Please answer these questions on decryption of modern ciphers
 From: "kentucky" <pam@xxxxxxxxxxxx>
 Date: Tue, 27 Jun 2006 20:50:12 +0930
Dear sci.crypt
I looked here at these results  DES key search
http://www.cryptography.com/resources/whitepapers/DES.html
I wondered about a particular principle:
Given:
p is the true and unknown plaintext  (assume ASCII).
k is the true key.
c is the related cipher text generated by c = E(p, k)
What follows are decryptions of c using trial keys K1 and K2 to
give possible plaintext P1 and P2.
1. P1 = D(c, K1)
2. P2 = D(c, K2)
Questions:
What is the truth of the following statements:
(1) When Ki approximates the true key with greater than
50 % of its bits matching the true key,
then the probability that Pi has the statistics of ASCII plain text
is greater than when Ki has little resemblance to the true key k.
(2) If you are armed with a sufficient collection of
Pi, which I now assume to approximate the true p,
one can use "superposition" of Pi to get even better
approximation, P', of the true plaintext, p.
(3) The bit errors in each byte of P' can be corrected
by noting that in each byte of P' the number of bit errors
will be 0, 1, or 2 mostly, and that the bit corrections shall
result in meaningful ASCII text.
Thank You
.
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