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Microsoft is deploying a new feature, WiFi Sense, which provides users a way to easily share passwords to wireless networks with all of their contacts. This introduces a new security failure mode: a user might decide to share a wifi network password that maybe they shouldn't have. All it takes one user to share the wifi network with their contacts, and now others who might not be authorized might gain access to the network.

What options are available to a network administrator who wants to ensure that their wireless network's password can't be shared through WiFi Sense?

Here's what I've found. Microsoft says you can prevent a wifi network's password from being shared by adding _optout to the network SSID. Also, it sounds like networks that use 802x EAP might be immune (is this true?). Are there any other methods?

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I don't know the technical details, but let me ask you this - how secure is your current setup? Have you shared your wifi password with friends/family? If so, did you change it after the last time you shared it with someone? If you're really concerned, I would look into a router with a guest network ability to isolate your own devices from someone using your wifi (though that won't really deter a skilled, determined attacker). – soong Jul 31 '15 at 5:26
@soong, I understand. The new risk is that a friend/family member/employee who would never think of posting the password publicly, might tick the "share" checkbox and share the password. Different people might evaluate the magnitude of that risk differently. You might not consider it a major risk, and that's fine -- I'm not trying to convince you otherwise, I just want to know what the options are for opting out of WiFi Sense, which is a purely technical question. Did you have a suggestion for how the question could be improved? – D.W. Jul 31 '15 at 5:31
Well, from what I'm reading, it seems like you're only allowed to share it if you're the one who typed it in, not if you had it shared with you. If that's not the case, then I'd say it would be risky. If you're worried about a corporate network, you might look into per-user wifi authentication, but I'm afraid I know very little about the methods for that. – soong Jul 31 '15 at 5:33
@soong, thank you for your comments. I appreciate that you don't consider it a risk. That's fine: I'm not looking to get into a debate on the magnitude of the risk or trying to change your mind. Chat would be a better place for that kind of discussion. I'm not asking for an evaluation of the magnitude of the risk -- I'm just asking what are the options for opting out. – D.W. Jul 31 '15 at 5:58
Keep in mind that while _optout may disable sharing among contacts, it is far from clear whether it also prevents the passphrase from being shared with Microsoft in the first place. – Sinan Ünür Aug 6 '15 at 15:27

Just to add on, _optout_ can be added anywhere in the SSID not necessarily at the end. However, Google's _nomap has to be placed at the end.

Yes, 802.11x will networks will not be shared through WiFi sense.
Official source: Microsoft WiFi sense FAQ. Look under "I'm concerned about sharing Wi‑Fi networks. Can you tell me a little more?"

Theoretically, another way to protect a network is use the "hidden SSID" feature. This feature disables the broadcast of the SSID in beacons. Thus, the client device will need to know the SSID to send a probe request to the AP. WiFi Sense will not work here because without the SSID, there is no way for the client device to check if it the SSID is among those that are shared.

Note: This is only in theory, I am unable to find information on the web proving or disproving the above.

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