PKI creed (was Re: Trustworthy contacts)

[Carl Ellison]

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At 02:17 PM 9/14/00 +0100, David Howe wrote:
>Owen Lewis <oml@eloka.demon.co.uk> wrote:
>> Interesting. Certainly one is never in a hierarchical relationship with
>> customers. Yet PKI offers little of especial for some such relationships.
>It solves the hard Key Distribution problem - if you wish to communicate
>securely with a customer, having to courier keymat (at your expense) to that
>customer before you can set up the link is prohibitively expensive;
>exchanging (or better yet, negotiating) a key using PK is cheap and
>effective.


PKI does not solve the Key Distribution problem, no matter how strongly and 
attractively Diffie and Hellman said it does.

PKI binds a key to a name, assuming the CA is trustworthy and that you have 
already solved the Key Distribution problem for the CA key itself.

However, what Diffie and Hellman missed is that you are now left with a Name 
Distribution problem -- exactly as difficult as the original Key 
Distribution problem -- with the CA Key Distribution problem on top of that 
and the CA trust problem on top of both of those.

This is a mistake Diffie and Hellman made in their original paper -- that 
has been propagated down through the decades.  They said to build a 
directory of names to keys, then you can look me up in the directory, get my 
key and send me a message.  Fine theory.  How do you find me in the 
directory?  You can't use a name.  There are too many Carl Ellison entries.

 - Carl


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+------------------------------------------------------------------+
|Carl M. Ellison         cme@acm.org     http://world.std.com/~cme |
|    PGP: 08FF BA05 599B 49D2  23C6 6FFD 36BA D342                 |
+--Officer, officer, arrest that man. He's whistling a dirty song.-+