Cyrus Vance, Jr., the Manhattan district attorney and an outspoken critic of encryption, called on Congress to adopt legislation mandating that mobile phone makers like Apple and Google bake backdoors into their smartphones.

Vance said it is "government's principal responsibility to keep its residents safe, and that a government cannot fulfill that responsibility if huge amounts of vital information directly related to public safety are inaccessible to the government."

The district attorney's proposal provided data saying that in a span of 12 months ending in October, as many as 111 prosecutions in his office for a variety of crimes like homicide, attempted murder, sexual abuse of a child, sex trafficking, assault, and robbery were hindered because of encrypted mobile phones connected to the cases. He also cited a litany of prosecutions in which evidence obtained from mobile phones helped solve the same types of cases.

"The federal legislation would provide in substance that any smartphone manufactured, leased, or sold in the US must be able to be unlocked, or its data accessed, by the operating system designer. Compliance with such a statute would not require new technology or costly adjustments. It would require, simply, that designers and makers of operating systems not design or build them to be impregnable to lawful governmental searches," according to Vance's position paper (PDF) on the topic released Wednesday.

The proposal made clear that the backdoor keys would not be provided to the government. The "keys would be held by the operating system designers," the paper said.

Vance's proposal comes nearly a week after the Paris attacks that killed 129 people, and as the French police discovered an unencrypted, unlocked phone in a trash bin outside the Bataclan concern hall in Paris that may have led the authorities to an apartment that resulted in a shootout, leaving dead two people suspected of participating in the attacks.. Last month, moreover, FBI Director James Comey said that the White House would refrain from pushing for the type of legislation that Vance is advancing. Comey said the federal government would continue lobbying the tech sector to provide backdoors.

"Technology benefits us in ways too many to count and in amounts impossibly large to calculate. But it can also be used to harm us, and unless we regulate it intelligently and carefully, we may suffer great harm. Smartphones are technological bank vaults, but unlike bank vaults, which, no matter how strong, are accessible to search warrants, smartphones are becoming beyond the reach of law enforcement," Vance said. "The result will be crimes that go unsolved, harms that go unanswered, and victims who are left beyond the protection of the law."

Fearing that encryption is undermining their surveillance capabilities, government officials from the US and across the pond in the UK have been increasingly decrying encryption or at least demanding a government-accessible backdoor to unlock said encryption.

The American Civil Liberties Union blasted Vance's proposal, which did not result in immediate public support from members of Congress.

"The report provides no clear evidence that encrypting devices has undermined the ability of law enforcement to do their jobs, particularly in light of the increasingly large amount of data that is available to police. Given this, calls to force private companies to weaken the security of their devices and software to ensure law enforcement access are misguided," Neema Singh Guliani, the group's legislative counsel, said in a statement to Ars. "This weakening will compromise the security of Americans by making their personal information and communications more vulnerable to cyberattack and theft."

Vance took the occasion to shame Google and Apple for baking encryption into mobile devices running at least iOS 8 and Lollipop 5.0 in the aftermath of the Edward Snowden National Security Agency spying revelations. That's because these companies and others have been going out of their way to encrypt products after the public learned that the US had embarked on a legally and morally suspect massive electronic spying operation against its own citizenry and the global community at large.

"The Manhattan District Attorney’s Office has previously sent letters to Apple and Google that asked some of the questions necessary to a fully informed debate regarding their technology and its implications for criminal cases, privacy, and security. Neither company has responded," Vance's position paper said.

Apple Chief Tim Cook has repeatedly said that Apple would not voluntarily bake backdoors into its products.

"Now, we have a deep respect for law enforcement, and we work together with them in many areas, but on this issue we disagree. So let me be crystal clear—weakening encryption, or taking it away, harms good people that are using it for the right reasons. And ultimately, I believe it has a chilling effect on our First Amendment rights and undermines our country’s founding principles," Cook said at a recent event.

The district attorney, which handles some 100,000 criminal cases yearly, asked Apple and Google several questions in his paper. One directed at Apple asked:

In this office’s experience (and, it appears, other offices’ experiences) with Apple’s responses to iCloud search warrants for devices running iOS 8, thus far, Apple has provided either no iMessage, SMS message, and MMS message content or has provided encrypted, unreadable message content. It is unclear why Apple is not providing decrypted, readable message content for iCloud accounts, particularly given that its law enforcement guidelines state that this content can be turned over to law enforcement pursuant to a search warrant (http://images.apple.com/privacy/docs/us_le_guidelines_final_20150916.pdf, p. 8). Why isn’t Apple providing decrypted iMessage, SMS message, and MMS message content from iCloud in response to search warrants? Why This Is Important To Know: iMessage, SMS message, and MMS message content is crucial to criminal investigations and prosecutions. Since there are no readily apparent obstacles to Apple providing decrypted message content from iCloud accounts in response to a search warrant, and since Apple’s law enforcement guidelines say that Apple can provide it, it should explain why it is not doing so.

A question posed to both Google and Apple asked:

If there are significant security problems posed by the ability of Apple and Google to decrypt data on devices with earlier operating systems, do those same security problems exist as to cloud data as a result of Apple’s and Google’s current ability to provide readable data stored on their cloud servers? If not, why not? Why This Is Important To Know: If there are security problems of importance that result from the ability of technology companies to decrypt data on their devices, it is difficult to understand why these concerns would not exist in relation to their ability to provide readable cloud data. If the same security problems exist as to data currently stored in the cloud, why aren’t the companies providing their customers with impregnable encryption for their cloud data? If the same security problems exist as to cloud data, but the technology companies don’t feel it necessary to impregnably encrypt that data, is it not fair to infer that the scope of the security problems solved by the current encryption schemes is limited?

The government cannot force the tech sector to build encryption end-arounds without legislation. The closest law on the books is the Communications Assistance for Law Enforcement Act of 1994, known as CALEA. The measure generally demands that telecommunication companies make their phone networks available to wiretaps.