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The following archive was created by hippie-mail 7.98617-22 on Thu May 27 1999 - 23:44:20
Alex Alten (Alten@Home.Com)
Fri, 02 Apr 1999 00:19:52 -0800
At 08:47 AM 4/1/99 -0600, Bruce Schneier wrote:
>At 11:49 PM 3/31/99 -0800, Alex Alten wrote:
>>
>>As a founding employee of TriStrata I want to apologize to the
>>crypto community for that "unbreakable" crap. As far as I can tell
>>none of us here ever made that statement, but somehow we got tarred
>>with it. If you handle the fundamentals correctly, a Vernam cipher
>>is a useful tool in the crypto bag, with its good and bad attributes.
>>RC4 is an example of one type. RKS is just another type.
>
>This explains how the "unbreakable" crap got into your literature. You
>confuse stream ciphers with Vernam ciphers. RC4 is an OFB stream
>cipher. It is not a Vernam cipher.
>
>I think you need to try again.
>
I haven't read all our literature over the years, is there a particular
piece that we published that mentions the word? Certainly I have
never considered it to be unbreakable, and I have been intimately
involved with its design, implementation and evolution for several years.
It occurs to me that you and I are saying the same thing, but disagreeing
about the definition of what a "Vernam cipher" means. So let me precisely
define what I mean when I say it. To me the core enciphering operation of
one is the following:
X[i] + Y[i] = Z[i]
Where X[i] is a random byte, Y[i] is the cleartext byte, and Z[i] is
the cipher text byte. And i goes from 0 to n-1 bytes (n = message length).
In practice the "+" is ones complement addition, i.e. an exclusive OR
operation.
For each byte i then you have a simple algebraic equation with two
unknowns, X and Y. The essence of a Vernam cipher is constructing
the random sequence of X[i] bytes properly in order to compute the
equation, i.e. encipher the Y[i] into the Z[i] bytes.
Since RC4 is constructing X[i] byte by byte from a randomly shuffled 256
byte array of numbers (which is reshuffled over time), I consider it to be
a type of Vernam cipher. RKS uses a different technique to construct
the sequence of random X[i] bytes. So it too, I consider to be a type
of Vernam cipher.
- Alex
--Alex Alten
Alten@Home.Com Alten@TriStrata.Com
P.O. Box 11406 Pleasanton, CA 94588 USA (925) 417-0159
The following archive was created by hippie-mail 7.98617-22 on Thu May 27 1999 - 23:44:20