Encryption technology used by Apple's iMessage makes it "impossible" for law enforcement to intercept the content of those messages, according to documentation from the Drug Enforcement Agency (DEA).

As reported by CNET, the DEA released an unclassified document that discusses how iMessage might thwart criminal investigations.

The DEA's San Jose office discovered last month that iMessages sent between Apple devices "are not captured by pen register, trap and trace devices, or Title III interceptions," the document says. "iMessages sent between two Apple devices are considered encrypted communication and cannot be intercepted, regardless of the cell phone service provider."

It's easier to intercept a message between an iOS and non-iOS device, the DEA said.

Apple introduced iMessage in 2011. By Nov. 2012, messaging data tipped a decline in text messaging for the first time in western markets - due in part to the switch to iMessage.

While you might find it heartening to learn that the feds cannot monitor the iMessages on your iPhone, the issue complicates efforts to collect evidence against those who are using their Apple gadget for criminal activity.

"Investigators may erroneously believe they have a complete record of text transmissions if they are unaware that iMessage communications between smartphones are not captured or provided by the cell phone service providers," the DEA said.

This happened recently when the DEA's San Jose office was preparing a Title III affidavit, the document says. Title III covers electronic surveillance including text messages, email, non-voice computer and Internet transmissions, faxes, communications over digital-display paging devices, and, in some cases, satellite transmissions.

The issue of how much access law enforcement should have to peoples' private gadgets has been a topic of discussion for quite some time - from security officials seizing laptops at the border to cops looking to access text messages between suspected criminals.

Back in 2011, much was made about how much data your wireless carrier retains about your activity. The data was made public after the American Civil Liberties Union (ACLU) filed a Freedom of Information Act (FOIA) request related to an investigation into cell phone location tracking by police.

Congress is currently looking into an update of Electronic Communications Privacy Act (ECPA), which was first enacted in 1986, well before the Internet, email, or smartphones. As a result, lawmakers have been pushing an update to make it more in line with today's realities. The Senate Judiciary Committee approved an update to the bill back in November so ECPA would apply to technologies like email, cloud services, and location data on smartphones. But it was not approved by the full Congress by the end of the session, and must be re-considered by both chambers this year.

Apple has stayed quiet on the inner workings of iMessage. But the issue is reminiscent of the battle between BlackBerry and foreign countries like India and Saudi Arabia, which requested access to BlackBerry Messenger.

Ultimately, BlackBerry granted Indian officials lawful access to BlackBerry Messenger and BlackBerry Internet Service e-mail, but did not extend access to BlackBerry Enterprise Server. A BlackBerry ban in Saudi Arabia was averted, but the country is now going after VoIP services like Skype.

For more, check out How Police Track Your Phone.

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