\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
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. 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
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)
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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