investigate crimes and prevent future criminal activity.”
The officials acknowledged that “law-abiding citizens have a legitimate expectation that their privacy will be protected.” But they argued that privacy needs to be balanced with law enforcement agencies’ “ability to stop criminals and abusers in their tracks” that Facebook should be able to provide access if a judge has issued a warrant.
Facebook’s current encryption system, and its plans to expand those protections, impedes law enforcement’s ability to investigate, they wrote. The encryption on WhatsApp blocks Facebook from gaining access to the information its users send on the platform, similar to the system used by the Signal messaging service, considered to be one of the most thorough at protecting users’ privacy.
“This puts our citizens and societies at risk by severely eroding a company’s ability to detect and respond to illegal content and activity, such as child sexual exploitation and abuse, terrorism, and foreign adversaries’ attempts to undermine democratic values and institutions, preventing the prosecution of offenders and safeguarding of victims,” Mr. Barr and the other officials wrote.
They pledged to seek access to Facebook and WhatsApp content only when public safety was at risk. The government official who briefed reporters also challenged the description of the Justice Department’s effort as a push for a “back door.” The term is inaccurate, the official said, because it implies a weakness in the encryption technology that hackers and others could also exploit.
But only platforms that use an encryption system that the company itself cannot break can be protected from hackers. Facebook cannot comply with the government’s new demand without undermining the protections they are trying to provide their users, experts said.
“There is simply no way today way to create an encryption back door that doesn’t undermine encryption broadly,” said Jules Polonetsky, the chief executive of the Future of Privacy Forum.
A recent report by the Carnegie Endowment for International Peace argued that technology companies and the government should focus not on altering end-to-end encryption systems, but on finding ways for law enforcement to gain access to devices they have lawfully obtained.
The joint letter comes at a somewhat awkward moment for Mr. Barr. His work with Australia and Britain has separately come under scrutiny as he has pressed for both countries’ cooperation with the Justice Department’s review of the origins of the investigation into Russia’s interference in the 2016 presidential election.
Julian E. Barnes and Katie Benner reported from Washington, and Mike Isaac from San Francisco.