Warning message at password prompt

Edward Avis epa98 at doc.ic.ac.uk
Thu Feb 14 02:54:03 EST 2002

Hash: SHA1

I've patched my local OpenSSH (currently 2.9p2, but the same
patch applies to 3.0.2) to allow the cipher 'none' for both SSH1 and
SSH2 connections.  With SSH1, there is already code to print a warning
that any password you enter will be sent in plain text.  However the
userauth_passwd() in sshconnect2.c does not have any such warning.  I
would like to discourage the users from sending plain-text passwords
across the wire, even if the rest of the session is unencrypted.

I can't work out how to do this, how to let userauth_passwd() take
different actions depending on what encryption is being used.  As far as
I can see this information is hidden from sshconnect2.c.  There is
access to the Options, which could tell you whether 'none' was
originally listed as an acceptable cipher but not whether it is actually
being used.

Could someone suggest a clean way to do this, to find out from
sshconnect2.c what encryption is being used?  Perhaps it is obvious and
I've just missed it.

BTW, the patch is at
<http://www.doc.ic.ac.uk/~epa98/work/patches/openssh/>, but it's a bit
dangerous to apply precisely because it sends plaintext passwords
without warning.  I would like to make it a bit safer while still
allowing the user to choose how much security is appropriate.

- -- 
Ed Avis <epa98 at doc.ic.ac.uk>
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