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1 | \versionid $Id: intro.but,v 1.6 2004/06/15 11:00:28 jacob Exp $ |
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2 | |
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3 | \C{intro} Introduction to PuTTY |
4 | |
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5 | PuTTY is a free SSH, Telnet and Rlogin client for 32-bit Windows |
6 | systems. |
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7 | |
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8 | \H{you-what} What are SSH, Telnet and Rlogin? |
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9 | |
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10 | If you already know what SSH, Telnet and Rlogin are, you can safely |
11 | skip on to the next section. |
12 | |
13 | SSH, Telnet and Rlogin are three ways of doing the same thing: |
14 | logging in to a multi-user computer from another computer, over a |
15 | network. |
16 | |
17 | Multi-user operating systems, such as Unix and VMS, usually present |
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18 | a command-line interface to the user, much like the \q{\i{Command |
19 | Prompt}} or \q{\i{MS-DOS Prompt}} in Windows. The system prints a |
20 | prompt, and you type commands which the system will obey. |
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21 | |
22 | Using this type of interface, there is no need for you to be sitting |
23 | at the same machine you are typing commands to. The commands, and |
24 | responses, can be sent over a network, so you can sit at one |
25 | computer and give commands to another one, or even to more than one. |
26 | |
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27 | SSH, Telnet and Rlogin are \i\e{network protocols} that allow you to |
28 | do this. On the computer you sit at, you run a \i\e{client}, which |
29 | makes a network connection to the other computer (the \i\e{server}). |
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30 | The network connection carries your keystrokes and commands from the |
31 | client to the server, and carries the server's responses back to |
32 | you. |
33 | |
34 | These protocols can also be used for other types of keyboard-based |
35 | interactive session. In particular, there are a lot of bulletin |
36 | boards, talker systems and MUDs (Multi-User Dungeons) which support |
37 | access using Telnet. There are even a few that support SSH. |
38 | |
39 | You might want to use SSH, Telnet or Rlogin if: |
40 | |
41 | \b you have an account on a Unix or VMS system which you want to be |
42 | able to access from somewhere else |
43 | |
44 | \b your Internet Service Provider provides you with a login account |
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45 | on a web server. (This might also be known as a \i\e{shell account}. |
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46 | A \e{shell} is the program that runs on the server and interprets |
47 | your commands for you.) |
48 | |
49 | \b you want to use a bulletin board system, talker or MUD which can |
50 | be accessed using Telnet. |
51 | |
52 | You probably do \e{not} want to use SSH, Telnet or Rlogin if: |
53 | |
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54 | \b you only use Windows. Windows computers have their own |
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55 | ways of networking between themselves, and unless you are doing |
56 | something fairly unusual, you will not need to use any of these |
57 | remote login protocols. |
58 | |
59 | \H{which-one} How do SSH, Telnet and Rlogin differ? |
60 | |
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61 | This list summarises some of the \i{differences between SSH, Telnet |
62 | and Rlogin}. |
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63 | |
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64 | \b SSH (which stands for \q{\i{secure shell}}) is a recently designed, |
65 | high-security protocol. It uses strong cryptography to protect your |
66 | connection against eavesdropping, hijacking and other attacks. Telnet |
67 | and Rlogin are both older protocols offering minimal security. |
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68 | |
69 | \b Telnet allows you to pass some settings on to the server, such as |
70 | environment variables. (These control various aspects of the |
71 | server's behaviour. You can usually set them by entering commands |
72 | into the server once you're connected, but it's easier to have |
73 | Telnet do it automatically.) SSH and Rlogin do not support this. |
74 | However, most modern Telnet servers don't allow it either, because |
75 | it has been a constant source of security problems. |
76 | |
77 | \b SSH and Rlogin both allow you to log in to the server without |
78 | having to type a password. (Rlogin's method of doing this is |
79 | insecure, and can allow an attacker to access your account on the |
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80 | server. SSH's method is much more secure, and typically breaking the |
81 | security requires the attacker to have gained access to your actual |
82 | client machine.) |
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83 | |
84 | \b SSH allows you to connect to the server and automatically send a |
85 | command, so that the server will run that command and then |
86 | disconnect. So you can use it in automated processing. |
87 | |
88 | The Internet is a hostile environment and security is everybody's |
89 | responsibility. If you are connecting across the open Internet, then |
90 | we recommend you use SSH. If the server you want to connect to |
91 | doesn't support SSH, it might be worth trying to persuade the |
92 | administrator to install it. |
93 | |
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94 | If your client and server are both behind the same (good) firewall, |
95 | it is more likely to be safe to use Telnet or Rlogin, but we still |
96 | recommend you use SSH. |