3.2. SessionTicket TLS Extension

The SessionTicket TLS extension is based on [RFC4366]. The format of the ticket is an opaque structure used to carry session-specific state information. This extension may be sent in the ClientHello and ServerHello.

If the client possesses a ticket that it wants to use to resume a session, then it includes the ticket in the SessionTicket extension in the ClientHello. If the client does not have a ticket and is prepared to receive one in the NewSessionTicket handshake message, then it MUST include a zero-length ticket in the SessionTicket extension. If the client is not prepared to receive a ticket in the NewSessionTicket handshake message, then it MUST NOT include a SessionTicket extension unless it is sending a non-empty ticket it received through some other means from the server.

The server uses a zero-length SessionTicket extension to indicate to the client that it will send a new session ticket using the NewSessionTicket handshake message described in Section 3.3. The server MUST send this extension in the ServerHello if it wishes to issue a new ticket to the client using the NewSessionTicket handshake message. The server MUST NOT send this extension if it does not receive one in the ClientHello.

If the server fails to verify the ticket, then it falls back to performing a full handshake. If the ticket is accepted by the server but the handshake fails, the client SHOULD delete the ticket.

The SessionTicket extension has been assigned the number 35. The extension_data field of SessionTicket extension contains the ticket.