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From: andersa@kuling.UUCP (Anders Andersson)
Newsgroups: sci.crypt
Subject: Re: passwd security
Message-ID: <304@kuling.UUCP>
Date: Thu, 21-May-87 21:50:37 EDT
Article-I.D.: kuling.304
Posted: Thu May 21 21:50:37 1987
Date-Received: Tue, 26-May-87 01:59:28 EDT
References: <1012@chinet.UUCP> <1615@Umunhum.STANFORD.EDU> <581@faline.bellcore.com> <3569@osu-eddie.UUCP>
Reply-To: andersa@kuling.UUCP (Anders Andersson)
Organization: Uppsala University, Sweden
Lines: 45

In article <3569@osu-eddie.UUCP> verber@osu-eddie.UUCP (Mark A. Verber) writes:
>It would seem to me that a public key crypto-system would be perfect
>for this kind of application.  You could query the machine for its
>public key, encrypt your password using that key and then transmit
>your encrypted password.  The machine which you are trying to access
>then decodes your password with it's private key and verifies login. 

I agree with the choice of method, but is it enough to encrypt just the
password? Packet radio connections seem to be perfect targets for active
intrusion (directed towards the host computer as well as the user's
terminal) just as well as passive "wireless-tapping".

Why bothering with finding the password, when it's possible to achieve
synchronization with the real packets and suddenly take part in the
conversation, giving malicious commands to the host? Of course the
legitimate user will notice that something weird is going on, but it
might be too late - and the faked terminal could act as a faked host at
the same time, maybe misleading both ends during the whole operation.

Is this a possible scenario, or have I overlooked something? My personal
experience with packet radio is still minimal, least to say. If I were to
solve the above problem, I would consider using the authentication
functionality of public key encryption, which would make for certain
(sort of) who's talking to who. I would still have the problem of
identifying the source of the public key which I first received, though...

Encrypting the password only is still a worthwhile thing to do, if the
password itself is something you want to protect, and not just your packet
connection (maybe you have both wired and packet connections to the same
host, but use packet relatively seldom). Note that the intruder can simply
save your encrypted password (and any other encrypted stuff) for later use
in a faked session, where he can replace the plaintext part with whatever
he wants, unless the key varies between sessions.

Just to complicate things, the Swedish PTT doesn't allow encrypted data
to be sent over amateur radio, but maybe they'll be able to make an
exception for digital communications... Anyway, I do agree with you that
the amateur nature of packet radio might perhaps not warrant such a high
level of security.

This is SM5POR - or at least I've made you believe that! :-)
-- 
Anders Andersson, Dept. of Computer Systems, Uppsala University, Sweden
Phone: +46 18 183170
UUCP: andersa@kuling.UUCP (...!{seismo,mcvax}!enea!kuling!andersa)