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Math Forum » Discussions » Software » comp.soft-sys.matlab

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

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Barry Williams

Posts: 311
Registered: 6/14/06
Re: Simply Decrypting
Posted: Sep 4, 2013 6:16 AM
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"Ar " <ariq.quazifc@gmail.com> wrote in message <l06916$hud$1@newscl01ah.mathworks.com>...
> 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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