u6.3 TLS Handshake

u6.3 TLS Handshake

1. Used for key establishment

2. To setup the secure channel between client and server before the application data is transmitted.

3. Agree parameters with which to set-up the secure channel

4. Each party has a notion of a current state that the connection is in and the current state determines the current level of protection.

   • During this current state the next state or 'pending state' is negotiated using the handshake protocol
     • The pending state defines the secure channel that is going to be used once the parameters are negotiated.
       • The initial state prior to the TLS session is called the 'null state'.
         • The negotiation sets up the pending state and what the keys will be
           • Once both sides are ready to move to the next state, the pending state becomes the current state.

5. The Negotiation specifies

   • bulk cipher with which to encrypt the session;
   • MAC algorithm with which to provide data integrity
   • key size
   • key material from which to produce the keys for authentication and encryption.

6. Handshake Steps

   • 1st - Exchange hello messages
     • Initiator sends a client hello which contains random numbers. The hello message includes a list of the suggested cipher suites to be used.
       • The responder replies with a server hello, this also contains random numbers & chosen cipher suite to be set up
         • 2nd - agree secret material for pre-master secret and authenticate parties
           • Both parties
             • Exchange the necessary cryptographic parameters to allow the client and server to agree on a pre-master secret.
               • Exchange certificates and crypto information to allow the client and server to authenticate
                 • Generate a master secret from the pre-master secret and exchanged random values
                   • Provide security parameters to the record layer.
                     • Allow the client and server to verify that their peer has calculated the same security parameters and that the handshake occurred without tampering by an attacker.
                       • Both parties confirm that the correct keys have been generated using Change Cipher Spec. and finished messages.

7. Following actions must be agreed to form a secure channel

   • Crypto Algorithms to be used
     • Encryption keys used to protect the channel
       • Verification of the identity of both parties
         • Verification of the integrity of the messages during the handshake protocol.