New Public key needs to be created when a user lost access to his User ID or someone has access to his account. If your user ID is stolen then you need to encrypt your data which can be readable to only you.
By using authentication protocol, user can request for a new public key:
Now when user will log in next time in Lotus notes, the request is processed by Domino and public keys are created. A dialog box of ‘Accept New ID Information’ will appear. Then click OK.