PuTTY has the ability to change its character set configuration in
response to commands from the server. Some programs send these
-commands unexpectedly or inconveniently. In particular, \I{BitchX} (an
+commands unexpectedly or inconveniently. In particular, \i{BitchX} (an
IRC client) seems to have a habit of reconfiguring the character set
to something other than the user intended.
\b \q{Change font size when maximised}: when the window is resized,
the number of rows and columns will change, \e{except} when the window
-is \i{maximise}d (or restored), when the font size will change.
+is \i{maximise}d (or restored), when the font size will change. (In
+this mode, holding down the Alt key while resizing will also cause the
+font size to change.)
\b \q{Forbid resizing completely}: the terminal will refuse to be
resized at all.
\cfg{winhelp-topic}{appearance.font}
This option allows you to choose what font, in what \I{font size}size,
-the PuTTY terminal window uses to display the text in the session. You
-will be offered a choice from all the fixed-width fonts installed on the
-system. (VT100-style terminal handling can only deal with fixed-width
-fonts.)
+the PuTTY terminal window uses to display the text in the session.
+
+By default, you will be offered a choice from all the fixed-width
+fonts installed on the system, since VT100-style terminal handling
+expects a fixed-width font. If you tick the box marked \q{Allow
+selection of variable-pitch fonts}, however, PuTTY will offer
+variable-width fonts as well: if you select one of these, the font
+will be coerced into fixed-size character cells, which will probably
+not look very good (but can work OK with some fonts).
\S{config-mouseptr} \q{Hide \i{mouse pointer} when typing in window}
During an interactive session, PuTTY receives a stream of 8-bit
bytes from the server, and in order to display them on the screen it
-needs to know what character set to interpret them in.
+needs to know what character set to interpret them in. Similarly,
+PuTTY needs to know how to translate your keystrokes into the encoding
+the server expects. Unfortunately, there is no satisfactory
+mechanism for PuTTY and the server to communicate this information,
+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.
-There are a lot of character sets to choose from. The \q{Received
-data assumed to be in which 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.
+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.
-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
\cfg{winhelp-topic}{connection.ipversion}
This option allows the user to select between the old and new
-Internet protocols and addressing schemes (\i{IPv4} and \i{IPv6}). The
-default setting is \q{Auto}, which means PuTTY will do something
+Internet protocols and addressing schemes (\i{IPv4} and \i{IPv6}).
+The selected protocol will be used for most outgoing network
+connections (including connections to \I{proxy}proxies); however,
+tunnels have their own configuration, for which see
+\k{config-ssh-portfwd-address-family}.
+
+The default setting is \q{Auto}, which means PuTTY will do something
sensible and try to guess which protocol you wanted. (If you specify
a literal \i{Internet address}, it will use whichever protocol that
address implies. If you provide a \i{hostname}, it will see what kinds
If you need to force PuTTY to use a particular protocol, you can
explicitly set this to \q{IPv4} or \q{IPv6}.
+\S{config-loghost} \I{logical host name}\q{Logical name of remote host}
+
+\cfg{winhelp-topic}{connection.loghost}
+
+This allows you to tell PuTTY that the host it will really end up
+connecting to is different from where it thinks it is making a
+network connection.
+
+You might use this, for instance, if you had set up an SSH port
+forwarding in one PuTTY session so that connections to some
+arbitrary port (say, \cw{localhost} port 10022) were forwarded to a
+second machine's SSH port (say, \cw{foovax} port 22), and then
+started a second PuTTY connecting to the forwarded port.
+
+In normal usage, the second PuTTY will access the host key cache
+under the host name and port it actually connected to (i.e.
+\cw{localhost} port 10022 in this example). Using the logical host
+name option, however, you can configure the second PuTTY to cache
+the host key under the name of the host \e{you} know that it's
+\e{really} going to end up talking to (here \c{foovax}).
+
+This can be useful if you expect to connect to the same actual
+server through many different channels (perhaps because your port
+forwarding arrangements keep changing): by consistently setting the
+logical host name, you can arrange that PuTTY will not keep asking
+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.
+
+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
+of the port you really connected to (since the typical scenario is
+like the above example: you connect to a silly real port number and
+your connection ends up forwarded to the normal port-22 SSH server
+of some other machine). To override this, you can append a port
+number to the logical host name, separated by a colon. E.g. entering
+\cq{foovax:2200} as the logical host name will cause the host key to
+be cached as if you had connected to port 2200 of \c{foovax}.
+
+If you provide a host name using this option, it is also displayed
+in other locations which contain the remote host name, such as the
+default window title and the default SSH password prompt. This
+reflects the fact that this is the host you're \e{really} connecting
+to, which is more important than the mere means you happen to be
+using to contact that host. (This applies even if you're using a
+protocol other than SSH.)
+
\H{config-data} The Data panel
The Data panel allows you to configure various pieces of data which
In this box you can type that user name.
+\S{config-username-from-env} Use of system username
+
+\cfg{winhelp-topic}{connection.usernamefromenv}
+
+When the previous box (\k{config-username}) is left blank, by default,
+PuTTY will prompt for a username at the time you make a connection.
+
+In some environments, such as the networks of large organisations
+implementing \i{single sign-on}, a more sensible default may be to use
+the name of the user logged in to the local operating system (if any);
+this is particularly likely to be useful with \i{GSSAPI} authentication
+(see \k{config-ssh-auth-gssapi}). This control allows you to change
+the default behaviour.
+
+The current system username is displayed in the dialog as a
+convenience. It is not saved in the configuration; if a saved session
+is later used by a different user, that user's name will be used.
+
\S{config-termtype} \q{\ii{Terminal-type} string}
\cfg{winhelp-topic}{connection.termtype}
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.
+\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
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 FIXME.
+
+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 the
+standard way. This can be found in OpenSSH's one-line public key
+format, or by concatenating all the lines of the public key section in
+one of PuTTY's \cw{.ppk} files. Alternatively, you can load a key into
+PuTTYgen, and paste out the OpenSSH-format public key line it
+displays.
+
+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
This option only affects SSH-2 connections. SSH-1 connections always
require an authentication step.
+\S{config-ssh-banner} \q{Display pre-authentication banner}
+
+\cfg{winhelp-topic}{ssh.auth.banner}
+
+SSH-2 servers can provide a message for clients to display to the
+prospective user before the user logs in; this is sometimes known as a
+pre-authentication \q{\i{banner}}. Typically this is used to provide
+information about the server and legal notices.
+
+By default, PuTTY displays this message before prompting for a
+password or similar credentials (although, unfortunately, not before
+prompting for a login name, due to the nature of the protocol design).
+By unchecking this option, display of the banner can be suppressed
+entirely.
+
\S{config-ssh-tryagent} \q{Attempt authentication using Pageant}
\cfg{winhelp-topic}{ssh.auth.pageant}
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
+
+\cfg{winhelp-topic}{ssh.auth.gssapi}
+
+The \q{GSSAPI} subpanel of the \q{Auth} panel controls the use of
+GSSAPI authentication. This is a mechanism which delegates the
+authentication exchange to a library elsewhere on the client
+machine, which in principle can authenticate in many different ways
+but in practice is usually used with the \i{Kerberos} \i{single sign-on}
+protocol.
+
+GSSAPI is only available in the SSH-2 protocol.
+
+The topmost control on the GSSAPI subpanel is the checkbox labelled
+\q{Attempt GSSAPI authentication}. If this is disabled, GSSAPI will
+not be attempted at all and the rest of this panel is unused. If it
+is enabled, GSSAPI authentication will be attempted, and (typically)
+if your client machine has valid Kerberos credentials loaded, then
+PuTTY should be able to authenticate automatically to servers that
+support Kerberos logins.
+
+\S{config-ssh-auth-gssapi-delegation} \q{Allow GSSAPI credential
+delegation}
+
+\cfg{winhelp-topic}{ssh.auth.gssapi.delegation}
+
+\i{GSSAPI credential delegation} is a mechanism for passing on your
+Kerberos (or other) identity to the session on the SSH server. If
+you enable this option, then not only will PuTTY be able to log in
+automatically to a server that accepts your Kerberos credentials,
+but also you will be able to connect out from that server to other
+Kerberos-supporting services and use the same credentials just as
+automatically.
+
+(This option is the Kerberos analogue of SSH agent forwarding; see
+\k{pageant-forward} for some information on that.)
+
+Note that, like SSH agent forwarding, there is a security
+implication in the use of this option: the administrator of the
+server you connect to, or anyone else who has cracked the
+administrator account on that server, could fake your identity when
+connecting to further Kerberos-supporting services. However,
+Kerberos sites are typically run by a central authority, so the
+administrator of one server is likely to already have access to the
+other services too; so this would typically be less of a risk than
+SSH agent forwarding.
+
+\S{config-ssh-auth-gssapi-libraries} Preference order for GSSAPI
+libraries
+
+\cfg{winhelp-topic}{ssh.auth.gssapi.libraries}
+
+GSSAPI is a mechanism which allows more than one authentication
+method to be accessed through the same interface. Therefore, more
+than one authentication library may exist on your system which can
+be accessed using GSSAPI.
+
+PuTTY contains native support for a few well-known such libraries,
+and will look for all of them on your system and use whichever it
+finds. If more than one exists on your system and you need to use a
+specific one, you can adjust the order in which it will search using
+this preference list control.
+
+One of the options in the preference list is to use a user-specified
+GSSAPI library. If the library you want to use is not mentioned by
+name in PuTTY's list of options, you can enter its full pathname in
+the \q{User-supplied GSSAPI library path} field, and move the
+\q{User-supplied GSSAPI library} option in the preference list to
+make sure it is selected before anything else.
+
\H{config-ssh-tty} The TTY panel
The TTY panel lets you configure the remote pseudo-terminal.
PuTTY's default is \cw{MIT-MAGIC-COOKIE-1}. If you change it, you
should be sure you know what you're doing.
+\S{config-ssh-xauthority} X authority file for local display
+
+\cfg{winhelp-topic}{ssh.tunnels.xauthority}
+
+If you are using X11 forwarding, the local X server to which your
+forwarded connections are eventually directed may itself require
+authorisation.
+
+Some Windows X servers do not require this: they do authorisation by
+simpler means, such as accepting any connection from the local
+machine but not from anywhere else. However, if your X server does
+require authorisation, then PuTTY needs to know what authorisation
+is required.
+
+One way in which this data might be made available is for the X
+server to store it somewhere in a file which has the same format
+as the Unix \c{.Xauthority} file. If this is how your Windows X
+server works, then you can tell PuTTY where to find this file by
+configuring this option. By default, PuTTY will not attempt to find
+any authorisation for your local display.
+
\H{config-ssh-portfwd} \I{port forwarding}The Tunnels panel
\cfg{winhelp-topic}{ssh.tunnels.portfwd}
such as \q{Local ports accept connections from other hosts} only take
effect on new forwardings.
+If the connection you are forwarding over SSH is itself a second SSH
+connection made by another copy of PuTTY, you might find the
+\q{logical host name} configuration option useful to warn PuTTY of
+which host key it should be expecting. See \k{config-loghost} for
+details of this.
+
\S{config-ssh-portfwd-localhost} Controlling the visibility of
forwarded ports
\b for a remote-to-local port forwarding, PuTTY will choose a
sensible protocol for the outgoing connection.
+This overrides the general Internet protocol version preference
+on the Connection panel (see \k{config-address-family}).
+
Note that some operating systems may listen for incoming connections
in IPv4 even if you specifically asked for IPv6, because their IPv4
and IPv6 protocol stacks are linked together. Apparently \i{Linux} does
but keepalives will not work and the session might be more
vulnerable to eavesdroppers than it could be.
-This is an SSH-1-specific bug. No known SSH-2 server fails to deal
-with SSH-2 ignore messages.
-
\S{config-ssh-bug-plainpw1} \q{Refuses all SSH-1 \i{password camouflage}}
\cfg{winhelp-topic}{ssh.bugs.plainpw1}
This is an SSH-1-specific bug.
+\S{config-ssh-bug-ignore2} \q{Chokes on SSH-2 \i{ignore message}s}
+
+\cfg{winhelp-topic}{ssh.bugs.ignore2}
+
+An ignore message (SSH_MSG_IGNORE) is a message in the SSH protocol
+which can be sent from the client to the server, or from the server
+to the client, at any time. Either side is required to ignore the
+message whenever it receives it. PuTTY uses ignore messages in SSH-2
+to confuse the encrypted data stream and make it harder to
+cryptanalyse. It also uses ignore messages for connection
+\i{keepalives} (see \k{config-keepalive}).
+
+If it believes the server to have this bug, PuTTY will stop using
+ignore messages. If this bug is enabled when talking to a correct
+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-hmac2} \q{Miscomputes SSH-2 HMAC keys}
\cfg{winhelp-topic}{ssh.bugs.hmac2}
This is an SSH-2-specific bug.
+\S{config-ssh-bug-maxpkt2} \q{Ignores SSH-2 \i{maximum packet size}}
+
+\cfg{winhelp-topic}{ssh.bugs.maxpkt2}
+
+When an SSH-2 channel is set up, each end announces the maximum size
+of data packet that it is willing to receive for that channel. Some
+servers ignore PuTTY's announcement and send packets larger than PuTTY
+is willing to accept, causing it to report \q{Incoming packet was
+garbled on decryption}.
+
+If this bug is detected, PuTTY never allows the channel's
+\i{flow-control window} to grow large enough to allow the server to
+send an over-sized packet. If this bug is enabled when talking to a
+correct server, the session will work correctly, but download
+performance will be less 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-chanreq} \q{Replies to channel requests after channel close}
+
+\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