Matt Apuzzo:

But in late 2014, the company said that it would begin adding sophisticated encoding, known as end-to-end encryption, to its systems. Only the intended recipients would be able to read the messages.

“WhatsApp cannot provide information we do not have,” the company said this month when Brazilian police arrested a Facebook executive after the company failed to turn over information about a customer who was the subject of a drug trafficking investigation.

The iPhone case, which revolves around whether Apple can be forced to help the F.B.I. unlock a phone used by one of the killers in last year’s San Bernardino, Calif., massacre, has received worldwide attention for the precedent it might set. But to many in law enforcement, disputes like the one with WhatsApp are of far greater concern.

For more than a half-century, the Justice Department has relied on wiretaps as a fundamental crime-fighting tool. To some in law enforcement, if companies like WhatsApp, Signal and Telegram can design unbreakable encryption, then the future of wiretapping is in doubt.