SSL Messages

 

The SSL messages are sent in the following order:

1. Client hello - The client sends the server information including the highest version of SSL it supports and a list of the cipher suites it supports. (TLS 1.0 is indicated as SSL 3.1.) The cipher suite information includes cryptographic algorithms and key sizes.

    

2. Server hello - The server chooses the highest version of SSL and the best cipher suite that both the client and server support and sends this information to the client.

    

3. Certificate - The server sends the client a certificate or a certificate chain. A certificate chain typically begins with the server's public key certificate and ends with the certificate authority's root certificate. This message is optional, but is used whenever server authentication is required.

    

4. Certificate request - If the server needs to authenticate the client, it sends the client a certificate request. In Internet applications, this message is rarely sent.

    

5. Server key exchange - The server sends the client a server key exchange message when the public key information sent in 3) above is not sufficient for key exchange.

    

6. Server hello done - The server tells the client that it is finished with its initial negotiation messages.

    

7. Certificate - If the server requests a certificate from the client in Message 4, the client sends its certificate chain, just as the server did in Message 3.

    

   Note: Only a few Internet server applications ask for a certificate from the client.

    

8. Client key exchange - The client generates information used to create a key to use for symmetric encryption. For RSA, the client then encrypts this key information with the server's public key and sends it to the server.

    

9. Certificate verify - This message is sent when a client presents a certificate as above. Its purpose is to allow the server to complete the process of authenticating the client. When this message is used, the client sends information that it digitally signs using a cryptographic hash function. When the server decrypts this information with the client's public key, the server is able to authenticate the client.

    

10. Change cipher spec - The client sends a message telling the server to change to encrypted mode.

     

11. Finished - The client tells the server that it is ready for secure data communication to begin.

     

12. Change cipher spec - The server sends a message telling the client to change to encrypted mode.

     

13. Finished - The server tells the client that it is ready for secure data communication to begin. This is the end of the SSL handshake.

     

14. Encrypted data - The client and the server communicate using the symmetric encryption algorithm and the cryptographic hash function negotiated in Messages 1 and 2, and using the secret key that the client sent to the server in Message 8.

15. Close Messages - At the end of the connection, each side will send a close_notify message to inform the peer that the connection is closed.