Question: In a USIM's EFKeys (Ciphering and Integrity Keys) file, how are the bits of the Ciphering Key (CK) arranged in terms of significance within the byte structure?
Option 1: The most significant bit of CK is the most significant bit of the 2nd byte, and the least significant bit of CK is the least significant bit of the 17th byte.
Option 2: The most significant bit of CK is the most significant bit of the 1st byte, and the least significant bit of CK is the least significant bit of the last byte.
Option 3: The arrangement of CK bits is identical to that of the Integrity Key (IK), with the most significant bit in the 18th byte and the least significant bit in the 33rd byte.
Option 4: CK's bit arrangement is not specified, allowing for variable placement within any byte.
Explanation: This correct answer reflects the specific coding details provided for the Ciphering Key (CK) in EFKeys, highlighting that the most significant bit of CK is located in the 2nd byte, while the least significant bit is in the 17th byte. This precise arrangement is crucial for correctly interpreting and utilizing the CK for ciphering operations in telecom networks, ensuring secure data transmission.