Re: Please Review a Diffie Hellman diagram

[Sanjay Rawat <sanjayr () intoto com>]

Hi Saqib:

The diagram is nice, but content wise, its not (esp. from Mathematics point 
of view). The chosen number R & T are not just any number (or just any 
prime numbers). please see the description below (I was lazy enough to 
write, so I stole it from a site!!!!):
----------------------------------------

The protocol has two system parameters p and g. They are both public and 
may be used by all the users in a system. Parameter p is a prime number and 
parameter g (usually called a generator) is an integer less than p, with 
the following property: for every number n between 1 and p-1 inclusive, 
there is a power k of g such that n = g^k mod p.

Suppose Alice and Bob want to agree on a shared secret key using the 
Diffie-Hellman key agreement protocol. They proceed as follows: First, 
Alice generates a random private value a and Bob generates a random private 
value b. Both a and b are drawn from the set of integers . Then they derive 
their public values using parameters p and g and their private values. 
Alice's public value is g^a mod p and Bob's public value is g^b mod p. They 
then exchange their public values. Finally, Alice computes g^(ab) = (g^b)^a 
mod p, and Bob computes g^(ba) = (g^a)^b mod p. Since g^(ab) = g^(ba) = k, 
Alice and Bob now have a shared secret key k.
----------------------------------------

Also, it your diagram under "step 4", it will be nice if you show the 
commutative law of multiplication to make the point (ie why both Alice and 
Bob would have the same number at the end of the protocol) more clear. this 
point is described in above paragraph -- "Finally, Alice computes.........."

Regards
Sanjay

At 07:01 AM 1/7/2006, Saqib Ali wrote:
> Please review the following visual depiction of Diffie Hellman Key Exchange:
>
> http://www.xml-dev.com/blog/index.php?action=viewtopic&id=196
>
> I would like to recieve corrections, or ideas on how to improve the
> diagram so it is self-explanatory.
>
> --
> Saqib Ali, CISSP
> http://www.xml-dev.com/blog/
> "I fear, if I rebel against my Lord, the retribution of an Awful Day
> (The Day of Resurrection)" Al-Quran 6:15
>
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