A keyword cipher relies on both a keyword and a key letter to increase the security of the cipher. So use row E and column A of the Vigenère square, which is E. { So if the keyword is 'CAT', the first letter of plaintext is enciphered under alphabet 'C', the second under 'A', the third under 'T', the fourth under 'C' again, and so on. Please help improve this article by adding citations to reliable sources. { Instead of a relatively short keyword, used over and over again, is uses a secret key of the same length as plaintext size. for(i=0; i < Size; i++) { } { CipherText = CipherText + CipherAlpha; Caesar’s nephew Augustus learned the code from his uncle, but encrypted his messages with a shift of only one, but without wrapping around the alphabet. Alberti This uses a set of two mobile circular disks which can rotate easily. Keyword Cipher. A keyword is then used to choose which ciphertext alphabet to use. First of all, you cannot uniquely determine the keyword of a Playfair cipher, or even the key table constructed from it, simply because there are multiple equivalent key tables that will produce the same ciphertext (and multiple keywords that will produce each table). for(count = 0; count < Size; count++) { The running key cipher distinguishes from other polyalphabetic substitution ciphers. The key letter is shown at the beginning of each row. The key used to encrypt and decrypt and it also needs to be a number. The Vigenère cipher is a method of encrypting alphabetic text by using a series of interwoven Caesar ciphers, based on the letters of a keyword. Sig. } This is done by looking at the letter in row L and column A of the Vigenere square, namely L. { CipherText = CipherText + CipherAlpha; Decipher this secret message – Use SECRET as the Keyword } { if (x == -1) }