Computer Science SSH and SCP

Introduction



Telnet and FTP are protocols designed to allow you to remotely connect to a machine and either run programs on them or copy files to and from them. They work reasonably well. However, many people are unaware that they both send your password, user name, and everything you do over the network in cleartext, or unencrypted form. This means that anyone on the network between the host computer and the machine you are connecting from could read your username, password, email, files, ect. in realtime during your telnet session.



So what?



With this information, they can log into the system as you. They can send email as you, read your mail, your files. Worse, they can launch attacks on other systems as you. This can get you into an enormous amount of trouble. In business, it could result in the loss of important information.



So what do I do?



Secure Shell (SSH) is an encrypted protocol designed as a replacement for telnet. A companion program, Secure Copy (SCP), allows you to transfer files to and from computers securely. All of our UNIX computers accept SSH and SCP connections from anywhere on campus, or from computers connected to the University dialup lines.

SSH is easy. Download PuTTY, a free Windows SSH client. We have a whole page dedicated to helping you get started with putty here. Simply download and run putty.exe. Make sure the radio button for SSH is selected (NOT the telnet option) and type in the address of the machine you want to connect to. (for example, wirth.cs.uakron.edu)

You will be prompted for your username and password, and then the login will proceed exactly as you are used to for telnet. It is completely transparent to the user.


Copying files with SCP



The easiest way to use SCP to securely copy files to the UNIX network from the wireless network or your home is to use WinSCP. This is a graphical interface that allows drag and drop file copying similar to many of the FTP clients available. Although the application is currently listed as being in Beta, it works very well. We use it here every day.

You can also use command line mode secure copy in Windows if you prefer. . Download pscp.exe from the putty site above. It must be run from the command line, unless you use a GUI interface. We are testing one and will include it here shortly.

To copy a file from your home computer to a remote host:

pscp sourcefile username@machinename:path/file

Example:

pscp a:\index.html unix304@wirth.cs.uakron.edu:public_html

To copy a file from a remote host to your home computer:

pscp username@machinename:path/filename localfile

Example:

pscp unix304@wright.cs.uakron.edu:public_html/index.html a:\index.html

Note that in both cases, you do not need to enter the full path to the file - the program starts you at your home directory.

Also note you can copy files from one UNIX system to the other using scp. The syntax is the same as above, except the program name is scp rather than pscp. Type 'man scp' for more details.