Subject: Re: Dorothy Denning opposes Clipper, Capstone wiretap chips

From: [email-masked] (Mike Godwin)
Date: Thu, 29 Apr 1993 21:06:19 GMT

In article <[email-masked]> [email-masked] (Brad Templeton) writes:

>Quite simply she says that the security should not DEPEND on the
>secrecy of the algorithm.  A secret algorithm can still be secure,
>after all, we just don't know it.  Only our level of trust is
>affected, not the security of the system.

Here's Dorothy's own response, as sent to Phil Karn:

>From [email-masked] Wed Apr 28 14:28:30 1993
~Date: Wed, 28 Apr 93 17:23:52 EDT
~From: [email-masked] (Dorothy Denning)
~Subject: Re:  Apparently conflicting statements?
To: [email-masked]
Cc: [email-masked]
Errors-To: [email-masked]

Phil,

        But in your own textbook you wrote:

>From Dorothy Denning, CRYPTOGRAPHY AND DATA SECURITY, Addison-Wesley
        1982,1983, page 8:

        "Cryptosystems must satisfy three general requirements:

        [...]

        "3. The security of the system should depend only on the secrecy
of the keys and not on the secrecy of algorithms E [enciphering] or D
        [deciphering]."

        Are you renouncing this principle?

        Phil

Two points:

1. Principle (3) does not say that you should make your algorithm public.
   If the key has 80 bits of uncertainty and the algorithm itself
   represents maybe thousands of bits of uncertainty, aren't you
   better off with that additional secrecy?  The STU-III's use a
   classified algorithm.  I haven't heard of anyone breaking it.

2.  Principle (3) assumes that the problem domain is message secrecy and
    authenticity.  The Clipper Chip is designed to do more than that,
    namely provide law enforcement access.  This introduces new areas
    of potential vulnerability and changes the problem domain
    somewhat.  Hence the requirements may be somewhat different.  I did
    not consider the law enforcement issues when I wrote my book.

Dorothy
P.S.  You may share this response if you want.

-- 
Mike Godwin,    |    Ariel Rose Godwin
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