Unique Domain Authentication ID (UDAI)
The Unique Domain Authentication ID, or UDAI, is a randomly generated unique identifier that is required to authenticate requests to transfer domain names from one registrar to another. A UDAI is generated when a domain name is registered, although the domain name's registrar can generate a new UDAI at any time if required. Registrars are obliged to promptly make UDAIs available to registrants upon request and may not withhold them to prevent a domain name from being transferred under any circumstances.
These are used for .NZ domains.
Extensible Provisioning Protocol (EPP)
The Extensible Provisioning Protocol, or EPP, is a flexible protocol designed for allocating objects within registries over the Internet.
The motivation for the creation of EPP was to create a robust and flexible protocol that could provide communication between domain name registries and domain name registrars. These transactions are required whenever a domain name is registered or renewed, thereby also preventing Domain hijacking.
These are used for international TLD's (.com, .org, .net, etc).