New SSH bug flag, for 'can't handle SSH2_MSG_IGNORE'. Another user

[u/mdw/putty] / doc / config.but

diff --git a/doc/config.but b/doc/config.but
index 27704ee..c36e818 100644 (file)
--- a/doc/config.but
+++ b/doc/config.but
@@ -2948,9 +2948,6 @@ enabled when talking to a correct server, the session will succeed,
 but keepalives will not work and the session might be more
 vulnerable to eavesdroppers than it could be.
 
 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}
 \S{config-ssh-bug-plainpw1} \q{Refuses all SSH-1 \i{password camouflage}}
 
 \cfg{winhelp-topic}{ssh.bugs.plainpw1}


@@ -2992,6 +2989,23 @@ will be impossible.
 
 This is an SSH-1-specific bug.
 
 
 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}
 \S{config-ssh-bug-hmac2} \q{Miscomputes SSH-2 HMAC keys}
 
 \cfg{winhelp-topic}{ssh.bugs.hmac2}