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1 | \C{intro} Introduction to PuTTY |
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3 | PuTTY is a free SSH, Telnet and Rlogin client for 32-bit Windows |
4 | systems. |
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6 | \H{you-what} What are SSH, Telnet and Rlogin? |
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8 | If you already know what SSH, Telnet and Rlogin are, you can safely |
9 | skip on to the next section. |
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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: |
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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? |