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Issue 19.5 ('Xojo Business Solution')
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FEATURE

Cryptography with the Polyalphabetic Substitution Cipher

Adjusting the frequency of letters used makes this cipher harder to crack

Issue: 19.5 (September/October 2021)
Author: Eugene Dakin
Author Bio: Eugene works as a Senior Oilfield Technical Specialist. He has university degrees in the disciplines of Engineering, Chemistry, Biology, Business, and a Ph.D. in Chemical Engineering. He is the author of dozens of books on Xojo available on the xdevlibrary.com website.
Article Description: No description available.
Article Length (in bytes): 16,645
Starting Page Number: 54
Article Number: 19505
Resource File(s):

Download Icon project19506.zip Updated: 2021-08-31 23:29:06

Related Link(s): None

Excerpt of article text...

A Cipher is the algorithm or method to convert a message into an encoded message. A Polyalphabetic cipher is a method that is much more complicated and more difficult to break. This article explores a more secure method of encrypting and decrypting information which is called the Polyalphabetic Cipher. All of the code has portable methods that can be copied and pasted for use in your own programs.

When hackers or crackers attempt to decode your confidential message, there is a natural frequency of letters that are used in the English language which is similar to the distribution shown in Figure 1.

Hackers use this information to determine that the most frequent letter is the letter "e" and then start assembling words. Using a Polyalphabetic cipher changes the frequency and the overall average of the letters used. Figure 2 is one of many possible letter distributions with a modified Polyalphabetic Frequency and multiple character shifts.

The way that the Polyalphabetic Cipher computes the encoded message is by adding the letter of the position of the Cipher Key String repeatedly into the original Clear Text message. The table below is a demonstration of what the above sentence means.

Letter S n a k e

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