Have you ever wanted to keep a secret from your friends or family? One way to do that is with a cipher, which is a way of encrypting a message so that only people who know the secret code can understand it. One type of cipher is called the Vignere cipher, and it’s a fun and challenging way to keep your messages safe.
History of the Vignere Cipher
The Vignere cipher was first described by Giovan Battista Bellaso in his 1553 book La cifra del. Sig. Giovan Battista Bellaso. However, it is named after Blaise de Vigenère, who popularized the use of the cipher in the 16th century.
The Vignere cipher was considered to be a relatively secure form of encryption for many years, and it was used by various governments and military organizations to encrypt sensitive information. However, in the 19th century, mathematician Charles Babbage developed a mathematical technique known as the Kasiski examination, which could be used to crack the Vignere cipher.
Despite this, the Vignere cipher continued to be used in various contexts, and it remains a popular cipher for educational and recreational purposes.
How do I use the Vignere Cipher?
To use the Vignere cipher, you need two things: a secret keyword and a message to encode. The keyword is a series of letters that you will use to encrypt your message. For example, if your keyword is “dog,” you would write it out like this:
D O G
Next, you need to write out your message in a grid, with each letter of the keyword repeating across the top and down the left side. So, using the keyword “dog” and the message “Hello, my name is Alice,” your grid would look like this:
| D | O | G | D | O | G | D | O | G | D | O | G | D | O | G | D | O | G | ||||
| H | E | L | L | O | M | Y | N | A | M | E | I | S | A | L | I | C | E |
D O G D O G D O G D O G D O G
H E L L O M Y N A M E I S A L I C E
Now, to encrypt your message, you need to find the intersection of each letter in your message with the corresponding letter of the keyword. So, the first letter of your message, “H,” would intersect with the first letter of the keyword, “D.” To encrypt this letter, you would find the letter that is “D” spaces away from “H” in the alphabet. So, if we count D, E, F, G, H, we would end up at “L,” which is the encrypted version of “H.”
You would repeat this process for each letter of your message, using the corresponding letter of the keyword to find the encrypted letter. So, the second letter of your message, “E,” would intersect with the second letter of the keyword, “O,” and we would count O, P, Q, R, S, T, U, V, W, X, Y, Z, A, B, C, D, E, F, G, H, and end up at “Q,” which is the encrypted version of “E.”
Using a Caesar wheel with
The easiest way to do this is by using a Caesar wheel. To use a Caesar cipher with the keyword “dog” to encrypt the phrase “Hello my name is Alice,” you would first convert the keyword into a number by adding up the numeric values of each letter. In this case, the numeric value of “d” is 3, the numeric value of “o” is 14, and the numeric value of “g” is 6, for a total of 23.
Next, you would shift each letter of the phrase by the numeric value of the keyword. So, the letter “h” would become “k”, the letter “e” would become “h”, and the letter “l” would become “o” . Using this method, you can encrypt the entire phrase, resulting in the encrypted message “ksroc sb bgps ov orlqk.”
To decrypt the message, someone would need to know the keyword (dog) and shift each letter back by the numeric value of the keyword. In this case, the letter “k” would become “h” (3 places back), the letter “s” would become “e” (3 places back), and the letter “r” would become “l” (3 places back). Using this method, the original message can be revealed.
Using this method, you can encrypt your entire message, and the only way for someone to read it is if they know the secret keyword.
How secure is the Vignere cipher?
The Vignere cipher is considered to be a relatively secure form of encryption. It uses a keyword to encrypt a message, which makes it more difficult to crack compared to other ciphers that use a simple numeric shift. However, it is not considered to be unbreakable, as there are mathematical techniques that can be used to decrypt a Vignere cipher. It is generally considered to be more secure than a Caesar cipher, but less secure than more modern forms of encryption such as AES.
What is the difference between the Vignere cipher and the Caesar cipher?
The main difference between the Vignere cipher and the Caesar cipher is the way in which they encrypt a message. The Caesar cipher uses a simple numeric shift to encrypt a message, while the Vignere cipher uses a keyword to encrypt a message.
The Caesar cipher is considered to be less secure than the Vignere cipher, as it is relatively easy to crack using mathematical techniques. The Vignere cipher is considered to be more secure, as it uses a keyword to encrypt the message, which makes it more difficult to crack.
Have a go yourself!
Can you try encrypting a message using the Vignere cipher? Give it a try and see if you can keep your secrets safe!