Wi-Fi password-sharing feature in Windows 10 raises security concerns

With the launch of Windows 10, anyone who walks into your house and gets your Wi-Fi password for their PC could potentially let all their friends onto your network, thanks to a new feature that has ignited controversy online.

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Called Wi-Fi Sense, the feature is designed to make it easier for people to get Internet access for their devices while they're on the go by automatically logging them into wireless hotspots. It does so with a two-pronged approach: by logging users into select open networks and also by allowing them to share secured connections with their friends (and vice versa). Perhaps unsurprisingly, that has drawn the ire of people who care about wireless security.

If someone with a Windows 10 device logs on to a new network, they can check a box to share that access with their contacts, who could include their Facebook friends, Outlook.com contacts and people on their Skype contact list. This isn't exactly a new feature -- Microsoft introduced it with Windows Phone 8.1 last year, but it didn't make much of a splash at the time because not that many people use Windows Phone.
Craig Mathias, a principal at the Farpoint Group who specializes in wireless technology, said in an email that the feature was "a cheap hack." He went on to say that the Wi-Fi Alliance's Passpoint technology, which makes it possible for some devices to connect securely to wireless networks without going through a login process, is "more important."

"And no one should ever leave Wi-Fi access wide open," he said.

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To hear Microsoft pitch Wi-Fi Sense, it's a security feature, not a flaw. Using the new technology, people can let their friends access their home network without having to provide them with the password, which cuts down on those annoying conversations that take place when someone is trying to get Internet access. What's more, contacts who are able to log into a network only using Wi-Fi Sense don't actually see the password.
According to a FAQ about the feature, a user who shares network access sends the password through an encrypted connection to a Microsoft server, where it's stored in an encrypted form before being handed off securely to any of their friends who needs it based on location data from their device. Microsoft says that someone who gets access through Wi-Fi Sense will have access only to the Internet and won't be able to get to any other computers or devices on the network.
Of course, all that relies on the feature working as intended. While it's not clear exactly how Microsoft is storing passwords on a client device, it's possible that someone sufficiently motivated would be able to find and extract the wireless password for a network they get access to thanks to their friends. An attacker could also friend people on Facebook in order to get access to networks using Wi-Fi Sense. All of this relies on the Microsoft database storing wireless network information remaining secure.

Wi-Fi Sense doesn't work with networks secured using 802.1X, which is often used by enterprises to keep their networks on lockdown, so that should give some comfort to corporate network administrators.
Ultimately, people who want to make sure that their Wi-Fi network is unavailable to Wi-Fi Sense users can rename it to include "_optout" at the end of the SSID. For example, a network called "foobar_optout" would be ineligible for sharing through Wi-Fi Sense, while one that's just called "foobar" would be usable with Microsoft's sharing feature.
If you don't want to change your network's name, Microsoft suggests that you manually enter the network's password for your guests and make sure the checkbox to share the network is turned off.