Surveillance researchers and privacy advocates published a report on Wednesday outlining what we do know, thanks to the period of discovery post-Snowden — and the overwhelming amount of things we don't.

The NSA's domestic surveillance was understandably the initial focus of public debate. But that debate never really moved on to examine the NSA's vastly bigger foreign operations.

"There has been relatively little public or congressional debate within the United States about the NSA's overseas surveillance operations," write Faiza Patel and Elizabeth Goitein, co-directors of the Brennan Center for Justice's Liberty and National Security Program, and Amos Toh, legal adviser for David Kaye, the U.N. special rapporteur on the right to freedom of opinion and expression.