| 1 | \C{intro} Introduction to PuTTY |
| 2 | |
| 3 | PuTTY is a free SSH, Telnet and Rlogin client for 32-bit Windows |
| 4 | systems. |
| 5 | |
| 6 | \H{you-what} What are SSH, Telnet and Rlogin? |
| 7 | |
| 8 | If you already know what SSH, Telnet and Rlogin are, you can safely |
| 9 | skip on to the next section. |
| 10 | |
| 11 | SSH, Telnet and Rlogin are three ways of doing the same thing: |
| 12 | logging in to a multi-user computer from another computer, over a |
| 13 | network. |
| 14 | |
| 15 | Multi-user operating systems, such as Unix and VMS, usually present |
| 16 | a command-line interface to the user, much like the \q{Command |
| 17 | Prompt} or \q{MS-DOS Prompt} in Windows. The system prints a prompt, |
| 18 | and you type commands which the system will obey. |
| 19 | |
| 20 | Using this type of interface, there is no need for you to be sitting |
| 21 | at the same machine you are typing commands to. The commands, and |
| 22 | responses, can be sent over a network, so you can sit at one |
| 23 | computer and give commands to another one, or even to more than one. |
| 24 | |
| 25 | SSH, Telnet and Rlogin are \e{network protocols} that allow you to |
| 26 | do this. On the computer you sit at, you run a \e{client}, which |
| 27 | makes a network connection to the other computer (the \e{server}). |
| 28 | The network connection carries your keystrokes and commands from the |
| 29 | client to the server, and carries the server's responses back to |
| 30 | you. |
| 31 | |
| 32 | These protocols can also be used for other types of keyboard-based |
| 33 | interactive session. In particular, there are a lot of bulletin |
| 34 | boards, talker systems and MUDs (Multi-User Dungeons) which support |
| 35 | access using Telnet. There are even a few that support SSH. |
| 36 | |
| 37 | You might want to use SSH, Telnet or Rlogin if: |
| 38 | |
| 39 | \b you have an account on a Unix or VMS system which you want to be |
| 40 | able to access from somewhere else |
| 41 | |
| 42 | \b your Internet Service Provider provides you with a login account |
| 43 | on a web server. (This might also be known as a \e{shell account}. |
| 44 | A \e{shell} is the program that runs on the server and interprets |
| 45 | your commands for you.) |
| 46 | |
| 47 | \b you want to use a bulletin board system, talker or MUD which can |
| 48 | be accessed using Telnet. |
| 49 | |
| 50 | You probably do \e{not} want to use SSH, Telnet or Rlogin if: |
| 51 | |
| 52 | \b you only use Windows machines. Windows machines have their own |
| 53 | ways of networking between themselves, and unless you are doing |
| 54 | something fairly unusual, you will not need to use any of these |
| 55 | remote login protocols. |
| 56 | |
| 57 | \H{which-one} How do SSH, Telnet and Rlogin differ? |
| 58 | |
| 59 | This list summarises some of the differences between SSH, Telnet and |
| 60 | Rlogin. |
| 61 | |
| 62 | \b SSH is a recently designed, high-security protocol. It uses |
| 63 | strong cryptography to protect your connection against |
| 64 | eavesdropping, hijacking and other attacks. Telnet and Rlogin are |
| 65 | both older protocols offering minimal security. |
| 66 | |
| 67 | \b Telnet allows you to pass some settings on to the server, such as |
| 68 | environment variables. (These control various aspects of the |
| 69 | server's behaviour. You can usually set them by entering commands |
| 70 | into the server once you're connected, but it's easier to have |
| 71 | Telnet do it automatically.) SSH and Rlogin do not support this. |
| 72 | However, most modern Telnet servers don't allow it either, because |
| 73 | it has been a constant source of security problems. |
| 74 | |
| 75 | \b SSH and Rlogin both allow you to log in to the server without |
| 76 | having to type a password. (Rlogin's method of doing this is |
| 77 | insecure, and can allow an attacker to access your account on the |
| 78 | server. SSH's method is much more secure, and typically requires the |
| 79 | attacker to have gained access to your actual client machine.) |
| 80 | |
| 81 | \b SSH allows you to connect to the server and automatically send a |
| 82 | command, so that the server will run that command and then |
| 83 | disconnect. So you can use it in automated processing. |
| 84 | |
| 85 | The Internet is a hostile environment and security is everybody's |
| 86 | responsibility. If you are connecting across the open Internet, then |
| 87 | we recommend you use SSH. If the server you want to connect to |
| 88 | doesn't support SSH, it might be worth trying to persuade the |
| 89 | administrator to install it. |
| 90 | |
| 91 | If you are behind a good firewall, it is more likely to be safe to |
| 92 | use Telnet or Rlogin, but we still recommend you use SSH. |
| 93 | |
| 94 | \# perhaps a section on terminal emulation? |