Vigenere Cipher
Vigenere Cipher
The Vigenere Cipher is a type of substitution cipher that uses a repeating key to encrypt plaintext, providing enhanced security compared to the simple substitution cipher. It employs a series of Caesar ciphers with different shifts, determined by the key, offering greater resistance to brute-force attacks.
What does Vigenere Cipher mean?
The Vigenere Cipher is a polyalphabetic substitution cipher that encrypts plaintext by using a series of Caesar ciphers with different shift values. It was invented in the 16th century by Italian cryptographer Giovanni Batista Bellaso and named after French cryptographer Blaise de Vigenere in the 19th century. The Vigenere Cipher is more complex than the simple Caesar Cipher, as it uses multiple shift values to encrypt the plaintext.
To encrypt a message using the Vigenere Cipher, a Key is used to determine the shift values for each letter of the plaintext. The key is typically a Word or phrase, and the shift value for each letter of the plaintext is determined by the corresponding letter of the key. For example, if the key is the word “KEY,” the shift value for the first letter of the plaintext would be 10 (the position of K in the alphabet), the shift value for the second letter would be 4 (the position of E in the alphabet), and so on.
Once the shift values have been determined, each letter of the plaintext is encrypted using a Caesar cipher with that shift value. For example, if the first letter of the plaintext is “A” and the shift value is 10, the encrypted letter would be “K.” The process is repeated for each letter of the plaintext to create the ciphertext.
Applications
The Vigenere Cipher has been used for centuries to encrypt military and diplomatic messages. It was particularly popular during the American Civil War, when it was used by both the Union and Confederate armies to encrypt messages. The Vigenere Cipher is also still used today for some non-critical applications, such as encrypting passwords and secret codes.
History
The Vigenere Cipher was first published in 1586 by Italian cryptographer Giovanni Batista Bellaso. Bellaso’s cipher was based on the work of earlier cryptographers, including Leon Battista Alberti and Trithemius. Bellaso’s cipher was later improved by French cryptographer Blaise de Vigenere in the 19th century. Vigenere added a key to the cipher, making it more secure.
The Vigenere Cipher was widely used for centuries, but it was eventually broken by Prussian cryptographer Friedrich Kasiski in 1863. Kasiski developed a Method for finding the length of the key used in a Vigenere Cipher, which made it possible to decrypt the ciphertext.
Despite being broken, the Vigenere Cipher is still considered an important cipher in the history of cryptography. It was one of the first polyalphabetic substitution ciphers, and it paved the way for the development of more complex and secure ciphers.