Washington (CNN)The head of the National Security Agency expressed deep concerns about terrorists' ability to avoid NSA surveillance, explaining that Edward Snowden's revelations of surveillance techniques and capabilities have had a "material impact" on NSA ability to prevent and detect terror plots.
NSA: Snowden leaks hurt ability to track terrorists
"I would say that it has had a material impact in our ability to generate insights as to what counterterrorism, what terrorist groups around the world are doing," Adm. Michael Rogers told a group gathered in Washington for a cybersecurity summit hosted by the New America think tank.
"Do you have new blind spots that you didn't have prior to the revelation," moderator and CNN National Security correspondent Jim Sciutto asked.
"Have I lost capability that we had prior to the revelations? Yes," Rogers responded. "Anyone who thinks this has not had an impact I would say doesn't know what they're talking about."
Snowden himself remains free in Russia. A film about him won an Academy Award on Sunday evening.
Rogers says he knew U.S. infrastructure would likely come under cyber-attack on his watch, but the target of Sony Pictures was a surprise.
"I fully expected, sadly in some ways, that in my time as the commander of United States Cyber Command the Department of Defense would be tasked with attempting to defend the nation against those kind of attacks," he said. "I didn't realize that it would be against a motion picture company, to be honest."
North Korea is widely believed to be behind the hack in response to Sony's production of the film "The Interview," which depicts a comedic plot to kill leader Kim Jong-un
Rogers declined to respond to a question if the United States was behind a retaliatory online attack that took down North Korea's Internet access.
When asked which nations had the ability to strike U.S. cyber interests Rogers declined to provide assessments of most countries.
"It's a matter of record, we've talked about China and our concerns about what they have been doing in cyber. Clearly the Russians and others have capabilities, we are mindful of that," he said.
One major topic of discussion was encryption and if developers should build a "golden key" or other ability for governments, including the United States, to access data that otherwise would be security.
Rogers was challenged by vocal NSA critic and current Yahoo! chief information security officer Alex Stamos, who asked if Internet companies were required to allow "back door" access to the U.S. government, should similar access be given to other governments around the world.
"Do you believe we should build back doors for other countries?" Stamos asked.
"It needs to be done within a framework. I'm the first to acknowledge that," Rogers said. "You don't want the FBI and you don't want the NSA unilaterally deciding, 'so, what are we going to access and what are we not going to access?' That shouldn't be for us."
Rogers said it would be a process, though.
"We'll have to work our way through it. And I'm the first to acknowledge there are international implications," he said. "I think we can work our way through this."
"I'm sure the Chinese and Russians are going to have the same opinion," Stamos responded.