How does the Vigenère cipher work?
The Vigenère cipher is a polyalphabetic substitution cipher that was invented by Giovan Battista Bellaso in 1553. It is named after Blaise de Vigenère, who introduced the concept of using a series of different Caesar ciphers, with different shift values, to encode text in 16th century France.
The Vigenère cipher uses a 26-letter alphabet (A-Z). To encrypt a message, each letter of the plaintext is shifted according to the corresponding letter of the keyword. For example, if the key is “KEY” and the message to be encrypted is “MEET ME AT THE PARK”, the ciphertext would be “QJII QI UA UIKG TGU”.
To decrypt a message, each letter of the ciphertext is shifted back according to the corresponding letter of the keyword. So, using the same key and ciphertext as above, the plaintext would be “LEEE LEA AAEA HARE”.
The Vigenère cipher is more secure than a simple Caesar shift cipher because it uses a keyword instead of a single shift value. However, it can still be broken by frequency analysis if the keyword is not long enough.