Attorney General William Barr Bill BarrHillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Bipartisan representatives demand answers on expired surveillance programs YouTube to battle mail-in voting misinformation with info panel on videos MORE in lengthy remarks on Tuesday said he believes encryption is allowing "criminals to operate with impunity" in the digital world, reopening a bitter fight between the U.S. government and tech industry over whether law enforcement should be given special access to encrypted messages.

Barr came out strongly against completely encrypted messaging, alleging that it has prevented U.S. law enforcement from tracking down criminals at the helm of drug cartels and even some responsible for murders.

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"The [cost of encryption is] ultimately measured in a mounting number of victims — men, women and children who are the victims of crimes, crimes that could have been prevented if law enforcement had been given lawful access to encrypted evidence," Barr told the crowd at a cybersecurity conference in New York City.

The country's top law enforcement agencies for years have warned that encrypted communications and data could pose national security risks, considering investigators cannot tap into those messages between potential criminals or terrorists even with a court order.

Encryption converts messages and data into code to prevent unauthorized access. Messaging services like WhatsApp and Signal tout end-to-end encryption, a system of communication where only the senders can read the messages.

The tech industry and cyber experts have defended encryption as a necessary privacy measure that offers a method of protecting communications from outside intrusion and hacking. Proponents of encryption have said creating "backdoor" access for law enforcement would undermine the security of messaging systems.

"Making our virtual world more secure should not come at the expense of making us more vulnerable in the real world," Barr said on Tuesday. "But unfortunately, this is where we appear to be headed."

He encouraged the tech industry to work with law enforcement to create back doors for law enforcement. "While we remain open to a cooperative approach, the time to achieve that may be limited," he warned.

The fight over "going dark" has stalled for some time following a highly-publicized push by former FBI Director James Comey James Brien ComeySteele Dossier sub-source was subject of FBI counterintelligence probe Judge will not dismiss McCabe's case against DOJ Democrats fear Russia interference could spoil bid to retake Senate MORE to gain access to an iPhone that belonged to a perpetrator of the terrorist attack in San Bernardino, Calif., in 2015.

But there have been hints in recent months that Barr and other top law enforcement officials plan to reopen the fight, opening the door to criticism from privacy hawks in Congress like Sen. Ron Wyden Ronald (Ron) Lee WydenHillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns On The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline Democratic senators ask inspector general to investigate IRS use of location tracking service MORE (D-Ore.).

Wyden has repeatedly battled with intelligence officials over government surveillance, and in a letter last year warned FBI Director Christopher Wray that building back doors for law enforcement in encrypted messaging could pose significant cybersecurity threats.