Some introductory blurb in the docs
[u/mdw/putty] / doc / intro.but
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e5b0d077 1\C{intro} Introduction to PuTTY
2
e571c4d7 3PuTTY is a free SSH, Telnet and Rlogin client for 32-bit Windows
4systems.
e5b0d077 5
e571c4d7 6\H{you-what} What are SSH, Telnet and Rlogin?
e5b0d077 7
e571c4d7 8If you already know what SSH, Telnet and Rlogin are, you can safely
9skip on to the next section.
10
11SSH, Telnet and Rlogin are three ways of doing the same thing:
12logging in to a multi-user computer from another computer, over a
13network.
14
15Multi-user operating systems, such as Unix and VMS, usually present
16a command-line interface to the user, much like the \q{Command
17Prompt} or \q{MS-DOS Prompt} in Windows. The system prints a prompt,
18and you type commands which the system will obey.
19
20Using this type of interface, there is no need for you to be sitting
21at the same machine you are typing commands to. The commands, and
22responses, can be sent over a network, so you can sit at one
23computer and give commands to another one, or even to more than one.
24
25SSH, Telnet and Rlogin are \e{network protocols} that allow you to
26do this. On the computer you sit at, you run a \e{client}, which
27makes a network connection to the other computer (the \e{server}).
28The network connection carries your keystrokes and commands from the
29client to the server, and carries the server's responses back to
30you.
31
32These protocols can also be used for other types of keyboard-based
33interactive session. In particular, there are a lot of bulletin
34boards, talker systems and MUDs (Multi-User Dungeons) which support
35access using Telnet. There are even a few that support SSH.
36
37You 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
40able to access from somewhere else
41
42\b your Internet Service Provider provides you with a login account
43on a web server. (This might also be known as a \e{shell account}.
44A \e{shell} is the program that runs on the server and interprets
45your commands for you.)
46
47\b you want to use a bulletin board system, talker or MUD which can
48be accessed using Telnet.
49
50You 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
53ways of networking between themselves, and unless you are doing
54something fairly unusual, you will not need to use any of these
55remote login protocols.
56
57\H{which-one} How do SSH, Telnet and Rlogin differ?
58
59This list summarises some of the differences between SSH, Telnet and
60Rlogin.
61
62\b SSH is a recently designed, high-security protocol. It uses
63strong cryptography to protect your connection against
64eavesdropping, hijacking and other attacks. Telnet and Rlogin are
65both older protocols offering minimal security.
66
67\b Telnet allows you to pass some settings on to the server, such as
68environment variables. (These control various aspects of the
69server's behaviour. You can usually set them by entering commands
70into the server once you're connected, but it's easier to have
71Telnet do it automatically.) SSH and Rlogin do not support this.
72However, most modern Telnet servers don't allow it either, because
73it has been a constant source of security problems.
74
75\b SSH and Rlogin both allow you to log in to the server without
76having to type a password. (Rlogin's method of doing this is
77insecure, and can allow an attacker to access your account on the
78server. SSH's method is much more secure, and typically requires the
79attacker to have gained access to your actual client machine.)
80
81\b SSH allows you to connect to the server and automatically send a
82command, so that the server will run that command and then
83disconnect. So you can use it in automated processing.
84
85The Internet is a hostile environment and security is everybody's
86responsibility. If you are connecting across the open Internet, then
87we recommend you use SSH. If the server you want to connect to
88doesn't support SSH, it might be worth trying to persuade the
89administrator to install it.
90
91If you are behind a good firewall, it is more likely to be safe to
92use Telnet or Rlogin, but we still recommend you use SSH.
93
94\# perhaps a section on terminal emulation?