One thing that might be valuable on this is to do sms contact syncing where people can provide soft proof that they share the same social circles. In essence, i

One thing that might be valuable on this is to do sms contact syncing where people can provide soft proof that they share the same social circles. In essence, if both parties have John Doe in their phone as 123-456-7890 , we can extrapolate that they both know him. Extend this across many contacts and it might be possible to see how much their direct networks overlap. One way of proving a person is indeed who they claim to be is by using a service like authillo.com