Support RFC 4419.

[PuTTY.git] / doc / config.but

diff --git a/doc/config.but b/doc/config.but
index 9044f9d85b258273ac992bd64ed585ccad592180..abfa51566367e13f8c4fc7d3507f385a8bdacc8e 100644 (file)
--- a/doc/config.but
+++ b/doc/config.but
@@ -3388,6 +3388,23 @@ 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}.
 
+\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