That's a question you'd have to present to people in the White House.

We've already seen shifts happening in some of the big companies - Google, Apple - that now understand how vulnerable their customer data is, and that if it's vulnerable, then their business is, too, and so you see a beefing up of encryption technologies. At the same time, no programs have been dismantled at the governmental level, despite international pressure.

One of the most frightening things, I think, is the capacity for retroactive searching, so you can go back in time and trace who someone is in contact with and where they've been.

I was in correspondence with an anonymous source for about five months and in the process of developing a dialogue you build ideas, of course, about who that person might be. My idea was that he was in his late forties, early fifties. I figured he must be Internet generation because he was super tech-savvy, but I thought that, given the level of access and information he was able to discuss, he had to be older.

That's a question you'd have to present to people in the White House.

Snowden is almost preternaturally prepossessing and self-possessed. I think of a novelist whose dream character just walks into his or her head. It must have been like that with you and Snowden. But what if he'd been a graying guy with the same documents and far less intelligent things to say about them? In other words, how exactly did who he was make your movie and remake our world?

One of the things that I think is true is that encryption actually is able to secure our communications, that every individual can use encryption, and that it's accessible and in many cases free.