VigenereCipher

A simple CLI & GUI Vigenere cipher tool. This tool will encrypt and decrypt text using the Vigenere cipher method. It's more secure than Caesar or ROT13.

Simple Explanation of the Vigenère Cipher:

The Vigenère cipher is a method of encrypting text by using a keyword. Unlike a basic Caesar cipher (which shifts letters by a fixed amount), the Vigenère cipher uses different shifts based on the letters of a keyword.

How It Works (Step-by-Step):

Step 1: Choose a Keyword

• You select a word, for example: KEY.

Step 2: Write Your Plaintext

• Suppose the message is: HELLO

Step 3: Repeat Your Keyword

• Repeat the keyword beneath your message, letter by letter:

Message:   H  E  L  L  O
Keyword:   K  E  Y  K  E

Step 4: Convert Letters into Numerical Values

• Assign numbers from 0 to 25 for each letter (A=0, B=1, C=2... Z=25):

Message	H(7)	E(4)	L(11)	L(11)	O(14)
Keyword	K(10)	E(4)	Y(24)	K(10)	E(4)

Step 5: Add the Numbers (Modulo 26)

• Add the numerical values of message and keyword letters together, then take the remainder when divided by 26 (modulo 26):

Calculation	(7+10)=17	(4+4)=8	(11+24)=35 mod 26=9	(11+10)=21	(14+4)=18
Result	17	8	9	21	18

Step 6: Convert Back to Letters

• Translate the numeric results back to letters (A=0, B=1... Z=25):

Result Number	17	8	9	21	18
Encrypted	R	I	J	V	S

The ciphertext becomes RIJVS.

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Decryption (Reversing the Process):

To decrypt, simply reverse this process:

• Convert letters back to numbers.
• Subtract keyword numbers from ciphertext numbers (using modulo 26).
• Convert numbers back to letters.

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Why Vigenère is Better than Caesar:

• It doesn't always shift by the same amount, making it harder to crack.

• It resists frequency analysis better, because each letter can be encrypted differently depending on the keyword.

• License

Distributed under the Apache 2.0 License.

Author

Joshua M Clatney (Clats97)

Ethical Pentesting Enthusiast

Copyright 2025 Joshua M Clatney (Clats97)