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Issue 19.6 ('Memorable Passwords')
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Cryptography with the Vigenere Cipher

A more advanced polyalphabetic cipher

Issue: 19.6 (November/December 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): 16,187
Starting Page Number: 35
Article Number: 19605
Resource File(s):

Download Icon project19605.zip Updated: 2021-10-31 22:33:31

Related Link(s): None

Excerpt of article text...

The Vigenere is a PolyAlphabetic Cipher, meaning the algorithm used to encode and decode the message uses multiple alphabets to change the distribution, frequency, and average of the letters used in the message. Changing these aspects makes it very difficult for a third party to determine the message by hacking.

Blaise de Vigenere (Simmons, Gustavus J. "Vigenère cipher" Encyclopedia Britannica, 9 Aug. 2017, https://www.britannica.com/topic/Vigenere-cipher, accessed 3 April 2021) is the inventor and for many years the cipher was believed to be impregnable and was known as le chiffre indechiffrable, which means "the unbreakable cipher."

This article also contains a supplementary program that is able to perform Encoding and Decoding according to the Vigenere Cipher method. Portable Xojo methods are also in the program to copy and paste the methods for use in your own programs.

A table is used that has an incremental change in the beginning alphabet for each column and row. Figure 1 shows the Vigenere table that is used to encode and decode messages.

This table has the alphabet along the top and left sides of the table. Along the left row is the beginning letter of the character in the alphabet, and once the last letter of the alphabet has been reached, then the alphabet is repeated.

The first explanation will be encoding a message that requires two pieces of information: 1) the repeating keyword and 2) the message.

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