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Re: CERT advisory
>The big issue, in my mind, is how the ftpd is going to get the key
>to unlock the *system's* private key... Do you compile it into the
>code? Should ftpd ask for it when it comes up?
Since active interception is not nearly so easy as passive listening,
it would be appropriate to use a Diffie-Hellman key exchange in this
situation. This protocol has no persistent private keys, so the issue
of keeping a private key around securely is not an issue.
But you still have to type a password to a command that itself could
have been compromised. (Not that D-H wouldn't be a tremendous help,
All of the hand-held authenticators I'm familiar with require that
the host -- or a dedicated, trusted, security server -- keep a secret
key per user. That's not a great idea. Bellcore's S/Key doesn't,
but I don't know of any hardware devices that implement it. Another
possibility would be hand-held digital signature boxes that could sign
a random challenge from the host.