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Topic: Simply Decrypting
Replies: 3   Last Post: Sep 4, 2013 2:19 PM

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Ar

Posts: 3
Registered: 9/2/13
Simply Decrypting
Posted: Sep 3, 2013 11:22 PM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

Trying to solve to problem, but have no idea where to start from.

One of the simplest methods to encrypt a message is by using a key that defines
how many positions the letters in the text is replaced.
If you encrypt a text with a key 3, all letters in the original text moves down the
alphabet by 3 positions.
If you decrypt a text with a key 3, all letters in the decrypted text moves up the
alphabet by 3 positions (i.e d a ; f c; etc )

e.g
if you encrypt the text ?trial? with a key of 3, it will become ?wuldo?
if you decrypt the text ?wuldo? with a key of 3, it becomes ?trial?

(a) Write an M-file to can decrypt the following message ?brx pdqdjhg wr gr
lw.? using a key of 3.
(b) Write an M-file that can load the text file ?encrypted_text.txt?

Notes:
i. Only alpha-characters have been encrypted. Punctuations and white
spaces have not been altered and as such in your codes, you should not
decrypt any punctuations or white spaces.
ii. The alphabet has 26 letters. So your encryption key should always be
between 1 and 26.
iii. You might use MATLAB inbuilt function ?find?
iv. See more hints in the lab4presentation file on moodle



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