One copy of the new session key is encrypted with client’s session key and inserted into the reply.ĪLSO READ: Understanding TCP Seq & Ack Numbers The service ticket includes information such as service name, client id, expiry date, a new session key, the client’s address etc. Step-4: The TGS creates a service ticket and encrypts it with another secret key which is shared between TGS and the File Server. When the TGS receives the request, it decrypts the TGT with the secret key shared with AS (AS’s master key). With this request, the client asks the server for a service ticket. Step-3: The client sends the TGT to the TGS with a TGS-REQ packet. It only has the shared secret key derived from the client’s password to decrypt the session key. The client does not have the AS’s master key to decrypt the received TGT. Beside the TGT, the AS encrypts the session key with the shared secret key derived from the client’s password and inserts the encrypted session keyinto the reply as well. and is encrypted with the AS’s master key.

The TGT contains information such as service name, client id, expiry date, a session key, the client’s address etc. Step-2: After verifying the client id, the AS replies the client with an AS-REP packet which includes a TGT. The following figure summarizes how the authentication process occurs and what packets are exchanged during the authentication.ĪLSO READ: How to setup and test AAA with NPS Server (Part 2) The KDC has two functions: An Authentication Service/Server (AS) and a Ticket Granting Service/Server (TGS). According to the authentication protocol, the client has to be verified through a trusted third party, which is called Key Distribution Center (KDC). Let’s suppose that a client would like to access a File Server like figure in below. Kerberos is designed to provide security and authentication. Both sides mutually authenticate each other through this protocol. The protocol works on the basis of tickets to allow nodes to communicate over a non-secure network to prove their identity.

Kerberos is a network authentication protocol that is used to verify the identity of a user or host. Analyzing Kerberos protocol packet by packet.Decrypting Kerberos Authentication packets with Wireshark.

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