Question: In 3GPP conformance testing for User Equipment (UE), what operation is employed in the test algorithm for generating the VSTK-key for VGCS/VBS key generation and encryption?
Option 1: Bitwise Left Shift
Option 2: Cyclic Redundancy Check (CRC)
Option 3: Advanced Encryption Standard (AES) Block Cipher
Option 4: Bitwise Modulo 2 Addition ("XOR")
Explanation: The correct answer is Bitwise Modulo 2 Addition ("XOR") because, according to the specified test algorithm for VGCS/VBS VSTK generation in UE conformance testing, this operation is used in the procedure, ensuring security and integrity of key generation processes, particularly for Voice Group Call Service (VGCS) and Voice Broadcast Service (VBS).