Manuel Balce Ceneta, File, Associated Press
In this Sept. 1, 2010, file photo, then-U.S. Attorney for the Northern District of Georgia Sally Yates, speaks to reporters during a news conference at the Justice Department in Washington. Federal law enforcement officials, including Deputy Attorney General Yates, now the No. 2 official at the Justice Department, are pressing their concerns about encryption before Congress, where they will argue to senators on Wednesday, July 8, 2015, that the right to privacy is not absolute and must be weighed against public safety interests. At issue is encryption technology in phones and computers that Silicon Valley companies say offers customers' invaluable security in their communications and protection from hackers and corporate spies. But law enforcement officials say that same technology has made it harder for them, even with a warrant, to monitor and intercept messages shared by criminal suspects.

WASHINGTON — Federal law enforcement officials warned Wednesday that data encryption is making it harder to hunt for pedophiles and terror suspects, telling senators that consumers' right to privacy is not absolute and must be weighed against public-safety interests.

The testimony before the Senate Judiciary Committee marked the latest front in a high-stakes dispute between the Obama administration and some of the world's most influential tech companies, placing squarely before Congress an ongoing discussion that has shown no signs of an easy resolution. Senators, too, offered divided opinions.

FBI and Justice Department officials have repeatedly asserted that encryption technology built into smartphones makes it harder for them to monitor and intercept messages from criminal suspects, such as Islamic State sympathizers who communicate online and child predators who conceal pornographic images. They say it is imperative that they be able, with a warrant, to access encrypted data while they're investigating a particular crime.

But they face fierce opposition from Silicon Valley companies, who say encryption safeguards their customers' privacy rights and protects them from hackers, corporate spies and other breaches. The companies in recent months have written to the Obama administration and used public speeches to press their case for strong encryption.

FBI Director James Comey, who has argued his case repeatedly over the last year before think tanks and in other settings, sought to tamp down tension on Wednesday. He told senators that he believed technology companies were fundamentally on the same page as law enforcement, adding, "I am not here to fight a war."

"Encryption is a great thing. It keeps us all safe. It protects innovation," Comey said. "It protects my children. It protects my health care. It is a great thing."

But he said criminals were using encryption to create a safe zone from law enforcement, with the Islamic State exploiting social media to recruit sympathizers and directing them to encrypted platforms.

"Our job is to look at a haystack the size of this country for needles that are increasingly invisible to us because of encryption," he said.

Deputy Attorney General Sally Yates said the Justice Department was not at the moment seeking legislation to address the issue and was instead hoping to work cooperatively with the technology companies. She expressed concern about end-to-end encryption in which only the user can access the communication. She said the department believed that individual companies — not the government — should retain access to a key to unlock encrypted data that can be used in response to a court order.

"The current public debate about how to strike the careful balance between privacy rights and public safety has at times been a challenging and highly charged discussion," Yates told the committee. Personal privacy and Internet security, she said, "are not absolute. And they have to be balanced against the risks we face from creating warrant-proof zones of communication."

Sen. Dianne Feinstein, D-Calif., echoed Comey's concerns about encryption, saying it could enable a "respite from any kind with law enforcement." But others reacted more warily.

Sen. Al Franken pointed out that the recent breach of Office of Personnel Management information involved unencrypted data and asked whether there was a "danger, if we do this wrong, of there also being a national security risk?"

And Vermont Sen. Patrick Leahy, the panel's senior Democrat, said he wasn't convinced how much it would help to facilitate law enforcement's access to encrypted material.

"Strong encryption would still be available from foreign providers," Leahy said. "Some say that any competent Internet user would be able to download strong encryption technology, or install an app allowing encrypted communications — regardless of restrictions on American businesses."

Tech companies call the concerns overblown and vow to protect customer privacy. They say that any "key" that could give law enforcement access to encrypted devices could presumably be exploited by hackers and criminals, too.

In a speech last month, Apple CEO Tim Cook said the company would not waver in offering encryption tools to customers and said weakening encryption would have a "chilling effect on our First Amendment rights and undermines our country's founding principles."

In a May letter to the White House, a tech-company coalition argued that strong encryption protects against "innumerable" threats and urged the government to "reject any proposal that U.S. companies deliberately weaken the security of their products."

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