Analysis At last week's RSA security conference, the halls were full of government speakers telling the tech community that it must do the impossible: invent a form of encryption that's strong, but also easy for law enforcement to crack.

Ever since Apple and Google enabled full-device encryption by default on their mobile operating systems, the law enforcement community has been kicking up a stink. The head of the FBI issued dire warnings of children dying if the crypto trend was allowed to continue. The head of the NSA agrees, and so too does the British Prime Minister.

During his RSA keynote last Tuesday, Jeh Johnson, the secretary of Homeland Security, invoked the souls of the 168 people killed in the 1995 Oklahoma City bombing to explain how, while privacy was important, encryption should not be allowed to stymie US law enforcement.

"Our inability to access encrypted information poses public safety challenges. In fact, encryption is making it harder for your government to find criminal activity, and potential terrorist activity," he pontificated.

"We in government know that a solution to this dilemma must take full account of the privacy rights and expectations of the American public, the state of the technology, and the cybersecurity of American businesses. We need your help to find the solution."

He was not alone. Michael Daniel, President Obama's cybersecurity coordinator, told the press that "there is no question that [encryption is] a public safety aspect" but that he – and his boss – had confidence that if anyone can find a system that does both, Silicon Valley can.

Daniel stressed that this must be a balancing act. The government has to weigh the needs of law enforcement and public protection with the desire for privacy. And while Daniel acknowledged the international and business cost dimensions to developing such an encryption system, he seemed convinced that one was possible, although he couldn't cite anyone in the crypto community who would agree with him.

Meanwhile, former Michigan congressman Mike Rogers – an ex-FBI agent who once headed the Senate Intelligence Committee – insisted that there has to be an encryption system that is both strong against everyone and, if a law enforcement official shows up with a court-obtained warrant, can be broken open to reveal the content.

"I don't understand why we can't have both," he complained. "I think we can have both, and we should have it."

Slaying a beautiful hypothesis with an ugly fact

There's just one problem with the government's idea as it stands: it's impossible from a technology, business, and international standpoint. Not a single one of the cryptography and security experts El Reg spoke to at the show could see any way such a system would work.

"It's impossible," Bruce Schneier – the man who literally wrote the book(s) on modern encryption techniques – told The Reg. "I can't create mathematics that works differently in the presence of a particular legal piece of paper. Math just doesn't work that way."

As Schneier has explained many times, strong crypto requires a sound encryption algorithm, correct digital signature handling, a random number generator that can't be fooled, and a working methodology to house all of these and that doesn't allow mistakes. Get one thing wrong and the whole system breaks down.

Another problem is that if a police-friendly encryption system was created, it would be highly unlikely that the police would be the only ones who could unlock it. If hackers – or indeed, nation states – knew there was a backdoor in a given encryption system, then they would immediately devote huge resources to finding a way to exploit it. It's more than likely that one of them would eventually succeed.

Jon Callas, former cofounder of PGP and currently CTO of secure messaging firm Silent Circle, was even more emphatic, telling us that the government's idea of a suitable encryption system was "bollocks." Even if such a system could be created mathematically, he explained, there's still the implementation to consider.

"It's a question of who keeps the second [decryption] key," Callas said. "If a company has it, they become judge, jury, and executioner. Apple doesn’t want to have to have to know the laws of 150 countries and be the one to execute such orders."

There's also the business problem of how such a system would go down with the technology-buying public. The NSA's reputation for trustworthiness isn't particularly high in the wake of the Snowden revelations, and it's highly unlikely that people will knowingly buy encryption that they know can be broken.

Then there's the international aspect. If police in the US can access crypto backdoors to protect national security, Callas pointed out, then what's to stop Chinese or Iranian police from asking for the same powers to crush pro-democracy campaigners or groups agitating for open elections?

Under those circumstances, companies would have little choice but to comply, Callas reasoned – particularly in the case of China. When US tech firms were "politely" asked for access to encryption backdoors, he said, they'd know that if they refused it might have severe repercussions for their Middle Kingdom manufacturing contracts, to say nothing of sales in the region.

There are a lot of things people want the technology community to invent, be they flying cars, uploading human minds for backup, or everlasting physical life. Those might be possible one day, but the government's view of the ideal encryption system is likely to take a lot longer to develop and implement, if it's even feasible at all. ®