DW: Having spent a few days in Germany, what sense do you get of the feeling of Germans towards these NSA revelations? Has your time here recently changed your outlook?

Michael Hayden: It has changed my outlook a little bit. I think the first and most powerful impression is the genuine depth of German feeling about this. Back home, we talk about things done for political effect, and frankly I suspect some of that goes on here too.

I've been in two meetings now at which I was the speaker - small groups, mostly Germans - and we had good discussions. But the depth of feeling is something that really strikes an American when he comes here.

Have you been surprised how many Germans take this as a very personal issue? Do they take it very personally because they like the United States but they've been really taken aback by the surveillance?

They have - and as I said before, that's genuine. Also genuine is my belief that all nations conduct espionage and occasionally espionage gets conducted with people you truly do consider friends. So it's a bit difficult having that discussion.

Chairman Mike Rogers from our Intelligence Committee was here yesterday and I think he put a good program on the table. He said, "Let's stick with the facts. Let's actually have an adult conversation about what it is our security services do and don't do." And, frankly, in order for that to be a good conversation, I think German citizens are going to have to have a better idea about what their security organizations do and don't do. I would be willing to bet that now, based on all these press accounts, most Germans know more about the NSA than about the BND [Germany's federal intelligence service].

One should not hold NSA or American intelligence up to some abstract idealistic model, but what has become accepted international practice, including practice conducted by the German security services. And there I think there may be differences, but they may not be nearly as dramatic as some people think.

But of course the NSA's capabilities and financial means a whole different realm compared to not just the BND but to everyone else. Nobody would ask the same questions of China or Russia, but of course they're playing in a different league.

I emphasize that every mature intelligence organization in the world is trying to do the kinds of things that the NSA does. I make no apologies that we may be better at it. For example, I know the question of metadata is one of great sensitivity here. Every single intelligence organization in the world knows you have to work metadata in order to deal with the volume of modern communications. I make no apologies that we may do it better, but everyone tries to do it.

I don't think many people doubt that you have to target terrorists or people with criminal intent. The question is: do you need to target everyone else and collect everyone's bulk data in order to catch this tiny minority and sacrifice everyone's digital lives for that means?

Let me first begin with the thought that if you think governments are sacrificing your digital life, just imagine what private commercial companies are doing with your digital life. The second thought is that the NSA is not a law-enforcement organization. We are interested in bad people, but our distinction is not between good people and bad people - our distinction is between communications that keep America and its friends safe and free.

Finally, getting a target takes a lot of time and energy, and even the NSA doesn't have limitless amounts of that. You really want to make sure you're up on the right person, on the legitimate and useful target. The problem is, how do you discover that. How do you figure out which frequency, which phone line, which phone number, which e-mail account is the one that you really should be up on in all meanings of the world "should" - ethically, legally and operationally? Frankly, metadata is one way that you arrive at those specific targeting conclusions in a way that certainly, from the American perspective, does not squeeze privacy very much because it is bulk collection, not particularized collection.

The big question now is how do you move forward with that? While everyone agrees you have to target terrorists and extremists, there are different understandings of intelligence collection and privacy. How do you get those two ideas to match up - especially between the US and German views?

First of all, the President Obama's speech and the presidential directive he sent out after the speech might be as good as it gets publically. Frankly, that's incredibly detailed. No other intelligence organization on the planet has portrayed its capabilities and its limits in the detail that the American services did two weeks ago.

Secondly, Germany is a good friend. To be very honest with you, what we may or may not have been doing with regard to the chancellor and her cell phone is not nearly as serious an offence by us as the fact that we couldn't keep that a secret. That put a good friend in a very embarrassing position, it offended her personally and it caused political problems for her. That's our fault - we wronged our good friend by not being able to keep this secret. We probably do owe the chancellor, the German government and the German people a little more transparency than we would otherwise be obliged to give, even between friends.

But a bilateral spying agreement that is bound by some kind of judicial standard is not on the agenda?

I cannot conceive that being on the agenda - which does not mean Germany is not a very good friend.