Warning message at password prompt

[Edward Avis]

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Since in principle the cipher used can be renegotiated at any time,
what's needed is a warning that the password _might_ be sent as
cleartext.  So the password prompt needs to find out whether 'none' is
included in the list of ciphers that the client accepts.  If none is not
in that list, then we know that down-negotiating to none is impossible
and it's safe to send a password over the link.

Previously I didn't want to use the options struct because I thought
that the cipher chosen by the user might not be the same as the one that
was negotiated.  However, since the warning should actually occur based
on the possibility of choosing 'none', perhaps the options struct is the
place to look to find whether none could be chosen.

Am I right in thinking that the options solely determines what ciphers
the client will accept in negotiation?

Another interesting possibility is to start off with say 3DES for the
initial authentication and sending of passwords, then renegotiate to
none or some faster cipher to send most of the data.  But that is beyond
the scope of what I want to do.

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