-\define{versionidconfig} \versionid $Id$
-
\C{config} Configuring PuTTY
This chapter describes all the \i{configuration options} in PuTTY.
so it must usually be manually configured.
There are a lot of character sets to choose from. The \q{Remote
-character set} option lets you select one. By default PuTTY will
-attempt to choose a character set that is right for your \i{locale} as
-reported by Windows; if it gets it wrong, you can select a different
-one using this control.
+character set} option lets you select one.
+
+By default PuTTY will use the \i{UTF-8} encoding of \i{Unicode}, which
+can represent pretty much any character; data coming from the server
+is interpreted as UTF-8, and keystrokes are sent UTF-8 encoded. This
+is what most modern distributions of Linux will expect by default.
+However, if this is wrong for your server, you can select a different
+character set using this control.
-A few notable character sets are:
+A few other notable character sets are:
\b The \i{ISO-8859} series are all standard character sets that include
various accented characters appropriate for different sets of
\b If you want the old IBM PC character set with block graphics and
line-drawing characters, you can select \q{\i{CP437}}.
-\b PuTTY also supports \i{Unicode} mode, in which the data coming from
-the server is interpreted as being in the \i{UTF-8} encoding of Unicode,
-and keystrokes are sent UTF-8 encoded. If you select \q{UTF-8} as a
-character set you can use this mode. Not all server-side applications
-will support it.
-
If you need support for a numeric \i{code page} which is not listed in
the drop-down list, such as code page 866, then you can try entering
its name manually (\c{\i{CP866}} for example) in the list box. If the
change your terminal setting. On modern Linux machines, you could
try \cq{xterm-256color}.
-\S{config-boldcolour} \q{Bolded text is a different colour}
+\S{config-boldcolour} \q{Indicate bolded text by changing...}
\cfg{winhelp-topic}{colours.bold}
When the server sends a \i{control sequence} indicating that some text
-should be displayed in \i{bold}, PuTTY can handle this two ways. It can
-either change the \i{font} for a bold version, or use the same font in a
-brighter colour. This control lets you choose which.
-
-By default the box is checked, so non-bold text is displayed in
-light grey and bold text is displayed in bright white (and similarly
-in other colours). If you uncheck the box, bold and non-bold text
-will be displayed in the same colour, and instead the font will
-change to indicate the difference.
+should be displayed in \i{bold}, PuTTY can handle this in several
+ways. It can either change the \i{font} for a bold version, or use the
+same font in a brighter colour, or it can do both (brighten the colour
+\e{and} embolden the font). This control lets you choose which.
+
+By default bold is indicated by colour, so non-bold text is displayed
+in light grey and bold text is displayed in bright white (and
+similarly in other colours). If you change the setting to \q{The font}
+box, bold and non-bold text will be displayed in the same colour, and
+instead the font will change to indicate the difference. If you select
+\q{Both}, the font and the colour will both change.
+
+Some applications rely on \q{\i{bold black}} being distinguishable
+from a black background; if you choose \q{The font}, their text may
+become invisible.
\S{config-logpalette} \q{Attempt to use \i{logical palettes}}
\I{ANSI colours}ANSI configurable colours (black, red, green, yellow, blue,
magenta, cyan, and white). You can also modify the precise shades used for
the \i{bold} versions of these colours; these are used to display bold text
-if you have selected \q{Bolded text is a different colour}, and can also be
-used if the server asks specifically to use them. (Note that \q{Default
-Bold Background} is \e{not} the background colour used for bold text;
-it is only used if the server specifically asks for a bold
+if you have chosen to indicate that by colour (see \k{config-boldcolour}),
+and can also be used if the server asks specifically to use them. (Note
+that \q{Default Bold Background} is \e{not} the background colour used for
+bold text; it is only used if the server specifically asks for a bold
background.)
\H{config-connection} The Connection panel
you to reconfirm its host key. Conversely, if you expect to use the
same local port number for port forwardings to lots of different
servers, you probably didn't want any particular server's host key
-cached under that local port number.
+cached under that local port number. (For this latter case, you
+could also explicitly configure host keys in the relevant sessions;
+see \k{config-ssh-kex-manual-hostkeys}.)
If you just enter a host name for this option, PuTTY will cache the
SSH host key under the default SSH port for that host, irrespective
\cfg{winhelp-topic}{ssh.protocol}
-This allows you to select whether you would like to use \i{SSH protocol
-version 1} or \I{SSH-2}version 2. \#{FIXME: say something about this elsewhere?}
+This allows you to select whether you would prefer to use \i{SSH protocol
+version 1} or \I{SSH-2}version 2, and whether to permit falling back
+to the other version.
-PuTTY will attempt to use protocol 1 if the server you connect to
-does not offer protocol 2, and vice versa.
+With the settings \q{1} and \q{2}, PuTTY will attempt to use protocol 1
+if the server you connect to does not offer protocol 2, and vice versa.
If you select \q{1 only} or \q{2 only} here, PuTTY will only connect
if the server you connect to offers the SSH protocol version you
have specified.
-\S{config-ssh-encryption} \ii{Encryption} algorithm selection
-
-\cfg{winhelp-topic}{ssh.ciphers}
-
-PuTTY supports a variety of different \i{encryption algorithm}s, and
-allows you to choose which one you prefer to use. You can do this by
-dragging the algorithms up and down in the list box (or moving them
-using the Up and Down buttons) to specify a preference order. When
-you make an SSH connection, PuTTY will search down the list from the
-top until it finds an algorithm supported by the server, and then
-use that.
-
-PuTTY currently supports the following algorithms:
-
-\b \i{AES} (Rijndael) - 256, 192, or 128-bit SDCTR or CBC (SSH-2 only)
-
-\b \i{Arcfour} (RC4) - 256 or 128-bit stream cipher (SSH-2 only)
-
-\b \i{Blowfish} - 256-bit SDCTR (SSH-2 only) or 128-bit CBC
-
-\b \ii{Triple-DES} - 168-bit SDCTR (SSH-2 only) or CBC
-
-\b \ii{Single-DES} - 56-bit CBC (see below for SSH-2)
-
-If the algorithm PuTTY finds is below the \q{warn below here} line,
-you will see a warning box when you make the connection:
-
-\c The first cipher supported by the server
-\c is single-DES, which is below the configured
-\c warning threshold.
-\c Do you want to continue with this connection?
-
-This warns you that the first available encryption is not a very
-secure one. Typically you would put the \q{warn below here} line
-between the encryptions you consider secure and the ones you
-consider substandard. By default, PuTTY supplies a preference order
-intended to reflect a reasonable preference in terms of security and
-speed.
-
-In SSH-2, the encryption algorithm is negotiated independently for
-each direction of the connection, although PuTTY does not support
-separate configuration of the preference orders. As a result you may
-get two warnings similar to the one above, possibly with different
-encryptions.
-
-Single-DES is not recommended in the SSH-2 protocol
-standards, but one or two server implementations do support it.
-PuTTY can use single-DES to interoperate with
-these servers if you enable the \q{Enable legacy use of single-DES in
-SSH-2} option; by default this is disabled and PuTTY will stick to
-recommended ciphers.
+You should normally leave this at the default, \q{2 only}. The older
+SSH-1 protocol is no longer developed, has many known cryptographic
+weaknesses, and is generally not considered to be secure. If you
+permit use of SSH-1 by selecting \q{2} instead of \q{2 only}, an
+active attacker can force downgrade to SSH-1 even if the server
+you're connecting to supports SSH-2.
+
+PuTTY's protocol 1 implementation is provided mainly for
+compatibility, and is no longer being enhanced.
+
+\S{config-ssh-sharing} Sharing an SSH connection between PuTTY tools
+
+\cfg{winhelp-topic}{ssh.sharing}
+
+The controls in this box allow you to configure PuTTY to reuse an
+existing SSH connection, where possible.
+
+The SSH-2 protocol permits you to run multiple data channels over the
+same SSH connection, so that you can log in just once (and do the
+expensive encryption setup just once) and then have more than one
+terminal window open.
+
+Each instance of PuTTY can still run at most one terminal session, but
+using the controls in this box, you can configure PuTTY to check if
+another instance of itself has already connected to the target host,
+and if so, share that instance's SSH connection instead of starting a
+separate new one.
+
+To enable this feature, just tick the box \q{Share SSH connections if
+possible}. Then, whenever you start up a PuTTY session connecting to a
+particular host, it will try to reuse an existing SSH connection if
+one is available. For example, selecting \q{Duplicate Session} from
+the system menu will launch another session on the same host, and if
+sharing is enabled then it will reuse the existing SSH connection.
+
+When this mode is in use, the first PuTTY that connected to a given
+server becomes the \q{upstream}, which means that it is the one
+managing the real SSH connection. All subsequent PuTTYs which reuse
+the connection are referred to as \q{downstreams}: they do not connect
+to the real server at all, but instead connect to the upstream PuTTY
+via local inter-process communication methods.
+
+For this system to be activated, \e{both} the upstream and downstream
+instances of PuTTY must have the sharing option enabled.
+
+The upstream PuTTY can therefore not terminate until all its
+downstreams have closed. This is similar to the effect you get with
+port forwarding or X11 forwarding, in which a PuTTY whose terminal
+session has already finished will still remain open so as to keep
+serving forwarded connections.
+
+In case you need to configure this system in more detail, there are
+two additional checkboxes which allow you to specify whether a
+particular PuTTY can act as an upstream or a downstream or both.
+(These boxes only take effect if the main \q{Share SSH connections if
+possible} box is also ticked.) By default both of these boxes are
+ticked, so that multiple PuTTYs started from the same configuration
+will designate one of themselves as the upstream and share a single
+connection; but if for some reason you need a particular PuTTY
+configuration \e{not} to be an upstream (e.g. because you definitely
+need it to close promptly) or not to be a downstream (e.g. because it
+needs to do its own authentication using a special private key) then
+you can untick one or the other of these boxes.
+
+I have referred to \q{PuTTY} throughout the above discussion, but all
+the other PuTTY tools which make SSH connections can use this
+mechanism too. For example, if PSCP or PSFTP loads a configuration
+with sharing enabled, then it can act as a downstream and use an
+existing SSH connection set up by an instance of GUI PuTTY. The one
+special case is that PSCP and PSFTP will \e{never} act as upstreams.
\H{config-ssh-kex} The Kex panel
-\# FIXME: This whole section is draft. Feel free to revise.
-
The Kex panel (short for \q{\i{key exchange}}) allows you to configure
options related to SSH-2 key exchange.
to choose which one you prefer to use; configuration is similar to
cipher selection (see \k{config-ssh-encryption}).
-PuTTY currently supports the following varieties of \i{Diffie-Hellman key
-exchange}:
+PuTTY currently supports the following key exchange methods:
+
+\b \q{ECDH}: \i{elliptic curve} \i{Diffie-Hellman key exchange}.
-\b \q{Group 14}: a well-known 2048-bit group.
+\b \q{Group 14}: Diffie-Hellman key exchange with a well-known
+2048-bit group.
-\b \q{Group 1}: a well-known 1024-bit group. This is less secure
-\#{FIXME better words} than group 14, but may be faster with slow
-client or server machines, and may be the only method supported by
-older server software.
+\b \q{Group 1}: Diffie-Hellman key exchange with a well-known
+1024-bit group. This is less secure \#{FIXME better words} than
+group 14, but may be faster with slow client or server machines,
+and may be the only method supported by older server software.
\b \q{\ii{Group exchange}}: with this method, instead of using a fixed
group, PuTTY requests that the server suggest a group to use for key
invent new ones over time, without any changes required to PuTTY's
configuration. We recommend use of this method, if possible.
-In addition, PuTTY supports \i{RSA key exchange}, which requires much less
-computational effort on the part of the client, and somewhat less on
-the part of the server, than Diffie-Hellman key exchange.
+\b \q{\i{RSA key exchange}}: this requires much less computational
+effort on the part of the client, and somewhat less on the part of
+the server, than Diffie-Hellman key exchange.
If the first algorithm PuTTY finds is below the \q{warn below here}
line, you will see a warning box when you make the connection, similar
problems. The SSH-1 protocol, incidentally, has even weaker integrity
protection than SSH-2 without rekeys.
+\S{config-ssh-kex-manual-hostkeys} \ii{Manually configuring host keys}
+
+\cfg{winhelp-topic}{ssh.kex.manualhostkeys}
+
+In some situations, if PuTTY's automated host key management is not
+doing what you need, you might need to manually configure PuTTY to
+accept a specific host key, or one of a specific set of host keys.
+
+One reason why you might want to do this is because the host name
+PuTTY is connecting to is using round-robin DNS to return one of
+multiple actual servers, and they all have different host keys. In
+that situation, you might need to configure PuTTY to accept any of a
+list of host keys for the possible servers, while still rejecting any
+key not in that list.
+
+Another reason is if PuTTY's automated host key management is
+completely unavailable, e.g. because PuTTY (or Plink or PSFTP, etc) is
+running in a Windows environment without access to the Registry. In
+that situation, you will probably want to use the \cw{-hostkey}
+command-line option to configure the expected host key(s); see
+\k{using-cmdline-hostkey}.
+
+For situations where PuTTY's automated host key management simply
+picks the wrong host name to store a key under, you may want to
+consider setting a \q{logical host name} instead; see
+\k{config-loghost}.
+
+To configure manual host keys via the GUI, enter some text describing
+the host key into the edit box in the \q{Manually configure host keys
+for this connection} container, and press the \q{Add} button. The text
+will appear in the \q{Host keys or fingerprints to accept} list box.
+You can remove keys again with the \q{Remove} button.
+
+The text describing a host key can be in one of the following formats:
+
+\b An MD5-based host key fingerprint of the form displayed in PuTTY's
+Event Log and host key dialog boxes, i.e. sixteen 2-digit hex numbers
+separated by colons.
+
+\b A base64-encoded blob describing an SSH-2 public key in
+OpenSSH's one-line public key format. How you acquire a public key in
+this format is server-dependent; on an OpenSSH server it can typically
+be found in a location like \c{/etc/ssh/ssh_host_rsa_key.pub}.
+
+If this box contains at least one host key or fingerprint when PuTTY
+makes an SSH connection, then PuTTY's automated host key management is
+completely bypassed: the connection will be permitted if and only if
+the host key presented by the server is one of the keys listed in this
+box, and the host key store in the Registry will be neither read
+\e{nor written}.
+
+If the box is empty (as it usually is), then PuTTY's automated host
+key management will work as normal.
+
+\H{config-ssh-encryption} The Cipher panel
+
+\cfg{winhelp-topic}{ssh.ciphers}
+
+PuTTY supports a variety of different \i{encryption algorithm}s, and
+allows you to choose which one you prefer to use. You can do this by
+dragging the algorithms up and down in the list box (or moving them
+using the Up and Down buttons) to specify a preference order. When
+you make an SSH connection, PuTTY will search down the list from the
+top until it finds an algorithm supported by the server, and then
+use that.
+
+PuTTY currently supports the following algorithms:
+
+\b \i{AES} (Rijndael) - 256, 192, or 128-bit SDCTR or CBC (SSH-2 only)
+
+\b \i{Arcfour} (RC4) - 256 or 128-bit stream cipher (SSH-2 only)
+
+\b \i{Blowfish} - 256-bit SDCTR (SSH-2 only) or 128-bit CBC
+
+\b \ii{Triple-DES} - 168-bit SDCTR (SSH-2 only) or CBC
+
+\b \ii{Single-DES} - 56-bit CBC (see below for SSH-2)
+
+If the algorithm PuTTY finds is below the \q{warn below here} line,
+you will see a warning box when you make the connection:
+
+\c The first cipher supported by the server
+\c is single-DES, which is below the configured
+\c warning threshold.
+\c Do you want to continue with this connection?
+
+This warns you that the first available encryption is not a very
+secure one. Typically you would put the \q{warn below here} line
+between the encryptions you consider secure and the ones you
+consider substandard. By default, PuTTY supplies a preference order
+intended to reflect a reasonable preference in terms of security and
+speed.
+
+In SSH-2, the encryption algorithm is negotiated independently for
+each direction of the connection, although PuTTY does not support
+separate configuration of the preference orders. As a result you may
+get two warnings similar to the one above, possibly with different
+encryptions.
+
+Single-DES is not recommended in the SSH-2 protocol
+standards, but one or two server implementations do support it.
+PuTTY can use single-DES to interoperate with
+these servers if you enable the \q{Enable legacy use of single-DES in
+SSH-2} option; by default this is disabled and PuTTY will stick to
+recommended ciphers.
+
\H{config-ssh-auth} The Auth panel
The Auth panel allows you to configure \i{authentication} options for
private key in another format that you want to use with PuTTY, see
\k{puttygen-conversions}.
-If a key file is specified here, and \i{Pageant} is running (see
-\k{pageant}), PuTTY will first try asking Pageant to authenticate with
-that key, and ignore any other keys Pageant may have. If that fails,
-PuTTY will ask for a passphrase as normal.
+You can use the authentication agent \i{Pageant} so that you do not
+need to explicitly configure a key here; see \k{pageant}. If a file
+is specified here with Pageant running, PuTTY will first try asking
+Pageant to authenticate with that key, and ignore any other keys
+Pageant may have. If that fails, PuTTY will ask for a passphrase as
+normal.
\H{config-ssh-auth-gssapi} The \i{GSSAPI} panel
The X11 panel allows you to configure \i{forwarding of X11} over an
SSH connection.
-If your server lets you run X Window System applications, X11
-forwarding allows you to securely give those applications access to
+If your server lets you run X Window System \i{graphical applications},
+X11 forwarding allows you to securely give those applications access to
a local X display on your PC.
To enable X11 forwarding, check the \q{Enable X11 forwarding} box.
by a colon, in the \q{Destination} box. Connections received on the
source port will be directed to this destination. For example, to
connect to a POP-3 server, you might enter
-\c{popserver.example.com:110}.
+\c{popserver.example.com:110}. (If you need to enter a literal
+\i{IPv6 address}, enclose it in square brackets, for instance
+\cq{[::1]:2200}.)
\b Click the \q{Add} button. Your forwarding details should appear
in the list box.
server, the session will succeed, but keepalives will not work and
the session might be less cryptographically secure than it could be.
+\S{config-ssh-bug-winadj} \q{Chokes on PuTTY's SSH-2 \cq{winadj} requests}
+
+\cfg{winhelp-topic}{ssh.bugs.winadj}
+
+PuTTY sometimes sends a special request to SSH servers in the middle
+of channel data, with the name \cw{winadj@putty.projects.tartarus.org}
+(see \k{sshnames-channel}). The purpose of this request is to measure
+the round-trip time to the server, which PuTTY uses to tune its flow
+control. The server does not actually have to \e{understand} the
+message; it is expected to send back a \cw{SSH_MSG_CHANNEL_FAILURE}
+message indicating that it didn't understand it. (All PuTTY needs for
+its timing calculations is \e{some} kind of response.)
+
+It has been known for some SSH servers to get confused by this message
+in one way or another \dash because it has a long name, or because
+they can't cope with unrecognised request names even to the extent of
+sending back the correct failure response, or because they handle it
+sensibly but fill up the server's log file with pointless spam, or
+whatever. PuTTY therefore supports this bug-compatibility flag: if it
+believes the server has this bug, it will never send its
+\cq{winadj@putty.projects.tartarus.org} request, and will make do
+without its timing data.
+
\S{config-ssh-bug-hmac2} \q{Miscomputes SSH-2 HMAC keys}
\cfg{winhelp-topic}{ssh.bugs.hmac2}
correct server, the session will work correctly, but download
performance will be less than it could be.
+\S{config-ssh-bug-chanreq} \q{Replies to requests on closed channels}
+
+\cfg{winhelp-topic}{ssh.bugs.chanreq}
+
+The SSH protocol as published in RFC 4254 has an ambiguity which
+arises if one side of a connection tries to close a channel, while the
+other side simultaneously sends a request within the channel and asks
+for a reply. RFC 4254 leaves it unclear whether the closing side
+should reply to the channel request after having announced its
+intention to close the channel.
+
+Discussion on the \cw{ietf-ssh} mailing list in April 2014 formed a
+clear consensus that the right answer is no. However, because of the
+ambiguity in the specification, some SSH servers have implemented the
+other policy; for example,
+\W{https://bugzilla.mindrot.org/show_bug.cgi?id=1818}{OpenSSH used to}
+until it was fixed.
+
+Because PuTTY sends channel requests with the \q{want reply} flag
+throughout channels' lifetime (see \k{config-ssh-bug-winadj}), it's
+possible that when connecting to such a server it might receive a
+reply to a request after it thinks the channel has entirely closed,
+and terminate with an error along the lines of \q{Received
+\cw{SSH2_MSG_CHANNEL_FAILURE} for nonexistent channel 256}.
+
\H{config-serial} The Serial panel
The \i{Serial} panel allows you to configure options that only apply
You should replace \c{a:\\putty.rnd} with the location where you
want to store your random number data. If the aim is to carry around
-PuTTY and its settings on one floppy, you probably want to store it
-on the floppy.
+PuTTY and its settings on one USB stick, you probably want to store it
+on the USB stick.
projects / PuTTY.git / blobdiff