From: Timothy Newsham <newsham@wiliki.eng.hawaii.edu>
Date: Sun, 11 Jul 93 15:08:06 PDT
To: jpp@markv.com
Subject: Re: Secure comm program, Sockets + LINK
In-Reply-To: <9307102248.aa04285@hermix.markv.com>
Message-ID: <9307112208.AA20350@toad.com>
MIME-Version: 1.0
Content-Type: text/plain


> 
>    From: Timothy Newsham <newsham@wiliki.eng.hawaii.edu>
> 
>    I assume you're talking about the link program I wrote.
> 
> Yes, I was talking about your program Link.  
> 
>    If so:   I never really considered the RSA exchange as authentication
>    although it can be thought of that way I guess.
> 
> Right.  The only person who can participate (on one side) of the
> exchange is the one with the private key which matches the other
> side's public key.  This does provide a weak level of authentication.
> (An opponent can record 'authentication' sequences, and replay them
> later.  For this to be usefull, the opponent will have to have
> discovered the session key which is/was being selected by the
> sequence.)

This is a matter of perspective.  You are thinking of the matching
keys as being 'public' and 'private'.  You can also think of them
both being half of a key, both being unknown to any third parties.
In such a case the mere possession of a matching key is a type of
authentication.   This because you only gave out one half to a
specific person in a private way, and you kept the other half for
yourself.

This is half way true in the sense of my link program but not
totally true, because both halves were generated on one machine
and one half transmitted (probably over an insecure channel) to
the remote.  This second key is secure in that it only got transfered
once and then exists in only one place that may be secure.  It is
insecure in that it might have been observed in that window of
vulnerability.  

Why is it that you want both sides to authenticate, btw?
In the case of a human<->human connection?
I can definitely add authentication (two way).