git.distorted.org.uk Git - u/mdw/putty/blob - doc/intro.but

   1 \define{versionidintro} \versionid $Id$
   2
   3 \C{intro} Introduction to PuTTY
   4
   5 PuTTY is a free SSH, Telnet and Rlogin client for 32-bit Windows
   6 systems.
   7
   8 \H{you-what} What are SSH, Telnet and Rlogin?
   9
  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
  18 a \i{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.
  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
  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}).
  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, \i{talker systems} and \i{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
  45 on a \i{web server}. (This might also be known as a \i\e{shell account}.
  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 \i{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
  54 \b you only use Windows. Windows computers have their own
  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
  61 This list summarises some of the \i{differences between SSH, Telnet
  62 and Rlogin}.
  63
  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.
  68
  69 \b SSH and Rlogin both allow you to \I{passwordless login}log in to the
  70 server without having to type a password. (Rlogin's method of doing this is
  71 insecure, and can allow an attacker to access your account on the
  72 server. SSH's method is much more secure, and typically breaking the
  73 security requires the attacker to have gained access to your actual
  74 client machine.)
  75
  76 \b SSH allows you to connect to the server and automatically send a
  77 command, so that the server will run that command and then
  78 disconnect. So you can use it in automated processing.
  79
  80 The Internet is a hostile environment and security is everybody's
  81 responsibility. If you are connecting across the open Internet, then
  82 we recommend you use SSH. If the server you want to connect to
  83 doesn't support SSH, it might be worth trying to persuade the
  84 administrator to install it.
  85
  86 If your client and server are both behind the same (good) firewall,
  87 it is more likely to be safe to use Telnet or Rlogin, but we still
  88 recommend you use SSH.