In an interview with Yahoo News chief investigative correspondent Michael Isikoff published today, National Security Agency Director Michael Rogers declared that the terrorists involved in last November's attacks in Paris used at least some encrypted communications to plan their actions, preventing NSA from being able to warn French officials in advance. Because of encrypted communications, he said, "we did not generate the insights ahead of time. Clearly, had we known, Paris would not have happened."

Rogers did not explicitly re-launch the campaign waged by FBI director James Comey to force technology companies to provide a "golden key" to encrypted communications. Rogers called encryption "foundational to our future" and added that arguing over encryption backdoors was "a waste of time." But he did say that encryption was making the job of the NSA and law enforcement more difficult.

The interview comes shortly after the FBI won an order requiring Apple to provide technical means to bypass the security measures preventing them from unlocking the iPhone 5C belonging to Syed Rizwan Farook. Farook, along with his wife, are responsible for the December mass shooting in San Bernardino, California.

"Is it harder for us to generate the kind of knowledge that I would like against some of these targets? Yes," Rogers told Isikoff. "Is that directly tied in part to changes they are making in their communications? Yes. Does encryption make it much more difficult for us to execute our mission. Yes."

Rogers' claims about Paris contradict the information that came out of France following the attacks. There were claims by former US intelligence officials that encrypted communications had been used by the Islamic State affiliated terrorists in the immediate wake of the attacks. But those claims were largely dismissed by French authorities when they looked at the actual communications on devices recovered from the group. According to statements from French law enforcement, the attackers had used standard SMS messages to communicate—not encrypted messaging apps on smartphones.

As Ars has reported, ISIS has been known to use encrypted communications, such as Telegram, to communicate and recruit. But despite those encrypted communications, the US did provide a warning of an impending ISIS attack in France, despite any encryption, over two months before the attack. Turkey also warned France about one of the attackers.

That warning led to a French bombing mission against Raqqa in an attempt to take out command and control for the attack. However, the cell-based nature of ISIS operations, which depend largely on a single trained individual creating a local group to carry out attacks, isn't one that can be easily disrupted by an air strike on ISIS leadership. And despite mass surveillance, France was unable to keep tabs on the suspect—possibly because it had too much information to work with. So it's not clear that an absence of cryptography would have made the work of French officials any easier.