[segmondy]

So here's how I implemented the recovery in my proof of concept. Your backup is performed using your backup private key, and the encrypted passkeys (private keys) are backed up to the server. If you lose your device, you obviously can't login and need your back up private key to recover. I implemented shamir secret sharing, it splits your passwords and you select from your contacts (other users who will agree to serve as your backup). So let's say you have 4/7, that means 4 people out of 7 people is all you need to recover your private key.

When you lose your device and reinstall the app. It asks you if you are recovering or a new user. If you select recovering your key. We will generate a new pub/private recovery key. Remember we are assuming you lost your phone. The app will then ask you to enter the phone number of the 4 people that will vouch for you. When you select those 4 people, a call is initiated to them where you must read off a code that the restoration server gave to you on your new device, they will then select that they are vouching for you. The idea is that these are your friends or people you trust. You have to convince them. Not just automated think. At that point their phone will send the pass key fragments to you (encrypted using your new pub key). When enough people give you the info you need. Your phone will decrypt with your recovery private key and then recover the backup private key.

It will then request the encrypted backup from the server. The server will provide it with the encrypted back at which point it will use the recovered private key to decrypt the backup and recover all pass keys.