Question: In a 3GPP Transparent end-to-end Packet-switched Streaming Service (PSS) with Digital Rights Management, what protocol is optionally used for carrying frequently changing encryption keys over User Datagram Protocol (UDP)?
Option 1: ISMACryp Key Exchange
Option 2: OMA BCAST Long-Term Key Messages
Option 3: OMA BCAST Short-Term Key Messages
Option 4: SDP Key Management Protocol
Explanation: In the context of protecting PSS streams with frequently changing encryption keys, efficiency and timely key distribution are crucial. The Open Mobile Alliance (OMA) Broadcast (BCAST) Short-Term Key Messages are specifically designed for this purpose, allowing for the secure carriage of often-updated keys over UDP, which is a connectionless protocol that doesn't guarantee delivery order or provide built-in security measures. This aligns with the need for dynamic key management in streaming services to ensure content protection without interrupting the stream.