Vigenere Cipher

See How the Vigenere Cipher Works

The Vigenere Cipher is polyalphabetic, meaning that instead of there being a one-to-one relationship between each letter and its substitute, there is a one-to-many relationship between each letter and its substitutes. The encipherer chooses a keyword and repeats it until it matches the length of the plaintext, for example, the keyword "SecureTrust":