🚀 go-pugleaf

dc91jld@brunel.ac.uk (John L Davies) writes:
>Obviously, if you know the key used, then DES is reversible - how else, can
>the plaintext be retrieved.  However, if you mean is it possible to reverse 
>the process to produce the plaintext & key from the ciphertext, then the answer
>is NO.

There have been a number of replies to Sam Hulick's article, and they all
say about the same thing.  However, I think Mr. Hulick has confused DES
with a public key system like RSA.  The question is, why can't you decrypt
a message with the public key?

I don't have a very good understanding of public key encryption, but I
think that the basic idea has two elements:
1) an extremely difficult problem
2) a trick for solving it quickly that only works when you have some
   special information (the secret key)
RSA is based on the difficulty of reversing exponentiation by large numbers
in modular arithmetic unless factors of the exponent are known (with a trick
discovered by Euler, of course) and the fact that multiplying two large prime
numbers together is much easier than factoring an even larger composite.
(At least, nobody knows of easy ways to do these things.  Yet.)  Conceptually,
it can be reversed, but the ammount of computation required is prohibitive.

swehtam bob