Former National Security Agency (NSA) contractor Edward Snowden, who leaked a trove of classified documents to the press revealing the scale of mass surveillance practices in the US and UK in 2013, said his actions were worth it.

In a wide-ranging interview with German newspaper Der Spiegel published on Tuesday (12 September), the whistleblower said the public now knows what was once "forbidden knowledge" because of those leaks.

"I wasn't trying to change the laws or slow down the machine," Snowden told Der Spiegel. "Maybe I should have. My critics say that I was not revolutionary enough. But they forget that I am a product of the system. I worked those desks, I know those people and I still have some faith in them, that the services can be reformed."

He added that it wasn't his personal goal to take down the CIA or the NSA but to "give the public a chance to decide where the line should be" with regards to surveillance practices.

Since 2013, Snowden has been living in asylum in Moscow to avoid extradition to the US, where he faces espionage charges.

In the interview, Snowden, 34, discussed a range of topics including government efforts to bypass encryption, Russia's alleged meddling in the 2016 US presidential elections, the DNC hack, President Donald Trump and the ability of mass surveillance programmes to stop terrorist attacks.

Snowden on Russia's alleged interference in the US election

Regarding the increased meddling on the part of intelligence agencies with the democratic processes of other countries, Snowden said he believes this is "something that has always happened."

"What is noteworthy nowadays is that it is happening much more visibly," Snowden said, noting that the US has previously used similar tactics in other elections. "Every government that has an intelligence agency is trying to do the same thing."

With regards to Russia, Snowden said, "They probably did hack the systems of Hillary Clinton's Democratic Party, but we should have proof of that. In the case of the hacking attack on Sony, the FBI presented evidence that North Korea was behind it. In this case they didn't, although I am convinced that they do have evidence. The question is why?"

As for the DNC hack, Snowden said he believes the NSA "almost certainly saw who the intruders were."

"Why wouldn't they?" Snowden asked. "But I am also convinced that they saw a lot of other attackers on there, too. There were probably six or seven groups.

"The Democratic National Committee is a big target and apparently their security wasn't very good. The DNC refused to provide these servers to the FBI, which is really weird. So, I think the reality here was it was narrative-shaping about the Russians."

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Edward Snowden said his decision to leak a trove of confidential documents to the press in 2013 was worth it REUTERS/Rafael Marchante

The ability of mass surveillance programmes to stop terrorist attacks

"We don't have any proof that these mass surveillance programs are stopping terrorist attacks," Snowden said. "But if you can't show us that cells have been uncovered thanks to these measures, and yet you say these are absolutely necessary, why is that? Because they are super interesting for other areas of spying."

He again asserted that none of the classified information leaked by him has helped criminals, rogue states and terrorists.

"This is very much a comfortable allegation for governments," he said. "Their basis for classifying this information is to say it will cause harm if it is revealed. I have sent lunch plans from the cafeteria that are classified as top secret. I'm not kidding.

"I came forward in 2013. We are now in 2017 and they have never shown any harm despite being asked by Congress and despite having spent more than two years investigating it.

"Even Michael Rodgers, the director of the NSA, said, "The sky isn't falling, we are still doing our work. Yes, it was disruptive, but life goes on.""

On government efforts to bypass encryption

"Not cracking encryption – the agencies are trying to bypass encryption," Snowden revealed. "They are looking for weak points on the device you use to see what you are writing before you encrypt your message.

"What they actually do is take over a website, infect it with a malicious software, and when you visit that website because, for example, you received a link, you get hacked. Then they own your computer or your phone. You paid for it, but they use it. I think this is far better than mass surveillance."

He also voiced his concerns over companies like Facebook and Google working with the government on surveillance.

"A company should never be deputised to do the work of a government," he warned. "They have entirely different goals, and when you start crossing those lines that creates unintended consequences at unforseen costs.

"Of course, companies can assist the government in terrorism investigations. But to see company records for example, they should have to convince a judge.

"I think this is where it gets quite dangerous, when we say: Google, you are the sheriff of the internet now. You decide what the law is."

Snowden then went on to address the rampant speculation that Facebook CEO Mark Zuckerberg may run for US president.

"Do we want the company that has the largest social media presence on earth, and has clear political ambitions, to start deciding what is permissible political speech and what is not?" he asked pointedly.

On Donald Trump

"The idea that half of American voters thought that Donald Trump was the best among us, is something that I struggle with. And I think we will all be struggling with it for decades to come," Snowden said.

With regards to Trump's influence on US intelligence services, Snowden doesn't believe the president alone can "meaningfully damage" them.

"These groups are so well represented in Congress, in the media, in culture, in Hollywood," he explained. "Some call it the deep state, but this is very much a pre-Trump thing.

"Donald Trump has nothing to do with the deep state. Donald Trump doesn't even know what the deep state is. The deep state is this class of career government officials that survive beyond administrations...

"The deep state realises that while it may not elect the president, it can shape them very quickly – and this is through the same means with which they shape us," Snowden added.