Question: In a SIP Digest context, when a User Equipment (UE) changes its password dynamically, how should the Serving-Call Session Control Function (S-CSCF) handle multiple hash values H(A1) to avoid service interruption?
Option 1: The S-CSCF should immediately discard all previously stored H(A1) values upon receiving a new one from the Home Subscriber Server (HSS).
Option 2: The S-CSCF may store at most two H(A1) values - the new one and one previously stored value - to allow for a transition period, trying authentication with both before deleting the oldest after successful verification with the new one.
Option 3: The S-CSCF should only update the H(A1) value during network-initiated re-registration processes to ensure synchronization.
Option 4: The handling of multiple H(A1) values is solely dependent on the UE's capability to manage passwords, not the S-CSCF's responsibility.
Explanation: This approach allows for a seamless transition when a user changes their password, minimizing service interruption. By storing up to two H(A1) values temporarily (the new and one old), the S-CSCF can attempt authentication with both, accommodating potential delays in the user adopting the new password. This method balances security with usability, as highlighted in the context of dynamic password changes in SIP Digest scenarios.