The Vigenere Cipher is a simple yet effective cipher created in the 16th century. It is similar to the Caesar Cipher but significantly more secure.
The Vigenere Cipher requires a message and a key, but unlike the Caesar Cipher, the key is a word or short phrase. Each letter in the plaintext is shifted a different amount based on the key.
I will be using the same message of "hello world" and using a key of "cipher".
Each letter in the key corresponds with a number, with "a" shifting 0, "b" shifting 1, and so on.
In this example, h would move 2 (h-i-j), while e would move 8 to m.
This would continue, but once you get to the o the key is ran out, as cipher has only 6 letters while the message has 10.
To solve this, you would go back to the start of the key, meaning you would shift o by 2.
After encrypting the full message, it results in "jmass nqzak"
This table shows each letter the ciphertext will be based on the plaintext and the key. In this example, a plaintext of N and a key of L results in a ciphertext of Y.
Decrypting the Vigenere Cipher is quite simple, as similar to the Caesar Cipher, all you have to do is shift each letter back based on the key, though letters are shifted by different amounts, which means that it is very hard to crack with brute force or letter frequency anylysis.
For example, with a cipher text of "jmass nqzak" and a key of "cipher", each letter is shifted back accordingly resulting in a plaintext of "hello world"
While the Vigenere Cipher is much better than the Caesar Cipher in most cases, it still has a few flaws.
Firstly, the Vigenere Cipher can be more annoying to decrypt, even with the key, than the Caesar Cipher, although this difference is quite minor with the key, and quite major without, which is what you want when encoding a message.
Additionally, while the Vigenere Cipher is nearly impossible to crack with brute force or letter frequency anylysis, this may not be true if you have a weak key. A one-letter key is no more secure than the Caesar Cipher, so it is important to have keys of decent lengths relative to the message
The Vigenere Cipher does not change spaces, numbers, puncuation, capital letters, or special characters, which may in some cases give away the message, or at least make it easier to crack (though often the message becomes all capital making that part irrelevent, but still maintaining the other flaws).
While more complex than the Caesar Cipher, the Vigenere Cipher is suprisingly simple for how secure it is.
As you can probably tell by this point, I find ciphers to be interesting more generally.
But that's all for the Vigenere Cipher
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