SSL/TLS for FTP connections

Question

I've built somekind of advanced ftp server, and i would now like to add SSL or TLS on the server.
Implementing implicit SSL is easy. I used some SSL sockets, and everything was working fine.
But if i want to use TLS or explicit SSL, i have a problem.
With an SSL socket, any attemps to read/write with the streams initiate an handshake.
But an explicit SSL connection is done that way:
-> Connecting to myftpserver.com port 21
-> Connected to myftpserver.com
Server: Welcome to this nice ftp
Server: Enjoy this nice server
-> AUTH SSL
Server: 234 AUTH SSL successful
-> Now negociating SSL session...
So, as u can see, some data(welcome msg, AUTH SSL command, etc) are exchanged BEFORE the SSL negociation.
I dont know how to do that since "any attemps to read/write with the streams initiate an handshake"
I hope someone will be able to help me :)
Dundee

Answer 1

What's wrong with my code then?You must make sure, before trying to send the first encrypted text, that both side are ready to negociate SSL.
I'm pretty sure your problem is about that.
Did you write both side (client and server) or only the client side?
Because if you are the author of the server side, you must also make sure the server will act as the server during the SSL negociation ( ((SSLSocket)s).setUseClientMode(false)).
So far, my understanding - based on my experimentation:
The client must ask to the server to start SSL communication, but MUST wait for the server to say it is ready before creating the SSL layer. This mean the client send - over the unencrypted communication - a command saying to the server: "i want to start to talk to you over SSL". Then the server answer "Ok, ,i'm ready". Then, and only then, the client create the SSL socket (over the already connected socket - as you seem to have done) and start the SSL negociation. By the way, it is not necessary to call SSLSocket.startNegotiate() explicitly, it will be called when sending the first block of data for the new SSL session.
I'm not sure if I made it clear. But I think the problem - the reason why you get the HandshakeException - is because the client try to negotiate SSL before the server is ready to accept SSL negotiation - maybe this should have been the only sentence of my answer ;-).
About the use of SSLContext; I feel that it only have value if you want to use your own customized X509TrustManager or X509KeyManager. For me, I found it very useful because my server certificate may not be valid as per the default validation algorithm. But basicly we can use the SSLContext the following way:
/* The creation of a KeyManager is a story in itself.
* The way I used it is to specify in my program the KeyStore to be used.
* I think it can be specified in other ways (-D java argument, for exemple).
* For now I not sure how useful it can be for the client side. (sorry)
KeyManager[] myKeyManagers= ....
/* The TrustManager give you the opportunity to do your own validation
* of the server / client - depending on the situation - certificate.
* For now, I don't know how to use TrustManager and KeyManager
* together.
TrustManager[] myTrustManager= new TrustManager[] {new MyX509TrustManager()};
/* The Key and Trust managers created above, can be used to initialize
* the SSL context below.
SSLContext context= SSLContext.getInstance("SSL");
/* Initialize the context with your customized managers.
* Note that all parameters are optional - they can be "null".
* You only specify those you have customized.
context.init( myKeyManager, myTrustManager, null);
/* Then later I can get my SSL socket factory, which will use my
* own customized key and trust manager and secure random.
SSLServerSocketFactory sslSSF= context.getServerSocketFactory();
SSLSocketFactory sslSF= context.getSocketFactory();I found an article in this forum about TrustManager.... seem very promising.
Hope this will help.
Hugues