Vigenere

The Vigenere cipher is a poly-alphabetic encryption method that uses a keyword and series of interwoven Caesar ciphers.

Preserve Capitals

Preserve Symbols

Preserve Whitespace

Encode

Keyword

Input Message

Output Message

Explanation

The Vigenere cipher adds more security compared to simple mono-alphabetic substitution ciphers like the Caesar cipher.

In the Vigenere cipher, encryption and decryption are performed using a keyword or keyphrase. The key is used to determine the shift applied to each letter in the plaintext, with different parts of the key determining different shifts.

Decryption is performed by applying the reverse process. Given the ciphertext and the keyword, the original plaintext can be recovered.

The Vigenere cipher provides stronger encryption compared to simple substitution ciphers because it uses multiple Caesar ciphers in a repeating pattern determined by the keyword.

However, it is still vulnerable to frequency analysis and other cryptanalysis techniques, especially if the keyword is short or if there are patterns in the plaintext.

Despite its vulnerabilities, the Vigenere cipher was considered unbreakable for centuries and was widely used for secure communication.

Facts

It was invented by Giovan Battista Bellaso in the 16th century and later misattributed to Blaise de Vigenere, hence the name.

It is one of the earliest known examples of a poly-alphabetic substitution cipher.

It was cracked in the mid-19th century by Charles Babbage's assistant, Friedrich Kasiski. The method now known as the Kasiski examination exploits the repeated patters in the ciphertext to determine the length of the keyword.