Editing Transport Layer Security (section)

=====Session IDs=====
In an ordinary ''full'' handshake, the server sends a ''session id'' as part of the '''ServerHello''' message. The client associates this ''session id'' with the server's IP address and TCP port, so that when the client connects again to that server, it can use the ''session id'' to shortcut the handshake. In the server, the ''session id'' maps to the cryptographic parameters previously negotiated, specifically the "master secret". Both sides must have the same "master secret" or the resumed handshake will fail (this prevents an eavesdropper from using a ''session id''). The random data in the '''ClientHello''' and '''ServerHello''' messages virtually guarantee that the generated connection keys will be different from in the previous connection. In the RFCs, this type of handshake is called an ''abbreviated'' handshake. It is also described in the literature as a ''restart'' handshake.

#Negotiation phase:
#*A client sends a '''ClientHello''' message specifying the highest TLS protocol version it supports, a random number, a list of suggested cipher suites and compression methods. Included in the message is the ''session id'' from the previous TLS connection.
#*The server responds with a '''ServerHello''' message, containing the chosen protocol version, a random number, cipher suite and compression method from the choices offered by the client. If the server recognizes the ''session id'' sent by the client, it responds with the same ''session id''. The client uses this to recognize that a resumed handshake is being performed. If the server does not recognize the ''session id'' sent by the client, it sends a different value for its ''session id''. This tells the client that a resumed handshake will not be performed. At this point, both the client and server have the "master secret" and random data to generate the key data to be used for this connection.
#The server now sends a '''ChangeCipherSpec''' record, essentially telling the client, "Everything I tell you from now on will be encrypted." The ChangeCipherSpec is itself a record-level protocol and has type 20 and not 22.
#*Finally, the server sends an encrypted '''Finished''' message, containing a hash and MAC over the previous handshake messages.
#*The client will attempt to decrypt the server's ''Finished'' message and verify the hash and MAC. If the decryption or verification fails, the handshake is considered to have failed and the connection should be torn down.
#Finally, the client sends a '''ChangeCipherSpec''', telling the server, "Everything I tell you from now on will be encrypted."
#*The client sends its own encrypted '''Finished''' message.
#*The server performs the same decryption and verification procedure as the client did in the previous step.
#Application phase: at this point, the "handshake" is complete and the application protocol is enabled, with content type of 23. Application messages exchanged between client and server will also be encrypted exactly like in their ''Finished'' message.