Attorney General Eric Holder, the US top law enforcement official, said it is "worrisome" that tech companies are providing default encryption on consumer electronics. Locking the authorities out of being able to physically access the contents of devices puts children at risk, he said.

Further Reading Apple, Google default cell-phone encryption “concerns” FBI director said during a Tuesday speech before the Global Alliance Against Child Sexual Abuse Online conference. “When a child is in danger, law enforcement needs to be able to take every legally available step to quickly find and protect the child and to stop those that abuse children. It is worrisome to see companies thwarting our ability to do so."

Holder's remarks, while he did not mention any particular company by name, come two weeks after Apple announced its new iPhone 6 models would be equipped with data encryption that prevents authorities from accessing the contents of the phone. At the same time, Google said its upcoming Android operating system will also have default encryption.

The encryption decision by two of the world's biggest names in tech is a bid to gain the trust of customers in the wake of the Edward Snowden surveillance revelations.

Holder said he wants a backdoor to defeat encryption. He urged the tech sector "to work with us to ensure that law enforcement retains the ability, with court-authorization, to lawfully obtain information in the course of an investigation, such as catching kidnappers and sexual predators."

Recent technological advances have the potential to greatly embolden online criminals, providing new methods for abusers to avoid detection. In some cases, perpetrators are using cloud storage to cheaply and easily store tens of thousands of images and videos outside of any home or business—and to access those files from anywhere in the world. Many take advantage of encryption and anonymizing technology to conceal contraband materials and disguise their locations.

The attorney general—who plans to step down from the position he has held for six years as soon as a successor takes office—is the highest-ranking member of the President Barack Obama administration to assail encryption in the wake of the Apple and Google announcements.

James Comey, the Federal Bureau of Investigation director, last week said he was concerned about the marketing of smart phones that can't be physically searched by law enforcement.

"What concerns me about this is companies marketing something expressly to allow people to place themselves beyond the law," Comey said. He said the bureau has reached out to Apple and Google "to understand what they're thinking and why they think it makes sense."

It seems that the law is on the tech sector's side, however.

Hanni Fakhoury, a lawyer with the Electronic Frontier Foundation, said in an e-mail that "There’s no legal obligation to facilitate law enforcement access into hardware." The law surrounding this issue is the Communications Assistance for Law Enforcement Act, commonly referred to as CALEA, he said.

CALEA requires telcos make their phone networks amenable to wiretaps but it doesn’t apply to ISPs or the actual physical cell phone hardware. Of course Apple can’t help a person obstruct justice or destroy evidence but if they are basically saying we’re designing our system so we can’t help you get access into the phone, there’s nothing the government can do to change that. That’s one of the reasons the FBI has pushed for CALEA 2.0 (and data retention) to deal with ISPs and the overblown problem of “going dark," but no specific legislation to address that issue has been introduced in Congress yet (and is unlikely to be introduced anytime soon).

Despite encryption, authorities with a valid court warrant could get records of text messages, calls, and even device backups that are stored on cloud services.