President  Obama meets with business leaders at a summit on cybersecurity and consumer protection on Feb. 13 at Stanford University in Palo Alto, Calif. From left are, Kaiser Permanente chief executive Bernard Tyson, Intel Corporation President Renee James, Obama, Stanford University President John Hennessy and Apple chief executive Tim Cook. (Evan Vucci/Associated Press)

President Obama tried to walk a very fine line on encryption, the technology that secures much of the communications that occur online, during his recent visit to Silicon Valley -- saying that he is a supporter of "strong encryption," but also understands law enforcement's desire to access data.

"I lean probably further in the direction of strong encryption than some do inside of law enforcement," Obama said during an interview with tech news site re/code. "But I am sympathetic to law enforcement because I know the kind of pressure they’re under to keep us safe. And it’s not as black and white as it’s sometimes portrayed."

But the technical aspects of encryption actually are quite black and white, experts say, adding that the example Obama used to illustrate the risks of encryption doesn't match up with how tech companies are deploying the security measure for customers. Obama suggested that the FBI might be blocked from discovering who a terrorist was communicating with by tech companies' recent efforts to beef up encryption. But that type of data would still remain available, technical experts say.

The White House declined to comment.

Tech companies have expanded their encryption offerings since details about the National Security Agency's efforts to get around security practices were revealed by former National Security Agency contractor Edward Snowden. Perhaps most notably, Apple and Google have made it so they are unable to unlock many mobile devices that use their operating systems -- even if served with a warrant.

This has set up a conflict between tech companies and law enforcement officials, who warn such technology can allow bad guys to "go dark" and evade legitimate attempts at surveillance.

Obama tried to explain a scenario where this might harm national security during his re/code interview:

Let’s say you knew a particular person was involved in a terrorist plot. And the FBI is trying to figure out who else were they communicating with, in order to prevent the plot. Traditionally, what has been able to happen is that the FBI gets a court order. They go to the company, they request those records the same way that they’d go get a court order to request a wiretap. The company technically can comply.

With the expansion of encryption, Obama said, a tech company may have secured that data so well that it would be inaccessible. But that's not actually how the iOS or Android default encryption works, technical experts say.

"The example he gives in his interview is one where encryption deployed by a company prevents them from being able to tell the government who someone is in contact with," said Christopher Soghoian, the principal technologist at the American Civil Liberties Union's Speech, Privacy and Technology Project. "That's not taking place right now."

Encrypting mobile devices means that a tech company would be unable to help the government get at the content stored on those devices. But the type of information Obama said the FBI would want to obtain in that example, details about who the suspect is contacting, is metadata that should be readily available with a court order through the user's e-mail provider or telephone carrier.

The encryption used by Apple and Google’s latest mobile operating systems put only the data kept on the devices themselves beyond the reach of police. Data kept on remote cloud services – which in many cases routinely back up device data such as photographs and other files – are generally available by court order. In some cases, however, the devices themselves have records of the content of communications, over such services as Apple’s iMessage instant messaging service, that may not be available to law enforcement any other way.

Although there may be some ways for bad guys to cover their tracks, such as using the anonymous browsing tool Tor, Soghoian said, that is not akin to the consumer encryption expansions major companies such as Google and Apple have been working on.

"No system that I know of can encrypt the metadata easily," explained Joseph Lorenzo Hall, the chief technologist at the Center for Democracy and Technology. Some solutions might help at least obfuscate that information, he said, but ultimately whatever service provider an individual is relying on will need to have routing data to make a connection work -- and that routing data can be used to map out who a person is communicating with in the way the Obama described.

Later in the interview, Obama said his administration was looking to find ways to narrow the gap between consumers having their communications secured and law enforcement's access needs -- suggesting he might favor the approach laid out by FBI Director James B. Comey and Attorney General Eric H. Holder Jr. last year which urged tech companies to include intercept capabilities for law enforcement in their products.

A senior administration official defended Obama's statements:

The United States Government firmly supports the development and adoption of strong encryption, which is a key tool to secure commerce and trade, safeguard private information, promote free expression and association, and strengthen cybersecurity.  However, there is no doubt that terrorists and other criminals use encryption to conceal and enable their crimes.  This poses serious challenges for public safety, and we need to work together to address them.  Misuse by a few, however, does not change the fact that responsibly deployed encryption helps secure many aspects of our daily lives, including our private communications and commerce.  We are committed to working together with technology companies and law enforcement to strike the right balance by ensuring that terrorists and criminals can be held to account without weakening our commitment to strong encryption.

But lawful intercept technology is fundamentally at odds with providing the "strong encryption" Obama said he supports, said Matthew Green, a cryptography expert and professor at the Johns Hopkins Information Security Institute. "It would require that someone have a master key that will allow them to unlock any conversation -- and then the question is not just who has access to that key, but how are they securing it, and how else might that weakness be exploited in unexpected ways."

It might not be impossible to implement, Green said, but any new form of access for law enforcement introduces a substantial amount of complexity and necessarily creates new targets for hackers to attack. The government has tried the approach before and failed: In the 1990s, the NSA promoted a technology called the "clipper chip" that was supposed to give the government a way to lawfully intercept encrypted telephone calls. It was later dropped after researchers discovered substantial vulnerabilities in the product that could be exploited by non-law enforcement actors to defeat the encryption.

Elsewhere around the world, technology designed to provide access to communications for law enforcement also has caused security problems. Lawful intercept capabilities built into a Greek mobile phone network were blamed for a wiretapping scandal that allegedly allowed hackers to bug the communications of the country's prime minister and at least 100 other high-ranking dignitaries a decade ago.

The disconnect between the administration's rhetoric on encryption and the realities of how it works concerns Green and many other encryption experts.  "I haven't seen any evidence that they have any idea of the technical aspects of what they're asking for," he said.

The ideas about allowing for a narrow intercept capability floated by the administration may sound intuitively plausible, Hall said, but don't account for "the technical realities of the situation."

"I know of no one in the technical community who thinks you can have a secure lawful intercept capability," he explained.

Some members of the technical community have criticized the shortage of technical chops among policy advisers supporting the president on cybersecurity matters-- particularly White House cybersecurity czar Michael Daniels, a longtime federal employee. He drew the ire of some cybersecurity experts last year when he told Gov Info Security that "being too down in the weeds at the technical level could actually be a little bit of a distraction" for his job.

But the president's apparently imperfect understanding of how encryption works surprised Soghoian, especially because the trip out to California was largely seen as an attempt to mend fences with tech companies and find common ground on consumer security issues.

"It's the thing you kind of hope the president would understand before he flew out to Silicon Valley," he said. "Either he doesn't understand it, he's not getting the truth from his briefing, or he just made a big mistake during the interview."

To Green, there was also a certain amount of irony in Obama's comments -- which came hours after he spoke at the White House organized summit on cybersecurity and consumer privacy: At the same time he was proposing a major effort to shore up the security of digital infrastructure by expanding information sharing between the private and public sector, Obama hinted at an openness to policies Green said would make online communications less secure and "squander the trust between tech companies and their consumers."

But the president also must grapple with the political realities of who will be blamed in the event of an attack. He said as much during the re/code interview: "The first time that attack takes place in which it turns out that we had a lead and we couldn’t follow up on it, the public’s going to demand answers."

Balancing the pressure of protecting Americans with concerns from the technology industry, which has become a significant source of political donations in recent cycles, is like walking a tight rope. But the president's effort to explain how encryption works shows that while it is easy to make broad statements that seem designed to placate both sides, the technical realities are harder to square.

Ultimately, the president didn't come down definitively on one side of the encryption question in his interview with re/code -- instead, he hedged by saying there would have to be a public debate about the issue. But an informed debate is difficult to have without a firm grasp of exactly how the technology works.

This post has been updated.