How does the Kerberos client authenticate the server after receiving the TGT?

The correct approach for how the Kerberos client authenticates the server after receiving the Ticket Granting Ticket (TGT) is through the use of a symmetric key for encryption.

In Kerberos, once the client has successfully obtained a TGT from the Key Distribution Center (KDC), it uses that TGT when requesting access to a specific server. When making this request, the client communicates its identity and a session key to the server, which allows the server to confirm the client's identity. This session key is shared only between the client and the server, and it enables secure communication and authentication without revealing sensitive information such as passwords.

Using symmetric keys in this context ensures that both the client and the server can encrypt and decrypt messages, maintaining confidentiality and integrity in their communications. This method is a core principle of Kerberos, leveraging symmetric encryption for efficiency and security in authenticating entities.

In this authentication scheme, options like hashing the user's password or sending the TGT back to the KDC are not applicable to the stage of client-server authentication after obtaining the TGT. Asking the user for permission does not align with the technical mechanisms Kerberos employs, as the process is designed to be automated and secure without manual intervention at that point.