At the State of the Net conference in Washington on Tuesday, US assistant attorney general Leslie Caldwell discussed what she described as the dangers of encryption and cryptographic anonymity tools like Tor, and how those tools can hamper law enforcement. Her statements are the latest in a growing drumbeat of federal criticism of tech companies and software projects that provide privacy and anonymity at the expense of surveillance. And as an example of the grave risks presented by that privacy, she cited a study she said claimed an overwhelming majority of Tor's anonymous traffic relates to pedophilia.

"Tor obviously was created with good intentions, but it's a huge problem for law enforcement," Caldwell said in comments reported by Motherboard and confirmed to me by others who attended the conference. "We understand 80 percent of traffic on the Tor network involves child pornography."