Last Modified: Tuesday, 03-Jan-2006 13:58:20 EST

External telnet access to the CSB core is not available.  At this time access will be allowed utilizing the Secure Shell client programs.  For a brief introduction to Secure Shell see SSH BASICS.

As of 8 December 2004, SSH version 1 connections are no longer supported, as version 1 is not secure. Most SSH clients should be version 2 by now.

Contents

What is SSH
How do I know if I have it
How do I get it
How do I use it
What to expect
What can happen

Secure Shell is a suite of programs which provide host authentication and encrypted sessions between two computers.  A brief description of Secure Shell can be found in the SSH Basics document on our web site.

How do I know if the machine I am using has SSH installed?

• Unix/Linux -- enter the command which ssh  If the ssh command is in your path this command should return its location.
• Windows -- hopefully there will be an icon on the desktop for the SSH Client program if not go to the Start button in the lower left corner and from the pop up menu select Find.  Select the C drive and in the dialog box which pops up enter SSH then click the Find Now button.  If it is installed its location should appear in the window.
• Macintosh --
  • OS X: Open a terminal window and enter the command which ssh.
  • Earlier MacOS: From the file menu select Find.  In the pop up box enter ssh in the space provided and click on the Find button.  If it is installed the location should appear in a box.

• Unix/Linux -- Most mainstream Linux versions, as well as sufficiently up-to-date SGIs, are distributed with SSH version 2 support.  Use the installation tools provided by the vendor to install the programs.  If SSH is not provided you can download, compile, and install OpenSSH.
• Windows -- Yale University provides for its community the ssh client program for free (as of January, 2006), at http://www.yale.edu/software. After clicking on access the software catalog and logging in with your NetID, select the Windows button, then go to the complete catalog and look for SSH. If this is for non university use the suite is available from SSH directly.
• Macintosh --
  • OS X: just like Linux, OpenSSH is included.
  • Earlier MacOS: download MacSSH, as long as you are running OS 7.5.1 or greater!  If you want a file transfer utility, and are running OS 8.1 or greater, download MacSFTP.  Note that although MacSSH is free, MacSFTP requires a $25 serial number purchase after 15 days. 

• Unix/Linux -- enter ssh sage.csb.yale.edu on the command line to start an interactive session with another host.
• Windows -- double click on the SSH Client program icon button.  Select Connect... from the File menu.  A dialog box will appear where you enter sage.csb.yale.edu for the hostname, and your Core username.
• Macintosh --
  • OS X: enter ssh sage.csb.yale.edu in a terminal window.
  • Earlier MacOS: double click on the MacSSH program icon, select Open Connection... from the File menu, and fill in sage.csb.yale.edu as the hostname in the dialog box which pops up.

• The CSB Core SSH Basics page contains a brief discussion of SSH and its authentication mechanisms along with a section about using SSH  which contains info on using SSH on Unix/Linux machines.

 
• On Windows machines a dialog box will pop up with  spaces for entering hostname and username.  After clicking the connect button your machine establishes a connection with gibbs.

If this is the first time you made a connection to gibbs a dialog box will pop up asking you if you want to accept the gibbs' public key.  (Host public keys are used for identifying hosts instead of using IP addresses which is a more secure method.  You must decide if the host you are connected to is indeed gibbs  or another computer masquerading as gibbs.)  Your possible choices are to accept and store the key for later identification, accept the key but not store it and to cancel the connection because you are not confident the remote host is gibbs.  If you accept the connection another dialog box will pop up and ask for your password; then a connection is established.
If you have gibbs' public key saved you will not see the host key acceptance dialog box unless the keys do not match.  Keys will not match if we have done maintenancd on gibbs, requiring us to generate a new key.  They also will not match if someone masquerading as gibbs has hijacked your network connection.  If the keys do not match a box will pop up informing you the keys do not match and asking you if you want to accept and save the new key or cancel the connection.
In the initial window which appeared if you select Edit from the Menu Bar and then select Settings there are numerous parameters one can set.  Under User Keys you can create you own public/private user key pair to use for authentication.  Under Host Keys you can manage the host public keys from all the hosts you connect to.    A brief discussion of these keys can be found in the SSH Basics document but you can ignore this part as user keys are not used by core computers.
• On the Macintosh when you launch the SSH program a window will appear with a list of hosts that have been previously entered.  If gibbs is not listed you can click on the add button and provide the information needed to add it to the table.  When you click on the hostname to connect to a host a dialog box will appear with three choices: Accept & Save the host public key to the public key file, Cancel the connection or Accept Once which will accept the key but not save it to the public key file.  A brief discussion of these keys can be found in the SSH Basics document.

If gibbs' public key is already in the key file this box will not appear and if the key does not match the stored key a box will appear telling you that the key has changed.  Keys will not match if we have done maintenance on gibbs, requiring us to generate a new key.  They also will not match if someone masquerading as gibbs has hijacked your network connection.  Once you select a key option a login pop up box will appear for logging into gibbs.  Once you supply your remote username and password you are logged into gibbs and things will appear as a normal telnet session.

• Unix/Linux -- The section on connection difficulties in the SSH Basics document gives a good explanation of connection problems and solutions.
• Windows -- If ssh is not supported or there is a version conflict with the remote host a warning box appears telling you that the host can not be contacted.  This can either mean that in fact the host can not be contacted or that it does not support SSH sessions.   If you can establish a telnet session with it then you can assume SSH is not supported.  If you wish to login using telnet remember your password is traveling across the internet in plain text form.
• Macintosh -- If ssh is not supported or there is a version conflict with the remote host a warning box appears telling you that the connection is refused.  You can then resort to insecure telnet to make the connection as SSH is not supported on the remote host.  A word of warning, telnet sends your password in clear text across the internet.

Last Modified: Tuesday, 03-Jan-2006 13:58:20 EST