Google captured and stored traffic from unencrypted WiFi connections. It is not really similar at all.

Could you actually design this feature in a way that didn't share all the raw WIFI passwords with Microsoft? I think it would be pretty difficult.

Bear in mind though that Google probably knows your wifi password if you or a friend syncs their phone's authentication data.

(Google's legal troubles were a separate issue btw)

I don't think it would be too difficult, design-wise.

Have every Win10 installation generate a public/private key pair. Share the public key with MS.

When you share a password with all your contacts, MS can send all of their public keys to you, where you then encrypt the password with them and send the results back to MS. MS can then send the encrypted passwords to the contacts, who can then retrieve the password with their private key.

Something tells me they probably didn't do it this way, but it doesn't sound like a particularly hard goal to achieve if one thought it was important.

Ah, but it's a per-user secret, not per-device. So each user needs a keypair which gets shared across all of their devices, transparently but also in a way that protects the private key from MS. Which sounds an awful lot like the original problem of sharing secret WIFI passwords without MS being able to read them...

I agree that it must be do-able, it's just tricky to make it work transparently and simply so every user benefits.