[ On Wednesday, February 3, 1999 at 20:19:16 (-0800), Joe Rhett wrote: ]
> Subject: Re: transfering files back along an existing connection
>
> If I am using a one-time hardware-based authentication mechansim, how
> exactly would the root user of this untrusted host do anything I wouldn't
> like, other than decrypting what I type/read? (we don't do much more than
> read mail and update source files)
Well, depending on exactly what the client machine consists of, and what
software and firmware it runs, the possiblities are *endless*.
The simplest example would be the installation of a trojan horse inside
your trusted network using your authenticated channel (and hiding the
covert activity, of course).
Auditing *might* catch such covert activities, but since you've only
your human brain at the client end to create corresponding audit logs
with, only the most inquisitive analysis of audit logs on the trusted
side might reveal truely covert activities, and of course since there's
no way for you to provide secure audit logs on the client side to
corroberate your activities, about the best you can hope for is that you
do not get implicated as an accomplice.
> The people who work remotely are aware that the encryption can be
> compromised on the host they are on, and don't do things like copy secret
> keys around. The strong authentication prevents another session from being
> opened by anyone else then or later. :-)
Losing secrets are the least of your problems. The real issue is that
you've opened a fully authenticated and authorized covert channel (or
multiples if you consider SSH's ability to tunnel connections!) for the
untrusted client machine to do with what it pleases, and to do so
completely without your knowledge.
The higher the risk level, and the stronger the authentication you use,
and the deeper you dive into your "trusted" home network, the more value
any threat might perceive for using the covert channel you've oppend for
them. Their risk may be relatively low compared with the immediate
pay-back they may profit from. Just because you know better than to
copy secret keys around doesn't mean the covert channel user will be
prevented from doing so.
If you really must trust a client's hardware and operating systems then
you may as well simply go all the way and trust them to keep your RSA
private key safe for the duration of your visit. You need only wipe out
their host keys (and perhaps your personal RSA keys for that site) just
before you get ready to leave (after which point at worst they'll be
forced to learn your password to make any use of the key copies they may
have retained without your authorization). Turning off
PasswordAuthentication will prevent even this, though doing so may imply
that you'll have to carry your personal RSA private key with you in
order to make the initial trusted connection.
--
Greg A. Woods
+1 416 218-0098 VE3TCP <[EMAIL PROTECTED]> <robohack!woods>
Planix, Inc. <[EMAIL PROTECTED]>; Secrets of the Weird <[EMAIL PROTECTED]>
