Saturday, March 25, 2006

SSL Protocol

    This is a simple informational posting. Since I am reading Java security, I thought I'd share some information about SSL with readers of this blog.

    SSL or Secure Sockets Layer is a layer above regular TCP/IP sockets which is used to encrypt and decrypt all data exchanged between the sockets. SSL is used for several reasons;
    - To ensure that the client and server know exactly who they are talking with.
    - To ensure the integrity of data that is exchanged.
    - To ensure that an eavesdropper cannot access the data while it is transmitted.

    Before the data exchange can actually begin, the client and server must establish an SSL connection using the following steps.
    1. The client send the server it's SSL version number, and cipher settings.
    2. The server send the client it's SSL version number, cipher settings, and it's public key certificate.
    3. The client authenticates the server using the certificate. After successful authentication the client generates a premaster secret, encrypts it with the servers public key and send it to the server.
    4. The server decrypts the premaster secret and generates a master secret.
    5. Both client and server generate session keys from the master secret. These will be used henceforth to encrypt and decrypt data that is exchanged.
    6. The client sends a message to the server saying that all future data will be encrypted with the session key, and also indicates that the client portion of the handshake is complete.
    7. The server sends a message to the client saying that all future data will be encrypted with the session key and also indicates that it's portion of the handshake is complete.
    8. The actual data exchange can now begin.

    In the above steps I have assumed that the server does not need to authenticate the client. If it does, then the client will also have to give it's certificate to the server using which the server will authenticate the client.

    Hope this posting was useful to either refresh your memory on SSL or to get a fundamental understanding if you did not already know what SSL was.

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