\b \c{&H} will be replaced by the host name you are connecting to.
+\b \c{&P} will be replaced by the port number you are connecting to on
+the target host.
+
For example, if you enter the host name
\c{c:\\puttylogs\\log-&h-&y&m&d-&t.dat}, you will end up with files looking
like
protocols offer no way of implementing them. (For an alternative, see
\k{config-tcp-keepalives}.)
-Note that if you are using \i{SSH-1} and the server has a bug that makes
+Note that if you are using SSH-1 and the server has a bug that makes
it unable to deal with SSH-1 ignore messages (see
\k{config-ssh-bug-ignore1}), enabling keepalives will have no effect.
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
+In normal usage, the second PuTTY will access the \i{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
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. (For this latter case, you
-could also explicitly configure host keys in the relevant sessions;
+could instead 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
first and the server decompresses it at the other end. This can help
make the most of a low-\i{bandwidth} connection.
-\S{config-ssh-prot} \q{Preferred \i{SSH protocol version}}
+\S{config-ssh-prot} \q{\i{SSH protocol version}}
\cfg{winhelp-topic}{ssh.protocol}
-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.
-
-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.
+This allows you to select whether to use \i{SSH protocol version 2}
+or the older \I{SSH-1}version 1.
-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.
+You should normally leave this at the default of \q{2}. As well as
+having fewer features, the older SSH-1 protocol is no longer
+developed, has many known cryptographic weaknesses, and is generally
+not considered to be secure. PuTTY's protocol 1 implementation is
+provided mainly for compatibility, and is no longer being enhanced.
-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.
+If a server offers both versions, prefer \q{2}. If you have some
+server or piece of equipment that only talks SSH-1, select \q{1}
+here, and do not treat the resulting connection as secure.
-PuTTY's protocol 1 implementation is provided mainly for
-compatibility, and is no longer being enhanced.
+PuTTY will not automatically fall back to the other version of the
+protocol if the server turns out not to match your selection here;
+instead, it will put up an error message and abort the connection.
+This prevents an active attacker downgrading an intended SSH-2
+connection to SSH-1.
\S{config-ssh-sharing} Sharing an SSH connection between PuTTY tools
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.
+It is possible to test programmatically for the existence of a live
+upstream using Plink. See \k{plink-option-shareexists}.
+
\H{config-ssh-kex} The Kex panel
The Kex panel (short for \q{\i{key exchange}}) allows you to configure
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. We no longer recommend using this method, and it's
+not used by default in new installations; however, it may be the
+only method supported by very old 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
exchange; the server can avoid groups known to be weak, and possibly
invent new ones over time, without any changes required to PuTTY's
-configuration. We recommend use of this method, if possible.
+configuration. We recommend use of this method instead of the
+well-known groups, 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.
+\H{config-ssh-hostkey} The Host Keys panel
+
+The Host Keys panel allows you to configure options related to SSH-2
+\i{host key management}.
+
+Host keys are used to prove the server's identity, and assure you that
+the server is not being spoofed (either by a man-in-the-middle attack
+or by completely replacing it on the network). See \k{gs-hostkey} for
+a basic introduction to host keys.
+
+This entire panel is only relevant to SSH protocol version 2; none of
+these settings affect SSH-1 at all.
+
+\S{config-ssh-hostkey-order} \ii{Host key type} selection
+
+\cfg{winhelp-topic}{ssh.hostkey.order}
+
+PuTTY supports a variety of SSH-2 host key types, and allows you to
+choose which one you prefer to use to identify the server.
+Configuration is similar to cipher selection (see
+\k{config-ssh-encryption}).
+
+PuTTY currently supports the following host key types:
+
+\b \q{Ed25519}: \i{Edwards-curve} \i{DSA} using a twisted Edwards
+curve with modulus \cw{2^255-19}.
+
+\b \q{ECDSA}: \i{elliptic curve} \i{DSA} using one of the
+NIST-standardised elliptic curves.
+
+\b \q{DSA}: straightforward \i{DSA} using modular exponentiation.
+
+\b \q{RSA}: the ordinary \i{RSA} algorithm.
+
+If PuTTY already has one or more host keys stored for the server,
+it will prefer to use one of those, even if the server has a key
+type that is higher in the preference order. You can add such a
+key to PuTTY's cache from within an existing session using the
+\q{Special Commands} menu; see \k{using-specials}.
+
+Otherwise, PuTTY will choose a key type based purely on the
+preference order you specify in the configuration.
+
+If the first key type PuTTY finds is below the \q{warn below here}
+line, you will see a warning box when you make the connection, similar
+to that for cipher selection (see \k{config-ssh-encryption}).
+
\S{config-ssh-kex-manual-hostkeys} \ii{Manually configuring host keys}
\cfg{winhelp-topic}{ssh.kex.manualhostkeys}
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.
+\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}.
+box, and the \I{host key cache}host key store in the Registry will be
+neither read \e{nor written}, unless you explicitly do so.
If the box is empty (as it usually is), then PuTTY's automated host
key management will work as normal.
PuTTY currently supports the following algorithms:
+\b \i{ChaCha20-Poly1305}, a combined cipher and \i{MAC} (SSH-2 only)
+
\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)
The Auth panel allows you to configure \i{authentication} options for
SSH sessions.
-\S{config-ssh-noauth} \q{Bypass authentication entirely}
-
-\cfg{winhelp-topic}{ssh.auth.bypass}
-
-In SSH-2, it is possible to establish a connection without using SSH's
-mechanisms to identify or authenticate oneself to the server. Some
-servers may prefer to handle authentication in the data channel, for
-instance, or may simply require no authentication whatsoever.
-
-By default, PuTTY assumes the server requires authentication (most
-do), and thus must provide a username. If you find you are getting
-unwanted username prompts, you could try checking this option.
-
-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}
By unchecking this option, display of the banner can be suppressed
entirely.
+\S{config-ssh-noauth} \q{Bypass authentication entirely}
+
+\cfg{winhelp-topic}{ssh.auth.bypass}
+
+In SSH-2, it is in principle possible to establish a connection
+without using SSH's mechanisms to identify or prove who you are
+to the server. An SSH server could prefer to handle authentication
+in the data channel, for instance, or simply require no user
+authentication whatsoever.
+
+By default, PuTTY assumes the server requires authentication (we've
+never heard of one that doesn't), and thus must start this process
+with a username. If you find you are getting username prompts that
+you cannot answer, you could try enabling this option. However,
+most SSH servers will reject this.
+
+This is not the option you want if you have a username and just want
+PuTTY to remember it; for that see \k{config-username}.
+It's also probably not what if you're trying to set up passwordless
+login to a mainstream SSH server; depending on the server, you
+probably wanted public-key authentication (\k{pubkey})
+or perhaps GSSAPI authentication (\k{config-ssh-auth-gssapi}).
+(These are still forms of authentication, even if you don't have to
+interact with them.)
+
+This option only affects SSH-2 connections. SSH-1 connections always
+require an authentication step.
+
\S{config-ssh-tryagent} \q{Attempt authentication using Pageant}
\cfg{winhelp-topic}{ssh.auth.pageant}
\k{puttygen-conversions}.
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.
+need to explicitly configure a key here; see \k{pageant}.
+
+If a private key 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. You can also specify a \e{public} key file
+in this case (in RFC 4716 or OpenSSH format), as that's sufficient to
+identify the key to Pageant, but of course if Pageant isn't present
+PuTTY can't fall back to using this file itself.
\H{config-ssh-auth-gssapi} The \i{GSSAPI} panel
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.
+protocol to implement \i{passwordless login}.
GSSAPI is only available in the SSH-2 protocol.
\lcont{
PuTTY proper will send modes that it has an opinion on (currently only
-the code for the Backspace key, \cw{ERASE}). Plink on Unix
-will propagate appropriate modes from the local terminal, if any.
+the code for the Backspace key, \cw{ERASE}, and whether the character
+set is UTF-8, \cw{IUTF8}). Plink on Unix will propagate appropriate
+modes from the local terminal, if any.
}
PuTTY in a variety of ways, such as \cw{true}/\cw{false},
\cw{yes}/\cw{no}, and \cw{0}/\cw{1}.
+\b The boolean mode \I{IUTF8 terminal mode}\cw{IUTF8} signals to the
+server whether the terminal character set is \i{UTF-8} or not.
+If this is set incorrectly, actions like backspace may behave
+incorrectly in some circumstances. However, setting this is not usually
+sufficient to cause servers to expect the terminal to be in UTF-8 mode;
+POSIX servers will generally require the locale to be set (by some
+server-dependent means), although many default to UTF-8. Also,
+\#{circa 2016} many servers (particularly older servers) do not honour
+this mode sent over SSH. When set to \q{Auto}, this follows the
+local configured character set (see \k{config-charset}).
+
\b Terminal speeds are configured elsewhere; see \k{config-termspeed}.
\H{config-ssh-x11} The X11 panel
ticking \q{Auto} should always give you a port which you can connect
to using either protocol.
-\H{config-ssh-bugs} \I{SSH server bugs}The Bugs panel
+\H{config-ssh-bugs} \I{SSH server bugs}The Bugs and More Bugs panels
Not all SSH servers work properly. Various existing servers have
bugs in them, which can make it impossible for a client to talk to
if the server is a version which PuTTY's bug database does not know
about, then PuTTY will not know what bugs to expect.
-The Bugs panel allows you to manually configure the bugs PuTTY
-expects to see in the server. Each bug can be configured in three
-states:
+The Bugs and More Bugs panels (there are two because we have so many
+bug compatibility modes) allow you to manually configure the bugs
+PuTTY expects to see in the server. Each bug can be configured in
+three states:
\b \q{Off}: PuTTY will assume the server does not have the bug.
and terminate with an error along the lines of \q{Received
\cw{SSH2_MSG_CHANNEL_FAILURE} for nonexistent channel 256}.
+\S{config-ssh-bug-oldgex2} \q{Only supports pre-RFC4419 SSH-2 DH GEX}
+
+\cfg{winhelp-topic}{ssh.bugs.oldgex2}
+
+The SSH key exchange method that uses Diffie-Hellman group exchange
+was redesigned after its original release, to use a slightly more
+sophisticated setup message. Almost all SSH implementations switched
+over to the new version. (PuTTY was one of the last.) A few old
+servers still only support the old one.
+
+If this bug is detected, and the client and server negotiate
+Diffie-Hellman group exchange, then PuTTY will send the old message
+now known as \cw{SSH2_MSG_KEX_DH_GEX_REQUEST_OLD} in place of the new
+\cw{SSH2_MSG_KEX_DH_GEX_REQUEST}.
+
+This is an SSH-2-specific bug.
+
\H{config-serial} The Serial panel
The \i{Serial} panel allows you to configure options that only apply
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