Open Letter.



Hi Paulo,

Can I explain what has led you to believe that my cryptography could
be broken by the simple ploy of ‘known plaintext’ attack.

This is due to the fact that the demonstration programs using
PlaintextFile_1.dat right thro’ to PlaintextFile_10000.dat and the
corresponding decrypted files CipherTextFile_1.dat thro’ to
CipherTextFile_10000 of the downloadable program Vector Cipher_2.dat
that you used initially were rather carelessly made by me with the
same state of database for all six demonstrations i.e. I should have
scrambled the database for each fresh demo but I didn’t. I hold my
hands up for this – its years ago since that was done.

Also, the packages of data that comprise my database that should have
been keyed in,ideally, were in some cases part ‘copy and paste’ jobs
and therefore contained some considerable number of repeated data. I
admit to being remiss in not getting round to correcting all of this
in the intervening years but it meant keying in some 24000 integers
and making sure that there were no repeats – a hugely time-consuming
task.

The test files I sent you for testing were taken from this errant
database that I describe but were routinely scrambled for each fresh
encryption as they should have been first day, so as to stop you from
the known attack that I knew you were mounting and it worked.

There are no winners or posers in this experiment – we are all winners
- I admire you for your effort.

The moral of the story is that I must (have done already) clean up my
act and get my packages of off-page data correct i.e. free of repeated
data and also I must scramble my database if I sense a need for this
(not always essential – just prudent) between encryptions. You
obviously spotted what you considered to be an innate weakness in my
cipher that wasn’t in the end - shame on me, not you.

Your contribution to this cryptography has been greatly appreciated by
me.

Very importantly – there is no weakness in the mutual data base
concept that can be exploited by the very simple ploy of known
plaintext attack.

The only attack that needs to be addressed is the ‘ciphertext-only’
attack and that is well covered.

Your help was invaluable.

From my point of view the most important thing is to allay fears by
other readers that there is some latent weakness in my cryptography
that is being covered up.

I hope you continue to interest yourself in it this cryptography for
the benefit of others. - adacrypt

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