Question: For inter-domain security in IP-based services (referring to interfaces between different networks for SIP capable nodes), what is the required cryptographic strength for privacy protection?
Option 1: Equivalent to or greater than AES
Option 2: Greater than DES (Data Encryption Standard)
Option 3: Exactly matching the strength of 3DES (Triple Data Encryption Algorithm)
Option 4: Less than or equal to Blowfish
Explanation: According to the specified security requirements for inter-domain security in IP-based services, privacy protection must be applied with a cryptographic strength greater than DES. This ensures a higher level of security than the older, less secure DES standard, without mandating a specific alternative, allowing for various stronger encryption methods to be used.