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Apple’s USB Restricted Mode: how to use your iPhone’s latest security feature

Apple’s USB Restricted Mode: how to use your iPhone’s latest security feature

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Photo by Chris Welch / The Verge

Apple quietly introduced a significant privacy safeguard as part of the new iOS 11.4.1 update that was released on July 9th. USB Restricted Mode prevents USB accessories that plug into the Lightning port from making data connections with an iPhone, iPad, or iPod Touch if your iOS device has been locked for over an hour. This seemingly small change goes a long way in blocking tools used by law enforcement to crack passcodes and circumvent Apple’s encryption and built-in measures designed to shield sensitive user data.

What is USB Restricted Mode?

Apple describes it as a new “security protection” that’s introduced as part of iOS 11.4.1. The company hasn’t said as much, but it’s believed that USB Restricted Mode is Apple’s effort to combat devices like GrayKey that are specially designed to help law enforcement crack an iOS device’s passcode and retrieve data that would normally be guarded by encryption. iOS has built-in security features that prevent constant passcode guesses — such as when it locks down your device after several incorrect attempts. But companies have seemingly found a way of avoiding those safeguards via USB and the Lightning port. Now, Apple is trying to eliminate this method of gaining entry to a recovered or confiscated device.

USB Restricted Mode works like this: after an hour of your iPhone, iPad, or iPod Touch sitting without being unlocked, iOS will basically cut off the Lightning port and limit it to charging only. This hour timeout should theoretically stop devices like GrayKey (which plugs into an iPhone and cracks the passcode within a few hours) from working successfully.

“If you don’t first unlock your password-protected iOS device — or you haven’t unlocked and connected it to a USB accessory within the past hour — your iOS device won’t communicate with the accessory or computer, and in some cases, it might not charge,” reads Apple’s support page on the security feature.

USB Restricted Mode is active when the “USB Accessories” toggle is disabled / on the left.
USB Restricted Mode is active when the “USB Accessories” toggle is disabled / on the left.

USB Restricted Mode is enabled by default after the update

Once you’ve installed iOS 11.4.1, Apple automatically turns on USB Restricted Mode right away. So you’ll need to unlock your iPhone or iPad to connect a USB accessory and get it working. After that — for as long as it’s attached — the accessory will remain connected and operational even if your iOS device is locked again.

Accessories might not be able to charge your iPhone unless you unlock it first

Apple notes that when a USB accessory is blocked from connecting to your iPhone, charging might also be prevented as a result. iOS devices will charge normally when connected to a USB power adapter, but if you plug in a gadget that normally delivers power over USB, you might have to unlock your iPhone or iPad first before things work (and charge) like normal. This is going to vary from accessory to accessory.

It’s easy to turn off USB Restricted Mode

If you’re not concerned about someone potentially breaking their way into your iOS device, you can disable the new security measure immediately. Just go to Settings —> Face ID (or Touch ID) & Passcode —> USB Accessories. Toggle this option to on (green) and your accessories will function the exact same way they did before iOS 11.4.1.

Apple says this might be a good idea for people who use assistive devices with their iPhone, iPad, or iPod Touch. “Many assistive devices will automatically turn on the setting to allow USB devices the first time they’re connected,” the company says. But if that doesn’t happen, disabling USB Restricted Mode just takes a quick visit to the Settings menu.

USB Restricted Mode isn’t foolproof

Soon after the feature’s release, it was reported by ElcomSoft that plugging in a USB accessory like Apple’s own iOS camera adapter before USB Restricted Mode is activated is enough to reset the 60-minute clock and prevent your iPhone from locking down its Lightning port. This is a workaround that Apple will likely patch sooner than later.