Communicating with an SSH Server for file access using pure Java

Question

I'm writing a program in Java using the sockets to communicate with a Telnet server which allows the users to access the file directory in an UNIX OS.

When using Putty to communicate with this server, it prompts me for my username and password, but using my sockets there is nothing from the server except for a string which states that it uses SSH 2.0 - I think.

I'm sure that this has to do with the Telnet protocol, but how do I get the server to ask me for my username and password. What set of commands would I need to give the server in order to access the file directory in an UNIX environment?

Correction: I figured that it's actually using SSH on port 22. It can be accessed using Putty or Microsoft Windows' Telnet program, but it doesn't actually use the Telnet protocol but the SSH protocol.

Answer 1

There is really nothing to the Telnet protocol for most uses...see this page for details. If the server on the other end is trying to negotiate a SSL connection, which is by far the most likely thing these days, try using a java.net.ssl.SSLSocket instead of a bare TCP socket.

Once you negotiate the connection (see the docs linked above) you should essentially print UNIX CLI commands to the socket and read (& parse) the results. If you just want to access files, maybe use FTP instead. Most modern servers are going to support SFTP.

Edit

With a little poking I found that using SSLSocket directly to connect to a SSH server is cumbersome at best because SSH has its own protocol. You probably don't want to reinvent the wheel on that one. Check out the answers to this question for some pure Java SSH client libraries. You can probably use at least one of these to solve your problem more directly than sending text commands over SSH.

Answer 2

Would it be a telnet server, it would be simple.

But what you have is a ssh server, and that is good as it is. telnet is heavily deprecated, as it is not encrypted.

You now have two options: Either use a ssh library or access the ssh command line client (or under Windows: the plink program) via its stdio.

Answer 3

SSH isn't telnet. SSH is a protocol that is a lot like telnet, but is encrypted and has a slew of other features. So it looks like youre expecting a plain-text exchange, but what you're getting is the ssh protocol trying to do a handshake.

Telnet runs on port 23, SSH on 22. I imagine you want to use 23. Note: Telnet is old and unencrypetd and dangerous to use over the internet (unless youre going over a VPN or something that encrypts the session).