Each user in the POST system possesses an account, which is associated with an identity certificate. The certificate is stored as a certificate block, using the secure hash of the user's name as the handle. Also associated with each account is a user identity block, which contains a description of the user, the contact address of the user's current trusted node, and any references to public metadata associated with the account. The identity block is stored as a public-key block, signed with the user's private key. Finally, each account has an associated Scribe group used for notification, with a groupId equal to the cryptographic hash of the user's public key.
The immutable identity certificate, combined with the mutable public-key block, provides a secure means for a trusted authority to bind names to keys, while giving users the ability to change their personal contact data without requiring subsequent interactions with the certificate authority. The Scribe group allows anybody waiting for news from that user, or anybody wishing to notify the user that new data is available, to have a common rendezvous point.