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

   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?