Generation of Key Matrix for Hill Cipher Encryption Using Classical Cipher

Hill cipher encryption is the first polygraph cipher in classical encryption. The main drawback of Hill Cipher is selecting the correct encryption key matrix for encryption. If the encryption key matrix is not properly chosen, the generation of decryption key matrix i.e. the inverse of encryption matrix is not possible. This is because if the encryption key matrix is invertible then only the inverse of encryption matrix is possible. As the selection of key matrix is performed randomly, sometimes it is not obtained correct encryption key matrix using one or two runs. Also there is no deterministic method is available in generating the key matrix. In order to avoid, this paper uses any one of the classical cipher viz., Playfair Cipher, ADFGVX Cipher etc. For that, plaintext and key are accepted as input where the plaintext chosen in this case is not the original plaintext to be encrypted as the ciphertext but it is the text which is only for generating the key and the positional value of the ciphertext is taken as numbers for the encryption key matrix for Hill Cipher. The novelty used in this paper that the key matrix is not generated randomly but its generated using sequential advancement and permutated predetermined procedures.