🚀 go-pugleaf

In article <9208191619.AA25204@news.cis.ohio-state.edu> Marc.Ringuette@daisy.learning.cs.cmu.edu writes:
>dla@raven.princeton.edu (Don Alvarez) writes,
>> There is no way to defend against this because there is no way to prove
>> who sent the message stating that machine foo has received an article.
>
>Sorry, Don, but you're just totally 100% wrong.  Digital signatures exist!
>They are practical, and they work.
>
>You might want to have a look at any tutorial on RSA, which will tell you
>how to do secure authentication (digital signatures) assuming RSA is secure.

I am well aware that RSA exists, and that you can use it for digital
signatures.  RSA is an encryption technique.  It happens to be a
particularly good one, but it is still just an encryption technique.

The problem has NOTHING to do with encryption.  No matter how you
encrypt/sign/etc your message, we are still faced with the fact that
you and I have never met and know nothing about each other.  I could
call you on the phone or walk up to you on the street and you still
wouldn't be able to trust whether I sent a message, because you just
plain don't know who I am.  That's why it's hard to be a spy, and
that's why it's hard to authenticate mail on the net.  Multiply this
problem by the tens of thousands of people using the net who have
never met each other, and you realize why authenticating messages on a
net-wide basis is a highly non-trivial task.

If you don't believe me, tell me how you and I can use RSA to let us
authenticate messages we wish to send to one another.  Remember that
(to the best of my knowledge) we have never met, and assume that
George Bush's evil twin Skippy wishes to prevent us from communicating
(which I personally doubt, but without an adversary we have no need to
authenticate anything).  We each have the suite of RSA code, as well
as any other software you think would be helpful.  You will quickly
find that we still can't communicate securely.  

If you think you have a way, post it, and I will post a way for Skippy
to spoof the method.  Skippy _doesn't_have_to_crack_RSA_.  Skippy only
has to figure out a way to prevent us from getting a bona-fide copy of
the other's digital signature validator.  Cracking RSA is hard.
Preventing us from getting bona-fide copies of each other's digital
signature validators is easy.

>You might want to have a look at any tutorial on RSA, which will tell you
>how to do secure authentication (digital signatures) assuming RSA is secure.

You might want to look at the literature on Key-distribution protocols.
THAT'S where the problem is.  How to START the communications link.
Once we each have copies of each other's public keys, then it's easy.

-don